250px Dob - Are BST Starguiders eyepieces extinct?

[SpoonyPizzas]

Good evening chaps,

After reading many positive reviews regarding the BST Starguiders eyepieces for the 250px Dob - I began searching for these but cannot find them anywhere! :-(

Do they have a new name?

Is this the same eyepiece?

http://www.365astronomy.com/15mm-bst-explorer-ed-eyepiece-p-3789.html

If they are no longer available, can anyone with a 250px Dob experience recommend alternatives?

Thank you all in advance

[knobby]

http://stores.ebay.co.uk/Skys-the-Limit-Astro-and-Optical?_rdc=1

But they are stocktaking ...

Celestron lx exel are a good alternative but slightly more expensive

[SpoonyPizzas]

I've just found a Williams Optics SPL 12.5mm for £50 - would that be suitable? (although I don't wear glasses) :S

Cheers,

[knobby]

And yes, the 365 astronomy one

Looks the same as the BST

[SpoonyPizzas]

http://stores.ebay.co.uk/Skys-the-Limit-Astro-and-Optical?_rdc=1

But they are stocktaking ...

Celestron lx exel are a good alternative but slightly more expensive

Thanks  

[SpoonyPizzas]

And yes, the 365 astronomy one

Looks the same as the BST

Cool thanks

[Karen]

Good evening chaps,

After reading many positive reviews regarding the BST Starguiders eyepieces for the 250px Dob - I began searching for these but cannot find them anywhere! :-(

Do they have a new name?

Is this the same eyepiece?

http://www.365astronomy.com/15mm-bst-explorer-ed-eyepiece-p-3789.html

They are the same but 365 astronomy only do two sizes. Peeps normally get them from Sky's the Limit on eBay but they are closed for stocktaking till end of month!

If they are no longer available, can anyone with a 250px Dob experience recommend alternatives?

Thank you all in advance

[gooseholla]

Yup Sky's the Limit/ Skies unlimited sell them, but as someone mentioned, they are stock taking this week.

[Charic]

SpoonyPizzas........Hi. some folk will mention that the BSTs may not work so well in f/4 telescopes, due to the increased  coma aberration, inherent in faster telescopes! therefore, coma correctors or better  quality "corrected" expensive" eyepieces are the norm? 

The BSt's are fairly flat-field and work very well on an f/6 telescope like my Skyliner. That said , once Alan has finished his stock take, try his BST's. You can purchase 2 or 3 lenses at a time (£49 each inc delivery) this allows you as the end user to see if they work for you, or should you need to decide between a 12mm or a 15mm. This is a brilliant offer, and if your not happy, you can return the un-wanted eyepiece for a full refund. You would be expected to pay for the return postage, which is not much. Try at http://stores.ebay.co.uk/Skys-the-Limit-Astro-and-Optical/BST-Starguider-ED-/_i.html?_fsub=2568750014 after Monday 31st!

Your original link to 365. That is a Starguider, its  2 pence dearer and then there's the £4+ p&p to add. Not sure 365 have the time to let you test them out first unlike the link I've sent you!

[John]

SpoonyPizzas........Hi. some folk will mention that the BSTs may not work so well in f/4 telescopes, due to the increased  coma aberration, inherent in faster telescopes! therefore, coma correctors or better  quality "corrected" expensive" eyepieces are the norm? 

No eyepiece design today (as far as I know) will correct for coma so a coma corrector is used with expensive well corrected (for astigmatism) eyepieces to reduce / remove the coma which is produced by the scope, not the eyepiece. 

A coma correcter will "tidy up" the edges of the field of view of even lower cost eyepieces though by removing coma which often combines with eyepiece produced astigmatism to distort the star images. You are still left with the residual eyepiece astigmatism though.

It's so easy to get confused about these two aberrations, their causes and cures 

[Charic]

Cheers John. Always thought it was either / or .  Correction lenses for Newtonian reflectors have been designed which reduce coma in telescopes below f/6. These work by means of a dual lens system of a plano-convex and a plano-concave lens fitted into an eyepiece adaptor which superficially resembles a Barlow lens.  So I'm lead (read) to believe?

