Eyepieces - Some Questions

[i-CONICA]

Hi,

I've got some questions about eyepieces, if anyone can answer even some of them, I'd be very grateful.

1. 1 I'm wondering if all eyepieces will fit/work with my telescope so long as they're 1.25, or do I need to stick to my brand (skywatcher) eyepieces?
   

1. 2 My telescope (SkyWatcher Synscan AZ GOTO 127 mak cass) came with 1.25mm eyepieces, do that mean I can't use 2 inch eyepieces?
   

1. 3 What's the difference between the two sizes?
   

1. 4 What is a rough price to pay for a good (not the rolex of eyepieces) eyepiece?
   

1. 5 How good/bad are the ones that came with my telescope likely to be?
   

1. 6 I've read that eyepieces with "H" or "kel" (maybe) should be avoided at all costs, if that's the case, why are these still manufactured?
   

1. 7 What is a Plössl eyepiece, what is a super Plössl? I know that word is the name of a chap, but does it hold any significance in the performance of the eyepiece? I read it's the design of the optics, and that they have short eye relief, if that's the case, why are they considered to be so good? Surely you'd rather sacrifice a few degrees of FOV in favour of comfortable viewing?
   

(EDIT: Sorry they're all labelled as 1, the BBCode interpreter on this VBulletin seems wonky...)

Thanks.

[PreludeToADream]

You don't need to stick to Skywatcher eyepieces, as long as they're 1.25" they'll be fine.

As far as I'm aware the telescope you have only fits 1.25" eyepieces.

The difference is... the 2" are bigger. You can get a wider field of view with 2".

Eyepieces can really vary in price. If you're looking to replace the eyepieces that came with you telescope but don't want to fork out a lot of money you should try the BST Explorers: 1.25" Eyepieces (the second one along). Here's the ebay store: 1.25 15mm BST Explorer Dual ED eyepiece items in Sky's the Limit Astro and Optical store on eBay!

If you got the 10mm and 25mm eyepieces with your telescope then in my experience they're not brilliant eyepieces, but there are worse. The 10mm could do with replacing if you want to. Of course you'll be able to get some good views using the equipment you already have. You don't need to upgrade straight away if you don't want to. It's good to see how you get on with what you've got and then change what you're not satisfied with.

This may be of help regarding eyepiece designs: Eyepiece - Wikipedia, the free encyclopedia

Hope this helps a bit!

[E621Keith]

4 Good eyepieces starts around £30 with the Vixen NPL Plossl. BST explorer cost around £40 and will be more comfortable to use at the shorter focal lengths than the plossl.

5 The eyepiece that comes with your scope is probably the same as ones that comes with SLT, which are quite poor. Replace the 10mm first. Shorter eyepiece are more demanding on the optics and hence harder to make well.

6 H, SR, MA are very cheap to make hence they are sold with cheap telescope. Those should be avoided and astro dealer will not sell those separately. K or Kellner is cheaper and easier to make than plossl, and they are not bad at the longer focal lengths.

7 Plossl is constructed using two achromatic doublets. It is a good general purpose design. Super Plossl was Meade's name for their Japanese made 5 element designs, however, the Chinese made Meade 4000 super plossls are just regular 4 element plossl. I haven't use the Japanese version, but people said it's optically better. There are many different designs of plossl and the quality varies between manufacturers. Plossl is the cheapest design where you can get good view at the shorter focal lengths, that's why they were popular. They have less glass elements and air-glass interfaces than more complex long eye relief designs, so high quality TV plossl have an advantage in transmission, scatter and contrast. Lower quality ones doesn't have these advantages, so you won't miss anything going for a BST.

[i-CONICA]

Hi, thanks for the responses.

I've been looking at these, First Light Optics - Celestron X-Cel LX eyepiece

They're apparently better for people wearing glasses, with longer eye relief, is that a trade off in quality?, to make them able to offer long eye relief?

Also, if through my 10mm eyepiece (which is really blurry, I think it's just not very good) I seen Jupiter but it was still quite small, would using the 2.3mm eye piece make it bigger? If so, why wouldn't people just buy a smaller telescope (same aperture) and just use smaller FL eyepieces?

Thanks.

[E621Keith]

They're apparently better for people wearing glasses, with longer eye relief, is that a trade off in quality?, to make them able to offer long eye relief?

Also, if through my 10mm eyepiece (which is really blurry, I think it's just not very good) I seen Jupiter but it was still quite small, would using the 2.3mm eye piece make it bigger? If so, why wouldn't people just buy a smaller telescope (same aperture) and just use smaller FL eyepieces?

Compare to cheape plossl, there are no trade off in quality going for the X-cel LX other than price. Long eye relief eyepieces are usually made by combining a long focal length eyepiece with a built in barlow to boost magnification to match that of a shorter FL eyepiece.

