May 2013

iStar Asteria AT 127-12 R30 OTA tested by Neil English

Wednesday; May 15, 2013: Well it arrived safely, late this morning. Opening up the large box, I removed the packaging and took a long hard look at it. ” Now here’s a proper telescope!” I said to myself, with a broad grin on my face. The instrument was exceptionally well packaged, with dedicated tube rings and a dovetail plate. Nothing moved or could move during transit. The Moonlite focuser I had chosen was packaged separately and thanks to the excellent machining of the optical tube (details to come) , it took just a minute to have it ready for mounting. Here are a couple of photos of the Asteria 127mm f/12, without its super cool, lightweight dust cap.

The iStar Asteria 127mm f/12 on my alt-az mount.

The beautiful objective lens on the Asteria.

A quick check with the chesire eyepiece reveals well aligned optics. I also had a quick look at the high power images of the willow tree I use for daylight testing. Very sharp images at 254x and 304x, respectively. Small amount of CA seen around branches at these powers  but more than acceptable!

This is an exciting telescope!

Tonight actually promises some clear skies, so much more to come.

May 16 00:15h

Just came in from doing some preliminary tests. Star testing on Vega shows some infocus colour – at high powers – but to the very modest extent that(for me at least) makes the images more beautiful! First and second magnitude stars show this. The first round of star testing took place after the instrument was left outside for three hours. The breezy conditions prevented any dew from forming anywhere on the tube. Stars focus sharply to nice round seeing disks. Contrast is lovely! And the rich colours of the stars really jump out at you. Examining the intra and extrafocal images reveals very pleasing similarity. The spherical correction is very impressive. I was able to confirm this by looking for the characteristic generosity of focus depth (as judged by examining the Lyrae Double Double) only seen in a well corrected optic. Were it merely diffraction limited, this magical property would be non-existent. So, as a rough guess, I’d estimate the figure to be a smooth 1/6th wave P-V. Examining the slightly defocused images of third magnitude stars at high powers (300x +) showed no astigmatism or signs of comatic flare. No green filter was used. The pattern was well defined without one, so it ought be even more impressive when tested at mid-visual wavelengths (550nm). That’s on my ‘to do’ list.

This is a large and imposing instrument, with the weight that comes with it. That said, I found the Asteria to be be adequately stable on my Skytee but with some notable adjustments. First, because the ‘scope is rather front heavy, owing to a large lens cell and dew shield, I elected to raise the tripod legs by about 10 inches or so for improved ease of use while pointing at higher altitudes. In addition, I added an extra 10 pound weight to the counterbalance system. That configuration worked very well even in the somewhat blustery conditions this evening. I’m also considering mounting it equatorially with my old Cooke tripod.

My student, Ross, enjoys the play of light on some emerging horsechestnut leaves at 300x.

The views served up in the evening sunlight were most impressive. One of my students, Ross, was gobsmacked by the images delivered  by  my 5mm orthoscpic giving 305x on the sprouting leaves of a horsechestnut tree, a few hundred yards distant. Later that night, dozens of stars were easily resolved in the Great Globular Cluster of Hercules and the Ring Nebula stood out razor sharp and stark against a near jet black sky(deepest twilight). The telescope, appears to be a most excellent splitter of double stars (as I expected). Izar was beautifully resolved (one of the most picturesque I’ve seen in a while), as was Delta and Mu Cygni. I deliberately left out Lamda Cygni from this first light vigil, as I will only attempt this system when it’s gained more altitude and the conditions are calmer. Herschel’s Garnet Star in Cepheus was a most lovely red colour. Clouded over by 00:30h.

Dismounted the instrument and carefully stored it away for the night.

All in all, I’m deeply impressed by the first light adventures with this telescope. I’m more sure than ever that these long focus refractors are the very best double telescopes we can ever invent.

As you’ll see, the quality of the workmanship that went into the instrument is equally impressive. Will post some high resolution photos of the entire instrument tomorrow.

It just needs a name now.

I know!

