I would normally avoid fluorite lenses as they are very prone to faults. They delaminate and it is impossible to clean the fluorite surface as it is soft. Fortunately, modern low dispersion glass formulations make fluorite obsolete. There was a time when some top end camera lenses also used fluorite elements, they tended to have short lifespans. The old Cooke is very rare not to have any optical deterioration that I can detect.

I have only tried it on my latest acquisition which I got by accident. An Olympus BHC. It had a start price of £120 and was being sold by a hospice charity near Swindon. They were reluctant to send it by post as it had failed PAT testing. I put in a higher bid expecting to get the ball rolling and turned out to be the only bidder. So I had a 122 mile drive to pick it up. A trinocular head, epi attachment, built in Kohler, a huge mechanical stage with 100mm movement in both axes. Also 5, 20, 40 and 100 parfocal MET plan objectives, all air gap in a five position turret. Two 10X wf eyepieces. And I already had an Olympus MET 10X which is parfocal with the others. It runs perfectly on LED lighting and I bought a biological mechanical stage which fits perfectly with a number of mods and interchanges with the original in seconds. The Biolam condensers fit, but the lighting system works very well without using one. The olympus 100 is 10mm longer than the 45 Cooke and the parfocal extender is needed to use it in its original form. If I fit it into a Vickers body with about 4mm spring movement, it can easily be that 10mm longer. I haven’t tried it in the Biolam R25 which will certainly have the greater movement.

In addition to that nice Cooke 45X, I also have a Cooke 95X NA 1.3 oil which also gives oustanding definition. The both are destined for fitting within the bodies of Vickers scrap objectives for making them sprung. I will be assembling a set of five to fit the Olympus BHC as follows.

Lomo 3.5 NA 0.1

Swift 10 NA 0.25

GS 25 NA not known

Cooke 45 NA 0.95 FL LWD oil

Cooke 95 NA 1.3 oil

I fancied getting a second nosepiece (turret) for the olympus but the prices of them was too high. Then a quintuple for the olympus BH2 came on ebay for a good price. They have a quick change wedge rather than the four screws for my older model. Close examination of the photographs comparing it to mine made me decide to take a chance and I got lucky, the wedge unscrews and then the only difference is the black plastic ring for turning the turret. Already having a full set of epi objectives on one turret and a full set of biological objectives on the other together with two lighting systems, both battery LED powered makes the Olympus the do everything microscope. I will have to think hard about my Lomo R25 and the Vickers M12.