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Istar Perseus 150mm F10 Achro - a few thoughts


Marki

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I love refractors and have been tempted by an increase in aperture for a while, so leapt at the chance to get this lovely 6inch scope for a very reasonable amount of money. I've had this scope for a few months now, and had a few chances to get it out and test it, although the seeing conditions haven't been so kind of late.

Anyway, a few thoughts so far.

Build/Size - The scope is very robust indeed. Tube rings are excellent. The whole thing is pretty darn heavy. Its physically big too - guess I should have realised that! Actually, its not so much the heaviness thats an issue - I'm reasonably fit but not very tall, only 5'6" and the scope with dewshield, extention tube and diagonal is almost as tall as me! The sheer size of the scope is quite difficult to handle, and its a struggle to get it onto the mount single-handed (getting easier with practice, though). To be honest it does require some discipline to make me get it out and set up (I'll often plump for one of my 4" 'fracs instead). It has also made me realise that a 6" f15 (something I've often dreamt about and seriously considered last year) would really be beyond what I can realistically manage, at least unless I could arrange a permanent observing position. Its certainly not something I could haul out to a dark site on the bus like Qulia does with his Moonshane, but it will just go on the backseat of my car if I take the dewshield off.

It may be just the recent weather, but despite the large and heavy dewshield, the objective has dewed up within 2hours on both nights that I've had the scope out this weekend. The tube metal is quite thick, so I'm not sure whether normal heater strips would be effective or not - something to worry about in the future.

Not massively impressed with the focusser (which I think is the Istar standard issue). It may need a little fettling - maybe some grit in it somewhere as it really grinds and squeals sometimes. Having to use an extention tube to get to focus is a pain, and there is a fair bit of slop or give in this arrangement. The whole thing is nowhere near as slick as the Baader Steeltrack fitted to my Skylight 4" f13. If I decide the Istar is a keeper, then a focusser upgrade is on the cards. The scope came without a finder, but I've bought a telrad to go with it, but I think I need a RACI given the weird contortions I get into especially observing anywhere near the zenith.

Mounting - I've got the scope mounted on a Skywatcher AZ-EQ6GT. I'd describe this as adequate, if not ideal. Needs to be in eq mode to lift the scope, and I really need to get an extention pillar, because I constantly end up with my head at knee height when observing close to the zenith (maybe the dob owners are right after all!). But then that would give me problems lifting the scope onto the mount!

And now to the good stuff. Tonight I have had the best views of the moon ever - absolutely crystal clear and sharp - astonishing detail up to x300! Also got to see M110 tonight, something I've really struggled with before. Jupiter looked really gorgeous, although as ever not receptive to lots of magnification, the aperture and clarity of the objective really helps to bring out detail I just don't get as easily with my 4" achro. I've had some fantastic widefield views of the double cluster (at low magnifications with a 30mm erffle), and of the assorted open clusters in Auriga tonight; beautiful scatters of pinprick sharp stars. At the other end of the scale I've had some lovely splits - sigma orionis a few nights ago really stands out in my mind, with the c componant clearly visible. Also Rigel too. If I'm super critical, the objective may need a very minor tweak in collimation, but its pretty much spot on - lovely and near text book diffraction rings etc. in and out of focus. The aperture is large enough to really bring out some good structure in the Orion nebula, but I struggled to see anything more than the standard 4 components of the trapezium (think that was more due to seeing though).

At f10 the colour is relatively well-controlled (not as good as my 4" f13, but seems better than my 5" f8.9) - certainly discernable around the limb of the moon and on Jupiter, but I don't really get disturbed by this. A simple moon or LP filter seems to effectively remove it anyway. 

Conclusions - the scope is really pushing the top end of what I can currently accomdate and physically manage and in the end I think my decision will be made on "liveability" - a 4" f15 (something like the Skylight televue f15 recently reviewed in AN) would be as long, but lighter (better colour control, be great for doubles and planets). A 5" at f10-12 (or an apo version) might be a better compromise in terms of aperture, size, generaly manageability and my budget (at least until I win the lottery and can get a droolworthy 200mm APM :p).

