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Fraunhoffer

32mm plossl vs 25mm BST ED

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Hello, as the minutes tick away to 2019 and its cloudy here - just wishing everyone clear skies for 2019.

Question - which would be better 32mm Plossl (50 deg) vs. something like the BST starguider 25mm (60 deg).
Thinking the target appear the same size but in a wider FOV with the BST and better eye relief?

Situation is that Ive acquired a couple of scopes (Celestron c8 SCT and  a Bresser 102s/600) with some older Plossl eyepieces.
I want to encourage my granddaughter to take an interest (she wears glasses) and also show things (some of the easier subjects) to the family (some of whom also wear glasses). The eye relief on the existing Plossl EPs is small and fairly useless for glasses wearers and people not used to peering into a scope (ok for me though and the 25mm Plossl is ok).
As an interim measure I bought a s/h 8-24 Seben zoom for family gazing, ease of use and connecting a camera (afocal projection).

Anyhow, im wondering whether to start a collection of BST Starguiders to keep everyone happy as they get good comments on here as elsewhere for eye relief and ease of use, starting with the 32mm and working down to an 8mm. 

Thanks.

 

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41 minutes ago, Fraunhoffer said:

...Anyhow, im wondering whether to start a collection of BST Starguiders to keep everyone happy as they get good comments on here as elsewhere for eye relief and ease of use, starting with the 32mm and working down to an 8mm. 

 

 

BST Starguiders are very good for their cost and remain comfortable to view through even in the shorter focal lengths, unlike plossls. 25mm is the longest focal length in the range but it shows very nearly as much sky as a 32mm plossl.

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22 minutes ago, John said:

BST Starguiders are very good for their cost and remain comfortable to view through even in the shorter focal lengths, unlike plossls. 25mm is the longest focal length in the range but it shows very nearly as much sky as a 32mm plossl.

Great, thanks that what I needed to know ?

 

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32mm plossl has quite a generous eye relief and it is very good performer.

There will however be advantage of using 25mm BST - they cover almost the same amount of sky, both have very good eye relief, but BST being shorter in focal length will give smaller exit pupil which can be beneficial in light pollution. Background sky will look darker and objects will be easier to spot and contrast will be better.

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I have owned or used all of the Starguiders except for the 15mm. I observe without glasses but have tested the 25mm with glasses. I found that I could just about see the whole field of view, but this required my glasses to actually touch the top of the eyepiece. Due to the rubber top there is no risk of damage but the feeling of the eyepiece touching the glasses isn't great, I found I prefer eyepieces with enough eye relief so there is a gap between the two.

The 25mm Starguider will also show astigmatism around the edge of the field - stars look like seagulls - in faster scopes. In your C8 I expect it would be fine, but it will show in the 102s. A 23mm SVBony Aspheric (ebay!) is better corrected in fast scopes and has more eye relief, although build quality of the eyepiece itself is obviously inferior (and even the top lens is plastic).

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4 minutes ago, vlaiv said:

32mm plossl has quite a generous eye relief

You'd think so, but practically every budget 32mm Plossl recesses the eye lens so much that you are left with only just enough eye relief to use with eyeglasses.  I measured 15mm of usable eye relief in my GSO and Sirius Plossls which means I have to make contact with the folded eye cup and press in slightly.

57 minutes ago, John said:

25mm is the longest focal length in the range but it shows very nearly as much sky as a 32mm plossl.

I have the 25mm Meade 5000 HD-60, and I measured the effective field stop to be 25mm vs 27mm for my 32mm Plossls, so very nearly the same.  The usable eye relief is 18mm, so 3mm better than the 32mm Plossls.  The BST Starguiders lose a bit of eye relief thanks to their eye cup design compared to the HD-60s, but it can be pulled off if you need that last bit of eye relief for comfort.  You just might risk scratching your eyeglasses if you're not careful, though.

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On 31/12/2018 at 16:58, Fraunhoffer said:

The eye relief on the existing Plossl EPs is small and fairly useless for glasses wearers and people not used to peering into a scope (ok for me though and the 25mm Plossl is ok).

