Nikkor Posted October 5, 2013 Share Posted October 5, 2013 I guess most of you actually know about this, I didn't hear of this until I noticed while taking some stills. Usually you read about some adapters not being sharp until a certain aperture value, but I've always forgotten about something very basic. You know that you can actually make your own iris on any lens if you wish to, you just have to put a paper with a hole in front of your lens. To calculate the f number you will just divide the focal length between the diameter, it's not perfectly accurate because some lenses have more distance to the front, but it accurate enough. So, when you put an anamorphic adapter in front of a lens you are actually making another aperture, so when you dial through the lenses apertures these will only count if they are below the one you have in front of the lens. Lets take an anamorphic with a backthread of 49mm. If you want to use a 135mm lens you will be limited to f≈ 1:2.8 (135/49) This seems perfectly fine as 135mm is already at the maximum longer end and 2.8 is enough, but with smaller adapters like the Bolex Möller 8/19/1.5x the backthread is 20mm so the limitations will be bigger. @50mm -> f =1:2.5 max @85mm ->f =1:4.25 max @135mm -> f =1:6.75 max Nothing dramatic, specially as this mostly limits the longer lenses but hey... Quote Link to comment Share on other sites More sharing options...
JohnBarlow Posted October 5, 2013 Share Posted October 5, 2013 Which is the exact reason why you need one of these if you want to shoot 2.8/200 on a 5D ;) Quote Link to comment Share on other sites More sharing options...
Gábor Ember Posted October 7, 2013 Share Posted October 7, 2013 I noticed this while shooting with my Helios-44M and SUN. On a sunny day I started to stop down the Helios and the exposure did not change, only the depth of field. Quote Link to comment Share on other sites More sharing options...
JohnBarlow Posted October 7, 2013 Share Posted October 7, 2013 Here is some proof for those that might be having difficulty grasping this physical effect transferconvert.co.uk/cinemania/F18desqueeze.jpg transferconvert.co.uk/cinemania/F28desqueeze.jpg transferconvert.co.uk/cinemania/F4desqueeze.jpg The images where shot with a 1.8/85mm behind a 32/2x Moller and the exposure were approx the same using shutter and flash intensity. Now look at the cuddly toy in the first two images, same level of OOF blur whereas the last image shot at F4 the cuddly toy is much sharper. The conclusion is that if you place a 1.8/85mm behind a 32/2x Moller the composite is F2.8. The actual limiting value is 85/32 = F2.65 Quote Link to comment Share on other sites More sharing options...
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