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Does an APS-C Crop on a FF Sensor Increase Background Compression?


herein2020
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5 hours ago, TomTheDP said:

DOF won’t necessarily be the same and different lenses vary slightly in terms of distortion.

One thing to note, for anyone reading this thread, is that small variations in DOF create a very large perceptual difference of how 3D an image seems.

I've previously compared a ton of lenses under test conditions and a 55mm lens seems much more 3D than a 50mm lens, when both are at the same aperture.   I know this is different to compression, but it's likely to get mixed up in this conversation at some point considering that all these things are interrelated.

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53 minutes ago, kye said:

One thing to note, for anyone reading this thread, is that small variations in DOF create a very large perceptual difference of how 3D an image seems.

I've previously compared a ton of lenses under test conditions and a 55mm lens seems much more 3D than a 50mm lens, when both are at the same aperture.   I know this is different to compression, but it's likely to get mixed up in this conversation at some point considering that all these things are interrelated.

Explain what you mean by 3D. I’ve heard people say one lens of the same focal length is more 3D than another of the same focal length. Not really sure what 3D means tho ...

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11 minutes ago, TomTheDP said:

Explain what you mean by 3D. I’ve heard people say one lens of the same focal length is more 3D than another of the same focal length. Not really sure what 3D means tho ...

The way I tested it was to block one eye and look through a tube at the image and test how convincing it was that I was looking at a real scene instead of a flat image.  I positioned the tube so that I could only see the image through that eye, so that the border to the image didn't ruin the illusion.

You can then flick back and forwards between images from different lenses taken from the same location and directly compare.  

Of course, going back to my original point, if you compare lenses of different focal lengths then you have to account for the different DOF because that has a huge impact on how 3D a lens looks.  I'd suggest that it's so large that much of the perceived differences between two lenses could be that one of them is actually just slightly wider open than the other and that's what you're seeing.

Of course, things like other types of distortions can also impact the impression of dimensionality, like the famous CZ 28/2 "Hollywood" lens and its distortions.

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9 hours ago, TomTheDP said:

85mm on FF and 50mm on APSC will have the same field of view but DOF will not be the same unless you shoot faster on the 50mm. 

And therein lies all of the confusion over compression. I really think people's definition of compression is two fold:

1-The background seems farther away

2- The background is more out of focus 

If you define compression as having to meet both criteria then yes it does not exist because the background is not really farther away it is just perception distortion. But if you define compression as a shallower depth of field when comparing a 50mm lens to an 85mm lens at the same aperture and distance from the subject then you could say compression is not a myth.

In my particular case I was focusing on the DOF and trying to figure out if the DOF would change when using the APS-C crop mode and the answer seems to be that no, it will not change, the only thing that will change is the FOV which is not an accurate representation of a true 85mm lens. But the ironic part is that the perception distortion would be equivalent to the longer lens because the subject would appear closer to the camera which would probably create the same perception distortion as a real 85mm. Personally I don't care about the perception distortion aspect and instead would rather have the shallower DOF instead. There is a great YouTube video on this but I cannot find it now; the one thing even that video did not go into though was a situation like this where the only thing that changes is the crop factor of the sensor.

 

7 hours ago, noone said:

The adapter is not an L mount to EF-s mount one  is it? (it would not matter if it was).     Canon made a variety of EF cameras with different crops and some were APSC with 1.6x and some were APSH 1.3x but they never made any APSH lenses.     There would be little point in an adapter changing the crop factor to match the other (donor) sensor size rather than the sensor size used in crop mode of the FF camera going to be used.    

That would be pointless and add pointless cost in making the adapter.      Nah, it will not give a 1.6x crop on a 1.5x crop camera and the only thing is there MIGHT be some lenses that vignette a little more (but I doubt it will matter).

I get what you are saying but in this particular case I am still not convinced. I don't think the adapter changes the crop factor, but I do think the adapter communicates with the camera's firmware and in the firmware I think it would be pretty simple to adjust the crop factor based on the type of lens and adapter connected.  The S5 definitely knows when the adapter is connected because it disables continuous AF, it also knows when a crop sensor lens is attached to the adapter because it disables FF mode. I do think you are probably right though in that it just sticks to a crop factor of 1.5x because my EF-S 10-22mm lens is unusable on the S5, yet all of my other EF-S lenses are fine. With the EF-S 10-22mm lens the barrel is clearly visible and the image is unusable; but then again this could simply be because the lens is older and does not properly communicate with the adapter.

I really think in this particular case the only way to know for sure would be to set up a static composition and compare a native L-Mount lens with APS-C mode enabled to an EF-S lens attached to the adapter with an identical focal length as the native lens to see if there is a difference in the FOV. The only reason that I think this matters is because for those of us using the adapter, it would be nice to know ahead of time which EF-S lenses work with the S5 without having to find out through trial and error.

The problem of course is that Panasonic does not care about Canon EF-S lenses and Canon does not care about Panasonic camera bodies so neither vendor has any incentive to produce a compatibility list of APS-C lenses.

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2 minutes ago, herein2020 said:

And therein lies all of the confusion over compression. I really think people's definition of compression is two fold:

1-The background seems farther away

2- The background is more out of focus 

If you define compression as having to meet both criteria then yes it does not exist because the background is not really farther away it is just perception distortion. But if you define compression as a shallower depth of field when comparing a 50mm lens to an 85mm lens at the same aperture and distance from the subject then you could say compression is not a myth.

Yeah I'd not consider DOF compression. 

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37 minutes ago, herein2020 said:

And therein lies all of the confusion over compression. I really think people's definition of compression is two fold:

1-The background seems farther away

2- The background is more out of focus 

I've never heard depth of field described as "compression." Generally what people mean by "lens compression" is perspective distortion. (I assume this is what you mean by perception distortion?) Perspective distortion of a subject changes as a function of distance from the camera to the subject, and is not related to sensor size, focal length, or aperture. Perspective distortion applies to 3D graphics and your eyes by themselves, not just cameras.

You can also look at nuances and distortions of individual lenses, e.g. barrel distortions, "3D pop" etc. but those are not perspective distortion.

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13 hours ago, herein2020 said:

Does an APS-C Crop on a FF Sensor Increase Background Compression?

Yes.  Anything that narrows the field of view increases "telephoto" compression.

 

So, cropping into a frame increases telephoto compression.

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