Cirkut "Gears" program discussion

[frobozz]

This thread could easily just be a continuation of this thread here:

(there was a url link here which no longer exists)

But I figured I'd start a new thread to make it easier for people to find when searching in the future. You should definitely go read that thread first though!

I haven't gotten a chance to use my #10 much but from what I can tell it has the original Turner-Reich triple convertible lens and the original scales on the bed and all the original gears, so I should be all set as far as that goes. My one test with it on 220 film looked like it had credible geometry, though I didn't shoot any squares and measure the negative. But I have a couple of other lenses I want to use someday, so I'm interested in figuring out precisely what gears I'd need for them, so when I get some cut they'll actually work. I'd prefer to test them and verify I was right, than find out they're a little off and need to cut more!

There seem to be two main ways to figure out gears. Jim Lipari described a pretty straightforward way in some notes I posted a copy of in that other thread:

http://cirkutcamera.com/docs/jim_lipari_notes_01.pdf

So far, if I run those equations on my camera, I come very close to the supplied gears, but not exactly - it gets farther off on the longer focal lengths. I haven't figured out why yet, perhaps I'm putting in some wrong numbers or have a math error. Or maybe Jim's method was only supposed to be approximate, expecting a little experimentation from the result, to be treated as a starting point. So I figured I'd use the near-legendary "Gears" program, which uses a lot more precise measurements of the cameras as inputs, so presumably would give a more precise result. The latest version was hosted on a website that no longer exists, but you can find it on the Wayback Machine:

http://web.archive.org/web/20070902025934/http://www.bigshotz.co.nz/gears.zip

Unfortunately, the online version of the program ( http://web.archive.org/web/20070807230835/http://www.bigshotz.co.nz/gears.php ) doesn't seem to function via the Wayback machine.

I rid myself of all things Windows a decade ago (and life has been much better!) but at work we do have Parallels running Windows XP so I extracted the program and fired it up there. I made pretty careful measurements of my camera but even if I was a little off you'd think I'd get reasonable results... but this was not the case. So I'm hoping someone that has successfully run this program can show me where I'm misunderstanding what value to measure, or doing something blatantly wrong.

Also, if anyone has the source to this program, in any language (even the original BASIC version) I'd love to get it, so I could port it to the Mac and run it natively - of course I'd share that again so everyone else could too!

Here is my input file, using the 18 inch setup of my triple convertible lens:

---

fp fp = Measure subject distance from FILM PLANE, np = REAR NODAL POINT
in in = units are inches, mm = units are millimetres
18 Actual focal length of lens
6 Large gear radius
3.661 Diameter of film drum with average amount of film
.559 Perpendicular distance from center of small gear to the LENS AXIS
-2.278 Perpendicular distance from center of small gear to the FILM PLANE (NEGATIVE IF FILM PLANE IS BEHIND GEAR)
.25 Slit width
32 Gear pitch (always Imperial)
----------------------------------------------------------------------------------------------------------------------------------

NOTE: Turn Word wrap OFF when editing or you will get confused.

The name of this file should be gearsInput.txt

It is the optional data file for the Cirkut Gears program.
Edit the data items above to suit your requirements.

The data items must be the first thing on the first 9 lines or the
program will not work properly. Everything after line 9 is ignored.
On each line there must be the data, at least 1 space, then the
descriptive text.

If this file doesn't exist or contains bad data the program will prompt
you for manual input.

---

When I run the program, it starts with a 40-tooth gear. I think the program figures out how big a gear it would need to use to produce nonsense results and starts there, then works down to the gear you tell it in response to its prompt, just to make sure it covers all possibilities. I used 30 as my smallest gear.

