Best DSLR or ILC for Night Sky Imaging?

Started Nov 8, 2017 | Questions
1llusive
1llusive Senior Member • Posts: 1,572
Re: If you want the best, a dedicated cooled CCD cameras are far better than all the DSLRs and ILCs

kiwi2 wrote:

Selene wrote:

Thanks and thanks again Roger and Landscaper for starting this thread. I am very new to this. As I live in a very light polluted place with lots of trees, I do most of my night sky photography elsewhere. Thus, being able to use a camera and lens is convenient for me. I am intrigued by astrotrackers, but I am still very much a beginner who has learned a lot from this discussion even though many on here understand technical details much better than I do. I like to kind of think that I am using night skies as parts of scenes I want to shoot. I am sure others have done many of the same shots, though sometimes I have been in places that aren't so heavily traveled. I appreciate that some of you who know so much, like Roger, are willing to help some of us learn. This is the great benefit of these kinds of forums--I can ignore the ones that are way over my head, while trying to get as much as I can from those I can follow. Thanks again for a most interesting and informative thread.

Don't be fooled. What Roger is leaving out in his formulas, is the inverse-square law. Light fades the further it has to travel. A longer focal length lens may have a larger aperture, but then the light also has to travel further over the focal length of the lens. For diffuse light subjects, it comes back down to f-ratio as the gauge of brightness.

That's why photographers and camera metres use f-ratio to calculate exposures rather than calculating aperture.

f/5.6 on any lens, be it 10mm or 500mm, is roughly the same amount of light reaching the sensor.

ie. Have a look at the EXIF of these two photos I have just taken out on the back lawn with the same shutter speed and ISO and f-ratio of f/5.6 and shot within minutes of each other...

The 10mm has an aperture of 1.7mm and the 500mm shot had an aperture of 89mm.

So where did the massive amount of more light from the larger aperture go as both photos are similarly exposed? (if anything, the larger aperture shot is a bit darker and underexpose)

In the wider angle shot, the light after passing through the front element only had to travel 10mm to the sensor. (loosely speaking. from the point of convergence technically) In the telephoto shot, the light had to travel 500mm to the sensor. That's why f-ratios are used as the constant/relative brightness of a lens.

This is true for brightness, but, correct me if I'm wrong, most of what Roger talks about relates to the time to achieve a decent signal to noise ratio. As aperture increases on telescopes, we see more detail.

Thoughts?

kiwi2
kiwi2 Veteran Member • Posts: 4,542
Re: If you want the best, a dedicated cooled CCD cameras are far better than all the DSLRs and ILCs

1llusive wrote:

As aperture increases on telescopes, we see more detail.

Thoughts?

Yes larger apertures on telescopes usually also come with longer focal lengths so you get more magnification and more resolution. Less diffraction due to a greater area of light relative to the edge.

For visual observing, it still also comes back down to f-ratio to how bright a telescope is for diffuse objects like nebulas and galaxies. A bigger telescope just gives you more magnification for the same brightness relative to its f-ratio. Which is why you get to see more detail in small dim galaxies with the bigger telescope you have.

But visual observers of such deep space objects wouldn't want to use a large f/16 refractor that was built for planetary observation. Deep space subjects would appear too dim in it.

They would rather use big newtonians between f/4 to f/5 like these...

http://www.obsessiontelescopes.com/telescopes/18/index.php

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JimH123 Senior Member • Posts: 1,940
Re: If you want the best, a dedicated cooled CCD cameras are far better than all the DSLRs and ILCs

1llusive wrote:

JimH123 wrote:

I have used many cameras for night sky imaging, but once I got a dedicated CCD camera, my opinions have changed. They are available in color or mono (I have both) and with the cooling, noise is greatly controled.

As an example using a mono Atik 460ex, here is one example of m27, the Dumbbell Nebula. This consists of 10 images stacked of 40 sec each taken with an Explore Scientific 102ed, a 4" objective with a focal length of 714mm. A camera like this far exceeds what any DSLR can do.

Hey Jim, do you have the FCD1 or FCD100 glass in your ES ED102? Great scope, but judging from your upper corners you may have focuser sag.

I don't know which type of glass it has.  And I do believe I have some focuser sag.  Once I add the proper extension tube, add the filter wheel, add the field flattener, plus proper extension tube and then the CCD camera, it is very long and heavy.

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JimH123 Senior Member • Posts: 1,940
Re: If you want the best, a dedicated cooled CCD cameras are far better than all the DSLRs and ILCs
2

kiwi2 wrote:

Selene wrote:

Thanks and thanks again Roger and Landscaper for starting this thread. I am very new to this. As I live in a very light polluted place with lots of trees, I do most of my night sky photography elsewhere. Thus, being able to use a camera and lens is convenient for me. I am intrigued by astrotrackers, but I am still very much a beginner who has learned a lot from this discussion even though many on here understand technical details much better than I do. I like to kind of think that I am using night skies as parts of scenes I want to shoot. I am sure others have done many of the same shots, though sometimes I have been in places that aren't so heavily traveled. I appreciate that some of you who know so much, like Roger, are willing to help some of us learn. This is the great benefit of these kinds of forums--I can ignore the ones that are way over my head, while trying to get as much as I can from those I can follow. Thanks again for a most interesting and informative thread.

