Istar 228 mm f7.7 build

[Viktor Z.]

My story started with a 6" Istar refractor and my great satisfaction with its excellent optics. It slowly started to blend with growing and growing aperture fever and a desire to build another telescope. I was really contemplating to either make a 10" to 12" Dobsonian that I can still handle or choose a large achro that may be less portable but wihout central obstruction.

My trust in Istar's optical quailty and love of refractors made me choose and purchase an Istar 228 mm f7.7 achromatic lens. Why did I choose this optics? Because I needed a short focal length system so that the telescope is portable enough for observing away from home under dark skies. Mike assured me that the optical quailty of this lens is of high standards of manufacturing as per Istar's high quality production requirements. The lens became available for me very soon: it was ready to ship only after three months wait. However, I asked for a much later delivery, since my situation about moving to a new place. This request was granted, and the lens have arrived in August. The lens arrived very well packaged, in two boxes for good, because the outer box was damaged during shipping. But inside the damaged box, the other smaller box with the lens remained impaccable.



The 228 mm achromatic objective is HUGE, above my expectation. I was so impressed with it!



I will continue with updates about assembling parts when the tube comes out ready from the painting booth and arrival of parts.

[jpb30]

Great purchase Viktor :)good luck for the continuation

JP

[Viktor Z.]

I finally completed the 228 mm f7.7 refractor build, and I would like to share about my experience in detail.

I chose to buy an Istar brand 228 mm f7.7 achromat earlier this year. My considerations of purchase were:
1. To acquire the largest aperture refractor lens that I can afford
2. To be able to use my existing AP 900 mount to support the new telescope's weight and length
3. To retain a limited portability of the equipment by choosing a relatively short focal length

The production and availibility of the objective lens was three months. The parts selection however, took quite a while: It was challenging to find a good 10” tube. Finally, I found a 6' long, 10” diameter irrigation tube with 0.096” wall thickness. The painting of the tube was completed by a local auto-body shop for a very friendly price.



The focuser is an Astro-physics 2.7” greased version rack-and-pinion that I bought used. I added a large AP focuser adapter to the flange side of the focuser for two reasons. At first hand, to reduce the tube length, and on the other hand, to leave the door open for the exchange of this focuser to a 4” AP large format focuser sometimes later. Didier Chaplain at Sky-Meca, France was so kind to accept order for machining both the refractor end plate flange and the counter-cell of the objective lens.



When all necessary parts arrived, I finally was able to build the system together. Please see the refractor mounted on the mount:




The refractor is not so heavy compared to its size, but its large diameter caused me some trouble carrying it. My AP 900 mount appears to be adequate for the size and weight, but I had to balance the mount carefully for a smooth ride. The pier proved to be not long enough for the refractor's 1800 mm focal length, therefore I will surely need a longer pier for more comfortable viewing. The other issue that needs to be solved is mounting the dew shield properly.

FIRST NIGHT OBSERVING
The first light was very promising with non-collimated optics. For the second night, however, I collimated the refractor with Howie Glatter and Chesire eyepiece and aligned both the focuser and the lens cell properly.
Saturn was my first target. It was very low above the horizon, and the continuos air turbulences disturbed the viewing a great deal. I still liked Saturn: the rings were nice and distinct, and I saw surface details on Saturn's globe during the still moments. I could right away spot three of its moons in the dusk, thanks to the large optics. Interestingly, I did not see any chromatic aberration on Saturn. The next target was the chubby Moon. The Moon was so amazing that I could not take my eyes off it! Usually, I would say: "Somebody, anybody, please, shoot down the Moon!" Not so when I scanned it with my 228 mm f7.7 Istar refractor! There were so many fine surface details that the telescope rendered sharp with different magnifications. I would say that a 200x magnification is easy for this scope, but the cost is an increased chromatic aberration on bright objects. The CA is undeniably present up to somewhere +2.5 mag stars at 200x magnification, which magnitude level is pretty bright in a 9” achromat. At lower magnifications, the CA is more and more negligible.
Double stars: I am aware that this type of refractor is not for high magnification observing, but I gave a try to see what it can do with double stars. Lyra's double double appeared as a yellowish- greenish quadruple in the 9 mm Nagler, at 200x, dividing Double Double confidently. At 104x, the telescope still separated them by a nick of hair. Eta CRB: I was not able to separate this double system tonight because the air was unsteady.
The star fields of the Milky Way appear sharp from edge to edge with both 36x and 200x magnifications. Deep skies: M13 is stunning with great resolution, even in the Moonlight, and the Ring nebula is beautiful, floating in the 3D space. The refractor's image quality is great visually despite the typical CA that is visible in this short focal length Fraunhofer refractor on bright objects.