And here is the resulting output (saved as a PDF to maintain the formatting):

http://backglass.org/duncan/apug/cirkut/gearsoutput_18_20150312.pdf

If I am understanding that data correctly, it's saying for 88 foot distances I should use a 38-tooth gear, for 45 feet I should use a 37-tooth gear, and for 24 feet I should use a 35-tooth gear...while in fact my camera is set up to use 43, 42, and 41 as shown here:

I'll show my work for the measurements:

fp - measuring subject distance (which is focusing distance, right?) from the film plane

in - using inch measurements

18 - focal length of lens (as spec'd; I have not measured it to verify)

6 - my large gear has a 12" diameter, so radius is 6 inches

3.661 - my film drum has an 11.5" circumference, so divide that by pi to get diameter

.559 - width of motor plate is 8-5/16" or 8.9375". Lens centerline should therefore be half that distance from one edge, or 4.46875". Edge of gear drive hole is 3.7845" from that same edge of motor plate, plus half the width of the hole, which is .25"/2 or .125", which puts the centerline of gear 3.9095" from the edge, and subtraction tells us it must therefore be .559" from the centerline of the motor plate (and thus the lens centerline)

-2.278 - Negative because film plane is behind gear. Gear hole edge to back edge is 2.4275", plus the height of the edge lip is .1105" plus half the gear drive hole diameter is .125" which puts the center of gear 2.663" from the top of the lip. But the film plane is down inside the camera .385" from that same lip, so we need to subtract that off, which results in a distance of 2.278" from center of gear to film plane. (The measurement sequence is that contorted because of what I can accurately measure between with my micrometer.)

.25 - slit width is spec'd as that. A little hard to measure accurately but it looks reasonable when I stick my micrometer in there. That shouldn't affect gear ratio anyway, should it?

32 - gear pitch, as spec'd

So what am I doing wrong on the input data? How does that compare to anyone else's input data for a #10? Or how am I misinterpreting the output data?

Thanks,
Duncan

 

[frobozz]

Hmmm, after some more thorough running of numbers, it would appear that gears.exe and the Lipari math notes produce more similar numbers than I realized at first (i.e. they are both a bad mismatch to the gears that came with the camera, for the 18" and 24" focal lengths.) Everybody agrees pretty well on the numbers for the 10-7/8 scenario, and in fact that's what I was using in my tests which turned out pretty undistorted. Guess I need to go run some more precise tests with film at all 3 focal lengths this weekend, when it's supposed to be gorgeous out, and conducive to Cirkut motor operation! Running the numbers the other way, the gears supplied with my camera would be more appropriate if the other two actual focal lengths were 16 instead of 18, and 21 instead of 24. I can try to do some measurements to see if that's the case with this lens.

Duncan

 

[jamie young]

If your camera is running the original lens with scales don't go messing with them till you see a reason to and that reason would be seeing bad film tests.
When I got my #16 it came without a lens (and a gearhead and a tripod and small gears It was pretty much just the camera and back). I found a lens that matched the original and had it measured when there were people still doing that for cirkuts. My 15/24/36" TR lens measured at 14.94/21.94/32.550" So there was a big variation with the TR lenses.with all the charts I got, it was still worth while to then do tests.I found it interesting that the lens did seem to match the original gear scales pretty closely

 

[frobozz]

I think I'm finally getting my head around the math involved in this concept... and I've either had an "aha!" moment... or I'm a cluelessly naive newbie who hasn't been paying attention in class.

My revelation is that almost none of those numbers used in all these various calculations really matter to us. They'd matter a lot if you were trying to design a spinning panoramic camera that worked properly, but all we're trying to do is successfully operate an existing camera that was designed "eh, close enough." In theory a camera like this should pivot exactly around the rear nodal point of the lens. This camera doesn't really try to, with the pivot point changing based on the size of the gear, and no amount of measuring gear offsets is going to change that. Maybe that can tell you how far away from ideal the pivot point is, but what can you do with that information?

It all comes down to the same way you test to tell if the gear is right: does the horizontal motion of the film match the vertical size of the image? Put another way, the lens and focus distance result in an image magnification; the film transport "magnification" needs to match that number. At 100' focus distance with any lens, if you were to take a 360 degree picture, you would be capturing 7539.82" of image. Your image magnification will tell you how many inches of film that should take up. Just to make up a number, say your magnification were .01. Then you would need to transport 75.3982" of film in that 360 degrees. On a Cirkut #10 with an 11.5" circumference take-up spool, that means it needs to spin 6.556 times. You know there are 384 teeth in the outer ring to make one revolution, and you know that the takeup spool and the gear socket spin at exactly the same rate (I need to verify this by counting teeth, but they appear to), so if the takeup is to spin 6.556 times in 384 teeth, it needs a 58.569 tooth pinion gear to do that.

