A Lesson Learnt

[DRCORTEX]

I read the advice, thought about it, read it again, then went ahead and purchased a 4mm GSO Plossl and jabbed it into a 2X Barlow - the result :scared:

With a DOB and handtracking - it simply dosn't work - at least for planets! - a waste of $40 - but a valuable lesson - now, I wonder what else I could use it for.

I am going to get one of these wide field 80 degree 11mm from the Andrews catalog - they look allright.

Hope its clear tonight at Linden - I want to "borrow" a few eyepeices ( especially the ones that have chains/dogs/alarms, connected to them ), and see exactly what the differnce is.

If I can't see one hell of a lot of difference, then I can't justify forking out $400+ on a top of the line eyepeice ( and thats' just one! )

A Telrad looks like a good bet as well - I simply can't damn well line up the crosshairs on the finder in total darkness

ciao

Lance

Lance

[janoskiss]

Makes a good spare dustcap for your focuser. When I sold my ED80 I included one as a dustcap (lost the original one after swapping various 2-to-1.25" adapters & barlows around all the time).


I thought the title of your post was "Lesson Learnt". :confuse3: Go get that 11mm cheapo widefield if you need another lesson. :P


You can get great eyepieces for around $50 and superb EPs for around $100, if you are willing to put up with a modest FOV.

yes, telrad good. Rigel quickfinder better for a small scope (i think... i have telrad and rigel quickie on the way).

[jjjnettie]

There was a write up on budget widefield eyepieces in Sky&Space Nov/Dec 2004 ( if you still have a copy). They tested and compared many brands and prices.

Here's what they said about the Andrews UW 80 degree 11mm

Like a compact version of its larger sibling, this eyepiece also looked a bit like military issue, with a matt black finish and no frills lettering etched into the black. I immediately had problems looking through this eyepiece, and couldn't see more than about half the field of view at any one time. Even with my eye hard up to the stiff rubber eyecup, I still felt as if something was getting in the way of seeing the whole view.
What could be seen looked good, with a sharp image and good light transmission and colour visible in the centre of the image, but I finally gave up, thinking there may have been a problem with this eyepiece, or with my viewing technique. Very frustrating! However, as mentioned above, eyepiece selection is a very personal choice so you may have a completely different reaction. Again, I couldn't compare my reactions to the Internet reviews, because the eyepieces appear to have been only recenly released.

Try to get hold of this copy of Sky and Space, the article is really very good.

[RAJAH235]

Lance, What size finder do you have, 8 x 50 or so? To illuminate your X hairs, see attached. HTH... :D L.
ps. Lesson 1 = Don't skimp on E/Pcs.....

[iceman]

Hi Lance.

A 4mm GSO Plossl on it's own will be most unsatisfactory 9 times out of 10.. barlowing it! omg, that's just asking for trouble! :)

What type of eyepiece are you looking for exactly? A planetary? or a deep space eyepiece to use barlowed as a planetary?

The 11mm widefield from Andrews is probably not the best choice in a fast dob for planets.. firstly, 11mm is too long for detailed views (not enough mag), and secondly the edge of the field of view will not show sharp views, so whenever the planet is near the edge it will distort badly.

For planetary, i'd be looking at something of reasonably quality in the 5mm-7mm range. These include UO HD Orthos ($125 each), Vixen LV's ($170ish each), or the new Burgess/TMB planetary eyepieces (probably around $150+ each). The Meade s5000 plossls would probably be ok too.

At least you only wasted $40, but I'd be careful about wasting more by buying the cheap widefields for use in a fast dob.

[janoskiss]

The Synta super plossls that Andrews is selling for $49 a pop are supposed to be very good (probably the same as MyAstroshop's super plossls). Like all regular plossls, the ones under 10mm are going to suffer from short eye relief. I am actually thinking of ordering one or two to compare with UO HDs & Televue plossls. I think the price of Televue plossls is too much for many new scope buyers, and the GS plossls are just not quite good enough to go the distance. The syntas SPs probably offer better performance/price.

[Starkler]

These are expensive in this context and whilst they have abberations well controlled, stars become blobs away from the centre at f5.

[Starkler]

Well said !

With fast scopes, cheapy wide field eyepieces almost always dissapoint and invariably get replaced for something better later on.

[asimov]

Correct. Therefore may as well get that 'something better' now rather than after going thru half a dozen cheap EP's.:)

[davidpretorius]

lance, keep the 4mm, as ice says, you need great seeing, but hopefully down the track, you will get some tracking and then you may be able to use on those great nights.

