Figuring out where to start with negative carrier, lens and base board.

[Tim Holmes]

After a few month's break from dark room work, I was struggling to get a negative (10x8) anywhere near in focus and wondering where to start with the lens vs neg carrier vs baseboard.

I have a Durst L184 and was using a 300mm lens. I have just converted it from a motorised head and baseboard to manual (with help from a very capable friend).
I had a brain freeze with where to start, so and turned to AI (argh)

Anyhow 3 prompts and a few minutes later and I have a 16kb calculator that runs on my iphone (or any web browser) and will calculate the starting point distances for neg to lens, lens to baseboard for all my enlarger lenses. It will also calculate enlargement factors. Feel free to down load and try.

 

[Ian Grant]

In my old house I used a 135mm lens for 5x4, when I bought a De Vere 5108 it came with a 300mm Symmar S, it is floor standing and I had to sink the base to get it into my cellar darkroom.

Mt current darkroom has an apex roof, and there's enough clearance to use the head at full height. However I decided it would be more practical to switch to use a 240mm Symmar S. It's not just the lens to paper. and lens to negative distances. you have to add the addition distance to the filter dials, another 7" to the white light (no filters) dial.

I tend to print two standard sizes 12.5x10, and just under 20x16. with the 300mm lens the negative to paper is around a foot more than with the 240mm, a lot easier to reach the filter controls. Of course I could drop the baseboard, but on long printing sessions I prefer to work at typical bench height.

Ian

 

[jhotopf]

I like to think of an enlarger as a camera in reverse so if you need a 16x20 print from your 8x10 neg that is a two time magnification one way but 0.5 x the other so the negative to lens plane would be 450mm and the print you want would be 900mm below the lens roughly, so a total height of 1350mm if using a 300mm lens enlarging lens. Correct me anyone isf my maths is wrong!

 

[Reginald S.]

I was struggling to get a negative (10x8) anywhere near in focus and wondering where to start with the lens vs neg carrier vs baseboard.

It depends on your magnification ratio.
For a 1:1 ratio as a starting point, given by physical laws and a formula you have to double the focal length 300mm for both distances neg/lens and lens/baseboard or easel. This gives a total distance of 1200mm from neg to base.
These are the same and mathematics as for your camera.

For the next, and all other ratio steps, you further have to add one focal length to the 600mm lens to paper distance.
So for 2x magnification you have to add 300mm , which will give jhotopf's 900mm distance, but you now have to shorten the neg to lens distance.
Unfortunately I forgot the second part of the formula, so we now have to ask jhotopf, we could have a look into my Durst Laborator book, or with the first formula you can figure out in an easy way, with shortening the neg to lens distance.