ISO Invariance ?

[Andy01]

I have a question regarding ISO invariance on my new Canon R8.

Given that my previous Canons (including 6D ii) were definitely not ISO invariant, and the R8 appears to be (if I am understanding this P to P chart correctly) ISO invariant (or very close to) from ISO 400 onwards, this is new territory for me.

Shadow Improvement of Photographic Dynamic Range versus ISO Setting

Am I understanding the chart correctly - that R8 is 0.81 EV at ISO and 0.75 EV at ISO 12,800 and fairly flat between those. By comparison the 6D ii was 1.53 EV at ISO and 2.96 EV at ISO 12,800.

Does that mean that there would be little difference between shooting stars at ISO 400 and boosting by 4 stops in post, or shooting at ISO 6400 directly ?

Which would produce a better result ? And before anyone suggests I try for myself, I have discovered that my "astro" or more accurately nightscapes lens, a Samyang 14mm f2.4 XP doesn't work at all with my R8 - just not compatible with the newer Canon R bodies. I am also in a city, so lots of light pollution (and no plans to escape for an overnighter in near future).

It is actually annoying because I am getting no response (other than "sorry for the inconvenience") from the Australian distributors of Samyang. So I am considering selling my Samyang XP, and getting either a Canon RF 16mm (which doesn't have great coma performance at f2.8), or a Pergear 14mm f2.8 Mark ii fully manual lens.

The Pergear Mark ii actually looks quite attractive because reviews seem to indicate that it's own real weaknesses are bad vignetting (common to most UWA), and quite bad flaring (which isn't usually an issue for nightscapes or Milky Way). It shows no distortion (good for daytime UWA) and no CA, and seems to have minimal coma, and is small and compact (not that light weight) for traveling, and is cheap (around AU420 or US$280). Also, being fully manual there is minimal issue with incompatibility with future Canon R bodies.

Any comments / thoughts on both the ISO question and / or the lens situation would be appreciated. Thanks.

 

[W5JCK]

Compare my Sony a7C with your Canon R8. They look almost identical in performance on that chart. I can’t speak to your R8, but my a7C looks good up to ISO 12800 in video in my suburban Bortle 8 location. However, if I’m shooting photos at several second shutter speeds I can’t (nor do I need to) go above ISO 400. You can crank the ISO up on video because you are shooting 1/25th sec or 1/30th sec. Dynamic range takes a big hit at ISO 12800 though. The better numbers to look at are the 1st base ISO and the 2nd base ISO. On my a7C 1st base ISO = 100 and 2nd base ISO = 640. Stay out of the extended ISO ranges as they are artificial. For photography, 1st and 2nd base ISOs will have similar dynamic range values. Go beyond that and dynamic range starts to drop rather fast. Granted for night sky dynamic range isn’t that big of a deal, but it is a big deal if shooting low light night scenes on city streets because it allows the camera to capture more in the shadows.

--1st base ISOV
Best Regards,
Jack
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Sony RX100M3, a6000, and a7

 

[Andy01]

Compare my Sony a7C with your Canon R8. They look almost identical in performance on that chart.

I have just looked and yes they do - very similar.

I can’t speak to your R8, but my a7C looks good up to ISO 12800 in video in my suburban Bortle 8 location. However, if I’m shooting photos at several second shutter speeds I can’t (nor do I need to) go above ISO 400. You can crank the ISO up on video because you are shooting 1/25th sec or 1/30th sec. Dynamic range takes a big hit at ISO 12800 though. The better numbers to look at are the 1st base ISO and the 2nd base ISO. On my a7C 1st base ISO = 100 and 2nd base ISO = 640.

That is very useful, thank you. On my R8 it appears to be 100 & 400.

Stay out of the extended ISO ranges as they are artificial. For photography, 1st and 2nd base ISOs will have similar dynamic range values. Go beyond that and dynamic range starts to drop rather fast. Granted for night sky dynamic range isn’t that big of a deal, but it is a big deal if shooting low light night scenes on city streets because it allows the camera to capture more in the shadows.

Another question - if I am shooting stars at ISO 400, do I need to bump it up (maybe ISO 12,800 ?) to get visibility while manually focusing and then drop back to ISO 400 to shoot, and then do the "brightening" using curves in PS ?

No thoughts on the Pergear manual lens ?

 

[W5JCK]

Another question - if I am shooting stars at ISO 400, do I need to bump it up (maybe ISO 12,800 ?) to get visibility while manually focusing and then drop back to ISO 400 to shoot, and then do the "brightening" using curves in PS ?

