Celestron 102AZ

[wicksee]

Hi guys,

i'm new here but have been casually observing for many years using a trusty old Celestron 70AZ.

I recently upgraded to a 102AZ (i got for £150, which i think is a good price).

i'm delighted with the image quality of the 102, crisp sharp images of Saturn and Jupiter.

What i'm not happy with is:

1. crappy mount! same as the 70AZ, has a frustrating droop after you tighten the alt-lock pan-handle, this is my single biggest bug bear!
2. plastic star diagonal - the eyepiece retaining screw has threaded the plastic so no longer retains the eyepiece!
3. focusing is very difficult at higher magnifications, the gearing seems harsh
4. at extreme end of focus, the focusing tube is just clinging on to the OTA body and flops around a bit!

i'm thinking of sending it back. but am i being unfair? am i to expect similar problems of any other scope at this price point?

would you expect to have to upgrade the diagonal and mount? am i expecting too much?

i'd be willing to spend cash to upgrade if i have to, as i think the image quality is really good.

(incidentally, the image quality is definitely better than the 70mm but the 70 still puts up a good fight!)

TIA for any answers.

[vlaiv]

Hi and welcome to SGL.

Old saying goes - if you get cheap accessories - most of your money went towards the optics - and that is a good thing.

Eyepieces and diagonal mirrors supplied with basic / starter (and sometimes even more expensive models) - are very basic and are usually replaced right away by more seasoned observers (who probably have good items anyway since good eyepiece and diagonal will last a lifetime and can be moved from scope to scope).

They are there to get you going with the scope but soon you'll want something better.

Unfortunately same thing goes for the mount on those beginner scopes. For example, take a look a this:

https://www.bhphotovideo.com/c/product/1353449-REG/ioptron_8710_80mm_f_5_achro_refractor.html

it is $130 for OTA only (optical tube assembly - means no mount).

If you want a decent mount, you'll have to spend more than what you paid for that scope with the mount. Have a look at Sky Watcher AZ4 or AZ5 or Vixen Porta II or similar class AZ mount for that scope.

As for focuser, well, you can adjust it somewhat to make it better and if you have prism diagonal - you will need to rack your focuser quite a bit out. Diagonal mirror will require less outward travel of focuser. So will 2" mirror/prism. Each of these components has certain optical path and longer their optical path - less compensation needed by focuser.

If you are having trouble with focus distance after changing to mirror - you can always use extension tube before diagonal mirror to create additional light path so that focuser does not need to be racked all the way out.

Have a look at this video:

https://www.youtube.com/watch?v=K89k3U9mPe8

It will show you how to adjust your focuser for best performance (replacing grease, adjusting tension and such). I think video deals with several different models, but I'm sure you'll find one that is like yours (there are crayford focusers and rack and pinion types ...).

[rwilkey]

Hi Wicksee, I have the C100 ED and the first thing I did was to replace the diagonal (with a 2" Sky Watcher one), I also bought a Vixen Porta II mount, expensive but solid as a rock, as is the Sky Watcher AZ4.  Just some thoughts about what I did.  Good luck and clear skies!

Edited September 9, 2020 by rwilkey

[Alan64]

What you have discovered is what I've known all along.  With entry-level telescope kits, you get what you pay for.  As you've found, you do get a good telescope, the optics, the objective of the telescope, and where it really counts.  But the mount, the accessories, oft fall short of the mark I'm afraid.  I've known this each and every time I've bought an entry-level kit for myself.

This is, or rather was(discontinued), the best 102/660 kit that Celestron offers...

https://www.harrisontelescopes.co.uk/acatalog/celestron-omni-xlt-az-102mm-refractor-telescope-22150.html

It hasn't been discontinued for long.  If you'd prefer that kit you may be able to find one.  Regrettably, Celestron has replaced it with this...

https://www.celestron.com/products/starsense-explorer-dx-102az

...and in "zooting" the discontinued kit up a bit with push-to technology.

