Seneca Extreme Wide Angle for 8x10 problem

[Gene McCluney]

I have this Seneca Extreme Wide Angle 8x10 barrel mount brass lens, it has a iris diaphram from 16 to 256...I assume this is obsolete scale, probably relates to f16 to f64. The glass elements are very small, and very clean. The problem is it won't produce a sharp negative. I can focus it wide open and it is a bit soft, but I can still focus, and then I stop completely down to take photo. The negative comes out very out of focus. I have other extreme wide angle lenses, perhaps even older than this, with stop wheels, and they make sharp negatives. I wonder what the issue is with this? There are no obvious parts missing. The front and back elements appear to be identical and screw into the central iris barrel, and appear to be original. Any ideas?

[Michael Graves]

It's probably that the lens is by nature soft wide open and then shifts focus as you stop down. Check your focus after stopping down and see if you can sharpen it up a bit.

[Gene McCluney]

Focusing stopped down doesn't improve the negative,.

[C. D. Keth]

Have you tried the trick of compensating for the difference between eye focus and chemical focus? I believe this could come into play if the lens is not achromatic.

[Ole Tjugen]

Have you tried the trick of compensating for the difference between eye focus and chemical focus? I believe this could come into play if the lens is not achromatic.

Not much, unless you're shooting wet plate or some other blue-only sensitive emulsion...

Is it evenly soft all over, or is some part worse than others?

Is the ground glass in exactly the same place as the film? These extreme WA's also have very shallow depth-of-focus.

I don't know that particular lens, but I use a 150mm Busch WA Aplanat on all sizes up to 24x30cm (9.5x12"), and only the last inch in the corners of that size is noticably softer than the rest - and the center is extremely sharp!

[Gene McCluney]

Not much, unless you're shooting wet plate or some other blue-only sensitive emulsion...

Is it evenly soft all over, or is some part worse than others?

Is the ground glass in exactly the same place as the film? These extreme WA's also have very shallow depth-of-focus.

I don't know that particular lens, but I use a 150mm Busch WA Aplanat on all sizes up to 24x30cm (9.5x12"), and only the last inch in the corners of that size is noticably softer than the rest - and the center is extremely sharp!

Other vintage lenses of this approximate focal length (150-165mm) are sharp for me on the negative, so I think the ground glass is positioned correctly.

[Michael Gudzinowicz]

Gene, You might try focusing on the lit filament of a clear glass electric bulb, and then stop down to see if focus shifts or if there's another problem. Try it on and off axis.