Deep sky observing with an automated mount and getting my scope fixed

[terrynak]

Since this was a night projected to have excellent transparency and good seeing, it was time to get back into some serious DSO observing. To maximize the no. of targets observed tonight, I dusted off my Celestron NexStar SLT goto mount that had been gathering dust in my living room for over 2 yrs. Fortunately, I had fully recharged the power pack only about 3-4 months back, so I wasn’t expecting the battery to die out in the middle of the session. (For those interested, this is an older SLT model which doesn’t have an extra Auxiliary Port on the base – there is only one for the hand controller. It originally came bundled with a NexStar 102GT 4” F/9.8 refractor):

For this session, I wasn’t looking to log any “new” objects (usually asterisms or open clusters) requiring my largest aperture scopes, but brighter objects that hopefully can be seen under heavy light polluted Bortle 9 skies (including light glare from surrounding buildings) under good transparency/seeing conditions.

I could have used Interstellarum Deep Sky Atlas to select the targets (especially if I were using one of my larger scopes), but in the spirit of my recent 60mm double star observations, I used as my source “Astronomy with a Small Telescope” by James Muirden, published in 1985. In this book he says, “It is being assumed that you are using a 60-mm refractor to observe the objects in this book”. Which of course, means that I attached a 60mm refractor to the mount.

Unfortunately, none of my long focal length 60mm refractors, including my Meade NG60-SM or any of my 60mm scopes with 0.925” focusers, allow a dovetail to be attached to the OTA, except for one: my fast Meade 60AZ-T (F/5.8) ‘frac (came out in 2005, discontinued by the early 2010s):

In the past I’d never use this scope because of the misshapen starry and planetary views it gave (which is why I took its smaller version – the Meade 50AZ-T 50mm refractor – as a grab-and-go for my first trip to Australia back in 2017 instead). I suspected it to be caused by pinched optics because I noticed the objective lenses on this scope were screwed on too tightly - and I couldn’t unscrew the retaining ring by hand. So, I finally got a strap wrench and after a few tries, was able to unscrew the retaining ring holding the lenses off the front-end, give the scope a very gentle shake, and then re-screwed the ring back on very lightly so you could no longer hear the lenses rattle inside:

Doing a collimation test with a Cheshire refractor eyepiece showed that the OTA was a little off collimation (which was confirmed with a star test):

But with the lenses loosened, no more misshapen stars and planets, with the disc of Jupiter looking good despite the heavy chromatic aberration (purple fringe) expected in such a fast refractor.

The EPs that I used: Plossl 32mm (11x) – primarily for GOTO alignment, Kellner 17.5mm (20x), Kellner 9mm (39x), Plossl 6.3mm (56x). The star diagonal came from the previous Meade 60mm F/11.7 scope I used (this scope came with a 45-degree terrestrial diagonal). I also tried my good Orion dielectric star diagonal on this scope, but there wasn't enough back focus for it to work.

Here were the DSOs:

M29 (OC) – difficult to see at 20x; easier at 39x; best at 56x.
M39 (OC) – obvious even at 20x.
M27 (PN) – barely detectable with AV at 20x; easier at 39x.
M71 (GC) – because of its location down the horizon, invisible at all powers.
M11 (OC) – difficult at 20x; slightly easier at 39x.
M15 (GC) – easy to spot even at 20x.
M2 (GC) – easy at 20x.
M31 (GLX) – obvious at 20x.
M52 (OC) – besides the primary star (mag=7.9), invisible at all powers.
NGC 663 (OC) – just visible at 20x; best at 56x.

Although this session was fun at first, the tougher objects on this list took their toll so that after these 10 DSOs, I was exhausted and called it quits.

It was good to get the Celestron NexStar SLT mount up and running after 2 yrs. of inactivity. It's a lot more fun doing automated astronomy than doing it manually via star-hopping, especially when you are working from heavy LP conditions. And without this session, I would not have made the effort to fix the Meade 60AZ-T, which is now in good working order and available as a grab-and-go, especially for Southern Hemisphere excursions.

[Unitron48]

Nice session and captures with the "little engine that could", Terry! Good job fixing the collimation!!

I thoroughly enjoy ringing out my 60mm frac from time to time. I used it to capture most of the doubles on the AL double star list.

Dave

[terrynak]

Nice session and captures with the "little engine that could", Terry! Good job fixing the collimation!!

I thoroughly enjoy ringing out my 60mm frac from time to time. I used it to capture most of the doubles on the AL double star list.

Dave

Thanks Dave!