I discovered how uncomfortable the Tele Vue 8mm felt on a quick test one cold and windy night, so took a dislike to them, despite their brand being world famous!
I did buy more Tele Vue Plössl's  again starting with the 8mm 11mm and so on, but found them no better than my partial set of Revelation Astro eyepieces.

After many tests covering several brands  I  favoured  and kept the Revelation Astro Plössl's.  I even trialled some Orthoscopics based on  their good reviews,  for Planetary and Moon observations, but you know what, by testing them myself, only then could I see and feel which was right for me, and my scope.

Some eyepieces will work  just great  for some folk, yet fail for others, and  some telescopes may require better corrected eyepieces  to get the best out of the scope in question with regards to the image detail in the outfield part of your view. I view on axis, so the field edge is not important to me visually, but next time I get out (weather permitting) I'll try and remember to put all the BST's through and see which if any are giving me any aberrations towards the edge of field.

If you bought  both eyepieces, you'll  soon know which is best, and either will re-sell if needed!
I have often enthused over the BST's, they work well for me, even considered their distribution? but to just say I'm happy with them is an understatement.

They're not  everyones choice, and at £49 or thereabout, are cheap, and cheap often relates to inferior, but they work, and work well.
Now my tests were not scientific, and often under pretty poor conditions too, but looking at my signature, my eyes  have looked through a few oculars, and at present will continue to happily use my Starguiders.

I've sold off  many eyepieces in favour to what works best for me. Even my dedicated Plössl set is now in the classifieds ? 

 

Edited by Charic
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Thanks for all the comments.

I think an eye cup design might be more suitable for us, so Im also looking at the Celestron X-Cel LX, but these are pushing my budget to the max so will have to consider which focal length EPs carefully.

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55 minutes ago, Fraunhoffer said:

Thanks for all the comments.

I think an eye cup design might be more suitable for us, so Im also looking at the Celestron X-Cel LX, but these are pushing my budget to the max so will have to consider which focal length EPs carefully.

Optically the BST Explorers are as good as the Celestron X-Cel LX's. The eyecups on both look a little different but both screw up and down to suit the glasses and non-glasses wearer. There have even been rumours that the X-Cel LX's share the same optics as the BST Explorers.

Both types are pretty good performers.

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4 hours ago, John said:

Optically the BST Explorers are as good as the Celestron X-Cel LX's. The eyecups on both look a little different but both screw up and down to suit the glasses and non-glasses wearer. There have even been rumours that the X-Cel LX's share the same optics as the BST Explorers.

The BST/Paragon/Starguiders have a similar design to the X-Cel LXs and HD-60s, but they seem to be a more compact design resulting in less usable eye relief.  The latter two might be closely related, but multiple folks report debris in the Celestrons but none in the Meades.  I like the HD-60 design and have the entire set.  Not only does the entire eye cup twist up and down, the traditional rubber eye cup can be flipped up or down.  That, and the eye lens is basically flush with the top in the lowest cup position when the eye cup is flipped down making them easy to use with eyeglasses.  Additionally, the silvery-metallic/red-anodizing/black rubber livery is very sharp looking.  The main downside is their cost, especially in Europe.

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I had a "debris" problem with a Celestron X-Cel LX 25mm. No matter how carefully I cleaned the lenses (particularly the heavily convex one at the top of the field lens group) I could not remove the particles. Otherwise it would have been a nice eyepiece.

Come to think of it, I recently had a 25mm BST Explorer that did not have such issues so maybe the design there is not quite the same ?

 

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3 hours ago, Louis D said:

I like the HD-60 design and have the entire set

I hear these are VG eyepieces.

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1 hour ago, jetstream said:

I hear these are VG eyepieces.

The 4.5mm, 6.5mm, and 9mm are basically indistinguishable from their more costly counterparts from TV, Pentax, and Baader as far as field flatness, edge correction, and on axis sharpness.  Where there might be slight differences would possibly be in scatter and stray light control.  Even there, the differences are subtle.