Having said that, despite a few niggles with the focusser and some concerns regarding adequate mounting arrangements, I think the Istar has real potential as a keeper. I've not been able to really crank up the mag so far (except on the moon), due to recent seeing conditions, but I'm really looking forward to getting this scope out to a decent dark site to see what it can do, or at least wait for one of those really crisp winter nights!

Thanks for reading - I'll post some piccies tomorrow, but in the meantime your thoughts, suggestions and comments are welcome!

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Thanks for the great un-bias'd review Mark and as a fellow Istar owner ( 127mm f8 ) I can vouch for the quality of the objective's , mine is as perfect as a 127mm f8 doublet can be , just awesome .

Hope you grab an extension pier and get to use the scope in an easier position , thay I am sure will help a lot in your enjoyment of this beauty .

Any chance of a few photos ? .

And you are right , 'Refractors are real telescopes'

ps. I have a friend down here in Australia building a 150mm f10 and cant wait to see it finished .

Here is mine .

Brian.

post-18525-0-21759700-1384133287_thumb.j

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Marki, sounds like your struggling a fair bit, i see where your coming from, i had same issues with the Antares 4" f15, to be honest im finding i prefer to use my 100rs over the 125r for these reasons..........maybe a 120ED would be a better bet, though it would not have the "soul" of a large Achro

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Mark,

Nice report, and congratulations on getting a really large piece of glass. One can really appreciate the views supplied by something like this compared to the ubiquitous 4-inch. While certainly less convenient to use, they do satisfy when conditions permit their full potential to be realized.

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Thats a very interesting report Mark  :smiley:

As the owner of a 6" F/12 Istar I full appreciate the issues connected with owning and using them - I have an additional 12" of tube to deal with too !

I'm especially interested in your reports on the suitability of the  Skywatcher AZ-EQ6GT mount as that was an option that I was considering for my scope. An EQ6 is still a possibility for me although I'm wondering whether even that will have enough "wellie" to handle these substantial tubes ?

On the dewing issue, I've hardly used mine so I've not encountered it but I've been wondering if having a "soft" dew shield alternative to the supplied metal one might i) be more effective at dew prevention and ii) reduce the weight / moment arm issues a bit.

My focuser is engraved "Istar Optical" but is made in the USA by Crawmach - is that the one that your scope has ?. I find mine quite acceptable though not as smooth as the Moonlite on my ED120.

I've come to the conclusion that owning and operating a really large achromat refractor is really a sort of "labour of love" in that they don't make a lot of logical sense but some of us still have the urge to make the effort for the thrill of being at the bottom end of that long tube with a dark sky overhead :smiley:

I'll look forward to your further reports and pictures of the scope  :smiley:

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Thanks for the comments, all!

@Brian - your enthusiastic reports on your Istar were in part responsible for me getting this beast :smiley: . I think the pillar extention is essential if I keep it - I'll just need to be more careful mounting/dismounting the scope (or get a step ladder - or draft Mrs Marki as a fulltime "observatory assistant" :laugh: )!

@Jules - I must admit I've thought a great deal about the 120ed's or those Meade 127s. Budget is an issue new. On the other hand, something like Brian's Istar 127 f8 might equally hit the spot! But to be fair, once I've got the 150 f10 set up - the detail it reveals are so lovely, and I forget all about the other niggles!

@David - thanks! I think if I get that crisp night I'm dreaming about, this scope will just make me forget any issues with its size - so far, optically its really pleasing!

@John - the AZ-EQ is certainly up to the job and drives the scope pretty well (I'd assume an upgraded EQ6 would do the same - they are both rated the same for capacity anyway). The weight is well within the mount's capabilities, but there is indeed a little "moment". I'm rapidly becoming accustomed to it (it damps down pretty quickly - and the scope tracks well without much noticeable wobble unless I manually move it or alter focus). A motorfocusser might be a useful addition. Interestingly, the "moment" is about the same with my Skylight f13 - I think the sheer mass of the Istar actually assists in damping down some of the movement. Your f12 being a fair bit longer might start to push the mount though, and I suspect the moment might be more noticeable. The focusser I have is the basic model, yours is the upgraded version which I've read is considerably nicer. If I decide to keep mine, a moonlite is where I'll go, budget permitting (although I'm pretty impressed with the Baader steeltrack on my f13 - that's be a cheaper option).