Don't be fooled. What Roger is leaving out in his formulas, is the inverse-square law. Light fades the further it has to travel. A longer focal length lens may have a larger aperture, but then the light also has to travel further over the focal length of the lens. For diffuse light subjects, it comes back down to f-ratio as the gauge of brightness.

That's why photographers and camera metres use f-ratio to calculate exposures rather than calculating aperture.

f/5.6 on any lens, be it 10mm or 500mm, is roughly the same amount of light reaching the sensor.

ie. Have a look at the EXIF of these two photos I have just taken out on the back lawn with the same shutter speed and ISO and f-ratio of f/5.6 and shot within minutes of each other...

The 10mm has an aperture of 1.7mm and the 500mm shot had an aperture of 89mm.

So where did the massive amount of more light from the larger aperture go as both photos are similarly exposed? (if anything, the larger aperture shot is a bit darker and underexpose)

In the wider angle shot, the light after passing through the front element only had to travel 10mm to the sensor. (loosely speaking. from the point of convergence technically) In the telephoto shot, the light had to travel 500mm to the sensor. That's why f-ratios are used as the constant/relative brightness of a lens.

One thing you are leaving out and that is stars are point sources of light, not extended objects. For them, the size of the objective, or mirror, is what is important, not the f-ratio.

As for nebula, they are extended objects. But the big scopes improve the signal to noise ratio such that it is possible to dig them out of the background.

Here is a shot of m31 taken with an Orion 8" Astrograph, a 800mm newton type scope with a f3.9 ratio. This image was done using the Sony Multi-frame Noise Reduction (6 images) for 25 sec each and ISO 3200 where the camera combines in camera with the result having much less noise. Since it is this Multi-Frame Noise Reduction, it could only be captured in JPEG. And because it was JPEG, it is not possible to do very much with the image and it is only lightly processed.

What you should see is that the 8" mirror does make the galaxy show up better than I was previously doing using the 300mm f2.8 lens at f3.2. Although I admit the the 300mm lens was using a lower ISO 800 for the same 25 sec.  But it was heavily stretched.

Had this been done in RAW and stacked with many images, the diffuse outer regions of the galaxy would have been even better.

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kiwi2
kiwi2 Veteran Member • Posts: 4,542
Re: If you want the best, a dedicated cooled CCD cameras are far better than all the DSLRs and ILCs

JimH123 wrote: One thing you are leaving out and that is stars are point sources of light, not extended objects. For them, the size of the objective, or mirror, is what is important, not the f-ratio.

Are the dpreview test scenes point source or extended objects? Perhaps you should explain the difference to Roger.

rnclark wrote:
"DPreview changes focal length while keeping f-ratio constant. That means lens aperture area changes between cameras, thus the light delivered to the sensor is changing, and that means the amount of photon shot noise is different due to the lens, not the sensor."

Here is a shot of m31 taken with an Orion 8" Astrograph, a 800mm newton type scope with a f3.9 ratio. This image was done using the Sony Multi-frame Noise Reduction (6 images) for 25 sec each and ISO 3200 where the camera combines in camera with the result having much less noise. Since it is this Multi-Frame Noise Reduction, it could only be captured in JPEG. And because it was JPEG, it is not possible to do very much with the image and it is only lightly processed.

What you should see is that the 8" mirror does make the galaxy show up better than I was previously doing using the 300mm f2.8 lens at f3.2. Although I admit the the 300mm lens was using a lower ISO 800 for the same 25 sec. But it was heavily stretched.

So you went from 300mm f/3.2 to 800mm f/3.9. That's half a stop difference. You then also went from ISO 800 to ISO 3200. That's two stops difference.

You are now recording more light with more magnification over a larger area of the frame. Of course it's going to look better.

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JimH123 Senior Member • Posts: 1,940
Re: If you want the best, a dedicated cooled CCD cameras are far better than all the DSLRs and ILCs

kiwi2 wrote:

JimH123 wrote: One thing you are leaving out and that is stars are point sources of light, not extended objects. For them, the size of the objective, or mirror, is what is important, not the f-ratio.

Are the dpreview test scenes point source or extended objects? Perhaps you should explain the difference to Roger.

rnclark wrote:
"DPreview changes focal length while keeping f-ratio constant. That means lens aperture area changes between cameras, thus the light delivered to the sensor is changing, and that means the amount of photon shot noise is different due to the lens, not the sensor."

