Using sheet film in a Polaroid SX70 camera

[Dan Pavel]

Polaroid SX70 is, for me, an object of admiration and a camera that has always intrigued me.

I have never understood why other reputed camera manufacturer didn’t follow the idea of a folding MF/LF SLR. An SX70-like 6x9 folding SLR with a motorized roll film back and all the electronic advancements of a 35mm SLR could have been an absolute killer camera, pocketable and even smaller than the SX70. But now it is, unfortunately, too late.

However, I turned one of my 2 SX70s into accepting i-type film and now it has a new PCB with Bluetooth and manual shutter speeds and I wondered: could it be made to accept negative sheet film instead of Polaroid film? And would it worth it?

To make a long story shorter, after A LOT of tests and try and error I managed to 3D print some film inserts and the needed parts to turn the Polaroid film holders into 6.5X9 holders for sheet films and took some test photos to see if the lens is good enough for enlargements.

I think it could be of interest to share some of them.

If the light is good and your hand is steady the lens can deliver something like this:

And an 100% detail:

In normal conditions it delivers something like this:

The film is 4x5 Fomapan400 cut to fit, exposed as 650 ASA (i-type film sensitivity) and developed normally.

Both photos are quick scans with the camera, they are ~70% crops and they have been prepared in PS for test prints. I have actually printed the first one to a 30x40 cm. paper (my usual enlargement) to check the detail.

 

[koraks]

Wow, that's really nice!

Did you do the new PCB yourself, or is that something that's available on the market? I'm sure people would be interested to hear more details about this!

 

[Dan Pavel]

It is the one available on the market. But sorry, I wasn't clear, I didn't installed the new PCB myself. A specialized guy in UK did it for me. I only made the sheet film adaptation.

 

[Donald Qualls]

The SX-70 advertising made a big deal about using a front-focus Tessar lens when the cameras first came out. A well-made Tessar is a good lens indeed.

 

[Jimskelton]

This sounds like a great idea! In effect, does your design hold one sheet per cartridge with a dark slide? And if so, can you reinsert the dark slide so you can unload the cartridge in daylight?

I found if you cut down a piece of sheet film to size, then slot out the corner that engages with the eject mechanism, you can load it into an old SX-70 cartridge (along with a dark slide), but it has to be unloaded in the dark after taking the photo. I did this with paper negatives to shoot direct positives by applying an ND filter over the electric eye.

I think the SX-70 camera is genius--the way it folds down and its small size), but the shutter/aperture mechanism sacrificed functionality for size. You don't have control over the aperture unless you can control the light level (which you can sort of do with ND filters.) Any shutter speed below 1/160 will shoot wide open and because the fastest shutter speed is in the 1/200 or so range, any exposure above that will shoot at a smaller aperture. Not many people care (or know) about this limitation because the camera was meant to be truly "one step" photography. But if you want to shoot a night photo with a small aperture, you're out of luck.

Actually, there's an interesting 3D file that splits the focus lever from the shutter/aperture stop used with flash, but there isn't a board that exploits that, and there seems to be no interest in exploiting it. I think it would be a great idea. For true manual control, internally, the camera would activate the solenoid that couples the focus lever to the aperture, but because it's uncoupled with the split knob, you would be able to control it using the knob. This would make me much more interested in this camera.

 

[mshchem]

Very nice. I found a 25 year old box of Polaroid pack film type 679, I have stashed in my film fridge. I tried it today. ISO 100, made a pretty good print, no streaks, decent muted colors,. If given the choice between Polaroid films and Kodachrome. I would choose Polaroid. I have some incredible 40 year old prints I made with 679 and a Polaroid Bigshot portrait camera using Magicubes.

The original Timezero SX-70 film was amazing. The flashbar flashbulbs gave beautiful light.

 

[Dan Pavel]

This sounds like a great idea! In effect, does your design hold one sheet per cartridge with a dark slide? And if so, can you reinsert the dark slide so you can unload the cartridge in daylight?

Yes, it involves one sheet per cartridge with a dark slide and yes, the goal is to load/unload the cartridge in daylight. I already have have 5 cartridges modified to sheet film.
I will detail a little.
My cartridges look like this:

They involve two 3Dprinted parts, a pressure plate:

And a film insert:

.

The dark slide is cut from a 4x5 slide and a 3D printed handle is added.

Two problems had to be checked and solved: the film position (to ensure correct focus) and the light tightness.

1-The film position.
I did some tests and, unexpectedly, the film position seemed to be a little too close to the lens. After thinking a bit on it the reason seemed obvious - the thickness of the moving mirror adds to the path when taking a photo.

After testing from 0.05mm to 0.05mm (resin printer) the best configuration seamed to be by positioning the film bed with 0.6mm deeper than the upper surface of the film insert. It’s quite convenient…

2- The light tightness.
This one proves to be really difficult to solve. I tested the light tightness of the my film holder by loading it with a 400 ASA film and let it rest for 2 days in direct, very strong sun light. That was the result:

I consider it a good result because in normal use no light leak can be actually noticed. The holder is “almost” light tight.

But the big problem is that SX70 is not really light tight until the front door is closed and therefore the film could see some light when you take off the dark slide or when you put it on again. And yes, in ~50% of the cases it does. The only way to solve this is to take off/put on the dark slide with the SX70 front door closed and that involves modifying the front door of the camera. This would be a permanent change and that's what I am working at right now. My SX70 will become a 6x9 film camera and it will no longer accept polaroid film.

