[pure-silver] Re: Wonky Enlarger Lens

Justin F. Knotzke a écrit : 
<quote who=Nick Zentena, date=[10/05/2006 6:35]/>

At 50mm from the negative stage you're making infinitely large prints. At 100mm you're making 1:1 size prints. I bet with the extra bellows you're even further then that. Instead of enlarging you're reducing. 


   Hmm, you've somewhat lost me.

At 50mm, using a 6x6 negative, if I pull the head all the way down to the paper I can get to somewhere in between 8x10 and 11x14.

If I hook up the bellows and extra cone, this gets me closer to the paper. So for instance, when printing 4x5 negatives and using a 135mm lens, I cannot print on 5x7 paper. I can however if I hook up the cone and bellows.

So putting the 50mm lens on the cone and bellows extension, I get closer to the paper and thus _should_ be able to print smaller then what I am getting without the bellows. But, the lens never resolves, ever. No matter at what height I put it at, no matter how I focus, it never resolves an image.

   I'll try again later tonight but I can't figure it out.

   J



Hi Justin !
Something puzzle me here : If you try to enlarge a 6cmx6cm negative, a 50 mm lens won't do it because it won't (usually, unless it is a wide angle design but I know none of 50 mm lenght in 6x6 negs size) cover the format. The angle of view of these lenses is narow soyou need a 50 mm to enlager a 24x36 neg, a 75~ 80 mm lens for 6x6 and a 135~150 lens for 4x5 inches negs.
You wrote earlier that you use the 135 for 8x10. I think you can only get a partial print (of circular appearence) because this lens won't cover 8x10 negs. (but is your enlarger big enough for a 8x10 neg ?)
Last but not least, generally, enlarger lenses of 80 mm focal lenght opened at F:4 are 4 lenses design, and ones opening at f:5.6 are six lenses design better corrected. The iris does not open more than 5.6 because the design is such. The front lens seems to allow for more opening, but it is often not true.
Enlargers are somewhat different designs than camera. If you want to make the smallest enlargment given a particular lens and negative, you should extend the bellow fully, and use the head raise/lower mecanism to bring the image into focus. This way, you'll have the smallest "enlargment" size you may obtain from this negative/lens combination.
Hope this helps.
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