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Darks spots on film scan


Derick Crucius
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Hey everyone,

I recently got some scans back and they look great, but on one shot in particular I noticed an issue with dark circles all throughout the images. I was wondering if this is a lens issue or an issue with my bolex prism? The lens was stopped down to f/22 and I also closed the shutter down an extra stop since these were shots of a bright sky.

I have also noticed this issue on previous scans. I did notice in my one Switar lens that there are a bunch of little droplets of what appear to be grease or liquid, could this cause such an issue? The spots are soft, almost identical to sensor dust spots on a digital camera, but they are much larger in diameter. 

Thank you in advance.

-Derick

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4 minutes ago, Bruce Greene said:

At f22 it certainly seems like it could be dust on your prism.  I think dust in the lens itself would present more as flare or low contrast than circles.

Thanks Bruce, do you have any tips on how to clean the bolex prism without damaging it? I checked it out and it seemed to be clean, but I could have missed something.

also, the specs inside of my Switar don’t appear to be dust, it definitely looks like a liquid of some sort.

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I'm guessing that cleaning the prism is a quite delicate process, and it might be very easy to damage it.

Try shooting another lens on your camera and see if that fixes the issue. Preferably a lens with the same focal length.  I know that these days another lens might not be so easy to find,  but you want to shoot with a Bolex and this is what you're up against shooting such vintage equipment these days.

If you know a lens technician with an optical bench, you might try bringing them the lens and projecting it and see if you see the spots.  Or you can just send it in for inspection and cleaning and repair.

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It's very unlikely you'd see anything on the front of the prism, which is too far away from the film plane, but possibly large specks on the rear might show up at f/22. With the turret rotated out of the way, you can flip up the prism to clean the rear surface if necessary. Use the folded tip of a tissue dabbed in isopropyl alcohol or lens cleaning fluid and swipe in one direction.

It can depend on the focal length and stop as to how clearly it shows up (worse with wide angles and stopped down), but if you have chips on the front element of a lens and shoot into the sun or a bright source you may see little circles or flare spots in the footage.  They tend to have the shape of the iris opening. 

I'm curious about the "drops of liquid" in the Switar.. sometimes separation of the element coating has the appearance of an oil slick, but I've also encountered hardened drops of oil that leached from the grease and settled in the centre of an inner element.. never with a Switar though. The other possibility is condensation that formed inside and left little water marks. None of those tend to photograph though, as Bruce said dust or other contamination inside a lens tends to just lower the contrast or create flare if reflective.

 

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2 hours ago, Dom Jaeger said:

It's very unlikely you'd see anything on the front of the prism, which is too far away from the film plane, but possibly large specks on the rear might show up at f/22. With the turret rotated out of the way, you can flip up the prism to clean the rear surface if necessary. Use the folded tip of a tissue dabbed in isopropyl alcohol or lens cleaning fluid and swipe in one direction.

It can depend on the focal length and stop as to how clearly it shows up (worse with wide angles and stopped down), but if you have chips on the front element of a lens and shoot into the sun or a bright source you may see little circles or flare spots in the footage.  They tend to have the shape of the iris opening. 

I'm curious about the "drops of liquid" in the Switar.. sometimes separation of the element coating has the appearance of an oil slick, but I've also encountered hardened drops of oil that leached from the grease and settled in the centre of an inner element.. never with a Switar though. The other possibility is condensation that formed inside and left little water marks. None of those tend to photograph though, as Bruce said dust or other contamination inside a lens tends to just lower the contrast or create flare if reflective.

 

Thanks Dom, I appreciate the information. I checked my prism again tonight and didn’t see anything out of the ordinary, but gave it a cleanings anyways. I inspected all of my lenses with a lighted loupe and all of them have some form of debris inside, but I have never had this issue with my lenses stopped down to f/22 before.

the only thing I could think of that may have caused it was that I shot a music video in a warehouse a few months back, maybe dust or something got into the film chamber when I changed reels (I did not have a dark bag) and kicked up behind the prism or perhaps it got on the prism when using the turret to swap lenses. 

I did notice it a bit on that footage when shooting a bright sky, and noticed the same on my recent footage shooting a similar scene. The spots are in the same exact place on both batches. 
 

assuming it is the prism, I suppose I should give it a quick look each time I load.

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3 hours ago, Mark Dunn said:

If you shot neg, dust spots would be white. If they don't move between lenses, it must be on the prism.

It would help a lot if you put up a sample of the footage, or even just a few frame grabs.

Hey Mark,

Sorry, I should have included a frame. I've attacked a Tiff below...I darkened the image with a cruddy grade to show what i'm talking about. They are faint and very soft. As i said before, its only in this particular shot because I was closed down, but it was also in a previous reel as well. I have since cleaned off my prism, although I didnt see anything out of the ordinary. 

This is probably a farfetched question, but there's no way debris could get etched into the prism glass, right? 

Also, just a note...I shoot a lot of expired stock....I'm wondering if it might have been flakes of emulsion that chipped off and flew onto the prism while the camera was running?

 

Crucius 16mm ECN 2K 11-21a.00_05_43_17.Still001_edited.jpg

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3 hours ago, Mark Dunn said:

  I don't see any spots because of the edge effects from the circles. Can you re-post without them?

No reason for expired stock to be prone to flaking.

For some reason my image doesn’t appear to be embedding in my posts. Hopefully it shows up below:

8E2B882B-4808-4827-9D82-56A4A47F8F9D.jpeg

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6 minutes ago, Robino Jones said:

Added contrast to your image to see the spots better. Could this be from the scan? Maybe you can't see the spots in other places because there's detail in the frame? Just a guess.. 

Without-circlesHC.jpg

I double checked, and no I don't think its from the scan. The reason is that the same spots appear in the same location on some B&W film that was scanned on a different scanner altogether.

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On 11/26/2019 at 8:49 PM, Derick Crucius said:

I double checked, and no I don't think its from the scan. The reason is that the same spots appear in the same location on some B&W film that was scanned on a different scanner altogether.

Unless you have shot the b/w  and color stocks with the same lens with the same focus and f/stop, i think  these are prism spots. Do not use f.22, but use a neutral grey filter or better set fast shutter speed if possible. You should set iris at about f5.6 for best definition. It is not so difficult to flip and clean the prism after all.

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