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Steve_s
Tinkerer
Username: Steve_s
Post Number: 108
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, March 06, 2008 - 09:47 am: | 
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Does anyone know where there is a really good general (non-camera-specific) guide to adjusting shutter-curtains?
Online would be ideal, but book recommendations would also be appreciated. |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 529
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, March 06, 2008 - 04:33 pm: |
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I could probably put something together that would be fairly general for cloth curtains. One problem, though, is that generally speaking shutter curtains do not go out of adjustment: they get dirty or sluggish from dried lubricant and that sort of thing, and that affects their speed and timing. If you don't address that problem first, adjusting the curtains will just mask the symptoms at best, and may make things worse. Although many cameras have curtain spring adjusters accessible without much disassembly, the cleaning will require more disassembly and that tends to be more camera-specific. |
Mikel
Tinkerer
Username: Mikel
Post Number: 80
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, March 06, 2008 - 08:12 pm: |
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You have to understand them before you can adjust them.
If you are looking for ONE book which explains this better than anything else, I would recommend the late Ed Romney's. I think it is the clearest one volume explanation, titled "Basic Camera Repair" or something like it. You can Google it or find it on ebay.
As Rick indicates, you need to get to the root of the problem and not just treat the symptoms.
If you have a specific, possibly high value camera, you should not start your camera repair hobby with it but should get more advice before proceeding. |
Steve_s
Tinkerer
Username: Steve_s
Post Number: 109
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, March 07, 2008 - 03:20 am: |
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Thanks for the input, Rick and Mikel. It's really the fundamental principles of how the shutter is supposed to work I'm looking for.
I've just started on my pile of Exaktas - all needing CLA of course! I've done the C & L on a rough VX1000 (with the help of Miles Upton's manual) which fortunately didn't need new curtains, but now I've started the "A" I really need to find out what I am doing. The sort of instructions that tell you "if 'x' is too high increase the tension on 'y'" are all very well, but without knowing what I am actually trying to do, sooner or later I always seem to find myself going round in circles!
Some of the questions I'm looking for answers to are: -
1. Should the 2nd curtain effectively be free-running OR should it be set slightly slower than the 1st, so that the 1st curtain pulls it along (at the faster speeds) and maintains the slit?
2. Should I be trying to set the curtain tensions so that there is as little acceleration as possible across the frame? This would require tensions much lower than the by-the-book values. If the curtains are supposed to accelerate across the frame, then presumably the slit width is supposed to increase, but I can't see how this could be done reliably. Adjusting spindle diameters by shimming, to widen the slit across the frame, could only work correctly at one speed.
It still seems a bit of a black art to me at the moment, but I'm sure if I knew how the darn thing was supposed to work it would all fall into place! I'll look out for Ed Romney's book. I've missed it a couple of times on eBay. |
Upnorthw
Tinkerer
Username: Upnorthw
Post Number: 3
Registered: 01-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, March 07, 2008 - 02:52 pm: |
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You can get Romney's books here. http://www.edromney.com/ |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 530
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, March 07, 2008 - 06:31 pm: |
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1. Except in a few interesting exceptions, the first curtain will not "pull the second curtain along"... they do not touch each other anywhere. The two curtains want to be set so that they move at exactly the same speed so that the slit width will remain constant for a uniform exposure across the field.
2. Setting the tension low will be easier on the ribbons and springs and possibly a bit quieter, but at the expense of being more sensitive to dirt and thus more likely to become inaccurate or hang up later on. If you know the factory settings it is best to use them... but you will not often have that luxury. The curtains do accelerate, but if in proper trim both of them accelerate at the same rate, so that the slit width remains constant.
For a very basic overview of principles of operation, I have some "How It Works" articles posted on my "Tech Notes" page. Unfortunately the Exakta is not one of them, but it is fairly similar to the Leica and Contax S shutters. Here is the Leica one:
http://rick_oleson.tripod.com/index-90.html |
Mikel
Tinkerer
Username: Mikel
Post Number: 81
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, March 07, 2008 - 07:26 pm: |
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I remember the last VX1000 I worked on, maybe four or five years ago. The curtains were in good shape but the shutter was erratic.
