TMB Fluorite vs SD Objectives?

Markus,

Would you help me understand the difference between a Fluorite and an SD objective? I am sure it is quite simple; nonetheless, it is a mystery to me. As your table indicates, the 80mm objectives are Fluorite, but the others are SD. The real question, "Is there a difference in quality of image and contrast between the two types?"

TMB 80 f/6 triplet Fluorite
TMB 80 f/7.5 triplet Fluorite
TMB 4" f/8 triplet SD
TMB 4.1" f/6.2 triplet SD
TMB 4.5" f/7 Triplet SD
TMB 175 f/8 triplet SD
TMB 8" f/9 triplet SD
TMB 9" f/9 triplet SD
TMB 10" f/9 triplet SD

Many thanks,
David

Hi David,

I'm not Markus, but I've been researching the same thing over the last couple of days as I've been contemplating a TMB-105F/650.

Two articles I found helpful were

http://voltaire.csun.edu/tmb/definition.html
and
http://voltaire.csun.edu/roland/color.html

Of particular note was Roland's comment on visual use vs photographic use... I suppose we need to extend his list for triplet Super ED, with the Russian equivalent of FPL-53 class glass, which to quote Back (in another essay) "reduce
spherochromatism even further, and keep the design diffraction limited out to 10000A in the near infrared. " in the case of Roland's designs, and I suspect his own as well?

Appreciations to Robert Provin for putting together such a nice site. ( If you hunt around, you can find lots of interesting photos... )

Hope you find the site helpful and interesting!

Cheers and Great Viewing!

Karl

The SD are made by the glasmaking company who is monopolist and do not sell the Super ED, but they have no interested to make the small 80 mm. The second manufactor makes the 80 mm, since he could not get the Super ED he is using Fluorite, the final results are the same, just diffrent material is used

best wishes
Markus