A question for all you optical gurus on the SM telescopes from FLO

[Alan White]

As per the title, A question for all you optical gurus on the Stella Maria telescopes from @FLO, but more so the doublet as that's what I know.
To be clear, 'this is asked from curiosity on the new glass combination' which by all accounts is superb and has no intent to be odd about this most interesting and equally curious scope for us visual observers, it's different, which is a good thing in my book.

What purpose does the 'Lanthanum' element play or bring to the party with the FPL53 ED element?
I ask in genuine curiosity as its a new glass combination to me as far as I know, or have i missed others done like this before?

The main second question is how much does the longer FL 800mm and ratio of f10 play in making a beautiful image here?

TIA for your replies folks.

 

[johninderby]

Lanthanum glass is supposed to reduce CA as it’s slightly yellowish tint helps cancel out any residual blue fringing. I belove Vixen uses Lanthanum as the mating element in their ED doublets. 

Longer focal lengths even in achros reduces CA and the longer focal length gives better depth of field. Comprimise is it does reduce fov a bit. Probably better suited to visual than AP though.

So far even with the limited observing time with mine have found this is one impressive scope. The optics are definately a step up from the old SW ED doublets. Just how much better will take more observing time to decide.

 

[mikeDnight]

A longer Focal length ED will theoretically be better able to control CA keeping the different wavelengths very tightly controlled. Much depends on glass types though. That will aid in giving a better over all image of extended objects such as the moon and planets, as well as producing very sharp star images. Not sure about lanthanum producing a yellow tint though? Vixen LV's and Pentax XW's have always appeared to give a Icey pure image to my eye, but I wore a dark green suit for a couple of years before others finally convinced me it was blue. 

[johninderby]

Came across the mention of Lanthanum glass having a slight yellowish tint in a discussion on CN.on mating elements used in doublets.

[Alan White]

@johninderby that is interesting about Lanthanum in Vixen ED scopes, I have a ED103s so that may be something I already experience already and explain the perceived improvement over my old SWED100.

[mikeDnight]

 To really experience the subtle differences, it would be nice to get half a half dozen top end apo's side by side, at a good site and over several nights having top class seeing and transparency.  That's wishful thinking I know!  Then of course there'd have to be a selection of top class eyepieces, at the very least three experienced planetary observers. After the initial compulsory star test, it's the planet's that will sift the wheat from the chaff with regard to how good the optics are. And as my choice, I'd like Jupiter or Saturn, or both to be high in the sky. With no domestic heat sources near by and a steady atmosphere each scope would be able to give of its best.                                                                                                                                                                                                                                           

 As for the choice of scopes, they would have to include an SW ED,  A Tak or Vixen fluorite, a Vixen ED and the rest I'd leave for others to decide. I'd like to see various focal ratio's in the mix. As a planetary observer, I'd be looking for the scope with the best definition as opposed to the best CA control. It would be good also if the scopes were all the same aperture, give or take 5mm or so. I suspect it won't be glass types or optical design, or even colour correction or focal length that will win the day, but the quality of the objective in terms of figure. 

You never know, we might all go away with a different refractor than the one we turned up with.

Edited February 6, 2020 by mikeDnight

[andrew s]

All these fancy glass types is to get round the inherent flaws in refractors 😊

Regards Andrew 

Edited February 7, 2020 by andrew s

[FLO]

6 minutes ago, andrew s said:

All these fancy glass types is to get round the inherent flaws in refractors 😊

You, sir, are a bad man 😄

Steve 

[Alan White]

3 hours ago, andrew s said:

All these fancy glass types is to get round the inherent flaws in refractors 😊

Regards Andrew 

A bit like the inherent flaws in reflectors and any other optical design I suppose 😝
 

[NGC 1502]

7 minutes ago, Alan White said:

A bit like the inherent flaws in reflectors and any other optical design I suppose 😝
 

Only way to sort this -  PISTOLS AT DAWN   😁

[andrew s]

11 minutes ago, Alan White said:

A bit like the inherent flaws in reflectors and any other optical design I suppose 😝
 

Not really you can coat almost any glass without its type have any effect. 😝🤪

Regards Andrew

[FLO]

7 minutes ago, andrew s said:

Not really you can coat almost any glass without its type have any effect. 😝🤪

You are opening a can of worms because a Newtonian mirrors glass type (think low expansion) together with its metallic and protective coating does have an affect. But I am guessing you already know that 😉 

Steve 

[johninderby]

23 minutes ago, NGC 1502 said:

Only way to sort this -  PISTOLS AT DAWN   😁

Yes indeed. 😁

[andrew s]

16 minutes ago, FLO said:

You are opening a can of worms because a Newtonian mirrors glass type (think low expansion) together with its metallic and protective coating does have an affect. But I am guessing you already know that 😉 

Steve 

Only intended as a little fun for a Friday afternoon!

Regards Andrew

[johninderby]

He, he 😁😁😁

[Alan White]

Did someone say a duel??  😉   Indeed Friday fun.

 

 

Edited February 7, 2020 by Alan White
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[mikeDnight]

4 hours ago, andrew s said:

Only intended as a little fun for a Friday afternoon!

Regards Andrew

I was wondering if you'd been on the Shandy Bass again Andrew?