What does one really sacrifice in using this shorter (than 300mm) focal length? I would be making maximum 20 x 24 enlargements of 8x10 negs. Am I going to notice reduced edge performance? I have used a 135 componon S for 5x 4 and have noticed no difference between this and a 150 rodagon on the print (up to 20 x 16). I realise that at huge enlargements, the shorter focal length may not have the coverage, but at what sort of enlargement might this come into play.
The added bonus of 240 is that it doubles for 5 x 7 conveniently.
Any guidance would be appreciated, however, I should have asked before I bought it...
No, you should not notice any degradation at that enlargement size going from a 300 to a 240. It is easy enough to check to see if you will have problems though. On you copy board with the neg in place; check the dimensions of the image rectangle through dead center vs an edge. If they are different, then you may have a problem.
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Originally Posted by Tom Stanworth
Michael Mutmansky is using a 240 mm lens on his 8X10 conversion of a Durst 138S. I am not sure if his is a Rodagon or another lens. I have the 240 mm Componon S that I planned on using if I get around to doing an 8X10 conversion.
He has all of the dimensional data related to that focal length used for 8X10 available. You might send him an email if that information would be helpful.
Don mentioned that I use the 240 with my homebrew enlarger. I actually have not used the 240 with an 8x10 negative yet, because I also have a 300 Rodagon, which I prefer for exactly the reasons you are concerned about.
I figure as long as I have the room to use the longer lens, I will use it. I don't typically crop the negs, so I can print a 20x24 on the 138 without any difficulty and the easel is not too low for comfort.
If I needed to print a smaller negative, or crop in on the 8x10, the 240 is going to be the only way to do this, because the geometry becomes difficult over about 2.5x magnification with the 300.
I asked a similar question before I built the enlarger, but I never got a suitable answer, so I just forged ahead with it, and designed it to accommodate the 300.
There is no question that the performance will be better with the 300, but the difference may be small enough that you can't really see it except at the largest size prints.
There are several issues to using a wider lens, and not all of them are tied to the optical performance of the lens. Some of them are geometry issues related to the enlarger head, which complicates the issue a bit.
At 16x20, while it may be possible to measure a difference in performance, it will probably not be noticeable on a print. At 20x24, I think the differences will start to show up. The most obvious will be the increased edge burning that you will have to use with the 240 lens. It may even be necessary to edge burn more on a 16x20.
I recommend you get a LPM swatch from Stouffer and make some tests. You would then be able to see how far the lens will enlarge before the sharpness falls off to much for your liking.
Regardless, if you have the room, the 300 is a better lens to use.
I have a 240mm El Nikkor and a 300mm Rodagon and used to have a 300mm El Nikkor. When I first got the 240mm, I did some comparisons with the 300's at 16x20 and 30x40 enlargements from 8x10 negatives.
The centers of the prints with any of the lenses were pretty much identical at both magnifications. I found the 240mm actually slightly sharper in the corners of a 16x20 print than the longer lenses, I assume because of less diffraction effects with the shorter focal length. In a 30x40 print the 300mm lenses were a little sharper in the corners due to more coverage with less extension, but especially with these larger prints, the longer lenses are more of a pain to use. The sharpness differences were very small and only really noticable with careful side by side comparisons. It's hard to remember, but I think the sharpness difference was larger at 16x20 than it was at 30x40. I didn't test at 20x24, but from the other two sizes, I wouldn't expect you to see any significant difference between the two focal lengths.
I could see no difference in the evenness of light with any lens with my enlarger--an 8x10 De Vere with a color head--but if your light source is only marginally large enough for 8x10 or it's located a long distance from your negative, the 300mm should give more even light (you don't need as big a light source because of the smaller angle of view).
I'm sure that there are some differences between different 240mm lenses. At some point, I tested a 240mm lens that Besler sold (actually the Rodenstok labeled verson of that lens, can't remember the name). At the center through slightly more than the coverage needed for 5x7 it was very similar to the performance for my El Nikkor. I would have been happy with the sharpness. However, at the edges of the print from an 8x10 negative, it was noticably soft, even without a comparison print.
I much prefer using the 240mm because of working distance. I rarely print bigger than 16x20 and haven't printed larger than 20x24 in years. If anyone is interested in a 300mm Rodagon, I'm willing to sell mine.
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