Reinventing the Bolex wheel

Andrew Saleen · September 23, 2007

I picked up an old H16 REX-1 body and serviced it back to working order. As it came with no lenses I resolved to use with my SLR lenses and a C-mount adapter, despite the focal length gain.

Reading up on the classic REX prism issue I was toying with the idea of replacing the front viewfinder optics and variable shutter with a mirrored shutter and omitting the glass between the lens and the gate.

I know this is probably some sort of travesty to be modifying a REX when I might as well be starting with a non-REX, but granted I am successful in constructing the new optics, would the removal of the prism be a significant quality gain?

Should I try to reinvent the wheel, or just be content stopping down?

Nick Mulder · September 23, 2007

"despite the focal length gain" ?? I just want to make clear that you understand that a lenses focal length is set and doesn't 'get longer' - the change is in the angle of view which is set by the format size in relation to the focal length... The terminology gets people in a twist ;)

Putting a mirror shutter in a bolex huh - an RX1 at that ... Sheesh, you're a glutton for punishment - first off who is going to do this work ? If its anyone but you you're in for a shock at the costs, its basically a design and build almost from scratch, think thousands at least... If its you, and its for some sort of educational experience then go for gold, I'd love to see it, I wont be holding my breath however.

Have you got a complete workshop ? mill, lathe, measuring tools might come in handy etc... An extra challenge might be to make it from first principles... start with a bucket of sand and a coconut husk

Depending, or should I say regardless of how you perceive money vs. time I'd hazard a guess that a complete set of the Switar Preset primes collimated for RX would be cheaper than the modification so to answer your question no the removal of the prism wouldn't be a significant quality gain.

But fun nevertheless ... I say do it! (or just stop down)

Patrick Neary · September 24, 2007

Hi-

The big problem with replacing the bolex shutter with a mirrored one is that the image would be reflected straight back out the lens. Not very useful. :)

kevin jackman · September 24, 2007

firstly, i know somebody that could do it and it wouldnt cost thousands.

i also wouldnt du the mirrored shutter. a pellicle system would do it. i even know where to get good ones. its really an interesting idea actually. it would give those old cameras some use.

Nick Mulder · September 24, 2007

firstly, i know somebody that could do it and it wouldnt cost thousands.

i also wouldnt du the mirrored shutter. a pellicle system would do it. i even know where to get good ones. its really an interesting idea actually. it would give those old cameras some use.

time:money - choose your point on the graph.

It would take an inordinate amount of fiddling time to get the finder showing an accurate image. The mirror would be heavy, (who will supply that to you in the right shape ?) thus potentially requiring a butterfly shutter (or counterweight), the butterfly shutter would require the gearing ratio to be halved - with either system who is going to extend the shaft and cut new gears on the new angle ? - much much machining - probably faster to make a totally new front end rather then modify the current one - measurements, measurements, measurements ... (then light leaks...) - thats just some quick concerns that could maybe be worked around... any ideas ?

Mind you thats referring to the original suggestion - I dont know how pellicle systems work and a (very)short search in google has left me none the wiser ... Do you have any links or info of this system ? I'd be keen to find out more ...

I will ask though, isn't everyone forgetting that these old cameras can already be used today with the prism and adjustable shutter that is in there already ?

Charlie Peich · September 25, 2007

time:money - choose your point on the graph.

It would take an inordinate amount of fiddling time to get the finder showing an accurate image. The mirror would be heavy, (who will supply that to you in the right shape ?) thus potentially requiring a butterfly shutter (or counterweight), the butterfly shutter would require the gearing ratio to be halved - with either system who is going to extend the shaft and cut new gears on the new angle ? - much much machining -

He could always pick up a used Arri 16SR and take the mirror shutter parts out of that camera. Those mirrors are perfectly balanced. :rolleyes:

kevin jackman · September 25, 2007

a pelicle viewing system uses a partially silvered peice of thin glass. will it work? i dont know, havent thought much about it. one issue is youd lose the extra back focus distance the prism gives you. and hey why not experiment. people do mods on cars. this is a similar thing.and isnt filmmaking based on ingenuity?

