Official Pentax K to Q lens adapter

Started Aug 25, 2011 | Discussions thread
godfrog Senior Member • Posts: 1,463
Re: Official Pentax K to Q lens adapter

MightyMike wrote:

image in a 40mm F2.8 becoming a 224mm F2.8 or even better a 43mm F1.9 becoming a 241mm F1.9...

how about a 70mm F2.4 becoming a 392mm F2.4 or a 77mm F1.8 becoming a 431mm F1.8

in DOF terms the 77mm F1.8 would be like a 431mm F10 on FF or a 287mm F6.7 (close enough to stopping down to F6.7 on a 300mm lens or the 60-250 @ 250 and not far off what you get with a 55-300)

Your 77mm F1.8 does not "become" a 431mm F1.8. It most certainly remains 77mm F1.8. In terms of field of view, depth of field and total shot noise it will be like using a 287mm F6.7 on APS-C, except resolution will be miserable, focus throw will be super short, mechanical tolerances much wider than what is used on 1/2.3" sensors, internal reflections from the lack of mechanical vignetting will zap contrast, and you'll have a lot less dynamic range in scenes where there is enough light to use base ISO on the APS-C camera.

Oh, and the Q does not have a mechanically shutter, so you will have the image degradation of using an electronic shutter as well. Alternatively, the adapter will contain a leaf shutter with limited top speed as well as the issues associated with putting shutters at any point besides the focal plane or the middle of a lens, see Joseph Wisniewski's elaboration in this thread:

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