Repair of stuck apature blades on a Mamiya 645 210 f4 lens

[ian_rose]

<p>I have been given 2 Mamiya 645 lenes 1 is a 210 f4 the other is a 45 f2.8. The 210 has a frozen apture the apture ring does move. Also the 45 lens has oil on the apture blades. So my question is does anybody have the tear down diagrams or any other insight on what order to dismantel these lenses. I have been a mechanical enginer for about 40 years. also what is the best cleaner to use on the blades and on reassmbly are the blades lubricated in any way.</p>

<p>thanks in advance<br>

Ian R</p>

<p> </p>

[rodeo_joe1]

<p>This has fooled me on a couple of occasions, so I hope you'll forgive me if I ask if you've checked the position of the Auto-Manual switch on the lens? This only needs a slight knock out of position to close down the aperture and prevent it opening fully.</p>

<p>If you're still determined to strip down those lenses. The best place to start is by dismantling them from the back. Remove the mount and work inwards. The 45 should be reasonably easy to strip back to the aperture blades, since the rear lens cell assembly will easily unscrew. But check the linkages before tearing into the lens. Sometimes the linkage gets a bit sticky and the blades themselves don't need to be touched. I can't advise specifically about the 210mm lens, since I've never had to strip one down, but again I'd start by removing the mount and examining the linkages and the springs. A spring that's got worn or popped off its mount will also stop the aperture working properly.</p>

<p>Actually, I'm surprised that there's oil visible on the blades. Mamiya 645 lenses are generally quite dry in operation and rarely suffer from an oily diaphram. Although the Leaf Shutter lenses are an exception to this. Sounds like some clown may have deliberately oiled the mechanism.</p>

<p>Best diaphram cleaner is acetone - pure if you can get it or good quality nail-varnish remover if you can't. If the grease is really stubborn try lighter fluid.</p>

[h_a_hough]

<p>Both these lenses are easily disassembled with spanner wrenches to expose the aperture mechanism after the front bezel is removed. I prefer naptha or lighter fluid over acetone as a grease solvent for this purpose as it won't have adverse effects if it somehow gets on a plastic surface.<br>

With the aperture blades exposed, one or two drops of fluid and an overnight soak followed by exercising the blades generally solves the problem.<br>

H2</p>

[charles_mason]

<p>I teach photography. In my beginning class, I always put the question "How do you spell that A-word that means your lens opening?" I tell them it is on the quiz ahead of time. Still I get a lot of inventive spellings for Aperture. So Ian it isn't APATURE, or APTURE, but APERTURE. Usually I get aper-A-ture, as a lot of people pronounce it that way for some reason. Sort of like Nuclear is often pronounced Nucular. Anyway, enjoy!</p>

<p> </p>

[adamjohnson]

<p>I can't offer much technical advice in cleaning because I never saw the point of bothering with repairs when the Mamiya-Sekor C lenses were so inexpensive. If you do destroy it during the cleaning process, just buy another. I think I paid $80 for my 200mm f/4 and loved the images it captured. I will say though that every single image I adore that came with the 200mm was shot at f/4. It was beautiful wide open, but lacking at anything beyond. The 2nd image was shot a few minutes after it had rolled off a rock and into the Whitewater River in Southeastern Minnesota.</p>

<p><strong>"Zippel Bay State Park"</strong><br>

<img src="http://farm3.static.flickr.com/2658/4101069173_27c26ba57d.jpg" alt="" width="368" height="500" /></p>

<p><strong>"Whitewater State Park"</strong><br>

<img src="http://farm3.static.flickr.com/2650/4233278088_0bd359a729_z.jpg?zz=1" alt="" width="640" height="470" /></p>

<p> </p>

[ian_rose]

<p>Thanks for the responses<br>

RE. H A thanks for the advise about going in through the front on this lens when I unscrewed the bezel the wole front element came out as 1 piece then the blade retaining ring then the blades and I could see that the problem was the return spring had become detaced from the moveing blade ring so had to dig a bit deeper. It took about 4 hrs to take apart and reassemble also making the lens spanner's as required out of solid 1/8 steel.</p>

<p>Re. Charles Spelling never was my strong point and since moving into computers I admit that I Have got lazy and rely to much on SPELL CHECKERS .</p>

<p>Re. Adam At the price paid $0. I figuared what have I to lose. And everthing to gain</p>

<p>Ian Rose</p>

[rodeo_joe1]

<p>If you'd gone in through the back like I suggested, then you might have come to the actuating spring a bit earlier than after 4hrs disassembly!</p>

<p>Attacking diaphram blades directly is never a good idea, since the goo sticking them has nearly always come from somewhere else and it's the source of stickiness that needs clearing up. Otherwise you'll just be repeating the job in a couple of weeks/months time.</p>

[chris_bradley4]

<p>Hi Rodeo joe, you grabbed my attention. I have just stripped my recently purchased a Mamiya 645 with a standard Sekor C 80mm f1:2.8. Iris was sticking as was focus. I have the blades freed and focus smooth now but the iris does not return to fully open. I suspect someone has already been inside this lens but would ask your advice please as to the spring that returns the iris to fully open. I am about to try and post an image of the lens dismantled and showing inside a blue circle where I suspect a spring may have been.<br>

I would appreciate any advice and help in locating any parts I may require to get the lens working again. Many thanks in advance. Chris.</p><div></div>

[rodeo_joe1]

