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.
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 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.
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'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'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.
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