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DaveGibbons

Istar 5" F8 Achromat

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DaveGibbons    53

Istar 5” refractor, an honest review.

Some of you may remember I purchased an Istar 5” f8 Achomat objective last winter and spent a little while constructing a scope machining various bits and modifying a meade ar5 tube adding a moonlite focusser and the promise of a review to follow. Well here it is!

Firstly I am not an optical expert or a great one for technical analysis with strehl ratios and p-v wavefront figures, I have, however, owned several dozen scopes and been an avid visual observer for 40 years and I know where the Istar sits optically within the Jumble of extensive data catalogued in my head- I just have a bit of trouble finding which bit goes with which scope these days!

I won’t go into construction as I have posted on this already.This post is all about what the scope can give under the night sky. Suffice to say It is a really substantial bit of kit fully collimatable with a genuine 127mm of clear aperture.

I had hoped the scope would prove to be a versatile, quick cooling good all rounder. In particular I had built it with binoviewing in mind and had cut down the donor tube to allow enough in travel to accommodate the extended light path binoviewers require. As It turns out I have had to reduce the tube length by a further 50mm and now do not require an ocr or barlow when binoviewing. It also sits nicely on my cg5 mount.

I was fortunate to own a truly excellent Tal 125r achromat refractor and I have always said if the Istar objective could match that I would be very happy. I’ve also owned several Meade Ar5 refractors- indeed one these supplied the tube used in the build, it had a poor objective.Also owned half a dozen Synta 6” f8’s as well as Tal 100r and 100rs, so have a good idea what Chinese and Russian optics are all about.

First thing I will state is that on highest power lunar, planetary and double star observation it comes a close second to the Tal 125r. The Tal could be taken to over 100x per inch on doubles on the very best of nights the Istar is good for 75x but then gets a little soft round the edges. Star tests are good but it definitely loses the stellar tightness before the Tal did. It is on par with the best ar5 I owned which is pretty good as this had a longer focal length of f9.4. I must add that last observing session I thought I detected the objective is not in absolute perfect collimation ,something I will address , but I still believe it would come just behind the Tal.

At f8 false colour is of course present on brighter planets and the moons limb. It is in my mind a tad less than is evident on the synta 6” f8’s and one thing I have noticed is when you do crank the magnification up it does not become overwhelming and is not an issue , I must add I have always found it easy to ignore false colour in an achromat but appreciate that some people can’t stand it and will never see past it. Although I would not wish to look through an achromat shorter than f8 !

It is very similar to the Tal125r on CA but is a magnitude worse than the f10 Tal 100’s as you would expect. Most definitely colour correction is slightly better than the Synta f8’s. It’s a trade off though with the Istar giving wider fields than the f10 scopes.

Where I have been blown away by the Istar is in it’s use as a wide field sweeper. I recently purchased a 2” skywatcher 38mm panaview eyepiece and it is a match made in heaven. I know it’s not in the league of super high end eyepieces but with the unchallenging f8 focal length it gives very sharp widefield images across 90% fov.

The fov just covers Orions belt with Alnitak and Mintaka being on the absolute edges of the view this is really impressive, a little under 3 degrees. The views of open clusters and starfields the double cluster etc, are absolutely stunning .Ah the colours of the stars are almost too beautiful for words, this is something people often miss about achromats but once you are looking at less than 1st mag stars the colours on show are jewel like and very vivid . I thought I had seen it all but many hours are going to be spent using this scope looking at galactic clusters and star fields and picking out brighter deep sky targets.

It’s wide field performance has surprised me, in as much as it has taken me in a direction I didn’t expect having always thought of myself as more interested in targets such as double stars, lunar and planetary observation, I just didn’t realise just how magnificent discovering the bits in between can be!.

I am so impressed I’ve decided to buy a sky tee alt-az and stick with pure star hopping and visual observation. I realise now that although I thought I knew my way round the sky and I do , there is so much I just have not seen.

