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johnrt

Altair Astro 6” Ritchey Chretien review

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Altair Astro 6” Ritchey Chretien review.

I have seen many people propose this scope as a possible purchase for either longer focal length DSO or planetary imaging, but I have yet to see anyone who has bought one post a detailed review. So, I thought I’d put my thoughts together after 9 months of owning this scope.

This same OTA is available under several different badges including GSO, Astro Tech and Altair Astro.

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Altair Astro market this as a 1370mm f/9 astrograph priced very reasonably at £399. They claim it to be “ideal for imagers”. I’m told the large central obstruction for the secondary mirror makes it unsuitable for observing. I am purely a DSO imager so cannot offer my opinion on either observing or planetary imaging with this scope.

The dimensions are:

Tube length 390mm

Outside diameter 198mm

Weight 5.4kgs

Central obstruction of 77mm

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Out of the box the first impressions I had was that the OTA was sturdy and well built with a nice finish. It came supplied with a variety of extension rings to attach the focuser so any combination of filter wheels, off axis guiders and camera can be brought to focus without difficulty. The OTA has vixen/skywatcher style dovetails mounted to the body on both the top and bottom, very handy to piggy back your guidescope with ease. I use an ST80/QHY5 combo on mine. It also has a standard skywatcher finder bracket fitted. I found the focuser a little cheap and plastic feeling and although the manufacturer says it is robust and will deal with a standard CCD & filter wheel, I find it is not quite up to the job and struggles to “wind in” working against gravity when the scope is pointing skyward. I plan to replace the focuser with a moonlight in due course. I also found the focuser draw tube to be very loose on delivery and required dismantling for adjustment to remove the play in the mechanism before it was fit for use.

As an astrograph out of the box for DSO imaging I find this scope unsuitable. The native f/9 is simply too slow to be effective (especially with the limited imaging time we get in the UK). A good reducer is required - I have used both a William Optics FF/FR II x0.8 reducer and an Astro Physics CCDT67 telecompressor with my Atik 314l+ with success. The Astro Physics x0.67 compressor being the most suitable, bringing the scope down to 900mm f/6, a reasonable spec for DSO imaging.

My second concern with this scope on delivery was the fact that the primary mirror was loose in it’s cell, causing it to tilt under gravity during use. The result was elongated stars and the image to always gradually drift across the field of view. Any sub exposures of over 2/3 minutes were unusable. This was infuriating, especially as it was the last place I looked after spending months tinkering with my balance, mount and guiding. Once I discovered the issue, it was a simple matter of tightening the compression ring which holds the primary in place and the problem was solved. *Warning you will invalidate your warranty removing the rear cell to make this repair*

Collimation at first is a little tricky, but once you know what to look for and how little adjustment is required it can be achieved in just a few minutes. A standard Cheshire collimating eyepiece is all that is required. Now the primary is secured in my OTA, it holds collimation well.

To conclude my overall impressions after 9 months of ownership are mixed. I only now feel after considerable trouble shooting I am ready to start serious imaging with my scope. The quality control in the manufacture of the instrument was poor causing it to be verging on unfit for purpose on delivery. However, now the issues have been resolved and I have matched the scope to a decent reducer I am looking forward to the results I anticipate it will deliver. I purchased this scope as an alternative to my ED80 triplet refractor, offering me the focal length the refractor could not give for smaller galaxy targets and planetary nebulae.

Would I recommend this scope to others?

If this is your first purchase of a scope for imaging then no, quality control is poor, and operation is certainly suited to a more experienced user. For someone willing to spend a little time and effort (and £’s) getting the scope up to scratch this will make a cracking little longer focal length imaging scope. Maybe I am expecting too much for £399 delivered, but I believe no scope should be delivered with the issues mine had on arrival. Hopefully this write-up will save you a little time if yours arrives in the same condition mine did.

Here are some sample images I have achieved so far with this scope. Please note they were taken before the primary mirror issue was fixed meaning sub exposure time was limited. They were also taken with the 0.8 reducer @ f7/2, slower than the f/6 I am now using the scope at with the APCCDT67 reducer.

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A very good appraisal, i had considered this scope, but im planetary so ruled it out

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can you be a bit more specific about fixing the issue of your primary colimation? didi you use this guide? http://deepspaceplac...8rcpointing.php

Yes the process was similar, but I didn't need to go as far as in that guide.

1. remove top and bottom rails (philips head screws)

2. remove remaining screws holding rear section of the scope & remove - at this point the mirror was obviously rocking about in the cell and I could even spin it round!!

3. unscrew and remove primary baffle tube.

4. loosen x2 hex screws in primary compression ring

5. tighten compression ring to stop movement of mirror.

It was simply a case of re-tracing my steps backwards. The collimation was off afterwards, but not by a huge amount.

John

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Nice review, sorry you had a few problems. I use mine only for visual and I find it very good. I don't know where all this rubbish comes from about it only being for astro photograpy. I had mine now for about 2 years and I use it a great deal, I still have not found the need to colimate it.

Alan.

