The mechanism is a bit different from the Helios I showed before. In this one, with the cover removed, a spring closes the diaphragm. When the cover is mounted, pin 4 (see photo) pushes against pin 1 to open the diaphragm. As for the Helios, I put some wire insulation around the auto pin (in white, number 3 in the photo). This keeps pin 4 away from pin 1.

Interesting is that turning the diaphragm ring (which is linked to lever 2) makes pin 1 rotate in opposite direction. Seems like a complicated construction.

So, the homepage for these lenses is here:
http://www.jupiter-optics.com/helios.htm

What does this tell us? First of all, all three versions appear to be still in production! This explains why there are M-6 lenses with a later serial number than an M-7.
The factory is called Optical-Mechanical Factory "Jupiter" (??????-???????????? ????? "??????", ??????). The factory symbol (you know, the shishkebab thingy) actually is a stylized russian letter "Ju" (?) (as explained here: http://www.zenitcamera.com/qa/qa-logos.html - the longest soviet-lens-logo list I've seen so far).
Since the factory is located in the city Valday (250 km from Moscow), it is also known as the Valday factory, or Valdayskaya.

Second, the ONLY difference between these three models is the optical resolution! In the center, 40, 45 resp. 50, near the border (at 19 mm) 20, 25 resp. 30 [no unit given, must be lines/mm]. Now the Zenit page (http://zenit.istra.ru/archive/lenses/helios-44.html) indicates that there is a difference in the amount of light these versions let through.

This leads me to believe that these three versions actually are one and the same, and that based on a resolution measurement at the end of the production line, they are divided into three groups, "5", "6" and "7".

The M-4 must be an earlier version... and it's the latest and only version for which a K-bajonett version exists. Sometime between 1990 and 1993 they must have changed from M-4 to M-5,6,7.

Sound like a good idea?
While it sounds complicated to make i'm sure it could be done without much effort.
When i get some time i'll try some initial designs

Let us know how it turns out! I'm very interested!
I saw similar design in my CZJ Tessar 50/2.8 (it's more like a lever - you push the button toward the camera) and CZJ Flektogon 35/2.8 (a button - you push it into the lens). It really is very practical! Unfortunatly, newer designs don't have this feature....

By the way- does anyone know if or when the aperture blades were 'painted' black on this lens? My m-4 version has bare metal (stainless?) blades.
I have coated blades with graphite in the past but it's nowhere near ideal.Has anyone found a good way of darkening the blades?
Maybe a black marker pen? (sharpie)

Another thought.Is everyone aware how Olympus lenses have the very cool stop down button? It would be very easy to modify this lens to do the same if anyone is interested .
See in Sjoerd's pic above-that long curving lever that starts at about 1 o'clock and curves anticlockwise to the 7 o'clock position? All you would need is some kind of button in the 10 to 12 o'clock position to push on this.
That way you could focus wide open and push the stop down button to take the pic.

Actually i was thinking about this the other day for the FD85/1.2L's i'm converting .The ideal would be a large button that also functions abit like a rocker switch.
In (say) the left position the aperture would be open by default then stopped down when pushed (and locked closed if pushed and moved to the left slightly).
In the right position the opposite would apply - closed by default,open when pushed and locked open when pushed and moved to the right.

Sound like a good idea?
While it sounds complicated to make i'm sure it could be done without much effort.
When i get some time i'll try some initial designs

I'm kinda in-love with my lenses and wouldn't want to hurt them in any way
So every modification I do to a lens, I do it in such a way, that I can reverse it with no harm!

I have a Helos 44M-4 MC (6 blades; BTW- didn't someone here said he will do a comparison of 8 vs 6 blades?). I took of rear mount - like Ron said there is a pin, that closes the iris when pushed. It's shaped like a nail - it has a larger cap inside, that pushes the lever (if you'll open it you'll see). Then I took a thin straw (for drinkig juce etc.; or you could take out the one in a pen) and cut a smal piece and put it on the pin. When I screwed the mount back on, the hole for the pin pushed the straw down and there you go - a manual iris. And it's 100% reversible!

