DOF w/TC versus w/o TC ???

[kirbinster]

I was wondering what is the impact of using a TC on depth of field? Let's say I shoot at f/5.6 on my 70-200 at 200mm focal length. Next let's say I put my 2.0 TC on and open up the lens to f/2.8 and shoot at 100mm which is an effective 200mm. Since the TC takes two stops my camera sees this as f/5.6 even though the Iris in the lens is set at f/2.8. So, my question is do I get a more shallow depth of field with the TC under this scenario or will the image be exactly the same for these two examples?

[RichardTaylor]

Will you be changing your subject distance to keep the image the same size?

If not changing the subject distance then this thread may provide the answer.

http://photography-on-the.net/forum/...d.php?t=796417

(I havn't used a TC for years so I can't give you a practical answer)

[kirbinster]

No no change in distance as effective focal length is 200mm for both shots. FIrst is at 200mm on lens, second is at 100mm on lens with a 2X TC.

[OsmosisStudios]

Your DoF gets thinner.

When you add a TC, you lose the light, but your aperture doesnt actually change. You're doubling your focal length while maintaining the same actual aperture size (the only thing that changes is light transmission).

Assuming nothing else changes, you'll be shooting 400mm and getting the DoF of f/2.8, but with the light of f/5.6

[kirbinster]

That is what I thought, but it won't be 400mm. I said that the first shot was taken with the bare lens at f/5.6 and 200mm while the second with the TC the lens is set at f/2.8 and 100mm so the effective results are f/5.6 and 200mm just like the first. In which case I am understanding that I will have the equivalent DOF as if it were actually f/2.8 which is what the lens is set out even though I have lost two stops with the TC.

[OsmosisStudios]

Sorry, then yes, your assumption is correct.

TC: 100mm at f/2.8 becomes 200mm f/5.6 for LIGHT, but is f/2.8 for DoF
No TC: 200mm at f/2.8 is 200mm f/2.8 for light AND DoF