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I have a small darkroom where I've just started making B&W prints from 4x5 negatives. Even when the negative is very in focus from edge to edge, and scans nicely, when I print 8x10 with my enlarger the details are sharp in the center but lose focus about 2-3" from the edges. Enlarging lens is a Wollensack 135mm f/4.5. I'm seeing this using f11 on that enlarger lens. I am using a glassless negative holder like this.

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What could be causing this focus fall off at the edges?

  • How long from the time you focus till the time you print? Film will move and buckle slightly as light (heat) is applied in a glassless carrier -- especially in larger formats. – bvy Jul 29 '17 at 16:45
  • @bvy I turn the light off between focusing and printing, but anywhere from 2min to 2hrs. I'm not sure the edges are ever in focus - my grain focuser doesn't seem to work at the edges of my projection. – steel Jul 29 '17 at 16:55
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    I have checked my favorite resource on enlarging lens - the Post Exposure book by Ctein, available here ctein.com/booksmpl.htm - and while there are some quality 135mm lens that cover 4×5 format your Wollensack does not seem to be one of them. In any case, you might want to check the Chapter 6 on enlarging issues (especially the lens tests towards the end). It is a bit dense read, but well worth it! – Jindra Lacko Jul 31 '17 at 16:59
  • @JindraLacko I hadn't heard of that book, thank you. Looks like I need a new, longer lens, which I think will at least partly address the second question I asked this weekend as well. – steel Jul 31 '17 at 18:17
  • glad to be of service! I was referred to the book by an online friend, and I found it a source of inspiration. The guy knows his positive process :) I agree you could use a better lens, good news is that they are very cheap on the well known auction site. – Jindra Lacko Jul 31 '17 at 19:13
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The most likely culprit is the lens. Most Wollensacks (this was a US brand with little presence in Europe, where I am based, so I am going by the specs; you might want to double check) were 4 element Tessar types, and these suffer from corner issues.

Consider a 6 element lens (Componon S, Rodagon and El Nikor have all good reputation and need not be expensive).

Just to rule out other possible causes:

  • check film flatness. Make a test print with a glass carrier.

  • check enlarger alignment. Make sure the film plane, lens board and paper easel are perfectly level.

  • it is unlikely you have a condensor problem (these tend to cause light falloff issues, i.e. light corners, not out of focus issues) but check that anyway. Make sure you have the appropriate condensor for your format and that the lens are properly aligned and centered.

  • it is unlikely your lens has diffraction issues. f11 on a f4.5 should be safe. Just to rule it out: with a glass carrier make a test print at f5.6 and f8.

A side note: I believe the corner performance (sharpness and light falloff) is overrated. In fact I almost always burn in my edges and corners. I feel it improves my pictures, drawing attention to the main subject.

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If this is a condenser enlarger, likely it has two large condensing lenses situated between the lamp and the negative. These are plano-convex lenses. Make sure the plano sides face the lens and the lamp i.e. the two convex sides face each other. Also check the location of the condensers. If it is adjustable to accommodate smaller negatives, it could be too near the negative. If adjustable, increase the space between condenser and negative. Also consider purchasing a better lens with a flatter field. When using a grain focuser, place it 1/3 out from the center. This will deliver a more uniform focus.

Addendum: The 135mm delivers too small a circle of good definition. For enlarging purposes a lens equal or greater than the diagonal measure is recommended. For the 4x5 negative the diagonal measure is 6.4 inches = 163mm. Suggested is a 150mm or longer for this task.

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    I had the impression condenser problems could be involved in light falloff issues (light corners) but not corner sharpness issues. It is on the other side of the negative. – Jindra Lacko Jul 30 '17 at 7:09
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    @ Jindra Lacko -- It’s called the Callier Effect - Andre Callier who discovered condenser enlargers yield higher contrast and apparent acuity due to light path scatter in the negative. However; on rereading - I have concluded that the real cause is; the focal length of the lens being used is too short. A lens with a focal length equal to the diagonal measure of the negative is recommended for optimum uniformity. The 4X 5 diagonal is 6.4 inches = 162.6mm. The circle of good definition of the 135mm is too small. The smallness suitable enlarger lens for 4X5 is 150mm or longer. – Alan Marcus Jul 30 '17 at 13:09
  • ... and 135mm is for the European format 9×12 cm. I thought so too. – Jindra Lacko Jul 30 '17 at 13:15

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