EP short comings

[LDUNN1]

Forgive the naive questions, but I have been wondering what the main design/specification/dimension drivers are on an EP that maybe responsible for making the following EP failings worse:-

1) kidney bean blackening

2) Eye floaters

....any thoughts / discussion on what makes these characteristics better or worse for a given EP focal length would be appreciated.....and/of what one can do to combat the effects

[SiriusB]

Re: floaters:

this is down to dead cells floating around inside your eye.Eyepiece design should have no effect on this, it becomes more noticable with small exit pupils. objective dia (mm) / magnification = exit pupil dia (mm)

Expect it to start getting anoying with exit pupils <1mm unless your blessed with a low floater count

Re: kidney beaning: caused by spherical aberration of the exit pupil.

As a rough rule of thumb seems more likely to occur in complex ep designs,especially in longer focal length ep's & large eye reliefs.

personally i find it very objectional, so best to check the reviews before purchase if it's likely to bug you.

I'm sure someone else can elaborate.

[LDUNN1]

thx for the explanation.

I appreciated that the 'floaters' issue was due to dead cell debris floating about in the eyeball, & thought that it became more apparent with higher mag EP's which have a smaller exit pupil.......so the only way to practically counteract this presumably is to use an EP with greater exit pupil diameter (circa >1mm) taking into account the scope its on, & then use barlow/powermate to increase the magnification?

I have one EP which tends to kidney bean readily - & I do find it irritating, luckily it is a cheap secondhand EP & the TV ones I have recently bought do not bother me this way anywheer near so much - but I have heard than some of the Naglers can exhibit this issue. I wondered if it has anything to do with Eye relief.....

[SiriusB]

If you use a barlow to increase the mag the exit pupil will still be the same for a given mag on a given scope,so i don't think that will help.

However Using a barlow with a kidneybeaning ep may well reduce the effect??

Yes I think large eye reliefs can exaggerate kidney beaning,all other things being equal.

[xboxdevil]

Binoviewers are a great way to mitigate floaters, they can be a bit fiddly but they are well worth the effort.

[LDUNN1]

ahhhhh - thats a great tip for binoviewers - thanks!

I've wondered about binoviewers & their worth - to me each eye must be receiving half the captured light, making objects already dim, even dimmer, unlike proper bino's where you have two lenses.

....but back to the floaters - so the idea of using barlows wont work then......

[great_bear]

Binos: Yes, greatly reduce the annoyance of floaters. The loss-of-light with binos is simply not an issue with lunar & planetary targets - the greater clarity seen greatly outweighs the light loss. For DSOs of course, most prefer monocular viewing.

Exit pupils: For any magnification, the exit-pupil size is fixed. No fiddling with optics can change this. It's an unchanging part of the equation.

Kidney Beaning: Caused by viewing too close to an eyepiece with a spherically-abberated exit pupil. The best solution is to buy or make an extention eyeguard, like this one <here>

[LDUNN1]

ahhh it is starting to make sense.......thx fro the clarifications, it has helped my understanding.

I guess for planets you want very high mags, but that invariably means small exit pupils & 'floaters' .....so go to binos makes sense to combat the floaters AND the brightness is not an issue.......kind of suggests that you may want some very low/short EP focal lengths for the binos to make the most of the planetry use......this would then seem to be the main combat to the small exit pupil / floater issue.

The EP I suffer kidney beaning on has indeed lost its rubber eye-cup, & is only a 20mm EP so not very tight eye relief I guess - which probably is resulting in my eye getting too close. I could not understand how I have other EP's with lower eye relief that I had little or no kidney beaning on, & yet the 20mm plossl with no eyecup seemed to really suffer.......it all makes sense now - I was thinking that low eye relief contributed to the kidney's, I had it totally wrong! Thx!!

[great_bear]

very high mags, but that invariably means small exit pupils & 'floaters'

No - it means getting a bigger scope...

kind of suggests that you may want some very low/short EP focal lengths for the binos to make the most of the planetry use.

A tip from telescope designer Roland Christen: Don't go lower than 12mm eyepieces on prism-based binos - use OCS/Barlow lenses to get the higher powers.

The EP I suffer kidney beaning on has indeed lost its rubber eye-cup

You can make a very comfy replacement by wrapping a piece of toweling into a tube around the eyepiece - and securing it in place with double-sided velcro <here>

[LDUNN1]

Ace, thanks for the pointers & suggestion ref the EP cup.

