Heat resistant collecting lenses for Zeiss?

[PeteM]

I've got an older Zeiss phase contrast scope with a fractured collector lens (the one right next to the 100 watt halogen lamp). The 12v 100w lamp housing is the older cylindrical housng one, sort of like a top hat with a dovetail connection coming out the side.

The cracked lens looks to be a plano convex about 25mm diameter and perhaps a bit less than 25mm in focal length. Don't want to spend too much fixing this up. Does anyone know:

1) An OEM Zeiss spae parts source for the lens?

2) What glass spec (I presume some sort of boroslicate) would be best to avoid having a replacement shatter from thermal shock as well if I source from, say, Edmund?

3) Can I assume the newer square 100 watt housings will fit? Male dovetail attachment on mine is about 43.4mm The newer square ones look to have better bulb mounts.

4) Are lens thermal failures in this older design so common I should just convert this to LED?

[PeteM]

Aiming to answer my own question - a guess is that I want a glass with both high transmittance (low heat input) and a low coefficient of thermal expansion. Anyone know otherwise or have Zeiss specific info?

https://www.edmundoptics.com/knowledge- ... cal-glass/

[hans]

If thermal stress was a concern, in addition to choosing glass with appropriate characteristics, possibly the original lens could have been tempered? (Not sure if tempering is feasible with a lens but I mention it because heat-absorbing filters are sometimes tempered.)

[PeteM]

Perhaps. The cracks, though, weren't typical of tempered glass. I've solved the problem, for now, by adapting an Olympus (I think) collector lens.

Does anyone know if the newer 100 watt Zeiss lamp housings also have the approx 43.4mm dovetail fitting?

[Charles]

Pete,

The fittings are the same for round or square 12V 100W lamp house and are interchangeable. The round lamp house seems to get a lot hotter than the square ones.

[PeteM]

Charles - thanks very much.