Finally Binoviewing with the Istar , what it was made for. Lunar viewing is a joy the amount of detail 2 eyes give is just stupendous. Looking at Plato 4 craterlets are evident and a hint of another. The contrast and texture of the lunar surface looks almost powder like I can see the dust! A wealth of detail is visible in Jupiter’s cloud system and the 4 inner moons show different colour and tiny perfect discs. It was worth putting the scope together for this alone.

Building the scope has been a really fantastic project, I even got to do most of the machining myself on tube and counter cell, a real labour of love that was. You will never see this in the for sales section as it is the only one in the world and it’s mine, make your own!

Here's a few more pics.

cheers

Dave

post-12720-133877714338_thumb.jpg

post-12720-133877714346_thumb.jpg

post-12720-133877714353_thumb.jpg

post-12720-133877714362_thumb.jpg

post-12720-13387771437_thumb.jpg

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Peter Drew    5,128

All very good news Dave. I have an Istar 6" F10 objective on order at the moment for a PST mod project, sounds like it will be well up to the job. Excellent job you've done, they would sell like hot cakes if only you had the time! :(

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John    16,714

What an interesting scope and report Dave. Thanks for posting and happy new year to you !.

The coatings on the objective look superb as does the lens cell machining :(

I suppose at the end of the day physics will determine the chromatic abberation but hopefully the quality of the lens figuring has minimised any spherical abberation - the majority of synta and GSO objectives that I've tried seem to be under corrected which seems to take the edge off their performance at magnifications over 30x per inch or so.

The TAL folks certainly know how to make excellent objective lenses though, don't they :o

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nightfisher    6,387

Dave, happy new year to you, a very enjoyable review on this superb Istar refractor, i have seen this scope and can vouch for how professionally it has been crafted. " You will never see this in the for sales section as it is the only one in the world and it’s mine, make your own!" Make sure you stick to that quote

Interesting to see how closely it performs to the Tal 125r that you owned, i have been searching for the tal for nearly a year and have finally given up the quest, having got close to sourcing a new one, but in the end that failed, maybe one day our importers will see fit to ship a consignment to the UK

Edited by nightfisher

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DaveGibbons    53

Collimation is now bang on! scope absolutely on par with my TAL 125R.

Showed 6 Trapezium stars with ease last night and shadow transit on Jupiter stunning in binoviewers. Error was with Moonlite focusser not sitting square on the tube. Happy camper!

Dave

Edited by DaveGibbons

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John    16,714

Good news Dave :D

Now engrave "this one is a keeper" on both sides of the tube.

Just in case you ever forget :)

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nightfisher    6,387
Good news Dave :D

Now engrave "this one is a keeper" on both sides of the tube.

Just in case you ever forget :D

"my track record on keeping scopes is not so good. If you ever see the Tal for sale please SHOOT me! "

I think you must have dodged the bullet on the tal :)

I do hope you keep this one as its a superb scope

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DaveGibbons    53
"my track record on keeping scopes is not so good. If you ever see the Tal for sale please SHOOT me! "

I think you must have dodged the bullet on the tal :)

I do hope you keep this one as its a superb scope

Don't worry Jules It will never appear in a for sale section, I really did learn my lesson with the 125r!

cheers

Dave

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DaveGibbons    53

Got a new camera today so took a couple of shots of the Istar. It's got go faster pinstripe now! Actually the bit on the back of my 9x50 finder is because the rear diagonal section rotates easily as the threads are knackered !

cheers

Dave

post-12720-133877765416_thumb.jpg

post-12720-133877765425_thumb.jpg

post-12720-133877765434_thumb.jpg

post-12720-133877765444_thumb.jpg

Edited by DaveGibbons

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John    16,714

Now thats what I call a dew shield Dave !

Lovely looking scope from all angles :rolleyes:

Whats that song ? - "Moonlight becomes you ......." :)

Edited by John

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DaveGibbons    53
Now thats what I call a dew shield Dave !

Lovely looking scope from all angles :rolleyes:

Whats that song ? - "Moonlight becomes you ......." :)

Ta John,

The longer the better I say! It's very light Acrylic material from an art shop. The objective has never dewed up even on the dampest of nights. It may look better if it was white but black is all they had.

