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Post by kevinbarker on Nov 16, 2012 2:45:39 GMT -5
I am emailing to introduce myself. My name is Kevin Barker and I am amateur astronomer who lives in Auckland, New Zealand. I am a big fan of refractor telescopes and today I ordered a big 180 f-8 anastigmatic lens. My intention is to make an ota. This is not the first time I have made a big refractor, along with help from my twin brother I have made about 15 years ago a 6 inch f-12 D&G. Great scope it was too but i sold it when moving to Auckland when I had briefly two Zeiss APQ scopes.(I currently own a 130) I have also made a couple of simple wooden achromat scopes including a 5 inch f 6.5 and more recently a 4 inch f-6. My twin has just finished a 127/1200 ota from a surplus shed lens. It performs well for a cheap lens. I am assuming the Istar anastigmatic scopes are a short flint design, maybe steinheil type?? I have a small Steinheil type Zeiss AS 80/840, Zeiss lens from the 1950's or 60's and a home made turned metal ota. (See attached jpeg. we were observing the recent partial eclipse at the school where I work) This probably also accounts for their relatively large mass. I have a friend in the US who has an AS 150/2250 which I have seen through. It was pretty impressive although very long. I rather like the design and manufacture of a 5 inch f-12 ota made by an Australian Andy Jackson recently and earlier Don Abbe another Australian. I am considering making a light but strong ota and alt az mount like this with marine ply but may also consider using metal. The D&G tube I made was made from irrigation tube, it was around 14-15 kg in mass. The images were pretty darn good, in fact excellent. On deep sky it really produced "WOW" views. I like a project, time will tell if this lens will be too big to mount simply!!!! Attachments:
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Post by Ales - iStar Optical on Nov 16, 2012 5:20:36 GMT -5
Hello Kevin, and welcome to Istar Scope Club! Im happy to see the family of Istar Scope owners to grow rapidly. Your choice of 180 F8 R30 doublet is a good one. This scope will perform as F10,4 classic achromat so the chromatic aberration is still visible but not too bothersome. Also, once we are done with first Raycor CA correctors, you will be able to achieve near APO performance with your doublet. At this moment our design is evaluated by several old school opticians from Zeiss and Meopta and if they give our design OK, it will go straight to production. So your choice is a wise one and Im sure that you will be happy with your 180mm doublet. I talked to Mike last night of CET and he mentioned another buyer ordering 250 F11 R30 (same lens Mike Carman got few months ago.. and being a happy camper claiming that he never saw a better star and planet images ever in his live thru any scope...) So Im so happy to see that more and more of the special R30 anastigmats are being introduced to the market. My own plan is to build 180 F8 R30 OTA for our upcoming public observatory in N. Arizona as well as the 250 F11 R30. This 10" refractor will require a serious mount.. but it will be the ultimate instrument for people to look thru. On other hand the 180 F8 is still compact enough to put in back of my car and drive to the dark sites around S. Utah or some local star parties. So thank you for becoming a new mamber of our growing family of refractor fans and keep everyone posted about news from your wonderful country. Some more pictures would be greatly appreciated! cheers, Ales
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Post by Ales - iStar Optical on Nov 16, 2012 5:25:34 GMT -5
and YES. the R30 doublets are designed around couple of different short flint glass types and a high quality crowns. Each design is a little different but we do not use the original Steinheil design at this moment. We did manufacture few of these two years ago but than we went back to classic "crown first". But this does not mean that we wont experiment with Steinheil further. Playing with different designs is both fun and rewarding. And yes, our R30 doublets are very thick and massive.. therefore heavy.. but the image improvement over classic achromat is well worth the extra weight. Anyone who looked thru one of our R30 lenes will agree with me. cheers Ales
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Post by kevinbarker on Nov 16, 2012 14:01:31 GMT -5
HI Matt I saw a post recently about the mount you restored, it looks beautiful. And the big achromat looks great on top of it.
A few years ago my brother and a few other members of the Canterbury Astro Society restored an old 5 inch Cooke telescope. They used the original pier and mounted the scope on top but used a more modern mount. Unfortunately RASNZ claimed the scope back a few years later and I believe it is now mounted in Wellington.
I have a couple of Zeiss mounts, one a 1b and another a T mount.
I did consider the 6 inch achromat, but went for aperture. I think the colour correction would be similar to what the R30 180 might deliver. 10/0.150 is about the same as 10.4/0.180
Personally I do not mind a bit of Ca for visual use, if I want colour perfection I use my Zeiss APQ.
I have attached a shot of a simple 100/600 achromat, A cheap lens made as a X mas present for a niece and nephew. It is made from scrap ply and some rafting timber I scavenged off a builder friend. A simple 50 mm elliptical secondary mounted on a 40 mm broom stick. It is really only good up to about 80 X and has a bit of SA.