Once I had cleaned the shutter curtain spindles, lubricated them with a tiny bit of Nyoil, I worked the shutter several time and then checked with the digital shutter speed tester.
The results were amazing. All of the speeds from 1/30 to 1/1000 were well within spec (10 percent or better). There was no adjustment needed. This exercise gave me an appreciation for the original engineering of this camera. If the curtains are in good shape, a CL may be all that you need.
Tomosy's book on restoring classic cameras covers the VX Exaktas in detail- probably all you need. But see if you can get Romney's book! |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 532
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, March 07, 2008 - 10:32 pm: |
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Mikel's experience is typical, if the curtains are in good condition. Unfortunately, an Exakta with good curtains is something of a rarity.... but they can be replaced. Cracked curtains, of course, will not work, but even if they're not cracked they are often hardened from age and this can prevent them from traveling normally. This problem is particularly common in 1950s Exaktas, Pentacon/Contax SLRs, and Praktinas; I assume Prakticas also would share the problem but I have very little experience with those. |
Steve_s
Tinkerer
Username: Steve_s
Post Number: 110
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 08, 2008 - 07:32 am: |
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Thanks, all. The reason for my first question was that if you hold on to the 2nd curtain spindle, fire the shutter, and let it run slowly, the gap runs across the film gate. In these conditions the 1st curtain is held back by a pin riveted inside the large 1st curtain drive gear touching a pin on the 2nd curtain gear. I was thinking that this is probably the way the curtains are meant to run, but this would prevent the slit from increasing as it runs across the frame, which it must be able to do to give an even exposure, if the curtains are increasing in speed, as they always do.
According to the Ihagee manual the approximate tensions are 26 gm for the 2nd curtain and 110 gm for the 1st, and they suggest 4 turns and 6 turns respectively as inital settings for the spring spindles. I tried to count the turns as I unwound them, and I reckon there were 4½ turns on the 1st, but the 2nd got away from me. Ihagee managed to make the tension adjustment incredibly fiddly! 4 turns on the 2nd curtain gives about the right tension; 4½ turns on the 1st gives about 100 gm which is as high as my spring-balance will go. 6 turns would obviously be rather high.
This is the third cloth focal-plane shutter I've attempted. The first, an Exa IIb, came good almost immediately (beginner's luck). The second, an Edixaflex, I could get nothing sensible out of at all, and after two weeks I abandoned it. This one is looking a lot like the Edixa. On both I've found it very difficult to prevent the 2nd curtain running faster than the 1st. My present plan is to put the ****** thing on one side for a couple of years while I try to gather as much information as I can!! I was going to include some test results, but I can't make the forum table formatting give a readable result, and "Enable html code in message" never seems to do anything, so in case anyone might be able to make sense of them, I've uploaded them to: -
http://www.ydo.abelgratis.co.uk/vx1000.html
They are rough figures each based on a single firing at "1/1000". My home-made tester has 3 photo-transistors at 15 mm separations to measure at beginning (a), middle (b), and end (c), and also enables me to measure curtain times between the transistors.
Thanks for the links, and book suggestions. I'm in the UK, so I'll see if I can source them here first. The Contax shutter doesn't look quite as scary as I'd thought, Rick, but I suppose I'll have to get through this one before I go there! |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 534
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 08, 2008 - 10:38 am: |
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The nicest thing about the Exakta shutter is that you have all kinds of elbow room when the body shell is off. I've never had a factory repair manual, and I don't think I've ever worked on a model later than the VXIIb.... |
Steve_s
Tinkerer
Username: Steve_s
Post Number: 112
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 09, 2008 - 02:27 pm: |
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That much is certainly true. In the Edixa the spindles are assembled into the body - but at least you can adjust the tensions without worrying about everything falling to bits. In the Exakta you have to use your left hand to control the screwdriver in the spindle slot as well as holding the whole thing down on to the bench so that the spring-spindle axles don't come out the bottom, while at the same time using the tweezers in your right hand trying to get a stupid little bit of spring wire in or out of the hole at the top! At least Ihagee had learnt their lesson by the time they got to the later Exas, which have a neat little ratchet-wheel on the spring-spindles, making them very easy, and adjustable by fractions of a turn.
