Confused about Crop Effect...after I thought I had it.

[rmfagan]

Hello all-

I've seen several posts lately which have left me confused. My understanding of the crop factor (1.6x in Canon's case) is that FOV is decreased by 1.6x, effectively cropping the photo. It doesn't replace focal length in that you do not gain additional telephoto compression. However, this crop effect could still be useful to the focal length limited photographer (let's say 300IS II + 2x TC III as opposed to a 500 or 600 prime) because to crop a FF image in post throws out pixels, while a sensor forced crop puts relatively greater number of pixels on target (ie a 7d2 vs a 5d3).

Now I've read posts alluding to a "real" benefit of closer to 1.2x due to increased camera movement. Why? Would this camera movement not also occur at a comparable FOV on FF? Would a 300 + 1.4x not have roughly the same movement as a 400?

Thanks in advance for clearing this up.

 

[jrista]

This has been a relatively great debate on these forums, for many years.


Personally, I'm of the opinion that your second paragraph sums it up perfectly. Your going to experience the same camera shake with FF and APS-C, so if it's enough to diminish IQ, it's going to diminish it regardless of what your using. On the flip side, if you work to minimize shake, smaller pixels mean you have the potential to resolve more detail. It doesn't matter if those smaller pixels are in a big or small sensor...smaller pixels are smaller pixels. When your reach limited, smaller pixels mean greater potential for more detail.


I don't care if you have to work harder to get that detail, the potential is still there. I primarily use a 5D III now, but I still believe my sharpest photos ever when reach limited were taken with the 7D and 500mm f/4 and 600mm f/4 lenses at faster apertures (so not diffraction limited.)

 

[rmfagan]

I tend to agree, but I don't know enough about the physics to be certain. The reason I ask is I am torn between buying a 300 IS II plus 7d ii or a 500 IS VER 1 for wildlife. Really tough call and this talk about only 1.2x advantage in reality is confounding.

 

[Terry Rogers]

https://www.youtube.com/watch?v=DtDotqLx6nA

https://www.youtube.com/watch?v=f5zN6NVx-hY

These are some of the best explanations I've seen explaining crop and how it relates to focal length and iso

 

[takesome1]

The camera shake issue is two fold.
Imagine holding a beam of light like a lazer on two squares, one square over twice the size of the other. Imagine your hand shaking so the light is moving up and down at the same amount on each square. The movement of the light on the smaller square will cover a larger percentage of its area than it will on a large square. Your hand shake is equal, but the area of the sensor on a crop is smaller and magnifying it. Most people don't get this, distance and FOV do not matter, they are not moving your hand is.
Second your pixels are smaller and if your vibration is over a pixel width your resolution advantage drops quick.

Camera shake is a small part of it, it can be increased by other factors.
You loose some light with the crop. Add to this you have to shoot at lower ISO than FF because of noise. To compensate for this you may be shooting at slower shutter speeds.

Those are just hand held problems, on a sturdy tripod where none of those issues matter I see about a 1.2 improvement.

But here is the deal with the improvement, you will only realize the improvement in resolution if you are focal length limited. If you can take a few steps closer a 5D III has a substantial advantage over the 7D II.

Clear as mud, right?

 

[takesome1]

But here is the deal with the improvement, you will only realize the improvement in resolution if you are focal length limited. If you can take a few steps closer a 5D III has a substantial advantage over the 7D II.

Clear as mud, right?

+1
I guess I should have said that. If you can fill the frame of a 36mm sensor camera then that should give the better IQ result. If you can fill the frame of a medium format that will be better than a 36mm SLR and on and on...till you get to that fellow who converted a lunch truck into a giant box camera.

What you do not hear much is the difference of the crop camera vs a FF with equal framing, for instance the FF at 100' and the crop at 160. In that situation the FF has a substantial resolution benefit.

 

[ritholtz]

You loose some light with the crop. Add to this you have to shoot at lower ISO than FF because of noise. To compensate for this you may be shooting at slower shutter speeds.

