Speed booster confusion in DOF

Started Jun 6, 2013 | Discussions thread
kkx
kkx
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Re: Speed booster confusion in DOF
In reply to DtEW, Jun 7, 2013

DtEW wrote:

kkx wrote:

Hi,

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).

Let's start here.  There is one other thing that is different that you omitted:  the photo's SNR.  It will be like the FF's SNR at ~ISO200.  Remember that you are losing/wasting light with a light circle way too big for the sensor.

I don't quite follow, please help. I might got some of this mixed up. Trying to understand what you are telling me.

The crop sensor is smaller, but the per-mm-square light energy should be the same (same shutter speed).

I can understand that due to denser pixel the crop sensor have a lower SNR compare to the FF sensor at the same ISO and light energy per-mm-square. Is that what you are referring to?

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.

You might begin to see what the prior statement was heading toward.  It actually won't be exactly like the reference photo, because it's SNR will be like if the reference FF camera is shooting at ~ISO200.  This now explains why it is shooting one stop faster than the reference photo.

(this is all assuming that the sensor technologies are comparable)

This is why I tell people that the Speed Booster more-or-lessy makes the NEX into a slow-focusing/manual-focusing FF, but stuck on ISO200 and greater.  All the shooting parameters are the same (just ignore all the "adds one stop" conversions, which is only true if you're thinking in APS-C terms), except you can never drop the camera down into a FF's ISO100 creamy smoothness and signal integrity.  It is a partial simulation of the performance envelope of a FF camera.  It does not exceed it in any way.

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