Tiberius……. or, more fully, Tiberius Sempronius Gracchus.

Tiberius Sempronius Gracchus.

Thursday, May 16, 2013

Took the telescope apart this morning to show you how well made it is compared to your mass-market bling.

The instrument is beautifully powder coated and professionally rivetted.

The professionally machined adaptor that allows one to mate a variety of focusers – including Moonlite, Feathertouch and iStar’s own brand – to the optical tube.

The high quality, dual-speed Moonlite focuser.

More evidence of high quality machining as well as showing that the tube is internally flocked – neat huh?

Check out the baffling on this baby – perfect!

I tried a variety of eyepieces last night; Kelners, orthoscopics, Plossls, Erfles,  modified achromats and Huygenians all work wonderfully well with this refractor. Heck, you can even use warm eyepieces with zero degradation in the image LOL!!

’tis the unassuming nature of high f -ratio optics that delivers this kind of performance.

The workmanship gone into this instrument is right up there with those I’ve seen from APM.

Now, do you really think you can get this kind of service – swift delivery, high quality fit-and-finish and fine optics – from even the likes of D & G Optical?

Still a Happy Bunny.

Monday May 20, 2013

The hottest day of the year thus far. Temperatures reached a very respectable 20C by the late afternoon. A sign of things to come? Well, we’ll see!

In the late evening, I mounted Tiberius on the Skytee in the hope that I might obtain a clear or partially clear sky this evening. The weather forecast gave me some grounds for optimism.

If conditions allow, I will be conducting further star testing of the instrument, together with answering a question that was raised by a poster to this blog. Can I verify the reduction in chromatic aberration by 30% over a regular achromatic doublet of the same specification?

I happen to own a choice Skylight 4″ f/15 achromat. As described in great detail elsewhere, it produces minimal secondary spectrum  around bright objects. Both Tiberius and the Skylight f/15(me Alvin) both have the same focal length, give or take a few millimetres – that is 1500mm. If I were to stop down Tiberius from 5 inches to 4-inches using a simple aperture mask, I ought to be able to see a difference on bright stars like Vega or Deneb or some such. So out came me Alvin for a short test against the iStar refractor.

Tuesday, May 21 02:05

I left both ‘scopes out for about two hours before commencing some tests. Weird, Haar like cloud (low altitude) moved in from the west-southwest (it usually comes from the east), slowly clearing off for short spells. I did most of my testing after midnight, in a prolonged period of twilight (not in the least sense helped by a setting Gibbous moon) but clear skies. Conditions were quite turbulent, yet I was able to effortlessly split Alula Australis at 254x using my Baader orthoscopic. I was genuinely struck by the view of Delta Cygni, set as it was just a little higher than the roof of my house. Using the same eyepiece I was able to resolve and hold the tricky companion despite the obvious turbulence.

From there, I swung my telescope over to Izar, now culminating and hence optimally positioned for observation. Once again, at 254x, I aimed Tiberius at the orange giant but to my chagrin, it was very poorly resolved! One moment it was there but for several more it appeared to have almost completely merged with its primary! Eh?

Looking up, I noticed the telescope was pointing just above a tree. I dismounted the telescope and moved the mount to a position where the instrument would enjoy an unobstructed view of the system. Well, the view in the Asteria couldn’t have been more different; this delicious colour-contrast pair was stably held and easily resolved with this 5-inch glass. Do trees create turbulence? I thought about that before but laid it on the back burner for a while. More to do here I think.

I ended the vigil with a long, relaxed look at Epsilon 1&2 Lyrae at 254x. Briefly promoted to disability, I was visited by a truly jaw-dropping apparition! I hadn’t felt this happy about a ‘scope since Tonya’s lens arrived back in the post from Cambridge (she now has a shiny new focuser?!)

I am continually impressed with how well the Skytee mount is handling this large OTA. Although the dampening times have increased to about five seconds, it is still more than acceptable for my needs.

After that, I went to testing the lens in other ways.

Temperature 12C, 1017mB rising slowly. Not as tranquil as I had hoped. Scintillation still obvious in high altitude stars.