So, how to measure magnification? There are some pretty straightforward math models for doing it based on focal length and focus distance, but it's going to matter how you determine focal length. Does the Cirkut use the distance from the rear nodal point? Is that sometimes radically different than the marked focal length of a lens, which might explain my supplied gear teeth which seem to be wrong according to all the programs? Perhaps. I need to dig into that more. But if I'm right, it's going to make gear selection a lot easier, and require a lot less measuring of cameras! All you would need is the number of teeth in your ring gear, the circumference of your takeup spool, and the measured "focal length" of the lens in question.

Duncan

 

[frobozz]

If your camera is running the original lens with scales don't go messing with them till you see a reason to and that reason would be seeing bad film tests.
When I got my #16 it came without a lens (and a gearhead and a tripod and small gears It was pretty much just the camera and back). I found a lens that matched the original and had it measured when there were people still doing that for cirkuts. My 15/24/36" TR lens measured at 14.94/21.94/32.550" So there was a big variation with the TR lenses.with all the charts I got, it was still worth while to then do tests.I found it interesting that the lens did seem to match the original gear scales pretty closely

Oh absolutely! I am taking the fact that my gears don't match what comes out of the program or formulas as an indication that I'm doing the program or formulas wrong, not that I've got the wrong gears! I'm using this as a sanity check. Once I can do some math with the existing lens and come up with those existing gear numbers, then I can be more confident in any numbers I produce for other lenses.

Duncan

 

[frobozz]

OK a quick check of my T-R lens, using a laser distance tool, says it's pretty darn close to 18 and 24. If it's off, it's not off by the 2-3" required to get the existing gears. So nothing left to do there but shoot some tests this weekend. Which will settle that question... but if the gears are right, it won't answer the question of what I'm doing wrong in the calculations. I get about the same gear answers with my new "aha!" strategy, so that would imply that the magnification would be based on the rear nodal point, and that point must be behind the physical lens. Or something.

(Showing my work again - with the 24" cell in the back of the lens, and focused on an object 130' (1560") away, the center of the lens is 24.5" from the ground glass. 1/(1/1560+1/24.5) = 24.12. Another project: make sure the ground glass position matches the film plane...)

Duncan

 

[jamie young]

Could the fact that the lenses used in their parts (not combined like the 10" length, with the glass behind the aperture, change the math and the nodal point somehow. Not really sure. I do know the cameras set up by the factory were all hand set to each individual lens group to correct for any lens variations.

 

[frobozz]

I thought to myself "I wonder if the original Cirkut patent delves into any of this?" WHY YES IT DOES!

I got all 6 Cirkut-related patents from USPTO.gov and put them up on my documentation page here:

http://cirkutcamera.com/docs/

The original Cirkut related patent is this one here:

http://cirkutcamera.com/docs/patent_776403.pdf

(The others deal with improvements that were mostly never implemented, and with features of the camera having nothing particularly to do with the panoramic functions.)

Here's the money quote:

The principle upon which this camera is constructed in order to accomplish the desired results is deduced from the fact that as the diameter of the pinion 28 is to the diameter of the stationary toothed wheel 29 so is the diameter of the feed-roll 15 to twice the focal distance of the lens desired to be used. Thus to illustrate assume that the diameter of the pinion 28 is three-quarters of an inch, the diameter of the stationary toothed wheel 29 is ten inches, and the diameter of the feed roll 15 is six inches. It will at once be seen that the focal distance of the lens must be precisely forty inches, or one-half of eighty. In other words, the diameter of the stationary toothed wheel 29 divided by twice the focal distance of the lens to be used must equal the diameter of the pinion 28 divided by the diameter of the feed-roll 15.

The first thing I noticed about that is that if you move the numbers around to solve for pinion diameter and simplify, you end up with exactly the equation that is in Jim Lipari's notes! "Constant"/focal length = teeth in gear (where "Constant" is derived from the teeth on the ring gear and the circumference of the takeup spool.) This is recognizing the fact that for a given gear pitch, the diameter of a gear is directly correlated with the number of teeth, so you can substitute "number of teeth" for all references to "gear diameter" and the equations still work. The second thing I realized is that this is just another way of describing my "aha!" concept. The ratio between the gears is the same as the ratio between the circle that is the image being taken (the 7539.82" circle I described in my earlier example of 100 foot focus) and the circle of resulting film (the 75.3982" strip of film from that example if the magnification factor is .01) Of course you can't just take the exact ratio between the gears; you have to take into account the circumference of the takeup spool to get the right number of turns. So my concept was talking about circumferences, while the patent talks about diameters, but diameters are just circumferences with all the Pi cancelled out.