Both kits come with a superior, metal focusser, and a somewhat better mount.  You'd still need a star-diagonal for best results at night.  

[wicksee]

Really good and helpful answers, thanks guys!

I think i'll stick with the 102mm OTA then, and look at better mounts (AZ5 looks nice with slo-mo cables). Also need a star diag!

I already have a Celestron 8-24mm zoom eyepiece, which is nice as it has a T-thread for eyepiece projection into my DSLR.

Am i right in thinking that the short focal length of my scope (660mm) can be compensated for by adding a Barlow (with the penalty of small amount of light loss) ?

[vlaiv]

6 minutes ago, wicksee said:

Am i right in thinking that the short focal length of my scope (660mm) can be compensated for by adding a Barlow (with the penalty of small amount of light loss) ?

Barlow will increase effective focal length of any scope, your scope included. Decent barlow lens won't cause any noticeable loss of light. Any darkening of the image will be due to increased magnification - same amount of light spread over large surface so brightness goes down - this happens without barlow as well - when you use shorter FL eyepieces.

Do bare in mind that your scope is achromatic refractor and observing at higher magnifications is going to show chromatic aberration more clearly. This scope is not the best for observing planets at high magnification as false color (chromatic aberration) is going to blur out details to some extent. Baader Contrast Booster filter can help somewhat with that - it will remove the most offending violet blur.

You can get similar effect from very cheap #8 wratten - yellow filter, only difference being that yellow filter will impact yellow tone to the view (Baader Contrast Booster will also "color" the view somewhat, but not as much - it is quite balanced).

[wicksee]

brilliant advice, thanks vlaiv!

i'll look at the Baader filter.

[Alan64]

 This is a Celestron 70mm f/13 achromat...

 

At f/13, the effects of the aberration are reduced considerably; no filters required.  But then, it's rather long, not as ergonomic, and requiring a larger, more-supportive mount to reduce vibrations.  With achromats, one chooses either ergonomics over optical-performance, or vice-versa.

I had gotten tube-rings for it, there on the right; on the left, with the bar affixed to the tube, and as it arrived.  With a longer dovetail-bar, you can balance the telescope, in sliding it back and forth, forth most likely, and when attaching your DSLR.  Tube-rings make that possible, and more.  Or, you can attach a longer bar to the telescope directly, although that's not as versatile.

[AstroMuni]

On 09/09/2020 at 17:28, wicksee said:

What i'm not happy with is:

1. crappy mount! same as the 70AZ, has a frustrating droop after you tighten the alt-lock pan-handle, this is my single biggest bug bear!
2. plastic star diagonal - the eyepiece retaining screw has threaded the plastic so no longer retains the eyepiece!
3. focusing is very difficult at higher magnifications, the gearing seems harsh
4. at extreme end of focus, the focusing tube is just clinging on to the OTA body and flops around a bit!

Looks like your existing mount (70AZ) has a Vixen type dovetail, so you should be able to upgrade just your scope (eg. https://www.firstlightoptics.com/startravel/skywatcher-startravel-102t-ota.html) which has a the same dovetail. The mount obviously needs an upgrade if you have trouble with it atm and sturdier mounts are expensive. But do look at the 2nd hand market too (eg at Astroboot.co.uk)

Edited September 11, 2020 by AstroMuni

[happy-kat]

If you find the focuser a bit course on adjustment, then try fitting a larger jar cap or similar to it, even a clothes peg would do it. A longer lever to turn the knob would make fine tuning focus easier

 

[Andy0306]

I have the Omni XLT version linked above by Alan64 and have to agree with the points made by the OP.

The mount does shake a bit when focusing (which feels a little stiff), but settles fairly quickly. I can live with it for now, but may replace at some point.

I'm looking at replacing the diagonal, possibly this one https://www.firstlightoptics.com/diagonals/stellamira-1-25-90-di-electric-diagonal.html as the thread has also stripped on the original.

It's a great grab n go scope and getting more use then my 150 Dob at the moment.

Edited September 12, 2020 by Andy0306