Sorry, I saw your question now.
Spacer rings were used when needed to adjust rear to front cell distance for best sharpness. For every pair of cells it may be required different ring spacers (normally) ranging from 0.5mm to 1.5mm
A lens may have no spacer, one spacer or more than one.
This is used to get best correction possible of aberrations for a particular lens. More distance makes aberrations provocated by front cell to spread more before the rear cell compensates it in the oposite way.
It is also possible that one spacing distance is better for the center and another is better for corners. Also a particular spacing can work better for near subjects or for infinite.
If I'm not mistaken, a process lens can be optimized for distant subjects by changing spacing, for example to be used for ULF.
To find best spacing you use a resolution target and an eyepiece, so you see the image "in the air". Projection on Ground Glass it is not good enough for that, as the frozen glass texture degradates the image quality.
At the end you see the resolution target through the lens with the eyepiece, and you unscreew to seek best Lp/mm in the center and/or in the corners, for macro or for distant subjects. You count the number of tours you unscreew the front cell until best image...
...and as you know the thread pitch you also know the good ring thickness.
This kind of optimization is useful for very sharp shots. If shot is not very sharp (f/32 diffraction) perhaps it won't be noticed. I've been playing with that, using a microscope 20x periplan as eyepiece, but I've pending learning about that.
Last edited by Pere Casals; 27-Jun-2017 at 15:22.
Interesting and informative replies here! Hereīs my two cents:
In my experience itīs best to look at your favourite focal length for formats you already shoot and buy appropriate for 4x5. When you start to get the hang of Large Format AND know WHAT you want to shoot with it, you will have a clear idea how to proceed with your lenses. Resale value most of the time is the same as purchase price so a little experimentation doesnīt hurt too much if on a budget.
I shot mainly with a Leica M before LF and my most used lenses were 40mm and 28mm. So as I started out I got two lenses for my field Camera, a 90mm Super Angulon MC and a 150mm APO Symmar. Surprisingly about 80% of shooting I did with the 90 SA (on Leica I used 40mm much more. BUT I was starting to shoot differently so for me the Format reflected into my photography style. Not only because of the Limitations of the Format but I started to seek other Pictures.
After a while I found 90mm just wasn't wide enough for what I wanted to shoot (a little bit landscape and a lot Urban Architecture) so I got a 75mm Nikkor f4,5. That was my kit for the last few Years. Sometime I carried all three lenses but most of the time only 75 and 150 or 90 and 150. (those WA lenses all weight about 500g...much rather carry three extra film holders)
Only last week I treated myself with a 300mm Apo Ronar and a 125mm Fujinon-W . both modern Multicoated versions so my Kit now consists of two sets. The 220IC gang (150APO and 90MC) and the 200mm IC pack (75 and 125)..the Ronar just lives in the bag, at under 300g I don't see a reason not to take it with me.
Don't worry about the first lenses for Field shooting, it will most definitely not be the last lens purchase you make!
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