Leica SL Sensor Measurements Published at PhotonsToPhotos

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bclaff Veteran Member • Posts: 4,446
Leica SL Sensor Measurements Published at PhotonsToPhotos
5

I delayed publication because of a discrepancy with DxOMark but have determined that my values are correct and that theirs are not (not very unusual).

In particular the SL sensor uses dual conversion gain.
That is not so unusual except that high conversion gain starts at ISO 200 which is lower than normal.
If you're not familiar with dual conversion gain the technical background is covered in this Aptina DR-Pix Technology Whitepaper.

One of the signs of dual conversion gain is a dip in Read Noise in DNs versus ISO Setting
as seen here:

The DxOMark derived data does not show this.

The higher conversion gain shows up as a boost at ISO 200 in the Photographic Dynamic Range versus ISO Setting:

"Thank you" to those who contributed raw files for the analysis.
I'm always looking for help measuring sensors that aren't in my database.
Contact me if you're willing.
It's a bit tedious but not hard for those comfortable with manual mode.

-- hide signature --

Bill ( Your trusted source for independent sensor data at http://www.PhotonsToPhotos.net )

Leica SL (Typ 601)
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jng204 Forum Member • Posts: 79
Re: Leica SL Sensor Measurements Published at PhotonsToPhotos

Thank you for this information Bill.

For studio use, what is the best ISO to select for maximum DR? ISO 50?

What is the native ISO?

Thanks,

Josh

 jng204's gear list:jng204's gear list
Leica D-Lux (Typ 109) Leica SL (Typ 601) Leica Tri-Elmar-M 16-18-21mm f/4 ASPH Leica Summilux-M 35mm f/1.4 ASPH Leica Summilux-M 50mm f/1.4 ASPH +2 more
bclaff OP Veteran Member • Posts: 4,446
Re: Leica SL Sensor Measurements Published at PhotonsToPhotos

jng204 wrote:

Thank you for this information Bill.

Always a pleasure.

For studio use, what is the best ISO to select for maximum DR? ISO 50?

Yes.

What is the native ISO?

Trick question. With dual conversion gain you have two native ISOs.
In this case ISO 50 and ISO 200.

Regards,

-- hide signature --

Bill ( Your trusted source for independent sensor data at http://www.PhotonsToPhotos.net )

vbd70
vbd70 Veteran Member • Posts: 5,523
Re: Leica SL Sensor Measurements Published at PhotonsToPhotos

bclaff wrote:

jng204 wrote:

Thank you for this information Bill.

Always a pleasure.

For studio use, what is the best ISO to select for maximum DR? ISO 50?

Yes.

What is the native ISO?

Trick question. With dual conversion gain you have two native ISOs.
In this case ISO 50 and ISO 200.

Regards,

-- hide signature --

Bill ( Your trusted source for independent sensor data at http://www.PhotonsToPhotos.net )

Thank you Bill, most interesting. I always thought that ISO 100 was the native ISO for the SL, but it appears I was wrong.

In your opinion, for long exposures (5+ minutes), which ISO would be better for less noise? Thanks in advance, best

Vieri

-- hide signature --

Vieri Bottazzini, Leica Ambassador, ABIPP EP
https://vieribottazzini.com
https://vieribottazziniworkshops.com

 vbd70's gear list:vbd70's gear list
Panasonic LX100 Leica SL (Typ 601) Voigtlander 12mm F5.6 Ultra Wide Heliar Voigtlander 15mm F4.5 Super Wide Heliar Leica SL 24-90mm F2.8-4 +6 more
bclaff OP Veteran Member • Posts: 4,446
Re: Leica SL Sensor Measurements Published at PhotonsToPhotos

vbd70 wrote:

bclaff wrote:

jng204 wrote:

Thank you for this information Bill.

Always a pleasure.

For studio use, what is the best ISO to select for maximum DR? ISO 50?

Yes.

What is the native ISO?

Trick question. With dual conversion gain you have two native ISOs.
In this case ISO 50 and ISO 200.

Regards,

Thank you Bill, most interesting. I always thought that ISO 100 was the native ISO for the SL, but it appears I was wrong.

You're not alone but I have no idea where the ISO 100 idea came from.
Even DxOMark shows the base as ISO 50 :

In your opinion, for long exposures (5+ minutes), which ISO would be better for less noise? Thanks in advance, best

Is this for astro-photography?
In any case the SL is very ISO Invariant from ISO 200 up :

So it depends on whether you're willing to trade highlight clipping for just a small amount of extra shadow recovery.
I would think ISO 200 to ISO 800 would be best.

Regards,

-- hide signature --

Bill ( Your trusted source for independent sensor data at http://www.PhotonsToPhotos.net )

vbd70
vbd70 Veteran Member • Posts: 5,523
Re: Leica SL Sensor Measurements Published at PhotonsToPhotos

bclaff wrote:

vbd70 wrote:

bclaff wrote:

jng204 wrote:

Thank you for this information Bill.

Always a pleasure.

For studio use, what is the best ISO to select for maximum DR? ISO 50?

Yes.

What is the native ISO?

Trick question. With dual conversion gain you have two native ISOs.
In this case ISO 50 and ISO 200.

Regards,

Thank you Bill, most interesting. I always thought that ISO 100 was the native ISO for the SL, but it appears I was wrong.