So imagine a camera spinning exactly around the rear nodal point of its lens (the place the light rays last come together to a point before spreading out again), with a perfectly circular band of film fixed in place at the focus point behind the lens. For a lens that is magnifying by .01 (i.e. reducing the size of the image by a factor of 100), you are getting a focused, geometrically correct image of everything that is at a distance 100 times farther away from the nodal point than the film is. Of course that would require you shoot through the film, so you don't do it that way. You shoot a narrow slit of an image, and pass the film across the focal plane as the camera turns. In this scenario, the film would still be standing still in that smaller circle, you're just making sure the part of film that is in front of the lens is not in the way for wherever the lens is. But that would require all sorts of calculations and adjustments for every different scenario, to make sure that the camera was spinning precisely around that nodal point every time. The genius of the Cirkut is that they fake it! They move the correct amount of film past the slit AS IF the camera were in that perfectly set up scenario, without worrying so much that it is. The film plane of the camera traverses some unrelated size circle in space, about some kind of random pivot point, but the film moves across it at a rate equal to the ideal scenario. Yes, that creates some sort of error, but it's such a small one, and the camera, by moving a narrow slit smoothly across the film, is compensating for that error in a continuous, very analog fashion, so you never notice it. Stitched images (film or digital) require the pivot point to be precisely the nodal point, to get rid of jarring parallax errors at the seams. The Cirkut is effectively stitching together an infinite number of images, so the parallax error at any given seam is infinitely small, so can be ignored. Brilliant!

They even cover this in the patent:

Constructing the camera on these principles the necessity of the pivotal axis being at any given point with regard to the transverse axis of the lens or relative to the point where the film is exposed is obviated. It may be at any desired position relative to the optical center of the lens, either at, in front, in the rear, or at either side thereof, either in front or in the rear. This principle also allows the exposing-slot 18 to be placed at any convenient point in the partition 4. However, it is desirable that the pivotal axis should be placed as nearly as possible at a point so that when the camera is in operation it shall be evenly balanced, having due regard to compactness of form and other requirements, because the placing of the pivotal axis of the camera in front of the lens or in the rear of the point of exposure will be at a loss of compactness.

I translate that as "keep it compact, and don't let it make the tripod fall over" !

All of which brings me back to a point I made earlier: the "gears" program is unnecessarily complex. You don't need all that stuff. Just the number of teeth on the big gear, the diameter or circumference of the takeup spool, and the focal length of the lens. But oh, it's so much easier to say "focal length of the lens" than to actually know it! Because that number is absolutely critical and must be precise if you want to know the correct gear. Alternately, you can just use what is marked on the lens and keep trying gears until the results on film are correct! The way all this math works out, what is needed is the rear nodal point of the lens... NOT because we're trying to avoid parallax, like in stitching panoramic work, but just because that's the precise point all this math is calculated from.

Jim's notes talk about an "extension" that is added to the focal length of the lens. This is just to give you the actual "focal distance" as mentioned in the patent, which is the distance from the nodal point to the film plane for a given lens focused at a given distance.... because a lens' focal length is that distance at infinity focus, and that distance increases as you focus closer. His formulas for calculating it look to me like distilled down basic optical formulas (the "F squared over D minus 2F" part) but I don't know where the additional multiplier comes from (1.12 for 11-12" lenses, 1.16 for 13-14" lenses, and so on). I'll probably figure that out some day but for now I'll just take all those formulas as fact, since the man was apparently brilliant at this stuff!

But that still leaves knowing the *exact* focal length of a lens at infinity, defined as the distance from the rear nodal point to the focal plane. I can write a program to do all of Jim's math for you, and spit out gear numbers vs distances for any given lens without all the crazy measuring... but if you don't know the precise focal length of a specific copy of a lens, it doesn't help much. I know how that number is determined if one has thousands of dollars worth of optical equipment, but I don't know how it's done by you and I. Maybe it isn't. That's my next thing to track down...