Here is a shot of m31 taken with an Orion 8" Astrograph, a 800mm newton type scope with a f3.9 ratio. This image was done using the Sony Multi-frame Noise Reduction (6 images) for 25 sec each and ISO 3200 where the camera combines in camera with the result having much less noise. Since it is this Multi-Frame Noise Reduction, it could only be captured in JPEG. And because it was JPEG, it is not possible to do very much with the image and it is only lightly processed.

What you should see is that the 8" mirror does make the galaxy show up better than I was previously doing using the 300mm f2.8 lens at f3.2. Although I admit the the 300mm lens was using a lower ISO 800 for the same 25 sec. But it was heavily stretched.

So you went from 300mm f/3.2 to 800mm f/3.9. That's half a stop difference. You then also went from ISO 800 to ISO 3200. That's two stops difference.

You are now recording more light with more magnification over a larger area of the frame. Of course it's going to look better.

Found this link from Starizona on point sources vs extended objects.  And not sure how to incorporate your above quote you used into this theory.  When it comes to stars, my 8" scope can easily see stars to the 17th magnitude (30 sec image) and with longer imaging, even dimmer than that.  I can see this myself with an eyepiece, but the camera can.  But these are point sources and all the captured light is concentrated on the point source.  Also, the 800x more light is the special case that an eyepiece with the appropriate focal length is concentrating the light down to a 7mm eye exit pupil size.  Instead, we are doing a prime focus and concentrating the light down to the sensor size with perhaps some light lost beyond the edges of the sensor.

https://starizona.com/acb/basics/observing_theory.aspx

One thing that sees to change the brightness equation is Photoshop Stretching. If we compare straight out of the camera, I do believe that surface brightness is not going to change. But when we use the Curves adjustment, perceived brightness is going to change. The theory links that I find leave the photoshopping out of the equation. But everyone who captures Nebula and Galaxies do indeed stretch, and this includes Hubble. If the image out of the camera, or the image created by stacking is really good, we can stretch it quite far. The range is really limited by the image we are working on. Some cameras are only 12-bit RAW. Some are 14-bit RAW. And my CCD cameras are 16-bit TIFF, and they stretch the farthest. In the case of capturing only JPEGs, the stretching is near useless. Now stretching is artificial and we play games with the range of values we are interested in, and we can make it look quite nice. But this is outside of the theory described in the link.

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kiwi2
kiwi2 Veteran Member • Posts: 4,542
Re: If you want the best, a dedicated cooled CCD cameras are far better than all the DSLRs and ILCs

JimH123 wrote:

Found this link from Starizona on point sources vs extended objects.

https://starizona.com/acb/basics/observing_theory.aspx

And here's a link more specifically talking about the f-ratio of a telescope...

https://www.astronomics.com/focal-ratio_t.aspx

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sharkmelley
sharkmelley Senior Member • Posts: 2,172
Re: If you want the best, a dedicated cooled CCD cameras are far better than all the DSLRs and ILCs
1

1llusive wrote:

This is true for brightness, but, correct me if I'm wrong, most of what Roger talks about relates to the time to achieve a decent signal to noise ratio. As aperture increases on telescopes, we see more detail.

Thoughts

I'm thinking about it. I wrote some nonsense here earlier which I've deleted.

Mark

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Trollmannx Senior Member • Posts: 5,529
Re: If you want the best, a dedicated cooled CCD cameras are far better than all the DSLRs and ILCs
1

kiwi2 wrote:

1llusive wrote:

As aperture increases on telescopes, we see more detail.

Thoughts?

Yes larger apertures on telescopes usually also come with longer focal lengths so you get more magnification and more resolution. Less diffraction due to a greater area of light relative to the edge.

Not quite so - aperture determines light grasp and resolution.

Faster telescopes (lower f/ratios) collect the same amount of light as similarly sized slower telescopes (higher f/ratios). Aperture is the key.

Resolution is diffraction limited. The aperture of the telescope determines resolution, not the focal ratio (f/number).

For visual observing, it still also comes back down to f-ratio to how bright a telescope is for diffuse objects like nebulas and galaxies. A bigger telescope just gives you more magnification for the same brightness relative to its f-ratio. Which is why you get to see more detail in small dim galaxies with the bigger telescope you have.

For visual use f/ratio is irrellevant.

For photographic use take a look at plate scale, extended objects, etendue and point sources of light...

Visual use:

Use different eyepieces with telescopes having similar aperture (we are talking telescopes here so aperture is the diameter of the objective lens or mirror) but different f/ratios to get the same magnification. What happens then?

But visual observers of such deep space objects wouldn't want to use a large f/16 refractor that was built for planetary observation. Deep space subjects would appear too dim in it.

Really?

They would rather use big newtonians between f/4 to f/5 like these...

This is more about price and portability than anything else...

