Opticstar AR90s Gold Unboxing and first light.

[Mr niall]

It’s been a bit of a saga to get here but I finally got my AR90s in the post yesterday. I’ve been looking at this scope for about 6 months and very nearly pulling the trigger but always held back. Do you ever see something and just decide you want it, and then spend the next few months convincing yourself it’s a vital addition to your kit? Yeah, well that’s sort of the case here. Haven’t really seen any reviews on this scope anywhere so thought I’d do my public service and write this one up!

Father Christmas and I famously fell out over the amount of expenditure required to fund Christmas, and I guess I wasn’t alone in having to shift a few items of beloved astronomy equipment to cover the cost. No regrets at all, but found myself without a main scope, and then (I’m not sure whether this is excellent luck or some sort of sick joke) was gifted both an az gti wifi by a kindly relative and received a delicious tax rebate at the end of Jan, so I had enough to replace my scope and sort of start again.

Having put much much thought into my purchase, I decided I wanted a scope that.

1. Had reasonably wide field views

2. Was good on planets and lunar

3. Useful on doubles

4 . Useful for AP

5. Had to come in at well under 5kg

6 cost absolutely no more than £200

so you can see that what I want is several different scopes... , I had narrowed it down to a SW 110 Mak, which seemed ok but was only slightly bigger than the (granted badly damaged) 90 Mak that I was already using. Actually pulled the trigger on this but then FLO said they were out of stock until March. Then thought the 130pds would be ok but FLO reckoned I’d by pushing the limits of the AZ GTI so didnt get that. Really liked the Altair Classic 102 f11. But it was over budget, and Altair never bothered to email me back. I read a couple of reviews that said the it was pushing things a little on an Eq3 so decided against that too in the end.

In the end decided to pull the trigger on “the unicorn” Ar90 and take the risk - on the rational that it would  at least be averagely good on all the thing s on my wish list which was fine with me, I’m  very much in the “budget astronomer” camp anyway!

So - it’s a 90mm achromatic fully multi coated objective with a slightly unusual F8.8 (800 mm) focal length. This was appealing to me for a variety of reasons - should still give just about give 2 degrees with a 32mm Plossl (which I don’t own yet!). Also should be able to comfortably handle up to about 125x for planets and doubles, and also the CA should be slightly less of an issue than much faster scopes, but still not be completely unusable for a bit of AP (friends and family stuff only of course).

The scope arrived well packed - has an unusual sort of pebble dashed texture effect off white paint that is both pleasing to touch And functional. It’s all metal and has a screw on lens cap for the dew shield which is also metal, and slides nicely but with no locking screws. Features a 1:10 focusser (1.25 and 2 inch) and tube rings and standard vixen dovetail. Also comes with a rather nice padded case and a good set of instructions.

Build quality is good and solid without being amazing. The words that spring to mind are “solid, robust, agricultural” rather than “sleek, gorgeous, elegant’, but it definitely looks and feels solid. Comes in at about 3.8kg with rings and eyepiece so ok on my mount.

However... immediately had an issue attaching the tube rings. These are nicely padded on the inside btw. Of the two supplied screws to attached the dovetail to the tube ring, one just wasn’t going to work, played around with ages with grease and varying levels of force but thought I’m just going to break something if I carry on, so ended up emailing Opticstar. As ever, Peter emailed back within half an hour to apologise and promised to send out a new set of screws, he’d also checked some other tube rings and screws  in the shop and said he’d found a similar thing and advised checking the tube rings carefully to make sure they were threaded and if there was an issue he could replace those too. Always amazes me how honest Opticstar are! A couple of times they have actually talked me out of pulling the trigger on accessories as they thought they’d weren’t really what I was looking for.

Also noticed the focusser works fine but is squeaky and grindy and a bit annoying. Have emailed Opticstar for advice but I think it just needs some disassembly and lubrication somewhere. Again, when considering the price of the scope I’m not too bothered.

First LIGHT!

Against all the laws of telescope ownership, last night was the first clear night in weeks. I managed to get the dovetail working with an M6 bolt borrowed from my EQ1 mount and I was up and running.

I had zero cool down and noticed the view so settled down within 10-15 Mins which was brill. First target was the moon - amazing contrast and clarity and razor sharp views across 85% of the fov. The 1:10 focusser made life easy. Easily fit the whole moon in with the 25mm Plossl, which was nice, did notice a tiny bit of stray light bouncing around somewhere inside though but this disappeared when looking head on, despite the “knife she baffles” that the scope comes fitted with. The cheap eyepiece may have played a part here though. Surprisingly little CA, sometimes there, sometimes not, just a slight purple or sometimes green fringe hovering around the edge but not off putting and surprisingly easy to ignore. Views with 10mm Plossl spectacular, razor sharp with bags of contrast.

Next was Pleiades - almost but not quite fitted into the fov with 25mm Plossl, lovely blanket of stars effect and very pretty. Again, tack sharp.

Then over to M31 - dreadful!! Picked out the core and little else! But not put off by that - seeing wasn’t great with high cloud around and the moon was out and causing trouble!

Last up Almach - easy split in the 10mm, very noticeable colour difference.

