Crestar lenses

uberprutser · Joined: 01 Dec 2012 Posts: 19

I've got two Creastar lenses that came with my recent Practika MTL-50 purchase.
On both of these lenses the aperture blades seem to be stuck.
Although I will meanly use the Pentacon 50mm it would have been nice if I had the option to switch to another focal length.
Is this something I could fix with a hammer and a chisel?

The picture was taken with the Pentacon 50mm at f16.

elliott · Joined: 16 May 2011 Posts: 170

It seems odd that they would both be broken, do they have an A/M (Auto/Manual) switch on them? If so, this needs to be set to Manual for the aperture to work properly when adapted to another camera. In Auto the aperture is held open for easy focusing, then a pin on the mount is pressed when the shot is taken to stop the lens down to the aperture you selected.

If there is no switch, you need to find some way to hold the pin down that is on the mount. Some people glue them, some do a reversible modification.

Excalibur · Expire: 2014-04-21

Stuck blades? Set the lens aperture to f22\f16, then hold the pin in (at the back) or set on "M" if available...then bang lens with the palm of your hand quite a few times...if this doesn't work then it's taking the lens apart and putting some lighter fuel on the blades...if that doesn't work then it's a complete strip down to take the blades apart to clean.
The first two methods have worked for me but haven't stripped the blades apart yet.
good luck

uberprutser · Joined: 01 Dec 2012 Posts: 19

There is no A/M switch on them.
When I open up the back of the camera and set it to bulb mode, the aperture does not close when I hold down the shutter.
The 28mm does noting at all but the 135mm now closes, very slowly, about half way to f22.
I guess I have to get my hammer now. Smile

luisalegria · Expire: 2018-01-18

Stuck aperture, certainly. Probably oil on the blades even if not visible. If you can remove the rear lens group which is probably the easiest, you should be able to use naptha aka lighter fluid on the blades and mechanism. A few treatments with that should do it.

uberprutser · Joined: 01 Dec 2012 Posts: 19

I have opened up the 135mm lens and could use some help on how to proceed.

FIrst of all, I'm amazed by the amount of oil inside the lens. I this usual?
I think it is because there was no indication that the screws were opened up before. (some paint came of when I unscrewed them)

I can see there is some oil (probably) on one of the aperture blades that could be the cause of the problem.
An other cause could be that the spring shown in the picture below is worn out. This spring is used for the auto stop down feature and is, at this point, not strong enough to close the aperture blades.
So what should I do? I could try and loosen things up with a few drops of white spirits. Or could go on and try to disassemble the lens even further.
The lens has not much value to me but I prefer fixing things instead of breaking them.

TrueLoveOne · Expire: 2013-12-24

In most cases, the spring will work again after you have cleaned the aperture blades. These springs are not very strong, and only work when your blades are really clean!

I don't know if white spirit will work.... i usually use a degreaser from the automotive sector and some Q-tips te remove residue.... easiest way to clean them is if you get them out completely, so no cleaner can get to your lenses.

Good luck!

Pancolart · Expire: 2013-11-18