Home

Please support mflenses.com if you need any graphic related work order it from us, click on above banner to order!
SearchSearch MemberlistMemberlist RegisterRegister ProfileProfile Log in to check your private messagesLog in to check your private messages Log inLog in

2 problem lenses: Isco 50/2, Vemar 12/8 (and a Petri 55 fix)
Post new topic   Reply to topic
Home   Equipment Care and Repairs
View previous topic :: View next topic  


PostPosted: Sun Sep 05, 2010 8:43 pm    Post subject: 2 problem lenses: Isco 50/2, Vemar 12/8 (and a Petri 55 fix) Reply with quote
I have problems. (Other than the obvious mental+moral defects.) The two I face now are among my efforts to hang lenses on my Pentax K20D.

1) I recently bought an Isco Westagon 50mm f/2 in what looks like a smooth Exakta mount, CHEAP!! (US$0.99 + $3 shipping) The glass and iris seem good. When I pulled the base, two tiny ball bearings fell out, but I can easily work the aperture. I will cut off the stop-down mechanism and rig the iris actuator for preset use. Mounting it on a Pentax or M42 body is no problem; I'll merely glue a cheap M39-M42 adapter ring onto the base. But focusing is nearly impossible. The focusing ring is nearly stuck. Maybe it just needs lubrication, but how? Can I just give it a squirt of 3-In-1 or other light oil? Or should I buy lens grease, and if so, where can I find a guide to further disassembling the lens?

Westagon: topside


Westagon: bottomside


Westagon: base removed


2) Not so recently, I bought an odd not-so-cheap fisheye for US$100, a 12mm f/8 fixed-focus T-mount toy badged as Vemar. It also goes by many other names. I have used both M42 and PK adapters on it. I was very disappointed at not being able to get a sharp image, so I put it aside. The camera shop guy who sold me the T-PK adapter said he thought it wasn't aligned properly. But I just tried it again, and I find that I *do* get a sharp image... at a working distance of about 50mm / 2 inches. So it's a no-infinity-focus issue. Does anyone know how to adjust focus on this?

Vemar: topside, and naked base


Then the good news: I have a Petri C.C. Auto 55/1.8 that cost NOTHING because the aperture is stuck wide open. I thought it would be a good test case for a PK conversion. I cut away the bayonet and other bits and tried various PK adapters but couldn't reach infinity focus. So I removed the 3 screws that attach the base cap to the body, and SuperGlued a cheap Bower-type infinity-focus M42-PK adapter directly to the body base. Success!! I would NOT recommend this for longer, heavier lenses. I don't really want to test the strength of the glue bond. But it works for a short lens.

Petri: topside, and adapted base


PostPosted: Sun Sep 05, 2010 10:41 pm    Post subject: Reply with quote
T2 adapter for Vemar is too thick. A CS adapter is needed. CS adapter has same M42 thread as T2, but is some mm thinner. BTW, nice self portrait on the front element! Very Happy

edit: that's wrong. The T2 adapter is thicker; see below for link to photo.

Last edited by visualopsins on Sun Sep 05, 2010 11:48 pm; edited 1 time in total


PostPosted: Sun Sep 05, 2010 11:01 pm    Post subject: Reply with quote
visualopsins wrote:
T2 adapter for Vemar is too thick. A CS adapter is needed. CS adapter has same M42 thread as T2, but is some mm thinner. BTW, nice self portrait on the front element! Very Happy


I thought 'CS' was the mount that was just like C-mount, but with a shorter flange-focal distance?


PostPosted: Sun Sep 05, 2010 11:46 pm    Post subject: Reply with quote
Scheimpflug wrote:
visualopsins wrote:
T2 adapter for Vemar is too thick. A CS adapter is needed. CS adapter has same M42 thread as T2, but is some mm thinner. BTW, nice self portrait on the front element! Very Happy


I thought 'CS' was the mount that was just like C-mount, but with a shorter flange-focal distance?


Spiratone CS mount...not CS video lens mount...

Anyway I am wrong about difference between T2 and CS; the CS adapter is thicker, so now I wonder does RioRico have a CS adapter when a T2 adapter is needed?

ref: http://photo.net/classic-cameras-forum/00QGou see first photo comparing adapter thickness...


