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


herein2020
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I have been thinking about this for awhile now. I have been shooting with the Panasonic S5 and sometimes I use the APS-C crop mode to better compose the shot without having to change my position. So for example if I am shooting with a 50mm and want a tighter crop, instead of coming closer I will just switch to APS-C mode. In APS-C mode since its a Canon lens I get a 1.6x crop to give me a FOV of 85mm.  Using this technique its almost like I have two primes on the camera at the same time. The part I keep thinking about though is if the background compression also increases to an 85mm equivalent or if its just an 85mm FOV. 

 

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EOSHD Pro Color 5 for Sony cameras EOSHD Z LOG for Nikon CamerasEOSHD C-LOG and Film Profiles for All Canon DSLRs

It's a common misconception that focal length or crop affects compression. If that were the case then smartphones and other small sensor cameras which have miniscule focal length lenses would have super distorted images, but they don't. The only thing that affects compression is your distance to subject. Wider focal lengths just mean a wider FOV, which will reveal more distortion, particularly when close to the subject.

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@FreshGiantand @RogerRabbit are correct.

The same image is hitting the sensor whether you  are using full frame or crop mode (or pixel to pixel). 

The only difference is in crop mode, the camera is throwing away pixels.

When 6K shooting comes to the S5, you can (I am assuming) just shoot in 6K and then crop in to 4K in post and get the same effect as shooting in 4K aps-c mode.

31 minutes ago, herein2020 said:

In APS-C mode since its a Canon lens I get a 1.6x crop to give me a FOV of 85mm. 

I think the actual crop amount depends on the camera, so with an S5 it would be a 1.5X crop, not 1.6X, but who's counting???

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I know actual compression doesn't exist but I guess my question is....will an 85mm lens produce an identical image on a FF sensor as a 50mm with a 1.6x APS-C crop on the same FF sensor if all else remains equal (i.e. distance to subject). Even though it is just throwing away pixels to achieve the crop, it is still bringing the subject closer to the camera without sacrificing resolution. 

 

@Mark Romero 2 Canon's crop is 1.6x and I'm using Canon lenses with the Sigma adapter so I am assuming that when it enters APS-C mode with the adapter and Canon lens attached that it will crop by 1.6x especially since Canon EF-S lenses which require that 1.6x crop vs 1.5x work on the S5.

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7 minutes ago, herein2020 said:

I know actual compression doesn't exist but I guess my question is....will an 85mm lens produce an identical image on a FF sensor as a 50mm with a 1.6x APS-C crop on the same FF sensor if all else remains equal (i.e. distance to subject). Even though it is just throwing away pixels to achieve the crop, it is still bringing the subject closer to the camera without sacrificing resolution. 

 

@Mark Romero 2 Canon's crop is 1.6x and I'm using Canon lenses with the Sigma adapter so I am assuming that when it enters APS-C mode with the adapter and Canon lens attached that it will crop by 1.6x especially since Canon EF-S lenses which require that 1.6x crop vs 1.5x work on the S5.

Yes 

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18 minutes ago, herein2020 said:

Now that is pretty cool, I kind of figured that, but I don't have an 85mm to test with and didn't want to compare a zoom to a prime.

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

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As above, if you simply switch into APSC mode, compression will not change as it is just a centre crop, ie you lose...or simply see less width and height that you just did in FF mode.

Your crop is 1.5x not 1.6x which is a Canon sensor crop and nothing to do with the lens.

 

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25 minutes ago, KnightsFan said:

@herein2020Not to self promote too much, but I made a comparison tool a long time ago that you might find useful https://gobuildstuff.com/tools/CropFactor/index.html

There's no way to change the distance from camera to subject in this tool at the moment, maybe I should add that.

That is a really cool tool. oh and my math was a bit off, 50mm with a 1.6x crop is 80mm. The tool confused me again though, it shows the background is more out of focus, whereas I think with the S5 the background bokeh stays the same with the crop.

