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3.2mm BST Explorer/Starguider eyepiece- Any good?


Donkeiller

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I used mine last night in my Skywatcher 150PDS and I could see the bands on Jupiter quite well - a little fuzzy perhaps but it was relatively low down in the sky and 3.2mm is approaching max magnification for my scope.

Eye relief is fine, I wear glasses but I also tried it without - extending the eyecup - and it was fine in that respect.

I'm no expert but it all seemed okay to me and at a smidge under £50 well worth it for the views I got.

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..........It should be as good as the other BSTs as regards to field of view, eye relief and comfortable to use. 

The atmospheric conditions  will be your enemy, but not only that, on your Celestron 8SE you'll be at about 635x power which is excessive, to say the least, so maybe not the EP of choice on this occasion?

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I used mine for the first time last  night in my SW 200 Dobson and I would say was near perfect had to keep moving of course this was witnessed by several member's of SGL south wales group meet at Blaenavon, I would not hesitate  and recommend it, I bought the 3.2mm as a wild card for those rare perfect conditions and last night was far from perfect but the lens performed nearly flawlessly.

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I used mine for the first time last  night in my SW 200 Dobson and I would say was near perfect had to keep moving of course this was witnessed by several member's of SGL south wales group meet at Blaenavon, I would not hesitate  and recommend it, I bought the 3.2mm as a wild card for those rare perfect conditions and last night was far from perfect but the lens performed nearly flawlessly.

Thanks that's what I wanted to hear.
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I once read wharthogs guide on here and ive used his rule since... that your max ep should be your focal length divided by 2 thirds of double your apperature, so in affore mentioned 200 dob thats... (400÷3x2=270)1200÷270=4.4mm. So a 3.2mm ep gives you 375x mag. and works? Where have i been going wrong?

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I use the focal ratio of the telescope to dictate the eyepiece. On my f/6  If I use a 6mm EP I'll have a 1mm exit pupil at 200x power. A perfect match for the telescope.

My maximum in theory should be 400x power ( twice the aperture ) this would equate to a 3mm EP for my Skyliner, right on the limit, but limits can be exceeded  when the conditions permit.

I was opting to build a William Optics SPL set of 3mm 6mm & 12mm The 6mm WO SPL I have came at a greatly reduced price, so had to take it. The 3.2mm just undercuts my maximum theory limits, and in keeping within the theory, BST does not do a 6mm Starguider, hence the WO SPL in its place.

So many folk also like the 12mm BST? on their 200 Skyliner's,  Its twice the focal ratio,  It hits the sweet spot!  many folk also like the 18mm, again, 3x the f/6 ratio. And for your widest EP. multiply the f/6 x7......Why?

7mm is reputed to be the widest your eye will dilate to, when dark adapted ( if your young enough )  An exit pupil  wider than this,  and your just wasting light, so getting the widest EP to match your own entrance pupil, will give you the brightest image to the eye. Calculating using a  desired 6mm exit pupil (36mm EP) I'm more than happy with my 32mm Panaview for the wide angles, 

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My 12" Orion Optics dobsonian has very good quality optics but I don't often find more than 318x useful. I get that from a 5mm Pentax XW. I have eyepieces of shorter focal length than that (4mm, 3.5mm and 3mm) but mostly I use those with my 102mm and 120mm refractors.

Sometimes it's fun to use very high magnifications on the Moon, tight double stars and even Saturn or Mars but the sharpest detail and most pronouced contrast of features seem to come at somewhere between 180x and 265x or 318x on the fine lunar features. I don't think i've used the theoritical maximum of 600x with my 12" more than a couple of times.

Donkeillers 90mm ought to support 187x OK though, under reasonably good seeing conditions.

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Thinking of getting one of these as my "occasional" high-power EP.

With my 90mm triplet it will give x187.

Has anyone any experience of this EP?

..........It should be as good as the other BSTs as regards to field of view, eye relief and comfortable to use. 