Thanks Olaf and others for the ideas! I like the straw idea very much, especially the pen version...
Since I had no fitting straw (and because of my electrotechnical background, no doubt) I thought of another solution: use the plastic insulation of electrical wire. A few millimeters of it around the pin will prevent it from popping up through the hole.

Here's a picture of my MC Helios-44M-6, with the plastic (see arrow) around the pin, before remounting the cover. On this lens, it is indeed a very easy and reversable operation, anyone can do it. Even the screws are of a pleasant size. Next on for the same operation is my Zenitar fish.

btw. since the serial number is on the cover, it is not at all impossible that it has been interchanged with that of another lens. So maybe the lens itself is not newer than the M-7 version after all...

I have a Helos 44M-4 MC (6 blades; BTW- didn't someone here said he will do a comparison of 8 vs 6 blades?). I took of rear mount - like Ron said there is a pin, that closes the iris when pushed. It's shaped like a nail - it has a larger cap inside, that pushes the lever (if you'll open it you'll see). Then I took a thin straw (for drinkig juce etc.; or you could take out the one in a pen) and cut a smal piece and put it on the pin. When I screwed the mount back on, the hole for the pin pushed the straw down and there you go - a manual iris. And it's 100% reversible!

The M-7 and M-4 are almost identical in looks - but the M-7 has a slightly slimmer focus ring, the front element is not as recessed, and it weighs about 15g less than the M-4.

Mine is 2 rings preset no switch, exactly the same on the link, I wish it has a switch. It has become my everyday lens, I got the Mir-1V and J-9 as well, but they are not as fast as the Helios in operating, the Mir is little dim to focus on my FM2 and J-9 has tight focusing, I am trying to re-grease it with little success.

Thanks again for the info! As for your Jupiter-9, did you try cleaning away some of the (old?) grease? Mine (new from the factory) was quite stiff until i applied some solvent and gave it a lot of excercise.
Btw, personally I like the preset system. Based on your info, I might try to add an M-3 to my collection - would be interesting to see how belorussian quality compares to russian quality...

lotech, the text on your lens says ??????, that's Gelios transliterated, we would say Helios. I suppose it looks like the one at http://m42.povlab.org/lens_detail.php?lid=154
The symbol on the one on povlab is the Belomo factory symbol.
I'm still curious about its mechanism for setting the diaphragm - is it preset, auto, with or without switch?

As for posting a photo, you'll need to host it somewhere, and then you can put a link towards it.

RedAlizarin - so it seems that M-4 to M-7 are all from Valdai, with six blades. I'm surprised by the production year of your 44M-7 - my 44M-6 has a serial number starting with 96... so the M-6 could be newer than the M-7?!
My 44M is from 1976, my 44 has an indication "N0460116", but I'm not sure if that says anything. I'm not even sure if it reads "No 46..." or "N 046...".

Mine read something like this (you have to guess it is in Russia) "MC TEANOC 44-3 [symbol] 2/58 9107274", it is preset no switch 8 blades clearly multi coated with greenish reflection and 52mm filter size. focusing mark in yellow M0.5,0.55,0.6,0.65,0.7,0.8,0.9,1,1.15,1.3,1.5,1.7,2,2.5,3,4,6,10 and infinity. I don't see another one of these on ebay I guess it is quite rare, I can't compare with new versions as I don't have one, but I guess no big difference.

Q: How do I post picture ?

MC Helios 44M-7, produced by Zenit Valdai, fully automatic diaphragm and no switch. Has 6 iris blades. (1993)
Helios 44M-4, produced by Zenit Valdai, fully automatic diaphragm and no switch.  Has 6 iris blades. (1990)
Helios 44-2, produced by KMZ, preset diaphragm with 8 iris blades. (1975)

I used a trick recommended in another post, and jammed the pin down with a tiny stub of cardboard - works like a charm.