You're not alone but I have no idea where the ISO 100 idea came from.
Even DxOMark shows the base as ISO 50 :

In your opinion, for long exposures (5+ minutes), which ISO would be better for less noise? Thanks in advance, best

Is this for astro-photography?
In any case the SL is very ISO Invariant from ISO 200 up :

So it depends on whether you're willing to trade highlight clipping for just a small amount of extra shadow recovery.
I would think ISO 200 to ISO 800 would be best.

Regards,

-- hide signature --

Bill ( Your trusted source for independent sensor data at http://www.PhotonsToPhotos.net )

Thank you Bill! No, it's not for astrophotography, it is for long exposure landscape photography - expressive use of long exposure, let's say, something like this:

I have been using ISO 100 so far, but I can see artefacts (little dots) on exposures of 10+ minutes. I think I'll go back to ISO 50 and see if this makes any difference. Best,

Vieri

-- hide signature --

Vieri Bottazzini, Leica Ambassador, ABIPP EP
https://vieribottazzini.com
https://vieribottazziniworkshops.com

 vbd70's gear list:vbd70's gear list
Panasonic LX100 Leica SL (Typ 601) Voigtlander 12mm F5.6 Ultra Wide Heliar Voigtlander 15mm F4.5 Super Wide Heliar Leica SL 24-90mm F2.8-4 +6 more
bclaff OP Veteran Member • Posts: 4,446
Re: Leica SL Sensor Measurements Published at PhotonsToPhotos

vbd70 wrote:

bclaff wrote:

vbd70 wrote:

bclaff wrote:

jng204 wrote:

Thank you for this information Bill.

Always a pleasure.

For studio use, what is the best ISO to select for maximum DR? ISO 50?

Yes.

What is the native ISO?

Trick question. With dual conversion gain you have two native ISOs.
In this case ISO 50 and ISO 200.

Regards,

Thank you Bill, most interesting. I always thought that ISO 100 was the native ISO for the SL, but it appears I was wrong.

You're not alone but I have no idea where the ISO 100 idea came from.
Even DxOMark shows the base as ISO 50 :

In your opinion, for long exposures (5+ minutes), which ISO would be better for less noise? Thanks in advance, best

Is this for astro-photography?
In any case the SL is very ISO Invariant from ISO 200 up :

So it depends on whether you're willing to trade highlight clipping for just a small amount of extra shadow recovery.
I would think ISO 200 to ISO 800 would be best.

Regards,

-- hide signature --

Bill ( Your trusted source for independent sensor data at http://www.PhotonsToPhotos.net )

Thank you Bill! No, it's not for astrophotography, it is for long exposure landscape photography - expressive use of long exposure, let's say, something like this:

I have been using ISO 100 so far, but I can see artefacts (little dots) on exposures of 10+ minutes. I think I'll go back to ISO 50 and see if this makes any difference. Best,

It's possible those are "hot pixels" that only show when really stressed.
You may have to take care of them in post processing.
Are they always in the same spots?

Regards,

-- hide signature --

Bill ( Your trusted source for independent sensor data at http://www.PhotonsToPhotos.net )

vbd70
vbd70 Veteran Member • Posts: 5,523
Re: Leica SL Sensor Measurements Published at PhotonsToPhotos

bclaff wrote:

vbd70 wrote:

bclaff wrote:

vbd70 wrote:

bclaff wrote:

jng204 wrote:

Thank you for this information Bill.

Always a pleasure.

For studio use, what is the best ISO to select for maximum DR? ISO 50?

Yes.

What is the native ISO?

Trick question. With dual conversion gain you have two native ISOs.
In this case ISO 50 and ISO 200.

Regards,

Thank you Bill, most interesting. I always thought that ISO 100 was the native ISO for the SL, but it appears I was wrong.

You're not alone but I have no idea where the ISO 100 idea came from.
Even DxOMark shows the base as ISO 50 :

In your opinion, for long exposures (5+ minutes), which ISO would be better for less noise? Thanks in advance, best

Is this for astro-photography?
In any case the SL is very ISO Invariant from ISO 200 up :

So it depends on whether you're willing to trade highlight clipping for just a small amount of extra shadow recovery.
I would think ISO 200 to ISO 800 would be best.

Regards,

-- hide signature --

Bill ( Your trusted source for independent sensor data at http://www.PhotonsToPhotos.net )

Thank you Bill! No, it's not for astrophotography, it is for long exposure landscape photography - expressive use of long exposure, let's say, something like this:

I have been using ISO 100 so far, but I can see artefacts (little dots) on exposures of 10+ minutes. I think I'll go back to ISO 50 and see if this makes any difference. Best,

It's possible those are "hot pixels" that only show when really stressed.
You may have to take care of them in post processing.
Are they always in the same spots?

Regards,

-- hide signature --

Bill ( Your trusted source for independent sensor data at http://www.PhotonsToPhotos.net )

That's what I do. No, they doesn't appear always in the same spot, they are a million, tiny ones, and appear randomly. I found that Capture One's "pixel noise" noise reduction does a very good job with them, regular noise reduction does nothing, and cloning them out in PP is a royal pain

Best,

Vieri

-- hide signature --

Vieri Bottazzini, Leica Ambassador, ABIPP EP
https://vieribottazzini.com
https://vieribottazziniworkshops.com

 vbd70's gear list:vbd70's gear list
Panasonic LX100 Leica SL (Typ 601) Voigtlander 12mm F5.6 Ultra Wide Heliar Voigtlander 15mm F4.5 Super Wide Heliar Leica SL 24-90mm F2.8-4 +6 more
Jared_Willson Contributing Member • Posts: 505
Re: Leica SL Sensor Measurements Published at PhotonsToPhotos

vbd70 wrote:

bclaff wrote:

vbd70 wrote:

bclaff wrote:

jng204 wrote:

Thank you for this information Bill.

