Speed booster confusion in DOF

Started Jun 6, 2013 | Discussions thread
EinsteinsGhost Forum Pro • Posts: 11,977
Re: Speed booster confusion in DOF

viking79 wrote:

To get exact same images between APS-C and 135 format full frame:

APS-C: 35mm f/1.8 1/100 ISO 100

Full Frame: 50mm f/2.8 1/100 ISO 250

This will give you the same noise performance (given similar sensor performance, like Sony 16 MP vs Sony 24 or 36 MP full frame) same field of view same shutter speed and same depth of field.  These are "equivalent" settings.

To figure these out, use the crop factor to get effective aperture and focal length and for ISO is it crop factor^2?  So if your crop factor is 1.52 you would multiply ISO by 2.31, rounding up to 250 since that is closest 1/3rd stop.  I haven't thought about the ISO one much, but instead just use an ISO chart and go up or down 1 1/3 stops [1] (actual is like 1.23 stops, but 1 1/3 is rounded).

The speed booster basically converts your lens focal length and aperture to a full frame equivalent (or nearly).  This is actually changing the physical focal length and f/stop, but the net result is it is a full frame converter for the camera.


You're also increasing the amount of light reaching the sensor by using a lens as a concentrator, which would otherwise be spread over a larger area. Consequently, increasing exposure.

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