I wouldn't. If the R8 is a decent camera the LCD should reflect a good view similar to the photos. If you need to brighten the image on the LCD for focusing, try increasing the shutter speed temporarily.

No thoughts on the Pergear manual lens ?

I'm not familiar with this lens. However, some cmeras do have metering issues with non-wired lenses, which might explain the LCD showing a too dark scene compared to an actual photo.

 

[Andy01]

Another question - if I am shooting stars at ISO 400, do I need to bump it up (maybe ISO 12,800 ?) to get visibility while manually focusing and then drop back to ISO 400 to shoot, and then do the "brightening" using curves in PS ?

I wouldn't. If the R8 is a decent camera the LCD should reflect a good view similar to the photos. If you need to brighten the image on the LCD for focusing, try increasing the shutter speed temporarily.

No thoughts on the Pergear manual lens ?

I'm not familiar with this lens. However, some cmeras do have metering issues with non-wired lenses, which might explain the LCD showing a too dark scene compared to an actual photo.

Thanks. I seem to remember that Canon users suggested turning off the exposure simulation on the screen/EVF to get a better view of what is going on.

 

[W5JCK]

Thanks. I seem to remember that Canon users suggested turning off the exposure simulation on the screen/EVF to get a better view of what is going on.

It seems like every camera company has a different way of determining the LCD preview image. I never trust it though, or the EV numbers it states. I always take a test shot and take a look to be sure I’ve got the settings correct. My Sonys usually show a fairly accurate preview, but occasionally they shank it!

 

[Jared Willson]

I don't own the R8, but do have a fair amount of experience with modern cameras doing astrophotography, so I will make a few recommendations based on that.

1. Do turn off the exposure simulation so the EVF will try to show you a properly exposed image
2. Even after making the above adjustment, you may need/want to temporarily raise the ISO towards the maximum value to aid in focus. Just raising the shutter speed doesn't help that much for autofocus since it slows down the responsiveness of the EVF tremendously, making evaluations of focus difficult. Nothing wrong with raising the gain for focus--just remember to put it back when you are done
3. From looking at the "Input Referred Read Noise" chart for your camera and at the "Photographic Dynamic Range" chart, I would choose an ISO of 1600 for imaging night skies. The thing I noted from the charts is that Canon applies noise reduction to all raw files below ISO 1600. See the "triangle down" reference in Photons-to-Photos. Noise reduction often results in lost stars, particularly with a wide angle lens where faint stars will frequently cover only one pixel. I haven't used this camera, so I can't say for sure, but my experience with other brand cameras that applied noise reduction to raw files was bad. You don't want that. So I'd use ISO 1600
4. The camera does appear to be ISO invariant through much of its range. No reason I can see to use ISO's greater than 1600. Stretching in post will yield equally good results in terms of noise, while reducing the number of clipped stars.

Good luck!

- Jared

 

[W5JCK]

I don't own the R8, but do have a fair amount of experience with modern cameras doing astrophotography, so I will make a few recommendations based on that.

1. Do turn off the exposure simulation so the EVF will try to show you a properly exposed image
2. Even after making the above adjustment, you may need/want to temporarily raise the ISO towards the maximum value to aid in focus. Just raising the shutter speed doesn't help that much for autofocus since it slows down the responsiveness of the EVF tremendously, making evaluations of focus difficult. Nothing wrong with raising the gain for focus--just remember to put it back when you are done
3. From looking at the "Input Referred Read Noise" chart for your camera and at the "Photographic Dynamic Range" chart, I would choose an ISO of 1600 for imaging night skies. The thing I noted from the charts is that Canon applies noise reduction to all raw files below ISO 1600. See the "triangle down" reference in Photons-to-Photos. Noise reduction often results in lost stars, particularly with a wide angle lens where faint stars will frequently cover only one pixel. I haven't used this camera, so I can't say for sure, but my experience with other brand cameras that applied noise reduction to raw files was bad. You don't want that. So I'd use ISO 1600
4. The camera does appear to be ISO invariant through much of its range. No reason I can see to use ISO's greater than 1600. Stretching in post will yield equally good results in terms of noise, while reducing the number of clipped stars.

Good luck!

- Jared

AF? I suggest one should never trust AF for astrophotography. Always use MF. A slightly out of focused dim star will simply disappear, so you need to manually fine tune the focus.

 

[Jared Willson]

I don't own the R8, but do have a fair amount of experience with modern cameras doing astrophotography, so I will make a few recommendations based on that.

