Let down by cheap eyepieces?

[WinchesterAstro]

I began with a 100mm SkyWatcher, but have recently picked up some 20 x 80 Opticron bins. The new bins are SO MUCH BETTER than the scope, even though the scope is bigger. Why is this? With the bins, Albireo splits beautifully at 20x; with the scope I need to use at least 40x. With the 20x bins I can just about see Saturn's rings; with the scope I need to go to at least 40x to have any hope. The binoculars also give nicer views of the moon too--clearer, crisper, brighter, somehow (though obviously not as far zoomed in).

Why is this? I appreciate that two eyes are better than one, but there's just a fuzziness about the scope; stars seem to have a sort of fringe. The Skywatcher heritage scope is fixed collimation so I assume it's not that. The binos just seem altogether higher quality optically. Is this an eyepiece issue, and if so will upgrading help me out?

[Waldemar]

To find that out, maybe you can borrow a better ep from a fellow astronomer or a local club.

[jacobingonzo]

Are you using the scope and the bins on the same target at the same time? The EP's may be the issue as the stock EP's that come with the majority of scopes can  leave a lot to be desired- The fuzziness you describe would normally suggest seeing or collimation issues but if you used then scope then the bins at the same time ,it would rule out the seeing.

Can you tell us which 100mm Skywatcher you have as there are different types- if not sure can you provide a picture- assuming you looked at the objects with both scope and bins at the same time  ruling out poor seeing  it would seem to suggest collimation issues-depending on what you have there are reports of coma issues or just poor quality primary fixation- you could do a star test to confirm that your collimation is spot on.  https://www.skyatnightmagazine.com/advice/how-to-star-test-a-telescope/

 

J

Edited December 21, 2020 by jacobingonzo

[Zermelo]

I see from another post that yours is the Heritage 100P.        

As you say, a fixed primary but it's not impossible that the collimation is out, do you have any tools to check it?
Can you describe the "fringe" any further? Is it coloured? Does it appear around all objects? As a reflector, it shouldn't be giving any chromatic aberration. The mirror is a decent parabolic sort, though very fast at F/4. That, in combination with the stock Skywatcher eyepieces, may cause some image degradation. The 25mm generally performs a bit better than the 10mm. The suggestion to borrow a better eyepiece, if possible, is a good one.

[jacobingonzo]

aaah The Heritage thanks Zermelo

[Tiny Clanger]

16 hours ago, WinchesterAstro said:

I began with a 100mm SkyWatcher, but have recently picked up some 20 x 80 Opticron bins. The new bins are SO MUCH BETTER than the scope, even though the scope is bigger. Why is this? With the bins, Albireo splits beautifully at 20x; with the scope I need to use at least 40x. With the 20x bins I can just about see Saturn's rings; with the scope I need to go to at least 40x to have any hope. The binoculars also give nicer views of the moon too--clearer, crisper, brighter, somehow (though obviously not as far zoomed in).

Why is this? I appreciate that two eyes are better than one, but there's just a fuzziness about the scope; stars seem to have a sort of fringe. The Skywatcher heritage scope is fixed collimation so I assume it's not that. The binos just seem altogether higher quality optically. Is this an eyepiece issue, and if so will upgrading help me out?

I'd first check if there is some sort of problem with the primary or secondary mirrors , even if they are fixed and non- collimatable or adjustable in any way, if you can trace the fuzzyness to a manufacturing fault you can get redress from the seller (assuming you bought it from new in the UK) Presumably the primary does not have a centre spot to help the usual collimation methods ,but if there are visible clips on the primary you might get some idea if anything is out of whack by using a simple, home made collimation cap , plenty of info about making & using them is available online.

If not, you could still try a star test : https://garyseronik.com/no-tools-telescope-collimation/

The nest thing I'd look at is the focusser, is it in some way loose ? Looking at images of the 'scope it's not the same plumbing-fitting- style lump as on my heritage 150, maybe there's a loose screw somewhere allowing the tube to slip?

Only if the telescope itself is absolved of fault would I think about the eyepieces, although the general opinion is that whilst the included 25mm is acceptable, the 10mm is not very good. My first accessory purchase was a basic skywatcher 17mm plossl for about £22 , and despite being low on the desirability scale for enthusiasts,  it was an appreciable step up in clarity.

Heather

[Ricochet]

3 hours ago, Tiny Clanger said:

Only if the telescope itself is absolved of fault would I think about the eyepieces

I would suggest the opposite. The supplied eyepieces are of a design that is intended for very slow focal ratios, but the scope is extremely fast. Until the eyepieces have been excluded, there is no way to tell whether there is a fault with the telescope.

[Tiny Clanger]

3 minutes ago, Ricochet said:

I would suggest the opposite. The supplied eyepieces are of a design that is intended for very slow focal ratios, but the scope is extremely fast. Until the eyepieces have been excluded, there is no way to tell whether there is a fault with the telescope.

Could a star test not establish if the collimation is badly out regardless of the quality of the eyepieces ?