I have a similar problem with a Bushnell SkyChief 60mm F/15 scope that has the objective end screwed on so tightly that it's giving me poor views of the stars and planets. It's a shame because it comes with a beautiful EQ mount. I'll need to try and unscrew it with the strap wrench, or some other means if that doesn't work.

[Bigzmey]

Nice session Terry! Observing DSOs from the city with a small scope is challenging but still fun. GoTo mount is a big help there.

[JayTee]

Hi Terry,

This is an excellent report from what sounds like a fun night out.

I don't mean to be contrary, so you can take this with a grain of salt, but the picture of your mount looks identical to my Celestron GT mount. Since the original scope's model (as given by you) is the NexStar 102GT, I firmly suspect that your mount is actually the GT mount. Although there is a slight difference in payload capacity between the SLT (8lbs) and the GT (5lbs), they are nearly identical. The HC from this mount will work with any of the Celestron AltAz mounts (GT, SLT, LCM, SE, CPC). I know this because I've tried it.



Cheers,

[terrynak]

Nice session Terry! Observing DSOs from the city with a small scope is challenging but still fun. GoTo mount is a big help there.

Thanks Andrey! A lot better with GoTo, since you don't waste time trying to star hop from the few stars that are visible from so much light pollution!

But I still have to star hop for many double stars and asterisms that are not in the NexStar GoTo database (which has 40,000+ objects).

Hi Terry,

This is an excellent report from what sounds like a fun night out.

I don't mean to be contrary, so you can take this with a grain of salt, but the picture of your mount looks identical to my Celestron GT mount. Since the original scope's model (as given by you) is the NexStar 102GT, I firmly suspect that your mount is actually the GT mount. Although there is a slight difference in payload capacity between the SLT (8lbs) and the GT (5lbs), they are nearly identical. The HC from this mount will work with any of the Celestron AltAz mounts (GT, SLT, LCM, SE, CPC). I know this because I've tried it.


Cheers,

Thanks for the clarification between a Celestron GT and SLT mount, JT! It looks like the GT mount is a discontinued version of Celestron's automated mounts, with only 1 AUX port instead of 2 for the SLT. The 4" F/9.8 Nexstar 102GT scope was overkill for the lighter GT mount.

[Bigzmey]

But I still have to star hop for many double stars and asterisms that are not in the NexStar GoTo database (which has 40,000+ objects).

Valid point. The two GoTo mounts I have can be operated using SkySafari app which has the most complete catalogs of doubles and DSOs, so I rarely run into something which is not in there.

[JayTee]

But I still have to star hop for many double stars and asterisms that are not in the NexStar GoTo database (which has 40,000+ objects).

If you are so inclined, the HC will allow you to input a "User Object". All you need is the Dec and current RA info. It's a bit tedious, but it works. I use this method to find comets.

[terrynak]

But I still have to star hop for many double stars and asterisms that are not in the NexStar GoTo database (which has 40,000+ objects).

Valid point. The two GoTo mounts I have can be operated using SkySafari app which has the most complete catalogs of doubles and DSOs, so I rarely run into something which is not in there.

Maybe when I become more tech saavy I'll use an IPhone app...

But I still have to star hop for many double stars and asterisms that are not in the NexStar GoTo database (which has 40,000+ objects).

If you are so inclined, the HC will allow you to input a "User Object". All you need is the Dec and current RA info. It's a bit tedious, but it works. I use this method to find comets.

Good to know that this option is available on the NexStar HC.

[kt4hx]

Well done Terry, fighting through your heavy LP with smaller aperture. It is indeed a challenge, but shows that one can do so with perseverance.

[John Baars]

Very nice report, remembers me of my old days with a 60mm refractor under Bortle 8/9 skies. The skies haven't improved since, but the instrument grew a bit. Accompanied by a small manual of how to loosen a too tight lens-cell and a lesson in pinched optics. Well done!

[terrynak]

Well done Terry, fighting through your heavy LP with smaller aperture. It is indeed a challenge, but shows that one can do so with perseverance.

Thanks Alan. A lot of us like to go back to using the instruments we used as a kid (50-60mm 'fracs) to see the things that we were never able to see back then because we didn't have the experience or the tools to help us out. These tools would include deep-sky charts and Goto mounts.

Very nice report, remembers me of my old days with a 60mm refractor under Bortle 8/9 skies. The skies haven't improved since, but the instrument grew a bit. Accompanied by a small manual of how to loosen a too tight lens-cell and a lesson in pinched optics. Well done!

Thanks John. It was great to finally get that retainer ring screwed off and objective lens loosened on that scope. Now I have a working scope, but there is one 60mm 'frac I have that I can't get the dust shield off of (so I can go inside and loosen the retaining ring). That scope is suffering from pinched optics.