Always a pleasure.

For studio use, what is the best ISO to select for maximum DR? ISO 50?

Yes.

What is the native ISO?

Trick question. With dual conversion gain you have two native ISOs.
In this case ISO 50 and ISO 200.

Regards,

Thank you Bill, most interesting. I always thought that ISO 100 was the native ISO for the SL, but it appears I was wrong.

You're not alone but I have no idea where the ISO 100 idea came from.
Even DxOMark shows the base as ISO 50 :

In your opinion, for long exposures (5+ minutes), which ISO would be better for less noise? Thanks in advance, best

Is this for astro-photography?
In any case the SL is very ISO Invariant from ISO 200 up :

So it depends on whether you're willing to trade highlight clipping for just a small amount of extra shadow recovery.
I would think ISO 200 to ISO 800 would be best.

Regards,

-- hide signature --

Bill ( Your trusted source for independent sensor data at http://www.PhotonsToPhotos.net )

Thank you Bill! No, it's not for astrophotography, it is for long exposure landscape photography - expressive use of long exposure, let's say, something like this:

I have been using ISO 100 so far, but I can see artefacts (little dots) on exposures of 10+ minutes. I think I'll go back to ISO 50 and see if this makes any difference. Best,

Vieri

-- hide signature --

Vieri Bottazzini, Leica Ambassador, ABIPP EP
https://vieribottazzini.com
https://vieribottazziniworkshops.com

I am an astrophotographer so know a fair amount about long exposures.  Here is where the little dots come from:

In a long exposure, there are some noise elements that start to make a difference in your exposure that simply don't exist in a shorter exposure.  The first of these is thermal noise.  Random motions in the silicon substrate of the chip cause signal to accumulate on the CMOS sensor that does not come from light.  This is why cameras do long exposure noise reduction--they subtract a second exposure with the shutter closed in order to reduce thermal noise.  It works pretty well, but it's not perfect.  On the Leica SL you can't turn it off or on--it simply runs whenever the exposure is greater than or equal to one second.  There are two problems with this simple dark frame subtraction.  The first is that the signal varies a little bit from one exposure to the next--it would actually be better to subtract an average of several (or even a few dozen) dark frames.  But nobody is willing to wait for that.  Astronomers make "master darks" during daylight hours and use those, but you can't do that with a normal camera.  The second issue is that the amount of thermal noise is dependent on the temperature of the chip, and the chip tends to heat up a bit during a long exposure.  Surprisingly, it's a fairly big deal.  A couple of degrees can make a noticeable difference.  The end result is that for a multi-minute exposure, the dark frame taken by the camera is often at a slightly higher temperature than the light frame of your actual image.  The subtraction of the dark frame is therefore less than perfect, leaving speckles behind.

There is a second source of noise in a long exposure at night, and this one comes from outside the camera.  Cosmic rays are routinely picked up by the camera as white speckles.  I know this sounds ridiculous, but it's absolutely true.  You can often see them as tiny little streaks, perhaps a couple or three pixels long.  These are from cosmic ray strikes during the exposure.  If your speckles are little streaks rather than a single pixel, it may well be from cosmic rays.  Normally you need a cooled astronomy camera to notice these since they are generally swamped by things like thermal noise in a digital SLR or mirrorless camera.

There is a third source as well that can be significant in some cameras.  The glass used in the cover slip over the CCD has radioactive iodine in it.  This creates beta decay that will also show up in a long exposure at night.  If you are seeing little streaks of perhaps eight or ten pixels in length that curve--like the beginning of a spiral pattern--that is likely from radioactive iodine in the glass over the CCD.  Again, it would be rare for this to be an issue with a digital SLR--this noise is usually drowned out by other sources of noise.

What you are seeing is mostly thermal noise that can't quite be corrected by the single dark frame with some smaller contributions from cosmic rays and radioactive decay.  Are you getting white speckles or black ones?  If it's black ones, it's likely that the dark frame is slightly over-correcting since the sensor will be hotter during the dark frame than it is during the actual exposure.

-- hide signature --

 Jared Willson

bclaff OP Veteran Member • Posts: 4,446
Re: Leica SL Sensor Measurements Published at PhotonsToPhotos

Jared_Willson wrote:
... This is why cameras do long exposure noise reduction--they subtract a second exposure with the shutter closed in order to reduce thermal noise. It works pretty well, but it's not perfect. On the Leica SL you can't turn it off or on--it simply runs whenever the exposure is greater than or equal to one second.
...

Really, Long Exposure Noise Reduction (LENR, the Nikon term) cannot be turned off?
So if you make a 5s exposure it takes 10s total ?

If you make a 5min exposure does it take 10min or is the black frame limited to say 30s ?

Regards,

-- hide signature --

Bill ( Your trusted source for independent sensor data at http://www.PhotonsToPhotos.net )

Jared_Willson Contributing Member • Posts: 505
Re: Leica SL Sensor Measurements Published at PhotonsToPhotos

bclaff wrote:

vbd70 wrote:

bclaff wrote:

jng204 wrote:

Thank you for this information Bill.

