Upgrading from Canon 70D (lens is MP-E 65mm)

[John S.]

I hope this is the right forum for this question.

I use a Canon 70D and MP-E 65mm. The camera needs repairs, so I'm thinking of getting another one instead. If I do, it will probably be either an 80D, a 5DMK2, or a 6D.

One question I have is, will working distance be different with a full-frame camera, assuming the same magnification (e.g. 1X)?

Another question I have is whether the image quality will be different. I assume that the 80D would be at least as good as the 70D in terms of image quality, if I use the same settings I've been using. But I'm not sure if the image quality (and depth of focus) of the full-frame cameras will be better or worse.

I understand a little bit about the difference between crop sensors and full-frame sensors. I know that, to get the same framing in a full-frame as I would in a crop-factor, I would have to increase the magnification a little bit. I also know that, with a crop-factor sensor, diffraction starts to creep in at slightly lower f-numbers than with a full-frame sensor. With the 70D, when I shoot at 1X, I use f/13. With a full-frame sensor, I expect that I would use f/14 at 1X, and f/13 at slightly-higher-magnification-that-would-match-the-framing-of-a-crop-sensor-at-1X, if that makes sense.

If it matters, I'm only interested in how my images look after being cropped, not before. (I shoot insects and always crop them to "just the bug.")

Thanks for any replies. If more information is needed, let me know.

[rjlittlefield]

I hope this is the right forum for this question.

It is.

One question I have is, will working distance be different with a full-frame camera, assuming the same magnification (e.g. 1X)?

Same lens, same magnification, same working distance.

But, same framing on different sensor means different magnification and different working distance. Those Canon APS-C sensors are 1.6X crop factor, so to get the same framing as 1X on APS-C, on full frame you need 1.6X . You can play with your MP-E 65 to see what difference that makes for working distance.

But I'm not sure if the image quality (and depth of focus) of the full-frame cameras will be better or worse.

There's a general rule that is pretty simple: if you have the same framing, and you set the effective f-number in direct proportion to the sensor size, then you'll get the same DOF and the same diffraction in the final images reproduced at same size. So, 1X at effective f/26 on APS-C is equivalent to 1.6X at effective f/42 on full frame. (42 = 26*1.6)

If you shoot with the same illumination and exposure time, increasing the larger sensor's ISO setting to compensate for the larger effective f-number, then you'll also get the same amount of pixel noise due to randomness of photon arrival (shot noise).

If you set the lens and camera in this way, then there's very little difference between full frame and APS-C.

The main advantage to full frame is that it has the potential to capture more light, which produces an image that has less pixel noise. To exploit this potential requires either brighter illumination, or a longer exposure time, or both.

Perhaps the main thing to consider is that for best image quality you want to fill the sensor with the subject that you care about. So, with the MP-E 65, APS-C cameras cover the range of field widths from 4.5 to 22.5 mm, while full frame covers the range from 7.2 mm to 36 mm. If you mostly want to shoot stuff smaller then 22.5 mm with the MP-E 65, then advantage goes to the APS-C sensor because of less cropping.

I understand a little bit about the difference between crop sensors and full-frame sensors. I know that, to get the same framing in a full-frame as I would in a crop-factor, I would have to increase the magnification a little bit. I also know that, with a crop-factor sensor, diffraction starts to creep in at slightly lower f-numbers than with a full-frame sensor. With the 70D, when I shoot at 1X, I use f/13. With a full-frame sensor, I expect that I would use f/14 at 1X, and f/13 at slightly-higher-magnification-that-would-match-the-framing-of-a-crop-sensor-at-1X, if that makes sense.

Sort of, especially if "a little bit" means a factor of 1.6. The MP-E closely follows the formula that effective f-number = nominal f-number * (magnification+1). So, a setting of f/13 at 1X gives an effective aperture of f/26 (=13*(1+1)). On full frame, if you still shoot at 1X and crop, then you would still shoot at f/13 (effective f/26). But then you're not really using a full frame sensor, you're using an APS-C sensor that happens to be surrounded by a lot of wasted silicon. To actually use the full frame sensor, you would need to increase magnification to 1.6X. At the same time, to get the same DOF and diffraction blur, you would change the aperture to effective f/42 (=26*1.6), which would be achieved by a setting of f/16 (because 42=16*(1.6+1)).

