Read this before you buy yours EPs!!!!

[Vince1963]

Like most people getting into Astronomy, I find that there is not enough emphasis on EPs (eye pieces), I think it could be the single most important reason why some people fall by the wayside and decide to give up on Astronomy because they have been disappointed with there views from there scope, This very same reason could quite easily have been me. I found this http://www.swindonstargazers.com/beginners/eyepieces.htm by Robin from Swindon stargazers very useful and when i personally emailed him with my dilemma he was very helpful and very informative, Just like many of the well informed and experienced armature Astronomers on here, New guys to astronomy need you guys..I personally want to thank you wise old sage's of the astro world (lol)...

[John]

And there was I thinking we discuss eyepieces too much !

That is a good piece by Robin. We are lucky that he is a member here too

[Sepharus]

Good read, thanks!

[Vince1963]

And there was I thinking we discuss eyepieces too much !

That is a good piece by Robin. We are lucky that he is a member here too

I see what your saying John, but we like EPs... Mmm! EPs. lol

[Naemeth]

I see what your saying John, but we like EPs... Mmm! EPs. lol

Careful or you'll get ECS (Eyepiece Collection Syndrome), it's also known as OECS (Obsessive Eyepiece Collection Syndrome) .

Seriously though, I read this a while back, and it's a well written article, it wasn't the first article like that I'd read and wasn't my last, but the information there was all helpful .

[SilverSeadog]

Thanks for passing this on. Some good advice from Robin.

Alan

[cgarry]

"I find that there is not enough emphasis on EPs (eye pieces)"

You surely cannot be talking about the same forum!

[AndyH]

Good read

Sorry to be a nit-picker , but I disagree with this bit....

I've had a number of various branded/age volcano topped ortho's come n go over the years and they've all been first rate.

Apart from that, a fine write up indeed !!

Andy.

[E621Keith]

Careful or you'll get ECS (Eyepiece Collection Syndrome), it's also known as OECS (Obsessive Eyepiece Collection Syndrome) .

Seriously though, I read this a while back, and it's a well written article, it wasn't the first article like that I'd read and wasn't my last, but the information there was all helpful .

We have a ECS sufferer group here on SGL. Their thread can be found here

http://stargazerslou...ye-piece-cases/

[cantharis]

Excellent article by Robin - added to my faves.

[Charon]

Robin does give very sound advice.

[Vince1963]

Hi Keith... I've looked on that thread.. Corr!.. there's some beauties on there.. Mmm!.... (Drool) EPs.... (in a sort of Homer Simpson voice )

[alan potts]

An excellent and well written piece, Well done Robin if you ever look in.

I don't think we talk about eyepieces too much we maybe talk about the same thing too many times.

Alan.

[Mike73]

Its funny but I think theres way too much emphasis on EP's.....the one thing that I think is more important than EP's, dark skies and aperture is dark adaption and its seldom talked about and costs nothing!

[E621Keith]

Just read the article, it's very informative, but I don't agree with his opinion on 1.25" and 2" eyepieces.

Eyepiece is only optically 2" when the field stop exceed the 1.25" barrel size. A 1.25" eyepiece can be fitted with a 2" barrel, but that does not make them a true 2".

Some 1.25" eyepiece designs have generous eye relief regardless of focal lengths (e.g. Hyperion and XW, both 20mm across the range and more then all 2" Ethos and Nagler). The eye relief in traditional designs such as plossl and orthos is a function of their focal length not barrel/field stop diameter. A 40mm 2" plossl will have the same eye relief as a 40mm 1.25" plossl. (but the 1.25" will have smaller FOV due to barrel restriction)

Low power eyepiece are not suitable for planetary observation on most scopes regardless of barrel diameter.

2" eyepieces is almost a necessity on an large SCT/Mak above 8". Their long focal length and narrow field means you need a eyepiece with a large field stop to get a reasonable FOV. I found I couldn't do without my 42 LVW when I observe with my C925. A 1.25" eyepiece can only see 0.7deg field with that scope, but the LVW gives me 1.3deg. It's narrow, but better than 0.7deg.