Duncan

 

[frobozz]

Could the fact that the lenses used in their parts (not combined like the 10" length, with the glass behind the aperture, change the math and the nodal point somehow. Not really sure. I do know the cameras set up by the factory were all hand set to each individual lens group to correct for any lens variations.

I believe it's more a case of "the longer the focal length, the greater the error between marked and actual" (for whatever reason. Probably inherent in optics theory.) Also it's possible that "focal length" as marked on lenses is different from "distance from the rear nodal point" - is the marked focal length perhaps the average of the front and rear nodal points? I really know very little about optics. So the focal length markings on a lens intended for general camera use may not apply when what you need is the distance from the rear nodal point.

What is needed is a quick-and dirty method for precisely determining this (seems like someone would have come up with that if it were possible!), or an inexpensive fast-turnaround place we can all send our lenses to get them measured.

Duncan

 

[frobozz]

I was setting up to do some tests earlier, with a measured-off 100 feet to the object to be photographed. The scales on my camera had the indicator pretty much dead-on 50 for the 10-7/8" lens, and pretty much exactly in between 50 and 100 for the 18" and 24". Is that some indication that this lens is not original to the camera?

I decided to run it with both the 50' and 100' gears for each focal length to see which was closer to being right. With that and a couple of other screwups I ran out of the film I had on hand so I probably didn't get the 24" tests on film. I was using 220 and actually ran it off the spool, d'oh! Had to extract it and load it onto a Nikor 220 reel all in the same changing bag - good thing it's a big changing bag ;-) Results later after I develop it.

Duncan

 

[jamie young]

Technically the gears had a specific focus point for the number of teeth ( maybe 74.5 feet for a 26 tooth gear for example), and they couldn't make a gear specifically for the distance of 50 or 100 feet, so they placed the marks at the right focus point for the tooth number and called it 50 or 100 depending on which gears would work best for either mark. Kind of a best choice approximation. The cameras tended to be set at rounded off numbers, like 25, 50 and 100 feet, but the markings would be precise for the number of gear teeth on the gear. Again- do the film test before assuming the set up is wrong. call me if you want to discuss this at all. Jamie

 

[Len Robertson]

Duncan - I have sheets Mr. Lipari sent when he measured the nodal points and made gears for a couple of my lenses. They show the actual focal length as measured with a nodal slide. At least I believe he used a nodal slide to determine FL. I can scan and send to you if you think they might help you. I recall the second lens he did having much more precise figures than the first. Possibly he used the Gears program for the second lens and the math for the first was done the "old fashioned" way.

I recall asking someone (not Lipari) how accurately he measured the nodal point. I believe he said to 0.001 inch. I suspect this is because his setup allowed him to measure to this accuracy, maybe with a 24" vernier caliper, rather than needing this degree of accuracy.

Someone else said no matter how well the math was done, he still always ran short test runs on film to see if fine tuning were needed. Jamie or someone probably has more experience with this than I do, and can comment.

Len

 

[frobozz]

Technically the gears had a specific focus point for the number of teeth ( maybe 74.5 feet for a 26 tooth gear for example), and they couldn't make a gear specifically for the distance of 50 or 100 feet, so they placed the marks at the right focus point for the tooth number and called it 50 or 100 depending on which gears would work best for either mark. Kind of a best choice approximation. The cameras tended to be set at rounded off numbers, like 25, 50 and 100 feet, but the markings would be precise for the number of gear teeth on the gear. Again- do the film test before assuming the set up is wrong. call me if you want to discuss this at all. Jamie

Oh! I assumed the scales were at the precise distance positions, and were then marked with the nearest gear. You're saying it's the other way around. That seems much harder to pull off from a manufacturing testing and setup standpoint, but would definitely make some sense.

Well this has been quite the day - I managed to have a lot of classic Cirkut screwups, and then a bunch of normal ones too.

Before I even packed everything up to go shoot, I wound up my original camera to make sure it worked now that it's warmer. It wasn't winding right. It never built up much tension. I'm going to guess one end of the spring is broken, or off its nub. It kind of catches and starts to get wound, but before much tension builds up you can feel something slip inside. Well that's why I got the parts camera, right? I go to put the #2 back on the #1 camera (I can't just use the #2 camera because its tripod hole is stripped out... and besides, it has no focusing scales on it to check the accuracy of!) and it won't fit. They must put the 4 catches on these things camera by camera as a pair at each point, so they're only guaranteed to match on the camera they came on. A little bit of kludging later ( remove two screws from the offending latches, allowing them to pivot into a position that will work) I have a complete camera that winds and runs.

