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> Large format shutters |
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#1
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Large format shutters
I made 4 negatives today with my Horseman 4x5 camera to see if my exposure and development tests had given me a useable system. The light here was pretty consistent during the afternoon. The exposures were all outdoors at the same location, and within a few minutes of each other. The first three negatives were quite dense, as if over exposed. The fourth looks normal. The only difference was that the fourth shot was at 1/8sec, whilst the first three were at 1/15sec. I haven't used this lens for 4 or 5 weeks. I have heard, but forgotten today, that shutters sometimes need to be 'exercised' before use. Is it possible that this (Copal 1) shutter needed firing a few times to bring it up to speed? Perhaps it needs a service? Any advice would be most welcome.
Alex. |
#2
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I'm not an expert on shutters, but I do know that slower nominal speeds use a different gear train than the faster ones. It's possible that Copal shutters transition from one gear train to another between 1/8 and 1/15, which would mean that all speeds 1/8 and slower are running slower than spec, thus overexposure. It's likely there's also yet another gear train for the very fastest shutter speeds (which frequently run slower than spec anyway), but you won't be using them often for LF anyway. I built my own speed checker using the simple design described in Way Beyond Monochrome and check all my shutters for accuracy from time to time, then paste the necessary corrections on the lens boards so I don't have to fumble around in my field notes (but the info IS in the notes as well). And yes, it's a good practice to fire the shutters a few (3?) times before making an exposure just to get the lubricants moving if they haven't been used for a while. I also do that before testing the speeds.
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#3
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With Copals or Compurs it's the slower speeds that hang not faster, so wrong way around. Best way to check a lens just before use is fire it at one second. You may need to fire it 3 or 4 times, if it's consistently slow or inconsistent it needs a CLA.
Are you sure you remembered to stop down ? Until you get into a good routine it's easy to make mistakes. Ian |
#4
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Sounds odd to me too Alex.
If you have a roll film back it might be worth giving it another try. Do you know anything about the history of the lens?
__________________
MartyNL “Reaching a creative state of mind thru positive action is considered preferable to waiting for inspiration.” - Minor White, 1950 |
#5
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Thanks for the replies. I got the lens from a reputable dealer last year. I don't know any more about it, but it is in good cosmetic condition. The light remained constant for the short period I was at the location, so I took an initial reading and worked from that. I settled on a combination of 1/15 @ f22-32 for the first three exposures. For the final one, I varied it to 1/8 @ f32-45 as I needed more depth. That negative looks fine. The other three are black! Having fired the shutter at various speeds since, it sounds ok. It has been lying unused, however, for several weeks. I am going to try it again and will see how it goes, taking care to rule out other potential errors. I think it's probably a good idea for me to compile a checklist of steps leading to exposure. If the problem persists, I can have it serviced.
Alex |
#6
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Quote:
Alex- When you stop down, you probably should look into the lens to make sure it is actually happening. Just a thought. Last edited by Jerry Bodine; 14th March 2016 at 05:05 PM. |
#7
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I bought an App for my i-phone that records the sound of the shutter and allows you to determine the shutter speed from the recording.
I seemed to get pretty reasonable results from it. I found all my shutters were inconsistent on the first two or three firings - across the entire speed range. So now I always exercise the shutter a few times before making a shot - regardless of how long it is since I last used the shutter at that setting. Once a shutter had become exercised at a particular speed, I was impressed how both consistent and accurate it was - all my shutters were within 1/6th of a stop across the usable shutter speed range. The App was not a lot of money (£2~£3) - it might be worth investing in - personally I would buy it again if I needed to. Martin |
#8
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Thanks Martin. I'll look into the App. I've seen them advertised, but never tried one. I made contact prints of the negatives last night. I'm beginning to suspect that this has been pilot error, rather than a shutter fault. I am favouring Ian's suggestion that I may not have stopped down after closing the shutter. The contacts suggested the dense negatives were more than 3 stops over exposed compared to the good one. I was in an area that is not usually open to the public, so I was keeping an eye on the gate to make sure I didn't get locked in! I only changed my settings for the last shot which produced the good negative.
Alex. |
#9
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You don't need an iPhone app you can just use free software like Audacity on a PC to record and measure the times of the shutter opening.
This is a Copal on a Caltar (Symmar S) 135mm lens An early Comur and an Acme 3. What amazed me was a pre WWI Compur was still very accurate at 1 second, it's the same witha similar aged Compound. Ian |
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