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DPChallenge Forums >> Photography Discussion >> Macro Detail - Full Frame vs. Crop Sensors
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09/20/2012 04:11:02 PM · #1
I've observed that when I'm doing 1:1 macro with the 5D, I don't like to do macro with it nearly as much as I do with the 50D...

I started thinking about why, and examining some images, and the conclusion I've come to is this: the 50D just resolves lots more detail using my 100mm 1:1 .

I decided to calculate this out, and I've found that on the 5D, I get about 15k pixels per square centimeter of subject, whereas with the 50D I'm getting 45k pixels per square centimeter of subject.

Originally posted by Calculations:


5D
4476X2954 = 13222104
24X36 = 864
pixels per cm2 = 15303.36111111111
124x124 px per cm

50D
4770X3177 = 15154290
14.9 x 22.3 = 332.27
pixels per cm2 = 45608.36067053902
214x214 px per cm


What that means, in effect, is that for any square centimeter of the subject, the 5D gives me a 124px X 124px image, whereas the 50D delivers a 214px x 214px image.

So, if my math is correct, this means my 50 actually delivers an effective magnification of just barely less than 2x over the 5D in terms of real resolvable detail. Seems like an almost crazy conclusion, but there it is.

For me, I think this means I'm going to be doing my 1:1 macro work with the highest resolution crop body I have from now on.

Anyone care to share their observations around this? What's your approach to shooting macro, can you think of a good reason to bother with a full-frame for macro work?

09/20/2012 04:36:16 PM · #2
Math? You needed math? ;-)

What I mean is, the image formed by the lens is 1:1, that is, life size. So the pixel pitch is a direct indicator of how fine detail you can render. The 5D has 8.2µm pixel pitch vs. the 50D's 4.69µm pitch.
Now, there's one fly in that ointment. The 5D has somewhat higher acuity (per pixel sharpness) than the 50D which means the 50D's advantage is reduced slightly. Still, the 50D starts with almost a 2:1 advantage.

ETA:
This is also one of those strange situations where you can argue that you have *less* DoF with the APS-C body than the 35mm body. If images are shot of the same subject and magnification using both bodies, and subsequently both are viewed at 100% scale, the one from the APS-C body will *appear* to have been shot at higher magnification, and also *will* have less DoF.

Message edited by author 2012-09-20 16:40:07.
09/20/2012 05:54:47 PM · #3
Originally posted by kirbic:

What I mean is, the image formed by the lens is 1:1, that is, life size. So the pixel pitch is a direct indicator of how fine detail you can render. The 5D has 8.2µm pixel pitch vs. the 50D's 4.69µm pitch.

However, aren't you trading resolution for quality? I thought that the 8-micron sensor cell should give better quality (more accurate color, better low-light performance, etc.) than the 5-micron sensor cell.

I suppose that may not be as applicable to macro work as so other genres ...
09/20/2012 06:00:53 PM · #4
Originally posted by GeneralE:

Originally posted by kirbic:

What I mean is, the image formed by the lens is 1:1, that is, life size. So the pixel pitch is a direct indicator of how fine detail you can render. The 5D has 8.2µm pixel pitch vs. the 50D's 4.69µm pitch.

However, aren't you trading resolution for quality? I thought that the 8-micron sensor cell should give better quality (more accurate color, better low-light performance, etc.) than the 5-micron sensor cell.

I suppose that may not be as applicable to macro work as so other genres ...


To some degree, yes. Assuming we're shooting at base ISO, illuminating with flash, then there's little advantage... except for possibly in acuity, as there definitely is here. The RAW files from the 5D will need *very* little in the way of sharpening, whereas the 50D RAW files are going to be a little less sharp out of the box. So a small part of the pixel density advantage goes away.
09/20/2012 08:38:50 PM · #5
Originally posted by kirbic:

Originally posted by GeneralE:

Originally posted by kirbic:

What I mean is, the image formed by the lens is 1:1, that is, life size. So the pixel pitch is a direct indicator of how fine detail you can render. The 5D has 8.2µm pixel pitch vs. the 50D's 4.69µm pitch.

However, aren't you trading resolution for quality? I thought that the 8-micron sensor cell should give better quality (more accurate color, better low-light performance, etc.) than the 5-micron sensor cell.

I suppose that may not be as applicable to macro work as so other genres ...


To some degree, yes. Assuming we're shooting at base ISO, illuminating with flash, then there's little advantage... except for possibly in acuity, as there definitely is here. The RAW files from the 5D will need *very* little in the way of sharpening, whereas the 50D RAW files are going to be a little less sharp out of the box. So a small part of the pixel density advantage goes away.


I wonder where the cross-over would be in terms of acuity vs pixel density and the resulting IQ.

