Ongoing issues with soft corners on scans

Digital Camera Scanning
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I’m currently at a loss at to how to make DSLR scanning work. I started off with an old copy stand a friend gave me, which appeared to work well. Eventually, I noticed that the corner areas of my 35mm scans were soft (often it was two sharp corners and two soft ones). Not the pictures, but the negatives themselves; it’s clear both in live view and on inspection in Lightroom.

This started me off on my quest to get that fixed. I had been using an Essential film holder for both 120 and 35mm negatives (separate holders); I bought a Negative Supply 35mm holder, thinking that would solve the problem. It did not. Then I bought a copy stand from NS, hoping that would make things right. That didn’t work either, mostly because it was too short for 35mm scans.

Next up— a more expensive Kaiser copy stand. Despite being apparently sturdy, my results on 35mm are worse than ever. I could return it, but I feel like anything I get in its place wouldn’t bring me anything meaningfully different or better.

I’m using a Nikon D810 and Nikon 105mm 2.8D macro lens (with a Kaiser slimlite plano). I had one soft corner on a 120 scan on the Kaiser stand, while I can see on live view that the 35mm negatives are all very soft in each corner. Refocusing on a corner results in the center going soft. This is true with both my 35mm negative holders.

I’ve set the stand up properly so far as I can see. Things look flat and straight. Is the only solution to get a longer macro lens? Is this a common problem for people? The lens works correctly, and every individual part of my setup seems to be in order. The one thing I’ll say that I’m not sure about is that for 35mm negatives, I’ve been filling the frame as much as possible when photographing/scanning it. Naturally, I’m stopping down the lens while photographing, so I know that’s not the issue.

At any rate, any help would be much appreciated. I’ve gotten good results with 120 scans for the most part, but 35mm scans just aren’t working. I get the sense that a longer macro lens would probably solve my issues, but I’d like to think that there’s something I’m overlooking that can be adjusted. That would be a lot less expensive.

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Welcome to the forum, @quietmind.

I propose that you invest some time to find out the cause of the issue(s) before investing money in something that might amplify the issue rather than attenuate it…

But first, let’s be clear that any kind of reproduction can NOT make things better than the originals. If the original negatives have blurred corners, your scans will have blurred corners.

How to get the most out of your setup.

  1. put a mirror in place of a negative
  2. make sure that the front of the lens is located in the center of the image
    (do this with the settings needed to scan 135 and 120 films each)
  3. shoot something definitely flat that has some structure
  4. find lens settings to make sure that everything is sharp, use f-stops between 7 and 11
    → If not everything is acceptably sharp, the lens seems to be the cause
    → if everything is acceptably sharp, go on
  5. shoot a negative from both sides and see, which of the shots has the most even sharpness
    → if one shot is more evenly sharp, scan this side from now on
    → if both shots are equally sharp or unsharp, then you found the limits of what you can do.

I suppose that you focus in live-view and shoot with mirror-up and at least 2s self-timer.

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If you have high standards for sharpness, then I’d say that what you describe is essentially the norm. With a high resolution camera, it’s very difficult to get an entire 35mm film frame pixel-level sharp at close to 1:1 magnification, even if your lens has a perfectly flat field. It’s just very difficult to get the film completely flat, and your depth of field is tiny at that magnification.

I’ve been using the Negative Supply film holder recently with an even higher res camera, and after much time spent adjusting the level, I’m getting something similar to what you describe - if the corners and edges are sharp, the centre is soft. The best result I’m able to get in a single shot is to set focus in between the two extremes and shoot at f/8. One way to do this is to focus roughly half way between the centre and one of the long edges.

To get a sharper image with this setup, the only way I have found is to combine multiple shots (focus stack). I have found that it’s possible to get near-sharp results across the frame at f/5.6 by combining two carefully focused shots. It’s a hassle but doable. f/5.6 is significantly sharper than f/8 with the lens I’m using due to lower diffraction.