Trollmannx Senior Member • Posts: 5,529
Re: If you want the best, a dedicated cooled CCD cameras are far better than all the DSLRs and ILCs
1

kiwi2 wrote:

JimH123 wrote: One thing you are leaving out and that is stars are point sources of light, not extended objects. For them, the size of the objective, or mirror, is what is important, not the f-ratio.

Are the dpreview test scenes point source or extended objects? Perhaps you should explain the difference to Roger.

Migh be a good idea to read what Roger said one more time...

If anyone here is familiar with photons is is Roger - actually a real life astronomer!

rnclark wrote:
"DPreview changes focal length while keeping f-ratio constant. That means lens aperture area changes between cameras, thus the light delivered to the sensor is changing, and that means the amount of photon shot noise is different due to the lens, not the sensor.

Here is a shot of m31 taken with an Orion 8" Astrograph, a 800mm newton type scope with a f3.9 ratio. This image was done using the Sony Multi-frame Noise Reduction (6 images) for 25 sec each and ISO 3200 where the camera combines in camera with the result having much less noise. Since it is this Multi-Frame Noise Reduction, it could only be captured in JPEG. And because it was JPEG, it is not possible to do very much with the image and it is only lightly processed.

What you should see is that the 8" mirror does make the galaxy show up better than I was previously doing using the 300mm f2.8 lens at f3.2. Although I admit the the 300mm lens was using a lower ISO 800 for the same 25 sec. But it was heavily stretched.

So you went from 300mm f/3.2 to 800mm f/3.9. That's half a stop difference.

Yes - but there is another variable, aperture.

You then also went from ISO 800 to ISO 3200. That's two stops difference.

ISO does NOT change the sensitivity of the image sensor - just amplify the existing signal.

You are now recording more light with more magnification over a larger area of the frame. Of course it's going to look better.

The key here is more light...

kiwi2
kiwi2 Veteran Member • Posts: 4,542
Re: If you want the best, a dedicated cooled CCD cameras are far better than all the DSLRs and ILCs

Trollmannx wrote:

kiwi2 wrote:

1llusive wrote:

As aperture increases on telescopes, we see more detail.

Thoughts?

Yes larger apertures on telescopes usually also come with longer focal lengths so you get more magnification and more resolution. Less diffraction due to a greater area of light relative to the edge.

Not quite so - aperture determines light grasp and resolution.

Faster telescopes (lower f/ratios) collect the same amount of light as similarly sized slower telescopes (higher f/ratios). Aperture is the key.

Resolution is diffraction limited. The aperture of the telescope determines resolution, not the focal ratio (f/number).

For visual observing, it still also comes back down to f-ratio to how bright a telescope is for diffuse objects like nebulas and galaxies. A bigger telescope just gives you more magnification for the same brightness relative to its f-ratio. Which is why you get to see more detail in small dim galaxies with the bigger telescope you have.

For visual use f/ratio is irrellevant.

For photographic use take a look at plate scale, extended objects, etendue and point sources of light...

Visual use:

Use different eyepieces with telescopes having similar aperture (we are talking telescopes here so aperture is the diameter of the objective lens or mirror) but different f/ratios to get the same magnification. What happens then?

But visual observers of such deep space objects wouldn't want to use a large f/16 refractor that was built for planetary observation. Deep space subjects would appear too dim in it.

Really?

They would rather use big newtonians between f/4 to f/5 like these...

This is more about price and portability than anything else...

So much wrong here I don't know where to start.

The focal length of the telescope determines the magnification. Just as the focal length on a camera lens does. Magnification for a telescope is the telescope's focal length divided by the eyepiece focal length.

So let's run the numbers over a couple of different telescope f-speeds.

Take the 24" f/4 scope from here.

It has a focal length of 2540mm.

A 40mm eyepiece is about the lowest magnification widest field of view available. So 2540 divided by 40 = 63 times magnification. A nice low power that keeps nebula and galaxies looking bright. (ignoring if this too low a magnification for the scope and exit pupil is larger than 8mm and wasting light, for now)

Then take the Great Lick Refractor as another example. A 36" f/19 scope with a focal length of 17,630mm. Drop in that 40mm eyepiece and you get 440 times magnification. The more you magnify something the dimmer it gets. 440 times magnification being the lowest power this telescope could do is still far too much for a lot of deep space objects.

But of course we already knew that just by knowing it was a f/19 scope. Even though it has a larger aperture, its longer focal length drives too much magnification and diffuse objects will look dimmer. Lunar and planets and resolving binary stars is what this telescope would be better at, as they are bright objects and benefit from the higher magnification.

You cannot solely look at aperture alone and ignore the f-ratio when choosing a telescope.