1. Do turn off the exposure simulation so the EVF will try to show you a properly exposed image
2. Even after making the above adjustment, you may need/want to temporarily raise the ISO towards the maximum value to aid in focus. Just raising the shutter speed doesn't help that much for autofocus since it slows down the responsiveness of the EVF tremendously, making evaluations of focus difficult. Nothing wrong with raising the gain for focus--just remember to put it back when you are done
3. From looking at the "Input Referred Read Noise" chart for your camera and at the "Photographic Dynamic Range" chart, I would choose an ISO of 1600 for imaging night skies. The thing I noted from the charts is that Canon applies noise reduction to all raw files below ISO 1600. See the "triangle down" reference in Photons-to-Photos. Noise reduction often results in lost stars, particularly with a wide angle lens where faint stars will frequently cover only one pixel. I haven't used this camera, so I can't say for sure, but my experience with other brand cameras that applied noise reduction to raw files was bad. You don't want that. So I'd use ISO 1600
4. The camera does appear to be ISO invariant through much of its range. No reason I can see to use ISO's greater than 1600. Stretching in post will yield equally good results in terms of noise, while reducing the number of clipped stars.

Good luck!

- Jared

AF? I suggest one should never trust AF for astrophotography. Always use MF. A slightly out of focused dim star will simply disappear, so you need to manually fine tune the focus.

Meant to say "focus", not "autofocus". Yes, definitely use manual focus for astrophotography. I stand behind the advice I gave, just without the wrong word.

 

[Andy01]

I don't own the R8, but do have a fair amount of experience with modern cameras doing astrophotography, so I will make a few recommendations based on that.

1. Do turn off the exposure simulation so the EVF will try to show you a properly exposed image
2. Even after making the above adjustment, you may need/want to temporarily raise the ISO towards the maximum value to aid in focus. Just raising the shutter speed doesn't help that much for autofocus since it slows down the responsiveness of the EVF tremendously, making evaluations of focus difficult. Nothing wrong with raising the gain for focus--just remember to put it back when you are done
3. From looking at the "Input Referred Read Noise" chart for your camera and at the "Photographic Dynamic Range" chart, I would choose an ISO of 1600 for imaging night skies. The thing I noted from the charts is that Canon applies noise reduction to all raw files below ISO 1600. See the "triangle down" reference in Photons-to-Photos. Noise reduction often results in lost stars, particularly with a wide angle lens where faint stars will frequently cover only one pixel. I haven't used this camera, so I can't say for sure, but my experience with other brand cameras that applied noise reduction to raw files was bad. You don't want that. So I'd use ISO 1600
4. The camera does appear to be ISO invariant through much of its range. No reason I can see to use ISO's greater than 1600. Stretching in post will yield equally good results in terms of noise, while reducing the number of clipped stars.

Good luck!

- Jared

Thanks Jared. I did not notice the downward triangles and what they implied.

I am wondering if Bill uses JPEG for his charts ? I always thought he used RAW ? As far as I know, Canon does not and has never mandatorilly applied noise reduction to RAW images, but perhaps this has changed with the newer models. Canon have certainly applied corrections (including noise reduction) to JPEG images (especially those shot in the "semi-auto" type functions, like HDR etc), but the RAW files had no corrections or NR applied (that I am aware of).

I personally do not use any in-camera corrections of NR unless I specifically want to use OOC JPEGS (which is rare). I almost always use Canon's DPP software to apply corrections (lens corrections and corrections to any camera settings like WB, Picture Style etc.). I never use LENR or High ISO NR (in-camera).

I must try to check this out - I still haven't finished reading the entire manual yet.

 

[Bill Ferris]

The primary advantage of ISO invariance is that a photo made using an ISO at the low end of the invariant range can be lightened in post to match the appearance of a photo made at a much higher ISO without revealing debilitating read noise.

A scenario in which invariance is often advantageous, is when photographing a high dynamic range scene with bright highlights and deep shadows. If you're limited to capturing the scene in a single exposure, choosing an ISO at the low end of the invariant range to protect details in the highlights will produce a photo with dark shadows that can be lifted in post without revealing heavy read noise.

It's important to call out that invariance doesn't affect shot noise, which is determined by the amount of light used to make an image. This is one reason why exposure stacking is so widely used in night sky photography. It's a technique that allows a photographer to increases the total light used to make night sky images.

So, while working with an ISO in a camera's invariant range will largely eliminate read noise as an issue, the shot noise in the resulting photo will still be determined by the total light used. A single exposure may meet your needs. But there's a chance it may not.

Good luck.

 

[Andy01]

Thanks Bill - good info.