I am not worried about the kidneys on this EP as it was a cheap 2ndhand purchase & I have subsequently bought much better EP's that replace it. I was just curious about what aspects effect & control the kidneys - just wanted to learn & understand. Thax to all for the explanations it has helped me.

[rwilkey]

Eyepieces with good eye relief often suffer from blacking out or 'kidney-beaning'. This happens when the eye is viewing inside the eye relief zone (too close), view slightly further away so that your eye is at least at the reported distance for eye relief, it means being a little bit patient, but this is one of the problems with eyepieces with good eye relief, you have to view at just the right distance or 'exit pupil'. Many quality eyepieces with good eye relief have twist-up eyecups, these are invaluable for setting the distance for the eye relief that is required for the viewing conditions, BST Explorers are a prime example. See also: http://www.swindonstargazers.com/beginners/eyepieces.htm

[LDUNN1]

That is a great link to the EP article - Many thx for that.....

......it now seems obvious that my understanding was the wrong way round - and that the greater eye relief the more risk of kidneys there is - if you get your eye too close.

As I don't (currently) wear glasses I don't need the higher eye relief EP's either......& the plossl that i have obviosuly has a good degree of eye relief AND without its eye cup, getting your eye in the right position can be hit & miss - I don't have this issue with other EP's as they have nice cups to 'guide' you.

[great_bear]

See also: Robins Eyepiece Guide

A very nicely-written article!

The only thing I'd dispute is referring to a Celestron (Circle-T) Ortho as a "starter" eyepiece and saying it's "not recommended"; on the contrary - Circle-T Orthos are highly recommended by many people and still hold their own in comparative tests in reviews: They are considered a "classic" eyepiece and are well-respected.

[rwilkey]

I agree with you, the Circle-T Ortho is highly respected, both here and elsewhere.

[LDUNN1]

......maybe I should ask what the perceived advantages of the Ortho's in general are then (vs other types of EP)......

[Vali x]

...good to know, thanks

[rwilkey]

Hi, Ortho's are good for planetary use, however, their main drawback is the AFOV, which is only 40-45', so the object soon goes out of view on a manual scope (like mine), IMO the Plössl has more to offer, with an average 52' AFOV. I have not tried the BGO's, which many on this forum rate very highly.

[LDUNN1]

......in the small hours of Monday morning, I was using a Nagler 3-6mm zoom & an 8mm Ethos to view jupiter via a WO ZS66ED with a combo of barlows available - TV 2.5x 1.25" Powermate, TV 2x 2" Powermate & Antares 1.6x 2".

The view through the E8 with powermate was very nice, I think I preferred the view through the E8+PM vs the Nagzoom at the 3mm or 4mm setting but it was close to my untrained eyes......maybe more time is required & more careful study between the two......but ultimately I'm operating at the limits of the scope.

I've read that Othos are good for planetry - but 'what' is it that makes them so good? Would they give sharper, contrastier or brighter views vs say the Nagzoom or PM'ed E8 or plossel? You often read about kit recommended for a task, but I like to understand what characteristic it is that makes it so suited to the task recommended......part of my understanding & learning I guess.

[MjrTom]

Its funny you should say that as I was out that same morning with my 80mm refractor and Nagler 3-6mm zoom. I was also testing out the 13mm Nagler T6 with the 2.5x powermate and thought that I preferred the views that the zoom gave. I felt the 13T6 & PM combination had noticeably less contrast when looking for surface detail on Jupiter. The extra FOV was very welcome though when using a scope on an Alt/Az mount.

An E8 & PM combination would be interesting to see! I bet its nearly as big as the ZS66

[rwilkey]

The 'green and blacks' are way out of my league, so I can't comment any further, and no experience of the BGO's perhaps someone else can comment?

[John]

I've tried a number of the BGO's and they are excellent examples of the orthoscopic design - they do deliver better performance than the classic "volcano top" ortho's as well - subtle but noticeable. Having given BGO's a thorough "run" though I've decided that I enjoy wider fields of view, longer eye relief and larger eye lenses more so I have parted with my BGO's. They remain though, in my opinion, about the best optical performers you can buy for an affordable price (ie: less than £200).