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Nice review, sorry you had a few problems. I use mine only for visual and I find it very good. I don't know where all this rubbish comes from about it only being for astro photograpy. I had mine now for about 2 years and I use it a great deal, I still have not found the need to colimate it.

Alan.

I really have no idea about visual stuff so really can't state anything for certain, but I get the impression this scope is dismissed as not suitable for observers off the back of the specs on paper rather than actual practical experience.

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I've been thinking of getting one of these, will probably have a look at them at AstroFest.

Can you say what mount you used for it? I'm thinking of hanging it on an AS-GT class mount. I'm currently using two 80mm scopes successfully and was thinking of something that will give a narrower FOV.

Chris

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I've been thinking of getting one of these, will probably have a look at them at AstroFest.

Can you say what mount you used for it? I'm thinking of hanging it on an AS-GT class mount. I'm currently using two 80mm scopes successfully and was thinking of something that will give a narrower FOV.

Chris

I use it with a HEQ5, which I was blaming for the poor performance. Since the fix I have found if handles the 6" RC & ST80 with ease.

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Great review, thanks for taking the time and sharing your encounters. I have been considering getting the 8 inch version of it an still undecided. And for the same reasons as you - to get better image scale on individual targets as opposed to wide field ED80 view.

Steve

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This scope has been on my list for a while now... thanks for the review.

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A recent (very) rare glimpse of space yielded this result with the (primary mirror fixed) 6" RC - 8 x 10 minutes exposures in Ha. This length of sub was impossible before the primary mirror fix.

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Excellent result John... the 314 & 6-8" RC is on my list for spring :)

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Great review John, thanks for putting it together.

Was wondering, how did you deduce that the primary was loose? I think the one on my 8" RC is okay but would like to check if that's easily done.

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That's a superb review and covers all the bases fairly.

What we see, yet again, is that the manufacturers are trying to go just a little too cheap. If they increased the price by about 30% I bet they would solve nearly all the problems and the instrument would be fit for purpose and not the starting point for a work in progress, as at present. It isn't surprizing that several firms are working on variants using proper mechanical construction and the original optics, which are clearly good.

And yet another 'dismal Crayford' story. These cheap ones are naff and should be sent back until they stop shipping the useless objects.

It would be good to know how large a chip can be covered using the telecompressor.

As for using them visually, clearly you can. But what possible advantage does the design bring over other Cassegrain variants with similar F ratios, and most notably the Maksutov? Cool down time? Maybe, but the huge central obstruction of the Ritchey Chrétien simply does reduce contrast and that's that. There's no point in railing against it but it is certainly worth pointing out that it gives a decent view if that's the case.

Olly

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PS, I should have added that those are great images - and from a scope costing less than a field flattener for a premium apo of simliar focal length! :Envy:

Ollhy

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Over on the Cloudy Nights forum, they are tons of pictures taken with this 6" and many people using it. I'm very close in getting one myself, in fact I'm going to put it in my birthday present list.... :grin:

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After seeing Tims C11 EDGE image at 2,800mm f/10 I now have no reservations about using one of these ' small ' Rc's at native focal lengths with the 314... :D

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Maybe it's just because I used to my ED80 triplet imaging at f/4.8 but I found f/9 on the RC almost unusable - I don't have the patience for that!!!

I agree Olly it's a real shame there isn't just a little more thought and planning in to these scopes - they do have the potential to be great, but that potential should be realised by the manufacturer not the tinkering end user!!

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Tim posted a fabulous image at F10 but I'm just not up for that. Ideally F4 would be my upper limit but life isn't like that! If you take an image at long FL and slow F ratio, but don't get enough data, then you might just as well have used a smaller faster scope because you won't be able to present the slow scope image at full size anyway.

Olly

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Just a quick update with a work in progress image - still to capture on this is the Ha and another dose of luminance.

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Hi John,

I have bought the CF 8" version and have got the upgraded Feathertouch focuser as well. I bought it as a job lot on ABS for half the price new. I think the collimation is very slightly out on mine - does it make that much of a difference in your experience? You said you used the Cheshire EP method. Is that all you did? From your encouters taking it apart do the screws on the rear cell adjust the mirror or the focuser plane?

Thanks, Steve

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Hi John,

I have bought the CF 8" version and have got the upgraded Feathertouch focuser as well. I bought it as a job lot on ABS for half the price new. I think the collimation is very slightly out on mine - does it make that much of a difference in your experience? You said you used the Cheshire EP method. Is that all you did? From your encouters taking it apart do the screws on the rear cell adjust the mirror or the focuser plane?

Thanks, Steve

Hi Steve,

Congrats on your new scope! It sounds like you got a bargain!!

The collimation of the secondary (front set of screws on spider) on my scope needs a regular check to keep it in good collimation.

The rear set of screws adjust the optical axis (primary mirror and baffle tube assembly) this shouldn't need adjusting often. If the primary is out that will make a huge difference, not so much the secondary. All I use to collimate is a cheshire eye piece. The trick is to make very small adjustments, you'll be surprised how much a small tweak on a screw will shift the mirror.

Just out of interest how much does your 8" CF weigh?

John

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