Always a pleasure.

For studio use, what is the best ISO to select for maximum DR? ISO 50?

Yes.

What is the native ISO?

Trick question. With dual conversion gain you have two native ISOs.
In this case ISO 50 and ISO 200.

Regards,

Thank you Bill, most interesting. I always thought that ISO 100 was the native ISO for the SL, but it appears I was wrong.

You're not alone but I have no idea where the ISO 100 idea came from.
Even DxOMark shows the base as ISO 50 :

In your opinion, for long exposures (5+ minutes), which ISO would be better for less noise? Thanks in advance, best

Is this for astro-photography?
In any case the SL is very ISO Invariant from ISO 200 up :

So it depends on whether you're willing to trade highlight clipping for just a small amount of extra shadow recovery.
I would think ISO 200 to ISO 800 would be best.

Regards,

-- hide signature --

Bill ( Your trusted source for independent sensor data at http://www.PhotonsToPhotos.net )

The suggestion that base ISO was actually at 100 rather than at 50 came from a couple sources. First, was Leica product management that indicated in an interview a couple years ago that ISO 50 was a "pull" value. Many people assumed this meant 100 was the actual base. I know I did. I also ran some tests to measure ISO on earlier firmware, and I achieved my highest DR at ISO 100, though the difference between 50 and 100 was small. Unfortunately, I don't have my original data, so I can't check to see if I made an experimental error. But I have certainly been using 100 as the base since I ran those measurements.

Last night I again measured DR at all ISO's from 50 to 1600, and I got numbers that were different from last time I ran the test (with the older firmware). I don't think any two testers have the exact same method of determining dynamic range, so values will never match exactly. At what dB do you put the noise floor, for example? What do you consider clipping at the white point? The sensor is far from linear at the top end, both because Leica applies a curve to the file and because the anti-blooming gate technology on all non-scientific cameras keeps things from being linear. At any rate, here are the values I got assuming an SNR of 10 dB constituted the noise floor:

ISO 50: 11.3 EV

ISO 100: 10.9 EV

ISO 200: 11.1 EV

ISO 400: 10.7 EV

ISO 800: 9.6 EV

ISO 1600: 8.2 EV

In other words, I show the same little bump at ISO 100/200 that Bill shows--he's suggesting it's from dual conversion gain.  If that explanation is correct, and I certainly don't have better one, you could consider either ISO 50 or ISO 200 as a "base" ISO with very similar dynamic range in each.  ISO 100 is slightly, but measurably, lower in dynamic range, so if anyone is using my guidance for rating that value as base, I would recommend instead using either 50 or 200.  The differences are pretty small, but they are there.

I'm not certain why the DXO data don't show this bump.  I know they, like me, did their measurements with a much earlier version of firmware since their review has been up  for a while now.  I believe Bill has noticed some differences in this blip in older firmware vs. current, but you'd have to ask him to confirm that since I don't any longer have data from an earlier firmware version.  Also, I believe Bill uses data volunteered from different cameras (including mine for read noise) to make his measurements, thus reducing sample variation as long as the tester is reasonably rigorous with the methodology.

-- hide signature --

 Jared Willson

Jared_Willson Contributing Member • Posts: 505
Re: Leica SL Sensor Measurements Published at PhotonsToPhotos

Correct, Leica (in their infinite wisdom) have determined that long exposure noise reduction is ALWAYS a good thing if your exposure is 1s or longer, so they always apply it.  That means every 3 minute exposure actually takes 6 minutes.  Every 10 minute exposure actually takes 20 minutes.  It makes it very challenging to do star trail photography, and eliminates any possibility of building and applying a master dark frame.

The reason for this, assume, is their emphasis on simplicity in menu structure.  I can't think of any other justification, anyway.  If very few people would want to turn it off (and it's true that it's generally a good thing), then why clutter up the menu?  I'm just speculating, but it's the only logical reason I can think of for not allowing the user to disable the long exposure noise reduction.  They have been consistent in most (all?) their cameras in this.  You can't turn it off on an M(240), an M9, a 'T', an SL, or a 'Q'.  Definitely frustrates me as an astrophotographer.  I just can't use my Leicas for most astrophotography.

-- hide signature --

 Jared Willson

Jared_Willson Contributing Member • Posts: 505
Re: Leica SL Sensor Measurements Published at PhotonsToPhotos

By the way, I should have given you some guidance on how the speckle issue is likely to be affected by ISO... In general, the goal for astrophotography (and your night landscapes would apply for this purpose) is to take exposures that are long enough that shot noise dominates, no matter what gain (ISO) you are using. That means, the noise from subject you are photographing should be much higher than the combination of read noise, fixed pattern noise, and thermal noise. With an astronomy camera that is fairly easy to do since they are cooled. But with a camera like the SL it's actually pretty challenging with a longer exposure. The thermal noise could well be the largest noise component in the image on a 5-10 minute exposure, especially during the warmer months.

If you are stuck with 8 minute exposures because that is producing the cloud blurring you want, then you can choose almost any ISO from 200 say 800 (assuming that won't result in blown highlights) and you will likely get about the same result. With the SL, as with most modern cameras, you'll find it's relatively ISO invariant, so shooting at a lower ISO and adjusting the exposure up in post processing should produce about the same result as shooting at a higher ISO and making fewer exposure adjustments in post. I'd certainly be comfortable anywhere in the ISO 200 - 800 range.

