Fault with BST StarGuider eyepiece? Advice needed.

[Beagle38]

I purchased a Star Watcher StarQuest 102MC Maksutov telescope a few months ago from FLO as a present. (first one ever purchased)

Due to previous advice (as this was the first scope I've bought) about how poor the boxed 10mm eyepiece is, I purchased a BST StarGuider 8mm eyepiece at the same time.

Apart from first setting it up, the first time we've had chance to start using it is with the recent clear skies.

With the standard 25mm eyepiece the quality is fantastic. 

The 10mm eyepiece is not good (as you all know), and then i've tried the 8mm eyepiece and this is as bad - if not slightly worse - than the standard 10mm eyepiece.

This was quite disappointing as I was expecting a reasonably sharp image from a specially made aftermarket eyepiece.

I've tried it both on the moon and also on closer objects (a chimney 1/4 mile away in perfect daylight) and the image can not be focused sharp with the 8mm eyepiece - and in both examples the standard 10mm is just as good.

Is the eyepiece faulty do you think, or something else?  

Mark.

[fifeskies]

your scope is 1300mm focal length

the 8mm eyepiece gives x 162.5 magnification.

This is very high magnification and will only really be giving you a clear image if the sky is very calm and settled.

Typically this will need you to have a very calm night and the telescope given an hour or so to settle down to ambient outdoor temperature.

This kind of magnification also requires a heavy duty solid mount, most small tripods will struggle to achieve this level of magnification.

There will also need to be nothing in the direction you are looking at that produces heat haze , such as looking over buildings or a car park cooling from the sun heating it during the day. Any turbulence due to gusty winds makes that kind of magnification impractical. 

 

also for a non goto mount the tiny piece of sky the 8mm gives you in this particular scope will make finding and staying on a target challenging for beginners

 

This all assumes you are in the UK, if you are at altitude such as the thin air of the crater floor at 10,000 ft in Tenerife it is a different story.

 

 

With my scopes I tend to use 80 to 100x as the highest clear magnification most nights, and if it is extra extra good conditions I may push it to 150x. ( the kind of conditions you only get a few times each winter)

with acclimatised scopes on a cold clear winters night in the early hours when the seeing tends to be best it may just be possible to push it further, though typically it is premium refractors that can go the extra magnification.

Looking at Jupiter last night for example , with my 4 inch ED refractor the view at 130x had become mushy while lower powers seemed far superior.

 

I think you have just got the wrong match to your scope with the 8mm,  a 12mm (x108) or probably better 15mm (x87)  will work best.

(the 8mm is more suited to scopes under 800mm focal length)

 

Get hold of a 15mm and you will get far better results from what is a very capable little scope. 

The 15mm also lets you see far more sky than the 8mm does, there are a lot of great targets that will match your scope and 15mm field of view.

 

Below is view you should get of M81 with the 2 eyepiece options.

 

 

 

 

the 15mm eyepiece is the better fit for seeing the whole moon at once in your scope. The 12mm doesn't leave enough space round the edge to appreciate it properly.

 

 

 

If you only have this scope you can always sell on the 8mm, they sell fairly easily.

 

Edited November 11, 2021 by fifeskies

[Beagle38]

Interesting info, fifeskies.

I shall have a good think of what you have said and consider a wider eyepiece. 

Thanks for your input!

[domstar]

@fifeskies Great advice. It's a rare day that I can get a better view at 150x than at 90x.

[Ags]

I have owned several 102 mm Maksutovs over the years, and I have had good results with various 9 mm eyepieces, but it takes patience waiting for clear moments and on most nights I had a more enjoyable view with a 13, 16 or 17 mm eyepiece.

Keep the 8 mm, it can be used sometimes, on very good nights with steady seeing. It will also be very useful for splitting certain double stars.

[Tiny Clanger]

First , and absolutely vital with a maksutov, because of its closed tube , you need to leave the 'scope outside to cool down for at least half an hour before it will give a decent view. Until then , air currents within the tube will make the view poor, and the more you magnify your view, the more you magnify your view of the air currents ...

Check your BST , is there a smear or fingerprint on the lens ? Is there a rattle if you give it a gentle shake ? Did you buy it new, or could a previous owner have taken it apart ?

Eyepieces are, physically, relatively simple things, there's not much to go wrong , so once the above factors are eliminated,  I'd be looking elsewhere in the setup to find the problem, it may be there is a weakness which the 8mm is simply showing up .

I've no experience (and can't find much about) that particular 'scope and mount, but I can tell you on a decently steady night (and after at least 30 minutes cooling)  I get a good view of the gas giant planets and the Moon at 187.5x with my BST 8mm in my 127 skywatcher mak, which has a slightly longer (1500mm) focal length than yours, but it is a bigger 'scope, and on a very sturdy AZ5 mount.

I'd suggest if your eyepiece has no obvious defects , first check that the diagonal is properly and firmly seated , the skywatcher one which came with my mak was pretty flimsy and I didn't trust it .

If that seems OK, maybe checking the collimation of the mak with a star test can confirm if the internal optics are out of whack . The starquest may not have the ability to be collimated, I don't know , if it does you should see  2 sets of 3 screws on the back plate , they are definitely not things to mess with casually  though. How to do a star test to check collimation https://www.skyatnightmagazine.com/advice/how-to-star-test-a-telescope/

If you try a star test, and it appears the 'scope is out of collimation, as it is fairly new I'd contact FLO rather than mess with it myself, even if there are the screws there to adjust it, it should have arrived in decent condition , and they will, I'm sure, help. Same if it  turns out the BST was a rogue one that slipped through QC (assuming you bought it from them).

I'd not buy another eyepiece before tracking down what is going on here. You don't say whereabouts you are, maybe a quick and easy way to get to the bottom of this would be to find an astro soc or  helpful  local who can have a look and has the experience to say if the view falls below what the instrument ought to give.

Heather

 

[fifeskies]

On 11/11/2021 at 14:24, Beagle38 said:

With the standard 25mm eyepiece the quality is fantastic. 

Since the OP gets good views with his other eyepiece it is hopefully not the case that the scope is out of collimation.

 

As Tiny Clanger suggests though, take a good look at the 8mm eyepiece as it s all too easy to get a fingerprint smudge that may not be easy to see from the outside but can ruin the view through it, and it is still possible there is a fault of some kind.

Only use a proper lens cleaning method, not the "t-shirt wipe" method as that will just make things worse. 🙀

 

 

You have a fairly travel friendly scope , so the 8mm may come into its own if you take it to a dark holiday site especially somewhere at altitude.

(The caldera (crater) at 10,000 ft in Tenerife at night as mentioned previously is a stunning place to go for near perfect darkness and superb seeing)

Edited November 13, 2021 by fifeskies

[Beagle38]

Thanks all for your thoughts.

Thanks Heather for all your advice - loads to go through!

Yes the eyepiece was new from FLO - bought with the scope.

I made sure it was all clean again and had a quick look this afternoon at a chimney about 1/2 mile away.

The same results as before: 25mm - brilliant; 10mm - okay; StarGuider 8mm - okayish!

I was wondering if I am expecting too much of the 8mm; but surely it should be sharper than the supplied cheap 10mm eyepiece?! 

I probably won't use it much ironically - as I don't like the field of view, etc, and will be better suited with a 15 or 12mm eyepiece - as fifeskies said. But it should be reasonably sharp when I do use it - conditions allowing. I will also have to make sure of allowing a scope to adjust to the climate in future.

I wonder if to speak to FLO about it; or if possible try it in another telescope first.  

Thanks all for your help.

Mark.