Cirkut #10 large-gear film-usage measuring tape thingy

[frobozz]

The label that goes around my large gear is a bit of a shambles. I'm going to assume those haven't been available new anywhere for, oh, about 70 years. Anyone already do a repro, or at least a file which could be printed to make up a usable one? If not, I'll gladly do it, as there seems to be enough of mine left to dope it out... I just didn't want to duplicate efforts if someone else has already done it. I may need some help with the exact text down near the 0 feet end, as that's the most torn-up part of mine.

Thanks,
Duncan

 

[jamie young]

No they aren't available anywhere . I've never really looked at mine and don't use them when shooting.

 

[Mark Crabtree]

Someone made some years ago, probably Jim Lipari. I mostly use the start and 180 degree mark to get my pictures the length I want. I think the rough guide would be handy especially at first, and since you seem to have interest in a wide variety of shots. I can't recall how accurate these were, but seem to remember they weren't really. I'd be inclined to make one based on film pull for specific commonly used gears.

 

[frobozz]

OK well I'll set up the basic structure of the thing with all the critical measurements laid out in a graphics file, and then it can be finished with the numbers appropriate for any gearing, as needed. The original literally looks to be the same technology as a flexible measuring tape, but I figure printing it in sections on paper, which can be precisely overlapped onto lamination film or something, would allow a pretty quick and easy reproduction, if it's of use to anyone.

Duncan

 

[jamie young]

Duncan Not sure what kind of printer you have but most epson printers would let you do longer prints so you can print it on one sheet. It would be wise to laminate though as the inks are water soluble

 

[frobozz]

So, who can complete this sentence:

"The three lower rows of figures indicate in inches the length of film exposed by revolving the camera the number of degrees as indicated on upper row according to..."

Duncan

 

[frobozz]

Someone made some years ago, probably Jim Lipari. I mostly use the start and 180 degree mark to get my pictures the length I want. I think the rough guide would be handy especially at first, and since you seem to have interest in a wide variety of shots. I can't recall how accurate these were, but seem to remember they weren't really. I'd be inclined to make one based on film pull for specific commonly used gears.

It's interesting that the gearing (i.e. focus distance) isn't mentioned anywhere on the scale. So already it's a guesstimate, so the fact that they calibrate it down to half inches is silly. Admittedly, the gears are all pretty close for a given lens, but I wonder which one they used to calculate these precise numbers for the tape?

Just playing with the numbers on this tape, it jumps out at me that at 60 degrees, the inches of film used is basically "focal length plus about an inch". So a 120 degree shot is going to take a little over 2 times the focal length inches of film, while a 180 degree shot is going to take a little over 3 times the focal length inches of film (those seem like the most common picture arcs I see.) I think that's a pretty handy way to think of it, rather than associating it with gear numbers, since it's a good assumption you've already worked out the right gear number for your focal length. I'm sure that rule of thumb falls apart with a 3" lens focused at 3 feet or whatever, but it looks good for the more common scenarios.

I suddenly got less interested in reproing this tape! I see why nobody uses it. But I'd still like to know what the missing words say ;-)

Duncan

 

[Mark Crabtree]

The rotating tape seems essential to me for noting the starting and stopping points. You check through the ground glass, then position the starting mark; rotate the camera and check the place you want to stop. It is all to easy to misjudge just eyeballing the camera with back on, especially the start. Of course you want to start early to allow the motor to get up to speed, and even more for some processing methods that don't give a clean end on the films.

The numbers can be handy to, but I seem to recall they are based on the actual focal lengths indicated, which are not at all the focal lengths of the converted Turner Reich. I didn't say that before because I need to check a lot of these details to clarify my memory, but just haven't had a chance.

I was writing more, but it is getting kind of long so I'll split that to a separate post.

 

[Mark Crabtree]

Do you have the simple formula for calculating gears? I can post it later; I also probably know that from memory, but do want to check myself on that one. The gear calculation program is more accurate, and especially at closer distances where the failures of the camera design to match a swing lens type geometry are more extreme (why the 24" gear skips some gear teeth at 25 feet). But the simple formula is handy for roughing things out.

I also have a modified version of the gear program that does the same basic calculations, but outputs the information in a form that seems more useful to me. It is still clunky, but really seems to deliver the goods. I have a friend who is a long time Cirkut shooter, and actually visited the last vestiges of the Cirkut department as it was winding down. He measures focal lengths and makes gears, but does not do computers. I ran some calculations for him based on focal lengths he measured for some of his lenses and he was amazed at how accurate they were when tested on film. For all these years he has been used to needing to fine tune the calculations based on film tests.

