Leitz Pradix Slide Projector, How to CLA?

[RicardoD]

As part of my dive into this Rangefinder business I picked up a working Leitz Pradix 150w slide projector. It just arrived in the mail today but I am in love with the thing already. It's just a small simple manual mechanical device to project slides. A very simple 2 slide changer that you slide back and forth, when one slide is being projected, you can reload the other.

I just ordered an original owner's manual for it from Pacific Rim Camera for $10.

Thankfully it was shipped to me as found by the previous owner untouched... meaning original cobwebs, grime and all are still intact (i.e. no damage by unnecessary cleaning).

I need to do a CLA on this thing. The 85mm Elmaron lens is filthy and the metal chassis which holds the light collector lens has surface rust on it. I want to take it apart, restore the chassis, clean the multiple lens, lubricate the lens barrel and slide holder mechanism and then put it back together. But I want to do it right and I want to do it myself. Some questions:

1)What is the proper way to clean the lens? And light collector?
2)What is the proper lubricant for the lens to lens barrel focus, you can see the spiral groove has dried out lube?
3)Proper way to clean the first surface parabolic mirror behind the bulb.
4)And I need to get rid of some of the surface rust on inner mirror chassis and possibly repaint this inner chassis. Outside body is fine.

Any advice would be appreciated.

 

[wyk_penguin]

First a question: Does it light up? If yes you could let it heat up and see if the helical will unfreeze itself. Also, this could be a way of checking if you really need to clean the mirrors and lenses.

1)What is the proper way to clean the lens? And light collector?
Projection lens: The usually methods of lens cleaning.
Condenser lens (the big thick glass in front of the bulb): It is just some uncoated glass. You can clean it with almost anything. Just don't scratch/ drop it.

2)What is the proper lubricant for the lens to lens barrel focus, you can see the spiral groove has dried out lube?
Heat from the bulb may do it. But if you intend to regrease it, choose something that won't flow under heat.

3)Proper way to clean the first surface parabolic mirror behind the bulb.
If it works, leave it alone. Mirrors generally don't like to be touched. If you're brave, try compressed air. 😀

4)And I need to get rid of some of the surface rust on inner mirror chassis and possibly repaint this inner chassis. Outside body is fine.
I haven't done it with 'precision intruments'. However, for other things I tend to disassemble everything, sand it and spray paint it. Just don't scratch the outside. 😛

 

[RicardoD]

The bulb works, unit turns on fine. The helical is not frozen but it doesn't glide smoothly either. Good point about a grease which won't flow under heat. Any suggestions? I have heard people suggest a Radio Shack Gel lube but not sure at what temp it starts flowing. I do have some high temp brake grease use to lubricate braking components on my precision german vehicle 😀

As far as non-lense general cleaning the recommendations I have read are isopropyl alcohol followed by lighter fluid if you have some really nasty de-greasing to do.

 

[wyk_penguin]

In the years when we were small, and didn't know what carcinogenic meant, and thought inflammable was equal to not flammable, acetone was a good choice.

 

[RicardoD]

Progress

Progress

Well I am making progress on refurbishing my Pradix. The most informative thing on this projector is an archive post I found from the Leica Users Group via Google:

The Pradix was introduced in 1963 and was dropped in 1976. An interesting
piece, as it had an aspherical condensor and, off the top of my head, I
cannot think of an earlier use by Leitz of aspherical optics. It was
available with the standard 2.8/85 Elmaron lens (31403), a 2.8/100 Elmaron
(31400) (dropped in the later 1960's, probably as the 150W bulb couldn't
project brightly enough to allow full use of this lens) or with a 2.8/50
Elmar, replaced with an Elmaron in 1966 (31456). The price for the 31403
was $81 in 1972, around $200 or a bit more today.

My Pradix has the 2.8/85 Elmaron lens. Tonight I cleaned all the subassemblies and its very easy to work on. I haven't touched any of the projector optics or lens yet. The slide holder/changing mechanism in particular is very nice design. I am a mechanical engineer so I get my thrills working on this thing. I did not have to unscrew a single fastener to get to this point. Its all cleverly designed sheet metal springs and tabs.

I have attached two photos. My cleaned up Pradix in pieces and a photo of the projector optics subassembly. You can see the parabolic mirror and the other pieces of glass (not an optical engineer so I don't know the proper names for each piece).

My challenge with this subassembly is to bend back some sheet metal tabs, remove the pieces of glass, then sand down the rust on the sheet metal, repaint flat-black, and re-install the cleaned glass. There is a very thick layer of dust/grime on each glass piece and mirror. Its odd cause some stampings look brand new but for some reason the projector optics stampings have surface rust.

 

[wyk_penguin]

I am not a mechanical engineer, but I would guess that the heat sped up the corrosion. That is probably why the lamp housing it designed to be removable as a whole.

I always liked good old sheet metal engineering. Not the cheap plastic stuff that only goes one way (nothing you can do after it comes out of the factory). When you try to bend some plastic tabs, 9 times out of 10 they snap. I am a bit worried about the metal tabs snapping because of rust as well. Don't push your luck. 😀 My idea would be to sand it a bit and see how the metal underneath looks. You can always stop and paint it back if it is too rusted to go on.

 

[RicardoD]

Last night I disassembled the sheet metal optical chassis. Just a single screw for the parabolic mirror spring holder and then I had to bend back 4 tabs.

At that point all the glass was free to be removed. I cleaned the 1st surface mirror using the following procedure suggested for cleaning telescopes:

How to Clean First Surface Mirrors

This worked great and the mirror looks brand new. I also used their lens cleaning procedure for the uncoated glass (3 pieces).

At this point all thats left is the sanding and re-painting the sheet metal bits and getting the courage up to clean the 85mm Elmaron lens.

 

[RicardoD]

Got my Pradix manual yesterday. Attached is the product description page from the manual. I didn't realize the condenser lens is supposed to be interchangable if you change out the main lens as well. They are a matched pair. I now know all the names of the various optical elements.

In addition the manual states the Projection Lens and the Condenser Lens are both coated.

 

[RicardoD]

Project Complete!

Project Complete!

This project is complete for me. I got my Pradix all back together and it works great. I pulled out some old slides and sat down with my wife and enjoyed the show. Manually changing the slides isn't much of an issue as I don't have too many and the small size and quick setup make it worth it.

Attached is a picture of the cleaned up optical assembly. I don't have another projector to compare against but my good slides seemed razor sharp.

In addition I also have now have the factory microfiche service manual which is really nothing more than a parts list but it was interesting to see anyway.

So if anyone else needs Pradix help please just email me.

 

[David Strachan]

lovely work Ricardo

lovely work Ricardo

This project is complete for me. I got my Pradix all back together and it works great. I pulled out some old slides and sat down with my wife and enjoyed the show. Manually changing the slides isn't much of an issue as I don't have too many and the small size and quick setup make it worth it.

Attached is a picture of the cleaned up optical assembly. I don't have another projector to compare against but my good slides seemed razor sharp.

In addition I also have now have the factory microfiche service manual which is really nothing more than a parts list but it was interesting to see anyway.

So if anyone else needs Pradix help please just email me.

Nicely done Ricardo,I expect to purchase one today. Did the Pradix come with a film-strip viewer?

Can you help me where I can get bulbs for the projector? An American or English supplier will do, even though an Australian one would be best.
cheers and regards...again a fine job of restoration.
David Strachan