Dave

Edited by DaveGibbons

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nightfisher    6,387

Dave`s dewshields are a work of art, i have his old 180pro with huge dewshield, though for some daft reason i keep thinking of selling this and getting the 150 pro, as it would be easier to mount, and do i really need a 180 for lunar work?

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Mr Spock    4,951

Terrific looking scope. There's nothing can beat a good 'proper' scope on doubles. I'd like something decent to replace my ageing Helios 120mm.

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nightfisher    6,387
Now thats what I call a dew shield Dave !

Lovely looking scope from all angles :)

Whats that song ? - "Moonlight becomes you ......." :D

Here is a pic of dave`s old skymax with HUGE dewshield

post-21509-133877766224_thumb.jpg

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John    16,714

Wow !

The dew stands NO chance !

Good for keeping stray light off the corrector as well.

Edited by John

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I am in the process of doing almost exactly wat you have done here Dave , I found an old Saxon 127mm x 1114mm f/l tube without an objective and my Istar 127,, f/8 should be here in Australia soon , I cut 150mm off the origonal tube with the bino viewing thing in mind as well .

I will post photos and a review when mine is finished and I have tested it , a month or 2 ??? hopefully.

Love your scope , sexy as .

Brian.

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John    16,714

Sounds an interesting project Brian - I'll look forward to following it :smiley:

I think putting an Istar objective into another OTA is a good way to move. I looked into an Istar 127mm F/12 optical tube with their R30 aspheric objective and the weight was what stumped me - around 40 lbs !.

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DaveGibbons    53

Good luck Brian!

I ended up with an amazing scope with a superb optic. I look forward to seeing how you get on, keep us posted as you go!

You can take my other scopes but the Istar is with me till the end.

Cheers

Dave

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Will do , and thanks all . Its just a waiting game now as everything is done eg. finder , diagonal , mount etc. and I am waiting for the objective to arrive .

Hopefully in about a week .

Yes these Istar's get good reviews everywhere on their quality .

Oh by the way mine was only $453 aud delivered here to Darwin , great price .

Waiting ,,, waiting ,,,, waiting ,,,,

Brian.

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Istar 5” refractor, an honest review.

Some of you may remember I purchased an Istar 5” f8 Achomat objective last winter and spent a little while constructing a scope machining various bits and modifying a meade ar5 tube adding a moonlite focusser and the promise of a review to follow. Well here it is!

Firstly I am not an optical expert or a great one for technical analysis with strehl ratios and p-v wavefront figures, I have, however, owned several dozen scopes and been an avid visual observer for 40 years and I know where the Istar sits optically within the Jumble of extensive data catalogued in my head- I just have a bit of trouble finding which bit goes with which scope these days!

I won’t go into construction as I have posted on this already.This post is all about what the scope can give under the night sky. Suffice to say It is a really substantial bit of kit fully collimatable with a genuine 127mm of clear aperture.

I had hoped the scope would prove to be a versatile, quick cooling good all rounder. In particular I had built it with binoviewing in mind and had cut down the donor tube to allow enough in travel to accommodate the extended light path binoviewers require. As It turns out I have had to reduce the tube length by a further 50mm and now do not require an ocr or barlow when binoviewing. It also sits nicely on my cg5 mount.

I was fortunate to own a truly excellent Tal 125r achromat refractor and I have always said if the Istar objective could match that I would be very happy. I’ve also owned several Meade Ar5 refractors- indeed one these supplied the tube used in the build, it had a poor objective.Also owned half a dozen Synta 6” f8’s as well as Tal 100r and 100rs, so have a good idea what Chinese and Russian optics are all about.

First thing I will state is that on highest power lunar, planetary and double star observation it comes a close second to the Tal 125r. The Tal could be taken to over 100x per inch on doubles on the very best of nights the Istar is good for 75x but then gets a little soft round the edges. Star tests are good but it definitely loses the stellar tightness before the Tal did. It is on par with the best ar5 I owned which is pretty good as this had a longer focal length of f9.4. I must add that last observing session I thought I detected the objective is not in absolute perfect collimation ,something I will address , but I still believe it would come just behind the Tal.

