Eyepieces

[gib77]

Hi I have a celestron advanced vx 8, if I use the 25mm eyepiece that came with the scope the images I get are quite good, I have some other eyepieces 10&15mm, when I try to use these images seem very poor and it is hard to focus with them, they were only cheap could this be down to the poor quality of the eyepieces?

[ronin]

The celestron advanced vx 8 appears to be an 8" SCT of a Newtonian, some retailers have one some the other.

Need to know the scope otherwise a bit of guessing is going top occur - will assume  the SCT form at present.

Any markings or text on the 10 and 15 ?

I would say you are right the 10 and 15 are just not up to the job.

However if SCT and if plossl's I may have expected reasonable viewing.

Do you wear glasses?

The choice of better eyepieces make this relevant.

Also the 10mm may simply have been too much magnification, 203x may have been too much for conditions. However the 15mm should then have been OK.

The 10mm may be a Kellner or Huygen design from another scope, they are not generally that good.

The 15mm is the "odd" one, not heard of a 15mm coming with many scopes so I could expect that to be a plossl that was purchased seperately.

[gib77]

Hi, it is the sct scope, the eyepieces are marked PL10 & PL15. I assumed the PL meant possible they were only a tenner each. I do wear glasses but usually remove them when viewing.

[saurabh dh]

hi  i think  ronin got it right, could the collimation issue cause the  bad seeing at higher power

if you have a barlow try it with 25mm ep,if the seeing is bad still you can put it to Atmosphere.

[rwilkey]

In my opinion, you get what you pay for, however, most ep's should work in an SCT, though the 10mm could be too much magnification.

[ronin]

Well PL will (should) mean Plossl. Although I have 2 boxes where PL is on two TMB PLanetary eyepiece box. We think that the Chinese people used PL for both.

They are a fairly simple eye piece but work well, very little to go wrong.

The 10mm is sort of at the limit - not sure what the atmospheric condotions were - but the 15mm should have been OK.

If both views are really poor then I wonder if someone has dismantled them (to clean) and got the lens in the wrong way round, doubtful but it is a possibility.

Being f/10 a plossl should be fairly good in the scope, the worst you will have is keeping the magnification down and so obtaining a reasonable field of view.

Really all I can suggest is check collimation, get a star in the centre and defocus - you want a sort of symetical doughnut result. Or buy another eyepiece of known quality.

GSO/Revelation plossl, Vixen plossl, BST Starguider, X-Cel.

Could you borrow one or two - assumes you are in a club, or intend to join one soon. Maybe a club you can get to has a "problem" fixing night. The one here people sort of drop in when they have their public evenings.

Getting it into a good focus is likely the focuser, I do however assume that it is a single speed focuser when I say this.

If you go for another eyepiece then 12mm to 15mm, depending on which brand/make you opt for.

Slight thought, to check collimation you may need an eyepiece that produces a decent image in the first place.

[LukeSkywatcher]

200mm aperture,1000mm focal length.............

Magnification = focal length / EP:

1000mm/10mm=100x magnification.

The 10mm EP should work fine according to the specs. If it doesnt, then there are other factors involved. It could be collimation, as you said the views with the 25mm were "quite good". They should be better than "quite good". It could be seeing conditions (transparency etc). It could be the quality of the supplied eyepieces. I'm gonna say they are Plossl's because i know Celestron supply those with this type of scope. It is possible to get one bad one with a scope, but not 3 bad ones.

Its a bit of a mystery. 

P.S.~~~1000mm f/l in an 8 inch SCT sounds short and strange to me. My Celestron 8 inch SCT has a f/l of 2032mm. I have had no issues with the supplied 10mm or 25mm (could be 20mm) EP's supplied. I know the scope in question and the 8SE are different (ish), but surely the mechanics should be the same?...........i mean the formula i posted above.

[C7tsj]

Have you tried focussing during the day on say a distant tree or streetlight? It could also be that you are turning the focuser slightly too much. It may just take the slightest of turns to achieve focus.

Always easier to troubleshoot in daytime, you will just get frustrated at night.

Perhaps a few pics might help?

Mark

[LukeSkywatcher]

Another thing to consider is the fact that this scope has a rack and pinion focuser (like a refractor). The screws that hold the base plate of the focus wheels to the scope could be too lose and are not allowing the cogs (teeth) on the focuser to bite onto the focusing bar within?. If so, focusing to a fine sweet spot could be impossible.

Just a thought.

[RT65CB-SWL]

Hi I have a celestron advanced vx 8, if I use the 25mm eyepiece that came with the scope the images I get are quite good, I have some other eyepieces 10&15mm, when I try to use these images seem very poor and it is hard to focus with them, they were only cheap could this be down to the poor quality of the eyepieces?

Hi gib77,

It would be interesting to who makes the cheap 10mm & 15mm Plossl's?

I use TeleVue 8mm & 15mm Plossl's in my Celestron C6/SCT and do not see any degradation in my viewing, so the 'bargain basement' Plossl's appear to be the culprit here, (ie poor workmanship/quality), unless the 'scope requires collimation or there has been poor skies in your area.