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Trollmannx Senior Member • Posts: 5,529
Re: If you want the best, a dedicated cooled CCD cameras are far better than all the DSLRs and ILCs

kiwi2 wrote:

Trollmannx wrote:

kiwi2 wrote:

1llusive wrote:

As aperture increases on telescopes, we see more detail.

Thoughts?

Yes larger apertures on telescopes usually also come with longer focal lengths so you get more magnification and more resolution. Less diffraction due to a greater area of light relative to the edge.

Not quite so - aperture determines light grasp and resolution.

Faster telescopes (lower f/ratios) collect the same amount of light as similarly sized slower telescopes (higher f/ratios). Aperture is the key.

Resolution is diffraction limited. The aperture of the telescope determines resolution, not the focal ratio (f/number).

For visual observing, it still also comes back down to f-ratio to how bright a telescope is for diffuse objects like nebulas and galaxies. A bigger telescope just gives you more magnification for the same brightness relative to its f-ratio. Which is why you get to see more detail in small dim galaxies with the bigger telescope you have.

For visual use f/ratio is irrellevant.

For photographic use take a look at plate scale, extended objects, etendue and point sources of light...

Visual use:

Use different eyepieces with telescopes having similar aperture (we are talking telescopes here so aperture is the diameter of the objective lens or mirror) but different f/ratios to get the same magnification. What happens then?

But visual observers of such deep space objects wouldn't want to use a large f/16 refractor that was built for planetary observation. Deep space subjects would appear too dim in it.

Really?

They would rather use big newtonians between f/4 to f/5 like these...

This is more about price and portability than anything else...

So much wrong here I don't know where to start.

The focal length of the telescope determines the magnification. Just as the focal length on a camera lens does. Magnification for a telescope is the telescope's focal length divided by the eyepiece focal length.

So let's run the numbers over a couple of different telescope f-speeds.

Take the 24" f/4 scope from here.

It has a focal length of 2540mm.

A 40mm eyepiece is about the lowest magnification widest field of view available. So 2540 divided by 40 = 63 times magnification. A nice low power that keeps nebula and galaxies looking bright. (ignoring if this too low a magnification for the scope and exit pupil is larger than 8mm and wasting light, for now)

Then take the Great Lick Refractor as another example. A 36" f/19 scope with a focal length of 17,630mm. Drop in that 40mm eyepiece and you get 440 times magnification. The more you magnify something the dimmer it gets. 440 times magnification being the lowest power this telescope could do is still far too much for a lot of deep space objects.

But of course we already knew that just by knowing it was a f/19 scope. Even though it has a larger aperture, its longer focal length drives too much magnification and diffuse objects will look dimmer. Lunar and planets and resolving binary stars is what this telescope would be better at, as they are bright objects and benefit from the higher magnification.

You cannot solely look at aperture alone and ignore the f-ratio when choosing a telescope.

Have been into telescopes and microscopes and photographic lenses and cameras for a lifetime, even worked in the photo buisiness for a while, and it seems like I (and some others here) have gotten it all wrong all the time... 

kiwi2
kiwi2 Veteran Member • Posts: 4,542
Re: If you want the best, a dedicated cooled CCD cameras are far better than all the DSLRs and ILCs

Trollmannx wrote:

Have been into telescopes and microscopes and photographic lenses and cameras for a lifetime, even worked in the photo buisiness for a while, and it seems like I (and some others here) have gotten it all wrong all the time...

Well, saying... "For visual use f/ratio is irrellevant" ...is showing your lack of understanding of the subject.

That is ignoring the focal length of the telescope which effects the magnification range you will get with your given eyepieces. Which effects the brightness of diffuse objects.

The size of the aperture relative to the focal length is the f-ratio.

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1DSmII Contributing Member • Posts: 803
Re: If you want the best, a dedicated cooled CCD cameras are far better than all the DSLRs and ILCs
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kiwi2 wrote:

What Roger is leaving out in his formulas, is the inverse-square law. Light fades the further it has to travel. A longer focal length lens may have a larger aperture, but then the light also has to travel further over the focal length of the lens.

I can't see how this can be correct. The inverse square law says that if you double the distance then you are left with 1/4 of the light (if memory serves).

Lets say you are imaging a star that is 100 light years away, then you would have to move a further 100 light years away from that star to be receiving 1/4 of the light that you were receiving at 100 light years, all other things being equal. The length of the lens is irrelevant, especially if the sensor remains at the same distance from the star.

A few inches, feet, or even miles difference between the first/front element and the sensor is not going to have any significant impact on the light intensity. Obviously, the light transmission of a huge optic would play a part, so for the experiment to work, the longer lens would need to have the same light transmission characteristics as the shorter lens you are comparing to.

If what you said was true then it would imply that if you image the same star in January, and again in August, the brightness of that star would be significantly changed comparing one image to the other, since we have moved millions of miles nearer to or further from the star, and this is simply not the case.