Using a light green filter fitted to a 6mm orthoscopic (250x), I repeated the star test on Vega. In focus, the star resolved down to a clean Airy disk with a faint first ring fragmenting and reforming stochastically in the seeing. No sign of zonal aberrations either.  The intra and extra-focal Fraunhofer diffraction patterns were nearly identical. The brightness and smoothness of the outermost ring either side of focus is a telling indicator of spherical correction as well as lens smoothness. All I can say is that Tiberius produces deeply satisfying results. I concluded once again, even in these less than perfect conditions, after studying the clearly illustrated diagrams on page 182-3 of Suiter’s (first edition), that the figure on this optic was somewhere midway between ¼ wave and 1/8 wave P-V.

I had to wait until after midnight before I got a good chance to compare the stopped down Asteria with the full aperture Skylight f/15 in regard to their colour correction. The test eyepiece was my 9mm orthoscopic yielding 167 diameters. That’s high enough to see the extent of the deep red-violet secondary spectrum. Concentrating once again on Vega, I judged the contrast of both images to be neck and neck, that is to say – beautiful! Was there a difference perceived in colour correction? Yes indeed! Where the Skylight presented Vega with a faint purplish halo round the Vegan Airy disk, its colourful display becomes more pronounced during more turbulent moments. The Asteria image was subjectively creamier, with less obvious secondary spectrum. Comparing the images many times (by mounting and dismounting each instrument) I felt comfortable reaching the conclusion that the iStar object glass was better corrected at shorter wavelengths than the Skylight. I assume that this tweak in perceived colour correction can be achieved by bringing shorter visual wavelengths into tighter focus with the all-important green wavelengths at the expense of longer, red wavelengths. The tweaking was modest though, similar in fact to that adopted on the far more expensive APM 6” f/8 Super ED doublet ‘scope I reviewed earlier this year for Astronomy Now. All in all, I’m thrilled to bits with the colour correction of this remarkable iStar refractor.

21:30h: Fortune continues to smile my way. Tonight looks good for more observing. No more tests for now though. I just want to enjoy my telescope. When an instrument like this comes along, it makes me wonder why I bother hoarding so many other instruments when I really don’t need them anymore. It all seems very silly, that’s all. Several instruments will now be seeking new homes.

My experiences thus far with this telescope leave me in no doubt that it was professionally made. The person who designed the optics clearly understood what he/she was doing. How else would I get such a nice telescope? Yet, just a few weeks back, the most remarkable thread appeared on a popular telescope forum, where some of the key characters attempted to assassinate the good name of iStar. All the evidence suggests that the quality control from this company is very high; certainly the three iStar telescopes I have had direct experience of (two of which I reviewed well before the current hupla commenced) presented no serious problems of any kind. It is also particularly noteworthy that the indivdual who had the greatest gripe against the company purchased a relatively complex design, which, I’m sure you’re aware of, are inordinately more likely to fall out of alignment while in transit. And yet when Takahashi, Astro-Physics or TEC, or some other high-end telescope company produce the odd lemon – no one shouts for their heads!

Oh you hypocrites!

Still, despite getting a full refund, this prickly Canadian – disgracefully in my opinion – continued his vitreolic rant against the company. Amusingly, the same guy settled on a large, Chinese-made Esprit triplet apochromat????!!!!

Other folk, despite writing long threads on their positive experiences with iStar telescopes ( yes, they can be accessed on tinternet), couldn’t quite bring themselves to supporting the company in their hour of need.

Hang your head in shame you cowards!

Should I be bothered where the optics of my telescope are derived from? Not really, but it would be nice to know. I am reliably informed that iStar produce all their optics in China but to a very high standard of quality control. The optical tubes are made in Europe and the United States. Have you got a problem with that? Where do Televue get their optics? Where do they assemble their optical wares? And what about that shiny William Optics ‘scope of yours?

Sententiam dixi.

Thursday, May 23, 2013.

The first clear night receiving my large telescope, I sat out on the roof of a three