Zeiss Standard failed field diaphragm

Have questions about the equipment used for macro- or micro- photography? Post those questions in this forum.

Moderators: rjlittlefield, ChrisR, Chris S., Pau

gpmatthews
Posts: 1040
Joined: Thu Aug 03, 2006 10:54 am
Location: Horsham, W. Sussex, UK
Contact:

Zeiss Standard failed field diaphragm

Post by gpmatthews »

One of my Zeiss Standards had a problem. I first noticed that when I closed the field diaphragm down for centreing the substage that the image of the field diaphragm aperture was not circular. It then became apparent that I had a loose diaphragm leaf, which entangled with the other leaves rendering the diaphragm inoperable.

I decided that as I had nothing to lose, I would attempt a repair.

There are three screws which hold the top of the assembly in place. I removed these and lifted off the top, revealing the leaves of the diaphragm.

When I lifted these out with a pair of forceps, it became apparent that they were all stuck together with a thin film of grease. So I cleaned them by swilling with a small amount of toluene (if you use this solvent, read the safety info, it is not the nicest stuff. It is, however, an excellent solvent for grease) and also cleaned the rest of the assembly to remove any grease, of which there was plenty.

One of the leaves was bent, but fortunately not badly kinked or creased, so I manually straightened this as best I could.

Re-assembly was extremely delicate. It is easy enough to start with and you can just lay the leaves in, overlapping them successively in the diaphragm fully open position. BUT you get to a point where the next leaf has to slide underneath the first you positioned and the next under the second you positioned and so on, with each having a pin at the far end that locates in a hole underneath the leaves already in place and is therefore unseen. Of the 13 leaves, there about 5 or 6 that had to be positioned blindly in this way.

Then, the final tricky bit, once all leaves are in place, is to place in position the top slotted driver plate ring, which has a lever which engages with the field aperture control ring. This was a nightmare to align because there always seem to be few slots that won't engage the upright pins on the diaphragm leaves.

Once re-assembled, however, my new clean field diaphragm operates with a delightful silky smooth action.

Normally, we are told, iris diaphragms are not lubricated, but that the surrounding parts, such as the manual control ring may be lightly greased. I have no reason to suspect that anyone had inadvisably lubricated this diaphragm, but I suspect with years of use, the grease had migrated onto the leaves and then, as grease does, become thicker and thicker until a leaf was dragged out of position by diaphragm use and the grease viscosity.

It seemed to me that in the sort of benign domestic environment I use my instruments in, there was no real need for any grease, so I am now using the whole assembly dry.

An interesting article on iris diaphragm repair can be found at http://www.microscopy-uk.org.uk/mag/ind ... -iris.html
Graham

Though we lean upon the same balustrade, the colours of the mountain are different.

g4lab
Posts: 1437
Joined: Fri May 23, 2008 11:07 am

Post by g4lab »

There are some expensive and difficult to find greases that wont oxidize and polymerize and become stiff. Teflon or synthetics the latter being easier to find.

I have some Zeiss teflon grease I use for some of these things. Made for SEM and TEM use and probably infinitely stable.

Just make sure there are no silicones in the formulation.

Dupont Krytox and Kel F are some of the names. You might find some synthetic grease at your local auto parts store that might be good to use.
I have enough varieties aroung that I haven't tried synthetic automotive grease but if the experiences I have had with synthetic oils are any indication
they ought to be great.

Charles Krebs
Posts: 5865
Joined: Tue Aug 01, 2006 8:02 pm
Location: Issaquah, WA USA
Contact:

Post by Charles Krebs »

Good for you Graham...!!!

Over many years I've managed to put together a small collection of jars and plastic bags containing the parts of various "repair" projects :cry:

.... think I have one or two with diaphragm blades in them. ](*,)

Post Reply Previous topicNext topic