70mm Bulk Questions
I have pretty much figured out all there is to know about unperforated 70mm, but I'm having a hard time figuring out the procedures with perforated film with Mamiya RB backs.
First off, what is the perf used for? Am I correct in that it is only used for spacing purposes and that it only needs perforations across the top half of the film for this purpose?
I know they don't sell perforated film in cassettes anymore, you have to roll your own, but I noticed that a cassette I got was loaded by Kodak, and it had words hole-punched into it with the film type, emulsion number and code. This got me thinking, how many frames on the front, or inches if you prefer, of film are going to get fogged or wound past the film gate in actually threading the back? Are any frames wasted on the end? What's a safe leader and footer length as far as the lab is concerned?
I don't want to file perf rollers off the top fo the film because I would like to have the images aligned evenly on the film, but is there anyway to reversably convert the back to taking unperfed film without any consequences like scratches, kinking, etc.?
How much film can I jam into the RB back safely with a cassette? Is it possible to fit more in without a cassette?
I'd like to get 15 feet in a cassette in the back, but I can't afford scratches or jams in the line of work I do.
How many sprocket holes wide is a frame of 6x7? Is it 15 or something smaller?
Last edited by FilmIs4Ever; 05-19-2008 at 10:52 AM. Click to view previous post history.
Reason: More Questions
A can is 15 feet. Plus leader I guess. I forget.
Somebody was selling a kit to upgrade blad backs to take non perf film. I forget if RB backs had different issues.
Hey Nick, thanks for the quick reply. Do you know the actual size of a frame on a 70mm back, or the number of frames? I know it's not exactly 7 cm, more like 6.8 cm, but there's also the space between frames to consider. I was thinking maybe it was more like 2 3/4 in. (right around 7 cm) per frame including spacing, but some of the frame estimates I've seem seem to indicate 2 7/8 in. or even almost 3 in. per frame.
Are the sprocket holes at the same intervals with 70mm bulk as they are with 35mm still? If that's the case, I know that 8 perforations measured evenly between the "zeroth" & first perforation and between the eighth and ninth perforations is exactly 1 1/2 inches. So if that'd make 16 perfs. exactly 3 in. Of course, I don't know how many perfs. a frame is. . .
No idea on Mamiya.
Don't the Kodak data sheets mention the type of holes? I thought the types had some sort of standard. B&H[ I think] being one spacing.
I've sucessfully shot a lot of perf'd 70mm in my 70mm Hassy Back. I have a Hassy bulk loader (never tried for more than 15 feet in a cassette).
Originally Posted by FilmIs4Ever
I Don't have any 70mm Mamiya backs - so don't know about them.
Everything is analog - even digital :D
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Hey Tom. Well, obviously the backs are going to work with perforated 70mm, as that is what they were designed to use. Have you ever used unperforated film successfully? I know it isn't optimal; I just have 1 100-foot roll of 70mm to use for testing, so I just need to make sure the back doesn't have any light leaks and advances film properly.
I've been crunching the math, and I THINK that 6cm square uses 12 perforations (or 11 1/2 if you want to be nit-picky) per frame. Is that correct?
By that line of thinning then, it'd mean that you'd have 14 perforations per frame for 6x7, including space between exposures. At 1 1/2" per 8 perforations (making another assumption that 35mm perf.'s have the same spacings as do 70mm ones), or 3/16" per perforation, that'd mean it's actually about 2 5/8" per 6x7cm frame with space. I'd need to fit 15' 3 3/4" of unfoggable 70mm into a cassette, so probably 15 1/2' of film total to get 70 exposures of 6x7cm per roll.
Can anyone check my math for me?
Isn't 70 exposures high for 6x7? I'm having trouble remembering but I thought 6x7 was closer to 50.
I'm just doing the math based on the number of perforations per frame. If you could tell me how many perf.'s for certain on a 66 or 67 frame, I could figure out for certain.
6x7 is going to be either 14 or 15 perf.'s 14 perf.'s is 2 5/8" and 15 is 2 13/16"
Maybe there's just a lot of film on the beginning and end of a spool that is wasted as leader?
I checked the math and it's only a couple of inches over 15 feet to fit 70 exposures of 14 perforation film into a cassette.
Don't mean to hijack the thread but can I ask if and where 70mm film is available (for Hass. 70mm back). I have not been able to track any down here in the UK.
Regards - Allan.
I'm into painting with light - NOT painting by numbers!
Allan, no problem. You can get Portra 160 and 400, and also Plus-Xin the UK. No idea who from. Call Kodak Ltd. and ask! IDK which you can get perfed, maybe only Portra 400 and Plus-X. For some reason they sell only Tri-X over here in 70 and only Plus-X over there in 70.
There are rather large minimums involved, so you may want to get in touch with an aerial mapping company; many of them use 70mm, although a lot use larger film sizes.
Can you please tell me how many sprockets per frame of 6x6? I can only guess as I've never shot any perforated 70mm.