I can't find Ed Romney's book available anywhere in the UK. Is Tomosy's book any good? I get the impression that much of it may deal with more modern Japanese cameras, which don't interest me.
I'm really not sure at present where to go on this Exakta. I have been assuming that since I haven't changed the curtains, I should be able to set it up just by getting the tensions right, but from my test results I am sure that even if I managed to get the exposure equal across the frame, the time would be much too slow. The ribbons on the Exakta 1st curtains are made from a material that has to be pre-stretched when fitting, so I am wondering if they might have stretched further over the years, which would widen the slit. Is this common on Exaktas?
Should I be looking at shimming the curtains? I had thought that this was a "last resort" tweak, but is it a regular part of the job of adjusting the shutter? |
Glenn
Tinkerer
Username: Glenn
Post Number: 296
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 09, 2008 - 06:34 pm: |
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Steve,
You are misguided in thinking the slit width needs to increase as the curtains move across the gate. As Rick previously stated - set up the curtain tensions so that both curtains move at the same speed. If you are having problems in this area, you should check for wear/damage in the mechanism. Curtain 'shimming' plays no part in setting up focal plane shutters of this type. |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 537
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 09, 2008 - 07:52 pm: |
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A good rule of thumb is to start from the assumption that the people who designed the camera knew how it was supposed to work. If you find yourself trying to change the diameter of a curtain drum, or filing a speed cam, or anything else that changes the geometry of the mechanism, pretty much by definition you're going the wrong way. If it seems to need that sort of adjustment, look elsewhere for the cause of the problem before proceeding. |
Steve_s
Tinkerer
Username: Steve_s
Post Number: 113
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 10, 2008 - 03:55 pm: |
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Thanks for the information and advice.
The reason for my belief that the slit must increase is that in every camera I have looked at, the curtains/blinds run faster over the second half of the frame than over the first. I don't think it is possible to prevent this, and as Rick has suggested above, even if you could, it would make for unreliability. Clearly, a constant gap will give a shorter exposure when it is running faster than when it is slower, so some tapering would be inevitable.
Since I was re-using the curtains on this Exakta, I marked all the gears carefully before dismantling, and have re-assembled it exactly as it was. One of the checks in the Ihagee manual is to release the shutter at 1/1000 while holding on to the 2nd curtain spindle. The slit at the start of the frame should be 1 mm, and mine is correct. On my camera, if you let the curtains run across slowly like this, the slit increases to 3 mm at the end. I realise that this doesn't mean it should increase like this in practice - if the curtains are running at equal speeds it would stay 1mm.
It is the high exposure time at the start that has been throwing me. Since the slit can't be more than 1 mm at this point (as in the test above), and I would not have thought it should be much less than 1 mm, then the curtain speed must be much too slow at this point. Miles Upton's instructions suggest that the viscosity of the grease on the idler-gear spindle is one of the variables to play with. I've used the lightest grease I can get hold of. Maybe I would be better off with oil. I'll give it a try tomorrow if I have time.
I thought it might be useful to look at what I had thought was the nearest thing I've got to a working Exakta (another VX 1000). This turned out to be virtually a carbon-copy at 1/1000 of the one I'm working on (2.5ms, 1.6ms, and 1.9 ms at start, middle, and end). Even the curtain speeds are the same, so that didn't prove a lot! |
Steve_s
Tinkerer
Username: Steve_s
Post Number: 114
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 11, 2008 - 03:09 pm: |
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Replacing the grease on the idler-gear spindle with oil didn't help, nor did a heavier grease.
