Aperture on tube lens

Harald · Post by **Harald** » Wed Jun 07, 2017 10:53 am

Hi there,
One question, maybe silly, but anyway....
I´m planing on using an Mitutoyo M Plan APO 5x on an 70-200 f/2.8.
Does the changing on the aperture on the tube lens have any impact on DOF since the Mitu only uses the center of the tube?

Pau · Post by **Pau** » Wed Jun 07, 2017 11:50 am

The main effect will be vignette, DOF is limited by the objective NA (and illumination) At 200mm you maybe could close the aperture to f4 with little effect if any on DOF but maybe a bit more contrast if the lens induce flare (not likely with a Canon L)

If you want to stop down the system aperture (more DOF - less resolution) you can put an aperture just between the objective and the tube lens as close as possible to the objective.

Harald · Post by **Harald** » Wed Jun 07, 2017 12:03 pm

Hi there Pau,
This is just as I thought. Wanted to ask to make sure.
Yes, it´s the Canon 70-200 f/2.8L.
I am so looking forward to try this set up, it´s been a long time dream....

Thanks for taking your time to answering me