Plasticca lens configuration
I have a question for those of you who have experience using a Plasticca lens. Have you tried using the cell mounted on the back of the barrel, as opposed to the front? The soft focus/diffusion effect appears quite different in that configuration. With the cell mounted on the front of the barrel (as designed, the convex surface facing toward the subject and away from the film plane/ground glass), the image appears relatively sharp in the center, but falls apart off axis. There doesn’t appear to be much diffusion in the central sharp area, and the off-axis areas looks defocused, like very severe field curvature. With the cell mounted on the back of the barrel (the convex element facing the film plane/ground glass), I see a nicely diffused image relatively evenly spread across the image, even in the center. I think it’s neat that you can create such different effects by simply moving the cell from front to back, depending on your preference. What optical principles might account for this?
Kind Regards,
Daniel
Re: Plasticca lens configuration
My Plasticca is virtually "as new" so I haven't dared to move the lens cell around! And it is loaned out at the moment so can't do a quick check.
If I understand you right, you are suggesting a reversal of the front face - in the same way that an achromat from a front Petzval cell is used in a soft meniscus. Or as I use a telescope achromat in soft lenses.
A simple movement of the lens further back will be the equivalent of stopping down a little with a front stop. This is something I have experimented with with using cardboard cut-outs placed in the front - but only at the GG examination face.
I am not the first person to have looked at the possibility of "taming the Plasticca" as a few years ago, a Plasticca set was sold in Sweden with a set of especially made "Imagon" style strainers with different central aperture sizes.
My Plasticca is the big 600mm and Stephane is comparing it with a smaller one (450mm?). He is having difficulties with getting a sharp focus/sharp negative on the 600mm. He may be trying front stops to get some more satisfactory sharpness.
My own theory is that above the 450mm size, there is too much spreading of the wavelengths (which increases with increasing focal length) to allow for sharpness on a panchromatic emulsion!
I am sure Stephane/Emil can contribute with more useful comments!
Re: Plasticca lens configuration
Quote:
Originally Posted by
dlin
I have a question for those of you who have experience using a Plasticca lens. Have you tried using the cell mounted on the back of the barrel, as opposed to the front? The soft focus/diffusion effect appears quite different in that configuration. With the cell mounted on the front of the barrel (as designed, the convex surface facing toward the subject and away from the film plane/ground glass), the image appears relatively sharp in the center, but falls apart off axis. There doesn’t appear to be much diffusion in the central sharp area, and the off-axis areas looks defocused, like very severe field curvature. With the cell mounted on the back of the barrel (the convex element facing the film plane/ground glass), I see a nicely diffused image relatively evenly spread across the image, even in the center. I think it’s neat that you can create such different effects by simply moving the cell from front to back, depending on your preference. What optical principles might account for this?
Kind Regards,
Daniel
Very interesting Dan. I will make some test shot and let you know. Thanks for sharing.
Re: Plasticca lens configuration
Plasticca 300mm (inverted)
4x5 Fortepan 200 in Pyrocat HD
Re: Plasticca lens configuration
Quote:
Originally Posted by
dlin
Plasticca 300mm (inverted)
4x5 Fortepan 200 in Pyrocat HD
This looks very promising. I will try some tests too..
Re: Plasticca lens configuration
The same effect can also be achieved with the Kalosat (see here), so it may be valid for other meniscii. Just got to check it out...
Re: Plasticca lens configuration
Re: Plasticca lens configuration
I have, eventually, acquired a camera on which to test my 24" Plasticca.
First of all, the coverage given in the Plasticca brochure (cameraeccentric) is distressing conservative. the 600mm is listed as being for 10x12" but covers my 30x40cm ground glass without any problems. I suspect it would have no difficulty with 14x17" either. This means the listing for other sizes is wrong too.
No 30x40cm film or paper around here yet so I have had to make do with playing with front stops. These do remove some of the soft effect and increase the circle of clarity as well as the usual depth of focus "bonus". Mine is version with yellow stained balsam. Until I get some registration material, I will make do with trying to see what different filters do to GG images.
And mount the lens board the other way around to compare images.
Which I have already done - but my photographic recall is not good enough to spot differences in images 30 seconds apart!
But certainly an OK image.