Interesting thought on the "soft" dewshield - keeping the weight down might allow me to push the tube up higher for increased comfort, plus it might work better with dewstrips. It may just be that the conditions over the last week or so have just been very "wet", so maybe I shouldn't worry about it too much.

It certainly is a labour of love, as you say, but memories of the views I've had of M42, and the lovely grouping of sigma orionis I got this weekend and a view of M13 I managed a month or so ago more than makes up for the hassle!

Will put some piccies up when I get home.

Cheers, 

Mark

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Hey Mark, Congratulations on the big Istar.  I had the same scope but with the Moonlite focuser and found it very good on most objects.  

I used the Baader SemiApo filter with mine to tone down the CA and it worked very well.

I have moved onto a portable rig but every now and then wish I had kept the big black scope.

Clear skies,

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Many thanks Matt - nice rig you have there! I like that adjustable weight system on the scope too.

BTW, got myself a telrad to use with the istar (just tied on for now) - thanks to your (and others) advice in another forum :-).

Clear skies here tonight (and cold!) so hoping to get out and try it out under a less mushy atmosphere!

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What a lovely mount for your Istar there Matt and I love the sliding tube counterweight - ideas there for my Istar 6"  :smiley:

Hope you get some more big frac views this week Mark. I'm picking up a mount for my big boy on Thursday so I'm hoping to get it fully up and running real soon now.

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Thank you Mark , I am honoured .

Any more sessions ? .

Brian.

Thanks for the comments, all!

 

@Brian - your enthusiastic reports on your Istar were in part responsible for me getting this beast :smiley: . I think the pillar extention is essential if I keep it - I'll just need to be more careful mounting/dismounting the scope (or get a step ladder - or draft Mrs Marki as a fulltime "observatory assistant" :laugh: )!

 

@Jules - I must admit I've thought a great deal about the 120ed's or those Meade 127s. Budget is an issue new. On the other hand, something like Brian's Istar 127 f8 might equally hit the spot! But to be fair, once I've got the 150 f10 set up - the detail it reveals are so lovely, and I forget all about the other niggles!

 

@David - thanks! I think if I get that crisp night I'm dreaming about, this scope will just make me forget any issues with its size - so far, optically its really pleasing!

 

@John - the AZ-EQ is certainly up to the job and drives the scope pretty well (I'd assume an upgraded EQ6 would do the same - they are both rated the same for capacity anyway). The weight is well within the mount's capabilities, but there is indeed a little "moment". I'm rapidly becoming accustomed to it (it damps down pretty quickly - and the scope tracks well without much noticeable wobble unless I manually move it or alter focus). A motorfocusser might be a useful addition. Interestingly, the "moment" is about the same with my Skylight f13 - I think the sheer mass of the Istar actually assists in damping down some of the movement. Your f12 being a fair bit longer might start to push the mount though, and I suspect the moment might be more noticeable. The focusser I have is the basic model, yours is the upgraded version which I've read is considerably nicer. If I decide to keep mine, a moonlite is where I'll go, budget permitting (although I'm pretty impressed with the Baader steeltrack on my f13 - that's be a cheaper option).

Interesting thought on the "soft" dewshield - keeping the weight down might allow me to push the tube up higher for increased comfort, plus it might work better with dewstrips. It may just be that the conditions over the last week or so have just been very "wet", so maybe I shouldn't worry about it too much.

 

It certainly is a labour of love, as you say, but memories of the views I've had of M42, and the lovely grouping of sigma orionis I got this weekend and a view of M13 I managed a month or so ago more than makes up for the hassle!

 

Will put some piccies up when I get home.

