160mm F -12 R30 or a 150mm R -12 R30

[dan]

From Ales post on 2sept15 at 8:16pm

we offered long focus modified Franuhofer OTAs in the past but there was virtually no interest from customers. We sold only 8pc of 150 F15 OTAs so I decided to discontinue this model about 2 years ago. We sell much more 150 F15 lenses than complete scopes.

Still, there is no such thing as high quality telescope for cheap price. Even if we offer a standard achromat in all CNC made, lightweight OTA, the price will still be around 2,000 dollars. This is the simple reason why most buyers go for inexpensive, mass produced Asian refractors. 

Regardless of this, we will redesign the older achromatic doublets, implement a different flint glass for better false color correction and offer 150mm or 160mm F12 OTA in the future, most likely by end of 2016. 

You guys can give me feedback about which model would you like to see and I will gladly consider your inputs!

Read more: istarscopeclub.proboards.com/thread/677/204-f12-r35#ixzz4K0TvTvYF


Ok, the 160mm at F -12 R-30 (or 150mm) would be about the longest OTA i could transport to a Star Party. I see the possibility of a 180mm F-10, but I think the sweet spot is the 160mm (I might consider that 180mm though if the cell didn't cost too much - same  mm FL).   As mentioned last fall in the older post dates for availability  "MOST LIKELY THE END OF 2016"  any updates on possibilities?

I  have completed a 7 inch  carbon tube and focuser end with focuser so it is time to find a quality lens cell. 

- Dan - 

[dan]

I see on the scope club under apos and super apos thread a July 5 of 2015 3:06pm ales posted in "New 160mm Ff8 and 180mm F/9 Semi APO DOUBLETS" comments on possibilities of interesting scopes. In particular the 160mm F/11 is most appealing.

My personal thoughts are for a doublet (less front end weight, less surfaces to figure or cause problems, less critical lens centering - 2 verses 3 to align, less cost) and a size that can be transported to star party events with a reasonable setup effort. Minimum aperture of 150mm (160mm very appealing), and a focal length maximum of 1800mm, minimum 1500mm (easy power, less critical focus depth, flatter feild for photography). Also the Focal ratio should be at least 10 to 12 for less CA.

A 160mm F/11 at 1760mm fl would be right on the spot. A 150mm F/12 at 1800mm fl would be ok (or even an F/10 if the CA could be minimized), but the 160mm F/11 is very appealing (most appealing to me).

Some type of ED glass combination at least to R-35, but even better would be nice.

What do you think is really possible?

[dan]

Also mentioned in the 5 July 15 post are a 180mm F/9 at 1620mm fl (within my target max length) and a 160mm F/8 at 1280mm.

The 180mm F/9 is pushing the weight of a CGEM-DX, but the fl is not too bad.

The 160mm F/8 has some appeal but, CA is probably more than an F/11. The post says it would be better than the R-35 anastigmat. The advantage of the F/8 is a shorter tube (less torque on the mount) and maybe a retrofit market for all those Celestron 6 inch F/8's out there.

[Ales - iStar Optical]

Hello Dan,
I just compared spot diagrams of 180 F9 and 180 F11. The F11 version is really approaching APO very nicely and I would expect slight bluish halo around bright stars only. Also, this doublet can produce a nice flat field over APS format chip and even at full frame the stars would not be overly distorted towards the corners of the image. I will leave this decision up to you guys. If I go for 180 I would much rather stick with F11 to tell you the truth. I think that even at F11 the tube length would be manageable, so would the weight. We would produce a new style design which would keep the weight down and making the scope much less front heavy. So everyone keep me posted about your requirements and I will decide which one to produce after I gather individual feedbacks from people interested in such instrument or lens.

[Ales - iStar Optical]

Hello again Dan,
yes, the 160 F11 also produced a very nice spot, tight with only small single color halo around bright stars. If produced properly, these lenses could be ideal for high resolution planetary, Moon and brighter deep space objects observing. So let me know what would be the ideal configuration for you and I will take it in serious consideration.

This is the first time we would use this non standard ED glass. I have no clue what to expect, really. I sure hope we can grind and polish good lenses out of this and if so, the finished results could be great. But on the other hand, it could turn into a complete disaster and whole project would be scrapped. So bear with me guys...

after we decide which scope to produce I will start taking pre-orders. If I get at least 3 people interested, we would go ahead and produce the lens and later on a complete OTA.

[Ales - iStar Optical]

Hello Don and everyone,
I looked into older production quotes and I think we can offer 180mm F11 or 180mm F9 lens in cell in 4000 dollar range. Complete OTA without focuser and rings would be about 1100 dollars more, possibly little less, not sure at this point. Lens cells would no longer be push-pull style but rather a slim cell, precision CNC machine without need of collimation. But 6 sets of screws would allow for more precision centering of each element and one could also turn the rear element to achieve the most ideal image quality, than lock in place.
160mm ED semi APO doublets would be in 3500 range.
These are rough estimates.
Let me know if you are still interested. I do not believe there is 180 F11 at this price range on the market but I could be wrong. There are other small lens makers possibly producing similar lenses.

So please keep me posted about your thoughts and decisions and I will do my best to produce one of these Semi APO doublets when ever Im Ok health-wise and back on track financially. Paying cash for all these medical procedures and surgeries is really making my life miserable and my budget tight...

[nobody]

Not wishing to be a total party pooper but even an f/11 7" [180mm] ED/ Semi-Apo is a very serious lump of OTA.
It is only about 7" shorter than my 180mm f/12 R35. Or about the length of the focuser short of 8'. 

I am busy building a massive, 2" shaft mounting to replace the totally inadequate, 1.25" shaft, 100lb vintage mounting I had been planning to use.
This oversized mounting [by modern Chinese standards] sits on a massive, welded steel pier and it still couldn't cope with the 7"!