It'd be interesting to put some REALLY great glass in front of one of those 41MP Pureview sensors that Nokia put in that phone.
09/20/2012 09:11:02 PM · #6
Originally posted by kirbic:

Math? You needed math? ;-)

ETA:
This is also one of those strange situations where you can argue that you have *less* DoF with the APS-C body than the 35mm body. If images are shot of the same subject and magnification using both bodies, and subsequently both are viewed at 100% scale, the one from the APS-C body will *appear* to have been shot at higher magnification, and also *will* have less DoF.


This sounds sorta misleading though. If you shoot with the same lens that goes to 1:1 on both bodies, and focus to 1:1 in both cases, you DoF should be equal. Now, I know you're saying that the relative size of the object in your image will not be the same (smaller on the FX), but in macro work you're looking at reproduction ratios and that will be the same, but the pixel density will not due to the difference in sensors.
09/20/2012 11:11:49 PM · #7
Originally posted by spiritualspatula:

This sounds sorta misleading though. If you shoot with the same lens that goes to 1:1 on both bodies, and focus to 1:1 in both cases, you DoF should be equal. ...


Ah, but there's the rub. The DoF is *not* equal. What is *truly* in focus is, in theory, only a plane. Nothing in front of it, nothing behind it. What we *perceive* as in focus is determined by whether the blur caused by being in front (or behind) the plane of focus is larger than than the resolution limit of the sensor.
So, change the resolution of the sensor, and the DoF changes. It's as simple as that. The only slight-of-hand is specifying that both images are viewed at 100%. This removes all the complexity of needing to know the size of each sensor, at what size each image is printed, calculating the reproduction ratio from each sensor, yada, yada, yada.

ETA: Thought Exercise...
We mount a macro lens in front of a subject, set it to 1:1. The lens is mounted solidly to a base, can't move. Now, we mount a Canon 5D to the back of the lens, take a photo. The smallest detail we can resolve in the photo is the Nyquist limit of the sensor, twice the pixel pitch, or about 16.5µm. Anything smaller can't be resolved, or at best will appear as false aliased "detail."
Now, substitute a camera with the same size sensor, but with only 0.79Mpx, we'll call it the 0D. Such a sensor would have a linear resolution exactly 1/4 of that of the 5D. The pixel pitch would be 33µm, and the smallest resolvable detail would be 66µm.
Now, when both resulting images are viewed at 100% on screen, an object that has an edge that is blurred by, say, 48µm will look clearly blurred in the 5D shot, as the blur is about six pixel pitches. In the 0D shot, we don't have a chance to resolve the blur, since it lies below the Nyquist limit. The object looks just as sharp as things that are closer to the theoretical plane of focus.

Message edited by author 2012-09-20 23:29:43.
09/20/2012 11:43:20 PM · #8
Do I have this figured out right?
Using the same lens, aperture, and magnification settings on both cameras, and at the same subject to sensor distance the image projected on the sensors by the lens should be exactly the same, except that the APC sensor would only be getting a smaller part of the projected image.

The two main differences in what comes out of the two cameras would be the overall size of the image, 35mm VS APC, and the other difference would be in the pixel pitch of the sensors.

If the resolving capability of the lens is less than that of the best of the two sensors, then that would tend to equalize the quality of the images.
Somehow I am thinking that there would be differences introduced by the software used to process the images in the camera as well.

Are we all talking about shooting both at 1/1 mag ratio, or, about changing the mag ratio to shoot the same subject, say a 35mm sensor sized object and getting the whole object full frame in both images by using less magnification for the shot done with the APC sensor cam, which would also change the perspective by having to be farther from the subject if a prime lens is used.

That's a good techy question Cory.
09/21/2012 01:34:26 AM · #9
Originally posted by MelonMusketeer:



Are we all talking about shooting both at 1/1 mag ratio, or, about changing the mag ratio to shoot the same subject, say a 35mm sensor sized object and getting the whole object full frame in both images by using less magnification for the shot done with the APC sensor cam, which would also change the perspective by having to be farther from the subject if a prime lens is used.



Absolutely the former, not the latter. :)

The whole point of this Gedankenexperiment is examining the characteristics of different formats at a 1:1 or greater magnification.

For me, it's really kinda fun that this is where some of the "rules" we think we know just start to get really funky, and the constants that work elsewhere no longer apply.

As far as glass quality, I can say with certainty the 100mm macro is at least good enough to show significantly more detail at a pixel pitch of 4.x vs. 8.x ..

I do wonder how this would work with that 41 MP sensor though, a pixel pitch of 1.4µm is more than 5.5 times more detail or magnification compared to the same lens projection on my 5D. As crazy as it sounds, this is basically the same as the iPhone, and we've all seen what that sensor can do. (not bad at all with the right light).

