Polaroid manual lens onto Polaroid packfilm camera... questions!

[namke]

I have a Polaroid Automatic 100 packfilm camera which has the (well documented) under-exposure-in-low-light problem. Because of that, I bought a 355 which is much better and I now use as my regular Polaroid camera.

So, I have an Automatic 100 which is spare. I also have a CU-5 camera outfit with a pair of lenses (the 3" and 5" - 75mm/f4.5 and 127mm/f4.7 respectively). What better project than to couple the camera body with one of these manual lenses and get a flexible - controllable - Polaroid camera?

I would like to use the 75mm lens for this project (since I'm a sucker for wide-angle shots), but from asking around (and searching) I get the impression that the 75mm lens is just not suitable... something about not being able to focus at infinity or something? (I have some ideas about modifying the locking position of the folding struts so that I can get down to the 75mm focal length BTW)

To add to the confusion, there seem to be different '75mm Tominon' lenses out there; the CU-5 version and the MP3/MP4 version. Does anyone know whether there is a real difference??

Seeing as the mount for the two lenses (75 & 127) is the same, I am tempted just to give the 75mm a go and see what happens - then switch to the 127mm lens if it really is unworkable.

Are the specs for these various lenses available online anywhere? I have done some searching but keep coming up against the impression that the CU-5 & MP4 lenses are 'different' in some way.

So many questions!

 

[Steve Smith]

It doesn't answer your actual question but I did this to mine:




Steve.

 

[namke]

That's the sort of thing What focal length lens did you use - something closer to the 'stock' 114mm??

There's a good page here about this kind of mod (showing a Polaroind Tominon 127mm lens mod), which I'm kind of taking as inspiration...

 

[Anscojohn]

It doesn't answer your actual question but I did this to mine:




Steve,

I'd be interested in how you did this.

 

[Steve Smith]

I think it's a 105mm lens.

I have a CNC drill/router at work which we used to use for PCB manufacture. We don't make PCBs any more but the machine gets used for making test jigs, assembly jigs,....... and camera parts!

It's just a piece of 9mm thick grey nylon cut to shape to fit in place of the plastic moulding originally fitted. Behind the large hole is a thinner plate about 1.6mm thick which the lens is mounted in.

With the lens fitted as shown, it can be focused in two ways. 1. Set the lens cell to focus at infinity and use the Polaroid focussing bar. 2. Set the Polaroid bar at infinity and use the scale focus on the front cell.

The rangefinder was quite accurate despite not being for quite the same focal length.




Steve.

 

[Anscojohn]

Steve,
How did you afix the CNC manufactured plate to the body? Epoxy? Was the thickness of the plate a function of the proper distance between the optical center and point of focus at the film plane?

 

[Steve Smith]

The plate has a vertical hole through one end, hand drilled hence that end being split into two pieces. It would have been impossible to drill all the way through in one operation, and a couple of screws from the bottom plate up into my nylon plate.

The vertical bar of the frame on the left goes all the way down to the bottom plate and through the CNC cut piece.

This is the way the Polaroid moulding is mounted so I just copied that. Note that I totally removed the Polaroid front and replaced it with my own. The bellows are mounted on the back of the lens and held in place with the lens retaining ring. I think I made another plate to sit inside the end of the bellows.

The thin plate behind the main plate allowed me to use various thicknesses of spacer until I got the lens in the right place. Ideally, I wanted the lens right on the front of the grey plate but it was too far forward so I used the second plate to recess it.

I have a scrap pack film holder with a piece of frosted polyester fitted to allow me to check the focus and adjust the lens shim. All by trial and error (mainly error).



Steve.

 

[namke]

Last night I stripped down the lens assembly of the camera (leaving the bellows attached, but removing the camera front). I bodged together a new front out of an old FP-100 film pack (thin plastic, easy to cut with a craft knife) and mounted the 75mm lens in approximately the right place. I then made up a 'ground-glass' out of the remains of the film pack and some drafting film...

What did I discover? Well, at f4.5 the DOF is miniscule (as might be expected) and the lens doesn't cover the complete film area at infinity (what a surprise!). There's some serious vignetting visible on the 'ground glass'). Focusing it is also a bit tricky

However, close up is fantastic

My next opportunity for experimentation will be at the weekend, so I'll try the 127mm lens in the same 'mount' then.

I also wondered about using the original lens elements in the 75mm lens' shutter... I don't know how compatible the element-spacing will be, but it might be worth a try?

 

[namke]

... more random thoughts... I have read that the 75mm lens is a 'reverse Tessar'; and I have done some experiments with reversing a standard lens for macro work (on 35mm SLR). So! What would happen if I switched the front and rear elements of the 75mm lens? Would it still be a 75mm lens? Would it then not be a macro lens??

So many questions - and google doesn't seem to be able to supply me with answers Are there any good online references to lens design/behaviour??

Thanks for the input so far...