Comparing lenses for full frame vs. APS-C sensors

[Tronhard]

For Canon R5 and R6 at least the autofocus is leading edge: using dual pixel autofocus in its latest iteration: Dual Pixel CMOS Autofocus II https://photographylife.com/reviews/canon-eos-r6/3 My own experience is that these cameras leave the best DSLRs from Canon in the dust.

From my reviews of the more recent Nikon units, they are similarly excellent. The days when digital cameras were poor focusing are, IMHO, not currently valid.

I had never heard this. I think this may no longer be true of some mirrorless cameras. I just searched, and it seems not to be true of the Canon R5:



https://www.canon.co.uk/cameras/eos-r5/specifications/


I have no idea if this is true of other new mirrorless models.

[DanK]

I just spent a bit of time looking, and I was unable to find a single source indicating whether the AF points on the Fuji XT-4 are cross-type.

[Tronhard]

The reason that cross-type autofocus points are not an issue with modern mirrorless cameras is because they use a different system, which is more accurate than the old systems in DSLRs. See:
https://digital-photography-school.c...%20cross-type.
and..
https://petapixel.com/2018/10/16/cam...st-hybrid-dfd/

I just spent a bit of time looking, and I was unable to find a single source indicating whether the AF points on the Fuji XT-4 are cross-type.

[DanK]

I haven't watched the video yet, but the first link is a pitch for contrast detection AF, arguing that it's better than phase detection because it is supposedly more accurate, even though it is slower and hunts. However, dual-pixel AF is phase detection; Canon makes a point of saying that it's superior to contrast detection. See https://www.usa.canon.com/internet/p...S-AF-Explained

What I don't understand after reading this explanation from Canon is what they mean when they say that 100% are both vertical and horizontal, which I took to mean cross-type.

[ajax]

...
FWIW

Many thanks for the elaboration. When I get around to serious birding I'll need to take all of that into account. It is worth a lot.

I think I've always grasped that pixel density can be advantageous. That is a prime reason I'm wanting more of them. In my case, the cropping occurs in the post processing rather than the capture phase. I think you've made a strong case for why other features of the camera make it advantageous to do that in the camera in certain situations.

I'd also say that your explanation makes it clear that when I get more serious about birding I'll need to upgrade the equipment I've been using for that as well. Now I know to keep crop mode under consideration and that such high quality cameras/lens are available.

[Tronhard]

I realized after posting that the video was for the earlier iteration of the R-series: the R and RP which used v1 of Dual-Pixel AF, the newer bodies use v2 of that which is vastly superior. All I can say is that I cannot find ANY MILC maker of a newer body that refers to AF points as being cross or not.

I was delayed 'cos I just went out and bought a Fuji X-T4 locally (I got tired of waiting for the one stuck in transit) and it has either 117 or 430 focus points, but again no mention of type. I get the feeling, based on quite a bit of research, that this is a term that is no longer used in the context of the new generation of sensors.

[xpatUSA]

"crop sensor" refers to a sensor that has the same size as the [APS-C] format (a film format). So yes, smaller sensor than a FF sensor.

Crop sensor is a standard term for a sensor that is moderately smaller than a "full frame" (i.e., 36 x 24 mm) sensor. It is typically applied to sensors that are 1/1.5 to 1/1.3 times FF size in length and width. It's generally not applied to smaller sensors. They are labeled by their inverse, e.g., 1.6 crop. AFAIK, the 1.3 crop has long since disappeared.

From the above two quotes, I get that some Canons at 1.6 crop, some Sigmas at 1.7 crop and all 4-3rds should not be called "crop sensors".

As to 1.3 crop, the Sigma 'sd Quattro H' has only just been discontinued, so presumably it is the Canon that has "long since disappeared". The Sigma was much-vaunted but actually quite a bit smaller than APS-H which attracted lots of odd discussion as to which Sigma so-called "APS-C" lenses would work on it when not in "crop mode"!

As to APS:

The film is 24 mm wide, and has three image formats:

• H for "High Definition" (30.2 × 16.7 mm; aspect ratio 16:9; 4×7" print) (1.25 crop compared to 36x24mm full frame)
• C for "Classic" (25.1 × 16.7 mm; aspect ratio 3:2; 4×6" print) (1.44 crop compared to 36x24mm full frame)
• P for "Panoramic" (30.2 × 9.5 mm; aspect ratio 3:1; 4×11" print) (1.36 crop compared to 36x24mm full frame)

It is rather surprising how far off some so-called "APS" sensors are from the above dimensions, especially as regards the aspect ratio for "APS-H".