@MrSMW - are you sure, I thought the image circle in the crop sensor lenses for EF-S lenses needed 1.6x crop to not see the lens barrel. I need to test with and without the adapter. So much to test...but I guess none of it really matters when you are out shooting.

 

 

 

Comparison-Tool.JPG

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32 minutes 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. 

I was hoping to get the DOF as well, but like everyone is saying, its just a crop, not an actual lens element change, can't have everything I guess.

31 minutes ago, MrSMW said:

Not 100% 🤪

I have both native and EF mount but setting up a scene and actually testing it sounds too much like work to me especially since I can't remove the EF adapter without first removing my tripod plate. 🙂

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Canon APSC CAMERAS have a 1.6x crop, NOT the lenses.     If you use a Canon APSC lens on an M43 camera it would be the same as any other M43 lens and a 2x "crop" so 50mm has a 100mm FF angle of view.

If you use the Canon 50mm APSC lens on a Sony APSC camera it would have a 75mm FF angle of view against an 80mm FF angle of view on Canon.

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Because the APSC lenses do not have to cover the same size sensor, they can be made smaller effectively and in some cases might not cover the entire sensor but that does not change the focal length.     A 50mm lens remains a 50mm lens regardless of the format but the angle of view differs with formats.    SOME Canon APSC lenses DO cover FF (you just can not use them on CANON FF DSLR cameras in many cases because of the lens design).     The cheap and cheerful Canon APSC kit lenses cover FF from about 23/24mm up (I use it on my FF Sony from time to time) so if you put a Canon kit lens on your FF camera and compared it to a native FF lens at 24mm (zoom or prime), the angle of view would be the same (well there may well be difference because lenses are not often exactly what the focal length says it is and one 24mm lens might actually be 23.5 while another might be 24.5) but essentially the same.

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26 minutes ago, noone said:

Canon APSC CAMERAS have a 1.6x crop, NOT the lenses.     If you use a Canon APSC lens on an M43 camera it would be the same as any other M43 lens and a 2x "crop" so 50mm has a 100mm FF angle of view.

If you use the Canon 50mm APSC lens on a Sony APSC camera it would have a 75mm FF angle of view against an 80mm FF angle of view on Canon.

I am aware that the lenses do not have a crop, my crop reference is strictly referring to the crop factor of the S5 specifically when the Sigma L mount to EF mount adapter is added AND when the S5 is then placed into APS-C crop mode.  The part I don't know is if the Sigma Adapter or the S5 firmware tells it to set the crop factor of the SENSOR to 1.6x because it detects a Canon EF-S lens or if it sets the SENSOR crop factor to 1.5x because it is a Panasonic.

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1 hour ago, herein2020 said:

That is a really cool tool. oh and my math was a bit off, 50mm with a 1.6x crop is 80mm. The tool confused me again though, it shows the background is more out of focus, whereas I think with the S5 the background bokeh stays the same with the crop.

Thanks! Based on your screenshots numbers, an 80mm lens at f2.8 will produce shallower depth of field compared to a 50mm lens at f2.8. That's why in your screenshots the image on the left has more depth of field than on the right. That's also why (depending on what equivalence you are looking for), you also need to factor an aperture change into your crop factor equivalence calculations.

Another aspect I tried to convey with the tool is that you should specify which dimension you are calculating crop based on. Typically people use the diagonal, but obviously with different aspect ratios that doesn't give the whole picture. A 16:9 video section of a 3:2 full frame photo sensor technically has a diagonal crop factor larger than 1. Just keep that in the back of your mind when comparing numbers as close as 1.5 vs. 1.6.

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1 minute ago, herein2020 said:

I am aware that the lenses do not have a crop, my crop reference is strictly referring to the crop factor of the S5 specifically when the Sigma L mount to EF mount adapter is added AND when the S5 is then placed into APS-C crop mode.  The part I don't know is if the Sigma Adapter or the S5 firmware tells it to set the crop factor of the SENSOR to 1.6x because it detects a Canon EF-S lens or if it sets the SENSOR crop factor to 1.5x because it is a Panasonic.

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).

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