How much Glass....

[FlashDrive (Poppy)]

I have a reasonable question to ask of those who have more experience than myself... when it comes to Refractors..

It's about how much ' glass ' in the optical path is ' BEST ' for ' visual 'use only.....forget Astro-Photography.

A ' doublet ' configuration or ' triplet ' ......and we are using either FPL-53 or Fluorite..... forget Achromats.

I know from reviews etc that ' triplets ' exhibit better colour correction or so we are told....but the more glass ( as some say ) only adds to ' more ' interference of the ' photons ' before it finally gets to the eyepiece.

or ....is this no big deal in the schemes of things for ' visual ' use....so do we make a choice ( budget depending) and go on our own instincts.

Col.....

[Derek Klepp]

Don'tnow if this is the answer you're looking fot Col but a few years back I took my now extinct Prostar 127mm APO with FPL 53 to Parkes to show my cousin the night sky he commented on how sharp the stars were and how crisp tyhe Globulars looked.
On a different note I was talking to my local camera store gut the other day and commenting on how sharp my 400mm f5.6L lense was compared to the 150-600 Tamron Zoom . His reply less glass and he,s a photo buff.
I also note that the 127 triplet and 100 Doublet have less colour fringing than my cheap 152mm f5 Petzvl
In the end as long as we're looking up I think thats a good thing regardless of the glass.
Cheers Derek

[casstony]

I read a comparison of an FS128 to a TSA120 where the reviewer concluded the scopes were equal in performance. Accurate figuring is probably more important than glass type.

[MortonH]

In reality there are too many other variables, such as figuring, etc as Tony says. However, I've read a number of posts over the years saying that doublets have a slight edge in contrast.

For example, the TV102 was considered better for planetary than the TV-101 (or maybe the NP-101) due to the fewer elements of glass.

This 'might' be a more valid comparison than the FS128 to TSA120 as the TV scopes were in production at the same time so 'presumably' would have been figured to the same standard and used the same quality of coatings, etc.

Then there are those who insist that you need real Calcium Fluorite, and some of the classic apo doublets use this glass. But how much do today's coatings, etc. compensate for, or even improve on, the best fluorite lenses? You can't just believe the marketing!

I think I'm glad I've never looked through a true apo. It might ruin me for my current scopes and I know a 5" Tak will never be in my budget.

[FlashDrive (Poppy)]

Thank You ... Derek / Tony / Morton for your inputs.
I do agree with the ' accurate figuring ' of the Lens....very very important.

Col