Ive only got two bargain basement Plossls at the mo 25 and 10mm, I think the next step is to expand this selection for even better views, but all in all very pleased.

I really am glad I took the risk on this scope and feel it is well worth the money, despite the niggles. A slightly unusual scope at a great price, and once these isues are sorted I  am confident I’ll get years of service from it. Also customer support from Peter at  Opticstar is excellent.

apologies for the very very long post!

[AdeKing]

Thanks for the write up, I discovered OpticStar for the first time the other day but couldn't find much user info about the scopes, but they did look temptingly priced.

Ade

[russp]

I have the 127mm carbon APO sold by Opticstar and have been very pleased with it - it is however an rebadged Explore Scientific scope so I had some confidence about it. 

[nightfisher]

I have the shorter AR90, not used it much but its a good scope

[Chris]

I had the shorter version too, I remember a cracking view of M81/82 with it at zenith. Like you say, a sturdily built scope at a good price. 

How does the az gti cope with it I wonder? From what I've heard, the sturdiness of the gti's tripod doesn't match the sturdiness of your new scope. no doubt though, a refractor looks good on this style of mount, I'm surprised they didn't do a refractor package with this mount.

 

 

[Mr niall]

33 minutes ago, Lockie said:

I had the shorter version too, I remember a cracking view of M81/82 with it at zenith. Like you say, a sturdily built scope at a good price. 

How does the az gti cope with it I wonder? From what I've heard, the sturdiness of the gti's tripod doesn't match the sturdiness of your new scope. no doubt though, a refractor looks good on this style of mount, I'm surprised they didn't do a refractor package with this mount.

 

 

It’s ok... bit of a wobble when focussing though (about 4 or 5 secs) and noticed a slight jitter from tracking with the 10mm on doubles. Thing there is room for improvement though, balance wasn’t perfect and didn’t have the accessory tray on or any weights addded so room for improvement.

[Alfian]

Nice write up and pics Niall. I pondered one of these some time ago (RVO do a version of it) and was very tempted, ticked a lot of boxes, but then the ED100 came along and... well you can guess. Please start saving for next Xmas, don't go selling such a nice scope!

[Ben the Ignorant]

On ‎25‎/‎01‎/‎2018 at 12:27, Mr niall said:

Also should be able to comfortably handle up to about 125x for planets and doubles, and also the CA should be slightly less of an issue than much faster scopes

The two unexpensive 80mm f/7.5 achros I bought (I gave one away) handle 150x under any conditions; and on an exceptional night Mars could be viewed at 254x (4.7mm Explore + Celestron Ultima 2x Barlow) without major loss of contrast, but only because Mars is a high-contrast planet. Jupiter was acceptable at that power, too, on a couple very steady nights. Starting from the commonly usable 150x for a neither-slow, neither-fast 80mm cheap achro, your high-end 90mm f/8.8 can absolutely reach 180x on any night. 

Thanks to the double-speed focuser and probably better glass, higher powers on calm nights are sure to be feasible, but 180x is already a lot, it's the magnification I use most often for planets with my 127mm Schmidt-Cass. I ogled that 90mm achro many, many times, but since I also owned an 80mm apo, it was not justifiable. When I was thinking of maybe acquiring one, I guesstimated it would show a bit less chromatism than my 80 achro, which does not show much purple relative to larger ones, like the 150mm f/8 we have at our club's countryside base.

What made this 90 achro especially more desirable in my eyes was the 2" double-speed focuser, and the finish.

[Chris]

All this talk is making me want another achromat! 

[michael.h.f.wilkinson]

That scope looks really nice. It could also be a very good performer for solar astronomy. With a Herschel Wedge and Solar COntinuum filter it should show very little CA, as you are only looking in the green. Likewise, adding a Ca-K module (expensive!) should give excellent images in that wavelength, especially compared to faster scopes which tend to show more spherical aberration in that wavelength. A Quark would make it a really nice H-alpha scope for close-up work too.

On 1/27/2018 at 21:24, Ben the Ignorant said:

The two unexpensive 80mm f/7.5 achros I bought (I gave one away) handle 150x under any conditions; and on an exceptional night Mars could be viewed at 254x (4.7mm Explore + Celestron Ultima 2x Barlow) without major loss of contrast, but only because Mars is a high-contrast planet. Jupiter was acceptable at that power, too, on a couple very steady nights. Starting from the commonly usable 150x for a neither-slow, neither-fast 80mm cheap achro, your high-end 90mm f/8.8 can absolutely reach 180x on any night. 

Thanks to the double-speed focuser and probably better glass, higher powers on calm nights are sure to be feasible, but 180x is already a lot, it's the magnification I use most often for planets with my 127mm Schmidt-Cass. I ogled that 90mm achro many, many times, but since I also owned an 80mm apo, it was not justifiable. When I was thinking of maybe acquiring one, I guesstimated it would show a bit less chromatism than my 80 achro, which does not show much purple relative to larger ones, like the 150mm f/8 we have at our club's countryside base.

What made this 90 achro especially more desirable in my eyes was the 2" double-speed focuser, and the finish.

