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05-19-2014, 10:01 AM   #1
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645 Lenses

I was just curious if Pentax made any lenses below f/2.8 for the 645 bodies? Also I know that the focal length is different from 35mm or flu frame digital so is the same true with how aperture works on a medium format? Does an f/2.8 lens let more light in on a medium format than a full frame digital?

Sorry this is so elementary, but I have no clue.


05-19-2014, 11:26 AM - 1 Like   #2
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Location: Fargo, ND
Posts: 113
F Stop is simply the relationship of the lens length to aperture. This constant allows you to measure light and apply it to exposure regardless of if you are shooting 35mm or 4x5. if you measure the scene with a light meter for that f stop and film ISO, you will use the same shutter speed regardless of camera.

2.8 will be the fastest lens you will find. The range of F stops will change as you increase the film size.

To exaggerate this but keep the science simple I will use 4x5 as an example. Your widest aperture would probably be 5.6,, now while you can not obtain the 2.8 on that format you will find that the depth of field will shift with the film size so that the look you would get at say 2.8 on 35mm will be similar to 5.6 on 4x5; similarly the DOF at F22 on 35mm will be like shooting at F64 on 4x5.

Last edited by johnsey; 05-19-2014 at 03:25 PM.

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