Whether the lack of cross-frame sharpness is caused by film curve or lens field curvature or a combination of both is not clear at present. Certainly the effect is consistent with a curved plane of focus, but I also know from past experience that film rarely lies completely flat. The lens I’m using is the Sigma 105mm macro DG DN. I’d be surprised if it showed significant field curvature, but without dedicated testing, I can’t be sure. I haven no knowledge of the lens you are using, but it might be worth testing for field curvature so you can eliminate this as the issue.

The only way I ever managed to get a 35mm frame completely in focus across the frame with a 50mp camera at f/5.6 was by sandwiching it between two sheets of AN glass. Unfortunately I got newton’s rings despite the supposed AN specification. That was using a different lens - the Sigma 105mm EX DG OS, so I can confirm that that lens did not have significant curvature.

What we can’t tell from your post is exactly how soft your corners are. I think there’s a good chance that many people who use a similar setup get similar results, but have lower standards than you and so don’t mention it. So there may not be anything particularly ‘wrong’ with your setup, except that it is imperfect in the same way that most such setups are imperfect.

So a few things to try:

  1. Test your lens for field curvature at 1:1 mag. You can do this by photographing something you know is completely flat and seeing whether you can get everything in focus.
  2. If you think field curvature is contributing, then you can change your lens, or one thing which might help is to reverse your film (shiny side down). It’s possible that doing this could make the film curvature match the lens curvature. This is something I need to try.
  3. Try focusing in between the two extremes to keep both the centre and the edges acceptably sharp.
  4. Focus-bracket and combine two or more shots. This is a pain at first but workflow can be refined to make it reasonably quick and easy.

Hope that is of some use.

1 Like
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This is one of the best replies I’ve gotten in the many years I’ve been posting online. Thank you very much for such a thoughtful post.

I thought I had considered all the variables, but one thing I had overlooked was the lens field curvature; didn’t occur to me at all. I think the Nikon 105/2.8D has a relatively flat field, but when the lens is very close to the subject (the negative in this case), any curvature will stand out. It’s not as much of a problem with 120 film, which I think is because the lens is further away from the negative.

I do have high standards for sharpness; I would say I’m exacting in that sense. I’ve scanned extensively with Imacon Flextight X1s, where everything is always flat and sharp. I didn’t get the same resolution or sharpness with my Epson V750, but I figured out a good system and was getting good results; then an upgrade to Silverfast (“upgrade”) broke everything. I had gotten to the point where I didn’t miss working on a Flextight and very much liked my flatbed scans.

I had considered attempting to use ANR glass in the way you described, but I’ve gathered that newton rings are still an issue (both from your post and elsewhere). I’ll save my money.

Attempting to put the film shiny side down is a new thought for 35mm-- I’ll try that and see how it works. Thank you.

One important question I have for you: How much of the frame are you taking up in the viewfinder or live view? I was working to fill the entire frame as much as possible, which required the lens to be particularly close to the negative. This has the advantage of high resolution, but means any flaws in the process are magnified.

Thank you again for your post-- really appreciate it.

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Glad the post was of some use!

I generally try to fill as much of the digital frame as possible, leaving a small amount of film base around the edge. I like to capture the entire film frame wherever possible, because I sometimes like to include it in the final image (something beautiful about that slightly soft edge).

However, the more you try to fill the frame without cropping, the more work it can be to align the frame accurately - and if you’re doing a lot, this adds substantially to the time taken. So if the holder system allows for a lot of vertical play, I would reduce the magnification a bit so that positioning the film requires less work. The particular Negative Supply 35mm holder I have used is very poor in this respect - the film oscillates up and down uncontrollably as I wind it through, so rather than have to move the holder each time to get it aligned, I have moved the camera up a bit to allow quite large borders around the edge of the film frame, so that the film frame takes up around 87% of the digital frame.

