# Relatively speaking does crop focus better?



## Hector1970 (Jul 21, 2016)

This is a variety of the crop giving you more reach question.
I have a 5DSR and a 7DII which have basically the same sensor.
I don't know if the 7DII focusing system is considered superior or whether they are comparable.

I was using a Canon 100mm L Macro lens on the 5DSR on Damselflies (which are quite thin).
I wasn't very satisfied with the absolute sharpness of the focusing.
I switched to the 7DII so the Damselflies at the same distance are bigger in the view finder. The camera seems to focus better and more sharply. I felt it was because it was more close up.

Part of it was probably I knew better when to press the button because I could see the subject larger in the viewfinder.

Does it matter to the focusing system whether the sensor is cropped or not. Does the image appear bigger to the focusing system in an APS-C Camera?

I did try the crop sensor setting in the 5DSR but the image in the view finder shrinks.


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## Mikehit (Jul 21, 2016)

This is one aspect of crop vs FF that I read very little about. I have read one (maybe two) comments comparing the 5D3 vs 7D2 where they make reference to the larger sensor making it more difficult to keep the AF point on the bird.
Now whether the issue you describe is the same, or whether it is about the relatively larger AF point in a FF camera or whether it is about the amount of light delivered to the AF sensors I don't know. It will be interesting to read other peoples' thought.


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## East Wind Photography (Jul 21, 2016)

Mikehit said:


> This is one aspect of crop vs FF that I read very little about. I have read one (maybe two) comments comparing the 5D3 vs 7D2 where they make reference to the larger sensor making it more difficult to keep the AF point on the bird.
> Now whether the issue you describe is the same, or whether it is about the relatively larger AF point in a FF camera or whether it is about the amount of light delivered to the AF sensors I don't know. It will be interesting to read other peoples' thought.



Af points on the full frame cameras are smaller. There is also a wider spread between phase sensors which will make the full frame Af more accurate. However in the case of 7d2 v 5ds, the cpu used to track objects on the 5ds has a lot more other things to do and therefore I have found the ability to track with the 7d2 to be much better. Mostly with subjects coming toward or away from you. For static subjects, the 5ds should be better or at least as good as the 7d2.

The wider Af sensor spread shows its worth in its ability to ignore foreground and background objects better than on crop sensors...all other factors being the same.

There are so many things that can affect af performance that you can't point to one aspect. It has to be evaluated as a system. Most of the 5ds burden is in pushing large numbers of pixels off the sensor and that seems to affect everything else using cpus.


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## [email protected] (Jul 21, 2016)

It may be due to the fact that the full frame sensor will effectively give you a thinner depth of field, so less will appear in focus at a given time. Coincidentally, the moment you'd most see this exaggerated is when you stuck a 100mm macro lens on your body and tried to focus close.


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## neuroanatomist (Jul 21, 2016)

[email protected] said:


> It may be due to the fact that the full frame sensor will effectively give you a thinner depth of field, so less will appear in focus at a given time. Coincidentally, the moment you'd most see this exaggerated is when you stuck a 100mm macro lens on your body and tried to focus close.



In fact, if you put that 100mm macro on crop and FF bodies and shot images at the MFD (i.e. 1:1 mag) on both, you'd find that the DoF is _shallower_ on the APS-C camera.


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## Mikehit (Jul 21, 2016)

[email protected] said:


> It may be due to the fact that the full frame sensor will effectively give you a thinner depth of field



It depends on how you are shooting. That only applies if you change position or lens to give you the same framing on the sensor.
If you take a classic wildlife shot with (for example) a 500mm on both cameras from the same position and you crop the FF to match the framing of the APS-C the DOF is identical. 
The only thing that affects it is the sesnor architecture (notably pixel density) and this in turn depends on the model: 5D3 vs 7D2 the Canon will have shallower DOF. If you compare 5DS vs 7D2 they will be pretty much identical.


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## Mt Spokane Photography (Jul 22, 2016)

Its been a few years, that question was asked of Chuck Westfall, and, as I recall, he said that AF on a FF body was more accurate, I think it was due to the shallow DOF potential of Full Frame. There may be exceptions, so its a generalization.

I did find this: Its a older Q&A session, and although old, it covers many common questions.

Dear Mr. Westfall!

I'd like to ask what is the tolerance of the current AF lineup? Long time ago there was an article in the Canon Pro site, but it has removed (I can only find a translation about it). What means the AF point is normal or high sensitivity?

