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focusing problems with CZJ Flek 20mm
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PostPosted: Wed Jul 30, 2008 2:31 pm    Post subject: focusing problems with CZJ Flek 20mm Reply with quote
I have a Flek 20/2,8 mounted with an M42 adaptor to my Pentax K10D.
Problem with this lens is, that I can focus it over infinity. Not a bit, but quite some more ...
(This doesn't hapen when I have my Flek 35mm mounted. This one focuses just perfectly to infinity and not over it.)

It doen't really disturb me, but what can be the real problem there ?

Thanks and cheers
Tobbsman


PostPosted: Wed Jul 30, 2008 3:51 pm    Post subject: Reply with quote
Look at my message, the 3rd one in this thread:
http://forum.mflenses.com/flektogon-20-2-8-infinity-setting-t7070.html


PostPosted: Wed Jul 30, 2008 6:43 pm    Post subject: Reply with quote
Quite common problem...


PostPosted: Wed Jul 30, 2008 9:10 pm    Post subject: Reply with quote
Thanks for your help guys !
I will read that thread ...

Cheers
__________ tobbsman


PostPosted: Wed Jul 30, 2008 10:53 pm    Post subject: Reply with quote
Peter, my Flek 20/4 reaches infinity between the 2m and 4m marks!

I guess I'm not sure what the "filter ring" is...I assume the outside ring that is threaded for filters? Does turning that ring also affect the distance of the front element? And finally, how do I loosen the filter ring, mine is pretty tight and I don't want to force anything until I find out.

Thanks, as always!

Larry


PostPosted: Wed Jul 30, 2008 10:56 pm    Post subject: Reply with quote
Damn Larry, sure must be hard to close focus. That thing has a hair trigger!


PostPosted: Thu Jul 31, 2008 12:01 am    Post subject: Reply with quote
maddog10 wrote:
Damn Larry, sure must be hard to close focus. That thing has a hair trigger!


Well, it IS difficult on my film camera; however, most of the time I've been using it with my Pentax K110D with focus confirmation, so I've been okay there. But, I do want to correct the lens, just to know it's up to it's optimum focusing ability.


PostPosted: Thu Jul 31, 2008 8:55 am    Post subject: Reply with quote
Laurence wrote:
Peter, my Flek 20/4 reaches infinity between the 2m and 4m marks!

I guess I'm not sure what the "filter ring" is...I assume the outside ring that is threaded for filters? Does turning that ring also affect the distance of the front element? And finally, how do I loosen the filter ring, mine is pretty tight and I don't want to force anything until I find out.

Thanks, as always!

Larry

Hi Larry, yes what I mean by the filter ring is the rim at the extreme front of the lens that projects beyond the focussing dial, threaded on the inside for filters or hoods. Normally this should be firm and not rotate in relation to the mount.

I haven't dismantled this lens to check how it's fixed, but often on other Zeiss lenses there are three screws under the label ring round the front lens which lock the knurled focus grip to the outer part of the threaded helicoid. With these two locked together, when you turn the grip the inner part of the helicoid (with the glass elements) moves in and out on the thread and thereby adjusts the focus. With the screws slackened the grip can be rotated without moving the helicoid, and this is how the lens is collimated so that it is truly focussed at infinity when the dial is at the inifinity stop.

What I think probably happens is that people grasp the filter ring to screw and unscrew the lens from the camera and the friction of the three screws isn't sufficient to prevent it turning slightly instead of unscrewing the mount, thereby throwing out the collimation.

The cure is to set the lens on actual inifinity focus in the viewfinder and adjust the dial to line up the infinity stop with the index mark without moving the helicoid, which means the filter ring has to be turned in relation to the lens index mark. If the ring on your lens really is immovable then you'll need to unscrew the label ring in the filter threads to get to the screws to slacken them, but remember the ring has been moved before and I found with my lens I didn't need to go that far.

This is really difficult to describe in words! Smile I'll see if I can find an illustrated article on it. This article describes collimation for movie lenses (the same principle), and explains how to do a temporary fix using paper shims between the lens and the camera mount. This only works if you can focus beyond infinity.
http://lavender.fortunecity.com/lavender/569/lenscollimation.html


PostPosted: Thu Jul 31, 2008 9:26 am    Post subject: Reply with quote
Last time I got a Flektogon 20mm with really bad focusing it not reached infinity at all. Repair man (an old very experienced guy) couldn't set as well at first time. In next round he suggested to set to my camera Shocked finally he could fix it well, it id work on any camera fine , but still not reach infinity at exactly at the end.


