Hello Alain
Your english (or dare I say Google’s translator) is great! No worries. I am interested in your experiences with light diffusers. To say the diffuser softens the captured image is not intuitive for me. Light diffusers will soften the image of a model being photographed. But your tests are surprising. I need to re read all these posts to better understand this information.
I cannot get to my equipment right away, so I won’t be able to make my own tests yet.
Still I want to drop some ideas, maybe they will help?
I read that the Difference between collimated light and polarized light is:
collimated light focuses on the direction of light rays (parallel or non-parallel), while polarized light focuses on the orientation of the electric field within the light wave."
I don’t fully understand what that means.
I use polarized lights and a polarized camera when shooting prints. I thought I would try using a polarizer with a light diffuser and negatives. Would that sharpen the image??
You seem to be only working with black and white film. Why not use an Infrared light souce. Digital cameras can be modified (not very expensive) to only see IR. There would be no chance for chromatic abberations without visible light?
It might also be possible to just use an IR filter on a color camera and an IR lightsource. Exposures will be long since color cameras try to filter out IR.
Film grain, a random and analog image pattern, when captured with an rigid digital array, will cause an unpleasant grain amplification. I have experienced this with small formats such as 8mm film. Then the image must be “softened” intensionally. I have not seen this problem with 35mm or or larger format negatives, but it might exist with high speed film stocks.
I don’t have enough theoretical knowledge of physics to have a credible opinion on this question. My experience as a photographer tells me that a polarizing filter acts on reflected light. Not much more. Could this have something to do with chromatic aberration?
I don’t see why not. Because in infrared too, wavelengths vary. Unless you could find a filter that would only let through a spectrum as narrow as my green LED ;-). I don’t know if such a thing exists.
I read your article with interest as I have experimented with collimated illumination of black and white negatives for digitisation also.
Instead of placing the camera facing up into the enlarger, I removed my Durst L 1000 enlarger’s lamp-house and condensers and installed them upside down in their correct relative positions in a custom built copy stand. There are condenser arrangements for 4x5”, 6x6cm and 135 film (24x36mm) which can be adjusted in height for specific lens focal lengths and enlargement factors. The lamp-house can also be adjusted in height. The setup currently uses a Photocrescenta 150W Opal Lamp, of the era.
The Durst instructions do recommend using a replacement point source illumination for greater sharpness and definition and one is currently available on eBay? However, using it requires the condensers to be “surface coated”, I assume to avoid flaring. Also the 12v 100W lamp requires a power supply, and the lamp is probably not replaceable. All this has been too much so I have dropped the idea, my current camera being only 24MP.
And, yes, polarising filters are only required for reflection copy work.
Oh good! Good idea to use a Durst 1000. It was a great enlarger. I had one in the '70s, I think. I really liked it. You’ve got a great tool for the job. Much better than the Krokus I used. But it was cheaper second-hand at a time when I really wasn’t sure yet.
That’s right. These condensers had the letter “T” added after their focal length. I’ve often looked for them, but to no avail.