5D depth of field issue

[LeeBase]

Given a scenerio where your position is fixed in relation to the
subject and if you use the 1.6 or FF cameras with a fixed zoom lens
(24-105) at 100mm, then the DOF will change...is this correct?

If you fix the distance, and use a ff and a crop camera to take the shot -- you will then chose two different focal length lenses.

Say an 85mm on the 5D and a 50mm on the crop camera. And the wider angle equates to more dof for the crop camera shot.

Lee

 

[Cal Dawson]

but last time I went to the zoo, I was only allowed up to the bars no closer....

There are going to be times when one is better than the other so really there is no good answer to the OP's question...

If you like shallow dof -- the 5D is better. Primarily it's
because for a given focal length lens you will stand closer to get
the same framing on a subject.

Take the 30D and Canon 85mm f1.8. At f1.8 and 16' away, you'd have
.72 feet of dof.

The Canon 5D with same lens at f1.8 and 15' would have 1.14 feet of
dof. However, you wouldn't stand that far away to get the same
shot. You'd stand at 10' and would have .44 feet dof.

Enough to buy the 5D over the 30D for that feature alone? Not
really. But in practice, I like the look of my wedding photos on the
5D better than my 20D when it comes to those dreamy narrow dof shots.

Lee

--
Cal

Put a Canon to your head, You deserve it....

http://funshots.smugmug.com/

 

[LeeBase]

Where you are in relation to the subject changes the perspective. For
the same shot with two cameras, we want the same perspective. That
means using a different lens. If you're going to use an 85mm lens on
a 30D, then the corresponding lens on the 5D would be a 135mm lens.
Using your example, the same depth of field as the 30D/85mm @ f/1.8
would be achieved with the 5D and 135mm lens at f/2.8.

30D with 85mm f1.8 at 30' and f1.8 = 2.55' dof
5D with 135 f1.8 at 30' and f1.8 = 1' dof

Of course, aperture affects dof. You can always step down the 5D to get more dof. You can't do anything to the 30D when you are already wide open to get less dof.

Of course, depending on the lighting -- you may have difficulty getting the shutter speed you desire at the smaller f-stop. Which goes back to the notion that the 5D is "different" not necessarily "better".

If you are already maxed out on your ISO -- and are already wide open -- and you need more dof -- you have it with the 30D and don't with the 5D.

Lee

 

[Guna M]

Of course, aperture affects dof. You can always step down the 5D to
get more dof. You can't do anything to the 30D when you are already
wide open to get less dof.

Of course, depending on the lighting -- you may have difficulty
getting the shutter speed you desire at the smaller f-stop. Which
goes back to the notion that the 5D is "different" not necessarily
"better".

If you are already maxed out on your ISO -- and are already wide open
-- and you need more dof -- you have it with the 30D and don't with
the 5D.

Lee

Have a better understanding now...

In the scenerio I'm faced with, the distance is fixed (you're not allowed to move).

Cannot change ISO as it is max. with 3200 and need S/S and aperture to expose correctly and catch moving subjects, thus, have seen what you have described, at certain special circumtances, the 1.6 can have advantages with more DOF.

thanks
--
Rgds
http://www.pbase.com/rakes

 

[joe mama]

I have seen a few references in the past over the depth of field of
the 5D when compared to the 30D but never understood whether it is
better on the 5D or worse..... could someone please enlighten me. If
it is 'worse' what precautions do you have to take.
Appreciate any help.

Long answer (but complete):

http://www.josephjamesphotography.com/equivalence/

Short answer:

Whatever FL you use on 1.6x, multiply that by the crop factor to get the FL you would use on FF (e.g. 30mm on a 30D --> 30 x 1.6 = 50mm on a 5D).

Whatever f-ratio you use on 1.6x, multiply that by the crop factor to get the f-ratio you would use on FF (e.g. f / 2.8 on a 30D --> 2.8 x 1.6 = f / 4.5 on a 5D). More conveniently, instead of multiplying the f-ratio by 1.6, you can add 1 1/3 stops instead (f / 2.8 + 1 1/3 stops = f / 4.5 -- if you're camera is set to 1/3 stops, that's four clicks of the wheel).

You may need to up the ISO to get a fast enough shutter. Whatever ISO you use on 1.6x, multiply that by the square of the crop factor to get the ISO you would use on FF to get the same shutter (e.g. ISO 100 on a 30D --> 100 * 1.6^2 = 256 --> ISO 250 on a 5D). Again, this is the same as adding 1 1/3 stops.

If you're worried about more noise, don't. The 5D at 1 1/3 stops higher ISO has the same noise as the 30D after you resample the 5D image to the dimensions of the 30D image (8.2 MP) or use NR. Your choice: more noise with more detail (12.8 MP vs 8.2 MP) or the same noise with the same detail.

Of course, if you don't need the shutter speed, then you can keep the ISO the same, and have both more detail and less noise. Depends if there's enough light.

Lastly, don't worry about diffraction. The 5D suffers the effect of diffraction 1 1/3 stops further up than 1.6x as well.

So, how'dya like the "short" answer? : )

Still confused? Read the essay:

http://www.josephjamesphotography.com/equivalence/

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/

Please feel free to criticize, make suggestions, and edit my photos. If you wish to use any of my photos for any purpose other than editing in these forums, please ask.