8mm Forum: Scope lens focusing problem

This is topic Scope lens focusing problem in forum 8mm Forum at 8mm Forum.

To visit this topic, use this URL:
https://8mmforum.film-tech.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=000862

Posted by Jean-Marc Toussaint (Member # 270) on November 02, 2004, 06:16 AM:

Hi all,

One of my scope lenses (the better one, *sigh*...) has recently become difficult to adjust. The focusing barrel requires some serious grip to rotate (I need to use both hands if I don't want to end up with vertical scope projection!) and sharp focus isn't easy.
Anybody ever encountered this kind of situation? Any suggestion to fix it?

Thanks.

Posted by Tim Christian (Member # 48) on November 02, 2004, 12:08 PM:

Two points:

First, the obvious one, is there a separate locking ring on the lens? I was caught out by this once. The focusing ring on one 'scope lens became very stiff - until I realized that half of it was a locking ring [Embarrassed]

Next, if it is not the locking ring, it may be that the lubricant (grease) has dried and hardened. Drop a little white spirit or paraffin into the thread and see what happens. If it is gritty, you may have to take it apart to clean it [Frown]

.

What lens type is it?

Posted by Jean-Marc Toussaint (Member # 270) on November 02, 2004, 12:26 PM:

Hi Tim, thanks for answering.

No, there's no locking ring on the lens. Gave it a good look when it started to get stiff.

White spirit, heh? Sounds a bit dangerous but I'll give it a try tomorrow and see what happens.

The lens is a Chretien/Hypergonar (from the people who invented CinemaScope) and is far more superior to the other lens I have (Kowa 16D).

Posted by Ugo Grassi (Member # 139) on November 02, 2004, 12:35 PM:

Hi Jean Marc,
is the focus worst than in the past? I suppose there is a little bit of grease vapored inside. It's possible the lub. inside is vapored, soiling the lens.
The only way - but very dangerous - is to open the objective.

ps. your signature is very funny! anyway it's the best to sweeten the italian coffe. Do you think it could be dangerous for my health?

Posted by Jean-Marc Toussaint (Member # 270) on November 02, 2004, 01:43 PM:

Ugo,
Nope, the lens is crystal clear, there seems to be nothing in there . Focus is just difficult to achieve because the barrel is a bit stiff.

Hope I won't have to open it... [Frown]

Posted by Jean-Marc Toussaint (Member # 270) on November 05, 2004, 07:07 AM:

OK, so far, so good.
The white spirit seems to work. The barrel is easier to turn but we're not there yet. I'll let it rest for another 24 hours.

Posted by Jean-Marc Toussaint (Member # 270) on November 07, 2004, 04:57 AM:

Problem solved! [Big Grin]

The lens is good as new (it makes an interesting "squish" sound now, but I guess it'll pass when the remaining white spirit is fully evaporated).

Thanks Tim and Ugo.

JMT

UBB.classic^TM 6.3.1.2