[ausastronomer]

Lance,

You need to appreciate your scope has a fast F-Ratio of F5, this is very "unforgiving" of cheap widefield eyepieces. The reason for this is because the angle of entry, of the light cone, into the field lens of the eyepiece increases exponentially as the F-Ratio of the telescope gets faster. In other words the light enters the eyepiece "closer to the edge" of the lens and away from the central axis.

That 11mm 80 degree Andrews eyepiece in an F5 scope would be Lesson Number 2 :)

When you have a scope with an F-Ratio of F5 you basically have 2 options only if you want good images and sharp stars towards the edge of the FOV.

Option 1. Buy premium widefield eyepieces at $400 to $500 each, these work well in an F5 scope. I would also warn you that a lot of the intermediate priced widefield eyepieces at $200 to $400 perform very poorly in an F5 scope. These include 2" UO Konigs and Widescans. These eyepieces do however work very well in slower F8 to F15 telescopes.

Option 2. Buy high grade simple design eyepieces like plossls and orthoscopics.
By high grade I do not mean the plossls that came with the scope, or what Andrews sells, these are fair and that's being very generous. High grade plossls are things like Celestron Ultimas, Parks Gold Series, Orion Ultrascopic, Antares Elite. Televue PLossls and University Optics orthoscopics are also very good. These will cost you between $100 and $200. These eyepieces give image quality as high as any of the premium widefields, the downside is the slightly narrower FOV and decreasing eye-relief as the focal length of the eyepiece decreases. These were exactly what you were needing but I think Dave has sold them.

http://www.iceinspace.com.au/forum/showthread.php?t=7348

CS-John B

[mickoking]

Not always the case. I have a gso superview 20mm e/p and for the price ($70) its fantastic. I also have a Televue panoptic 27mm e/p and for the price (over $500) it is also fantastic but alas expensive. The superview does suffer some edge abberations on f5 scopes while on the panoptic it's very slight, but the superview has better light transmission (can see fainter) and does'nt suffer from the kidney bean effect. While the Panoptic is over 700% more expensive than the Superview it's performance in only about 25% better.

Saying all that however, I generally agree with the advise that you get what you pay for.

[janoskiss]

I guess it all depends on what you can tolerate. You say the Pan is 25% better. I bet ausastronomer John would say it's "infinitely" better. :lol: I'm somewhere in between. My 30mm superview in f6 is tolerable, but not very nice to look through. Aberrations are apparent quite close to centre of the FOV and get very bad in the last 30-40%. Panoptic on the other hand... :astron: Even if I had 10 SVs they could not replace one Pan, so is it worth 10x as much? Yep! But clearly, this sort of thing is subjective.

As you are comparing the 27mm Pan and the 20mm SV, I'd say you can see fainter because of the higher magnification, not because of better transmission. The coatings on the Superview are okay, but not as good as on the Panoptic.

[Starkler]

I also bought a 20mm superview and couldnt wait to get rid of it !

Any extra field over that given by a plossl was inhabited by seaguls and abberations in my f5 scope. As for the inner field, I felt it was no better than a cheap Chinese plossl.

As for seeing deeper than a 27mm panoptic, thats an unfair comparison given the differing focal lengths. IMO, the 27mm panoptic is one of the best eyepieces on the market.

[mickoking]

I took the extra magnification into account :thumbsup:

It's a lonely buisness playing devils advocate :wink2: :)

[janoskiss]

Micko, try comparing the 19mm Pan with the 20mm SV if you get the chance. ;)

OTOH, there is the Stratus and Hyperion EPs that can be had for under $AU200. Stratus work very well in my f6 and reported to work well in faster scopes too. The 60 degree Pentax XFs should also work well at not much over the $AU200. (but only come in 12mm & 8.5mm. I'd really like to try one of these!)

[ausastronomer]

Some people are more sensitive to Edge of Field (EOF) aberrations than others, hence one person may rate an eyepiece as a better performer than someone who is more demanding in good EOF performance. I am a hard marker. Having said that, I have used a 15mm and 20mm GSO superview in my own 10"/F5 dob at the last SPSP (March 2005), both of which belonged to Glenn Dawes. I thought they were pretty average and that was being generous. Glenn has just recently sold them both, because he was unhappy with the performance.

I would much prefer to use a high grade plossl or othoscopic than the 20mm Superview every day of the week, despite the narrower field of view. A no brainer IMO. If you like the 20mm GSO Superview in an F5 scope you're easy pleased IMO. That doesn't mean either of us is right or wrong, just that we have entirely different expectations on what constitutes good eyepiece performance. FWIW I actually own a 2" 30mm GSO Superview and I found the 2" versions of the GSO Superviews to be clearly better performers than the 1.25" versions.