You don't want a 2.3mm (652x), it will be too powerful on your 127 mak and UK sky. I suggest a 7mm (214x).

Generally longer eyepiece is more comfortable to use, so planetary scope tends to have longer focal lengths. Tinvek put it this way in the other thread

think of the quality of the viewing as the comfort of a car, the focal length as the gearing and the eyepieces as the revs (exept a smaller eyepiece is more revs)

if you wan to go at 70 mph you can either do it at say 2500 rpm in 5th or 8000 rpm in 2nd, similarly if you want say 250x mag, you can either do it with a 2500 mm focal length and 10mm eyepiece or a 500 mm focal length and a 2mm eyepiece.

both get you to 70mph / 250X but whilst the 8000rpm solution may be fun for a short while you sure as hell wouldn't want to spend a night driving down the motorway like that.

[hemihaggis]

If so, why wouldn't people just buy a smaller telescope (same aperture) and just use smaller FL eyepieces?

Thanks.

in general the rule of thumb for max usable magnification is the same as your lens diamater ..in your case with the 127 mak around x150 magnification maybe up to x200 from a dark site with good conditons , a 2.3 would be absolutly unusable , even on the moon .

the best upgrade i ever bought fo my 127 mak was a 32mm widefield ep .

the 25mm that came with the scope is quite good , but the 10mm is very poor

[i-CONICA]

Thanks Keith.

So someone with. 1200mm scope can achieve the same magnification as my 1500mm scope by using a smaller eyepiece, but that'll be less comfortable to use than a more powerful scope with a bigger eyepiece? Hope I've grasped it now...

So if I look at the moon with my scope with my biggest (25mm) eyepiece and it's too close, I want a wider view, I just buy a bigger (40mm) eyepiece?

One of the main reasons I got that scope was to hopefully see some DSOs, like M42, but some are suggesting I may have been looking right through it, rather than at it, when using my x2 Barlow and 25mm EP.

[E621Keith]

Thanks Keith.

So someone with. 1200mm scope can achieve the same magnification as my 1500mm scope by using a smaller eyepiece, but that'll be less comfortable to use than a more powerful scope with a bigger eyepiece? Hope I've grasped it now...

So if I look at the moon with my scope with my biggest (25mm) eyepiece and it's too close, I want a wider view, I just buy a bigger (40mm) eyepiece?

One of the main reasons I got that scope was to hopefully see some DSOs, like M42, but some are suggesting I may have been looking right through it, rather than at it, when using my x2 Barlow and 25mm EP.

Yes to the first question. To achieve 100x with your scope, you need a 15mm eyepiece which is just about usable for glasses wearer. To achieve 100x on my 120 achromat with 1000mm fl I will need a 10mm eyepiece, which is not usable for glasses wearer if the eyepiece is not one of the long eye relief designs.

If you want to get wider view of the moon, you have two options. 1) get a 32mm plossl, which will give you a lower magnification, essentially a zoomed out view. 2) get a wide field eyepiece such as Hyperion 24 or X-Cel LX 25. They have a larger AFOV (the black circle around the image) than your 24mm so they will give you a wider FOV.

When you look at M42, you should use your 25mm without barlow. I normally observe it between 35x to 95x magnification depending scope. Your 25mm + barlow gives you 120x, a bit high IMHO.

[hemihaggis]

yes ... a lot of dso`s require wide field of views , and little mag ..

[i-CONICA]

Ok, getting to grips with it now.

One last thing, if many DSOs require little magnification, such as 1500mm with a 25mm eyepiece, why are large aperture scopes of such huge focal lengths of its not really needed? Such as 4000mm? I know larger apertures allow in more light, but surely such a powerful scope can only be used for very deep objects?

[E621Keith]

Ok, getting to grips with it now.

One last thing, if many DSOs require little magnification, such as 1500mm with a 25mm eyepiece, why are large aperture scopes of such huge focal lengths of its not really needed? Such as 4000mm? I know larger apertures allow in more light, but surely such a powerful scope can only be used for very deep objects?

The focal length is part of their design. When you scale up the aperture, focal lengths scale with it. One of the advantages of Newtonian reflector designs is they can maintain a relatively short focal length for a given aperture. A typical 16" dob has a focal length around 2m, while a 16" SCT is around 4m. However, while the more common DSO in the Messier catalogue does not need a lot of magnification, you will need it once you start going after the more obscured DSO in the NGC and IC catalogues.

During a Stargazing Live event last week, I was asked if I can point my C9.25 at the Pleiades, unfortunately with the eyepiece I had, the lowest power I could get was around 100x, which looked straight through it. The view through the finder (13x) was quite nice in comparison.

[hemihaggis]

differnt scope are designed for different puposes ,

sct and mak scopes are great on planets and moons

reflectors are more designed for dso`s

ect ect

but these are only rough guidlines