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1DSmII Contributing Member • Posts: 803
Re: Best DSLR or ILC for Night Sky Imaging?
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Despite the ruffled feathers, I think this has been a very enlightening thread, and I just want to say thanks for every person's contribution, especially Roger's. I commend his efforts to make this complex subject more understandable for people like myself who have a hard time getting their head around the subject.

I would love to see this thread brought to the attention of the DPR staff, so they could address the concerns raised by Roger here about their testing procedures.

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kiwi2
kiwi2 Veteran Member • Posts: 4,542
Re: If you want the best, a dedicated cooled CCD cameras are far better than all the DSLRs and ILCs

1DSmII wrote:

kiwi2 wrote:

What Roger is leaving out in his formulas, is the inverse-square law. Light fades the further it has to travel. A longer focal length lens may have a larger aperture, but then the light also has to travel further over the focal length of the lens.

I can't see how this can be correct. The inverse square law says that if you double the distance then you are left with 1/4 of the light (if memory serves).

Lets say you are imaging a star that is 100 light years away, then you would have to move a further 100 light years away from that star to be receiving 1/4 of the light that you were receiving at 100 light years, all other things being equal. The length of the lens is irrelevant, especially if the sensor remains at the same distance from the star.

A few inches, feet, or even miles difference between the first/front element and the sensor is not going to have any significant impact on the light intensity. Obviously, the light transmission of a huge optic would play a part, so for the experiment to work, the longer lens would need to have the same light transmission characteristics as the shorter lens you are comparing to.

If what you said was true then it would imply that if you image the same star in January, and again in August, the brightness of that star would be significantly changed comparing one image to the other, since we have moved millions of miles nearer to or further from the star, and this is simply not the case.

The lens is creating a projection onto the sensor. So it is that projection that now becomes relevant as it has a finite amount of light from the aperture. The projection of the 500mm lens was 50 times the distance over the projected distance of the 10mm lens.

That's why the 1.7mm aperture of a 10mm lens can put the same amount of light onto the sensor as the 89mm aperture of the 500mm lens and the f-ratio is a constant across all lenses of any focal length...

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Astrophotographer 10 Forum Pro • Posts: 13,143
Re: Best DSLR or ILC for Night Sky Imaging?
1

landscaper1 wrote:

I want to thank everyone who responded to my initial post. I've learned a few things (well, maybe more than a few) that I didn't know before. I posted this query because I really didn't know whether my Canon 5Div was an optimum performer when it came to minimal noise at higher ISOs.

The information about the Sony A7s was news to me and very interesting. In principal, I can afford to buy an A7s (plus a Metabones adapter so my EF mount lenses will work on the A7s). However, while my budget may be capable of absorbing that expense, my 40 years of managing other peoples' money still governs my instincts. That's not to say "economy at any cost," but rather "evaluate whether the additional cost is justified by the performance gains."

That led me to check DPR's review of the A7s and compare noise levels at ISO 6400 for both the A7s and the 5Div. I'll concede the A7s has the edge, but it seems to me that it's an almost imperceptible edge over the 5Div. However, the 5Div's edge is, based on Rogers comments, its 5.35 micron pixel size despite being a FF sensor.

On that basis, it seems to me there is really no point in acquiring the Sony A7s no matter how affordable it might be. Does anyone disagree with that assessment? If so, please explain.

I am not a huge fan of the Sony A7s from the standpoint of I have not seen many nightscapes I liked from that camera. The pixels are large and the res is a bit low plus it does not seem to show the sprinkling of stars in Milky Way shots as well as it could.

Another thing I noticed with A7s images is colour. Its colour seems off.

I have seen some spectacular images from an A7s that was modified. Lovely patches of red nebulosity that unmodded cameras usually don't show at all.

5D4 is probably a good all round camera for nightscapes. I personally am not a Canon fan due to the lack of technical innovation Canon is putting into its cameras but they are still solid well thought out cameras.

I would go for a 6D. From my view the best images I have seen were from modded 6Ds. I tend to chose gear based on images I see I admire rather than spec sheets so much ( I look at both but the final image is the proof of performance).

My Sony A7r2 is good, my Sony A7r was also good. My Nikon d800e was very good.My Fuji XT2 is good. None are perfect. The 6D seems to have the least drawbacks and those drawbacks are more about lack of tilt screen and poor live view both able to be overcome.

There have been some lovely images from a Nikon D5300 modded on this site. That would be worth a look.