I know, these are lots of numbers, which can be challenging to follow. I'm sorry about that that. But if we're going to talk numbers, we ought to have the right ones and to be clear where they're coming from.

Unless you have some other reason to prefer full frame, I suggest sticking with APS-C for your macro work. It's a better fit for small subjects, particularly if you eventually move on to using microscope objectives.

--Rik

[John S.]

Thanks for the advice and info, Rik. I ended up getting the 80D.

[klevin]

Why'd you get another dslr instead of mirrorless?

[John S.]

Why'd you get another dslr instead of mirrorless?

I think I assumed a mirrorless camera would be outside my budget, which is around $600. I'll look and see. I still have a few days to return the 80D if I want.

I'm already considering returning the 80D and getting a full-frame. If I had a full-frame, I think I would expand my use of the MP-E to include somewhat larger subjects. I do already photograph larger subjects; I just use an sx50hs+Raynox for them. I use a twin-flash with both setups, but I think the image quality is better with the DSLR, so I guess the more subjects I can make work with a DSLR, the better.

I haven't actually tried my 80D yet (my lens is being repaired), but I don't expect any problems with it.

[klevin]

I find live view with a flip up viewfinder to be indispensable for macro. And live view comes automatically with a mirrorless.

Your 70D had it. Did you use it?

But yes, dslr are much cheaper now, for a reason of course. One other advantage of mirrorless which could be relevant for macro, is the absence of mirror slap. Not having to worry about mirror lockup is a blessing.

[John S.]

I find live view with a flip up viewfinder to be indispensable for macro. And live view comes automatically with a mirrorless.

Your 70D had it. Did you use it?

Thanks for the additional thoughts. By "flip up viewfinder" I assume you mean Live View with an articulating LCD screen.

Basically, I've used the articulating LCD screen only in reviewing photos. Let me add that all my work is hand-held, although I brace my hand or rig against things when possible. I think I tried using Live View a few times when shooting insects on a blacklight sheet that offered little opportunity for bracing, so of course Live View wouldn't work well for that, whether the screen is articulated or not. Maybe that experience made me think the MP-E just wasn't suited to using Live View, at least when shooting hand-held. All I know is, I've taken almost no lateral photos of insects near the ground or on a wall or ceiling, and those are indeed the situations where using the viewfinder (as opposed to Live View) is so difficult. I'll try the Live View--with and without the articulating screen--when my lens comes back in a few business days, to take lateral photos of things near the ground, and see how it goes.

[John S.]

One other advantage of mirrorless which could be relevant for macro, is the absence of mirror slap. Not having to worry about mirror lockup is a blessing.

I didn't know what mirror lockup was till I read your post and looked it up. I hadn't thought about the mirror slap causing vibration, but it makes sense, of course. I read that mirror lockup may not make a difference if you're shooting handheld and depending on the speed (I generally shoot at 1/250 with the MP-E), but maybe I'll try it out and see if I can tell a difference and how inconvenient it is.

[Chris S.]

Mirror lock-up is very useful for macro, but I'd find it very difficult to use hand-held. With the mirror locked up, the viewfinder goes black. Also, it generally requires two pushes on the shooting button, and my hands would probably move if I tried to do that.

At least on my Nikon bodies--so likely on Canon as well--there is the option of shutter delay. With shutter delay, one press of the shutter button raises the mirror, causes the camera to wait a second (or more--it's selectable), then shoot the picture. Still likely challenging handheld, but with your hand or rig braced against something as you do, perhaps workable.

--Chris S.

[John S.]

I have both bodies now and am comparing them. One quick question. If I increase magnification from 1X to 1.6X, I lose .6 stops of light, correct? (all else being equal, of course)

Thanks for the mirror lockup/shutter delay comments, Chris.

[rjlittlefield]

If I increase magnification from 1X to 1.6X, I lose .6 stops of light, correct?

Sorry, but no. The light is spread over an area that is 1.6*1.6 = 2.56 times larger. The intensity drops by that same factor, 2.56. But each stop is only a factor of 2, so this is about 1.36 stops. (To check, 2^1.36 = 2.5669 .)

--Rik

[John S.]

Just an update. I chose the 80D and am happy with it. Thanks for all the advice.