The reason you can see fainter in the 20mm Superview is because it gives higher magnification than the 27mm Panoptic and creates a smaller exit pupil, not because it has greater light transmission. The higher magnification improves contrast and allows you to see fainter. As the magnification is continually increased you start to go back the other way again in terms of limiting magnitude, once you go past a certain point. An eyepiece that creates an exit pupil between 2mm and 4mm is usually the one that will allow you to see faintest, in your F5 scope thats a 10mm to 20mm focal length. If the 27mm Panoptic was of equal focal length to the superview it would in fact go deeper.

The 27mm Panoptic does not suffer from Kidney beaning or blackout, I own 1 as well. It is in fact, a very easy, comfortable eyepiece to use. Your problem may be that you are used to using the cheaper eyepieces that generally have shorter eye relief and you are placing your eye too close to the eye lens. The 27mm Panoptic has about 19mm of eye relief and you need to have your eye about this distance away from it, otherwise you will get "blackouts". The Pentax XW's are exactly the same, they have 20mm of eye relief and you need to use it, if you get too close they blackout as well. Back off that 27mm Panoptic a fraction and you should be fine.

CS-John B

[ausastronomer]

Steve,

I think those 2 eyepieces you mention, could well be pretty good performers at F5. I am waiting for Rod's 17mm Stratus to arrive to try it in my F5 scope. I also think the new Burgess/TMB planetary eyepieces could be another good option. These new eyepieces may be great options for people looking for reasonable performance at a medium price with a fast telescope. I haven't tried any of them yet to comment specifically. However, I don't class any of these as true "Widefields", they are all in the 60 degree bracket.

The cheap 80 degree things, I rate as very very average at F5. Actually, only suitable as a focuser plug for keeping dust out of the telescope when your not using the scope. I hear countless people tell me how "GREAT" they are, my opinion on them differs :)

CS-John B

[ausastronomer]

Yes Steve similar to comparing a Bentley with a Fiat Bambino.

CS-John B

[mickoking]

Performance, that's an interesting point. I'm quite happy mixing up my premium eyepieces with the el cheapo's coz they generally have a different purpose. My pan 27mm is exclusively used on my refractor as a general deep sky eyepiece while my superview is used on my short tube as a very low power wide field scanning eyepiece (instead of binoculars). I actually prefer simple 4 element plossl's to wide fields e/p's because of their better performance (as in light transmission and contrast). I am just starting double star viewing and for that disapline I demand pin sharp and 'trasty images. I don't have lower standards or that I am easily pleased It's just a matter of horses 4 courses :)

BTW the Panoptic eyepiece is my favorite e/p but a humble Meade 16mm plossl is my most used. Getting out under the stars is wot it's all about ;)

[DRCORTEX]

Nice, wish I'd seen that before I bought the "telrad" clone.

Lance

[DRCORTEX]

Thanks for all advice. My advice to myself now is - see before you buy. I think I'll simply ask my comrades in arms to lend me there Ep's for a few minutes during a session, and satisy myself.


Never know, one I do really like might cost me less than I thought.

Edit: I ended up getting a 2" Synta 42mm WF $49 down from $100 - I shouldn't have any problems with this one. It really is for DSO objects, which my scope seems to handle pretty well. Yeah, yeah, I know, I contradicted myself. I just couldn't help myself, like a kid in a lolly factory. When I have the cash for the scope I really want, the good EP's stay, the other go with my old scope, assumeing I eventually do sell it.

Lance

[mickoking]

Good onya that's wot its all about.

Clear skies :)

[janoskiss]

Don't worry. Illuminated cross-hairs are no replacement for a telrad, which is a 1x ("naked eye") finder . Nice to have the illuminated finder as well, though. You cover the whole range with: telrad -> finder -> wide TFOV EP -> close-up EP

[Argonavis]

John

What is the difference between kidney beaning and blackout?

[janoskiss]

As I understand it, kidney beaning is (partial) black-outs due to sensitivity of the EP to eye placement perpendicular to the optical axis (e.g., sideways head movements). Plain old black out is due to sensitivity to eye placement along optical axis (eye too close to or too far from lens).

[ausastronomer]

Steve,

You have hit the nail on the head. However, lots of people use either term to describe both effects including me. Caused by spherical aberration of the exit pupil.

CS-John B