If you are shooting at ISO 100 now and are choosing the 8m exposure in order to get a "correct" exposure rather than to get the particular blurring effects you are looking for in the sky, I would definitely recommend changing to a higher ISO and shortening your exposure. A 1 minute exposure at ISO 800 should be equivalent to an 8 minute exposure at ISO 100, but the thermal noise will be significantly lower. In other words, higher ISO/shorter exposure should actually reduce the speckling from thermal noise. Shooting lower ISO will actually tend to emphasize thermal noise. It's the opposite of what you might think.

-- hide signature --

 Jared Willson

bclaff OP Veteran Member • Posts: 4,446
Re: Leica SL Sensor Measurements Published at PhotonsToPhotos

Jared_Willson wrote:

bclaff wrote:

vbd70 wrote:

bclaff wrote:

jng204 wrote:

What is the native ISO?

Trick question. With dual conversion gain you have two native ISOs.
In this case ISO 50 and ISO 200.

Thank you Bill, most interesting. I always thought that ISO 100 was the native ISO for the SL, but it appears I was wrong.

You're not alone but I have no idea where the ISO 100 idea came from.
Even DxOMark shows the base as ISO 50 :

The suggestion that base ISO was actually at 100 rather than at 50 came from a couple sources. First, was Leica product management that indicated in an interview a couple years ago that ISO 50 was a "pull" value. Many people assumed this meant 100 was the actual base. I know I did. I also ran some tests to measure ISO on earlier firmware, and I achieved my highest DR at ISO 100, though the difference between 50 and 100 was small. Unfortunately, I don't have my original data, so I can't check to see if I made an experimental error. But I have certainly been using 100 as the base since I ran those measurements.

Last night I again measured DR at all ISO's from 50 to 1600, and I got numbers that were different from last time I ran the test (with the older firmware).

Yes, the Leica engineers definitely changed things up between firmware revisions.
This includes bug fixes so people really should be updating their firmware.

I don't think any two testers have the exact same method of determining dynamic range, so values will never match exactly. At what dB do you put the noise floor, for example? What do you consider clipping at the white point?

Engineering Dynamic Range is well defined.
Certainly the floor is (pixel) read noise.
Clipping is usually taken at Analog to Digital Converter (ADC) saturation.
This may seem generous but given the logarithmic nature the effect is very small.

The sensor is far from linear at the top end, both because Leica applies a curve to the file and because the anti-blooming gate technology on all non-scientific cameras keeps things from being linear.

I very much doubt any curve is applied to the raw file.
Except for Foveon sensors I've not seen that elsewhere.

At any rate, here are the values I got assuming an SNR of 10 dB constituted the noise floor:

ISO 50: 11.3 EV 13.1
ISO 100: 10.9 EV 12.2
ISO 200: 11.1 EV 13.3
ISO 400: 10.7 EV 12.4
ISO 800: 9.6 EV 11.5
ISO 1600: 8.2 EV 10.5

I have added my values in BOLD next to yours.
The are from Read Noise in DNs versus ISO Setting

In other words, I show the same little bump at ISO 100/200 that Bill shows--he's suggesting it's from dual conversion gain. If that explanation is correct, and I certainly don't have better one, you could consider either ISO 50 or ISO 200 as a "base" ISO with very similar dynamic range in each. ISO 100 is slightly, but measurably, lower in dynamic range, so if anyone is using my guidance for rating that value as base, I would recommend instead using either 50 or 200. The differences are pretty small, but they are there.

I'm not certain why the DXO data don't show this bump. I know they, like me, did their measurements with a much earlier version of firmware since their review has been up for a while now.

Even the earliest firmware showed a "blip" just in a different spot.
So it's just a mystery as to why DxOMark doesn't see this.

I believe Bill has noticed some differences in this blip in older firmware vs. current, but you'd have to ask him to confirm that since I don't any longer have data from an earlier firmware version. Also, I believe Bill uses data volunteered from different cameras (including mine for read noise) to make his measurements, thus reducing sample variation as long as the tester is reasonably rigorous with the methodology.

Regards,

-- hide signature --

Bill ( Your trusted source for independent sensor data at http://www.PhotonsToPhotos.net )

bclaff OP Veteran Member • Posts: 4,446
Re: Leica SL Sensor Measurements Published at PhotonsToPhotos

Jared_Willson wrote:

Correct, Leica (in their infinite wisdom) have determined that long exposure noise reduction is ALWAYS a good thing if your exposure is 1s or longer, so they always apply it. That means every 3 minute exposure actually takes 6 minutes. Every 10 minute exposure actually takes 20 minutes. It makes it very challenging to do star trail photography, and eliminates any possibility of building and applying a master dark frame.

The reason for this, assume, is their emphasis on simplicity in menu structure. I can't think of any other justification, anyway. If very few people would want to turn it off (and it's true that it's generally a good thing), then why clutter up the menu? I'm just speculating, but it's the only logical reason I can think of for not allowing the user to disable the long exposure noise reduction. They have been consistent in most (all?) their cameras in this. You can't turn it off on an M(240), an M9, a 'T', an SL, or a 'Q'. Definitely frustrates me as an astrophotographer. I just can't use my Leicas for most astrophotography.

