Different Types Of Eyepieces And Their Purpose

[altii12498]

Hi there,

I am brand new to astronomy and was reading a couple articles about eyepieces and I had no idea what the difference in them are! I would like some clarity on different types of eyepieces and their function, for example how a Plossl differs from a Hyperion.

I was also wondering if eyepieces are specific to different types of telescopes, for example if a certain eyepiece can only be used on a refractor.

Any response is greatly appreciated.

[John]

Hi and welcome to the forum

It's quite a complex topic as there are more eyepiece types around than scopes !

This is a good primer (apologies if you have already read it):

http://stargazerslounge.com/topic/43171-eyepieces-the-very-least-you-need/

This is also a good introductory piece from the Sky & Telescope magazine:

http://www.skyandtelescope.com/astronomy-equipment/telescope-eyepiece-guide/

Hope that helps a bit - feel free to ask more questions to clarify things though

[LittleSkink]

interesting question - I shall follow this also

what I have learnt is pretty limited but builds on my interest in old manual focus camera lenses - where the "character" (ie flaws) of simple lens designs is a potential benefit. In Astro use that seems much less true

3 lens designs (Kellner among others?) are pretty basic and due to design have issues with aberrations and colour. Got a 9mm Skywatcher "modifed" Kellner at it works okay

4 lense symetrical (Plossl) are also basic but much better with aberration control. Alas they also only offer eye relief at 80% of focal length so short (<12mm ish) are poor for glasses wearers like myself.

Hyperion are computer designed multi element designs - probably very efficient and lacking in "character" - alas I have never used one

This is an excellent read (and no doubt a fellow on here)

http://www.swindonstargazers.com/beginners/eyepieces.htm

[John]

......Hyperion are computer designed multi element designs - probably very efficient and lacking in "character" - alas I have never used one

This is an excellent read (and no doubt a fellow on here)

http://www.swindonstargazers.com/beginners/eyepieces.htm

Hyperions are good in slower scopes eg: F/7, F/8, F/10 etc but do show some distortions in the outer parts of their field of view in faster scopes than that (eg: F/6, F/5 etc)

Robin is a member here and thats a great piece of his

[ronin]

Generally not specific to a scope type.

The design is usually to impart properties to the eyepiece, wider field of view being the obvious one.

A plossl gives about a 50 degre view, to get a bit more they found that you could add an extra lens and the view increased.

With that increase the edges would be a bit out of sharp focus, so perhaps add a corrector for this.

So 4 lens became 5 and that became 6.

Adding more glass can cause problems of say additional chromatic aberration so another bit of glass to reduce that, 7 elements.

Some eyepieces do not work well at fast f numbers is likely the main criteria to look for.

"Simple" eyepieces tend to have a narrow field but the image in the centre is sharp, off centre is a different matter.

Since planets are small and usually you sit them in the centre then a good but simple plossl, ortho etc work well. If however you are observing a cluster like the Pleiades or Hyades then you want a wider view and good images at the edges, so they do not do as well. So you pick a different eyepiece with different properties.

[altii12498]

Hyperions are good in slower scopes eg: F/7, F/8, F/10 etc but do show some distortions in the outer parts of their field of view in faster scopes than that (eg: F/6, F/5 etc)

Robin is a member here and thats a great piece of his

What do you mean by "slower scopes." As in the time it takes light to travel through the eyepiece?

[John]

What do you mean by "slower scopes." As in the time it takes light to travel through the eyepiece?

No it's not that !.

The focal ratio of the scope is the focal length divided by the diameter of the main mirror or objective lens. So a scope with a 100mm diameter objective lens and a focal length of 1000mm has a focal ratio of 10 which is described as F/10. A scope with a 150mm main mirror and a focal length of 750mm has a focal ratio of 5 = F/5 and so on. It's not exact but scopes with focal ratios of around F/8 and above, eg: F/10, F/15 etc are termed "slow" wheras scopes with focal ratios of F/6, F/5 etc are termed "fast".

This website has some useful info on scopes and some videos explaining the concepts better than I can

http://www.eyesonthesky.com/Videos/TelescopeBasics.aspx

[ronin]

What do you mean by "slow?" As in how long it takes for light to travel to the eyepiece?

It is a carry over or term from the world of photography.

But there are characteristics/properties that are relevant in astronomy.

It is I suspect used more in astronomy then in photography now with the advent of DSLR's that are programmed to do everything.

[Astro_Baby]

http://en.m.wikipedia.org/wiki/Eyepiece

Wiki has a fair primer on EPs, its not fully inclusive but its not a bad starting point.

[bomberbaz]

I have watched this thread and its interesting to see a lack of posts. I am assuming that is because it is a tin of worms question really. As John pointed out the variety, number of designs etc is ever expanding and I think it is sometimes as much down to personal preference as it is to design. 

My own thoughts ref differing EP's are tempered by several considerations, one being I wear glasses, two I have a farly fast main F4.9 scope and three I do like a decent FOV at lower magnifications. Also lack of viewing has led me to change my collection as i couldnt justify the money I had tied up in so much very nice but expensive glass as I previously had.