Set up where I plan to shoot (100' from a tennis court with a chain link fence that I can measure various horizontal and vertical features of and compare that ratio to the image on the negative) and I'm having trouble focusing on the ground glass at anywhere near the right places on the scales for the 10-7/8" lens. Oh yeah DUH forgot to pull the screen bellows out. Much better! Decide to run about a 90 degree sweep with each of the gears marked for 100' and 50'. Do that, then remove the back in preparation for focusing the lens in the 18" configuration...and I'm staring at an unfolded focusing screen. Argh! this back from the #2 camera doesn't have the wood block to prevent precisely that problem, and therefore I fell victim to it! Fold up the screen, reinstall the back, put the lens back to 10-7/8", run those two tests again. Sigh.

I rewound the film because at that point it was going to be out, and put in my second roll, the last one I had with me (I wasn't planning to shoot two gears for each lens!) Run the tests at 18", no further problems. Run the tests at 24", realize the camera pulls a LOT more film with longer lenses and at some point when I wasn't looking it ran off the end of the 220 spool and is all on the takeup spool. Then I notice I forgot to stop the lens down again after focusing the 24" lens. But hey, it doesn't matter, because that was after the film was gone anyway. And I have no more film with me.

I get home and successfully load the film off the takeup spool, onto a 220 stainless reel, all inside a changing bag. Go to set up stuff to develop the film, and drop the stainless tank from 2 feet above the ground. When it hits the ground, the main lid pops off. OHHHHNOOOOOOOOO!!! Quickly put it back on, but yeah right. As if that several seconds of light isn't going to have trashed the film. I've been developing film for over 40 years now and that's a first for me! I developed it anyway, and it's as horribly lightstruck as you can imagine. But there's possibly enough image remaining on it to do my measurements to check the gears. I'll scan it once it's dry tomorrow. I then developed the other roll of film (10-7/8" tests, including the exciting pictures of the back of the ground glass.) without incident.

Someday I'll get semi-competent at this. Cirkut is a humbling experience!

Duncan

 

[frobozz]

Duncan - I have sheets Mr. Lipari sent when he measured the nodal points and made gears for a couple of my lenses. They show the actual focal length as measured with a nodal slide. At least I believe he used a nodal slide to determine FL. I can scan and send to you if you think they might help you. I recall the second lens he did having much more precise figures than the first. Possibly he used the Gears program for the second lens and the math for the first was done the "old fashioned" way.

I recall asking someone (not Lipari) how accurately he measured the nodal point. I believe he said to 0.001 inch. I suspect this is because his setup allowed him to measure to this accuracy, maybe with a 24" vernier caliper, rather than needing this degree of accuracy.

Someone else said no matter how well the math was done, he still always ran short test runs on film to see if fine tuning were needed. Jamie or someone probably has more experience with this than I do, and can comment.

Len

Len - you know me, Im always happy for you to send me more documentation! I don't think a program whose output gets rounded to the nearest whole gear really needs input data to 3 decimal places. But if you have the data, might as well use it! And I agree, all the theory and calculation in the world won't be as accurate as an actual test on film, so that should always be the last step when trying to come up with gears for a newly acquired lens.

Duncan

 

[jamie young]

sounds like the spring had disengaged from the screw that holds it to the shaft. This has happened to me a few times. Probably and hopefully not broken. You can fix a spring that breaks around the hole for the screw if that is the case. If you have to remove from cylinder remember there is a lot of "spring" in that spring and it's edges are sharp enough to seriously hurt you if you are not careful and let it unwind in an uncontrolled manner At this point just get a good lens test to see if the camera is set right and figure out the details of setting up other lenses later. Each camera did get made for it's back, so if you are switching backs just check to make sure film plane is at the same distance as the back from the other camera. It's also worth checking that the ground glass focus plane still matches film plane, just to make sure. It will get easier.

