The LED cold light reduces the heat and power requirement issues... by a factor x10. I use 100w RGB leds, ...cheap
About the lens:
20x24 has a 31" circle, need a 800mm circle. Some enlarging lenses cover around 50º, APO Nikkor 600 covers 37º
Here you have Dan's list of apo nikkors:
http://www.galerie-photo.com/apo-pro...ikkors-en.html
> To calculate the needed lens select required circle to cover the negative (the diagonal), then select a focal (450mm or 600mm) and get the covering angle of the lens you consider,
> use plain trigonometry (or solidworks)
to know the minimum bellows draw that will cover your circle with the coverage angle you have, for example with 800mm circle and 50º coverage: bellows draw has to be at least 867.8mm, so a 600mm (with 50º coverage) will not focus on a wall that is at very long distance, but as you give bellows draw to focus closer then the circle expands and will cover the 20x24 when the draw is 867.8mm or more:
Attachment 174426
...from the focus formula get the maximum working distance that the minimum bellows draw will allow while covering the negative , here says how:
http://www.largeformatphotography.in...=1#post1400399
So it looks that a 450 may cover the 20x24 for "smaller" prints, a 600mm may cover really big godzilla prints and a 900mm would not have limitations.
Anyway if you PM a focal and a coverage angle of a lens you consider I would tell you what maximum enlargement is possible while covering a negative size. Also consider that a shorter focal will end in a greater fall off in the corners, this can also be calculated aprox with the cos^4 rule...
You can start with a LOMO O-2 600mm , I got mine for $50 new (now there are 2 listed in ebay at $200, but offer way less in the case), later you may go to more refined APO nikkor lenses, but
if not wanting more than x2 enlargements (this is 50" prints !)
just use the O-2, you may not notice anything in the print with a superior lens, at least if not exploring the print with a magnifier.
Regards
Bookmarks