Category Archives: Lenses

Cleaning the cat … 500mm reflex

I wanted to try out this oddity of a lens. I shoot a lot of wildlife, so a long focal length lens is handy. Even handier is a physically short and lightweight lens. I snagged this lens for a bit less than normal because there was obvious dust/stuff inside.

I first thought of just removing the front element by unscrewing the ring … but it would not budge. I checked the web, and others show a disassembly … Ok, doesn’t look that hard.

Tools – philiips screwdriver, cleaning stuff, and painters tape

First thing to do is get the tape out, set the lens to infinity focus and place a tape reference on the outside between outer focus ring and body.

TIP: try not to rotate anything during disassembly.

Next you need to take off the PCB board with the contacts. There are two screw holding it on and there is a spring underneath one side.

Next remove the screws from the mounting ring.

Pull off the mounting ring a bid and then maneuver the PCB through the hole to separate them.

The outer body is held on by the four screws.

Note that the PCB and chip are attached to this part, so try not to damage it … and it sits in a slotted area.

At this point you might want to get the tape out again and make more reference marks on any rotatable parts.

In order to remove this rotating focus collar you will need to remove some gears … make a tape reference to its position.

Tip: pull the lens while slowly unscrewing, and as soon as the two release place a tape marker. You’ll thank me when you put it back together.

Two screws hold the gears on.

Try not to lose any parts when you remove it … and also try to keep the lube.

Pull off the column.

Then just unscrew the two parts.

Clean up, and try not to scratch the mirrors.

 

 

Those tape marks will come in handy to make sure you correctly get the correct position of everything.

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Holy Schmidt-Spiegel Batman … its the Minolta 500mm reflex !!!

The Minolta Maxxum AF 500mm f/8 Relex lens was brought out in 1989, and is a Schmidt-Cassegrain catadioptric lens.

In 1672, Laurent Cassegrain designed a telescope using two mirrors to reflect incoming light to the eyepiece. This design corrected spherical aberrations and also made the telescope shorter. Later on the Catadioptric system was created, and his utilized both refraction and reflection … corrective lenses and mirrors.  In 1930 Bernhard Schmidt redesigned the mirror shape and added an aspherical lens to correct for coma, and astigmatism aberrations. The Schmidt-Cassegrain design is currently one of the most popular telescope design used today … and it also caused many camera lens manufacturers to use that also. Almost everybody made one (well not really), but Minolta was the only one to incorporate it into their Auto Focus system.

The Maxxum 500mm reflex is a stubby barrel of a lens. Due to the way it is designed it can produce donut or crescent shaped bokeh … which probably explains why this lens is not more popular. As I mentioned before, this is an AF lens which can support centre point focus … and since this is a gear driven lens, the body has a direct influence on AF speed. You’ve got one aperture size of f8 so it can cause the AF to hunt … IQ is pretty good on this lens … you just have to know how to work the bokeh … overall I really like this small handful lens.


Separation, leads to divorce, and a new coupling.

Sometimes you encounter a lens that has some internal blemishes that you cannot seem to clean off … can look like rainbow rings (ring of fire), a cloudy ring round the edge, a crescent beige tint, bubbles, or even a flowery/snowflake pattern … and it always seems like it’s trapped between two lens elements.

This old LTM lens has an almost complete ring haze. Now, it could possibly be just haze on the back of the element … but I suspected it was more than that.  After talking it apart it was apparent that it was separation of the front two elements.

Yes, in fact it is between two lens elements. Most lens designs require two lens elements to be bonded/cemented together (doublet) with adhesive to eliminate the glass air gap. By reducing exposed surfaces, cementing reduces refraction and ghost images from reflections, and allows the use of thinner flint elements. 

Older lenses used Canada Balsam as it had a high index of refraction, which is optically a good thing to have. It is derived from good ol Canadian trees … yup good ol sap … yes, its not just only for maple syrup.

Development of resins to cement elements started in 1785. Eventually changed to a synthetic resin because of WWII … high altitude aerial photography caused issues with Canada balsalm, so they developed a synthetic cement that could handle low and high temperatures … this is the MIL-A-3920 standard optical adhesive. UV curing adhesives appeared in 1966 to reduce the curing time for high production.

When the “cement” has degraded and no longer seals the two elements together, the separation will create artifacts that will change the refractive properties of the lens. Sometimes it is not very visually apparent … sometimes it is. The only real solution is to separate and re-cement them.

This topic has been discussed much on the web … FotomozaicLargeFormatForumskgrimes

With Canada balsam, it requires heating to soften the resin so the elements can be separated. The newer synthetic resins require special chemicals … and in some cases the elements cannot be separated without damaging it.

Once separated, new resin can be applied to cement the elements. Then new resin can be applied to cement the elements … modern day resins are UV cured, so makes it much quicker to get a lens back to working condition.