I'm quite pleased with my Panasonic LX-1 because of it's native 16:9 aspect ratio which gets cropped horizontally to format the other two popular ratios.

[pschlute]

I have always referred to aps-c sensor cameras as "crop". I have no idea if that is technically correct or not

The fact that there is more than one size of aps-c sensor complicates matters !

If I put my FF camera into "crop" mode it gives me two options..... aps-c 1.5x or square basis the height of the FF image. No idea what the square image should be called.

Logically any sensor size smaller than a FF could be called a crop sensor, but does that make sense ? i don't generally hear users of micro 4/3 refer to their cameras as crop sensor, as they tend to specifically identify the format. Would it make any sense to refer to my phone sensor as a crop ?

[xpatUSA]

...

Logically any sensor size smaller than a FF could be called a crop sensor, but does that make sense ? i don't generally hear users of micro 4/3 refer to their cameras as crop sensor, as they tend to specifically identify the format. Would it make any sense to refer to my phone sensor as a "crop" ?

Probably not. As you should know, small sensors are often described by the fractional "inch" system, see:

https://en.wikipedia.org/wiki/Video_camera_tube

From https://en.wikipedia.org/wiki/Image_...maller_sensors
.

[tclune]

Probably not.

Right. My sense is that one usually reserves the term "cropped sensor" for smaller-sensor cameras that accept FF lenses without requiring an adaptor.

[xpatUSA]

Right. My sense is that one usually reserves the term "cropped sensor" for smaller-sensor cameras that accept FF lenses without requiring an adapter.

Oh dear!

My "1.7 crop" Sigma accepts Full-Frame Sigma SA-mount lenses without requiring an adapter but 1.7 crop is nowhere near APS-C ...

... Quite a dilemma!

[Tronhard]

I would disagree with limiting the term Crop to APS-C sensors. It makes no sense to me to do so - the term APS-C in itself is enough for this group of sensors. Or, in other words, APS-C is one category of crop sensors, in the same way that Micro 4/3 is another. The principle that any smaller sensor deliver a cropped image compared to that of a FF camera is true for any sensor that has smaller dimensions. That ties in with the fact that a crop factor exists for all sensor sizes:



I refer to this from Adobe on the subject:
https://www.adobe.com/nz/creativeclo...ull-frame.html

Specifically, this:
How a crop sensor works.A crop sensor is smaller than the standard 35 mm size, which introduces a crop factor to the photos these cameras take. This means that the edges of your photo will be cropped for a tighter field of view. For example, if you use a 50 mm lens on a crop sensor camera with a multiplier effect of 1.5x, your effective focal length will be the same as a 75 mm lens.

“Different camera bodies have different crop factors,” says photographer Whitney Whitehouse. “Canon has a 1.6x crop sensor, while Nikon, Sony, Sigma and Pentax have a multiplier of 1.5x and Panasonic and Olympus are 2x.”

To find the equivalent angle of view for a lens on a crop sensor body, simply multiply the magnification amount by the focal length of the lens. The two most common crop sensor sizes are APS-C and Micro Four Thirds, which have a 1.6x and 1.5x crop factor respectively.

Within the APS-C group: Nikon DX has a crop factor of 1.5, while Canon has a crop factor of 1.6

[xpatUSA]

I would disagree with limiting the term Crop to APS-C sensors. It makes no sense to me to do so - the term APS-C in itself is enough for this group of sensors. Or, in other words, APS-C is one category of crop sensors, in the same way that Micro 4/3 is another. The principle that any smaller sensor deliver a cropped image compared to that of a FF camera is true for any sensor that has smaller dimensions. That ties in with the fact that a crop factor exists for all sensor sizes:

Yep, that's what I thought, Trev.

I refer to this from Adobe on the subject:
https://www.adobe.com/nz/creativeclo...ull-frame.html

<snip> The two most common crop sensor sizes are APS-C and Micro Four Thirds, which have a 1.6x and 1.5x crop factor respectively.

Did Adobe really say that?! Pardon my pedantry ...

[Tronhard]

I gave you the link, all you have to do is follow it and read it on their site. It would appear that they had an editing 'moment'!
Obviously, Micro 4/3 has a crop factor of 2!

Yep, that's what I thought, Trev.
Did Adobe really say that?! Pardon my pedantry ...

[rpcrowe]

It is generally accepted that you are able to get a more narrow DOF by shooting with a full frame sensor than you can by using a crop sensor format camera.