In terms of detail capture, I think it’s generally better to have the frame as large as possible. However, as you get close to filling the frame, it’s a case of diminishing returns, as DOF gets shallower, forcing a smaller aperture (assuming your film isn’t flat) and therefore greater diffraction. I would still advocate getting the frame as large as is practical though - I don’t think you will get any better by going to a lower magnification. There will be less differential between centres and corners, but only because there’s less detail in the sharp parts.

In terms of field curvature, yes most macro lenses can be expected to have a fairly flat plane of focus, but as you suggest, ‘fairly’ is not necessarily good enough for this purpose! Your lens may well be completely flat. I just think it’s worth eliminating field curvature as a possibility. If your field is flat, then you know your problems are to do with film curvature.

I’ve used the Flextight X1 quite a bit also, and have been able to compare results from that against what I’ve got so far from the camera scanning setup (I’m using a Sony A7R IV). 35mm only so far. In a nutshell, shooting at f/5.6 and combining two shots with differential focus, I’d say detail capture across the frame is very close indeed. With a single shot at f/8, focused ‘optimally’ for the whole frame, the camera setup falls a bit short, though it’s still pretty good. This is for frames which are not next to a strip end. As you have probably found yourself, frames which fall at the end of a cut strip are not held very flat at all, and sharpness suffers a lot at the part of the frame next to the cut.

Anyway, do report back if you do any further testing - I’m very interested to know how it goes. I will do the same.

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Are you certain the sensor plane and the film plane are identically oriented? They must be parallel. I have a small spirit level I use to check the top surface of the EFH against the top surface of the camera back. I check it in both directions (East-West and North-South). The only time I’ve had focus issues is when the camera slips to one side on the tripod screw.

Are you orienting the film with the emulsion FACING the lens? That’s dull side up… You will have to flip it over in post. You want the grain or dye clouds closest to the sensor, not underneath a layer of film and gelatin.

Are you using a MODERATE aperture? f/6.3 should be about right on that lens. I would not use any aperture smaller than f/8.

The EFH is a great device and I’ve not had any issues with it. I do disassemble it from time to time and clean all surfaces with an Ilford Antistaticum cloth. I tighten all four wing nuts evenly when reassembling it.

My light source is a Viltrox L-116t video light panel, which is reasonably color accurate (CRI 95+), can be powered by battery or AC, has two sets of LEDs (yellow and blue), is adjustable from 3300 to 5600 Kelvin, and has a brightness adjustment knob. It’s under $50 and works great.

You might be interested to know that my copy stand is home made from PVC plumbing parts, some stock shelving, and a thick oak dowel rod. It’s not fancy, but it works.

Some films do curl more than others. I really like working with HP-5, because it stays flat. 50-year-old Tri-X is curved, so I have to be careful to keep the screws tight on the EFH.

I hope these suggestions help. Have you tried photographing flat art at 1:1 with that lens to see how sharp that is?

Nikon normally makes great macro lenses. I’ve used two of them for decades. One is from the mid-1960s. However, occasionally, a lens slips through the cracks with serious problems. I had a 24mm f/2.8 Nikkor that was the worst lens of any brand I’ve ever used. It was “repaired” twice before they replaced it with a slightly less mediocre copy. So I’d make sure my lens was great before blaming anything else.

I use single-point autofocus with my macro lens, to be sure the grain is sharp when I expose. I use the electronic shutter, and a two-second self timer delay.

I hope these suggestions help. Let us know how you solve this.

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Hi all,

I’ve extensively investigated field curvature for various lens options, and in my experience the 105 2.8 Nikon was sufficiently flat for my purposes, but I’m limited to 16 mpixel shots. I do use a custom holder since I didn’t trust stuff I could buy (and I’m a cheapskate) but found that taking pictures of flat millimeter paper is a great way to investigate field curvature. I just posted in “show us your setup” my findings. Perhaps there’s some ideas that might help in there.

Cheers,

Arno