Referring to LDUNN1's post above, I also use 8mm and 6mm Ethe with an Antares 1.6x barlow and find their performance superb (equal to the BGO's in my view). It's an expensive prescription though

[LDUNN1]

I agree the E's are not cheap......but the score highly on the comical look front on my scope......in the dark sometimes you don't know which way around you should have it ;-)

.......I'm just starting out in astronomy, so i have a lot to learn, but having looked through someone elses E & had that 'wow' feeling I decided that I'd buy a couple higher quality EP's rather than a case of cheaper ones......that 'wow' feeling was important to me as it eases future astro purchases when the wife goes 'wow' too ;-)

I figure that I'll keep my EP's for the rest of my life & they will go with any 'scope I get in the future. I went for the Nagzoom as I felt that I liked the idea of tailouring the top end to the viewing conditions &/or to the limitations of the scope. When funds permit, I can see that I will probably add a longer focal length EP when i get a longer focal length scope, & I might go for a shorter Ethos eventually too - maybe.

I don't think I have viewed through the non-zoom Naglers yet - or if I have i did not know it, I think the Nagler zooms are quite different in character to the Nagler fixed EP's though. It will be nice to compare in future.

None of this explains what the characteristics are of the orthos that make them great at planetry......I am really curious about that.

I've wondered if the simpler EP designs provide a brighter view for example that might make dim DSO's more obvious. In short, while I love the views through the Ethos I don't know if other designs might offer benefits in areas over the Ethos.

ref the Nagzoom vs the PM'ed Ethos - I may have preferred the view from the E purely because of the big wide view.......maybe more experienced eye's may pick up on improved sharpness/constrast with the Nagzoom - I just don't know, I could not make my mind up which gave the better surface detail of the planet, but the overall view i felt the E had it. I was also playing around with a baader semi-Apo filter too......I had many variables that I was playing with experimenting with all the combos I could, but i lacked structure to my testing.

[great_bear]

I figure that I'll keep my EP's for the rest of my life & they will go with any 'scope I get in the future.

Unfortunately it doesn't always work out that way. When you get a scope that has a different focal length, you can find that what was once a high-mag planetary is now a mid-range eyepiece with perhaps not enough field-of-view. Similarly, there may be specific magnifications you want to shoot for. I find that both 75x and 150x (for example) are great choices on the moon. However, if a change in focal length made my 75x eyepiece into a 100x one, I would no longer be able to fit the entire moon into the field-of-view and would have to get a different eyepiece.

None of this explains what the characteristics are of the orthos that make them great at planetry......I am really curious about that.

Oh that's easy: A design that minimises reflections, using a small number of lenses finished to a high standard of polish.

I've wondered if the simpler EP designs provide a brighter view for example that might make dim DSO's more obvious.

Unfortunately there's just too many variables involved in eyepiece manufacture to hold such assumptions as true in the general sense.

[LDUNN1]

......yes, I recognise that the purchase of different 'scopes in the future may impact the EP's I'd want to use with them........as & when that happens, I'll use it to expand my EP collection as I 'fill-in' the missing areas......but that will be adding to the EP collection, rather than just replacing an existing EP with something better, or just 'different'.

okay, so the Orthos are low numbers of lens elements with high standards of finish - BUT what is the impact on that on what one actually see's? I'm thinking in terms of image characteristics - sharpness, brightness, contrast, colour, etc etc rather than the physics characteristics of the EP hardware........or is that too general too as you get good & bad examples of Orthos.

I guess what I am trying to learn & understand, is how would the view differ from say an Ethos vs an Ortho for a given magnification (other than the obvious 100 deg afov of the ethos). On say a planet, or lunar, would the ortho appear sharper, contrastier, 'clearer'?

[John]

I've tried quite a few Ortho's and the views seem pretty good through all of them. The Baader GO's are a (small) cut above the classic volcano top orthos in my opinion as they seem to reduce scattered light around bright objects to very low levels which helps pick out low contrast features.

I have compared both Baader GO's and the classic orthos directly with equivalent Ethos eyepieces and, again in my opinion, found the Ethos able to deliver similarly excellent images coupled with the massive field of view and more eye relief (the distance between the eye and the top lens of the eyepiece). It has to be borne in mind though that an Ethos costs 6 times as much as a Baader GO.