Hi takesome1,
Why do you think, we loose some light with the crop and shooting at slower speeds. Exposure values are same for both. In order to get picture with similar dof, one needs to stop down by 1 1/3 stop with FF and increase ISO by that much.

Thanks

 

[Ryan85]

There is much disagreement on this subject and no easy answers.

My explanation, for which I am charging you nothing, is more or less this:

Reducing the pixel size and increasing the number of pixels creates an increase in image resolution.

But it does not cause an equivalent increase, if you double the number of pixels on a full frame sensor you will not get a 2x increase in resolution. What you actually get varies but it's much less. This is due to a lot of complicated physics I don't fully comprehend. No one does.

This is essentially what a crop frame sensor is. 2x the pixels. In order for a crop sensor to achieve a 1.6x increase in resolution it would require the equivalent 2x increase in resolution discussed above. This is not possible with present technology.

So what do you get? This is the hard part. Most reasonable people believe that you should see an increase in resolution of about 20% in a good crop sensor relative to a full frame sensor cropped to the same field of view.

While this may not seem like a big deal it certainly is. In order to get a lens that is 20% higher in resolution you often have to pay as much as 2-10x the cost of the lower resolution lens.

So, in a nutshell. The crop camera does yield a full 1.6x magnification but only about a 1.2x increase in resolution.

Therefore, when looking at a 1.6x crop camera image vs a full frame image with the same number of pixels, the crop will appear to have less resolution. The crop body image will look soft in comparison.

When the full frame image is cropped to the same field of view as the image from the 1.6x cropped body, the 1.6x cropped body image will have more resolution. The full frame will then look soft in comparison.

Some folks don't think the resolution advantage is significant enough to justify the crop cameras increased noise. Which is a byproduct of the smaller pixels. Others believe the advantages significantly outweigh the disadvantage. It's up to you to decide which works best for you.

That's about the best explanation I can give. I'm sure some one will come along and explain how completely wrong I am.

This is how I understad it too. The more I think about it the more confused I get. You summed it up nicely.

 

[ritholtz]

What you do not hear much is the difference of the crop camera vs a FF with equal framing, for instance the FF at 100' and the crop at 160. In that situation the FF has a substantial resolution benefit.

I think, that is how TDP lens comparison tests are done. Crop is always looks bad in those tests.

 

[Ryan85]

In my experience, closer is always better, regardless of equipment. Just don't get eaten by a bear...or whatever toothy critters live in your neck of the woods...

+1 I totaly agree. I've had one close call with a brown bear in Skagway Alaska. So yeah be careful of bears!

 

[Ryan85]

Lol I hear you and absolutely agree!

 

[takesome1]

You loose some light with the crop. Add to this you have to shoot at lower ISO than FF because of noise. To compensate for this you may be shooting at slower shutter speeds.

Hi takesome1,
Why do you think, we loose some light with the crop and shooting at slower speeds. Exposure values are same for both. In order to get picture with similar dof, one needs to stop down by 1 1/3 stop with FF and increase ISO by that much.

Thanks

Try metering side by side and see if what you say is true. I am getting a 1/3 to 2/3 stop light advantage with the 5D II and 1D IV.

The problem with stoping down is that is fine during bright daylight hours, but the advantage of the crop is at you longest focal length. In my case that is a 500mm F/4. Anything less I can cover with a FF. So with the 500mm I need a fast shutter speed to compensate for the long lens and often to stop action. It is always a struggle for light at the prime wildlife times and I seldom shoot over F/4.5.

YMMV since your longest lens and shooting interests may be different.

 

[Mt Spokane Photography]

The reason you need to take more care with a crop body is because of the longer effective focal length.

A shutter speed of 1/2 X eff focal length means a faster shutter speed to prevent blur from vibration. Once a user takes that into account, things get better as far as blur from camera vibration. The smaller pixels add another increment of vibration blur, so even more care is needed. Once again, understanding the situation means you can deal with it, unless the light is low.
\
APS-C cameras struggle a bit more in low light, and a faster shutter speed means less light on the sensor. In bright daylight, that's usually not a big issue, but adding TC's to a already small aperture telephoto lens combined with faster shutter speeds and the resulting higher ISO settings can mean lost opportunities.

