70mm Bulk Questions

[FilmIs4Ever]

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?


Thanks.

 

[Nick Zentena]

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.

 

[FilmIs4Ever]

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. . .

 

[Nick Zentena]

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.

 

[Tom Hoskinson]

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?


Thanks.

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).

I Don't have any 70mm Mamiya backs - so don't know about them.

 

[FilmIs4Ever]

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?

 

[Nick Zentena]

Isn't 70 exposures high for 6x7? I'm having trouble remembering but I thought 6x7 was closer to 50.

 

[FilmIs4Ever]

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.

 

[Allan Swindles]

70mm Film

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.

 

[FilmIs4Ever]

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.

 

[Allan Swindles]

No, sorry, can't help. My interest was aroused by the sheer mention of 70mm.
Having just got my EL/M back into commission, I found 70mm backs available at silly prices compared with A12's, but my subsequent search for film proved negative and so I abandoned my intended project. Ideally, I would like colour reversal film, perhaps I will have to be content with regular magazine changes.

 

[Kino]

Should be the same as Imax Film images;

"65/70mm film has about 64 perfs per foot, same as 35mm.

So 15 perf frames come at 4.267 per foot.

Strictly speaking, the perf pitch (like 35mm) is 0.1870 inches, so there are 64.17 perfs in a foot, and therefore 4.278 frames per foot."

See here: http://www.cinematography.net/IMAX15perf_70mmTechSpecs.htm

Warning! Some digt@l content!

 

[FilmIs4Ever]

Just a follow-up to those who are interested:

I finally got my hands on a Mamiya RB Pro-S handbook, and they list the holder as capable of taking 55 frames of 70mm full-frame (~13 feet/3.9m). However, the counter goes up to 65 frames, which leads me to believe that it is capable of taking 65 frames with a 16-foot/4.86m load, leaving maybe 3 frames worth of leader.

So this is cramming an extra foot into the cassette over what people normally say they can fit in at the max, but since it is just leader, it is lost anyway, and can, as such be threaded into the other cassette. I'll need to test to make sure the final three frames will fit into the take-up cassette, especially without scratching, but this is much better than 50 some have said was the maximum amount of film exposures, although it isn't the 70 exposures I'd hoped for, which would have required 17 feet/5.2m of film, and another five increments on the film counter, although I guess it'd still be doable if I loaded the 70mm film in the mag without protective cassettes, which requires me to have at least a half-dozen 70mm cassettes at my disposal, since it'd be impractical to change one in a dark bag every 70 shots.

Anyway, 65 shots allows me to shoot 3 1/4 times as much film without reloading, almost as much as shooting in RAW+JPG Basic on some DSLRs with a 1 gig memory card. Cool!