I am with Roger on this. Camera is of less importance these days as most modern cameras would be able to do the job. Lens would be more important and most important of all is access to a dark site. Without that you will need to check out light pollution filters and everything will be so much harder. As far as fast lenses though the list of lens that don't show bad coma in the corners at F1.4 would be almost a non-existent list. I see the Sigma Art 35 1.4 is a common choice. I have not used it myself but it seems one of the very very few that is good in the corners. Almost all F1,4 are very poor in the corners and need to be stopped down to F2/F2.8 before they are usable unless you plan to crop 1/3rd of your image out. Keep that in mind. Fuji has a number of F1.4 lenses none of which show round stars in the corners at F1.4. That's the usual story,

As far as pixel size go that is a new datum for me as in the telescope world pixel size is matched to focal length and atmospheric seeing conditions. Seeing conditions don't come into night scapes as they are so widefield tiny star blur from bad seeing is imperceptible. Its very perceptible in long focal length telescopes. Generally larger pixels work better at long focal lengths (around 2 metres and beyond) and smaller pixels work better at shorter focal lengths (under 1 metre roughly). Smaller pixels in telescope world suffer from small well capacity so this means you can get bloated bright stars if the exposures are not short enough.

A large pixel with deep wells makes it easier to image at the full dynamic range of the camera. It will hold highlights longer. How that applies to nightscapes I am not sure if its even really a factor as the camera isn't really being pushed that hard in terms of dynamic range.

A dark sky is by far the most important factor and you can talk about pixel sizes, noise, etc ad infinitum but without dark skies you really are limited no matter which camera you use.

Greg.

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1llusive
1llusive Senior Member • Posts: 1,572
What I think is missing from the discussion
1

kiwi2 wrote:

1llusive wrote:

As aperture increases on telescopes, we see more detail.

Thoughts?

Yes larger apertures on telescopes usually also come with longer focal lengths so you get more magnification and more resolution. Less diffraction due to a greater area of light relative to the edge.

For visual observing, it still also comes back down to f-ratio to how bright a telescope is for diffuse objects like nebulas and galaxies. A bigger telescope just gives you more magnification for the same brightness relative to its f-ratio. Which is why you get to see more detail in small dim galaxies with the bigger telescope you have.

But visual observers of such deep space objects wouldn't want to use a large f/16 refractor that was built for planetary observation. Deep space subjects would appear too dim in it.

They would rather use big newtonians between f/4 to f/5 like these...

http://www.obsessiontelescopes.com/telescopes/18/index.php

I'll share what little I do know. Resolution and detail increase with aperture size. A smaller aperture telescope will never achieve the same detail as a larger one. You can try to magnify with an eyepiece and the image will be fuzzy. You can try to integrate long exposures forever and the image will still be fuzzy. How do you solve this problem? A larger aperture. But, can the smaller telescope focus the same relative brightness onto an image sensor? Of course, these are the same physics that camera lens designers have to work with. You can (keeping aperture the same) build a shorter focal length telescope/lens or install a focal reducer and achieve a lower f-ratio, but then the image won't be the same resolution or scale. So to better illustrate the effect of aperture size, let's try to keep focal length the same:

100mm aperture, 500mm focal length = f/5

80mm aperture, 500mm focal length = f/6.25

The 100mm aperture telescope/lens will not only concentrate more photons onto the sensor per square mm, it will also resolve more detail. This is the real effect of a larger aperture. This would in fact capture more signal per second of exposure, backing up Roger Clark's statements.

Please feel free to tell me where I am wrong about this.

Astrophotographer 10 Forum Pro • Posts: 13,143
Re: If you want the best, a dedicated cooled CCD cameras are far better than all the DSLRs and ILCs

swimswithtrout wrote:

JimH123 wrote:

I have used many cameras for night sky imaging, but once I got a dedicated CCD camera, my opinions have changed. They are available in color or mono (I have both) and with the cooling, noise is greatly controled.

As an example using a mono Atik 460ex, here is one example of m27, the Dumbbell Nebula. This consists of 10 images stacked of 40 sec each taken with an Explore Scientific 102ed, a 4" objective with a focal length of 714mm. A camera like this far exceeds what any DSLR can do.

I totally agree !!!

But the OP and most everyone else here can't accept that fact. Unfortunately, 99.9 % of the users here think that "Astrophotography" is just a WA shot of the MW with a noisy foreground.

With the prices of all of the new CMOS based, cooled sensors, in 4/3 / APS-c format dropping down to less than the price of a FF camera. the day of the dSLR for AP is over.

Quite true these new cooled CMOS one shot colour cameras and mono are very nice. But now you need a power supply and a laptop. So its a bit out of the I want to take some night landscape type shots.

Usually there are no L brackets for these cameras as well so mounting them so you can get the angles would be something to consider. Possible but not straight out of the box.

Adapters to fit regular lenses at the right flange distance comes into it as well.

But yes some of those nice QHY cooled cameras with the Sony 36mp one shot colour with true unmonkeyed with RAW would be divine.

You can control some brands with a smartphone now. How you store the images and focus and have a portable power supply is still an issue. But a car battery and a laptop would do it

Greg.