Charlie Peich · September 25, 2007

a pelicle viewing system uses a partially silvered peice of thin glass. will it work? i dont know, havent thought much about it. one issue is youd lose the extra back focus distance the prism gives you. and hey why not experiment. people do mods on cars. this is a similar thing.and isnt filmmaking based on ingenuity?

Kevin,

The pellicle mirror is what the Pathe' 16mm reflex camera uses. Pathe' on eBay It's also used in the Mitchell BNC reflex conversions and in some of the Fries 35mm reflex conversions.

The Pathe' 16mm camera takes regular C-mount lenses, no "RX" type lenses. I seem to recall loosing 1/3 stop with the Pathe' camera. It's fragile.

Nick Mulder · September 25, 2007

He could always pick up a used Arri 16SR and take the mirror shutter parts out of that camera. Those mirrors are perfectly balanced. :rolleyes:

hmmm - actually the bolex has a pull down which takes up more than 180deg per frame - youd have to sticky tape some cinefoil onto your SR shutter

... buuuut then you could modify the SR to have an adjustable shutter !

you'd be head cheese of the AV club at school if you brought that in for show and tell

pellicles - i wonder why they didn't use them to begin with ... something about the light reaching the glass at different points in its travel as the pellicle angles up causing unwanted image yuck ? - the prism instead has a constant 'position' with regards to the light from top to bottom of frame - yes, no ? I'd like to see a camera that uses one up close

Sam Wells · September 26, 2007

The Kenworthy Snorkel system "Type A" which I worked with a lot had a pellicule mirror for the video tap

(I" Vidicon camera) -- I pulled focus via the tap on B&W monitors many times -- video camera gained up a bit :)

also of course checked focus at critical points on the Mitchell gg w/ a test chart if in doubt after a take...

It didn't seem to do the film image any harm - although I never tested with/without for comparison. I would suppose Paul K had done so, tho...

-Sam

Charlie Peich · September 26, 2007

The Kenworthy Snorkel system "Type A" which I worked with a lot had a pellicule mirror for the video tap
(I" Vidicon camera) -- I pulled focus via the tap on B&W monitors many times -- video camera gained up a bit :)

also of course checked focus at critical points on the Mitchell gg w/ a test chart if in doubt after a take...

It didn't seem to do the film image any harm - although I never tested with/without for comparison. I would suppose Paul K had done so, tho...

-Sam

Sam,

What ever happended to the "Type A" system? I worked with it in the late 80's with Paul.

Charlie

Sam Wells · September 26, 2007

Sam,
What ever happended to the "Type A" system? I worked with it in the late 80's with Paul.

Charlie

Long story short re the rig we had at Allscope - Paul came to Princeton; took the optics (he said he could rent it to Disney) gave me the rail & carriage system & controllers (later being good props for a 50's sci fi movie ! IOW Nettmann CamRemote controller was a **BIT** more advanced....) so I had everything but the Snorkel tube ---- the rail and carriage rig was way cool but I couldn't find a place to set it up - I even tried to foist it off on Garrett Brown and Jurgen Jurgens in the Skyworks era.

I gave it to a DP friend of mine who had it working as some kind of video tabletop rig in a studio in Pallisades Park NJ -- but I've lost touch and have no idea.

There were Type A systems in Tokyo & I think UK altho the latter wasn't operating at this time - 1986.

I have no idea what became of them or what you used in LA.

PM if you want to. Takes me back :)

Sam

Jean-Louis Seguin · September 26, 2007

I picked up an old H16 REX-1 body and serviced it back to working order. As it came with no lenses I resolved to use with my SLR lenses and a C-mount adapter, despite the focal length gain.

Reading up on the classic REX prism issue I was toying with the idea of replacing the front viewfinder optics and variable shutter with a mirrored shutter and omitting the glass between the lens and the gate.

I know this is probably some sort of travesty to be modifying a REX when I might as well be starting with a non-REX, but granted I am successful in constructing the new optics, would the removal of the prism be a significant quality gain?

Should I try to reinvent the wheel, or just be content stopping down?

JK Camera used to sell a rack-over reflex front for the Bolex that did just what you're talking about. Of course, you could only see through the viewfinder when the camera was stopped and the mirror racked-over.

Jean-Louis