Bob Lang (Robert J. Lang) is the person who wrote that program and deserves a lot of credit. I believe his name will show up if you print the code from the program. My non-technical take on this is that Bob wrote a mathematical model of Cirkut Camera operation, then wrote a BASIC computer program that uses that model. A math professor friend of mine felt there was a slight error in the formula; Bob does not agree. The math is way over my head, so I don't have an opinion, but the program I use has been modified over the years and I can't document the changes.

I feel I should also speak up for Ron Klein here again since he was such a strong proponent of Cirkuts on APUG early on. Ron has a problem with the program since it uses slit width in the calculation. Jamie may also have spoken to Ron about this and have some thoughts about it. My feeling is that Bob Lang put every variable for a Cirkut type camera into his model and that the things we think of in calculating film pull, gear, etc (like takeup drum size and large gear diameter) have a big impact on the result and that other things have very minimal impact but are simply part of a complete model of the working of the camera. This can seem unnecessary to #10 shooters (most of the Cirkut professionals), but means the program can work accurately for any Cirkut Camera or Outfit.

Anyway, I've been happy with the results from the gear program. Variations in different people's lens focal length measurements seem to contribute way more to any slight errors (no two measurements ever seem to agree). I think Robert Lang's work was a major contribution.

 

[Mark Crabtree]

So, who can complete this sentence:

"The three lower rows of figures indicate in inches the length of film exposed by revolving the camera the number of degrees as indicated on upper row according to..."

Duncan

"The three lower rows of figures indicate in inches the length of film exposed by revolving the camera the number of degrees as indicated on upper row according to..."

"...according to the focus used." Focus meaning focal length (as on the scale).

 

[frobozz]

The rotating tape seems essential to me for noting the starting and stopping points. You check through the ground glass, then position the starting mark; rotate the camera and check the place you want to stop. It is all to easy to misjudge just eyeballing the camera with back on, especially the start. Of course you want to start early to allow the motor to get up to speed, and even more for some processing methods that don't give a clean end on the films.

The numbers can be handy to, but I seem to recall they are based on the actual focal lengths indicated, which are not at all the focal lengths of the converted Turner Reich. I didn't say that before because I need to check a lot of these details to clarify my memory, but just haven't had a chance.

I was writing more, but it is getting kind of long so I'll split that to a separate post.

Yes, I'll definitely want some way to know where I'm starting and stopping, it just seems like with such an easy rule of thumb to remember for inches of film pulled, I maybe don't need to bother with reproducing all the markings. Something that marked off every 10 or 60 degrees, say, and could slide around to match the camera once set up.

Are you saying that the T-R does not actually have, in the real world, the stated focal lengths? Because the tape matches the stated focal lengths of my T-R (well, it admits that "10" is really "10-7/8")

Duncan

 

[frobozz]

Do you have the simple formula for calculating gears? I can post it later; I also probably know that from memory, but do want to check myself on that one. The gear calculation program is more accurate, and especially at closer distances where the failures of the camera design to match a swing lens type geometry are more extreme (why the 24" gear skips some gear teeth at 25 feet). But the simple formula is handy for roughing things out.

I also have a modified version of the gear program that does the same basic calculations, but outputs the information in a form that seems more useful to me. It is still clunky, but really seems to deliver the goods. I have a friend who is a long time Cirkut shooter, and actually visited the last vestiges of the Cirkut department as it was winding down. He measures focal lengths and makes gears, but does not do computers. I ran some calculations for him based on focal lengths he measured for some of his lenses and he was amazed at how accurate they were when tested on film. For all these years he has been used to needing to fine tune the calculations based on film tests.

Bob Lang (Robert J. Lang) is the person who wrote that program and deserves a lot of credit. I believe his name will show up if you print the code from the program. My non-technical take on this is that Bob wrote a mathematical model of Cirkut Camera operation, then wrote a BASIC computer program that uses that model. A math professor friend of mine felt there was a slight error in the formula; Bob does not agree. The math is way over my head, so I don't have an opinion, but the program I use has been modified over the years and I can't document the changes.

I feel I should also speak up for Ron Klein here again since he was such a strong proponent of Cirkuts on APUG early on. Ron has a problem with the program since it uses slit width in the calculation. Jamie may also have spoken to Ron about this and have some thoughts about it. My feeling is that Bob Lang put every variable for a Cirkut type camera into his model and that the things we think of in calculating film pull, gear, etc (like takeup drum size and large gear diameter) have a big impact on the result and that other things have very minimal impact but are simply part of a complete model of the working of the camera. This can seem unnecessary to #10 shooters (most of the Cirkut professionals), but means the program can work accurately for any Cirkut Camera or Outfit.

