[elena_]

Hi! I've used a Pentacon 29mm 2.8 on my analog camera Olympus FTL for 3 years. Everything worked just fine until last summer, but now I noticed the light meter indicator's was not moving as I changed the aperture, so I checked my lens and the blades are stuck open. Nothing happens as I turn the diaphragm's ring.
I took the lens out of the camera and it doesn't work either, but it does close and open normally if I press the small steel/iron pin on the mount (sorry, don't know the technical term) while I turn the ring. Any ideas about what could be the reason and is there something easy I can attempt without disassembling the lens or should I bring it straight to a repair shop?
I remember I brought it for a quick check in a shop for another issue in the camera (the shutter sometimes gets stuck) and the guy handled the lens a bit badly trying to take it out from the camera without pressing the proper release button. He could have bended something? For sure I'm not taking it back to that shop!
Thank you in advance

[Medex]

If your lens has Auto/Manual switch, set it to Manual (M). If this lens has not A/M switch, you should fix the pin somehow in depressed position. Then aperture ring rotation will change the diaphragm

[Bob 256]

Ordinarily, pushing the camera meter button will close down the lens for metering (by depressing that small pin while you're metering) and the aperture ring will control the aperture during that time. Otherwise you wouldn't expect the diaphragm to close, even using the f-stop ring unless it is in manual (if it has a manual mode). If you take the lens off your camera and push the pin, the aperture should close to what you have set on the aperture ring, so what you described sound's like normal operation. Can you see the image darken through the viewfinder (assuming your camera is an SLR) while you meter? It may be that your metering battery is dead, hence the indicator not moving.

[Not a Number]

Looking at photos of this lens on eBay and other sources it looks to me that it has an auto/manual switch on the ring nearest to the camera mount. It looks like the way it is designed that it would be very easy to change the setting when screwing the lens in or out. As suggested by Medex set this to Manual.

[antipattern]

The old Pentacon lenses are notorious for sticky apertures due to oil residue on the aperture blades. Medex and Bob 256 already gave hints that will help you diagnose the problem. If you still experience problems and the aperture does not close even if you press the pin, this might be the cause.

If so, this is relatively easy to fix. you need to disassemble the lens until you get to the aperture blades. The following video gives you a good idea about how to proceed:

You Tube

You Tube

You need some cotton buds and 99.X% alcohol.

The most minimal surgery requires disassembly until you get to the aperture blades, e.g. until 4:07 mins. Whether you disassemble the front or the back doesn't matter. It's best to remove both sides of the lens assembly, so you don't dirtify the lenses as you clean, but sometimes it's easier to use the most minimally invasive technique if you are not experienced in disassembling lenses. Then you dip your cotton buds into the alcohol and carefully drip it onto the aperture diaphragm. This should be enough to enable the aperture blades to open whilst the alcohol is has not evaporated, but you still need to clean off the oil. Then you use alcohol-dipped cotton buds to carefully, gently, clean off the oil off the blades. Open and close the blades carefully as you clean the lens, make sure they don't jam, replacing the cotton buds when the get too dirty. Keep doing this until the cotton buds remain relatively clean, making sure you dislodge the oil on the other side as well. Use dry cotton buds to wipe off any excess alcohol that doesn't evaporate and to check that you removed the oil and the blades are functioning again. Once you are happy with the result, check that the lens elements are clean and you can reassemble the lens and use it for many more years.

Of course, it would be better to fully disassemble the lens aperture blades, and give them a proper soak and clean, but if you haven't disassembled lenses and aperture blades before, there are too many things that could go wrong and can be incredibly fiddly. The above method tends to work well with old East German lenses that are not worth enough to warrant sending off to a proper repair facility.

[Not a Number]

According to the User Manual (pg 22):
https://www.butkus.org/chinon/olympus/olympus_ftl/olympus_ftl.htm
"STOP-DOWN MEASURING METHOD
When extension ring, bellows, non-Olympus interchangeable lenses are used with the FTL, correct exposure must be determined by "stop-down" measuring, because the meter coupling pin does not connect with the lens.
When non-Olympus lenses are mounted on the camera, press the pre-view button to close the aperture diaphragm to take readings. in case of extension ring and bellows are used, lock the preview button by pressing it down since the diaphragm closes as you set the aperture ring. Then looking through the viewfinder, rotate the aperture ring and the shutter speed dial to the point that the meter needle and follow pointer match.
Any Olympus interchangeable lens mounted on the camera directly without close-up equipments cannot be used in the stop-down method.
To prevent extraneous light entering from the eye-piece, use the eye-shade while taking readings."

So it would seem that the FTL some sort of aperture stop-down flapper as in Spotmatics. With the lens off actuate the pre-view button and see if the "flapper" moves. If it doesn't or looks damaged then the "repair" person probably damaged it.

[elena_]

Thank you everyone for taking the time to reply! I tried to open and close the blades a few times with the pin down and played a bit with the lens and it now works. I don't know if it was just sticky and playing a little with it made the curtain work again, or more likely, it has to do with the Auto/Manual switch back to the Manual position - I didn't know about the purpose of this switch as I had never used it and I am learning now about the different Auto/Manual option, so thank you for mentioning that!

So now in Manual mode, the blades move as I turn the diaphragm ring, and the exposure needle moves accordingly in the viewfinder. In Auto mode, the blades are stuck open and the needle only moves according to shutter speed and not according to the diaphragm ring, and this is probably due to the fact that it's not an original Olympus interchangeable lens (it has a M42 mount and no connection rings, though).

I have an original Zuiko 50mm in another home and I will get it next weekend and see the different behavior to confirm all this, but the problem is hopefully solved without any worse issue in the lens! Maybe further suggestions about dismounting the lens to clean it and fix it will come handy in the future, so thank you all for any contribution, I really appreciate it