 

[frobozz]

sounds like the spring had disengaged from the screw that holds it to the shaft. This has happened to me a few times. Probably and hopefully not broken. You can fix a spring that breaks around the hole for the screw if that is the case. If you have to remove from cylinder remember there is a lot of "spring" in that spring and it's edges are sharp enough to seriously hurt you if you are not careful and let it unwind in an uncontrolled manner At this point just get a good lens test to see if the camera is set right and figure out the details of setting up other lenses later. Each camera did get made for it's back, so if you are switching backs just check to make sure film plane is at the same distance as the back from the other camera. It's also worth checking that the ground glass focus plane still matches film plane, just to make sure. It will get easier.

Yes, when I get a chance I'll (ever so carefully!) pull apart that spring again and see what's going on. And I need to do the ground glass vs. film distance test no matter what configuration I end up with. I will probably end up with back #2 returned to camera #2 just because that camera is cosmetically vastly superior, the hidden buttons are still hidden and not falling out, etc. But that will mean fixing the tripod mount at the very least, which is why I'm doing these tests on the other body for the moment.

For the 18" at least, despite the light striking of the film, I can tell that the 43T gear, which is what the scale indicates for 100', provides pretty dead-on results shot at 100', even though the pointer was not showing 100' on the scale. With the 50' gear (42T), there is noticeable horizontal stretching of the details. So that's good so far. In a moment I'm going to go reshoot the 18" tests, and rerun the 24" tests but on film instead of air this time ;-)

Upon high magnification, I can see that I'm getting some intermittent slurring of details in a vertical band. Basically at fairly regular intervals the film is moving significantly more rapidly past the slit, but just for an instant. I'm going to guess this has something to do with my using 220 film - either the film isn't landing on the takeup spool evenly, or my little adapter is causing surging of the film somehow. I'm not going to get too worked up about that error unless I see it on real 10" (or 9.5" aerial) film.

Once I process the rerun tests, I'll post pictures of everything.

Duncan

 

[frobozz]

OK, some pictures, all shot at a measured 100' from the subject (a fence) and using the gears shown on the plates for the 100' distance and then the 50' distance, even though in all cases the pointer on the bed was about dead between the two measurements. I chose to shoot the fence because I could measure from top to bottom and pole to pole in real life and compare it to the pictures, but even easier it's pretty easy to tell when the square holes in the chain link aren't square. You can also see in each pair of pictures how the poles are more spread out in the 50' gear picture.

First the 10-7/8" lens:

Next is the 18" lens:

Last the 24" lens:

I'd say in all cases the 100' gear looks squarer, but it's also plausible that as Jamie said, I'd need to be dead on the mark for a gear to properly use that gear, so I'm actually a little narrow on the 100' gear and a little wide on the 50' gear.

Here's an example of that regular slurring pattern I was talking about, from the 24" lens test:

Now that I think about it, it can't be the film speeding up. What could make film go faster than the motor is pulling it? It must be the camera slowing down (while the film keeps transporting at a constant speed.) Gear backlash maybe? I was doing the "don't mesh them too hard" thing to prevent binding, but maybe they need to be meshed pretty tight. Or maybe this is where the "gentle helping hand" on the camera comes into play.

Duncan

 

[jamie young]

As far as gear meshing you DON"T want it pushed all the way together. My method is to make sure the camera is straight on the big gear first, then push all the way together while it's straight, then back off a hair. It really should be a small amount. Don't tighten the tripod screw (the screw that goes into the camera body from the large gear head) tight either. Keep it a little loose. The film rewind shaft that turns when the camera drum is moving film should be oiled lightly as well.

 

[frobozz]

As far as gear meshing you DON"T want it pushed all the way together. My method is to make sure the camera is straight on the big gear first, then push all the way together while it's straight, then back off a hair. It really should be a small amount. Don't tighten the tripod screw (the screw that goes into the camera body from the large gear head) tight either. Keep it a little loose. The film rewind shaft that turns when the camera drum is moving film should be oiled lightly as well.

OK, I was definitely doing the back it off a hair thing. The tripod screw has a collar that keeps it from going in far enough to pull the camera tight to the platform, are you saying don't even get it that tight? And aha, I had not oiled the rewind shaft at all. Trying it now it seems pretty smooth, but this camera hasn't been used in at least 20 years, so for sure that's something it probably needs. It occurs to me I forgot to put a drop of oil on the big gear center shaft too, though again that's pretty smoothly moving as it is.