[Dreadz]

Ive got a 250px and currently 3 of the bst's (5,15 & 25mm). They're a vast improvement over the stock ep's that came with the scope but they do have some shortcomings but having nothing else to which to compare am not sure how many of them are due to the ep itself.

Coma does become apparent but it certainly doesn't completely ruin the view. For the price I think they're exceptionally good value, even more so when you realise that when sold under the orion branding they're twice the price!

Sent from my GT-I9300 using Tapatalk

[Charic]

Dreadz.......if only more people could agree with you about the BST's on faster scopes.

Folk should remember its the scope that causes the coma. Not the EP. The "wrong" EP just makes it more noticeable?  BST's are flat-field to some extent, so work quite well. If I have coma on my scope, I  don't look for it.  I have a Dob PuTo (Push Too?)  I just centre focus on the subject and follow to my  hearts content. Simple.

[wolfpaw]

Dreadz.......if only more people could agree with you about the BST's on faster scopes.

Folk should remember its the scope that causes the coma. Not the EP. The "wrong" EP just makes it more noticeable?  BST's are flat-field to some extent, so work quite well. If I have coma on my scope, I  don't look for it.  I have a Dob PuTo (Push Too?)  I just centre focus on the subject and follow to my  hearts content. Simple.

Expensive eyepieces make coma more noticeable. Cheap ones just show astigmatism.

I wouldn't advise SpoonyPizzas to get any BST eyepieces. I had the 5mm Starguider and it was practically unusable in my f4.7 telescope. I had so much 'ghosting' (or whatever) with Jupiter that I gave us using it. Apparently the BSTs work well in an f/6. Really, fast telescopes e.g. f/4.7 are such an enormous pain in the ass I wonder why anyone uses them at all!

[Charic]

All I'm saying is, its worth a trial, I've highlighted some salient  personal choices?...........

Dreadz says............Ive got a 250px and currently 3 of the bst's (5,15 & 25mm). They're a vast improvement over the stock ep's that came with the scope but they do have some shortcomings but having nothing else to which to compare am not sure how many of them are due to the ep itself. 

Coma does become apparent but it certainly doesn't completely ruin the view. For the price I think they're exceptionally good value, even more so when you realise that when sold under the orion branding they're twice the price!

Sent from my GT-I9300 using Tapatalk 

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wolfpaw says.........Expensive eyepieces make coma more noticeable. Cheap ones just show astigmatism.

I wouldn't advise SpoonyPizzas to get any BST eyepieces. I had the 5mm Starguider and it was practically unusable in my f4.7 telescope. I had so much 'ghosting' (or whatever) with Jupiter that I gave us using it. Apparently the BSTs work well in an f/6. Really, fast telescopes e.g. f/4.7 are such an enormous pain in the ass I wonder why anyone uses them at all!

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 EP's are a personal choice, its what your prepared to pay for and accept at the end of the Day. Trial / Use  is the only qualified method where you as an individual,  can see the result.

[Dreadz]

.................................... Really, fast telescopes e.g. f/4.7 are such an enormous pain in the ass I wonder why anyone uses them at all!

Whilst there's no getting away from the fact that they are less forgiving in many ways it does to a very large degree remove the need for a ladder for viewing objects close to zenith by allowing scopes to become far more compact. I for one appreciate the ability to be able to view sitting down comfortably.

[russ]

The eyepiece choice at the bargain basement end of the market is very limited when wanting an eyepiece that performs well in a fast newt. A secondhand TV Plossl is probably the best choice. Or my personal favourite at the budget end, the Celestron X-Cel LX. They come up for £40-45 secondhand, so approx about the same as the TV Plossl. I think they are a step up from the BST, so worth the extra £10. And while some may argue the TV is sharper, its only by the tiniest of margins. And the Celestron counters by being a far nicer eyepiece to use, especially at 8mm. I sold my TV 8mm to buy the X-Cel LX. 