At f8 false colour is of course present on brighter planets and the moons limb. It is in my mind a tad less than is evident on the synta 6” f8’s and one thing I have noticed is when you do crank the magnification up it does not become overwhelming and is not an issue , I must add I have always found it easy to ignore false colour in an achromat but appreciate that some people can’t stand it and will never see past it. Although I would not wish to look through an achromat shorter than f8 !

It is very similar to the Tal125r on CA but is a magnitude worse than the f10 Tal 100’s as you would expect. Most definitely colour correction is slightly better than the Synta f8’s. It’s a trade off though with the Istar giving wider fields than the f10 scopes.

Where I have been blown away by the Istar is in it’s use as a wide field sweeper. I recently purchased a 2” skywatcher 38mm panaview eyepiece and it is a match made in heaven. I know it’s not in the league of super high end eyepieces but with the unchallenging f8 focal length it gives very sharp widefield images across 90% fov.

The fov just covers Orions belt with Alnitak and Mintaka being on the absolute edges of the view this is really impressive, a little under 3 degrees. The views of open clusters and starfields the double cluster etc, are absolutely stunning .Ah the colours of the stars are almost too beautiful for words, this is something people often miss about achromats but once you are looking at less than 1st mag stars the colours on show are jewel like and very vivid . I thought I had seen it all but many hours are going to be spent using this scope looking at galactic clusters and star fields and picking out brighter deep sky targets.

It’s wide field performance has surprised me, in as much as it has taken me in a direction I didn’t expect having always thought of myself as more interested in targets such as double stars, lunar and planetary observation, I just didn’t realise just how magnificent discovering the bits in between can be!.

I am so impressed I’ve decided to buy a sky tee alt-az and stick with pure star hopping and visual observation. I realise now that although I thought I knew my way round the sky and I do , there is so much I just have not seen.

Finally Binoviewing with the Istar , what it was made for. Lunar viewing is a joy the amount of detail 2 eyes give is just stupendous. Looking at Plato 4 craterlets are evident and a hint of another. The contrast and texture of the lunar surface looks almost powder like I can see the dust! A wealth of detail is visible in Jupiter’s cloud system and the 4 inner moons show different colour and tiny perfect discs. It was worth putting the scope together for this alone.

Building the scope has been a really fantastic project, I even got to do most of the machining myself on tube and counter cell, a real labour of love that was. You will never see this in the for sales section as it is the only one in the world and it’s mine, make your own!

Here's a few more pics.

cheers

Dave

Hi Dave , here is a photo of my new Istar optical 127mm f/8 cell ( minus the optics , as they are in the Vixen cell being tested , nice too )

See the differance in the engraving ? quite differant .

Brian.

post-18525-0-28511300-1354431068_thumb.j

post-18525-0-73018500-1354431090_thumb.j

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paulastro    3,035

Hi Dave. A long time no see. I really enjoyed your review. I've just bought (it's being delivered next Monday) an ISTAR 6" f10 telescope, which was advertised on Peak to Valley's used instrument page on their website. I hope I have some similiar views to the ones you have reported, especially of the wide-field variety. Thanks again Dave, a very enjoyable and informative review. Best regards, Paul

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John    16,714

Hi Dave. A long time no see. I really enjoyed your review. I've just bought (it's being delivered next Monday) an ISTAR 6" f10 telescope, which was advertised on Peak to Valley's used instrument page on their website. I hope I have some similiar views to the ones you have reported, especially of the wide-field variety. Thanks again Dave, a very enjoyable and informative review. Best regards, Paul

I'll be interested to see what you think of it Paul. I've made an offer for one of the clearance ones as well :rolleyes2:

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Peter Drew    5,128

I also have an Istar 6" F10 objective and am very happy with the performance for the price. :smiley:

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