I just bought a Schneider IV for a Nikkor 90mm f/4.5. I've been told I should open 1 1/2 stops when using it. Also is there anything special I should know when using it or how it's made?
I just bought a Schneider IV for a Nikkor 90mm f/4.5. I've been told I should open 1 1/2 stops when using it. Also is there anything special I should know when using it or how it's made?
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Yes and no.
Yes, you need to check the lens to know how far to stop down when using the CF. Most LF wide angle lenses suffer mechanical vignetting at large apertures because the barrels occlude the exit pupil. Center filters more-or-less offset optical vignetting (cos^4), do nothing for mechanical.
To check, open the diaphragm as wide as it will go. Then hold the lens at arm's length with the shutter open, rear cell facing you. Rotate it slowly (around a vertical line through the diaphragm) until the exit pupil touches the edge of the barrel. Stop down 1/2 stop. Repeat. Eventually the exit pupil will be so small that it will just touch the edge of the barrel when rotated through approximately half the angle the lens is supposed to cover. Use that stop or smaller when using the lens with its CF.
Bob gave you a rule of thumb, not a test procedure. Testing is better.
No, how the density gradient is created is irrelevant to how the CF should be used. But and however, if you think the gradient is due to a variable density layer of paint or something on the outside of the filter, be very careful when cleaning that side of the filter. My Schneider CF III seems to have something on the rear surface, its front surface is clean. Best not to rub the rear surface.
Thanks for that info. I've asked this elsewhere. But I've been told it's best to use 88mm BW contrast filter and polarizer filters between the lens and CF. Of course that leaves grad ND filter (square) on a holder outside where the CF is 105mm vs 82mm for the lens side. Any recommendations or considerations?
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Alan, CFs are designed to sit as close to the lens as possible. If you put anything between the CF and the lens you risk mechanical vignetting. If you put anything in front of the CF it has to screw in, otherwise, again, you risk mechanical vignetting.
If you don't use movements you may be able to get away with doing what you want. Its worth trying, but be prepared for it not to work well.
And be aware, if you will be photographing anything with large expanses of sky from edge to edge that areas of the sky are naturally polarized. If you use a polarizer with a wide angle under that condition you will get banding in the sky from those naturally polarized areas.
I've always suspected there was some kind of physical differences between new and old Schneider CFs. Also, multicoating perhaps?
A data point: I at one time had an older Schneider 3B CF and a newer one at the same time. The older one flared horribly in many conditions and it seemed to cause some loss in contrast. The newer one was unnoticeable in use. Some time ago I gave the old one away, else I could look at it more closely.
Dan and Bob, Thanks for the tips. So how do you use CF's and other filters with 90mm and 75mm lenses?
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Bob, I'm confused. Why would I stop down? Don't I have to open the lens 2 stops for the CF?
Let's make this simple for me. My meter indicates the exposure should be F22 at 1/4 sec.
1. What should my setting be with the CF mounted?
2. What should my setting be with the CF dis-mounted?
3. What do you mean I have to be stopped down two stops from wide open?
Flickr Home Page: https://www.flickr.com/photos/alanklein2000/albums
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