Curious. I have an APM 80mm F/6 triplet, which gives very tight star images, and I have pushed it to about 150x on the moon (8mm Delos and 2.5x PowerMate), on a night where my C8 easily handled 290x with a Pentax XW7. Pushing well beyond 150x gave poor results, as expected from the size of the diffraction disk, even on a high contrast target like the lunar terminator. I cannot see myself look through any 80 mm and push it well beyond 160x without being annoyed by the blur. One reason for different experiences people have might be visual acuity. Mine is consistently measured as between 1.6-1.75 by the optician, so I should see the diffraction pattern at much lower magnification than people with an average visual acuity (1.0).

[Ben the Ignorant]

2 hours ago, michael.h.f.wilkinson said:

Curious. I have an APM 80mm F/6 triplet, which gives very tight star images, and I have pushed it to about 150x on the moon (8mm Delos and 2.5x PowerMate), on a night where my C8 easily handled 290x with a Pentax XW7. Pushing well beyond 150x gave poor results, as expected from the size of the diffraction disk, even on a high contrast target like the lunar terminator. I cannot see myself look through any 80 mm and push it well beyond 160x without being annoyed by the blur. One reason for different experiences people have might be visual acuity. Mine is consistently measured as between 1.6-1.75 by the optician, so I should see the diffraction pattern at much lower magnification than people with an average visual acuity (1.0).

I own a clone of that triplet which can go 204x (Explore 4.7 + Ultima 2x Barlow) on good nights, and 240x (TS 4 + Ultima 2x) on exceptional ones. My achro reaches more than 150x only when air waviness is very tenuous, but it happens, and when it does powers superior to the norm are permitted for a while. I never had my visual acuity measured, so I can't compare that, but I observe since childhood, practice makes me see nearly all there is to see.

My 80mm semi-apo (how did I end up with three 80mm scopes?) does 140x (TS 4mm) on any calm night, and that's rather effortless for it, tightness and color correction are a delight to see. Higher magnifications are no problem when the atmosphere does not blur things too much, so I'd say your triplet should go higher than 160x; maybe it is a tad decentered, and a little tweaking would allow powers around 200x without breakdown?

My friends' FPL-53 doublets have often split very tight stars and shown a good Jupiter at enlargements higher than 200x, so there is no reason why a high-end trilpet like yours should be limited to 150x. Have you checked the mechanical and optical collimation?

Lastly, the size of the diffraction disk is not the whole story on resolving power. Take something like a postage stamp or a bank note, and make two pinholes very close to one another on a dark part of the paper where many intricate details are present. Mount that on a flashlight, and put it at a distance such that the Airy disks from the two holes can just be split. Thanks to the flashlight shining through the paper, or ambient light, you'll see lines and curves much narrower than the size of the diffraction spots.

Some opticians use an irregular slit on the same metal plate as round holes to compare the "Airy resolution" with the "hairline resolution" (Wolfgang Rohr does that sometimes). Another proof there are two kinds of resolving power is you can easily see electric power lines from several kilometers away with the eye alone. That's because they are long, and they contrast very well against the daytime sky. But two dots of the same angular size and separation as the cable's width would be impossible to separate.

[michael.h.f.wilkinson]

The simple reason is called wave optics. The moment I go above 160x I start seeing the diffraction disk. 

[CloudySeeing]

As soon as I saw the note about "5kg" I knew I'd found another person with the Skywatcher GTI mount (ordered from the UK a few months ago).  Mr. Niall, now that you've had it for a month what are your thoughts?  Do you find the length causes wobble issues vs. a shorter 90mm OTA?

I am currently using an ES 90mm with a Herschall wedge for outreach.  There is plenty of chromatic aberration but that isn't an issue for solar.  The reason I'm upgrading is that I need a two-speed focuser.

 

(also, do you find that the mount "unscrews itself" when you have it on the stand-tube?)

[Mr niall]

14 hours ago, CloudySeeing said:

As soon as I saw the note about "5kg" I knew I'd found another person with the Skywatcher GTI mount (ordered from the UK a few months ago).  Mr. Niall, now that you've had it for a month what are your thoughts?  Do you find the length causes wobble issues vs. a shorter 90mm OTA?

I am currently using an ES 90mm with a Herschall wedge for outreach.  There is plenty of chromatic aberration but that isn't an issue for solar.  The reason I'm upgrading is that I need a two-speed focuser.

 

(also, do you find that the mount "unscrews itself" when you have it on the stand-tube?)

Well... just never managed to get on with the GTI mount - had quite a bit of trouble aligning it nightly (could be due to where I live though), and the AR90 was actually pushing it quite a bit (possibly cos of the relatively long tube though). Did struggle with wobble at higher magnifications and think this tube was maybe just a little bit too much. Also I didnt massively enjoy the interface.

I was incredibly lucky though - FLO very kindly accepted the AZ GTi back as a return and replaced with a star adventurer mount - very pleased with this and will stick with the EQ for the AR90.

[CloudySeeing]

Thanks for the feedback.  I was worried about wobble and you confirmed it, now thinking I'll get a small tube and then a big 157mm and a larger mount.