Derick Crucius Posted November 25, 2019 Share Posted November 25, 2019 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 Link to comment Share on other sites More sharing options...
Bruce Greene Posted November 25, 2019 Share Posted November 25, 2019 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. Link to comment Share on other sites More sharing options...
Derick Crucius Posted November 25, 2019 Author Share Posted November 25, 2019 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. Link to comment Share on other sites More sharing options...
Bruce Greene Posted November 25, 2019 Share Posted November 25, 2019 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. Link to comment Share on other sites More sharing options...
Premium Member Dom Jaeger Posted November 25, 2019 Premium Member Share Posted November 25, 2019 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. Link to comment Share on other sites More sharing options...
Derick Crucius Posted November 26, 2019 Author Share Posted November 26, 2019 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. Link to comment Share on other sites More sharing options...
Mark Dunn Posted November 26, 2019 Share Posted November 26, 2019 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. Link to comment Share on other sites More sharing options...
Derick Crucius Posted November 26, 2019 Author Share Posted November 26, 2019 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? Link to comment Share on other sites More sharing options...
Mark Dunn Posted November 26, 2019 Share Posted November 26, 2019 (edited) 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. Edited November 26, 2019 by Mark Dunn Link to comment Share on other sites More sharing options...
Derick Crucius Posted November 26, 2019 Author Share Posted November 26, 2019 2 minutes 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. Sure thing Mark, unfortunately I have to squash the file down to JPEG. Here you are: Without circles Link to comment Share on other sites More sharing options...
Derick Crucius Posted November 26, 2019 Author Share Posted November 26, 2019 Without circles Link to comment Share on other sites More sharing options...
Derick Crucius Posted November 26, 2019 Author Share Posted November 26, 2019 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: Link to comment Share on other sites More sharing options...
Robino Jones Posted November 26, 2019 Share Posted November 26, 2019 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.. Link to comment Share on other sites More sharing options...
Derick Crucius Posted November 26, 2019 Author Share Posted November 26, 2019 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.. 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. Link to comment Share on other sites More sharing options...
Roberto Pirodda Posted November 28, 2019 Share Posted November 28, 2019 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. Link to comment Share on other sites More sharing options...
Premium Member Phil Rhodes Posted November 28, 2019 Premium Member Share Posted November 28, 2019 Seconded - that looks almost exactly like sensor dust spots on a DSLR, which appear at very high f/ numbers. Link to comment Share on other sites More sharing options...
Dennis Toeppen Posted November 29, 2019 Share Posted November 29, 2019 This thread is stress-inducing. Nothing worse than spots from an unknown source. Link to comment Share on other sites More sharing options...
Roberto Pirodda Posted November 29, 2019 Share Posted November 29, 2019 5 hours ago, Dennis Toeppen said: This thread is stress-inducing. Nothing worse than spots from an unknown source. Ahah, what is it, if one is stressed by this thread , well do not read it ! PERIOD Link to comment Share on other sites More sharing options...
Derick Crucius Posted November 29, 2019 Author Share Posted November 29, 2019 Thanks everyone, I appreciate the feedback. I cleaned the prism and all of my lenses as best as I could. Hopefully my next batch of film comes out fine now. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now