Anyway, I've been happy with the results from the gear program. Variations in different people's lens focal length measurements seem to contribute way more to any slight errors (no two measurements ever seem to agree). I think Robert Lang's work was a major contribution.

I have the gears.exe program, but not the actual formula behind the scenes. I may try to dope some of that out again myself, just to make sure I understand it thoroughly.

To my mind, the only thing slit width alters is exposure, but then I am certainly no expert. It needs to be wide enough to give exposures that can be used with real world lighting and film speed conditions, but it shouldn't be so wide as to allow any lens distortions to affect the image. But I can't really understand how it would affect gear selection?

Thanks for completing that sentence, that was bugging me! Only someone with 36 inches of room to write would compose a sentence that clunky and wordy though, or maybe that was just how they talked in the early 1900's ;-)

Duncan

 

[jamie young]

I'm honestly not sure how slit width affects the gear selection. I have used the gear program and it's a good start but testing is usually necessary to fine tune. Slit width obviously affects exposure. As far as the image goes, the narrower the slit width the sharper the image, but it also makes for more noticeable banding with anything but a very smooth mechanism. Some of the early fan #10 and#16 cameras had an adjustable slit width, but it was gotten rid of later and the stock width works just fine.

 

[Mark Crabtree]

I'm honestly not sure how slit width affects the gear selection. I have used the gear program and it's a good start but testing is usually necessary to fine tune. Slit width obviously affects exposure. As far as the image goes, the narrower the slit width the sharper the image, but it also makes for more noticeable banding with anything but a very smooth mechanism. Some of the early fan #10 and#16 cameras had an adjustable slit width, but it was gotten rid of later and the stock width works just fine.

I didn't mean to start a debate about slit width; just felt the need to mention Ron's objection to this program. As Jamie says, it is something almost all Cirkut shooters can ignore.

The Cirkut gear program works great for me, but as I mentioned, the one I run has been modified a bit over the years. The simple formula for a #10 would work out to something like 17,670 divided by effective focal length of the lens equals the number of teeth for the small gear. This gives good results at long distances; the program also solves for the problem of the Cirkut not pivoting on the nodal point of the lens, so yields accurate results at close distances. Plus the program calculates distances at the same time.

BTW, drum diameter does vary a little and I don't recall the exact number used here, but it is fairly easy to figure all this out. Plus drum diameter increases as the film rolls on, so you want to figure based on having about half a shot on the drum. It ends up not being very fussy in real life.

 

[frobozz]

I'm honestly not sure how slit width affects the gear selection. I have used the gear program and it's a good start but testing is usually necessary to fine tune. Slit width obviously affects exposure. As far as the image goes, the narrower the slit width the sharper the image, but it also makes for more noticeable banding with anything but a very smooth mechanism. Some of the early fan #10 and#16 cameras had an adjustable slit width, but it was gotten rid of later and the stock width works just fine.

It seems to me that with a lens with zero distortion across the portion of the image circle that shines on the slit will not be less sharp for having a wider slit. So slit width should only affect sharpness if you have a distorting lens. Meaning, Fisheye: bad, Process lens: good? I can see where an adjustable slit would just tend to get photographers in trouble (one more thing to set wrong, worse results with poor lens choice, etc.) so fixing in one good overall usable width it was probably a good idea.

Duncan

 

[frobozz]

I didn't mean to start a debate about slit width; just felt the need to mention Ron's objection to this program. As Jamie says, it is something almost all Cirkut shooters can ignore.

The Cirkut gear program works great for me, but as I mentioned, the one I run has been modified a bit over the years. The simple formula for a #10 would work out to something like 17,670 divided by effective focal length of the lens equals the number of teeth for the small gear. This gives good results at long distances; the program also solves for the problem of the Cirkut not pivoting on the nodal point of the lens, so yields accurate results at close distances. Plus the program calculates distances at the same time.

BTW, drum diameter does vary a little and I don't recall the exact number used here, but it is fairly easy to figure all this out. Plus drum diameter increases as the film rolls on, so you want to figure based on having about half a shot on the drum. It ends up not being very fussy in real life.

Thanks for the simple formula.

I need to think more about all this. I've found the couple of threads on here discussing the theory. Upon further reflection I can't rule out slit width affecting gear choice! If the film didn't move, the slit width would purely affect exposure, but the film does move, so maybe it matters to the movement too.

Duncan

 

[Mark Crabtree]

Not really an issue.

 

[frobozz]

Oh, thinking about the theory doesn't take a moment away from getting the thing running. I can do both ;-) And yes, I would also like to archive some of this knowledge while it's still out there.

But first I'd like to go back to 192x and smack the guy who screwed my lens holder tilt plate down in totally the wrong position...

Duncan