I currently have the 1st curtain tensioned by 6 turns, and the 2nd by 3 turns, and the curtain speeds match fairly well. The only problem is that the exposure at 1/1000 sec is about 4 ms at all three positions! |
Mikel
Tinkerer
Username: Mikel
Post Number: 82
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 11, 2008 - 08:10 pm: |
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Just catching up again Steve.
Tomosy put out several books, the most common being the two volume set of basic camera repair. For Exaktas, his book "Restoring Classic & Collectible Cameras" is much more useful.
Cloth focal plane shutters of this type are going to run faster as they gain speed after release. This is normal. Keep in mind that shutters of the VX era were within tolerance at plus or minus 20 or 30 percent, particularly at the upper speeds. I have looked at your table and although I am sure that you are mortified and disappointed by your results, you are probably doing much better than you think. You can chase these shutters around all day but you will never get even close to the performance of a copal or seiko quartz controlled shutter, particularly in the uniformity of speed across the entire focal plane.
If you test it at 1/1000 in the center and you are getting a millisecond plus or minus 30% and it's not capping, I would call it good and run some film though it.
Mike |
Steve_s
Tinkerer
Username: Steve_s
Post Number: 115
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, March 13, 2008 - 05:21 am: |
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Thanks for the reassurance Mikel, and thanks for the book info. I hadn't heard of the "Restoring Classic and Collectible Cameras" book, and would wrongly have bought the 1st volume of the "Maintainance and Repair" books.
I'm still a very long way from any sort of usable result with this camera, but at least I believe can now see how it should work. In retrospect, perhaps it was a bad idea to start on my worst Exakta first. I thought it would be a good one to learn on without worrying too much whether I wrecked it. I haven't wrecked it, but I've spent about 5 weeks repairing and replacing parts before even getting to the adjustment, and my enthusiasm is wearing a little thin!
I reckon I'll have to put it on hold for a while, and get on with something I actually can fix. I will have another go when I can face maybe stripping the curtains out again and trying different lubricants.
Both the Romney and Tomosy books seem much more available on eBay in the USA than here in the UK, so I'll probably get them from over there, and have a read, before I go much further. |
Steve_s
Tinkerer
Username: Steve_s
Post Number: 116
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, March 13, 2008 - 06:54 am: |
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Turns out Amazon UK had one copy each of the Tomosy "Restoring Classics" and "Maintenance - Book 1" books, so I've ordered those, and just need to get the Ed Romney book. |
Mikel
Tinkerer
Username: Mikel
Post Number: 84
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, March 13, 2008 - 06:30 pm: |
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Steve-
Take a well deserved break!
The books you have ordered will not be a Baedecker's Guide to travel providing you with each and every step to provide the solution to all of the camera repair problems you might face, but nothing can.
What you will be facing is some very interesting reading from one of the best authors in the field.
But keep after the Romney book!
Mike |
Francis_otto
Tinkerer
Username: Francis_otto
Post Number: 21
Registered: 12-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 15, 2008 - 12:17 pm: |
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Pig-ignorant as I am, I had always thought that, with a focal-plane shutter, 'shutter speed' was a result of ribbon-speed x slit-width, the variable always being the slit-width; I have one or two Micro-Press cameras with F/P shutters, where changing the 'speed' changes the slit-width.
Now, I know that they make a satisfying shoo-oop sound - the -'oop' sounding quicker - or louder- than the 'shoo-': is it this that is confounding Steve S? How can you measure the speed of blind-travel, to establish that "the curtains/blinds run faster over the second half of the frame than over the first." |
Steve_s
Tinkerer
Username: Steve_s
Post Number: 118
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 15, 2008 - 03:30 pm: |
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You are right about the curtain-speed x slit, of course, but I haven't seen a shutter yet where the curtains didn't speed up across the frame. Maybe some are better regulated.
My home-made tester is of the type that plugs into my computer sound board. It has a phototransistor near the start of the frame, one in the middle and one at the end, at 15 mm spacing. This means I can measure the time each curtain takes to travel between each of the phototransistors, and calculate the speed.
I don't know about the "shoo-oop", the Exakta is more of a "ker-thunk"! |
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