I wonder if this old Nikon hack has any effect - turn off the camera while it's taking the second exposure.
Nikon used to do an "emergency" dump of the truly raw file when it sensed the user was powering off.

Just a weird idea

Regards,

-- hide signature --

Bill ( Your trusted source for independent sensor data at http://www.PhotonsToPhotos.net )

Jared_Willson Contributing Member • Posts: 505
Re: Leica SL Sensor Measurements Published at PhotonsToPhotos

It's been tried, unfortunately.  It keeps taking the dark frame even with the power off.  If you pull the battery, you lose the entire exposure.  There is no known workaround, and it's been a complaint since 2006 for various Leica cameras.

-- hide signature --

 Jared Willson

Jared_Willson Contributing Member • Posts: 505
Re: Leica SL Sensor Measurements Published at PhotonsToPhotos

bclaff wrote:

Jared_Willson wrote:

bclaff wrote:

vbd70 wrote:

bclaff wrote:

jng204 wrote:

What is the native ISO?

Trick question. With dual conversion gain you have two native ISOs.
In this case ISO 50 and ISO 200.

Thank you Bill, most interesting. I always thought that ISO 100 was the native ISO for the SL, but it appears I was wrong.

You're not alone but I have no idea where the ISO 100 idea came from.
Even DxOMark shows the base as ISO 50 :

The suggestion that base ISO was actually at 100 rather than at 50 came from a couple sources. First, was Leica product management that indicated in an interview a couple years ago that ISO 50 was a "pull" value. Many people assumed this meant 100 was the actual base. I know I did. I also ran some tests to measure ISO on earlier firmware, and I achieved my highest DR at ISO 100, though the difference between 50 and 100 was small. Unfortunately, I don't have my original data, so I can't check to see if I made an experimental error. But I have certainly been using 100 as the base since I ran those measurements.

Last night I again measured DR at all ISO's from 50 to 1600, and I got numbers that were different from last time I ran the test (with the older firmware).

Yes, the Leica engineers definitely changed things up between firmware revisions.
This includes bug fixes so people really should be updating their firmware.

I don't think any two testers have the exact same method of determining dynamic range, so values will never match exactly. At what dB do you put the noise floor, for example? What do you consider clipping at the white point?

Engineering Dynamic Range is well defined.
Certainly the floor is (pixel) read noise.
Clipping is usually taken at Analog to Digital Converter (ADC) saturation.
This may seem generous but given the logarithmic nature the effect is very small.

The sensor is far from linear at the top end, both because Leica applies a curve to the file and because the anti-blooming gate technology on all non-scientific cameras keeps things from being linear.

I very much doubt any curve is applied to the raw file.
Except for Foveon sensors I've not seen that elsewhere.

At any rate, here are the values I got assuming an SNR of 10 dB constituted the noise floor:

ISO 50: 11.3 EV 13.1
ISO 100: 10.9 EV 12.2
ISO 200: 11.1 EV 13.3
ISO 400: 10.7 EV 12.4
ISO 800: 9.6 EV 11.5
ISO 1600: 8.2 EV 10.5

I have added my values in BOLD next to yours.
The are from Read Noise in DNs versus ISO Setting

In other words, I show the same little bump at ISO 100/200 that Bill shows--he's suggesting it's from dual conversion gain. If that explanation is correct, and I certainly don't have better one, you could consider either ISO 50 or ISO 200 as a "base" ISO with very similar dynamic range in each. ISO 100 is slightly, but measurably, lower in dynamic range, so if anyone is using my guidance for rating that value as base, I would recommend instead using either 50 or 200. The differences are pretty small, but they are there.

I'm not certain why the DXO data don't show this bump. I know they, like me, did their measurements with a much earlier version of firmware since their review has been up for a while now.

Even the earliest firmware showed a "blip" just in a different spot.
So it's just a mystery as to why DxOMark doesn't see this.

I believe Bill has noticed some differences in this blip in older firmware vs. current, but you'd have to ask him to confirm that since I don't any longer have data from an earlier firmware version. Also, I believe Bill uses data volunteered from different cameras (including mine for read noise) to make his measurements, thus reducing sample variation as long as the tester is reasonably rigorous with the methodology.

Regards,

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Bill ( Your trusted source for independent sensor data at http://www.PhotonsToPhotos.net )

I doubt we actually have any disagreement here.

1) I'm sure you are right about the Leica changing things up during firmware revisions.  No reason to doubt--you've looked and I haven't.

2) I agree that engineering dynamic range is fairly well defined--DR = 20 log (Full Well / Read Noise).  I, like you, do not find those values particularly realistic for photographers.  I was reporting out my version of Photographic Read Noise, and we don't quite have the same assumptions for that.  For example, you use a SNR of 20 as the noise floor.  I was using 10.  That's why I reported out a DR that is slightly larger than you did in your original post.  I wasn't trying to contradict your values--just show that the trends I found were in agreement with the trends you were finding. It's on the definition of a useful photographic dynamic range that I don't believe there is a strong consensus.

3) You're right that I was jumping the gun in assuming the lack of linearity near the clipping point is because Leica applies a curve.  It could just be the anti-blooming gate kicking in.

4) Like you, I am confused why DXO isn't showing a blip in their data, even if Leica have changed the ISO for the crossover point.  I definitely see it--just as you do.  I've run the tests twice now on my camera, and it is definitely there.  It's not huge, but it's definitely too big to just be a simple measurement error.