<p>Chris, I'm not familiar with the inside of the 80mm lens, since none of mine have given me any trouble yet - if it ain't bust don't fix it! Is that the old C lens or N? It looks like an N lens to me, but it's not too clear from the picture. The iris leaves on my 80mm N lens have their "spikes" overlapping at the rear of the lens, but that shouldn't really affect their operation.</p>

<p>The main return spring should be on the parts you haven't put back yet. The Iris as you show it should be really free to move when its controlling collar is pushed round. If that's not the case then the iris needs another looking at.</p>

<p>Although I can't tell you about this exact lens, here's the general principle of nearly all Mamiya 645 lenses: The stop down mechanism (not yet fitted) should couple onto the iris collar and rotate it to fully open. There are usually two springs, a weak spring that pulls the iris shut, and a stronger spring that holds it open. The stop down mechanism relieves the pressure from the stronger spring to allow the iris to rotate and stop down. The click stop mechanism governs how far the iris is allowed to rotate by regulating the taper on the iris collar (seen at about 4 o'clock in above picture).</p>

<p>It looks to me as if the weak iris tensioning spring may have been fitted where you've circled and been fixed to a small post that should screw into the open threaded hole at 11 o'clock. If that's the case then both the spring and its fixing post are missing. However, before you panic have a good look at the parts that you haven't yet replaced. Sometimes manufacturers revise mechanisms to save parts and cost, so an empty screw hole might not mean anything. Hold the stop down mechanism in place after engaging its coupler in the iris collar. Then try the stop down lever. If the lens stops down normally then all is well and you can screw the assembly together again.</p>

[ian_rose]

<p>Hi Chris<br>

On the 210 f4 lens that I rebuilt the spring went from the brass post that you have circled on the moveing plate to a post on the fixed plate at about where the chrome dot is at about 3 oclock the spring goes between the 2 plates . the spring is about 5/8" long by about 3/32 dia.</p>

<p>Ian R</p>

[chris_bradley4]

<p>Thanks guys. Closer inspection shows two threaded holes on the assembly plate and a groove machined in the brass pin to locate the spring. Blades now move freely when I move the brass pin. I use brake cleaner to clean these. A can of brake cleaner aerosol gives a great pressure to wash out any residue and evaporates totally. It's very cheap to buy from any car accessory shop. I have cleaned many lenses this way with great success. Back to my 80mm Sekor C. Do you think it is a scrapper? Chris</p><div></div>

[rodeo_joe1]

<p>Right. Now that we can see the brass pin it definitely looks made to take the loop of a spring. I also think the chrome stud at 3 o'clock that Ian mentioned is the "stopper" for selecting the aperture, and nothing to do with the spring. Although that's not to say that there isn't an anchor point in that area that we can't see.</p>

<p>The pressure spring for the iris is quite thin wire and tightly coiled. It obviously needs to be the right length to fit between the brass pin and wherever its mounting point is, with just a little tension. I'm pretty sure that it should be anchored where that vacant threaded hole is though. It needs enough turns to allow the collar to rotate to the fully stopped down position without undue pressure - in other words it needs to be "close-wound" with the turns touching before expansion. From memory the diameter will be around 2.5 to 3mm. If you can get some fine spring wire (about 30-32 SWG) it would be possible to wind such a spring by hand; perhaps over a biro refill or similar.</p>

<p>I'll try to show what the finished spring should look like: OiiiiiiiiiiiiiiiiiiiO</p>

<p>The fixing post could be a simple bolt of the correct thread with a nut attached to fix it in place. Or you could just jam a piece of rod tightly in the threaded hole to hold the spring. A notch filed with a swiss-file would retain the spring.</p>

<p>This doesn't have to be a pro quality repair, just good enough to get the lens working again. After all, the lens isn't really worth the cost of buying proper spares and paying a repairer to reassemble it. So what have you got to lose?</p>

[rodeo_joe1]

<p>Maybe I misjudged the wire gauge - should probably be more like 36 SWG on reflection.</p>

[ian_rose]

<p>Rodeo Joe / Chris<br>

The finished spring shape is : 0--iiiiiiiii-------0 the easist way to make a spring is to wrap the wire round the shank of a small twist drill the wire dia would be about .020 / .025". At the moment I am in the process of making a tool to remove the 77mm dia ring on the 45 mm lens.</p>

<p>Ian Rose</p>

[ian_rose]

<p>Chris Rodeo Joe was right about where the spring goes to and from and also about the shape of the spring attched are 2 images 1 showing the back of the 45mm lens and 1 a 100% crop of the spring.</p>

<p>Ian R</p><div></div>

[ian_rose]

<p>and now the 100% crop of the spring the distance between the spring posts is 12.5mm</p><div></div>

[chris_bradley4]

<p>Thanks guys, I have just been offered another lens that had been dropped and rendered inoperable. Hopefully I will be able to make a good lens from two duff ones. I was surprised to see a simple coil spring used for this purpose however. I suppose there is not a lot of room for much else. Once again I appreciate your help and hope I never need to trouble you again. Unless of course I cannot manage to put the PD prism finder back together which is lying in bits on my desk at the moment. Best Wishes, Chris</p>

 

[b_m5]

<p>Hey,<br>

I have Mamiya 45mm 2.8 lens that has sticky aperture (just as discussed here). I was able to remove the rear element easily. However, I cannot see how to remove the front element. Could somebody help with this?</p>

<p>Furthermore, the focussing does not go beyond 1m or so- it seems stuck internally. Where should I start?</p>