Having said that it is lovely to use. I painted it red and white with left over paint, last week we used this scope and my AS80/840 to show 6-700 people the solar eclipse from Auckland(87%)
Kevin Barker
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Post by kevinbarker on Nov 16, 2012 14:02:56 GMT -5
Home made 4 inch Achromat. Attachments:
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Post by kevinbarker on Nov 16, 2012 14:17:23 GMT -5
Hi Ales Thank you for the reply. As I live in a city I am hoping to make the ota so that it can fit into our Toyota Corolla Station Wagon!!!!
Will the 180 use the same glass types as the R30 127 and 150 or perhaps the same as the 250 ??
I recall the reason for Steinheil designs is to protect easily weathered glasses. I guess with modern hard coatings this is not such an issue nowadays. Steinheil's also end up with very pronounced curves(short R's) which must be a challenge to produce.
I think the older Takahashi Fluorites may have used flint first designs??
As soon as you know the dimensions and mass of the lens I have ordered do let me know so I can start on an ota.
Kevin Barker
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Post by Ales - iStar Optical on Nov 18, 2012 11:19:00 GMT -5
Dear Kevin, well, 180 F8 will be approx. 1510mm including the 350mm dew shield. Without dew shield subtract 350mm. The 150 F8 is approx. 930mm without dew shield. You must decide. Regarding materials, we use several different glass types, each one of these R30 doublets uses a slightly different one. For example 250 F11 R30 and 150 F5 R30 use same glass combination but 150 F8 R30 has a different flint, 127 F8 has a differnet crown AND flint etc.. but overall they all perform at R30 to R35 ratio. We are playing around with yet another short flint design using thin element doublet but so far we were not able to achieve current level of optical performance as weith the thick, heavy doublets currently in production. Also the thin doublets would be more expensive since the special flint cost more than the one we use in thick doublets... Your info about Steinheil is kind of mixed up to my own best knowledge. You always try to hide flint (in the history since most of modern flints are stable) behind the crown. Best way is to simply put unstable flint in between two crowns like in most CaF2 designs. The Fluorite is playing a role of Flint.. so putting the flint first would actually make no sense if you know what I mean. These days the Steinheil is nice to play with but you dont realyl need this design... since the optical glass types advanced greatly. I hope that my reply make sense, be well, talk to you soon, cheers, Ales
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Post by kevinbarker on Nov 18, 2012 13:22:18 GMT -5
Thank you Ales I always thought of CaF2 as being a crown glass in a doublet. It has a low refractive index and a very high Abbe number. But I guess in triplet's it is not quite so simple. In fact lens design is pretty complex Still it is fun trying to figure out the maths etc
I have a popular book on telescope optics (Rutten and van Venroijj) which I enjoy reading!! In it the authors describe the Fraunhofer doublet as having a positive crown at front and a negative flint at rear. In the Steinheil the negative element is the front lens and the positive element at the rear. It then quotes " The Steinheil design is used when it offers better correction of aberrations or when the positive element has poor resistance to weathering(as fluorite does). However , because it has stronger curves, it is seldom used unless necessary..."
When making the metal counter cell for my wee Zeiss AS80/840 I had to remove the elements. This was so the glass was not damaged when trying the threads etc I recall that yes the flint was first. I must say the lens is very heavy for such a small aperture. That is where my comment on mass came from.
Surprisingly my Zeiss APQ 130 triplet lens is quite light(around 2.2 kg) I believe the AS doublet would be more massive perhaps around 3 kg. A Fraunhofer doublet of this aperture might be well under 2 kg depending on the type of lens cell.
Thank you for the reply
best
Kevin
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Post by bn1777 on Dec 23, 2012 17:15:50 GMT -5
Hi Kevin , as an x-pat Kiwi now working in Australia and an Istar127mm f/8 achro owner I can tell you that these Istar lenses are really , really good . I finished my build a couple of weeks ago and have used it a lot and like the views , nice lense. And Hi Matt , I finally joined . I will post my own thread when I sort out how . Brian.( Darwin )
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Post by kevinbarker on Dec 24, 2012 2:47:53 GMT -5
Hi Brian The scope looks great, I had heard from Gary Beal you were an astronomer in darwin.
I was in Darwin briefly this year before and after observing the Venus transit. I bet it is hot there at present.
if you are ever in Auckland let me know.
I'd be interested in your observational reports and also comments on how the new lens performs on the stars.
I have always been amazed at how well a 5 inch lens can work on deep sky and planets etc.
best wishes
Kevin
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Post by bn1777 on Dec 24, 2012 20:03:13 GMT -5
I will definatly do that Kevin , next time I am in NZ , On Gary Beal I have known him for a long time , he is a great guy . We have observed together at the Auckland astro societys dark sky weekends at Waharau , thats a good weekend . I normally came down from Whangarei with Maree , she has a C11 and ed80 . Cheers mate and I will do a report here when the weather clears here , its the middle of the wet season and only 35degrees and 89% humidity , good telescope making and beer drinking weather , thats about all . I have a Zeiss as well as 3 Takasahi's , and my Istar fits in with these very well . A bit of a scopeaholic I'm afraid ? Brian.
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