wide angle lens for 12x20 format

[Dave Wooten]

I would suggest one take a look at the web site of Carl Weese.

[Really Big Cameras]

I disagree. This weekend I did a 8x20 picture with 355 G-claron (orange filter) on sunny day, I've got a significant falloff. According to my calcucation by densitometer almost full stop between center and corners.

Actually, I'm surprised that's all the fall-off you measured. The C Claron is a standard design (no tiling entrance pupil like the Biogon and derivatives like the Super Angulon, Grandagon, Fujinon SW and Nikkor SW). So, the theoretical best case fall-off will be cos^4. For a 355mm lens in the corners of an 8x20 negative, that works out to about 1 1/3stops. Of course, that assumes you are focused at infinity (the worst case scenario). As you focus closer the angle theta decreases and so does the fall-off.

For a modern wide angle with a tilting entrance pupil the fall-off closely follows cos^3. However, the longest lens of this type I know of is the 300mm Fujinon SW. If such a lens did exist in the 355mm focal length, the fall-off in the corner of an 8x20 negative would be just under 1 stop.

Of course, how much anyone would notice this is a matter of personal sensitivity. I personally don't find fall-off of 1 1/3 stops objectionable on high contrast color transparency film. Once the fall-off gets up around 1½ stops on Velvia, I reach for the center filter. On lower contrast black and white materials, my person sensitivity to fall-off is less.

Every lens has fall-off. The wider the lens, the more the fall-off. The tilting entrance pupil design of many modern wide angles lenses helps reduce this fall-off, but doesn't come close to eliminating it. Even center filters are not designed to give totally even illumination. They are typically designed to reduce the fall-off to a tolerable level for most people. If you've got a stop of fall-off corner-to-corner, most people wouldn't find that offensive. In fact, unless you have a VERY even toned subject (white geese in a snowstorm), most people won't even notice.

Kerry Thalmann
Really Big Cameras

[Really Big Cameras]

I would suggest one take a look at the web site of Carl Weese.

And, the key comment by Carl in this thread was:

"No objectionable light falloff either."

Not, no measurable fall-off.

There is a significant difference between these two statements.

Kerry Thalmann
Really Big Cameras

[Jorge Gasteazoro]

I disagree. This weekend I did a 8x20 picture with 355 G-claron (orange filter) on sunny day, I've got a significant falloff. According to my calcucation by densitometer almost full stop between center and corners. With distance, center is 355mm from nodal point, corners are 448mm from nodal point, approximately 25% further than center of the filmholder.

SAS.... buddy, this is a thread from the year 2000..

PS. Don't know what you didi, I use a 355 frequently in my 12x20 and see no fall off...are you sure your filter ring did not cause vignetting?

[SAShruby]

I know Jorge, , but I searched for G-Claron fall off thread and I found this one. I didn't want to start new thread.
You know, you got it. This is it! I just realized it, (blushing). I stopped lens to f11 only for fast exposure. Aaaach.

I gotta check it out if I had full circle in my corner! Highly likely not

[imageshooter]

I have a nuArc 8-1/4" F8 Process Lens that came along with a Sinar P 4x5 with Digital shutter. This lens is mounted on a small thick board 4" square. As I am brand new to LF photography I do not have clue about what the camera's previous owner used it for. It doesn't have shutter speeds, and doesn't seem to be able to talk to the Digital Shutter. Any feedback will be appreciated.

Richard

[Archphoto]

I think that if you want to use this lens you will have to put it onto a Sinar lensboard.
And no, this lens will never be able to talk to this shutter, but is there a need for it ?
As long as you can set the shutterspeed on the shutter you could give it a try.

Peter

PS would it not have been wiser to start a new thread ???

[imageshooter]

Thanks for the reply Peter. As I am new at this stuff I just thought you jumped in and started asking Qs. I just went to the top of the page and saw the new posting button.

Thanks for the tip off

Richard