Meyer-Optik Primotar 3.5/135 Exakta

[iangreenhalgh1]

Hi folks

I just picked up a nice condition Meyer-Optik Primotar 3.5/135 in Exakta mount cheap.

I only paid 6.60 for the lens but Exakta to EOS converters are 20 quid!!!!

Why are Exakta converters so expensive? Is there a simple, non destructive way of using this lens on an EOS?

I hear some other Meyer lenses in M42 have the same rear tube as the Exakta Primotars so if I but an M42 Meyer lens can I swap the rear tubes to convert this Primotar to M42?

[martyn_bannister]

I have discovered the same thing. I picked up a Triotar and a Flektogon, both in Exakta, but haven't used either of them yet because I haven't stumped up for the adapter. I am about to order one though because, if you split the cost across the number of lenses, it gets cheaper by the lens

[iangreenhalgh1]

[Attila]

Not easy to make good Exakta EOS adapter and not many people buy it , 20 GBP is not much at all. Even if adapter support infinity with a lens , not sure it will do same with others.

[woodrim]

I know there are two schools of thought on this, and I'm in the one that says to hell with worrying about making changes to a cheap (inexpensive?) lens. Looking at the registers, the Exakta is 44.70 and the Canon is 44.00. The M42 adapters are typically 1mm thick at the base, so you can remove the bayonet portion of the Exakta and affix the M42 adapter and only be off by .03mm, or sand down the Exakta base after removing the bayonet portion by .03mm. I did tis very thing but with a Sony adapter.

[RioRico]

My approach: Shave the adapter, not the lens. To make a 44.7mm register Exakta fit on a 45.46mm register Pentax camera, with infinity focus, I do this:

1) remove and save the Exakta lens index screw;
2) glue an ultra-cheap M39-M42 adapter ring around the Exakta bayonet;
3) grind away ~0.7mm from the flange of a cheap-clone M42-PK adapter;
4) mount and shoot!

I grind the adapter by running it over 100-grit sandpaper taped to a very flat hard surface. If you have a PK-EOS adapter already, to leech our fine K-mount lenses, you can try this. Or it might work with cheap M42-EOS adapter -- do such exist? Sorry, I don't know EOS from a hole in the ground.

[luisalegria]

Thats an interesting approach RioRico.

I did mine similarly, but the hard way, with drills, taps and filing, and homemade brass springs to mechanically hold things together. Strong, but a lot of labor.

Shaving the adapter is an improvement on what I was doing, it should improve the infinity focus problem. I will try that in my next experiment.

I found that you can also buy an M39-PK adapter, which simplifies the problem. Thats what I'm probably using for my next one.

I do think that glue may not be secure enough for many lenses.

[RioRico]

[iangreenhalgh1]

If you're using glue, epoxy resin is by far the best solution.

I'll be modifying this lens methinks as I have a few M42-EOS adapters lying around, I'll swap the Exakta bayonet for the adapter and see if it hits infinity. Then I can shave down the adapter if necessary until it does hit infinity.

I'll let you know how I get on with the adaptation.

[RioRico]

[woodrim]

Okay, more detail... On the one Exakta mount I modified, I did remove the raised bayonet, then inserted the mount into a hole I had cut in a thick board so that the top of the mount was flush with the board. I then ran the board through my surfacing sander several times while making micro adjustments until I had sanded off the desired amount of metal. I then used a good gel type cyanoacrylate glue, putting small drops all the way around the surface, then applying the M42 adapter. Cyanoacrylate is excellent for nonporous surfaces and doesn't really add to the final thickness. In the end, we all use whatever is available to us.

As for being able to reverse the modification, I don't really care, but this was a removable mount system anyway, so a new mount can be applied - I just didn't have a M42 mount to use on it.

[iangreenhalgh1]

I've used epoxy to stick so many things over the years. The key thing is to leave it at least 24hrs to fully harden. If you leave it to fully harden before using it should stick extremely strongly as it effectively becomes a polymer plastic.

I agree with woodrim about cyanoacrylate (super glue) being good for non-porous surfaces, I tend to use epoxy in any situations where there isn't a tight fit as it is good for filling in gaps.

[iangreenhalgh1]

Well, turns out the diameter of the exakta bayonet is 39mm so a M39-EOS converter fits snugly over it. Held in place with a liberal amount of epoxy and it works perfectly directly mounted to the body, easiest conversion ever!

Some test shots taken with my Meyer Primotar 3.5/135 with 15 blades, all wide open:

Bokeh test:





Sharpness test:





100% crop:





100% crop:



To me, it has lovely, smooth 'creamy' bokeh and is acceptable sharp wide open, just waiting for some sunshine to test it outdoors stopped down!

[iangreenhalgh1]

No comments?

I was hoping some folks who own the CZJ 3.5/135 and Pentacon 2.8/135 would chime in, I'm interested to see how this Primotar compares to those lenses, particularly the latter as it is a later model from the same factory and also has 15 blades...

I was going to buy the Pentacon 2.8/135 but saw this Primotar very cheap.

[BRunner]

I had this black Primotar 3.5/135 for a while... I already sold it, too soft for me. Not comparable to Pentacon 2.8/135 wide open, not to mention the Sonnar.
But I'd like to get silver version of this lens for my Meyer collection...

[iangreenhalgh1]