is it really worth switching from APS-C to the full frame sensor? - Forums

Topic starter

Oct 19, 2023

Hi everyone, for astrophotography I have always used my ordinary photo gear, currently consisting of a Canon 90D which I only recently had it to be modified in UR-IV cut and, usually, a Sigma 150-600mm zoom lens, multiplied 1.4x or 2.0x when needed.
I have never switched to astronomical camera and telescope and, at least for the moment, I have no plans to make the investment, considering that I still have a lot of room for improvement in working with the DSLR and that it is still giving me good satisfactions.

On the contrary, I have been thinking about buying a new camera for some time, with the intention of switching to a mirrorless, and I am very undecided. Remaining in the Canon world, since I have all the optics and the complete ecosystem, I am fond of APS sensors due to the advantage of their crop factor, especially in the field of nature photography and, obviously, in astrophotography: with the Sigma extended to 600mm and the 2x teleconverter I can reach an equivalent focal length of almost 2000mm.

Nonetheless, I am tempted to switch to full frame sensor, perhaps having it to be modified into full spectrum, since full frame is certainly less noisy and more sensitive than APS-C.
I just wonder if it is really worth losing the key advantage of the crop factor, which today, in the absence of telescope, it makes me a difference when shooting at most of the DSOs, even without the need to use teleconverters: using a full frame camera I would have to mount them almost always and I would not yet reach the focal lenght I can approach today.

In summary, is it really worth switching to the full frame sensor in astrophotography, remaining in the world of regular DSLR or mirrorless camera?

andrea tasselli

Frequent contributor

Oct 19, 2023 · Edited: Oct 19, 2023

I guess you have confused what the crop factor is. It isn't about the focal length but about the field of view so, as far as the image is concerned, the focal length is unchanged switching for an APS-C to a FF. FF sensors and cameras are in themselves no more sensitive or less noisy than APS-C sensor-based cameras.

Arun H

Frequent contributor

Oct 19, 2023 · Edited: Oct 19, 2023

Carlo Paschetto:
I am tempted to switch to full frame sensor, perhaps having it to be modified into full spectrum, since full frame is certainly less noisy and more sensitive than APS-C.

In an astrophotography context, full frame is not less noisy than APS-C. Generally speaking, pixels of the same size and similar generation sensors will have similar read noise and sensitivity characteristics. And in any case, read noise is one of the least important and most easily manageable sources of noise in astrophotography. Go with full frame if you want an increase Field of View, not because you think it has superior noise or sensitivity.

Even in terrestrial photography - remember that the "superiority" of full frame mainly comes from the fact that, for the same image, you'd be standing a lot closer to the subject using a full frame camera than a crop sensor. That means more light for a given aperture lens, hence better SNR.

Edit: also that you get the full FOV of wide angle lenses designed for full frame - but again, this gets to the field of view desired.

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Björn Arnold

Oct 19, 2023

The crop factor is a term which I strongly recommend to ditch. 250mm focal length are 250mm focal length, no matter if your camera has a single pixel or a full frame sensor.
The term is fine to quickly compare FOVs between full frame and cropped sensors for a given lens but otherwise, I never found any meaningful way using it.

It is absolutely not „certain“ that a full frame sensor has less noise or better signal. You definitely have to take a close look at each specific sensor. There are APS-C sensors that perform better than some full frame sensors.

I‘m sticking with APS-C as many telescope optics perform excellent on these while on a full frame the quality on the edges rapidly deteriorates. This is a very general statement and should be understood as a word of caution. The larger the sensor the more precise everything has to be. There are of course scopes that handle full frame well.

Long story short: I recommend staying with APS-C for the purpose of being able to use all that you already have.

Björn

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Carlo Paschetto

Topic starter

Oct 19, 2023

andrea tasselli:
I guess you have confused what the crop factor is. It isn't about the focal length but about the field of view so, as far as the image is concerned, the focal length is unchanged switching for an APS-C to a FF. FF sensors and cameras are in themselves no more sensitive or less noisy than APS-C sensor-based cameras.

i was meaning that the FOV I get with 600mm mounted on a APS sensor is equivalent to the one I have with 960mm on a FF, or in other words what you get working with a 600mm on an APS-C is like what you get working with a 960mm on a FF (not to mention that I work with a 32Mp sensor which allows me to widely crop images still keeping a good resolution for printing).
To simplify, I can shoot at M42 at 600mm exactly filling a 32Mp frame. To get a similar result using, say, a Canon R, I should use a 960mm focal length. On the contrary, using my 600mm on a Canon R means loosing lot of details (or I am loosing something?)

andrea tasselli

Frequent contributor

Oct 19, 2023

Carlo Paschetto:
i was meaning that the FOV I get with 600mm mounted on a APS sensor is equivalent to the one I have with 960mm on a FF, or in other words what you get working with a 600mm on an APS-C is like what you get working with a 960mm on a FF (not to mention that I work with a 32Mp sensor which allows me to widely crop images still keeping a good resolution for printing).
To simplify, I can shoot at M42 at 600mm exactly filling a 32Mp frame. To get a similar result using, say, a Canon R, I should use a 960mm focal length. On the contrary, using my 600mm on a Canon R means loosing lot of details (or I am loosing something?)