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 Jared Willson

vbd70
vbd70 Veteran Member • Posts: 5,523
Re: Leica SL Sensor Measurements Published at PhotonsToPhotos

Jared_Willson wrote:

vbd70 wrote:

bclaff wrote:

vbd70 wrote:

bclaff wrote:

jng204 wrote:

Thank you for this information Bill.

Always a pleasure.

For studio use, what is the best ISO to select for maximum DR? ISO 50?

Yes.

What is the native ISO?

Trick question. With dual conversion gain you have two native ISOs.
In this case ISO 50 and ISO 200.

Regards,

Thank you Bill, most interesting. I always thought that ISO 100 was the native ISO for the SL, but it appears I was wrong.

You're not alone but I have no idea where the ISO 100 idea came from.
Even DxOMark shows the base as ISO 50 :

In your opinion, for long exposures (5+ minutes), which ISO would be better for less noise? Thanks in advance, best

Is this for astro-photography?
In any case the SL is very ISO Invariant from ISO 200 up :

So it depends on whether you're willing to trade highlight clipping for just a small amount of extra shadow recovery.
I would think ISO 200 to ISO 800 would be best.

Regards,

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Bill ( Your trusted source for independent sensor data at http://www.PhotonsToPhotos.net )

Thank you Bill! No, it's not for astrophotography, it is for long exposure landscape photography - expressive use of long exposure, let's say, something like this:

I have been using ISO 100 so far, but I can see artefacts (little dots) on exposures of 10+ minutes. I think I'll go back to ISO 50 and see if this makes any difference. Best,

Vieri

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Vieri Bottazzini, Leica Ambassador, ABIPP EP
https://vieribottazzini.com
https://vieribottazziniworkshops.com

I am an astrophotographer so know a fair amount about long exposures. Here is where the little dots come from:

In a long exposure, there are some noise elements that start to make a difference in your exposure that simply don't exist in a shorter exposure. The first of these is thermal noise. Random motions in the silicon substrate of the chip cause signal to accumulate on the CMOS sensor that does not come from light. This is why cameras do long exposure noise reduction--they subtract a second exposure with the shutter closed in order to reduce thermal noise. It works pretty well, but it's not perfect. On the Leica SL you can't turn it off or on--it simply runs whenever the exposure is greater than or equal to one second. There are two problems with this simple dark frame subtraction. The first is that the signal varies a little bit from one exposure to the next--it would actually be better to subtract an average of several (or even a few dozen) dark frames. But nobody is willing to wait for that. Astronomers make "master darks" during daylight hours and use those, but you can't do that with a normal camera. The second issue is that the amount of thermal noise is dependent on the temperature of the chip, and the chip tends to heat up a bit during a long exposure. Surprisingly, it's a fairly big deal. A couple of degrees can make a noticeable difference. The end result is that for a multi-minute exposure, the dark frame taken by the camera is often at a slightly higher temperature than the light frame of your actual image. The subtraction of the dark frame is therefore less than perfect, leaving speckles behind.

There is a second source of noise in a long exposure at night, and this one comes from outside the camera. Cosmic rays are routinely picked up by the camera as white speckles. I know this sounds ridiculous, but it's absolutely true. You can often see them as tiny little streaks, perhaps a couple or three pixels long. These are from cosmic ray strikes during the exposure. If your speckles are little streaks rather than a single pixel, it may well be from cosmic rays. Normally you need a cooled astronomy camera to notice these since they are generally swamped by things like thermal noise in a digital SLR or mirrorless camera.

There is a third source as well that can be significant in some cameras. The glass used in the cover slip over the CCD has radioactive iodine in it. This creates beta decay that will also show up in a long exposure at night. If you are seeing little streaks of perhaps eight or ten pixels in length that curve--like the beginning of a spiral pattern--that is likely from radioactive iodine in the glass over the CCD. Again, it would be rare for this to be an issue with a digital SLR--this noise is usually drowned out by other sources of noise.

What you are seeing is mostly thermal noise that can't quite be corrected by the single dark frame with some smaller contributions from cosmic rays and radioactive decay. Are you getting white speckles or black ones? If it's black ones, it's likely that the dark frame is slightly over-correcting since the sensor will be hotter during the dark frame than it is during the actual exposure.

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Jared Willson

Jared,

thank you for the comprehensive explanation - much appreciated indeed.

I see both white-ish speckles AND black, bigger ones; I thought either appeared randomly, but now I have a better understanding of the phenomenon.

Would making the back frame shorter than the actual exposure help in limiting these? Some manufacturer use to have a black frame shorter than the actual exposure, and I thought this might be the reason why.

Thanks again, best

Vieri

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Vieri Bottazzini, Leica Ambassador, ABIPP EP
https://vieribottazzini.com
https://vieribottazziniworkshops.com

 vbd70's gear list:vbd70's gear list
Panasonic LX100 Leica SL (Typ 601) Voigtlander 12mm F5.6 Ultra Wide Heliar Voigtlander 15mm F4.5 Super Wide Heliar Leica SL 24-90mm F2.8-4 +6 more
vbd70
vbd70 Veteran Member • Posts: 5,523
Re: Leica SL Sensor Measurements Published at PhotonsToPhotos

Jared_Willson wrote:

By the way, I should have given you some guidance on how the speckle issue is likely to be affected by ISO... In general, the goal for astrophotography (and your night landscapes would apply for this purpose) is to take exposures that are long enough that shot noise dominates, no matter what gain (ISO) you are using. That means, the noise from subject you are photographing should be much higher than the combination of read noise, fixed pattern noise, and thermal noise. With an astronomy camera that is fairly easy to do since they are cooled. But with a camera like the SL it's actually pretty challenging with a longer exposure. The thermal noise could well be the largest noise component in the image on a 5-10 minute exposure, especially during the warmer months.

