85L on a crop act like a 135L?

Would this be the case?

I'm really eyeing a 135L but my brother keeps telling me not to get one and to just borrow his... saw a deal today on a 40D and could use a back up.

Would the 85L give similar results at f/2 on a crop camera as a 135L on a FF in terms of bokeh and isolation?

85mm on a cropped sensor would give pretty much the same field of view as a 135mm on a full frame.

As for 85mm on a crop at f2 vs 135mm on a full frame at f2, the 135mm would give a shallower depth of field though. However, I'm not sure about the depth of field if you use f1.2 though, I'd figure it would be pretty similar to the 135mm at f2 on a full frame. Just a guess though.

Use one of the various FOV/DOF calculators. Run a search on your favorite search engine.

f/1.2 on 85L on APS-C should give about the same background blurring and DoF (and virtually identical focal length) as 135 at f/2 on full frame. The trade-off is AF speed vs. light gathering ability. The 135 might be a little sharper wide open.

For identical subject framing:
APS: 135mm @ f/2 w/ focus distance of 10 ft - DOF = 0.19 ft.
APS-C: 85mm @ f/2 w/ focus distance of 10 ft - DOF = 0.31 ft.

That's more than a 50% difference (APS-C over APS). Definately not "about the same"

http://www.dofmaster.c​om/dofjs.html

*corrected my math*

Thanks for the info. That's all I needed to know

Poe wrote in post #9808040
For identical subject framing:
85mm on APS-C gives 0.22 ft depth of field @ 8.5 ft away
135mm on APS gives 0.35 ft depth of field @ 13.5 ft away.

That's more than a 50% difference. Definately not "about the same"

http://www.dofmaster.c​om/dofjs.html

It's the same !!! if 85mm is at 1.2 and 135 @ F2 ..
at 5m dof is 15cm for a 50D+85L1.2@F1.2
at 5m dof is 16cm for a 5DMKII+135L2.0@F2 ..
5DMKII can go to higher isos so can compensate the opening easily

Today I made some test .. But wide open 5DMKII+135 gets better results due to less diffraction and a bit sharper, but bokeh is really better on full frame ..
I 'll put some picture tomorow..

Just imagine Crop cameras to have either a built in 1.6x (7D, XXD, rebels) or 1.3x (1D) teleconverter... lol

newworld666 wrote in post #9808122
It's the same !!! if 85mm is at 1.2 and 135 @ F2 ..
at 5m dof is 15cm for a 50D+85L1.2@F1.2
at 5m dof is 16cm for a 5DMKII+135L2.0@F2 ..
5DMKII can go to higher isos so can compensate the opening easily

Today I made some test .. But wide open 5DMKII+135 gets better results due to less diffraction and a bit sharper, but bokeh is really better on full frame ..
I 'll put some picture tomorow..

The OP was interested in comparing DOF at F/2, not at different apertures.

I assumed that the OP also wanted to do this comparison with the same subject framing as well. The numbers I posted are for that case at F/2 (forget the aperture part).

The numbers you report are for constant DOF.

Poe wrote in post #9808200
The OP was interested in comparing DOF at F/2, not at different apertures.

I assumed that the OP also wanted to do this comparison with the same subject framing as well. The numbers I posted are for that case at F/2 (forget the aperture part).

The numbers you report are for constant DOF.

This is my mistake because of a faulty question. Really I should have asked, Can the 85L produce similar results on a crop camera as the 135L @ f/2 on a FF camera?

My bad guys.

MigsVuitton wrote in post #9808269
This is my mistake because of a faulty question. Really I should have asked, Can the 85L produce similar results on a crop camera as the 135L @ f/2 on a FF camera?

My bad guys.

DOF calcs are your friend!

f1.2 @ 80mm on full frame, 5m from subject = DOF of 27.7cm
f2.0 @ 130mm on full frame, 5 m from subject = DOF of 17.3cm

f1.2 @ 80mm on crop, 5m from subject = DOF of 17.53cm
f2.0 @ 130mm on crop, 5m from subject = DOF of 10.95cm

Due to the crop factor, the full frame image will be cropped by a factor of 1.6 so the DOF really isn't any more shallow. So....5 x 1.6 = 8m to frame the same way on full frame.

f1.2 @ 80mm on crop, 8m from subject = DOF of 45.18cm
f2.0 @ 130mm on crop, 8m from subject = DOF of 25.49cm

To answer your question, yes.

Poe wrote in post #9808200
The OP was interested in comparing DOF at F/2, not at different apertures.

I assumed that the OP also wanted to do this comparison with the same subject framing as well. The numbers I posted are for that case at F/2 (forget the aperture part).

The numbers you report are for constant DOF.

plasticmotif wrote in post #9808401
DOF calcs are your friend!

f1.2 @ 80mm on full frame, 5m from subject = DOF of 27.7cm
f2.0 @ 130mm on full frame, 5 m from subject = DOF of 17.3cm

f1.2 @ 80mm on crop, 5m from subject = DOF of 17.53cm
f2.0 @ 130mm on crop, 5m from subject = DOF of 10.95cm

Due to the crop factor, the full frame image will be cropped by a factor of 1.6 so the DOF really isn't any more shallow. So....5 x 1.6 = 8m to frame the same way on full frame.

f1.2 @ 80mm on crop, 8m from subject = DOF of 45.18cm
f2.0 @ 130mm on crop, 8m from subject = DOF of 25.49cm

Your analysis are really not fair to keep same aperture or format ..
If you change format and lengh .. you have to change aperture to be consistant for analysing any results -> otherwise it has no meaning, I would say even stupid !!!..

.. I did the test .. dof is not the problem .. you get almost the same

For me -> problem is sharpness, bokeh and CA which is in favor of 135mm + FF
but color is in favor of 50D+85mm ..

newworld666 wrote in post #9808435
It's not fair to keep same aperture .. if you change format and lengh .. you have to change aperture to be consistant ..

.. I did the test .. dof is not the problem .. you get same

For me -> problem is sharpness, bokeh and CA which is in favor of 135mm + FF
but color is in favor of 50D+85mm ..

Yes. I agree. I'd rather have the 135L on FF than the 85L on crop. The 135 is an amazing portrait lens.

MigsVuitton wrote in post #9808269
This is my mistake because of a faulty question. Really I should have asked, Can the 85L produce similar results on a crop camera as the 135L @ f/2 on a FF camera?

My bad guys.

If you're trying to hold DOF constant at f/2, yes you can get a DOF value close, if not equal, with the 85L on APS-C vs. 135L on APS.

However, you won't have the same subject framing.