Thank you for your reply, br,
Tamas Koncz

Chuck's Answer: The standard tolerance for AF precision with EOS cameras is within the depth of focus according to the maximum aperture of the lens in use. We don’t state a specific numerical value, but it varies slightly according to the size of the image sensor. Most current EOS digital SLRs are equipped with a combination of standard precision and high precision focusing points; the high precision sensors are used with lenses featuring maximum apertures of f/2.8 and larger (or f/4 and larger for the center AF point on EOS-1 series cameras). The high precision sensors have a wider baselength for AF measurement than the standard precision sensors, which improves focusing precision, but the trade-off is that the high-precision sensors require the use of high speed lenses as outlined above.


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## Orangutan (Jul 22, 2016)

Mt Spokane Photography said:


> Its been a few years, that question was asked of Chuck Westfall, and, as I recall, he said that AF on a FF body was more accurate, I think it was due to the shallow DOF potential of Full Frame. There may be exceptions, so its a generalization.
> 
> I did find this: Its a older Q&A session, and although old, it covers many common questions.
> 
> ...



I interpret that to mean they choose to put better AF systems in FF, not that it's inherent. Since a "crop' sensor is positioned the same relative to the lens as FF, I see no reason there would be any inherent difference at the same focus distance. There may be differences based on same-framing, but that's due to distance-to-subject. If the AF sensors were positioned identically in crop and FF, they would be optically identical, and therefore have identical performance.


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## Hector1970 (Jul 22, 2016)

Thanks for all the replies.
I had thought maybe APS-C had a less shallow depth of field so objects appear sharper might be part of what I was seeing but that seems to be debunked.
For my eye on APS-C I'm closer to the subject (if the full frame camera is in the exact same shot).
If I was manually focussing both it would be easier to focus with APS-C because the image size is bigger in the viewfinder.
I was wondering if it was the same for the autofocus sensor?
I think you are saying it's not.


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## Mt Spokane Photography (Jul 22, 2016)

Hector1970 said:


> Thanks for all the replies.
> I had thought maybe APS-C had a less shallow depth of field so objects appear sharper might be part of what I was seeing but that seems to be debunked.
> For my eye on APS-C I'm closer to the subject (if the full frame camera is in the exact same shot).
> If I was manually focussing both it would be easier to focus with APS-C because the image size is bigger in the viewfinder.
> ...



It is true that cameras with small sensors can have larger steps in the autofocus. I'd call that less precise autofocus, but its accurate enough to put things in sharp focus, which is what counts. I'm talking cell phones and P&S cameras. Many of the older box cameras had a fixed f/8 lens and everything was supposed to be in focus from some number like 5 ft to infinity.


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## -1 (Jul 22, 2016)

Hector1970 said:


> Thanks for all the replies.
> I had thought maybe APS-C had a less shallow depth of field so objects appear sharper might be part of what I was seeing but that seems to be debunked.
> For my eye on APS-C I'm closer to the subject (if the full frame camera is in the exact same shot).
> If I was manually focussing both it would be easier to focus with APS-C because the image size is bigger in the viewfinder.
> ...


That that Orangutang says, I think is that the AF sensor is independent of the imager and thus don't "care" if it's a crop camera or not. Given that it is the same AF sensor, processor and lense. It would be different in live view...


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## takesome1 (Jul 22, 2016)

From experience I have to say it does not focus better, not as accurate or precise.
the 7D II < 5DsR

You have copies of both bodies as do I. Perhaps the AF of your copy of the 7D II is better than the one I have.

I would speculate the differences you experience with the damselflies is more about framing and technique than AF superiority.


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## East Wind Photography (Jul 22, 2016)

-1 said:


> Hector1970 said:
> 
> 
> > Thanks for all the replies.
> ...



Accept for the fact that a ff camera has more area available and thus can use a larger af sensor. It does not use the imager but the rest of the system, mirror, prism, viewfinder to support the imager all play a role as to how large the af sensor can be. Canon does choose to use larger sensors in full frame cameras now which allows better phase detection in lower light levels.


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## -1 (Jul 22, 2016)

East Wind Photography said:


> -1 said:
> 
> 
> > Hector1970 said:
> ...


The interesting part here is that the imager and AF are separate: The fact that Canon might chose a larger AF sensor in the 1-series than the 7-series does not depend on the size of the imager but is a marketing and technical decition since the 7D* has a more cramped body than the 1D* and also brings the MF more money per unit...


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