[Ricochet]

2 hours ago, Tiny Clanger said:

Could a star test not establish if the collimation is badly out regardless of the quality of the eyepieces ?

It would depend how badly the eyepieces perform and if the coma from the scope could be distinguished from the aberrations from the eyepiece. A proper star test would require a shorter focal length eyepiece than those supplied with the telescope. 

[Tiny Clanger]

I'm trying to come up with helpful, practical suggestions for checking a £99 telescope which do not involve throwing more money at it, a course of action which may perhaps be out of the question . I'm guessing a suitably low aberration, shorter focal length eyepiece would cost around the same as the 'scope itself ?

Would a simple, home made collimation cap show up a major problem, even if there is no centre spot on the primary ?

[Jasonb]

Just looked at a video of the Heritage 100P and while the primary is fixed the secondary looks like its adjustable, so collimation could definitely be an issue, or at least something to try!

[Ricochet]

3 hours ago, Tiny Clanger said:

I'm trying to come up with helpful, practical suggestions for checking a £99 telescope which do not involve throwing more money at it, a course of action which may perhaps be out of the question . I'm guessing a suitably low aberration, shorter focal length eyepiece would cost around the same as the 'scope itself ?

Would a simple, home made collimation cap show up a major problem, even if there is no centre spot on the primary ?

The problem with a collimation cap is that it is really a tool for checking/adjusting the primary collimation when the primary is centre spotted. If a few pounds can be spent then short cheshires are available on eBay for less than £10 directly from China. Assuming that the primary is centre spotted, this would be a much more accurate tool to check collimation. If a collimation cap is all that is to hand then it is better than nothing, but it may be hard to judge the collimation accuracy using it, especially as in a fast scope the secondary shadow will be quite offset.

With regards to an eyepiece to test, an 8mm Starguider and 2X barlow would do the trick, or an eyepiece from the "Planetary" line of eyepieces. The key here would be to buy something that has a negative element in the nose so that the light cone is narrowed by the time it gets to the main groups of lenses that form the image when that eyepiece is used without the barlow.

A problem with collimation would move coma into the centre of the field of view, but I don't think that this would exclusively lead to the description of "fringing", which sounds like there are other issues in the eyepieces on top of the coma from the telescope.

[WinchesterAstro]

Thank you all for your thoughtful suggestions. I have checked collimation very roughly with a collimation cap, but it may be worth buying a better collimation tool, since I intend to be doing astronomy for some while yet.

Ditto eyepieces, which are a good long-term investment, right?

The Sky at Night review mentions seeing cloud bands on Jupiter, which I've never managed.

http://www.opticalvision.co.uk/user/reviews/BBCS@N_Aug2014_heritage%20review.pdf

[Ricochet]

4 minutes ago, WinchesterAstro said:

The Sky at Night review mentions seeing cloud bands on Jupiter, which I've never managed

Probably to do with the altitude of Jupiter at the time of the review more than anything else.

Eyepieces are a good investment so long as you purchase decent quality eyepieces and choose useful focal lengths.

[WinchesterAstro]

Yes, this crossed my mind. I've used this scope since 2018, I think, and Jupiter has been sitting pretty low in the sky.

Just now, Ricochet said:

Probably to do with the altitude of Jupiter at the time of the review more than anything else.

Eyepieces are a good investment so long as you purchase decent quality eyepieces and choose useful focal lengths.

 

[WinchesterAstro]

I have managed to get a picture with the collimating cap. First time I've collimated anything, but it doesn't look quite right to me. Particularly worrying is that the central dot *moves* slightly from side to side when I slide the focuser up and down:

 

 

[KP82]

7 hours ago, WinchesterAstro said:

I have managed to get a picture with the collimating cap. First time I've collimated anything, but it doesn't look quite right to me. Particularly worrying is that the central dot *moves* slightly from side to side when I slide the focuser up and down:

 

 

Unless it's the angle of your phone when you took the picture, there is very obvious vignetting to the top right. Your secondary mirror could be out of collimation.

[WinchesterAstro]

1 hour ago, KP82 said:

Unless it's the angle of your phone when you took the picture, there is very obvious vignetting to the top right. Your secondary mirror could be out of collimation.

Thank you for taking a look. Good news in that the secondary is adjustable on this scope, whereas the primary is fixed.

[Stu]

10 hours ago, WinchesterAstro said:

Thank you for taking a look. Good news in that the secondary is adjustable on this scope, whereas the primary is fixed.

Doing a star test is probably as useful as anything. If you use Polaris, it is about the right brightness to be useful and doesn’t move much! Make sure it is central (to avoid coma or other off axis issues, and just check that everything is concentric as you move from defocussed into focus. Use the 10mm eyepiece, not ideal from a mag perspective but better than nothing.

[johninderby]

Also keep in mind a meaningful star test requires good seeing and not too much turbulence in the atmosphere.

[WinchesterAstro]

Hello friends. Only one screw could be adjusted on the secondary, namely the one in the centre of the spider. It let me rotate the mirror. Is the collimation pictured below any better? I *think* the dot is more central now.