Did you purchase the eyepieces at the same time you when you purchased the 'scope or are they new. If 'new', then I would email or send a letter and speak with the salesperson or outlet as they should offer some guarentee against defects, which is what you are experiancing. In this case I would think of it as a case of not of merchantable quality or not fit for purpose. If they do not 'play-ball' then I would consider contacting your local Trading Standards/Consumer Protection officer at your council offices https://www.gov.uk/consumer-protection-rights  If you purchased them on-line the law is different but I think you still have protection. However, if secondhand from an individual or retail outlet then you should have been informed you at the time of sale that they may not be perfect. You are going to "bite-the-bullet" and put it down to experiance and purchase elsewhere.

Just a thought! Have you used the in another 'scope for comparison?

DISCLAIMER

I am not au-fait with the system of GB/UK law and legal. Please do not quote me or my name on any of the above. Thank you.

[LukeSkywatcher]

Hi gib77,

It would be interesting to who makes the cheap 10mm & 15mm Plossl's?

I use TeleVue 8mm & 15mm Plossl's in my Celestron C6/SCT and do not see any degradation in my viewing, so the 'bargain basement' Plossl's appear to be the culprit here, (ie poor workmanship/quality), unless the 'scope requires collimation or there has been poor skies in your area.

Did you purchase the eyepieces at the same time you when you purchased the 'scope or are they new. If 'new', then I would email or send a letter and speak with the salesperson or outlet as they should offer some guarentee against defects, which is what you are experiancing. In this case I would think of it as a case of not of merchantable quality or not fit for purpose. If they do not 'play-ball' then I would consider contacting your local Trading Standards/Consumer Protection officer at your council offices https://www.gov.uk/consumer-protection-rights  If you purchased them on-line the law is different but I think you still have protection. However, if secondhand from an individual or retail outlet then you should have been informed you at the time of sale that they may not be perfect. You are going to "bite-the-bullet" and put it down to experiance and purchase elsewhere.

Just a thought! Have you used the in another 'scope for comparison?

DISCLAIMER

I am not au-fait with the system of GB/UK law and legal. Please do not quote me or my name on any of the above. Thank you.

My first scope was a Celestron 90mm refractor and the eyepieces (10 and 20mm) were Kellner. I thought they were good til i moved up to a Celestron Eye opener kit of Plossl's............which i loved until i started to upgrade to Vixen NPL's. 

I also have Skywatcher EP's and the 10mm is pretty rubbish, while the 25mm is pretty good.

All i really use now on any scope is my Hyperion 8-24mm zoom.

[John]

Hi gib77,

It would be interesting to who makes the cheap 10mm & 15mm Plossl's?

I believe many manufacturers in China and Taiwan produce the plossl design. There are good ones and not so good ones. Even a humble plossl has a number of lens surfaces to be figured, polished and coated - 4 glass to air surfaces and 4 glass to glass cemented ones in fact. The glass quality used needs to be suitable, the figuring and polising good and the coatings carefully and evenly applied. The lenses then need to be accurately mounted in relation to each other and the surrounding internal areas properly blackened and baffled to prevent stray light issues.

Plenty of room for small errors which will effect final performance. As Robin says above you tend to get what you pay for. Tele Vue test 100% of their eyepieces before they go for sale and check that they work well even in F/4 scopes. That sort of quality control costs !

[gib77]

Thanks for all your replies, just to clear a few thinks up the focal length is 2032 the eyepieces in question did not come with the scope they were purchased separately, the main problem really is things seam a lot darker and not as clear as with the celestron ep

[gib77]

I thought the cheap eyepieces might be the problem I thought I would get some opinions before splashing out on better one's, but it's one step at a time

[RT65CB-SWL]

£10.00GBP each, nothing much lost, apart from your pride.

[RC4U]

also to consider if the scope was cooled or to temp.then maybe bad waves?? just a thought.

[gib77]

This is the scope in question, the focuser is not the wheel type just a know that sticks out that turns.

[gib77]

This is the scope in question, the focuser is not the wheel type just a know that sticks out that turns.

*knob

[ronin]

The assumption is the PL means they are a plossl design, have heard of ones that are not. Mention of this came up on CN recently, I think the person found out his plossl was a Huygens.

Also there comes the anti-reflection coating, a poor one loses light, then many blacken the lens edges to reduce light reflection and scatter. It could simply be they are not very good plossls.

You seem to have little choice - go buy an eyepiece.

Th TV ones are excellent but they are not inexpensive.

May as well consider which make/brand you would likely select for future use and get one of those. I have presumed here one of the mid price options (around £50) here not a £300 item. Or as said beter still borrow something from someone if it is possible.

[John]

The assumption is the PL means they are a plossl design, have heard of ones that are not. Mention of this came up on CN recently, I think the person found out his plossl was a Huygens.

Thats a mean trick to play but I wouldn't put is past an unscrupulous manufacturer to mis-label their goods

[gib77]

Thought I'd post a picture of the eyepieces also