Is the weirdness I'm seeing there just how "banding" manifests itself when you have something as finely detailed as a chain link fence? I considered banding to be an exposure variation, which would definitely be a matter of inconsistent speed of film past the slit, but this looks more like inconsistent speed of camera around the turntable. Though I'm not sure you can really separate those two issues, what with the whole thing being locked together by gears! (Which is why I thought maybe it was backlash.)

Oh, now is probably a good time to ask what the official definition of "camera straight on the big gear" is. There's a vertical groove in the edge of the top ring on which the camera sits, which I assume is to help lining things up. When the camera is square with the webbing of the head, that groove lines up with the hinge point of the ground glass, which also puts it at about the same place as the hole for the gear. Rather than, you know, dead center which is where I might expect it to be. Is that correct? Or does that groove line up with something else I haven't figured out yet?

Looking in the original instruction book to see if they mentioned that groove (they do not) I see that they say to only mesh the gears HALFWAY! "If the gears are meshed too closely the camera will vibrate and cause vertical and irregular lines in the picture." So maybe my move-back-a-hair was still way too close and thus causing the problem I'm seeing. That might be worth another test run today to find out. They also warn about tightening the tripod screw too tightly ("an unsteady movement will be caused, producing vertical lines in the negative.") so I guess I may have been overdoing that too.

Duncan

 

[paul_c5x4]

Gear backlash maybe? I was doing the "don't mesh them too hard" thing to prevent binding, but maybe they need to be meshed pretty tight.

Gears need a certain amount of clearance to operate correctly. How much depends on the pitch, number of teeth, and the quality of manufacture. When setting up a gear train, I often use a strip of ordinary printer paper between the gears to gauge the distance. For closer fits, a cigarette paper folded in two gives just the right clearance.

 

[frobozz]

Gears need a certain amount of clearance to operate correctly. How much depends on the pitch, number of teeth, and the quality of manufacture. When setting up a gear train, I often use a strip of ordinary printer paper between the gears to gauge the distance. For closer fits, a cigarette paper folded in two gives just the right clearance.

So just to make sure I understand: in this case you're saying to put a piece of printer paper between the gears, slide the camera into mesh (trapping/mangling the paper in between), then rotate the camera to free the paper, and that's now the correct mesh distance?

Duncan

 

[paul_c5x4]

Yup, that's pretty much it.

I'm assuming one or more gears are mounted on a movable post that is locked in to place ?

 

[frobozz]

One gear is screwed into the drivetrain in the bottom of the camera. That then meshes with the large fixed ring gear that forms the base of the tripod. The camera sits on a platform that can rotate above that base on little wheels.

Duncan

 

[frobozz]

The film rewind shaft that turns when the camera drum is moving film should be oiled lightly as well.

Took this apart on both cameras for cleaning and putting all the best parts on the back I was using and will continue to use. Lo and behold, that back was missing the little fiber washer inside the body housing, which means the spring end was just scraping along the metal there! You could see it had been this way for a while, a bunch of gouging was present on that surface. Put the fiber washer in there from the other camera, lubed it all up and it's a lot smoother now. I also see that an important feature of any spool in the camera is that it pushes up on the rewind shaft a bit, so the handle is not riding down on the surface of the body housing. I think the way I was using my 220 adapter that was the case, but another thing to make absolutely sure of at the time of shooting.

Duncan

 

[frobozz]

Just scanned in the film from my tests earlier today. Lubed all the mentioned points, cleaned/polished the living heck out of the ring gear surface and the wheels, gapped the gears pretty widely as the instructions say to, and... not a bit of difference! I ran one test just letting the camera run like I had before, then another one where I gave it the old gentle helping hand. No difference. Then I looked at the negative with my own eyes using high magnification, just to make sure this wasn't some scanner artifact. Nope, that problem is on the negative.

It's 100% possible the issue is with my 220 adapter. I could respool some 220 onto a 10" Cirkut spool to try to help rule that out I guess. (I have no way to easily develop 5" or 10" film right now, thus my sticking with 220 for tests, despite having tons of B&W aerial film to play with in the long run.)

Duncan