So I have two wide field ep's at 1.5 and 1 degree field of view that covers much of my open cluster and nebula viewing. ( I should point out I use a coma corrector for these)

I have a 25mm plossl for viewing small area, dull dso's at low mag. (x60)

next is 3x Vixen Lanthanum glass ep's. Only have limited experience with these that wont be more than maybe an hour but they are lovely and sharp which I use/or intend to use for things including smaller open and larger globular clusters and other smaller nebula. (0.6 to 0.4 fov and 83 to 125 MAG)

Then I have got a as yet untried higher quality orion ultrascopic barlow to increase these 3 eyepieces to 166x magnification and above. this is the planetary, small globs, moon area. (I am something of an all rounder when it comes to viewing although I think planetary and nebula viewing is my favorite ) 

Anyway, thats my eyepiece set up. Hope this helps in someway although the fact I have not yet used some of my recently revamped kit doesn't help but I am sure the methodology is at least clear. That said, I am very confident that both the new eyepieces and barlow will perform very well together.

[Dave In Vermont]

These are the best one's I've found, and they are posted on my walls:

http://www.quadibloc.com/science/images/eyevar34.gif

http://www.handprint.com/ASTRO/IMG/eyepieces.gif

Clear Skies,

Dave

[bomberbaz]

These are the best one's I've found, and they are posted on my walls:

http://www.quadibloc.com/science/images/eyevar34.gif

http://www.handprint.com/ASTRO/IMG/eyepieces.gif

Clear Skies,

Dave

Great diagrams Dave, I will try and figure out what I actually have now, only kidding. i have no idea and happy to live in blissful ignorance as long as they wrok 

[YKSE]

I agree with Astro_baby that Wiki is a good starting point.

If you feel for reading more, you can try these links:

http://www.handprint.com/ASTRO/ae5.html

http://www.quadibloc.com/science/opt04.htm

http://howardastro.org/presentations/evolution_of_eyepieces.pdf

This link has some general info about eyepiece choice, worth to read a couple of time to understand it, IMHO.

[Astro_Baby]

The reason I have shied away from an answer here is I dont think I could really explain all the issues of eyepieces and scopes succinctly.

Bearing in mind the OP is very new it might be way too much to cope with when you consider all of the factors....thats perhaps why not many posts have been made.

Generally most EPs will work with most scopes but there are issues regarding the focal ratio of the scope ( how 'fast' it is ), the dittings on the scope itself ( does it accept 1.25" and 2" EPs) , the eye relief requirements of the user, how much abberationis acceptable ( I dont mind efge abberations too much but others might have a different criteria and critically how much the user wants to spend.

In a nutshell heres a one line review of EPs I have owned.......

Least expensive...all 1.25 fitting will mostlybwork ok at F5 but longer FL will impeove them a lot.

Celestron Plossls....quite good on the whole , 32mm was may favourite, eye relief tight at shorter focal lengths. Ok down to F5

Skywatcher SP Plossls.....only used the 25mm and it was about on par with the Celestrons

TAL Gen II Plossl..no longer available but superb

Vixen NPL Plossls....shaded the others with much better contrast but the casings were a bit plasticky, can fault the optics

UO Orthos, safly no longer available, comfy, narrow view but very sharp and I find work ok down to F5 so long as yoi dont mind the edge goong a bit iffy. Less attractive for anyone without a tracking mount due to narrow field of view...tight eye relief at smaller focal lengths.

Baader GO Orthos...touted as better than UO orthos, I found them less comfy to use and never saw a difference in the view.

TMB Planetary II..unique lens design optimised for wide angle than a Plossl..I liked mine but moved on. bST starguiders ate supposed ro be the same and are well thought of

Bit more pricey..mostly 2" fitting mostoybwork fine down to F5 but with some aberrations.

Baader Hyperions...generally liked mine, dont think they have kept pace with tye market, worked acceptably at F5 but better in slower scopes. Dual 1.25 and 2" fitting.

Skywatcher Panaviews...nice wide angle view, porthole in space, very contrasty but people averse to any edge aberrations will tend to dislike.

Explore Scientific 82' .....only used the 30mm and it was very fine, would give much more expensive EPs a run for their money, probably the best bang for the buck in the mid market. The bigger ones like the 30mm get pricey and tyey are VERY heavy. Some of these will be 1.25 fitting at smaller sizes.

Very pricey.....1.25 and 2" fitting deoending on E P focal length...will all work fine down to F5 with no issues at all.

Explore Scientific 100'..2" fitting only, expensive but still cheaoer than the Televue Ethos, hard to tell the views apart but personally I a, not struck on 100' eyepieces. Find them a bit overkill. 100' the ultimate floating in space experience ( at least until the 120' versionss get cheap enough )

Pentax XW...70' field of view, glass so fine that only an ortho can rival its sharpness and contrast, the 10mm is possibly the finest 10mm eyepiece ever made but they aint cheap..dont get a Pentax habit or you will dind yourself trying to sell a kidney fortunately the bigger ones are out of production.

Hope tyats of some help

[Kriss Craik]

Thanks guys really interesting conversation. Some food for thought