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Aphototaker
Tinkerer
Username: Aphototaker
Post Number: 4
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, December 10, 2009 - 03:10 pm: | 
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Hello,
Attached is a picture took with a Canon AE-1 Program camera.
There is a vertical region that is underexposed on the left hand side of the photo. I suppose this means the right hand side of the negative was underexposed while in the film compartment.
Any idea what could be causing this problem? Could it something to do with the curtain speeds?
IIRC, the speed used in this photo was 1/1000. A few other photos also show a similar problem, and IIRC they were also shot at the same speed.
Photos shot with slower speed are all okay.
Thanks. |
Mikel
Tinkerer
Username: Mikel
Post Number: 183
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, December 10, 2009 - 07:46 pm: |
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You are looking at "capping" caused by the second curtain catching up with the first curtain before the exposure is completed.
The proper way to fix it is to take the camera apart to the point you can clean the curtain roller bearings, re-lubricate, test, and adjust the curtain tension to get the correct speeds.
The quick and dirty method is to crank up the tension adjuster for the first curtain. |
Aphototaker
Tinkerer
Username: Aphototaker
Post Number: 5
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, December 11, 2009 - 06:28 am: |
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Hi Mikel,
Could you explain a bit more?
I am not familiar with the exact workings of a shutter assembly.
I suppose the dark band is actually on the right hand side of the negative when the camera is held in normal position (upright, lens facing away). So I know that the problem is when the shutters are just starting to move (unwind) toward the left hand side.
But I would like to understand how come this problem, second curtain catching up with the first one, causes underexposure only on the left of the image and not throughout?
Thanks. |
Mikel
Tinkerer
Username: Mikel
Post Number: 184
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, December 11, 2009 - 09:34 am: |
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The image on your film is actually inverted in the normal picture taking position so the problem is as I stated; it's at the closing side of the exposure.
Normally the curtains will run at the same speed all of the time. The shutter speed selected affects only the time interval between the release of the two curtains.
Curtains can not only run at different speeds, but can vary in speed as they move from one side to the other. The usual variation is that curtains speed up during travel. |
Aphototaker
Tinkerer
Username: Aphototaker
Post Number: 6
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, December 11, 2009 - 11:21 am: |
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Yes, the image is inverted. So the left hand side of the scene is on the right hand side of the negative, if seen from behind the camera, holding the camera in the normal orientation (upright, lens facing away).
Also, on the AE-1 Program, I see that during the next frame wind, the curtains are made to travel from left to right (from the film cartridge towards the shutter release button).
So when the shutter is released, the curtains travel from right hand side to the left of the camera, thus exposing the left hand side of the real world scene first and traveling to the right hand side of the real world scene.
If I understand you correctly, the closing side of the exposure should be on the right hand side, and that is where the second curtain is catching up to the first. Yet the way I see it, as I explained above, the dark side is the opening side (left hand side of the scene,i.e. the right hand side of the negative).
We both cannot be correct. What am I missing here?
Thanks. |
Gez
Tinkerer
Username: Gez
Post Number: 164
Registered: 09-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, December 11, 2009 - 12:32 pm: |
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About 90% of cases like this the problem is indeed shutter tapering, but is sometimes complicated by first curtain bounce. The first curtain at the end of its travel bounces back into the frame. In that case the first curtain brake neeeds adjusting.
Curtain bounce can occur at all speeds not just 1/1000 sec. |
Mikel
Tinkerer
Username: Mikel
Post Number: 185
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, December 11, 2009 - 01:24 pm: |
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I think what you are missing is that you are visualizing the film as you would see it from the rear of the camera but the image is on the front of the film, not the back.
It's easy to check for capping and/or shutter bounce. Remove the lens, open the back, and point the camera at a well illuminated wall. Fire the shutter at 1/1000 and see what you get. If it's cappping, you will see a darker band at the left of the 24x36 opening.
Try it a 1/500 and slower speeds. If it goes away, it's capping. If not it could be bounce or a film chip stuck in the way.
Let us know what you find. |
Aphototaker
Tinkerer
Username: Aphototaker
Post Number: 7
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, December 11, 2009 - 06:43 pm: |
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Yes, it is true that the image is formed on the front of the film. However, it does not change the fact that the left hand side of the real world scene is formed toward the right hand side of the camera (while looking from the view finder), i.e. toward the shutter release button side. This way, it does not matter which way one looks at it, the scene's left hand side falls on the shutter release button side of the negative.
Sorry for keeping at it. But I don't see the connection between the looking at the film from behind or from front of the camera in this case (other than flipping the left/right sides). It is irrelevant to the fact that the real world scene's left side falls toward the shutter release button side (because the image is inverted) and thus toward the side *from* which the curtains travel while shooting a frame, and hence on the side of the shutter opening (if I am understanding correctly what "shutter opening" means).