I'd certainly be tempted to buy a high quality desk USB microscope that was built around the Pureview chip.

Message edited by author 2012-09-21 01:34:55.
09/21/2012 01:44:05 AM · #10
Originally posted by kirbic:

Originally posted by spiritualspatula:

This sounds sorta misleading though. If you shoot with the same lens that goes to 1:1 on both bodies, and focus to 1:1 in both cases, you DoF should be equal. ...


Ah, but there's the rub. The DoF is *not* equal. What is *truly* in focus is, in theory, only a plane. Nothing in front of it, nothing behind it. What we *perceive* as in focus is determined by whether the blur caused by being in front (or behind) the plane of focus is larger than than the resolution limit of the sensor.
So, change the resolution of the sensor, and the DoF changes. It's as simple as that. The only slight-of-hand is specifying that both images are viewed at 100%. This removes all the complexity of needing to know the size of each sensor, at what size each image is printed, calculating the reproduction ratio from each sensor, yada, yada, yada.

ETA: Thought Exercise...
We mount a macro lens in front of a subject, set it to 1:1. The lens is mounted solidly to a base, can't move. Now, we mount a Canon 5D to the back of the lens, take a photo. The smallest detail we can resolve in the photo is the Nyquist limit of the sensor, twice the pixel pitch, or about 16.5µm. Anything smaller can't be resolved, or at best will appear as false aliased "detail."
Now, substitute a camera with the same size sensor, but with only 0.79Mpx, we'll call it the 0D. Such a sensor would have a linear resolution exactly 1/4 of that of the 5D. The pixel pitch would be 33µm, and the smallest resolvable detail would be 66µm.
Now, when both resulting images are viewed at 100% on screen, an object that has an edge that is blurred by, say, 48µm will look clearly blurred in the 5D shot, as the blur is about six pixel pitches. In the 0D shot, we don't have a chance to resolve the blur, since it lies below the Nyquist limit. The object looks just as sharp as things that are closer to the theoretical plane of focus.


That's my point though- and it's important to note the 100% part. What I'm saying is that if you keep the composition the same from one to the other (cropping the FX shot to mimic the crop sensor) there should be zero difference from fx to dx assuming equal pixel densities. I'm saying any differences to DoF are incurred by pixel densities and have nothing to do with the formats themselves, keeping the same composition from shot to shot. In this particular case, yes, what you noted is true, but it is peculiar to this case and these cameras compared. The phrasing made it sound as though it would always be true, but it is purely a product of density, which varies from camera to camera. Cory was discussing fx vs crop generally, with his cameras as a specific example. The results of this comparison would be very different if you compared the D800 with my D300, for instance. In this hypothetical case, you will see the opposite effect.

It's also important to note the difference between perceived and actual DoF, which is at the heart of this. The projected image does not change. The recording medium does, which is what reproduces the image, hence why we have differences when the recording medium is altered. These differences are not due to the physical size of the medium, but rather it's recording characteristics, which is all I was wanting to clarify here. In other words, we agree, but I thought your phrasing could lead one to assume that this is uniformly true (less DoF on crop) of the formats, which is not necessarily true.
09/21/2012 07:56:49 AM · #11
Yep, we agree. I may have misinterpreted your first post. You are correct that any differences are due *purely* to the manner in which the image is recorded. Format is irrelevant to that.
In most cases, though, the pixel densities of APS-C cameras are much higher than those of 35mm cameras. So when making comparisons, we will usually find that the depth of "critical sharpness" is lower in the APS-C shots. Of course, if we re-frame the question (literally) so that the shots are framed the same, the difference will pretty much go away, assuming that the camera pixel *counts* are roughly the same.
09/21/2012 08:44:08 AM · #12
I usually use my 60d for macros. the flippy outy screen means can get into all crazy angles and stuff without having to contort my neck to see what i'm shooting.
09/24/2012 02:43:21 AM · #13
Originally posted by kirbic:

Yep, we agree. I may have misinterpreted your first post. You are correct that any differences are due *purely* to the manner in which the image is recorded. Format is irrelevant to that.
In most cases, though, the pixel densities of APS-C cameras are much higher than those of 35mm cameras. So when making comparisons, we will usually find that the depth of "critical sharpness" is lower in the APS-C shots. Of course, if we re-frame the question (literally) so that the shots are framed the same, the difference will pretty much go away, assuming that the camera pixel *counts* are roughly the same.


Amusingly, today I was listening to some past podcasts, and found a good discussion of this topic and what we were going over, but perhaps a bit less esoteric for other users than the way we were discussing things.

Tips From The Top Floor- DoF Can Of Worms

Marquardt is entertaining and the show is decent. It's the longest running photography podcast as well, so lots of good info there.
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