Another Lot Of Questions About Eyepeices

[Yendor]

Ive asked already about eye relief, so when I get my scope, do I have to replace the eyepieces with new ones giveing the correct eye relief OR are the existing eyepeices modified by something I buy?

Also

If I buy another scope of a different kind do I have to buy yet another set of eyepeices.

I suppose simply put are all these things interchangeable?

Last question Honest!!

Are the eye pieces supplied with scope not good, I see many references to buying better ones?

[ChrisEdu]

Yes, they are interchangable, but results may / will differ from one scope to another.

[Yendor]

ahh ok. Do you mean in terms of quality of image, or performance. I was also thinking, if at some point I join or attend a club, wont I need to take my eyepieces with me, as they would probably be the only suitable ones for me to use? I am sorry for all these questions, I guess really there is no substitute for actual experience........... The sooner I can get "hands on" the better.

[Nova]

i dont know of anything available that will change the eye relief of an ep. you will have to by an ep with the required eye relief. the ep's that come with scopes are normally (certainly the entry level ones not sure if this applies to the more expensive end of the market) are normally low end ep's. they are still more than adequete to start with but as soon as you look through a more expensive one (televue for example) you will notice the difference.

[Ags]

It will all make sense when you get your scope. Eyepieces fit like a cork into the end of the telescope. You can either use the EPs that come with your scope, or you can buy a few extra, but you can only fit one at a time in the scope... :-) They come in two standard sizes (1.25" and 2") so they are freely interchagneable. Some scopes (like both of mine) only accept the smaller 1.25" eye pieces.

You typically select an eyepiece for a given magnification (e.g. 150x for Jupiter) and field of view (so you would pick a low magnification for a wide field of view to admire the andromeda Galaxy, for example).

All my EPs have long eye relief, but I find short eye relief OK too. I think you mentioned in another thread that you have astigmatism. I have heard that at high magnifications, astigmatism is suppressed so your glasses may not be obligatory for viewing planets. (Do a search for 'astigmatism and exit pupil').

[Yendor]

Thanks this is brilliant help your giving me all of you. I have read about the exit pupil and eye relief in another posting of mine about eye relief. I didnt fully understand, I think it's best I read up about it over the weekend when I'm more relaxed and dont need to worry about work.

So once I buy more suitable and better equipment it'll be an investment.

I imagine then that one would possibly use an eyepiece with a good field of view, then use something with a bit more magnification to focus up nice and close to what it is I want to view.... I have read and understand that too much magnification is as bad as little or none and can have a detrimental effect on whats being viewed.

I'm really looking forward to buying my scope in a few weeks. I'm trying hard to be patient, ;-)

[Nova]

you may eventually want to upgrade your scope but a good ep collection could last you a lifetime, an investment for sure. as for magnification it depends what you want to look at. you may want fairly high magnification for planets but generally dso's will be better viewed at lower magnification but as with pretty much eveything in this hobby its all about personal preferance. play with your ep's and see what suits you best.

[John]

i dont know of anything available that will change the eye relief of an ep.....

A barlow lens changes the eye relief of an eyepiece - it tends to make it longer.

[ronin]

Plossl's tend to have eye relief that is related to the eyepiece focal length, just cannot recall what it is - think it is something like 2/3 the focal length.

Assuming this, (probably incorrect but closeish) then a 5mm eyepiece would mean getting your eye about 3 mm from the eyepiece, however this will be the lens of the eyepiece, which is set back a little.

So your eye ends up very, very close to the eyepiece, sometimes uncomfortably so.

Plossl's come, as most things, in all quality levels and performance levels. Someone said that in general you get what you pay for.

GSO plossl's seem to have a good reputation, but still they will show a lack of relief at the shorter focal lengths - the ones that everyone wants and is itching to try out for that huge magnification they promise.

Alternatives are SWANS and planetery eyepieces.

SWANS owing to their wide views can start to show poor images at the edges, equally you look at things with them central, extended DSO's could be a bit of a problem, M31, M42, M45.

Planetery's also get good reports and their field of view is a little larger the plossls. Skysthelimit do a fair range of TMB clones at about £35-37, so plossl prices.

A lot will depend on the scope ypu decide to get.

The supplied ones are not great, usually the 25mm is adaquate and the 10mm isn't usually so good. They are supplied for general use and as such are a compromise with regards magnification.

[Nova]

A barlow lens changes the eye relief of an eyepiece - it tends to make it longer.

didnt know that. cheers

[CAB]

Hi, I am shortsighted and have astigmatsim too. I have EPs that give good eye relief for my own scopes but don't worry about joining a club and looking through other peoples telescopes and eyepieces with your glasses most people who bring their scopes along have decent eyepieces to look through and I find it ok to use my glasses - you will be fine. It is is also a great way to see what sort of EPs you like before you buy. I agree a good EP collection built up carefully will last you forever and go from scope to scope. I also don't need my glasses when using my 4mm eyepiece as this bypasses my astigmatism.

I am trying out some new varifocal contact lenses for astronomy - two weeks in and so far so good.

[Yendor]

My word this is information overload...I love this forum.

I think it's time I had an eye re-test. I think before I try or certanly buy anythink I need to make sure my current prescription is up to date. I winder if the optician could advise also? maybe worth asking him/her. Thanks again for all the info, will try hard to learn from it and share anything I find out.

[haitch]

You may find your EP requirements change if you change to a scope of a different focal length as the focal length of the scope divided by the focal length of the EP (units unimportant as long as you stick to the same units) give you the magnification. Ihave a 14" dob with a f/l around 1.6 metres and a William Optics Megrez 88 with a focal length of under 0.5 metre. My EPs give less than a 1/3 the magnification in the Megrez. It's not that they don't work in it just that they don't give all the magnifications I want. A barlow or Powermate (or the Meade equivalent a TeleXtender) can solve this or just another EP or 2 to fill the gaps (just down to personal preference).