A question like that needs a lot of qualifiers to be properly answered but if you were to use the same lens the most likely outcome is that the 600/R combination would produce a better image than the 960/R combination. And resolution would be the same.

tjm8874

Oct 19, 2023

Carlo Paschetto:
To simplify, I can shoot at M42 at 600mm exactly filling a 32Mp frame. To get a similar result using, say, a Canon R, I should use a 960mm focal length. On the contrary, using my 600mm on a Canon R means loosing lot of details (or I am loosing something?)

You get more than Twice photons when you use...
600mm f/5 APS-C vs 920mm f/5 Full Frame = 1 : 2.34

You get same photons when you use...
600mm f/5 (reducer) APS-C vs 920mm f/7.7 Full Frame = 1: 0.99

Telescope Aperture rules astrophotography.

SemiPro

IOTD Staff

Oct 19, 2023 · Edited: Oct 19, 2023

Everyone above has covered the basics, but just to reiterate a few things:

I can't stress enough that you need to leave terrestrial photography terms at the door. They do not really help you in astrophotography and will lead to a lot of confusion and headaches. Here are some quick tips:

As @Björn mentioned, focal length is focal length. There is no "crop factor" in astrophotography. There is "no equivalent focal length". As he says, 250mm focal length is 250mm focal length. But why? It is because the focal length of a telescope is used to calculate very important factors to us such as image scale, focal ratio, and the FoV in arc-seconds. If you try and use "equivalent focal lengths" it can mess you up.
It is time to get used to expressing FoV in arc-seconds, not milimetres of focal length. In astro, your FoV could be something like 2.1 x 3 arc-seconds, but its never going to be expressed in focal length, or an equivalent focal length.
Without touching on things like atmospheric seeing or the Dawes Limit, your resolution is determined by the size of your pixels and your focal length. That is it. So a full-frame and APS-C camera will have the exact same resolution if their pixels are the same size and you use the same lens or telescope. What changes is the FoV, because the full-frame camera has a bigger chip.

So, to actually answer your question there are a few things to consider about full-frame sensors in astrophotography:

Most lenses and telescopes cannot handle them. The corners of the images usually fall apart unless you paid for very expensive and high quality optics. You also need to be concerned about vignetting because in astro every bit of light counts and we want to evenly illuminate the entire frame.
Even if you do have the optics, you are going to be forced to painstakingly adjust for back-focus and tilt to eliminate aberrations in the corners. Astrophotography is easily the most technically demanding subset of photography, because we are dealing with point sources of light (stars) and it's not always easy to make them look nice.
Speaking of expenses, full-frame makes everything more expensive. The optics are more expensive, the camera is more expenive, and the filters and associated accessories are more expensive.

Carlo Paschetto:
Nonetheless, I am tempted to switch to full frame sensor, perhaps having it to be modified into full spectrum, since full frame is certainly less noisy and more sensitive than APS-C.
I just wonder if it is really worth losing the key advantage of the crop factor, which today, in the absence of telescope, it makes me a difference when shooting at most of the DSOs, even without the need to use teleconverters: using a full frame camera I would have to mount them almost always and I would not yet reach the focal lenght I can approach today.

And, just to be clear full-frame cameras are not less noisy, nor do they offer any other special technical perks. You gain a bigger FoV, that is it. Stuff like noise and resolution is dependent on mechanical parameters of the camera and have nothing to do with how big the chip is.

What you should be asking yourself is if the expanded FoV is worth it to you, because you are going to pay for it in both financial and technical headaches.

https://astronomy.tools/calculators/field_of_view/

You should play around with that and see what how the FoVs of your prospective setups compare. As a final note, it's time to leave the teleconverters behind. They have an adverse affect on your focal ratio which you do not want in astrophotography.

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Joe Linington

Oct 20, 2023 · Edited: Oct 20, 2023

What they said. I was a landscape photographer and had nothing but full frame cameras for many years. When I started astrophotography I modified a 36mp FF mirrorless camera that is now basically retired. I mainly use my 2 u4/3 cooled mono cameras now and occasionally use my colour OSC camera. Your money is much better spent on a telescope, mount and cooled Astro cameras. Mono if you want the best results.

Impressive gallery BTW, you have really gotten every ounce out of that lens and mount.

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Carlo Paschetto

Topic starter

Oct 20, 2023

@Joe Linington Thank you very much!

Torben van Hees

Oct 20, 2023

I'm currently contemplating adding a fullframe mono camera to my RC setup which works at 1600mm f/6.4. I'm quite certain image quality will be decent to excellent out to the full frame and I'm well aware of the pitfalls concerning tilt and perfect collimation necessary. The financials involved seem steep but if it'll let me shoot more/better frame targets, I'ld go for it.