[John]

The eyepiece choice at the bargain basement end of the market is very limited when wanting an eyepiece that performs well in a fast newt. A secondhand TV Plossl is probably the best choice. Or my personal favourite at the budget end, the Celestron X-Cel LX. They come up for £40-45 secondhand, so approx about the same as the TV Plossl. I think they are a step up from the BST, so worth the extra £10. And while some may argue the TV is sharper, its only by the tiniest of margins. And the Celestron counters by being a far nicer eyepiece to use, especially at 8mm.

Good points Russ 

In favour of the Tele Vue plossls:

 - With a field of view of 50 degrees you simply see less of the off axis field of the newtonian and coma increases the further away from the optical axis you go so you see less coma too.

- Like all TV eyepieces, they are designed and tested to work well, in terms of eyepiece related aberrations, in scopes down to F/4. And they are all individually tested before sale too.

I know their eye relief (like any plossl) gets tight below the 11mm focal length so a good quality barlow lens might be the best way to get the shorter focal lengths.

While wide fields of view are tempting I'm not convinced you are really going to see the benefit of them in newtonians faster than F/5 without adding a coma corrector AND investing in really well corrected eyepieces.

[Karen]

I found this info on Astronomics.com. With flat field planetary (high power) eyepieces coma should barely be noticeable.

"The diameter of the effectively coma-free field of a reflector is roughly equal (in millimeters) to one-half the square of its focal ratio. An f/5 scope has a coma-free field of approximately 12.5mm (5 squared = 25, divided by 2), an f/4 scope has an 8mm field (4 squared = 16, divided by 2), etc. A 40mm eyepiece usually looks at an area about 28mm in diameter in the center of the telescope image. At low powers, then, up to 50% of a fast reflector’s image can show coma’s distracting fan-shaped stars.

Inexpensive modified achromatic eyepieces typically suffer from curvature of field (an inability to bring the center and edges of the field into focus at the same time). Not only are some of the stars fan-shaped in a modified achromatic eyepiece due to coma, but they’re out of focus as well! Reflectors with fast focal ratios (below f/6) are therefore at their best with flat field eyepieces such as Plössls and those designed for fast focal ratio use (Naglers, Panoptics, Super Wide Angles, etc.) rather than modified achromatics.

Coma is not usually a problem at high magnifications. A high power eyepiece looks only at the central 5mm to 12mm area of the image and doesn’t see the comatic outer portions."
 

[wolfpaw]

Good points Russ 

In favour of the Tele Vue plossls:

 - With a field of view of 50 degrees you simply see less of the off axis field of the newtonian and coma increases the further away from the optical axis you go so you see less coma too.

- Like all TV eyepieces, they are designed and tested to work well, in terms of eyepiece related aberrations, in scopes down to F/4. And they are all individually tested before sale too.

I know their eye relief (like any plossl) gets tight below the 11mm focal length so a good quality barlow lens might be the best way to get the shorter focal lengths.

While wide fields of view are tempting I'm not convinced you are really going to see the benefit of them in newtonians faster than F/5 without adding a coma corrector AND investing in really well corrected eyepieces.

I found this info on Astronomics.com. With flat field planetary (high power) eyepieces coma should barely be noticeable.

"The diameter of the effectively coma-free field of a reflector is roughly equal (in millimeters) to one-half the square of its focal ratio. An f/5 scope has a coma-free field of approximately 12.5mm (5 squared = 25, divided by 2), an f/4 scope has an 8mm field (4 squared = 16, divided by 2), etc. A 40mm eyepiece usually looks at an area about 28mm in diameter in the center of the telescope image. At low powers, then, up to 50% of a fast reflector’s image can show coma’s distracting fan-shaped stars.

Inexpensive modified achromatic eyepieces typically suffer from curvature of field (an inability to bring the center and edges of the field into focus at the same time). Not only are some of the stars fan-shaped in a modified achromatic eyepiece due to coma, but they’re out of focus as well! Reflectors with fast focal ratios (below f/6) are therefore at their best with flat field eyepieces such as Plössls and those designed for fast focal ratio use (Naglers, Panoptics, Super Wide Angles, etc.) rather than modified achromatics.

Coma is not usually a problem at high magnifications. A high power eyepiece looks only at the central 5mm to 12mm area of the image and doesn’t see the comatic outer portions."

