DOF and tele-extenders?

M

mcbob

Veteran
So how does this work...

Let's say I use a wide, fast lens (about 6mm/1.2) and add a tele-extender, theoretically yielding a 12/3.0 or so. Would it have the DOF qualities of f3 or of f1.2? Phrased differently, does a tele-extender act more like a ND in terms of its light loss?
 
It would act like the 12mm, f/2.4 lens you have in effect turned it into, in all respects including DOF. (Assuming you really did mean f/1.2 in your parentheses. I'm not sure where f/3.0 comes from; two stops down from f/1.2 to account for the exposure correction due to the converter would be f/2.4.)

Now where did you find a 6mm, f/1.2 lens to convert? I've seen lenses of those specs for super 8 film cameras and very small sensor surveillance and other video cameras, but in order to work on the AF100 with a teleconverter, it would need to be able to cover the 2/3" sensor or 16mm film frame, approximately, to start with.

- Greg
 
The lens is a Tamron 4-12/1.2 for 1/2" Cmount, with a C/P 2x tele-extender. It's giving full coverage with the tx, but its actual light performance (as measured by calibrating Y-get readings off the same swatch of wall) matches f3 on my 20/1.7.

And its covering the full frame
 
mcbob said:
The lens is a Tamron 4-12/1.2 for 1/2" Cmount, with a C/P 2x tele-extender. It's giving full coverage with the tx, but its actual light performance (as measured by calibrating Y-get readings off the same swatch of wall) matches f3 on my 20/1.7.

And its covering the full frame
Click to expand...

Gotcha. An interesting find, even if you are losing some light in there someplace. At those focal lengths you are going to get pretty deep DOF even fairly wide open. It's impressive that it will cover 4/3 with the converter although designed for 1/2".

- Greg
 
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