But - I'm really not sure if there are many. I scoured several catalogs and telescopius as well as this side - and found only very few targetsthat really benefitted from the larger FOV. Pretty much all galaxies (including M101), small PNs and many smaller emission nebulae are all small enough to fit in my current APS-C FOV (IMX571). The larger nebulae and the few big galaxies are better framed with my Epsilon-160+APS-C(also IMX571). This basically leaves a handful of very faint SH-2 emission nebulae, a few reflection nebulae (which are difficult from my backyard - much rather shoot bigger ones with the E-160ED) and some "mid-sized" PNs.

In contrast, there's a huge amount of targets that would benefit from the larger FOV if I put a FF camera on my Epsilon - but I'm not quite ready yet for that adventure.

Am I missing any obvious category?

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Joe Linington

Oct 20, 2023

Torben van Hees:
I'm currently contemplating adding a fullframe mono camera to my RC setup which works at 1600mm f/6.4. I'm quite certain image quality will be decent to excellent out to the full frame and I'm well aware of the pitfalls concerning tilt and perfect collimation necessary. The financials involved seem steep but if it'll let me shoot more/better frame targets, I'ld go for it.

But - I'm really not sure if there are many. I scoured several catalogs and telescopius as well as this side - and found only very few targetsthat really benefitted from the larger FOV. Pretty much all galaxies (including M101), small PNs and many smaller emission nebulae are all small enough to fit in my current APS-C FOV (IMX571). The larger nebulae and the few big galaxies are better framed with my Epsilon-160+APS-C(also IMX571). This basically leaves a handful of very faint SH-2 emission nebulae, a few reflection nebulae (which are difficult from my backyard - much rather shoot bigger ones with the E-160ED) and some "mid-sized" PNs.

In contrast, there's a huge amount of targets that would benefit from the larger FOV if I put a FF camera on my Epsilon - but I'm not quite ready yet for that adventure.

Am I missing any obvious category?

It is way cheaper to buy a smaller scope then to get FF gear. There are several options that keep your speed up like a SharpStar 76 or 61 and the Starizona Apex or the Askar FRA400 and 0.7 reducer. All of those options get you under f/4 for less than $1500. A 6" or 8" RASA or HyperStar is also an option. Just some thoughts.

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Arun H

Frequent contributor

Oct 20, 2023 · Edited: Oct 20, 2023

A full frame camera on a 430-530mm f/3.3 scope is a different matter entirely. As you note, the challenge of doing this is not to be underestimated. I owned an Epsilon - for a short period of time! There is 20+ page thread of discussion on this topic. If you are patient and dogged and resources and rich, you’ll end up with exceptional images. For the rest of us plebes, as Joe notes, we are better served with a short focal length refractor. No, you won’t get too many IOTDs with it, but your blood pressure will be lower and you’ll live longer.

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Björn Arnold

Oct 20, 2023

Torben van Hees:
I'm currently contemplating adding a fullframe mono camera to my RC setup which works at 1600mm f/6.4. I'm quite certain image quality will be decent to excellent out to the full frame and I'm well aware of the pitfalls concerning tilt and perfect collimation necessary. The financials involved seem steep but if it'll let me shoot more/better frame targets, I'ld go for it.

But - I'm really not sure if there are many. I scoured several catalogs and telescopius as well as this side - and found only very few targetsthat really benefitted from the larger FOV. Pretty much all galaxies (including M101), small PNs and many smaller emission nebulae are all small enough to fit in my current APS-C FOV (IMX571). The larger nebulae and the few big galaxies are better framed with my Epsilon-160+APS-C(also IMX571). This basically leaves a handful of very faint SH-2 emission nebulae, a few reflection nebulae (which are difficult from my backyard - much rather shoot bigger ones with the E-160ED) and some "mid-sized" PNs.

In contrast, there's a huge amount of targets that would benefit from the larger FOV if I put a FF camera on my Epsilon - but I'm not quite ready yet for that adventure.

Am I missing any obvious category?

Hi Torben,

I think you're hitting the nail. Obviously, most targets are small because most targets are very distant.
In my case, instead of using a larger camera, I'm using a different telescope. My camera's sensor is a small 1-incher and used at 2000mm native FL on the SCT. That means my FOV is about half a degree. However, nearly all galaxies, all PNs easily fit into this FOV. For resolution, I am binning 2x2 to be at 0,94"/pxl, making an effective f/5 scope out of the f/10.
If there's a larger object, I'm switching to 450mm (WO Zenithstar) and even further down to 250mm (WO RedCat) both at about f/5. Obviously, both are undersampled.
The essence of all this is: the only critical element is the back focus of the reducer of the ZenithStar which should be more or less accurate but due to the fairly small sensor, I never had issues with tilt or any other optical aberrations. All of the optics perform outstanding over the whole sensor.
That's why I never go beyond APS-C.

But of course, that's just my position.

CS, Björn

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Daniel Carter

IOTD Staff

Oct 20, 2023

One of the benefits of having the full frame camera (I have a Sony A7IV) is that I can shoot in APS-C mode if needed (if I have a lens made for a crop sensor camera). I think most new mirrorless cameras have a way to shoot in crop mode.

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