[joe_coke]

NICE ARTICLE, THANKS FOR POSTING

[great_bear]

Robin has a nice writing style, but his article has lots of errors in it - factual errors, not matters of opinion - which may lead to confusion when trying to understand the subject of eyepieces.

[mert]

Thanks for posting.

[alan potts]

Its funny but I think theres way too much emphasis on EP's.....the one thing that I think is more important than EP's, dark skies and aperture is dark adaption and its seldom talked about and costs nothing!

Mike,

Put up a post on it, why not, I for one never really thought of it until now. It is important!

Alan.

[fredster]

Just read the article, it's very informative, but I don't agree with his opinion on 1.25" and 2" eyepieces.Eyepiece is only optically 2" when the field stop exceed the 1.25" barrel size. A 1.25" eyepiece can be fitted with a 2" barrel, but that does not make them a true 2".Some 1.25" eyepiece designs have generous eye relief regardless of focal lengths (e.g. Hyperion and XW, both 20mm across the range and more then all 2" Ethos and Nagler). The eye relief in traditional designs such as plossl and orthos is a function of their focal length not barrel/field stop diameter. A 40mm 2" plossl will have the same eye relief as a 40mm 1.25" plossl. (but the 1.25" will have smaller FOV due to barrel restriction)Low power eyepiece are not suitable for planetary observation on most scopes regardless of barrel diameter.2" eyepieces is almost a necessity on an large SCT/Mak above 8". Their long focal length and narrow field means you need a eyepiece with a large field stop to get a reasonable FOV. I found I couldn't do without my 42 LVW when I observe with my C925. A 1.25" eyepiece can only see 0.7deg field with that scope, but the LVW gives me 1.3deg. It's narrow, but better than 0.7deg.

Yes i found it strange Robin considered a 2" widefield eyepiece a poor match with an SCT. I know people with big SCT's that couldn't get by without their SWAN 40mm or Meade 56mm Plossl.Also agree with Andy about the Volcano top orthos, they were my first decent eyepieces and cost peanuts.But a good article none the less.

[Vince1963]

Robin has a nice writing style, but his article has lots of errors in it - factual errors, not matters of opinion - which may lead to confusion when trying to understand the subject of eyepieces.

Hi Great bear.. Can you explain?, if its helpful i/we would love to hear it.

[great_bear]

Sure, but there's too many to list.

This isn't a personal criticism of Robin - and I'm sure many people find the article helpful, but in the first 40% we have:

1. "It is perhaps a travesty to learn that with your first telescope that you may have spent two or three hundred pounds for came with eyepieces that are barely fit for purpose, and even the well established manufacturers provide only the most basic specification eyepieces with which to start."

This is too much of a sweeping statement. Meade telescopes often come with a Series 4000 26mm Plossl which is about as good as Plossls get before paying Tele Vue prices.

2. "the 2" eyepiece will probably have better eye relief"

There are two main reasons for the use of a 2" fitting on eyepieces:

1) The eyepiece has a field stop greater than that which can be accommodated in a 1.25" eyepiece.

2) If the eyepiece is so heavy (thing ES 9mm 82 degree) that it's a bad idea to use a 1.25" fitting.

Apart from these, there is no intrinsic difference between 1.25" and 2" eyepieces of identical focal lengths in terms of image quality, eye-relief, or any other optical parameter.

3. "2 inch eyepieces may not perform so well with SCT's or Maks because of the telescopes' long focal length"

On the contrary - having a long focal length is precisely the reason you need 2" eyepieces to get the lower powers. Typically, any problems with the use of 2" eyepieces in Maks and SCTs are related to the restricted aperture at the back of the scope, not the scope's focal length.