PostPosted: Mon Sep 06, 2010 1:01 am    Post subject: Reply with quote
visualopsins wrote:
Spiratone CS mount...not CS video lens mount...

Anyway I am wrong about difference between T2 and CS; the CS adapter is thicker, so now I wonder does RioRico have a CS adapter when a T2 adapter is needed?

ref: http://photo.net/classic-cameras-forum/00QGou see first photo comparing adapter thickness...

That thread also says that CS means Contax Screwmount (Contax invented M42) and that the adapter body height differences are extremely minor.

I have tried numerous adapters. One, from an old Spiratone tele, is marked CS and its body is the same height as my known T2 adapters. My PK adapter is marked "for T2-Pentax" and its body is the same height. I've pulled T2-M42 adapters off of 3 other lenses: all the same body height, all the same ~50mm focus. An experiment: I switched to a T2-M42 and a flanged (no infinity focus) M42-PK adapter, whose flange is about 1mm thick. Now my close focus drops to ~30mm. I also tried the flanged M42-PK adapter by itself, but of course it is much too thin.

How I measure close-focus distance: I switch the camera to LIVE VIEW, push a ruler against my laptop screen, and slide the camera along the ruler until the image is sharp. Clumsy, but close enough.

Anyway, it seems like the Vemar mount itself needs to be moved a couple mm's, or a thinner adapter is needed, or I need to grind down an adapter. That means I must search through many boxes for my power grinder, which is still packed from my last move. Bother...

visualopsins wrote:
BTW, nice self portrait on the front element! Very Happy

Yes, its' perfect. Nothing is revealed. Whew. [/me sighs with relief]
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _

And does anyone have any ideas about the Isco Westagon?


PostPosted: Mon Sep 06, 2010 10:31 am    Post subject: Reply with quote
Thanks for clearing that up for me, visualopsins. Cool


RioRico wrote:
I also tried the flanged M42-PK adapter by itself, but of course it is much too thin.

Just to double check- if you either partially unscrew the M42-PK adapter, or just hold the lens in front of the camera, can you get the focus good enough for an acceptable picture?

It would be a shame to spend all of the time modifying adapters (or the lens Shocked) only to find that something is wrong with the lens. Neutral


PostPosted: Mon Sep 06, 2010 10:40 am    Post subject: Reply with quote
Sounds like the problem I had with the 200mm Tele Tokina...the mounts are different.I have a CS mount and another T mount...which do not fit.
Quote:
Anyway, it seems like the Vemar mount itself needs to be moved a couple mm's, or a thinner adapter is needed, or I need to grind down an adapter. That means I must search through many boxes for my power grinder, which is still packed from my last move. Bother...

This was my last resort.I have not done anything yet...I am hoping to score a mount that will fit it eventually... Sad it may take awhile!

My post...http://forum.mflenses.com/tele-tokina-4-5-200mm-tokyo-koki-t30995,highlight,auto+tokina+200mm.html


PostPosted: Mon Sep 06, 2010 9:08 pm    Post subject: Reply with quote
Scheimpflug wrote:
RioRico wrote:
I also tried the flanged M42-PK adapter by itself, but of course it is much too thin.

Just to double check- if you either partially unscrew the M42-PK adapter, or just hold the lens in front of the camera, can you get the focus good enough for an acceptable picture?

It would be a shame to spend all of the time modifying adapters (or the lens Shocked) only to find that something is wrong with the lens. Neutral

Yes, those *would* be shames. Yes, I *did* hold the lens in front of the camera, and got an acceptable image. Unfortunately, I can't quite measure just where the lens must be positioned, to get that acceptable image. The M42-PK adapter plus a thin ring to push the lens out a little, are 3mm deep and that's not enough. The T2-M42 and T2-PK adapters are ~9mm deep and that's too far.

But I just noticed something. On the lens' T2 mount, threading stops ~2-3mm from the lens body. No matter which adapter I use, whether T2 or the flanged M42-PK, the body of the adapter does not jam tightly against the lens body -- there's a ~2mm gap.

How to close that gap? Well, the T2 adapters I have are all in two pieces: the inner T2 core, and an outer mount piece. Instead of grinding down an entire T2-whatever adapter, maybe I can just grind off ~2mm from an inner core? I have an extra. Now I must find the grinder. And grind the ring smoothly, without removing my fingers. Grrr...


