Cleaning rear element on Pentax-110 70mm f2.8

[KingRoach]

Hello.

As per title, I have a Pentax-110 70mm f2.8 lens with some drops formed on the inside of the rear element.
For the life of me I could not figure out how to remove that element for cleaning. The holding ring does not have the usual two notches where you can use a spanner.

Anybody has any idea? Maybe it's glued? If so, should I try with some... WD-40?

Advice on a complete disassembly of the lens might also help because I could not find any screws so cannot access the element from the other end. The only currently-removable element I can see is the front element's holding ring with its two spanner notches, but I can clearly see a drop of glue holding it in place.. but at least I know what's going on here.

Thanks for reading. Waiting for your advice.

Best regards


UPDATE Issue solved. I've posted pictures below and also wrote about it HERE

http://photographeronbudget.blogspot.co.uk/2013/12/cleaning-rear-element-on-pentax-110.html

Hope this is of help to anyone. Share your thoughts.

[Attila]

Welcome, if not get any answer that is not means we are not a friendly community, enjoy your stay!

[KingRoach]

[Lloydy]

Don't use WD40, it WILL creep and leave an oily deposit everywhere. And definitely don't spray it from an aerosol can!

If you need to get something into the threads use a wooden toothpick and dip it in some Zippo lighter fuel then carefully drip the fuel along the thread. I sometimes use a very fine artists brush dipped in fuel as well.

Some lenses have the rear elements together in a short tube with a flange - the flange will be towards the inside of the lens and possibly only accessible when the mount ring is removed. If it's the flange mounted type then the screws should be visible.
Once the tube is out, it might / should / maybe will unscrew by hand?

I've had lenses with that arrangement, but I've not had the lens you want to dismantle.

[KingRoach]

[Lloydy]

In this topic on the PhotoNet forums Hin Man is talking about modifying the iris on 110 lenses, he's all over the internet so he might be worth chasing for some ideas.

http://photo.net/pentax-camera-forum/00a8nv



.

[KingRoach]

I got it. Lens disassembled and cleaned. It was just silly me forgetting there are three screws under the rubber focusing ring (I knew they were there but completely dismissed them because I wanted the rear mount, and the middle of the lens did not seem like a good place to start, but what do you know, they were the only screws there are).

I will post pictures maybe tomorrow for everybody's information and to help anyone who wants to disassemble this lens. I know this will be the first input on this lens's disassembly online.

I could see from the inside how beautiful this lens really is.

[philslizzy]

yay well done!

[KingRoach]

I'm back, with some photos to show the lens disassembled. It's a very easy process really. You'll need a very fine straight screw driver only.

This is the lens in question: Pentax 70mm f2.8 for Pentax 110 SLR system. This lens has no aperture diaphragm, only constant f2.8. The aperture in this system resides in the camera body and has only two values depending on how much light there is.



I needed to clean the rear element, but there is absolutely nothing to access on the rear end. No screws, no notches, nothing. The only three screws holding this lens together are the ones right under the rubber focusing ring.




Once you remove the three little screws, the whole assembly can then be unscrewed. Basically, you have the front elements' cone-shaped group, and the rear group which is screwed to the rear mount from the inside. Between them the ring with the focusing distance markings also functions as a limiter so you do not turn beyond infinity or under 1.5m. Unscrew the whole thing and be careful because the threads are well greased so do not touch them to the glass of the rear group. Once unscrewed, you can turn the rear group to unscrew it from the rear mount. This is what you should end up with.



From left to right: rear cap, rear mount, rear group, focus markings and limiter, front group, front cap.



The part which I needed to clean was the inner face of the rear-most element so I need to unscrew the rear ring holding that element from the rear group. See how beautiful the glass of this group looks from the inside.



And this is the ring I need to unscrew. Rear element already has my fingerprints at this stage so be careful with yours.



This ring is also difficult to turn. Even though I unscrewed it, but I still could not tell whether it was glued or just tight to turn. I used an ever so slight dab of WD-40 on a cotton bud to swipe the sides of the ring, making sure the fluid touches the inside but also that it's never enough for the substance to run. This is because I am worried about using this material near coated lenses.

I waited until the next morning and still couldn't turn it. These things are said to be so thin than when you press with your two fingers as you turn them, you actually twist the thing and make it hold faster in place. The only solution is to use a kind of spanner or a round cap or anything that turns the circles from many sides at once.

Well... this is not how I did it. I was preparing to do that, so I cut many pieces of electrical tape, in order to create a thickness that would reside between the ring and whatever I use to turn it (the plan was to use a whiteboard marker's cap since the size was good) but then I turned it with my fingers and with all the tape helping, it worked.

Here's the removed ring. The rear glass element is already removed in this picture.



You should be able to see the layer of black electrical tape that helped me span the ring out of place.



And here's the rear element. Notice that it is, after all, two optical elements glued together. All the more reason for you not to use any material like WD-40 near these things.



The rear element has been cleaned, put back in place and the whole thing was screwed back together. Again, be careful not to touch any of the internal glass, protect it from dust at all times, and BE CAREFUL when you put it all together not to touch the grease on the internal threads with the glass of the rear group.

Last but not least, it is ideal if you can put it back just as it was, so you can pay attention to the marks left by the three little screws and alight them right, but more important is getting the focusing distance right.

So screw the whole thing all the way in and use the distance marker to alight with infinity, mount it on your Pentax 110 camera body, hold the whole thing in place with the distance marker aligned to your screws positions, turn the whole thing back to 1.5m and look through the viewfinder to verify that the focal plane is indeed 1.5m away. Use measuring tape or whatever.

This insures you are as close as possible to the right assembly. Put one screw in, use the other two holes to alight with screw marks, tighten it, then put the other screws back in. Now put the rubber ring back in place and the lens is good as new.

And here it is on my DiY-gripped EOS-M using my own DiY Pentax 110-EOS adapter.



Let me know what you think. (and where to upload the pictures other than my DropBox. I want a permanent service in case I leave them there forever).

[KingRoach]

It's here now:

http://photographeronbudget.blogspot.co.uk/2013/12/cleaning-rear-element-on-pentax-110.html

[Lloydy]

Excellent, I like the blog as well.

[philslizzy]

A fantastic tutorial. Not one I can ever imagine using but one that needs to be there for many other people with the same problem.

If you upload yer pix to this forum they will stay here and if the title of the thread is good enough it will be easy to find on google even in years to come!