Or am I just missing something very critical but immensely obvious here!
Also, I tried to look through the curtain while shooting at 1/1000. It is hard for me see if there is any darkness on either side of the frame while the curtains are open. But I am reasonably sure that it does not occur at 1/500. So if it is there, as you say it should be capping.
I have tried to play with the shutter tensions and shot a roll with some frames at 1/1000 and others at 1/500 and some at other slower speeds. I will know the outcome in a few days.
Regards. |
Monopix
Tinkerer
Username: Monopix
Post Number: 61
Registered: 11-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, December 12, 2009 - 01:57 am: |
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Mikel, Based on the evidence here, Aphototaker is correct and the band is at the begining of the curtain travel and not the end. On the other hand, this does look like capping or possibly curtain bounce and I can't come up with any other solutions.
Aphototaker, Is it possible you've flipped this image at the scanning stage? Have you checked the actual neg, held it in place in the back of the camera and confirmed the orientation of it?
Just a thought... |
Aphototaker
Tinkerer
Username: Aphototaker
Post Number: 8
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, December 12, 2009 - 08:58 am: |
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Monopix, the film was given for processing and scanning at a photo shop.
I also checked the negatives. Taking the slight curve in the film strips, I fixed the side of the film facing the subject (or the camera lens) and verified its orientation (left side right, upside down) and saw that the underexposed stip is toward the frame advance crank, as I was thinking.
And from other google reading, it does appear to be capping. Apparently shutter bounce back happens at every speed and capping only at higher speeds.
So all this leaves me confused again since I still cannot work out the mechanism of capping.
Moreover, Mikel does seem to make sense and appears to know what he is talking, but his explanation leaves me even more confounded.
So if somebody can explain the mechanism of capping, that would be great.
Thanks. |
Mikel
Tinkerer
Username: Mikel
Post Number: 186
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, December 12, 2009 - 09:57 am: |
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If the band appears in a photo, but not in the test I suggested, it may be intermittent. What conditions may have changed between the photo and the test? Perhaps the temperature.
In testing visually at 1/1000 your light source may have been too dim. Try 1/1000 on the sky on a bright day if 1/500 has been the fastest speed you can actually see.
If you have a band on the wind lever side of the frame, it is not capping, but some other problem. |
Aphototaker
Tinkerer
Username: Aphototaker
Post Number: 9
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, December 12, 2009 - 12:20 pm: |
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I got back the film that I shot yesterday. The images show no more capping. Neither at 1/1000 and nor at 1/500.
What I changed was the following.
1. Slowed down the 1/1000 speed by a bit (though as Mikel pointed out, this should have no bearing on capping, since it fixes just the interval between releasing of the two curtains).
2. Cleaned the second curtain magnet slightly (didn't want to disassemble it, so just did what was possible).
3. Reduced the tension in the second curtain by one notch. The change is shown by the two green lines in the photo attached. The gear was rotated using a pair of forceps in the clockwise direction, as shown, by one notch.
4. Further, I took most of the new test photos indoors, not in -10C. I realized this, and then took a few additional ones after returning while the camera was still cold (it was -10C or so outside). This was just to see if the low temp. was causing the problem. Doesn't appear to be the case here though. No capping in both cases.
So, looks like the problem is gone for now.
But I would still like to understand how a shutter release mechanism and capping work for various kinds of shutters (L->R, R->L, T->B, B-T(?)).
Regards.
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Monopix
Tinkerer
Username: Monopix
Post Number: 62
Registered: 11-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, December 12, 2009 - 02:27 pm: |
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Capping, as Mikel said, is when the second curtain catches up the first one before the exposure is complete.
With fast shutter speeds, the sutter is never fully open. The second curtain is released before the first one completes its travel so you end up with just a slit, formed by the two curtains, that traverses the frame. Ideally, this slit remains the same width for the whole exposure but, if the two curtains run at different speeds, the width of the slit may become less as it traverses the frame. This is called tapering. If the problem is so bad that the second curtain actually catches up the first one, then it's called capping.
It's the same whichever way the shutter runs. |
Gez
Tinkerer
Username: Gez
Post Number: 165
Registered: 09-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, December 12, 2009 - 03:43 pm: |
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Aphototaker's line of reasoning makes sense, but seems to go against photographic intuition.
We are all agreed that tapering /capping and curtain bounce will affect the left hand side of the frame when viewed from the rear of the camera, BUT the effects of these malfunctions will be visible on the right hand side of the resultant print?
Am I missing something??
PS second curtain bounce will admit more light to the frame edge producing a lighter band in the picture. |
Aphototaker
Tinkerer
Username: Aphototaker
Post Number: 10
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, December 15, 2009 - 09:36 am: |
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Monopix, thanks for the explanation.
Gez, yes, I am still not able to resolve this. I have tried to search for an explanation on google, but haven't found much.
Regards. |
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