THE SECOND NIGHT
The air is unsteady tonight, same bad as yesterday. After the initial saying goodbye watch towards the wavy Saturn and a little wait, I tuned the telescope on to the Moon again. The huge “clay ball” was just breathtakingly wonderful, I could not stop watching it, I found it so rich in details. Then, I continued to re-visit a lot of bright old friends again, such as M22, M28, M13, M27, M31, M57, M15, M82, M82, Double Clouster, just to mention a few. The background was bright in the FOV due to the moonglow, but I was happy with the new telescope's resolution and image quality. Magnifications used: 36x, 64x, 104x and 200x.
For those amateur astronomer friends, who prefer to evaluate telescopes by written reports of Airy disks, I would like to add that this specific area is not of my expertise, unfortunately. Moreover, the air turbulences were so bad that I did not have a clear, steady view of an Airy disk to successfully compare it to images from books.

THIRD NIGHT
I had a long day, but it was so worth to take the effort to observe! I continued to be amazed by this refractor. M92 was so beautiful with great resolution; M13 looked like a giant bright diamond spider. The tight core or center of M15 was glowing, radiating the many star lights out towards me and just looking at it was simply a beautiful visual experience. In addition, it was very comfortable viewing these objects both at 64x at 200x. The spiral arms of M33 using 64x show so much more in the 9” refractor compared to the 6”, I was amazed by the extra details.
But the highlight of this short night was Iota Cassiopeia. This system lies 133 light years away from us with separation of 0.6”. I was able to separate this pair easily, at 150x! Based on the view in the 12 mm old orthoscopic eyepiece, I found that Iota Cass is truly a triple star system because besides the tight bright pair lies a third fainter star, too. I estimated that the third star's position is roughly 150-160 degree angle from the line marked by the tight double. I double checked it with SkySafari Pro, and indeed, the software displayed the fainter star's position close to my guesstimation while at the eyepiece.

To sum it up, I am very happy that Istar Optical made the 228 mm Fraunhofer achromat available for me. In addition, I enjoyed a lot about the planning and building of this refractor, too. Finally, it turned out that I own a telescope system that has a high performance and great image quailty. I believe that this instrument will give unforgettable moments of observation both for me and other people. My new telescope certainly has the potential to be a great outreach equipment that will bring a lot of joy for many people while discovering the Universe.

Again, I would like to give a public THANK YOU to all who contributed to my telescope either with advice, encouragement, work or/and parts:)

Viktor Zsohar

[astromanuk]

Excellent build Viktor. It is remarkable that you have managed to keep a refractor of this aperture so portable. Look forward to more observing reports!

[rgm]

Excellent report. Thanks for sharing your first nights. Please give us further info once the Moon is gone and you get some good seeing conditions.

[Viktor Z.]

Because I got a lot of questions from people about the performance of my 228 mm f7.7 refractor, especially about planetary performance, I take the opportunity to post my last planetary observation.

This Easter Saturday, it was an excellent early night for planet observation despite of the full Moon. Very good seeing and excellent transparency. Venus: the planet was so bright in this large refractor. It was glowing like a white diamond with colourful halo. The Moon-filter helped to reduce the brightness and eliminated CA. Sharp planet contour, but no surface details, of course, since I don't have a Venus-filter.

Jupiter: with one word: wonderful!The telescope showed beautiful and sharp image of the Jupiter, for my utmost happiness. The GRS was sharply distinct from the surrounding "ocean", like a floating island. The belts also had fantastic details visible in my refractor, with darker and lighter brown areas. I promise to look up the belt names next time. I saw quite a few belts both on N and S planispheres with lots of details. I used a 6 mm Zeiss eyepiece (1800/6= 300x magnification) resulting sharp planet image in the long still air-moments, but the 10 mm Zeiss eyepiece gave me a more comfortable viewing (180x). Excellent lens, excellent refractor! The only thing reminded me that my refractor is not an APO was the well-defined, faint violet halo around the jovian disk "edge".

If I have to rate 0 to 5 scale, I would say for the Jupiter details: 4.5 out of 5, EXCELLENT! A violet colouring around the planet was present, but it was well controlled, and I could easily pay my attention to the planet details. It means that the colouring did not distract me from examining the surface details of the Jupiter.It is not bad at all from an f7.7 simple doublet! Therefore, I did not deduct points for chromatic aberration when decided about this high rating. I don't know if it would be righteous to rate 4.0 out of 5 incl. CA, just because it is there? Because it "comes" with the design of the lens.

I am not comparing results with a longer focal length scope, or a different 9" lens design (APO) that cost approx. 20x more, and where you could of course, achieve higher magnifications and a most likely improved CA. I can't be objective about CA, it is a subjective judgement, and it may be a different experience by the individual person.

I would like to add, that I love so much the wide-field low-magnification deep-sky images of this scope! Please, see my posting above about deep-skies. In addition, the nebulas near Zeta Orionis were easily visible in the Istar 228 mm f7.7 refractor during a moonless night in March this year. I got so excited about it, that I acquired an H-beta filter and now waiting for the next opportunity to see the Horse-head nebula CCD-less:) Still quite a bit of challenge I believe...

To sum it up, I highly recommend the 228 mm f7.7 iStar lens as an all-around large refractor if your main focus is on deep-sky and comet observing, if you love high quality wide field, low to medium magnification views and you occasionally do planet and Moon observing. For an avid planetary observer, of course it, is not the right scope, but it still provides very pleasant, excellent images of Jupiter, Saturn and the Moon.