If you are stuck with 8 minute exposures because that is producing the cloud blurring you want, then you can choose almost any ISO from 200 say 800 (assuming that won't result in blown highlights) and you will likely get about the same result. With the SL, as with most modern cameras, you'll find it's relatively ISO invariant, so shooting at a lower ISO and adjusting the exposure up in post processing should produce about the same result as shooting at a higher ISO and making fewer exposure adjustments in post. I'd certainly be comfortable anywhere in the ISO 200 - 800 range.

If you are shooting at ISO 100 now and are choosing the 8m exposure in order to get a "correct" exposure rather than to get the particular blurring effects you are looking for in the sky, I would definitely recommend changing to a higher ISO and shortening your exposure. A 1 minute exposure at ISO 800 should be equivalent to an 8 minute exposure at ISO 100, but the thermal noise will be significantly lower. In other words, higher ISO/shorter exposure should actually reduce the speckling from thermal noise. Shooting lower ISO will actually tend to emphasize thermal noise. It's the opposite of what you might think.

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Jared Willson

Jared, thank you for this. Unfortunately for me, I don't do night landscapes necessarily, in fact I mostly do very long exposures during the day; and as you said I do them for expressive reasons, so for me - taking your example as an example - if I need, say, 8 minutes at ISO 100 for the clouds to be blurred just so, going for 1 minute at ISO 800 is not an option.

So in short - you are saying that exposure time being equal I am better off using ISO 200 rather than ISO 50 or keeping noise down? Thanks!

Best,

Vieri

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Vieri Bottazzini, Leica Ambassador, ABIPP EP
https://vieribottazzini.com
https://vieribottazziniworkshops.com

 vbd70's gear list:vbd70's gear list
Panasonic LX100 Leica SL (Typ 601) Voigtlander 12mm F5.6 Ultra Wide Heliar Voigtlander 15mm F4.5 Super Wide Heliar Leica SL 24-90mm F2.8-4 +6 more
Jared_Willson Contributing Member • Posts: 505
Re: Leica SL Sensor Measurements Published at PhotonsToPhotos

vbd70 wrote:

Jared,

thank you for the comprehensive explanation - much appreciated indeed.

I see both white-ish speckles AND black, bigger ones; I thought either appeared randomly, but now I have a better understanding of the phenomenon.

Would making the back frame shorter than the actual exposure help in limiting these? Some manufacturer use to have a black frame shorter than the actual exposure, and I thought this might be the reason why.

Thanks again, best

Vieri

-- hide signature --

Vieri Bottazzini, Leica Ambassador, ABIPP EP
https://vieribottazzini.com
https://vieribottazziniworkshops.com

I haven't seen anyone scaling their dark frames, but it is certainly possible to do.  It's a little more process intensive.  Here is the standard process:

Take a light frame, for sake of argument 5 minutes duration

Take a dark frame, the same five minutes

Subtract the dark frame from the light frame.  That's your new final exposure.

Here is what you would do for a scaled dark:

Take a light frame

Take a bias frame (shortest possible exposure with the shutter closed--just read noise)

Take a shortened dark frame, say half the length of your light

Subtract the bias from the dark frame

Multiply all values in the dark frame by two

Subtract the bias from your light frame

Subtract the new 2x dark from the light

The result is your new, final exposure

Scaled darks work fairly well as long as the exposures aren't long enough for hot pixels to be clipping.

I'm not certain how best to address them aside from what you are already doing.  In astrophotography, most people choose to use master darks (which will create a better result than a single dark frame) and dither their images--each image is slightly mis-aligned from the last, and then they are averaged together using a statistical method such as "sigma clip" to completely remove hot and cold pixels.  That is technically possible with a terrestrial image as well.  You could take five separate two minute exposures or so with the tripod moved ever so slightly between frames, then use a sigma clip combine to average the frames.  Of course, Photoshop and Lightroom don't have sophisticated stacking algorithms so you'd have to use some astronomy software for that, and most astronomy software doesn't do a great job on aligning terrestrial images since it expects point sources to be available, but it is definitely doable.  I have done it occasionally.  I wouldn't recommend it, though, unless you just can't accomplish what you want to with the techniques you are already trying.

Perhaps an incremental solution would be to cut your exposure duration significantly (to lower the thermal noise), boost your ISO to compensate, then take multiple exposures and average them together in Photoshop without any re-alignment.  You wouldn't get the benefits of dithering, but you would start out with lower thermal noise.  This comes at the cost of higher read noise in your image, but I bet you could find a reasonable balance.  For example, instead of one single 8 minute exposure at ISO 100, try 8 separate one minute exposures at ISO 800 averaged in Photoshop as separate layers.  You can do this with the "smart object" tool.  That should give you an overall cleaner result without requiring any more time when shooting.  I'm not quite sure what it will do to the clouds, but it might work quite well.  Give it a shot.

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Jared Willson

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