PostPosted: Tue Sep 07, 2010 2:41 pm    Post subject: Reply with quote
RioRico wrote:
... But I just noticed something. On the lens' T2 mount, threading stops ~2-3mm from the lens body. No matter which adapter I use, whether T2 or the flanged M42-PK, the body of the adapter does not jam tightly against the lens body -- there's a ~2mm gap.
...


That's what I'm tryin' to say to you...the lens is a CS mount, it needs a CS adapter not a T2 adapter. The CS adapter will screw on all the way flush with the lens, get the lens closer to the sensor to give infinity focus.

more link:

The Strange Case of the 12mm Fisheye


PostPosted: Tue Sep 07, 2010 6:12 pm    Post subject: Reply with quote
visualopsins wrote:
RioRico wrote:
... But I just noticed something. On the lens' T2 mount, threading stops ~2-3mm from the lens body. No matter which adapter I use, whether T2 or the flanged M42-PK, the body of the adapter does not jam tightly against the lens body -- there's a ~2mm gap.
...

That's what I'm tryin' to say to you...the lens is a CS mount, it needs a CS adapter not a T2 adapter. The CS adapter will screw on all the way flush with the lens, get the lens closer to the sensor to give infinity focus.

And now I'm confused (still). As I mentioned, I have an adapter from on an old Spiratone 400/5.6 long-tube lens that's marked CS, and it's body height is the same as the T2-M42(P) adapters, and it produces the same results. So, outside the cine / C-mount world, are there thinner T2-like adapters? I've googled more than a few combinations of C.S lens.mount -video and found nothing useful. Yet. Or do Mamiya CS or Hassy C-mounts play some role here?

Like I said, these T2 mounts and the CS all consist of an inner T2 thread ring and an outer camera mount ring. If I remove the inner ring and thread it onto the lens, it fits snugly. That 'gap' is only apparent when I add the outer mount ring. The lens body base tapers slightly, thus causing the gap. These inner adapter rings are all ~0.25" / 6+mm thick, as measured with my hardware-store gauge. (Darn, where did my micrometer go?) I apparently need a T2 or CS or whatever inner ring that's ~4mm thick.

Quote:
more link:

The Strange Case of the 12mm Fisheye

Thanks for providing that link. I've read the piece a few times in the past couple years, but not lately. I note that the author says that the lens takes T-mount (1-piece) or T2 (2-piece), with no mention of CS. So I'm confused (still).
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

UPDATE:

I can't get at my grinding wheel, it's buried amongst too much other stuff. My bench vice is back there somewhere too. I have a pitiful grinding bit for a power drill, and small vice-grip pliers, so I applied those to the sacrificial T2-thread ring. Two hours later (with rest breaks) I've removed maybe 1+mm from that ring. Set on the lens, it raises the focus distance from~50mm to ~200mm. That's a little better. Stopped to f/16 with long exposures, I can get usable close-ups but with fuzzy infinity, where infinity = 1.5m. Watch out for direct light -- flare!

Enough grinding for today. I'll bother one of the in-laws has a vice and/or grinding wheel. But somehow I doubt this Vemar will keep my from using my Pentax DA10-17. Some new AF zooms are better than some old manual primes, eh?


PostPosted: Wed Sep 08, 2010 6:51 pm    Post subject: Reply with quote
Well at least I was confused. Here's what I think I know now. Laughing

CS stands for Contax Screwmount. CS is identical to M42. The adapter marked CS is a T2 to CS adapter.

The adapters for Spiratone YS (not CS) mount lenses have T2 threads on the lens side and other mounts such as M42, Nikon, and FD, on the other side. The M42 threads on the YS-M42 adapter extend 0.5mm farther than T2-M42 adapter (I measured with calipers), however the distance lens is held from camera body is identical to T2 adapter.

When T2 thread is screwed onto M42 mount, there is a 1-2mm gap between adapter and mount faces. i.e., if 12mm lens has M42 mount, screwing on a T2 adapter there is a gap of 1-2mm. Try a M42 to PK adapter, attach to camera. Very Happy
Post new topic   Reply to topic
Home   Equipment Care and Repairs
Page 1 of 1