As the song from Porgy and Bess goes, "It ain't necessarily so"

If you are shooting with the same focal length, same f/stop and focused at the same distance with a full frame sensor, your DOF will actually be wider than if you were shooting with a crop sensor camera

Here are the different depth of fields when shooting with a Canon full frame camera and a Canon 1.6x crop sensor camera as per the DOF Master Program:

FULL FRAME SENSOR using 50mm at f/2.0 focused at 10 feet:
Near: 9.33 ft. Far: 10.8 ft. Total DOF: 1.45 feet

1.6x CROP SENSOR using the same 50mm at f/2.0 focused at 10 feet:
Near: 9.56 ft. Far: 10.5 ft. Total DOF: .91 ft.

Obviously a DOF of 1.45 feet when using the full frame camera is wider than the .91 feet achieved with the crop sensor camera.

So why all this talk about full frame sensor cameras having a more narrow DOF than crop sensor cameras

The answer has to do with the field of view. If I am shooting with a crop sensor camera using a 50mm focal length and I want the same field of view using a full frame camera, I would need to use an 80mm lens and thus my DOF would be .56 feet - much more narrow than the image with the crop camera. If I didn't have an 80mm lens for the full frame camera, I would need to use the 50mm and move in closer which would also reduce the DOF.

Obviously this would also apply when using a 1.5x crop sensor camera with slightly modified numbers.

[xpatUSA]

I gave you the link, all you have to do is follow it and read it on their site.

Yes, I probably should have checked. Unfortunately, I hate Adobe even more than the word "crop", so I didn't.

[DanK]

Re Richard's point: the best terse summary of this, with more detail following, is this:

https://www.bobatkins.com/photograph...igitaldof.html

[Tronhard]

There are a couple of video demonstrations of the impact of sensor size on DoF:
The first, from Northrop - although I am not, by any means a fan, this video is a valid demo of the issue IMHO
https://www.youtube.com/watch?v=f5zN6NVx-hY I note that Northrop's terminology is sloppy - he keeps talking about focal length changing when a smaller lens is attached, of course that is not correct - it is the resultant Field of View, but otherwise the demonstration makes its point.
The Second, from Filmaker IQ covers several issues within this area
https://www.youtube.com/watch?v=lte9pa3RtUk

Re Richard's point: the best terse summary of this, with more detail following, is this:

https://www.bobatkins.com/photograph...igitaldof.html

[xpatUSA]

I have often thought that the "crop factor" of 2 is wrong for the micro four-thirds system because of the differing aspect ratios (4:3 vs 3:2) but just now I checked. Based on sensor diagonals, the factor is almost exactly 2!! (1.999381).

I feel that that is no accident. Anybody?

And maybe that is one reason why the Panasonic DMC-GH1's aspect ratios all have the same diagonal measure.

And why the factor based on the GH1's actual oversized sensor is less than 2.

And why your non-GH1 micro four-thirds camera set to an aspect ratio other than 4:3 has a slightly different effective crop factor than 2.

Pardon the pedantry from outside the CaNikOny pale ...

[ajax]

Because of the discussion herein, I’ve just come to realize something about my current equipment. As previously mentioned I bought what might be called an entry level bundle that included a camera and 2 zoom lenses as follows:

• Canon Rebel T6 camera
• Canon Zoom Lens EF-S 18-55mm 1:3.5-5.6 IS II
• Canon Zoom Lens EF 75-300mm 1:4-5.6 IS III

Apparently my 75-300mm lens is a FF lens. Based on what I’ve learned herein FF lenses can be used on APS-C cameras but in this case the focal length is actually 120-480mm. As best I can tell, the 480mm is getting pretty close to the maximum focal length for zoom lenses offered by Canon. I also suspect, this likely is one of those that Trev referred to in his excellent article titled “An Overview of Canon 70-300mm Zoom” when saying “… (for optics and build) to the pretty horrific 75-300 standard kit zooms that have mediocre optics and build, and are unstabilized.” which goes a long way toward explaining my interest in upgrading equipment.

I’ve also now read Trev’s excellent article titled “Focal Length, Field of View, Shutter Speed, Sensor Size & Equivalence” which defines Focal Length as “Distance from lens’ optical centre to the Centre of Focus”. Since my lens is nowhere near 300mm long (much less 480mm) this implies that “distance” is NOT quite as simple to understand as some might like. My guess (if I simply missed that point in the articles) is that, at least in a zoom lens, the elaborate construction involved in allowing the value to be changed accounts for that discrepancy. I’ll have to admit when I read specifications for zoom lenses, something that might be called the “Optical Design” which refers to the number of “Groups” & “Elements” is pretty meaningless. Is it possible that there is some basic reason one should want to know about this? Is it possibly someone knows of an entry level article that describes how zoom lenses work?

Might it be that on a lens with a fixed focal length (maybe better referred to as a prime lens?) the focal length does correspond to a simply measurable distance?