Sounds easy … not !!! Heating sometimes does not work, or even worse causes the element to crack … and there are cemented group that are encased in a metal sleeve which has to be removed first (without damaging the glass, and you may have to find something to replace it) … or, as mentioned before, it just doesn’t work.

One day I will make a serious attempt at re-cementing … meaning, my half-ass attempt sucked, and I will try again.

Summers Optical makes many different types of synthetic resins for optical cementing … and you can still buy Canada Balsam, as it is still used for microscopic slide mounting and painting.

Sometimes the lens separation is not so bad in terms of affecting the image, especially if it is around the edges like the lens pictured above … but when it sits right in the centre, it will most likely cause apparent visual effects. Mounting this lens on my Sony NEX-6 and taking some shots, I could not really notice it until I got some light hitting the front and the separation starts adding some flaring/fogging.


My latest victims …

The Yashica-MAT EM had been sitting on my workbench for the past two years … finally got assembled today. It came to me in rough shape, the focus knob was almost falling off, the winder was stuck, the shutter was jammed, broken screws, etc.

The only thing I could not fix was a glitch in the winder release mechanism … sometimes after winding the crank it will not complete, so you have to press the shutter button again to engage the winder release. Also I could not get into the light meter because all the screws were jammed. I don’t think I will continue to restore it with new leatherette, as I have grown weary of it.

The Canon IV sb with lens, was rusting all over … and I took the chance on buying it on the hopes the lens did not have haze/fungus.

The Canon IV sb and the Canon Serenar 50mm f/1.8 were a lot easier to handle. The IV sb needed a cleaning and removal of the top plate. Rusted/seized screws prevented me from going further, so I could not check the shutter for leaks.

The lens was completely disassembled and cleaned. The lens did not end up with any haze or fungus … but I did discover some decementing of the rear elements starting to occur.

 

The family of Yashica TLRs and Canon Barnack type rangefinders are all very similar in design, so if you have worked with one model the rest are almost the same … including lenses and shutters.

Well, my fixer upping will be going to slow down for a bit as it is becoming economically more difficult to get cameras … I will keep hunting for BB (broken bargains.)


Sony SAL16105 … DT 16-105mm f/3.5-5.6 lens

I don’t tend to work with modern lenses, but I got this one anyway just to work on something newer.

It was described as having a problem with the focusing. It could be used manually, but the auto focus had problems … I made a guess it was something stuck in the focus gears.

Should either be an easy fix … or something that I would need to replace part(s).

It turns out that it is was both ??

First is to remove the inner ring

Remove the two screws holding the contact pin pcb

Remove the three screws on the black ring

When pulling out the black ring you will have to maneuver around the pcb

Now you can remove the mounting ring.

Remove the four screws

Be careful will pulling off the ring as there are shims underneath it.

… also the screw drive pin may come off with the ring.

Gently take the shims out.

Do not bend the shims and keep them right side up.

Pull out the focus drive pin

The outer cover (the one with the orange ring) is held on by three screws. You will first need to pull off the rubber zoom grip. This should just slide off with a little work. It is held on by tension … there should be no adhesive.

Now you will see an area that has a metal plate

Underneath there is another place with mutliple contacts.

You really do not need to remove these … though you need to be aware of them as the thin metal can be bent easily when you put this back together.

Remove the three screws.

Pull off the outer cover.

Remove the three screws

There is one more thing that needs to be done in order to take this layer off.

On the sides of the lens you will see three long screws within slots. These are coupled to the inner zoom ring.

Unscrew and remove them.

You can now pull the assembly off gently as there is some metal contacts within.

Take the piece that you just removed … sadly, I am missing the picture I took of the inside … Look inside and you will find a ring that looks like this.

You can gently pull it out … note the contacts that are attached, try not to bend them too much.

As you can see from this image this ring is broken. This is called the focus differential ring.

The screw drive from the camera turns this ring. The protruding part couples with the focus cam, which moves the lens element group.

When the AF mechanism is engaged this ring will jam … which is why it was described that manual focusing worked.

OK. Now I just need to figure out how to fix it.

I tried a number of adhesive ideas, but they all failed … you can’t just plop a bunch of epoxy on it as it needs to fit back into the lens assembly … though it could also be because I am not the most knowledgeable person about using adhesives.

I gave up after a couple of weeks and ordered a $20 replacement part.

Getting back to the rest of the lens … you should now be left with this.

Since I was here, I decided to clean out the back to the lens assembly.

You can unscrew the rear element with a spanner wrench.

When putting the lens back together, remember that some of these components have metal contact arms … these do not like to be bent too much, and some have very thin fingers.

You will need to position the aperture arm and focus arm so that they fit the levers below.

When putting the lens mount ring back on you will need to use another screwdriver to align the holes in the shims.


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