127 F12 R30 Anastigmatic Doublet

[Mike]

Istar design and new glass combination allows 30% less chromatic aberration compared to most common doublets including the Fraunhofer design.

Lenses are hand figured and fully multicoated for excellent resolution that is suitable for lunar, planetary and brighter DSOs.

This one will be getting special mention but can't reveal by who yet

Price $427 US

Attachments:

[kitsch]

I ordered one about two months ago.
Ales said it would be about 60 days. so I'm chewing my nails waiting for news. Do you have any Mike?

[Mike]

Let me see what I can find out. Send me a private message with your full name etc.

[plyscope]

I ordered mine in early January and received it in mid April. I paid $462 plus shipping.

Andy

[istarmullet]

Is that going to be available in an OTA assembly? If yes, price and wait time por favor.

[Mike]

I am going to say that every lens that Istar makes is available in an OTA. In fact, there is going to be a lot of emphasis on complete scopes. We will always offer lenses only but a large market wants turn key. I will get an answer for you as far as price and turn around. What all do you want on the OTA. Focuser? Rings? Or just lens and tube?

[alcofribas]

Hello
I've just a question : what is the meaning of "anastigmatic" in this case ?
Does it mean "free of astigmatism" ?
I don't really understand how it is possible to have a significant reduction of the astigmatism for a thin doublet, as this depends on the position of the aperture stop.

[Mike]

Per Ales:

These lenses are now being produced in large numbers (for Istar), that is, 14 more sets. A few have already been produced and sold. So now, we have ordered tubes from Austria cut to size. We will produce scopes in about 4 month time and YES we will take pre-orders since we have a good idea about the final BARE OTA price which will be in 1149 dollar range.

[Mike]

Simple definition:
An Anastigmat or anastigmatic lens is a photographic lens completely corrected for spherical aberration, coma, and astigmatism.

Anastigmat is limited to a photographic lens. A wrong assumption. Since most articles people "google" refer to Anastigmat as Photographic lens this is where the idea comes from (usually 4 elements). Anastigmat is ANY lens (including a doublet) which corrects for astigmatism, coma and spherical aberration. Contrary to a classical Fraunhofer (Aplanat) which corrects only for coma and spherical aberration. More can be found in any serious book about optics and optical design.

Personally I have no idea why anyone would produce a Fraunhofer (the REAL Fraunhofer which is a glued doublet). Well, glued is not the right word but you get the point. Most well designed doublets, these days, SHOULD be Anastigmats.. and Istar is going that way. We will still produce modified Fraunhofers as they are cheaper by 30% and this is what many people prefer, price over performance.

[alcofribas]

I didn't make this assumption, but another one : for a thin component, such as a doublet, the astigmatism is cancelled by a large shift of the aperture stop => there should be little possible reduction of the astigmatism on a thin doublet if the aperture stop is on the doublet. This is confirmed in "Modern optical design", W. Smith.
The other thing is that with 4 surfaces, it seems to me that if the aperture stop is fixed on the lens, there are just enough degrees of freedom to correct spherical aberration and coma.
But my assumption that this doublet is thin may also be wrong.

Do you have a comparison of the astigmatism between this 127 F12 doublet and a same diameter/same aperture Fraunhofer doublet ? (values of S3 and S4 Seidel sums for example).
Is the astigmatism really cancelled, or just slightly reduced ?
Just for curiosity. Anyway, the astigmatism is small on any F12 doublet.

[Mike]

Hello, I am not ignoring your question I just don't have the figures I need for the 127 F12. I emailed our Optician. I will get back to you with the comparison ASAP. I am assuming you want to order the 127 R30?

[alcofribas]

Hello
It was just curiosity about the real meaning of "anastigmat" for this kind of lens (I already have a 150mm F12 standard achromat, and my next purchase will more probably be a larger aperture).
For a 127 mm F/12 thin doublet, with the aperture stop on the doublet, the low order ptv astigmatism is around 0.18*lambda = lambda/5.5 for a 0.5° field angle.

[Mike]

Alcofribas,
I think I may have forgotten what your original question was. You originally asked for a comparison between a Fraunhofer and our Anastigmatic. But then you sort of answered yourself with “Anyway, the astigmatism is small on any F12 doublet.” I did email our Master Optician for those figures as I thought it was going to help you with a purchasing decision. We only sell “modified” Fraunhofers anyway.
Because I supervised an optical laboratory for 17 years in Cincinnati, Ohio, I enjoy exercising optical semantics. However, since it requires long and late hours answering questions for current and potential Istar customers, I just don’t have time for that privilege. It is 11:35 PM and I still have many emails to go. I mean no disrespect. Maybe one of the other member would enjoy continuing this conversation. If you have a question to help you with selecting a product, be sure and post here again (In the “Ask Ales” section).

[alcofribas]

Hello

I am still interested in the real meaning of "anastigmat" for a thin doublet.
I'm very interested to see the aberrations curves of the "150mm F/5 Anastigmat", for example.
Not for purchase (at least for the moment), just a curiosity from an optical engineer.