However desirable a 7" long focus ED-Semi-Apo might seem on paper it still has to be carried about and mounted by the owner.

Ales has already mentioned how few "classical" [long focal length] achromats he has managed to sell.
It is not for nothing that long focus refractors are commercially unpopular.
Probably because there is no remotely affordable, remotely adequate mounting to hang them on!

No affordable, suitably tall tripod/pier is available either.
Not if you have any interest in any object much over 30 degree altitude.

They couldn't even mount the dinky little 6" f/8 refractors and do a half decent job of it!
Now add another 4-5' of 8" main tube and a 10" diameter dewshield a good couple of feet longer!

Just as a bit of friendly advice I have posted about the problems of managing larger refractors on my blog.
I wanted a 7" for bragging rights over a 6" and a long focus before I became too old to safely manage it.
I am remarkably fit for my age but still seriously struggle with the 50lb OTA.
In retrospect this lens was a huge and expensive mistake:
But I shall press on with the huge and several hundred pound mounting.
There is nothing quite like a big refractor pointing purposefully up at the sky!

fullerscopes.blogspot.dk/2016/09/warning-sheer-size-and-weight-of-7-f12.html

PS: If you want to sell more bigger and longer lenses, Ales, fit them all with rotary bayonet, cell-countercell mountings.

I found being able to remove the lens in seconds without needing re-collimation is a huge advantage.
It saves carrying and lifting an extra 10lbs minimum when handling the OTA.
It greatly reduces the fragility and value of the complete OTA when carrying it in and out of doors and storing it.
The OTA can even be covered and left outside on a permanent pier without worrying about the precious objective.
Or the OTA can be stood up on its nose for a tiny storage footprint until needed.
The lens can be kept safely indoors where it won't be endlessly troubled by dew, insects and dust.

Chris

[dan]

Sept 17, 2016 8:10:38 GMT -5 Ales - iStar Optical said:

Hello Dan,
I just compared spot diagrams of 180 F9 and 180 F11. The F11 version is really approaching APO very nicely and I would expect slight bluish halo around bright stars only. Also, this doublet can produce a nice flat field over APS format chip and even at full frame the stars would not be overly distorted towards the corners of the image. I will leave this decision up to you guys. If I go for 180 I would much rather stick with F11 to tell you the truth. I think that even at F11 the tube length would be manageable, so would the weight. We would produce a new style design which would keep the weight down and making the scope much less front heavy. So everyone keep me posted about your requirements and I will decide which one to produce after I gather individual feedbacks from people interested in such instrument or lens.

Ales,  yes the F-11 180mm would be a wonderful telescope. But I have to agree with "nobody" below about the size and necessary mega mount. And if you look at his picture showing the mount on wheels it is a basic work of beauty. His quote about bragging rights over just one more inch I can actually feel the draw, but I think this size scope really needs its own mini observatory  and even though it would be a great scope I think to be portable for a star party the 160mm F - 11 is the better choice for me. I would like to  see about 1600mm plus or minus a bit and not more than 1800mm FL nor less than 1500mm FL to keep the OTA length manageable and still have good CA control. Considering that I will be using a CGEM-DX with a 12 inch extension. I think the 160mm F - 9 while a good length may be greatly out performed by the F -11. Ideally a F - 10  could be a good compromise,  but that would depend upon how much better the F -11 would be as to an F - 10.  Could a F - 10 be a possibility and how would it theoretically perform between the  F -9  and the F -11 ???   - Dan - 

[dan]

Sept 22, 2016 15:20:10 GMT -5 dan said:

Sept 17, 2016 8:10:38 GMT -5 Ales - iStar Optical said:

Hello Dan,
I just compared spot diagrams of 180 F9 and 180 F11. The F11 version is really approaching APO very nicely and I would expect slight bluish halo around bright stars only. Also, this doublet can produce a nice flat field over APS format chip and even at full frame the stars would not be overly distorted towards the corners of the image. I will leave this decision up to you guys. If I go for 180 I would much rather stick with F11 to tell you the truth. I think that even at F11 the tube length would be manageable, so would the weight. We would produce a new style design which would keep the weight down and making the scope much less front heavy. So everyone keep me posted about your requirements and I will decide which one to produce after I gather individual feedbacks from people interested in such instrument or lens.

Ales,  yes the F-11 180mm would be a wonderful telescope. But I have to agree with "nobody" below about the size and necessary mega mount. And if you look at his picture showing the mount on wheels it is a basic work of beauty. His quote about bragging rights over just one more inch I can actually feel the draw, but I think this size scope really needs its own mini observatory  and even though it would be a great scope I think to be portable for a star party the 160mm F - 11 is the better choice for me. I would like to  see about 1600mm plus or minus a bit and not more than 1800mm FL nor less than 1500mm FL to keep the OTA length manageable and still have good CA control. Considering that I will be using a CGEM-DX with a 12 inch extension. I think the 160mm F - 9 while a good length may be greatly out performed by the F -11. Ideally a F - 10  could be a good compromise,  but that would depend upon how much better the F -11 would be as to an F - 10.  Could a F - 10 be a possibility and how would it theoretically perform between the  F -9  and the F -11   - Dan - 

Ales,  I have returned from work offshore.  ready for updates.

[dan]

Still following this thread, any updates?

[Ales - iStar Optical]

We stopped production of OTAs about one year ago. I am seriously considering the production of only 180mm F6 APO astrograph. This design was originally developed by ex-iStar optician Prof. Zdenek Rehor and recently redesigned by Mike Jones, ex-Lockheed Martin designer. This 180mm F6 is capable of good quality images wall beyond full frame. Price of this instrument could be in approx. $6,900 range.
I am not considering the production of additional OTAs at this time.