I agree that coma wouldn't be a major issue with high powered eyepieces in a fast scope. It's limited mostly to low power eyepieces. But then other factors also come into play with a fast scope and budget eyepieces. As I said earlier, my BST 'Starguider' 5mm was practically unusable in my f/4.7 but apparently it performs very well in an f/6.

[russ]

I agree that coma wouldn't be a major issue with high powered eyepieces in a fast scope. It's limited mostly to low power eyepieces. But then other factors also come into play with a fast scope and budget eyepieces. As I said earlier, my BST 'Starguider' 5mm was practically unusable in my f/4.7 but apparently it performs very well in an f/6.

I think at the end of the day, if you have a fast newt, which the original OP does. And you have a limited budget for eyepieces, which OP possibly does. You just have to except there will be abberations that will be present, simply cannot be avoided. Some folks are more susceptible to abberations than others. Some people will see the first hint of CA, coma or astigmitism and declare the setup unusable. While others will wonder what all the fuss is about.

When i had my 250PX my eyepiece line up changed a couple of times. Initially it was:

25mm TV Plossl at the low end, 15mm TV for medium and 8mm TV at the higher end.

I then made good use of the excellent ES 82 deals in the states and changed it around too:

24mm ES 82, 14mm ES 82, 8mm X-Cel LX and ES 82 6.7mm

The ES eyepieces are simply spectacular for the money (£119). They show a small amount of coma at f4.7, only a little more than a T6 Nagler. In fact i would just buy one ES 82 and forget building a BST set. Get the 14mm and a good barlow. That's a top draw workhorse eyepiece working at 86x and then barlowed becomes a 172x planetary eyepiece.

[John]

I regularly post this link on here but I do feel it's a rather good explanation of eyepiece and scope aberrations with the emphasis on newtonians. Worth a read I my opinion:

http://www.umich.edu/~lowbrows/reflections/2007/dscobel.27.html

[SpoonyPizzas]

^{I think at the end of the day, if you have a fast newt, which the original OP does. And you have a limited budget for eyepieces, which OP possibly does. You just have to except there will be abberations that will be present, simply cannot be avoided. Some folks are more susceptible to abberations than others. Some people will see the first hint of CA, coma or astigmitism and declare the setup unusable. While others will wonder what all the fuss is about.}

^{When i had my 250PX my eyepiece line up changed a couple of times. Initially it was:}

^{25mm TV Plossl at the low end, 15mm TV for medium and 8mm TV at the higher end.}

^{I then made good use of the excellent ES 82 deals in the states and changed it around too:}

^{24mm ES 82, 14mm ES 82, 8mm X-Cel LX and ES 82 6.7mm}

^{The ES eyepieces are simply spectacular for the money (£119). They show a small amount of coma at f4.7, only a little more than a T6 Nagler. In fact i would just buy one ES 82 and forget building a BST set. Get the 14mm and a good barlow. That's a top draw workhorse eyepiece working at 86x and then barlowed becomes a 172x planetary eyepiece.}

^{Excellent - thank you}

^{Money isn't really an issue - I'd rather spend the extra and be done with it than spend a little and think 'what if....'} 

^{I've decided to go for an ES 82 14mm for the time being - could you recommend a good barlow?  (£300-£500 budget - preferably closer to £300 else gf will 'possibly' kill me )}

[John]

^{Excellent - thank you}

^{Money isn't really an issue - I'd rather spend the extra and be done with it than spend a little and think 'what if....'} 

^{I've decided to go for an ES 82 14mm for the time being - could you recommend a good barlow?  (£300-£500 budget - preferably closer to £300 else gf will 'possibly' kill me )}

Are you going to invest in a coma corrector too ?. 

Obviously, as discussed in this thread, a well corrected 82 degree eyepiece in an F/4.7 scope will show coma.

[SpoonyPizzas]

Are you going to invest in a coma corrector too ?. 

Obviously, as discussed in this thread, a well corrected 82 degree eyepiece in an F/4.7 scope will show coma.

Yes certainly will - can you recommend one?

Thanks

PS.  Price £300-£500 includes the £160 for the 14mm ES 82