The 12mm is a step behind the market best in terms of field flatness and edge correction, but still very good.

The 18mm and 25mm are quite a bit behind the best of breed in terms of field flatness and edge correction.  However, these two have the most eye relief of the entire series.  If you have a slower scope like a Mak, they are actually quite good.  It's at f/6 and below where it becomes obvious they're struggling.  However, if you always look on-axis, they are very sharp in the inner 50% of the field with no blackouts or kidney-beaning.

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As a follow up to my post in Observing Reports regarding only being able to see half of the Pleiades with my Baader zoom at 24mm (50 degrees FOV).

I've just ordered a Skywatcher SP Plossl 32mm EP from FLO.

Alas poor finances dictate going for a budget EP and I'm aware it may have issues with astigmatism etc. around the outer FOV, but i"ll give it a go, not losing much at £29!

If it is truly awful I'll just have to save up for a better item.

Perhaps some of you have experience with this SW Plossl EP in fast scopes, I'd like to know?

Here are the results given by the Sky & Telescope Calculator.....

Focal Length:  1525mm   
Magnification: 48x
True Field of View: 1°   (The Pleiades could fit snugly into the field of view)
Exit Pupil: 6.4 mm
Theoretical Resolving Power: 0.38 arc seconds
Approximate Limiting Magnitude of Telescope: +13.4 (under dark, moonless skies)

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The 32mm Skywatcher plossl is of decent quality Geoff. It should work pretty well with your 12" dob and will show quite a lot more sky than the Baader zoom at 24mm can.

Most deep sky objects will fit into a 1 degree true field of view :smiley:

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7 hours ago, Geoff Barnes said:

I'm aware it may have issues with astigmatism etc. around the outer FOV

The astigmatism in a 32mm Plossl at 50 degrees AFOV is quite mild compared to that of a typical, cheap 24mm Erfle/Konig 65 degree wide field.  I'm sure you'll find it quite acceptable.

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On 03/01/2019 at 19:46, Louis D said:

The 4.5mm, 6.5mm, and 9mm are basically indistinguishable from their more costly counterparts from TV, Pentax, and Baader as far as field flatness, edge correction, and on axis sharpness.  Where there might be slight differences would possibly be in scatter and stray light control.  Even there, the differences are subtle.

The 12mm is a step behind the market best in terms of field flatness and edge correction, but still very good.

The 18mm and 25mm are quite a bit behind the best of breed in terms of field flatness and edge correction.  However, these two have the most eye relief of the entire series.  If you have a slower scope like a Mak, they are actually quite good.  It's at f/6 and below where it becomes obvious they're struggling.  However, if you always look on-axis, they are very sharp in the inner 50% of the field with no blackouts or kidney-beaning.

What scopes are you using the HD-60's on Louis? You were doing so well at convincing me they were excellent eyepieces until you mentioned only 50% of the field was sharp. My scope is an 100mm F7.4, so how do you think they will cope at that F ratio? 

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2 hours ago, mikeDnight said:

What scopes are you using the HD-60's on Louis? You were doing so well at convincing me they were excellent eyepieces until you mentioned only 50% of the field was sharp. My scope is an 100mm F7.4, so how do you think they will cope at that F ratio? 

I think it is only the 18 and 25mm that suffer, as is the case with the similar Starguiders that I have tested. Presumably the general design is the same, that there is a common 4-element top section and a 2-element barlow lower section. The different focal lengths are created by varying the strength and distance of the lower section. Effectively the short focal lengths see every scope as slow and are well corrected but the long focal lengths have weak barlows and see scopes as similar to what they are, with varying levels of correction for different focal ratios. If my 25mm Starguider is anything to go by then at f6 things are a mess but in the binoviewer at ~f12 the correction is very good. However, I think that the real issue for you would be how good are the coatings? I don't think you would be happy with those on the Starguiders for planetary observation,

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I own 4 of the BST Starguiders ( 7, 9, 15 and 25 mm ).  Surprisingly, I find that their 58 degree field of view is equal to or better than some older 67 degree Super Wides.  The 25 shows a bit of astigmatism near the edge but not the other shorter focal lengths because they have one or two extra elements that essentially perform as a Barlow lens. The twist-up eye cup is easy to use- a no frills eyepiece.  At 4 times the cost I bought a single 9 mm, 76 degree Morpheus ( 8 elements ) which is excellent in every respect, but the 9 mm BST is almost just as sharp minus the extra FOV. 