In limited light, my old 7D really struggled with a slow telephoto. The 7D MK II is going to be a lot better at high ISO's.

 

[Ryan85]

The reason you need to take more care with a crop body is because of the longer effective focal length.

A shutter speed of 1/2 X eff focal length means a faster shutter speed to prevent blur from vibration. Once a user takes that into account, things get better as far as blur from camera vibration. The smaller pixels add another increment of vibration blur, so even more care is needed. Once again, understanding the situation means you can deal with it, unless the light is low.
\
APS-C cameras struggle a bit more in low light, and a faster shutter speed means less light on the sensor. In bright daylight, that's usually not a big issue, but adding TC's to a already small aperture telephoto lens combined with faster shutter speeds and the resulting higher ISO settings can mean lost opportunities.

In limited light, my old 7D really struggled with a slow telephoto. The 7D MK II is going to be a lot better at high ISO's.

+1

 

[jrista]

The camera shake issue is two fold.
Imagine holding a beam of light like a lazer on two squares, one square over twice the size of the other. Imagine your hand shaking so the light is moving up and down at the same amount on each square. The movement of the light on the smaller square will cover a larger percentage of its area than it will on a large square. Your hand shake is equal, but the area of the sensor on a crop is smaller and magnifying it. Most people don't get this, distance and FOV do not matter, they are not moving your hand is.
Second your pixels are smaller and if your vibration is over a pixel width your resolution advantage drops quick.

Neat little example. A single point of light pointing at the center of a square. Now, compound the number of squares a few million fold, and instead of one beam of light, you have trillions. All shaking concurrently and synchronously all over this array of a few million squares. Camera shake is camera shake. It's going to soften the image regardless. Light that should fall onto one square is going to fall on more than one square. Acutance is going to drop off precipitously at the first tiny bit of camera shake, and after that it's a diminishing effect.


I have to hold my 5D III as steady as I have to hold my 7D to get the most crisp, sharp shot. In the field, there isn't any difference...I don't think "I can handle X amount of shake with the 5D III" or "I can shake N times more than with my 7D"...I simply hold the lens steady, as steady as humanly possible period, and burst my shots to get a good number of frames so I can pick the sharpest one. There isn't any difference in tactic here, you use FF and APS-C the same way, birds, wildlife, or otherwise.


Do you want to maximize the potential of the system, or not? That's either yes, or no. If yes, then you do everything you can to extract the absolute best out of the system. There is no difference in effort to do that regardless of format...we can't compensate for the microscopic differences in pixels when were out in the field concentrating on a bird. You AFMA with both FF and APS-C. You use IS with both FF and APS-C.


There isn't any difference here. Either you maximize your camera system's potential, or not. You either hold the lens as steady as possible, or not. No one thinks about the size of a pixel or the relative differences in pixel sizes in the field...they simply think: "Keep it stable."

Camera shake is a small part of it, it can be increased by other factors. You loose some light with the crop. Add to this you have to shoot at lower ISO than FF because of noise. To compensate for this you may be shooting at slower shutter speeds.

Conversely, you have to shoot at a higher ISO and a narrower aperture with FF to get the same depth of field. I have been shooting at 1200mm f/8+ for most of the week, to fill the frame with small birds. That results in an incredibly thin DoF. Shooting at 1200mm f/8 roughly normalizes the 5D III FoV, normalizes the DoF, normalizes the amount of light at the sensor, normalizes the amount of noise with an APS-C. If were talking equivalence here, let's truly be equivalent. For all my efforts at 1200mm on FF, I still get even sharper results with a 7D and a 500/4 (which should be expected...at f/8+ I'm getting diffraction limited...at f/4, the 7D is at a perfectly ideal aperture for maximum sharpness).

APS-C has an advantage when it comes to DoF and getting pixels on subject. Yes, it's when your reach limited...but that is most often the case when your not a pro with tens of thousands of dollars worth of gear, or the ability to spend every day of the weak learning how to get extremely close to your subjects.

