ED 80mm - Confused???? Which one?

[chris lewis]

Hi - this may help.http://tech.groups.yahoo.com/group/S.../message/67874

[netwolf]

Paul, wonder over and join this yahoo group
http://tech.groups.yahoo.com/group/Stellarvue/
Indications from SV are that it is not from China. It is customer made for them to there spec and tested by them before its used.
Vic does indicate that no doublet under F9 unless its a very very well made Petzval or Triplet (from reputable sources) will not be 100% color free. The doublet however can be made very close to color free and thats what they have done with the NHNG.

Regards
Fahim

[chris lewis]

Apparently they use FK-51 Glass - which is similar to FPL-51 but has slightly better CA reduction. Reading more about this thou other factors have to be taken into account like the mating glass, optical polishing and quality of assembly. With these factors the differences between the glass types visually may not be so apparent. AP may be different. Schott FK51 has an Abbe number of ~84.FPL51 has an Abbe number of ~82.FPL53 has an Abbe number of ~95.(decimal values rounded for convenience)
The higher the Abbe the better. FPL-53 is similar to pure Fluourite glass but not as fragile..

[StarLane]

Thanks Chris and Fahim, Thats exactly the info I've been looking for.

Cheers.

[AstroJunk (Jonathan)]

Originally Posted by StarLane

Do you know are they made in USA or China/Taiwan etc??

I believe the objectives come from Russia. The European market sees most of the output from the former military optical works, TAL for eg. Lots of very capable optical workers were trained by the Soviet war machine and are producing some very nice bits of kit now that the cold war has thawed out a bit.

[kosh]

I will be looking for and 80mm spotting scope soon myself and I was thinking about the Meade 5000 series. APO Triplet with ED glass at F/6. Sounds good to me for about $799 from bintel. I haven't really seen it meantioned here. Does anyone know something about this scope that would put anyone off from buying one?

[chris lewis]

There are a few reviews filtering thru and they appear to be the 'equivalent' to they current crop of FPL-53 doublets in CA correction / images.
The use Hoya FCD-1 glass which is 'similar' to Ohara FPL- 51 in its Abbe value.
[The Abbe value is 81.6 for FPL-51 / Hoya FCD-1 glass. Schott FK-51 is 84. [ Night Hawk glass ]. FPL-52 is about 90 and FPL-53 has an Abbe value of 95 almost the same as pure Fluorite glass - the higher the Abbe value the less dispersion / CA - a minimum Abbe number of 80 is required for it to be called ED glass].
They make it a triplet to get the improved color correction but being a triplet the maching and tolerances have to be more exact.
Ohara FPL-53 gives 40% better color correction then the FPL-51 / Hoya glass but a triplet design should eliminate that somewhat. FPL-53 glass is 2-3 times more expensive then the FPL-51. Visually the differences are not so apparent. A.P maybe. The Bintel staff would have 'reviewed' them and should give you some honest feedback. The 127mm version is not being released by Meade.
http://www.astromart.com/articles/ar...article_id=534