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4 hours ago, mikeDnight said:

What scopes are you using the HD-60's on Louis? You were doing so well at convincing me they were excellent eyepieces until you mentioned only 50% of the field was sharp. My scope is an 100mm F7.4, so how do you think they will cope at that F ratio? 

The 18mm and 25mm do quite well in my f/12 127mm Mak.  In my f/6 Dob and ED refractor, not so much.  If you want much better correction at those focal lengths and have the budget for them, there's the 18mm and 24mm APM UFF eyepieces.  Going further upscale, there's the 17.5mm Baader Morpheus.

If you've got a 2" focuser and $500, the 17mm ES-92 is pretty sweet and shows slightly more TFOV field than a 32mm Plossl but at about twice the power with no aberrations.  I was enjoying sweeping the region around the Double Cluster in my AT72ED last night with it just seeing what large open clusters I had been missing with my longer focal length scopes.  It was amazing. ?

At 17mm, I've also got the Nagler T4 and AstroTech AF70.  The Nagler is obviously quite good, but I much prefer the ES-92.  The AF70 is the same as the older Celestron Ultima LX and newer SkyWatcher SWA 70, Olivon 70, Omegon Redline, TS Expanse, and Tecnosky Superwide HD.  It has some astigmatism and chromatism at 20% to the edge, but is otherwise quite good.  If you can find one for under $70, they're a good deal used or on closeout.  The Redline/AF70 style also has the best 1.25"/2" conversion method of any eyepiece I've ever used.  The 2" skirt just screws off completely and the 1.25" barrel is then usable at basically the same focal position.

556015058_17mmEyepieces1.thumb.jpg.2cf61115172b160c6c31eb957d4c7913.jpg

1 hour ago, davejlec said:

At 4 times the cost I bought a single 9 mm, 76 degree Morpheus ( 8 elements ) which is excellent in every respect, but the 9 mm BST is almost just as sharp minus the extra FOV.

Agreed.  I have the 9mm Morpheus, 9mm Vixen LV, and 9mm HD-60 (and 10mm Delos), and the HD-60 easily holds its own against the more expensive competition:

418422651_9mm10mmEyepieces1.thumb.jpg.77065ff5762ea9ef93b00e663e8539a9.jpg

That 17mm to 24mm range is a tough one to fill on a budget and still be usable with eyeglasses.  If 50 degrees is acceptable, try hunting down used 20mm or 25mm Vixen LV eyepieces for $60 or less.  Unfortunately, those are the most difficult to find eyepieces of that line on the used market.

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On ‎06‎/‎01‎/‎2019 at 03:13, Louis D said:

The 18mm and 25mm do quite well in my f/12 127mm Mak.  In my f/6 Dob and ED refractor, not so much.  If you want much better correction at those focal lengths and have the budget for them, there's the 18mm and 24mm APM UFF eyepieces.  Going further upscale, there's the 17.5mm Baader Morpheus.

If you've got a 2" focuser and $500, the 17mm ES-92 is pretty sweet and shows slightly more TFOV field than a 32mm Plossl but at about twice the power with no aberrations.  I was enjoying sweeping the region around the Double Cluster in my AT72ED last night with it just seeing what large open clusters I had been missing with my longer focal length scopes.  It was amazing. ?

