lens focusing

mo · 2-Oct-2001, 00:37

I have just bought a Nikkor 90mm f8 lens. However the focusing screen remains da rk. 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 professionall y made all to no avail. Would using a recessed lens board on the camera (field t ype view camera) make any difference or should I just buy another 90mm lens with F5.6 and below. Constructive comments are welcome.

Mo Kenny

**Dave Schneidr** · 2-Oct-2001, 01:07

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.

**giancatarina** · 2-Oct-2001, 05:54

did you check the shutter ? is it open ?

**Mike Mahoney** · 2-Oct-2001, 07:14

what brand of field camera of camera and bellows? - you should be able to get some kind of image. if you're getting a totally dark screen, check to see if the lens is open, and that it's not stopped down.

**Ellis Vener** · 2-Oct-2001, 13:23

Are you focusing with the elns wide open or stopped down to your working aperture?

**Doug Paramore** · 2-Oct-2001, 13:48

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.

Regards,

**Jim Brick** · 2-Oct-2001, 13:59

The only way to get a brighter ground glass image is to have a lens with a wider maximum aperture.

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

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.