Speed booster confusion in DOF

Started Jun 6, 2013 | Discussions thread
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kkx Regular Member • Posts: 308
Speed booster confusion in DOF


I am trying to understand this before buying the adapter.

Read many posts and articles here and on the net in general, but still not certain.

I hope someone who understand this can help me out. Best of all, if you have the adaptor, so test will be fantastic.

Say I have 100mm 2.8 lens mounted on tri-pod. Focus and framing is fixed.

If I mount a FF camera (say 6D?) and expose at ISO 100 f2.8 1/1200 I will get a photo that I will use as reference.

Now swapping the camera (550D or Nex via simple no lens adaptor) and expose at ISO 100 f2.8 1/1200, I will theoretically get a photo with the same exposure (brightness), absolute DOF as the ref photo above, but the framing will be different, it will be cropped (1.6 or 1.5).

If I know swap the camera with nex + the speech booster and I expose at ISO 100 f2.8 1/2400: I will get a photo that is exactly the same (brightness, DOF and framing) as the first reference photo.

I.e, I can use faster shutter because of the 1-stop of light increase, and the framing is the same as FF. But the DOF is aslo the same as FF.

There are a lot of "info" saying that the lens will be effectively f2.0 because of the light/speed increase of 1-stop. So I am confused.

Is my expectation correct? From what I have "learn" from internet with 2x tele-converter, if you don't change the framing, using the same lens with and with-out the tele-converter will mean exposure difference of 2-stops, but DOF is not changed. DOF is only affected by FL vs entry pupil size.

Can anyone help me confirm this?

Thanks in advance.


 kkx's gear list:kkx's gear list
Sigma DP1 Merrill Sigma DP3 Merrill Canon EOS 550D Pentax K-5 Canon EOS 5D Mark III +7 more
Canon EOS 6D
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