At 17mm, I've also got the Nagler T4 and AstroTech AF70.  The Nagler is obviously quite good, but I much prefer the ES-92.  The AF70 is the same as the older Celestron Ultima LX and newer SkyWatcher SWA 70, Olivon 70, Omegon Redline, TS Expanse, and Tecnosky Superwide HD.  It has some astigmatism and chromatism at 20% to the edge, but is otherwise quite good.  If you can find one for under $70, they're a good deal used or on closeout.  The Redline/AF70 style also has the best 1.25"/2" conversion method of any eyepiece I've ever used.  The 2" skirt just screws off completely and the 1.25" barrel is then usable at basically the same focal position.

556015058_17mmEyepieces1.thumb.jpg.2cf61115172b160c6c31eb957d4c7913.jpg

Agreed.  I have the 9mm Morpheus, 9mm Vixen LV, and 9mm HD-60 (and 10mm Delos), and the HD-60 easily holds its own against the more expensive competition:

418422651_9mm10mmEyepieces1.thumb.jpg.77065ff5762ea9ef93b00e663e8539a9.jpg

That 17mm to 24mm range is a tough one to fill on a budget and still be usable with eyeglasses.  If 50 degrees is acceptable, try hunting down used 20mm or 25mm Vixen LV eyepieces for $60 or less.  Unfortunately, those are the most difficult to find eyepieces of that line on the used market.

The Morpheus and Delos look huge. 
I think Im moving towards the Celestron Omni 32mm Plossl, having played around on Astro tools for a bit for the larger EP and maybe the X-Cel LX for a couple of smaller EPs (when funds allow). So many choices...  

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4 hours ago, Fraunhoffer said:

The Morpheus and Delos look huge. 
I think Im moving towards the Celestron Omni 32mm Plossl, having played around on Astro tools for a bit for the larger EP and maybe the X-Cel LX for a couple of smaller EPs (when funds allow). So many choices...  

In comparison to traditional Kellners, Orthos, and Plossls, the Morpheus and Delos do look huge.  In comparison to the Ethos (and other 100 degree eyepieces), the ES-92s, many Naglers from the past and present (and other 82 degree eyepieces), and longer focal length Panoptics (and other 68 degree eyepieces), the are actually quite svelte in weight although still a bit tall and thick.

The 32mm Plossl is a really good choice.  It's hard to go wrong with one.

Good luck building your eyepiece collection.  I've been at it for over 20 years and am still not done. ?

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12 hours ago, Louis D said:

In comparison to traditional Kellners, Orthos, and Plossls, the Morpheus and Delos do look huge.  In comparison to the Ethos (and other 100 degree eyepieces), the ES-92s, many Naglers from the past and present (and other 82 degree eyepieces), and longer focal length Panoptics (and other 68 degree eyepieces), the are actually quite svelte in weight although still a bit tall and thick...

 

The Ethos 6mm and 8mm are actually a touch smaller and lighter than the Delos 6mm and 8mm. Strange but true ! :dontknow:

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I’ll not hear a word against the Delos range.?. But they do get bigger and bigger as the focal length gets shorter!

Very strange.

The BST’s are a great place to start a collection. Comfortable to use, nice and sharp. Many never need more.

Paul

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6 hours ago, Paul73 said:

I’ll not hear a word against the Delos range.?. But they do get bigger and bigger as the focal length gets shorter!

Very strange.

Not really.  All of the negative/positive designs do this to maintain constant eye relief.  Basically, the upper, positive, image forming section is nearly the same across all eyepieces within a line, be it Delos, XL, XW, Morpheus, LVW, Starguider, HD-60, TMB Planetary, Edge-On, etc.  Thus, they all view pretty much alike comfort-wise.  What changes is the negative (and on newer lines, intermediate) section.  As the power of the eyepiece to magnify grows, the power of the negative section grows as does its separation from the positive section, making the eyepiece longer and longer as the focal length gets shorter and shorter.  I just realized that not everyone may know that the magnification factor of a Barlow/Smyth lens (negative element) grows with increasing separation from an eyepiece.  Technically, it should be possible to simply grow the power of the negative section by making the curves deeper, but that tends to lead to increased chromatic and exit pupil aberrations.  I believe that the new intermediate section in some eyepieces is there to help correct these issues.

p61.gif

Edited by Louis D
Added explanatory image
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