4. "If you would like to use 2" eyepieces with your 1¼" diameter focuser there is nothing to stop you doing so, all you need to do is buy a 1¼" to 2" convertor, which costs around £20"

Whilst unstated, this strongly implies that there might be benefits to doing this, and that doing so may be a good idea. In fact there are no benefits to doing so. The only reason for doing this might be if you were stuck and the only eyepiece lying around happened to be a 2" (which would be a very unusual position to find yourself in) or possibly if you were doing some kind of projection photography where such a weird arrangement proved beneficial in a very specific set of circumstances with a very specific set-up.

5. "Advantages: One: More comfortable viewing and able to view for longer, Two: 2" eyepieces are good with Barlows (clever little extension for magnifying an existing eyepiece by x2), Three: Eye relief is usually better (x2 normally) and so more comfortable."

2" eyepieces are not intrinsically more comfortable than their 1.25" models (see earlier), nor do they optically behave better with Barlows (with the one possible exception of full-field), and their eye-relief is identical to 1.25" eyepieces of equivalent design.

6. "Generally speaking, the more elements that an eyepiece has, the better its performance should be."

This is an unfortunately misleading over-generalisation, which has a strong risk of leading beginners in the wrong direction with regard to eyepiece choices.

7. "10 - 17mm - Medium magnification - Good for globular star clusters and medium detail, and some Deep Sky objects"

This is not true if you've got one of those ubiqutous 127mm Maks that a lot of people start off with; the 10-17mm eyepiece range would class as HIGH magnification, not medium, and the stated range of "2.5-8mm Good for planetary and lunar viewing" would for the most part be unusable.

8. "Eye relief refers to the closness to the eyepiece that the human eye needs to be in order to see the object being viewed, this is often called 'exit pupil'."

No it isn't. "Exit pupil" measurements are actually the diameter of the bundle of rays leaving the eyepiece at any given angle (within the relevant angular range) this is a completely different parameter than "eye relief".

9. "greater magnification = smaller field of view, and this in itself requires you to be viewing at a much closer range for the pupil to engage the object being viewed"

The field of view does not dictate the eye relief in this manner.

10. "in eyepieces of greater focal length (6.4mm and above) there is a certain amount of choice that can be made by the amateur astronomer when reviewing the eyepieces that can be chosen."

There is no magic figure above which "a certain amount of choice that can be made by the amateur astronomer" - they have a broad range of choices across all useful eyepiece focal lengths.

11. "if an eyepiece has a narrower field of view then inevitably the eye relief will not be as great."

This is not true. To all practical intents and purposes, eye relief is a function of eyepiece design and not all eyepiece designs will utilise such scaled implementations.

I don't have time to review the remaining 60% of the article, but there are further issues.

As I say - not a personal criticism of Robin - and I wasn't going to mention specific errors at all, but you did ask...

rgds,

J.

[E621Keith]

11. "if an eyepiece has a narrower field of view then inevitably the eye relief will not be as great."

This is not true. To all practical intents and purposes, eye relief is a function of eyepiece design and not all eyepiece designs will utilise such scaled implementations.

One good example is the Abbe vs Plossl. Abbe with 40deg AFOV generally have greater eye relief than the 55deg plossl. The ER on an Abbe orthoscopic is about 80% of its focal length vs 60% for plossl.

The ER on modern designs are almost independent of AFOV, in fact 70deg designs such as LVW, Hyperion, Delos and XW generally have greater ER than 82deg and 100deg such as Nagler and Ethos.

[great_bear]

Yes indeed - but then I figured maybe Robin was talking about actual FOV not apparent FOV - but thinking about that, it still didn't add-up, since (as per my comment) eyepiece ranges with very short focal lengths typically don't use a scaled design e.g, the lowest lengths of Ultrascopics, or the lowest three of Radians, or the Delos, or TMBs, BSTs, LERs - the list goes on.

[Vince1963]

Well Greatbear that was a very interesting read, I am pleased you wrote that, It is after all best to be well informed, After all EPs can and are expensive and some of us don't have a large amount of money.