 

Cheers, 

 

Mark

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A few pics:

Its nearly as big as me!

post-20607-0-95115800-1385221438_thumb.j

post-20607-0-61862600-1385221440_thumb.j

Some details:

post-20607-0-90871400-1385221442_thumb.j

post-20607-0-24354300-1385221445_thumb.j

Mounted on the AZ-EQ6GT (has to be in EQ mode to get the scope clear of the ground!).

post-20607-0-66594800-1385221447_thumb.j

post-20607-0-65342600-1385221449_thumb.j

post-20607-0-73887700-1385221451_thumb.j

Hoping to get out tonight - real life has got in the way a bit over the last week!

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These are BIG scopes  :smiley:

Nice pics Mark  :smiley:

I believe tubes are made in Austria, finished in the Czech Republic then shipped to USA to have the optics fitted. The lenses are made in China but finished, tested and mounted in the USA. These are not mass produced scopes !

How do you find the cool down time Mark ?. I find my 6" F/12 Istar needs 60-90 minutes. 

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"Made in European Union" First time I've seen that. Do you find it common, nowadays?

Hi David - I don't often see that, it has to be said! Tend to see it more on products made on the continent, as opposed to here on our rainy island :). Make's a change from "made in China" though :grin:

really nice, but after the Antares experience i could not go back to a long frac, i find maks better for me

Hi Jules - I have some sympathy with that; I found myself missing the convenience and compactness of the Celestron 8SE I sold (which was to fund this scope!) over the weekend, when I put the scope out and then it clouded over and I had to bring it in almost straight away!.

It is rather tall isn't it :D.

Lovely looking scope though :).

Thanks Naemeth - although in all fairness, I'm not that tall...so maybe the scope looks bigger than if John for example was standing next to it!

These are BIG scopes  :smiley:

Nice pics Mark  :smiley:

I believe tubes are made in Austria, finished in the Czech Republic then shipped to USA to have the optics fitted. The lenses are made in China but finished, tested and mounted in the USA. These are not mass produced scopes !

How do you find the cool down time Mark ?. I find my 6" F/12 Istar needs 60-90 minutes. 

Thanks John. Nice to see the info on the production chain. Quite a multi-national partnership endeavour! 

As for cool down, your figure is pretty much exactly the same as my experience - minimum of 60 mins I find. I tend to bung it out as soon as I get home, then go out after I;ve had my tea - that's usually about 2 hours. That solid and thick tube must hold its temperature pretty well.

Forecast clear for tonight, and I;m not working tomorrow...keeping my fingers crossed for a decent session!

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Looks nice mounted on the EQ6AZ , just need longer hard wood legs for the tripod ( 400-500mm ? longer) .

that's always the problem with mounts today , legs to short and spindly .

Our old mate Matt down here building his 6 inch f12 has an EQ6 and has made TALL!!! Tasmanian oak tripod legs for his Istar and it works ok for visual I am told , looks sweet as well .

Brian.

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  • 9 months later...

Well, the 150mm f10 has gone to a good home today. I hope its new owner will get as much pleasure as it gave me, and will hopefully get much more use from it. In the end, I found it was too much to manage, and the recurrance of an old back injury made simply lifting the tube onto the mount an ordeal and somewhat chancy.

If I had a permanent set-up or obsy I might have been tempted to keep it - it provided such wonderful, sharp and beautifully contrasty images which will stick with me for ever. However, for now I'll be content with my TAL125r and Skylight 100mm f13 (until the aperture bug strikes again...!).

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I'm certainly don't regret buying it otherwise I'd have missed the experience of owning such a magnificent scope - no matter the practical issues with mounting it. If I ever get to a position where I can afford or have the space for a permanent pier mount/obsy set-up, I'd happily look at Istar again. In the meantime, I might look into the TCR designs, and I'm glad the f10 will (hopefully) get more time under the stars than I could manage to give it :).

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TCR design is innovative and certainly more manageable weight wise.I had a lengthy conversation with Ales as i had concerns about lens dewing up on this design,specially for us being in sort of moist UK climate,however,he assured me that this should not be the case and they havent had this issue with neither of they TCR designs.If solid scopes weight is an issue,TCR is deffo they way to look for it.They still havent produced any sort of sleeve or shroud for this design,but i am sure this could be done at home if required.I personally like the truss idea of refractor.

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