 

[Dan Pavel]

I think the SX-70 camera is genius--the way it folds down and its small size), but the shutter/aperture mechanism sacrificed functionality for size. You don't have control over the aperture unless you can control the light level (which you can sort of do with ND filters.) Any shutter speed below 1/160 will shoot wide open and because the fastest shutter speed is in the 1/200 or so range, any exposure above that will shoot at a smaller aperture. Not many people care (or know) about this limitation because the camera was meant to be truly "one step" photography. But if you want to shoot a night photo with a small aperture, you're out of luck.

Yes, the camera has these limitations. One should know what it can do and what it can't and use it accordingly. But in good light it is a joy to use compared to any old 6x9 folder or rangefinder I ever used (at least for me). It is light in weight and not much bigger than a folder, you have a large and luminous image for framing and focus (SLR) and the sheet film results are good enough for the enlargements I make. Not to mention the strait out of the camera close focus capabilities. It made me enjoy again using 6X9 sheet film on daily basis.

What you shouldn't expect from it:
- landscapes and generally pictures with large depth of field in dim light, even with a tripod;
- to use it hand-held in dim light;
- portraits and generally pictures with a creamy background in good, strong light. With ND filters this could be, hopefully, overcome.

"Actually, there's an interesting 3D file that splits the focus lever from the shutter/aperture stop used with flash"
Interesting! Could you, please, provide a shortcut to the file?

 

[Jimskelton]

Yes, this would be the smallest 6x9 out there! How did you decide to power it? Using old cartridges with good batteries or an add-on unit?

This is a great SX-70 hack, and it could be used for other film types such as b&w or colour paper which can be reversed into a positive, sort of like instant photography. If the shutter/aperture could be controlled by a shutter control mechanism which basically simulates the light level necessary for the desired shutter speed/aperture setting which is directed toward the photocell, you could get a level of manual control over the camera, sort of like this project:

I wonder whether you can 3D print an alternate film door that works with the cartridge and is light proof instead of destroying the original. It's easy to remove the old door...

I'm thinking if you didn't mind destroying the whole film handling mechanism, it would be possible to replace the bottom with a 120 6x9 roll film handling mechanism like this one I designed: https://www.thingiverse.com/thing:6426546 . It would have to be enclosed with a 3D printed replacement for the bottom of the camera. You could then get rid of the whole film handling mechanism including motor, gear train, etc. You would want to keep some of the wiring intact to keep the camera and mirror operational such as the door switch, and figure out how to tell the camera that film ejected...

And the split knob can be found here--it was experimental for the OpenSX-70 project but a feature that didn't get off the ground -- https://www.thingiverse.com/thing:4461397

 

[Dan Pavel]

Very interesting ideas and projects!

I think that the led control is a nice idea and it could, eventually, work but as long as speed and aperture controls are not split the level of control it could offer is like the one offered by the new PCBs available on the market.

I don't really understand how the split knob works, but if it could split the aperture/speed control of the camera it would be a huge feature.

Your 6X9 roll film adapter is really nice but I doubt that something similar could be done for SX70. I thought of something similar for SX70 but, in my opinion, the only 6 mm. available at the back of the cameras' film room are not sufficient for mounting a roller for the safe film return. The motor can't be removed to make space because it powers the mirror return mechanism. But probably a 6x7 roll film adapter could be made in a form similar with Adapt-a-Roll. I checked if my Adapt-a-Roll would fit in the film room of the camera and it almost does. If one removes, with a CNC, ~1-1.5mm from its' upper side it could fit in but, again, only a ~6x7 part of its' frame could be used and the film position will be too far from the lens for a proper focus. But I really like using sheet film more than roll film. The perfect film flatness, the ability to only shoot few frames, possibly over/under expose each as desired and have them proper developed separately better fits my habits. That's why I gave up the adapting a roll film project.

I have two SX70s and keeping one for Polaroid film and permanently modifying the other for sheet film is convenient for me. However, a 3Dprinted front door might be possible but it involves metal parts I can't make. Even a more elaborated film cartridge, entirely new designed, could be light tight with the front door removed and without modifying the camera. But it can't be 3D printed - at the small thickness needed for the upper side of the cartridge the black resin is not entirely opaque. A combination of 3D printed parts and a laser cut thin steel sheet is something I am considering for a new project.

How did you decide to power it? Using old cartridges with good batteries or an add-on unit?

I have one of my two cameras modified for i-type film and with a new PCB with Bluetooth capabilities that allow for manual exposure settings. It is now powered by 2 external batteries. That's the one I am using with sheet film.

 

[Jimskelton]

About the split knob: The existing focus knob has a gear and a cam. The gear focuses the lens, and the cam controls the aperture when the solenoid engages it (when the flash is plugged in). The cam is connected to a lever which stops the shutter from opening fully during exposure. When focused close, the shutter only opens a bit, closing down the aperture of the lens. When focusing on a subject further away, the cam positions the lever stop so the shutter can open up further. By decoupling the 2 functions, you can focus the lens closer without closing down the lens. The aperture half of the knob has a tab which you can move to control the aperture.

To implement this, you would need to activate the solenoid that normally gets powered when the flash is plugged in. There's probably a way to get this to turn on with a switch, or electronically via a PCB.

What are your plans with your design?

 

[Dan Pavel]

Nice idea! Have you tested it?

What are your plans with your design?

To finish making it completely light-tight by modifying the front door and, if I can find a laser-cut facility available nearby to make the 3D printed film holders completely light-tight with the front door removed and without any modification of the camera.