 

[Ryan85]

I always try to hold my cameras as steady as possible too. But if I'm using a crop sensor I'll use a faster shutter speed while hand holding because of the crop factor. I try to follow the the 1 over the focal length for my minimum shutter speed. So if I'm shooting a 400 mm lens on my FF I generally won't shoot under 1/400th with a 400mm on a crop sensor I generally won't shoot under 1/640th.

 

[jrista]

I always try to hold my cameras as steady as possible too. But if I'm using a crop sensor I'll use a faster shutter speed while hand holding because of the crop factor. I try to follow the the 1 over the focal length for my minimum shutter speed. So if I'm shooting a 400 mm lens on my FF I generally won't shoot under 1/400th with a 400mm on a crop sensor I generally won't shoot under 1/640th.

I used to follow those rules, but I think once you get a handle on stability, they don't matter as much. I have shots as low as 1/100th and even slower, hand-held, with IS enabled on my 600mm f/4. At that point, burst rate is really what matters most...as it's the movement of the subject that matters most. The faster the burst, the more likely you are to nab a razor sharp shot, even down to shutter speeds a fraction of the focal length.


For example...Chickadee, 1200mm f/10 1/100s ISO 800. This is 1/100s! SIX STOPS lower than the 1/focalLength rule would dictate I shoot at, and two stops lower than my IS system supposedly allows for. Shot at f/10 with a 2x TC (diffraction limited, which is probably where the sharpness limit is ultimately coming from, although I may be a notch or two off on my AFMA as well):

Original:

Sharpened:

Processed:

You maximize the potential of the system in hand. The amount of effort you put in is high regardless of whether your shooting APS-C or FF. So, personally, I don't really believe the notion that bigger pixels mitigate issues from camera shake or anything like that, or that just taking a step or two forward is going to fix the reach issue. I was getting shots like this with a 500mm f/4 on the 7D. F/4...the diffraction-limited performance of an ideal lens at that aperture is higher than any current DSLR sensor on the market, significantly higher than the diffraction-limited performance of a lens at f/10 (key benefit of using faster lenses on APS-C...smaller pixels that can maximize the performance of a high resolution lens at a fast diffraction-limited aperture).


Faster aperture, more light, sharper details from nearly the same distance as a 1200mm FF in the end (pretty much right on top of the MFD).


Like this:

Or this:

Now, these days I can get close enough to use my bare 600 at f/4-f/6.3 and get phenomenally sharp results with the 5D III. I've just been having fun with the 1200mm f/8 focal length this week, and have been seeing how much I can extract from that particular system. It's useful out in the field, vs. in my back yard, where it is a lot harder to get close to the songbirds I want to photograph.


You maximize the system in hand...and you don't skimp on doing everything that's possible to maximize your results (not if you want the best results possible, anyway). I don't put less effort in to keep my lens stable when using FF than when using APS-C...I put in the maximum effort either way. I think the notion that you cannot get the most out of a sensor like the 7D, or the 70D/7D II, or the even higher resolution NX1, that your perpetually limited to barely any better than what FF can do...I think it's all a myth. If you learn how, and put in the effort, if you use all the features of your system (lens IS, sensor IS, any kind of stabilization, external supports like tripods, beanbags, bracing your arms against your body when handheld, etc.) you can experience camera shake so small that it doesn't affect even the smaller pixels of an APS-C (or the pixels of say the D800, which are quite smaller than anything from Canon's FF sensors...and thus, one would expect, susceptible to the same problems.)

 

[takesome1]

The camera shake issue is two fold.
Imagine holding a beam of light like a lazer on two squares, one square over twice the size of the other. Imagine your hand shaking so the light is moving up and down at the same amount on each square. The movement of the light on the smaller square will cover a larger percentage of its area than it will on a large square. Your hand shake is equal, but the area of the sensor on a crop is smaller and magnifying it. Most people don't get this, distance and FOV do not matter, they are not moving your hand is.
Second your pixels are smaller and if your vibration is over a pixel width your resolution advantage drops quick.

