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lens focusing


mo_kenny

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I have just bought a Nikkor 90mm f8 lens. However the focusing screen remains dark. I cannot get a clear or focused image on the focusing screen. (The camera is new and my 210 mm f5.6 lens focuses well).

I have changed focusing screen and I have also used fresnel screen professionally made all to no avail. Would using a recessed lens board on the camera (field type view camera) make any difference or should I just buy another 90mm lens with F5.6 and below.

Constructive comments are welcome.

 

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Mo Kenny

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What camera are you using? I would suggest removing the lens and

measuring from the lens mounting surface to the ground glass with the

standards as close together as possible. It doesn't need to be real

precise, are you measuring somewhat less than 90mm? If not you will

need a recessed lens board. Can you focus on something close, perhaps

2 meters away? The bellows would be extended quite a bit for this

close focus. Maybe you are just not use to focusing a wide angle

lens. You don't get a bright full screen image with a wide angle F8

lens, at least nothing like you see with the 210mm lens.

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Mo: I use an f8 90mm lens and while not as bright as my other lenses,

I am able to see quite well to focus. You should not have any

problems with the Nikkor. Do check to make sure your camera will

close up close enough to focus the 90mm without the recessed

lensboard. Adjust your lens' f-stops while looking into the front of

the lens to make sure the aperature is opening and closing properly.

It really shouldn't be a problem to focus if everything is working

properly.

 

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Regards,

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The only way to get a brighter ground glass image is to have a lens

with a wider maximum aperture.

 

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Wide angle lenses need to have wider max openings than longer lenses.

 

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This is why I bought Rodenstock Grandagon f/4.5 wide angle lenses

(55, 75, & 90). My 120 & 180 are f/5.6, my 270 is f/6.3, 360 is f/8,

500 is f/11, and 720 is f/16. But all equally bright when viewing and

focusing.

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