Cleaning MTO ZM-6A

[cihan]

Hi all,

I'm a real newbie both to the forum and photography, so I apologize for all the mistakes, lacking and misleading information I could give about the topic and questions in advance.

I have a Soviet MTO ZM-6A and I have mounted it on an EOS 20D. I use a EMF M42 to EOS adapter with AF confirmation from big_is with pin stop down flange. However it's impossible to screw in the lens inside the adapter completely since the lens hits the flash and I'm not using any extension tubes. I've screwed the lens inside the adapter 2,5 turns until the lens contacts the flash and I make sure the contact is tight enough not to let the lens turn freely or shake inside the adapter threads.

The problem is all the photos I shoot are never as sharp as the samples I've seen from the same lens mounted on different cameras. I made sure the sensor is clean at the %60 centre by taking sky photos with the broken EF-S 18-55 IS which cannot auto focus and has the aperture stucked at f/22 and examining carefully.

When I look inside the lens carefully under daylight at a certain very narrow angle and inspect the big mirror closer to the body when mounted, I see very fine dust specs around the outer part of the mirror. I can only see the dust on outer part since the light doesn't directly reflect on my eyes from the inner part of the mirror and it's possible to see the dust there. However I'm sure the same dust is there in the inner part too since the dust is spreaded homogeneusly and continuously from phi = 0 to 2 pi and r = (4r / 5) to r on the mirror.

I searched a lot to find a guide to clean the lens in English and quite a lot in Russian on google however I couldn't find any results.

As I've read, the thin dust particles on the mirror doesn't affect the photo quality at all and Maksutov-Cassegrain telescope users claim the same on telescope forums. So I've started to think if there's something worng with this lens. The lens seems so well cared for and I'm almost sure that it was never dropped down. I'm not sure if it's the dust causing this unsharpness since I've never had the opportunity to see photos from the same mirror lens when it was very clean and dirty.

So I'm asking for your opinions if I should clean the lens or wouldn't cleaning help at all?

Is it possible for the alignment of the mirrors and lens shift in time with usual usage and without dropping? Could rapid thermal changes cause shifting on the alignment of the mirrors?

I'll try to post samples from this lens to show the unsharp images and I'll try to shoot the dust particles on the mirror too.

Thanks in advance for all the replies and help.

[Attila]

Dust impact only picture quality if you can't see throw lens, and make pictures to contrast less , but not unsharp. If lens was cleaned and not properly build up, this is a possible reason why it is not sharp.

These lenses has lare diameter , usually works only on mirror less cameras or similar digital slr like Olympus E-300 (brick ) shape.

Can you lend from somebody a mirror less camera or E300 to try it out lens properly mounted ? Or with a film camera body ?

[cihan]

[Attila]

What you described as homogenous dust in English term people call 'haze' it can be impact contrast , but not sharpness.

I don't know any maksutov lens dissasemble guide. If you can't find in Google I am afraid you can't get much help

[cihan]

Ahh yes, it seems like haze however I can still select the very tiny dust particles too. Maybe the lens was used in extreme cold temperatures in Ukraine and then vapour was condensed on the mirror when it was brought indoors suddenly and little dust particles could have sticked on the mirror and they could have remained on the mirror after vapour on the mirror evaporated.

It seems like I'll try to take apart it myself after reading some other disassembly guides for general knowledge.

I can also prepare an explanatory guide with photos if I do it.

However I should find a substitution for spanner wrench first.

[Attila]

Before test it on other camera I don't think so good idea to open it with zero experience.

[cihan]

Thank you, I'll try to mount it on a film camera or micro four thirds however it doesn't seem possible now.
The only option seems like I can try it on a micro four thirds once Canon decides to launch one with EF mount at an electronics market
Maybe I can buy a 35mm SLR if I can find something cheap

By the way Jesito has cleaned fungus on a Samyang SP500 that had fungus on the glass holding the upper mirror and he has posted some images. I think I can see inside once I open the upper glass and I could borrow some little mirrors from a dentist friend to see inside. These 2 lenses look similar.

The sample I saw before was shot by a EOS 5D and I'm expecting similar results. Does it make sense if I try to mount it on a full frame EOS body? I know it sounds nonsense however the samples I saw from a 5D were much sharper.

[Attila]

I don't have experience with full frame cameras, sharpness is not sensor size depend I think.

[xjjohnno]

Is it possible you are not quite there with the focus, I have the 3M-6A and it is very unforgiving if you don't get the focus spot on.

[cihan]

I don't think that it's about focus since I've tried to take photos of both far field and near field with very small increments in focus however the best results were still unsharp. It is possible to read a text on a 30cmx40cm plate from 120m however the text is still never sharp. I don't have a quality tripod but the photos were shot indoors from window since there was no wind and I also used self timer and mirror lock up too.

@xjjohnno
Which body have you monted ZM-6A on ?

[martyn_bannister]

[cihan]

@Martyn
Thank you so much for your warning, I'll keep that in mind. I think I'll have to buy some tiny screwdrivers for those tiny screws.

[BETLOG]

You may actually want to disassemble the front element, however in my experience photographic catadioptrics are more easily disassembled by completely unscrewing the focus helix.
So: FYI:
On the ZM-6A there are two roughened grip surfaces about an inch wide that form two grip-strips around the circumference of the lens. One that is the focus dial, and another behind it that does not move. Between the two are the range digits and red triangle to indicate center. On the rear roughened section are 3 grub screws,radially around the lens diameter. There are also 3 smaller grub screws on the section of lens with the aforementioned range numbers. One of the grubs is immediately underneath the infinity symbol.
Loosening all 6 grub screws will allow the focus helix to simply unscrew completely off the lens. Thus 'breaking' the lens into two easy to manage parts.
Most cats seem to be designed similarly. The Sigma 600mm/8 for example; has a strip of clear tape underneath its rubberized grip that holds the lens together.

[Attila]