The 3.2mm will be within parameters for your 90mm

Unfortunately it won't. A well made 90mm f6.6 refractor under a good sky will handle 187x magnification but the exit-pupil would be 0.48mm. Exit-pupils around 2mm and larger provide comfortable observing but once the exit-pupil gets down to around 1mm the laser-like beam of light highlights floaters (tiny specks and strings of debris floating inside your eyeball fluid) as it travels through your eye. I personally don't like using exit-pupils much below 1mm. Some double-star observers will go down as low as 0.5mm, possibly even lower, but that has more to do with their need to measure separation. I doubt they are experiencing a 'pleasing' view. 

Regarding maximum exit-pupil diameters - don't get hung up on 7mm. Refractors don't have secondary obstructions so you can take the magnification as low as you like to frame the target. Yes, if the exit-pupil diameter is larger than your eye pupil diameter you are wasting light, but there is already plenty of light reaching your eye at those low magnifications so it isn't a real-world concern. (For Newtonians, SCTs and other telescopes with secondary obstructions then 5-7mm is a safe maximum). 

HTH, 

Steve 

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.... I had a chance to enjoy the moon with it for about 30 minutes so far used with my TS50mm ED f6.6 refractor.

Good eye relief, comfortable views, very decent FOV - a winner in my books.

I believe you but it doesn't make sense to me. Your 50mm f6.6 also produces a 0.48x exit-pupil. I have never enjoyed comfortable views with such a small exit-pupil. Perhaps you have especially clean eye fluid...  :smile:

Steve

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I have one of these and an assortment of refractors, the reason I bought it was one small refractor.

Concerning magnification, exit pupil etc, I have to say I never really think about them, especially when stood outside in the dark and feeling cold.

If the 8mm works I will maybe try the 5mm, if that delivers the goods I will likely drop the 3.2mm in and see what comes out - good/bad. Rarely does magnification pass through my mind, and I can divide quickly and easily, and exit pupil simply never gets a consideration.

Getting a value for exit pupil means ?????

If you have an exit pupil of say 0.8mm does that mean a good or bad view, and by the time I have worked the numbers through I will simply have tried the eyepiece and know how it is.

Even magnification is a guide, it may or may not work for you. There is no well defined cut off value. 120x good, 125x bad just does not happen.

Don't get hung up on the numbers too much.

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I used mine for the first time last  night in my SW 200 Dobson and I would say was near perfect had to keep moving of course this was witnessed by several member's of SGL south wales group meet at Blaenavon....

Near-perfect views at 375x with an exit-pupil of 0.5mm! I like this thread because pretty-much anything seems possible  :smile:

It might just be I'm jealous. I think the last time I achieved a good view at magnifications like that was... Probably only once back in 2007! 

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Steve,

I do have floaters but up to about that exit pupil, I find that they don't really bother me or "get in the way" of my observing, but solely for lunar viewing.

For double star observing it could be a different story, but I am still in the "testing" phase of this tiny refractor and have yet to test it on doubles.

I've gone to even smaller exit pupils on the moon with a Mak Cass and binoviewers. The brain compensates for floaters when you have signal coming in from both eyes.

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Even magnification is a guide, it may or may not work for you. There is no well defined cut off value. 120x good, 125x bad just does not happen.

Don't get hung up on the numbers too much.

Looking back in the mirror here:

http://stargazerslounge.com/topic/217269-new-rolls-royce-planetary-eyepiece/?p=2330933

You got the 3.2mm BST more than half a year ago, weather maybe had not been perfect, but there should be quite some Moon observing chances so far with this eyepiece, how many times have you got a satisfatory view?

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Near-perfect views at 375x with an exit-pupil of 0.5mm! I like this thread because pretty-much anything seems possible  :smile:

It might just be I'm jealous. I think the last time I achieved a good view at magnifications like that was... Probably once back in 2007! 

http://stargazerslounge.com/topic/235003-blaenavon-meet-saturday-jan-25th/page-2

L8-Nite wrote:-Daiwelly's 3.2mm eyepiece showed very good detail on Jupiter.

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