Kodak Medalist unusual out of focus areas on negative

[Hunter_Compton]

I got a couple rolls of Kentmere 200 and wanted to test one of them using my (up to this point highly reliable) Kodak Medalist. Film was transferred onto one 620 metal spool and then back onto another in a method that I have used many times with Kodak Tri-X, Gold 200 and Ilford FP4+ and Pan F without issue.

Upon development I found frames 3, 4 and 5 had unusual and inconsistent out of focus regions towards the center of the frame. The other frames on the roll were tack sharp as I would expect from the 100mm f/3.5 Ektar on this camera. I verified the areas of improper focus are visible on the negative with a loupe and not just on the scan.

The frames in question were all shot at either f/8 or f/11, whereas this frame was shot at f/4 and is sharp across the frame as expected.

I'm not inclined to think this is a lens adjustment or rangefinder issue. My leading theory right now is the film is buckling or warping and the pressure plate isn't keeping it flat enough, but I'm curious to hear other peoples interpretations and why I'm only running into it now.

Full size TIFF files can be viewed here: https://www.flickr.com/photos/158396499@N04/albums/72177720326903841/

(Please disregard the dust and imperfect cropping, these are pretty much straight off the scanner).

 

[BAC1967]

I just noticed the same thing on some shots with my Medalist from a few weeks ago. Ilford Delta 100 developed in Beerenol. I don't remember the settings, they were slow shutter speeds both done with a tripod. In the first one you can see the roof and top front of the building is a little out of focus. The rope below the roof which is on about the same plane as the upper portion looks to be in focus. The roof slopes back and looks out of focus but the right side of the building is in focus. The second shot looks fine.

Fort Borst Blockhouse by Bryan Chernick, on Flickr

Historic Borst Home by Bryan Chernick, on Flickr

 

[koraks]

My leading theory right now is the film is buckling or warping

It's a film-flatness issue for sure. I don't think it's buckling as I'd expect to see the typical higher-density crescent shapes you get where the film kinks. This looks like a more smooth bulge on the film instead. It's probably only very slight. I suspect the hand-rolling has a lot to do with this and I imagine it can be pretty difficult to tightly roll everything up, consistently.

 

[Harry Callahan]

@Hunter_Compton:

The strange thing is that the plane of sharpness does not seem to be shifted anywhere. In your first picture the road sign in the foreground is unsharp - and the tree behind the house also is unsharp. If film flatness was impaired plane of sharpness should be shifted into the foreground or background it think...

But your problem might be depended on how long the film rests inside the camera after advancing. I once did take two shots of the same subject with a medium format camera, one with filter one without filter. The film had been put into the holder weeks ago and two or three pictures were taken, then the film was sitting in the holder for several weeks, then i took two pictures of the same subject within one or two minutes.
Sharpness of the first picture was a little lower in the middle of the picture, while sharpness of the second picture was excellent.
I can see that the subject you took at f4 is on the house (Dydon Deopt) you took at f8 or f11. If you took the picture of the house first and then quickly went to the sign at the house, giving the film only one or two minutes to rest in the camera after advancing you may have gotten better flatness - as the film had no time to "curl" after advancing.

Maybe you can reduce this problem by advancing the film just before exposure.

 

[koraks]

The strange thing is that the plane of sharpness does not seem to be shifted anywhere.

The film will have warped in the direction of the lens, decreasing the lens-film distance. This means the focal point will have shifted off into the distance, likely beyond infinity. A focal shift beyond infinity can never be reflected in the subject matter and everything will be out of focus.

What rival explanation do you offer that in your view would better explain the phenomenon?

 

[Harry Callahan]

I`m not saying that i have a better/different explanation, i was just surprised that plane of sharpness had disappeared from the film. I mean how much has film to warp towards the lens to get this effect with a subject being like 30ft away from the camera? When the lens is set at 30ft, setting it to infinity may move the lens 1mm closer to the film - so the warp of the film had to be more than 1mm to produce this effect...

...anyway my idea of solving this problem is based on film warping inside the camera, so i`m taking it. I was surprised that it can be that bad.

 

[koraks]

...anyway my idea of solving this problem is based on film warping inside the camera, so i`m taking it.

Yeah, i figured that too, although I wasn't quite sure whether you may also have been thinking about something related to moisture etc. Not that I think that's it, and I really think it's warping. I also understand your surprise, although given the small difference at the film plane between infinity focus and let's say 30-100ft out, I can see how a tiny bulge would create a significant problem. What I find more surprising is that it seems to be such a localized bulge, like a little mound. When film bulges, I'd expect it to create ripples, waves and ridges.

 

[Harry Callahan]

As the plane of sharpness did disappear entirely i was thinking for a minute that the film may had moved during exposure - like a slide popping when getting warm in the projector - but i consider this unlikely to maybe impossible. Also i was wondering whether the Ektar lens, which should be made from rare earth glass may somehow interact with the film, if the film had extended spectral sensitivity - but BAC1967 used a different film and Hunter_Compton got sharp results at f4 where interaction with the lens should be greater than at f11... so i settled rather fast for warped film.

Well, the Medalist is a medium format camera, so the focal length should be around 105mm. Going from 30ft to infinity may move the lens even more than 1mm - so the warp had to be pretty big.
Hm... the middle of the negative is where the film gate is farthermost - so the edges of the image are in focus but the middle isn`t... similar to a slide popping in its frame.