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Astrophotographer 10 Forum Pro • Posts: 13,143
Re: Best DSLR or ILC for Night Sky Imaging?

rnclark wrote:

kiwi2 wrote:

Astrophotographer 10 wrote:

I have used a Nikon D70, Canon 20D, 40D, Nikon D800e, Sony A&r, Sony A7r2, Sony Nex 6, Fuji XE1, XT1, XT2.

Nice write-up. "Best" of anything is subjective as most things have their pluses and minuses.

Fuji XT2 is an excellent astro camera. If you use the DPR comparison tool you will see the XT2 is one of the lowest noise APSc cameras. The Xtrans colour filter array is designed to reduce luminance noise by using a bigger block of pixels for creating an individual image pixel and its features are fabulous. Dual axis tilting screen, a cleaner EVF at high ISO for focusing, small and light and cheaper, it can use any lens (non Fuji need adapters), It has a built in intervalometer. It allows exposures up to 15minutes without having to use an external intervalometer. The Samyang 12mm F2 is cheap and wonderful for widefield nightscapes. Hard to fault this camera. Poor battery life is one negative. Same with Sony unless its A7r3. A7s to me has poor colour output, suffers from the star eater issue the most due to the larger pixels and is not really that useful for day photography with the lack of resolution. So Sony made a nightscape camera and then crippled it with poorly thought out noise suppression firmware.

You echo how I feel about my X-T2. I knew when I bought it that it wasn't going to be technically the best astro camera around. But as an overall package and a general use day to day camera as well, it was going to be the best to me for bang for the buck.

The thing is, it doesn't have hardly any colored chrominance noise. It mainly has luminance noise, so it looks more like old film grain and can clean up very well in post without all that digital looking colored noise lurking in the shadows...

Boy you guys are still at it. Don't be fooled: many things change in those dpreview comparisons. XT-2: aps-c 3.93 micron pixels, 5DII: full frame 6.4 micron pixels, 80D: aps-c 3.7 micron pixel size, a6000: aps-c 3.92 micron pixels. They change the lens between formats, and it looks like they change the focal length within formats too. They keep f-ratio constant to keep exposure the same, but that means absolute light levels change, which means photon noise levels change. Then the demosaicking algorithm changes between cameras. Small tweaks of settings in the raw converter will make huge changes in results. Or a different raw converter, like rawtherapee will make huge improvements in results.

And the noise is not representative of the noise in a night sky image, which is dominated noise from the sky.

The only real issue between camera bodies are which ones have banding issues at the ISO used for night sky photography, and dpreview does not show banding. (The ancient generation 5DII has banding issues.)

No one should be doing night sky photography at iso 12800.

The differences between cameras in short exposure night sky images as by far more affected by the lens and exposure time (e.g. 20 versus 30 seconds). The differences between modern cameras given the same lens is on the order of less than 1/3 of a stop.

OK, rant over--go back to obsessing over camera bodies.

Roger

Hehe. I agree with what you say that the modern camera is less of an issue but this is a gear forum so to ask which camera is better is a very valid question.

Noise in shadows I would rate as very important. Banding is really only a Canon problem I have not heard of it with anyone else nor seen it in Sony, Fuji or Nikon cameras.

Noise grain is nicer in some cameras than others. As pointed out XT2 has a nice grain (all Fuji's do) Sony noise grain is not as good.

Having tried both A6000 and Fuji XT2 DPR flaws aside the noise shown is representative of how they perform. The A6000 is considerably noisier than the XT2 which is about as clean as any.

When you talk about small pixels being better this is in an urban light polluted environment?

Dark skies are in fact the dominant factor above everything else. Most cameras at a really dark site will produce an awesome image. Larger pixels may retain star colour data for longer exposures than smaller pixels. I have been surprised how well my A7r2 retains star colour despite high ISO and 30 seconds. Much like my dedicated deep well large pixelled (9 microns) astro camera which can take a hiding from bright stars and still not overexpose and retains detail.

But some cameras are better at it than others and some have features that make the process a lot easier and more enjoyable. Light weight, smaller, lighter lenses, lens selection, tilt screens, EVF or OVF, built in intervalometer or not, noise levels, uncompressed RAW or lossless compressed RAW, level indicator, amp glow or none or little, longest exposure time allowed in camera (XT2 goes to 15minutes in camera) timer countdown so you can see how long the exposure has been going, accessories like L brackets etc, modified or not. Lots of things.

But high ISO noise performance, no banding in shadows, tilt screen would be high on the list of priorities. Banding would be a bad one as that is really not correctable in post processing. Most other issues are.

Noise is easily handled by stacking if its really a bother. So is aperture of the lens. Get more light by stacking multiple image like everyone else does in Astrophotography.  Stacking is normal. So colour noise in a DSLR style nightscape is really a problem in stacking and then the complexities that introduces which the OP may not want to have to address. Understandable as I am experienced at all that processing and I don't want to have to do it!

Greg.

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