Neat little example. A single point of light pointing at the center of a square. Now, compound the number of squares a few million fold, and instead of one beam of light, you have trillions. All shaking concurrently and synchronously all over this array of a few million squares. Camera shake is camera shake. It's going to soften the image regardless. Light that should fall onto one square is going to fall on more than one square. Acutance is going to drop off precipitously at the first tiny bit of camera shake, and after that it's a diminishing effect.


I have to hold my 5D III as steady as I have to hold my 7D to get the most crisp, sharp shot. In the field, there isn't any difference...I don't think "I can handle X amount of shake with the 5D III" or "I can shake N times more than with my 7D"...I simply hold the lens steady, as steady as humanly possible period, and burst my shots to get a good number of frames so I can pick the sharpest one. There isn't any difference in tactic here, you use FF and APS-C the same way, birds, wildlife, or otherwise.


Do you want to maximize the potential of the system, or not? That's either yes, or no. If yes, then you do everything you can to extract the absolute best out of the system. There is no difference in effort to do that regardless of format...we can't compensate for the microscopic differences in pixels when were out in the field concentrating on a bird. You AFMA with both FF and APS-C. You use IS with both FF and APS-C.


There isn't any difference here. Either you maximize your camera system's potential, or not. You either hold the lens as steady as possible, or not. No one thinks about the size of a pixel or the relative differences in pixel sizes in the field...they simply think: "Keep it stable."

Camera shake is a small part of it, it can be increased by other factors. You loose some light with the crop. Add to this you have to shoot at lower ISO than FF because of noise. To compensate for this you may be shooting at slower shutter speeds.

Conversely, you have to shoot at a higher ISO and a narrower aperture with FF to get the same depth of field. I have been shooting at 1200mm f/8+ for most of the week, to fill the frame with small birds. That results in an incredibly thin DoF. Shooting at 1200mm f/8 roughly normalizes the 5D III FoV, normalizes the DoF, normalizes the amount of light at the sensor, normalizes the amount of noise with an APS-C. If were talking equivalence here, let's truly be equivalent. For all my efforts at 1200mm on FF, I still get even sharper results with a 7D and a 500/4 (which should be expected...at f/8+ I'm getting diffraction limited...at f/4, the 7D is at a perfectly ideal aperture for maximum sharpness).

APS-C has an advantage when it comes to DoF and getting pixels on subject. Yes, it's when your reach limited...but that is most often the case when your not a pro with tens of thousands of dollars worth of gear, or the ability to spend every day of the weak learning how to get extremely close to your subjects.

Maximizing your equipment is knowing your equipment. The crop has limitations and it has benefits.

You shoot at faster shutter speeds to overcome camera shake. You can use a flash. If you are shooting in ample light with a fast enough shutter speed then camera shake isn't much of an issue. My 500mm I prefer 1/1000, at 1/500 I can still get fair wildlife pics off the monopod. Go less it starts getting difficult. Light starts to drop close to sunset, my ISO limit is set at 1/1600 on the 7D II and I will push to 1/3200 on FF. Camera gets pushed there to get the speed I need. Same is true of aperture, it goes to F /4. So normalizing for DOF in low light conditions just doesn't happen, you take what you get.

Of course as I said YMMV, if a persons longest lens is 300mm they would notice camera shake and loss of light even less. With focal length limited situations one should analyze how much they usually crop. If you have more pictures that are properly framed than need to be cropped then the benefit of FF on the majority of your pics may be greater than benefit you receive on your cropped photos.

 

[Loswr]

You maximize the potential of the system in hand. The amount of effort you put in is high regardless of whether your shooting APS-C or FF. So, personally, I don't really believe the notion that bigger pixels mitigate issues from camera shake or anything like that...

Your belief or lack thereof doesn't change the underlying geometry that determines the relationship between pixel size and the effect of angular motion.

I don't put less effort in to keep my lens stable when using FF than when using APS-C...I put in the maximum effort either way.

I'm sure that's true, but it's irrelevant...what matters is the results. You can put in your maximum effort in running as fast as possible on a 5% grade hill either way, but you'll go much faster if you're running down that hill than up.

 

[TexPhoto]

Could this be the next AF vs MF? IS vs no IS? Dare I say it?, UV filter vs bare glass?