PostPosted: Thu Jul 31, 2008 10:02 am    Post subject: Reply with quote
OK, I removed the name-ring on my lens with a piece of rubber but I can't see any screws. I think they might be obscured by the front lens element but I'm not going to remove it to check.

If you grasp the lens mount firm in one hand and turn the filter ring with the other, it is left hand thread. Turning it clockwise as you look at the front moves the helicoid outwards, away from the camera. This is the direction to turn it if the lens focuses beyond infinity. If it won't reach infinity, turn the filter ring anti-clockwise. The thread is fairly coarse, so only a very small amount of rotation is needed.

Correct adjustment can be checked on a film camera on a tripod with the shutter held open and a ground glass screen (or tranlucent tape) taped to the film rails in the film compartment. You'll need a magnifying glass. On a DSLR it's trial and error by taking pictures.


PostPosted: Thu Jul 31, 2008 10:15 pm    Post subject: Reply with quote
It's done! I did simply move the filter ring without needing to loosen any screws. I turned it about 5/16ths of an inch clockwise, checked the "general" setting at infinity, and presto! It's in focus much better now at infinity, with the infinity mark line up.

However, I am going to collimate for sure, just to make sure I am "right on the money" at last.

I also received in the mail this morning, a very nice Heliopan rubber hood for the Flek!

THANK YOU!


PostPosted: Thu Jul 31, 2008 10:24 pm    Post subject: Reply with quote
I am glad you could solve it easily!


PostPosted: Fri Aug 01, 2008 11:33 am    Post subject: Reply with quote
Thanks for all the comments !!
I'll try that. The filter ring is not turning with mine ... I am going to get my screw driver just now Smile

Hope I can't destroy something on my lovley Flek.

Whish me some good luck Wink ...

Cheers
Tobbsman


PostPosted: Fri Aug 01, 2008 1:19 pm    Post subject: Reply with quote
tobbsman wrote:
The filter ring is not turning with mine ... I am going to get my screw driver just now Smile

Hope I can't destroy something on my lovley Flek.

Whish me some good luck Wink ...

Cheers
Tobbsman

You have to use considerable force to turn the filter ring. The more the better really, because like that it will be more likely to remain in the right place. As I said, someone moved it out of position before you had it so it should go back OK. I'd only recommend a screwdriver as a last resort!

Anyway, good luck Smile

Last edited by peterqd on Fri Aug 01, 2008 1:22 pm; edited 1 time in total


PostPosted: Fri Aug 01, 2008 1:20 pm    Post subject: Reply with quote
Laurence wrote:
It's done! I did simply move the filter ring without needing to loosen any screws. I turned it about 5/16ths of an inch clockwise, checked the "general" setting at infinity, and presto! It's in focus much better now at infinity, with the infinity mark line up.

However, I am going to collimate for sure, just to make sure I am "right on the money" at last.

I also received in the mail this morning, a very nice Heliopan rubber hood for the Flek!

THANK YOU!

Well done Larry! Glad to hear to hear you managed to correct it. Have you got a link for the hood? I need one too.


PostPosted: Fri Aug 01, 2008 8:22 pm    Post subject: Reply with quote
peterqd wrote:
Laurence wrote:
It's done! I did simply move the filter ring without needing to loosen any screws. I turned it about 5/16ths of an inch clockwise, checked the "general" setting at infinity, and presto! It's in focus much better now at infinity, with the infinity mark line up.

However, I am going to collimate for sure, just to make sure I am "right on the money" at last.

I also received in the mail this morning, a very nice Heliopan rubber hood for the Flek!

THANK YOU!

Well done Larry! Glad to hear to hear you managed to correct it. Have you got a link for the hood? I need one too.


Peter (and anyone else), I obtain a lot of equipment from this guycalled CameraHunter on eBay....David is a WONDERFUL guy, just give him a yell via email. I got the VERY nice Heliopan hood for $15.00...it was marked $46 with an original price tag on the original box.

From: David Wombacher <dwombacher>
Subject: RE: You've received a question about your eBay item, NEW 77mm Rubber Lens Hood ~ DOUBLE THREADED ~ FRESH NEW
To: "'Laurence Smith'" <smith_laurence>

Attila:
I take off his email to protect him against spammers.
If he has website publish that link instead of his email.


PostPosted: Fri Aug 01, 2008 9:50 pm    Post subject: Reply with quote
I have made a couple of purchases from David as well.
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