Bokeh of f2.8 lens on full frame sensor vs f1.4 lens on APS-C sensor

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Senior Member
Jan 17, 2002
So help me here.

I'm trying to decide between a 5D MkII and a 7D.

My lens collection is decidedly biased towards EF-S.

I love the bokeh on my Sigma 30 mm f1.4 but miss the zoom.

I would like to know whether you can get equivalent (or better!) bokeh effect of let's say 50 mm f2.8 on the full frame sensor that you can get with the 30 mm f1.4 on an APS-C sensor.

In other words, if I get a full frame camera and an f2.8 zoom, I would like the bokeh effect to be as good as or better than I could get with the Sigma 30mm f1.4 on the APS-C sensor. Otherwise I'll just get the 7D and stick to my EF-S lenses.

If anyone has both types of DSLR and can post pictures to help compare, I would be grateful.

The pictures I would like are 50mm f2.8 on fullframe vs 30mm f1.4 on APS-C (Obviously you'd need to own the Sigma 30mm f1.4).


Sep 28, 2008
my gut feel on this 50mm f1.8(FF) will beat the 50mm f2.8(FF) and 30mm f1.4(APC).
so can sell ur sigma and buy 2 canon 50mm ?lol


New Member
Aug 10, 2008
How much of the frame your subject takes up is another factor.

If you keep the size of subject that fills up the frame same on both bodies, you will have to move closer with the full-frame body compared to the cropped sensor body. The calculator will tell you that a newer distance to the subject will give you a shallower depth of field. Hence, "more bokeh".

Dec 14, 2008
bokeh characteristic will be different

on full frame the angle of view contribution of the background of defocus is wider, you may have a slightly more colorful bokeh as more of the background is taken into perspective

but on an APC, at f1.4, due to the narrower FOV, you will have less of background contribution, it could be smoother though


Senior Member
Nov 28, 2005
If you are the exact same distance, the amount of background blur (which is NOT bokeh) will be the same, but you'll have a lot more of the surroundings in frame and your subject will appear smaller since there's no crop. But the actual circle of confusion does not change.

If, when using full frame, you walk closer to your subject to get the same framing as APS-C, then of course there will be a difference.

Jun 7, 2007
on a 50mm, maybe F2.8 will give good bokeh, i still prefer f1.4. on a 30mm, f1.4 is a must. on a 200mm, f2.8 is enough.

when you focus on a subject which is close to the camera, it will has more "bokeh" than if the subject is far away.

when using a DX camera, you have to step a bit further away from the subject as compared to FX camera, therefore less "bokeh".

in your case 30mm 1.4 on DX, you need to focus further than on a fx and hopefully, at that distance you can fully frame whichever subject that you may have and retain the "bekoh". i tried sigma 30mm 1.4 before. to achieve "bokeh" on dx you need a very short focusing distance. anything below f1.4 is not useful to me.

50mm 2.8 on FX, maybe the focusing distance and the framing is similar to the above. based on the calculator, the result is 30mm 1.4 on dx (0.17) beat 50mm 2.8 on fx (0.18). i would use f1.4 on 50mm on dx (0.9) and on fx (0.6) any day.

i would choose fx because i like to be closer to the subject. space is not always enough and closer proximity to the subject and dont have to move a lot. i miss my 24mm on slr perspective.

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