15mm BST Starguider question

[NGC 1502]

Hi all.  Could anyone let me know if the 15mm BST Starguider has a Smyth lens within the chrome barrel?

(Smyth lens - extra lenses).   I know the 12mm BST does have a Smyth lens, and the 18mm does not.

Thanks in advance, Ed.

[Louis D]

Just checked mine, and yes it does have a lens in the chrome barrel.  It's up there a ways compared to the shorter focal lengths, but it's definitely with the barrel.

Thanks for the heads up about the 18mm.  I knew the 25mm didn't have a Smyth lens in the barrel, but never realized that the 18mm didn't either.  In fact, both have their field stop below the field lens, so they're actually positive-only designs.

I compared them to the Meade HD-60 18mm and 25mm which both appear to have lenses in the barrel.  That's probably why they have better correction at the edge than the BST Starguiders/AT Paradigms.

[Ricochet]

11 hours ago, NGC 1502 said:

the 18mm does not

My 18mm does. It's right at the top of the barrel, but it is there.

[NGC 1502]

34 minutes ago, Ricochet said:

My 18mm does. It's right at the top of the barrel, but it is there.

Many thanks, that’s interesting. I’ve just carefully rechecked my 18mm BST, no Smyth lens in the chrome barrel. The field stop is separate.  I bought it very recently from someone who purchased it new 3 months ago.  Perhaps the optical design has changed, the BST/Paradigm range has been in production for years.

Considering the amazing low retail price with a discount for multiple purchase, the factory price must be incredibly low.

Ed.

[NGC 1502]

5 hours ago, Louis D said:

Just checked mine, and yes it does have a lens in the chrome barrel.  It's up there a ways compared to the shorter focal lengths, but it's definitely with the barrel.

Thanks for the heads up about the 18mm.  I knew the 25mm didn't have a Smyth lens in the barrel, but never realized that the 18mm didn't either.  In fact, both have their field stop below the field lens, so they're actually positive-only designs.

I compared them to the Meade HD-60 18mm and 25mm which both appear to have lenses in the barrel.  That's probably why they have better correction at the edge than the BST Starguiders/AT Paradigms.

Many thanks for that👍

[Don Pensack]

The 18mm has one fewer lens than the 15mm.  The 15mm is 6 elements, the 18mm is 5.

Either the negative lens is gone, and the correction is applied in the upper positive design, or a very weak negative lens is place close to the upper section.

[Louis D]

On 04/09/2021 at 13:01, Ricochet said:

My 18mm does. It's right at the top of the barrel, but it is there.

 

21 hours ago, Don Pensack said:

The 18mm has one fewer lens than the 15mm.  The 15mm is 6 elements, the 18mm is 5.

Either the negative lens is gone, and the correction is applied in the upper positive design, or a very weak negative lens is place close to the upper section.

I unscrewed the chrome barrel from my 18mm Paradigm/BST, and it does indeed have at least one lens at the very top of it.  I didn't try to ascertain whether it was a single lens or a doublet.

[NGC 1502]

3 hours ago, Louis D said:

 

I unscrewed the chrome barrel from my 18mm Paradigm/BST, and it does indeed have at least one lens at the very top of it.  I didn't try to ascertain whether it was a single lens or a doublet.

Hmm…..so is that a Smyth lens?   If it is I may be mistaken in saying the 18mm BST doesn’t have one. It’s certainly less corrected off axis than the 12mm. The 12mm definitely does have a Smyth lens within the chrome barrel.

[Don Pensack]

It's difficult to know if the 18mm is a negative/positive design without dismantling one.

That information is not published anywhere.

[0rcrest]

just reading this ,about to choose between the 12/15/18 bst  starguider  i already have the 25mm and 3.2 on f5 130p struggling with the 3.2 but moon and saturn good though on a good night 25mm lovely

[KP82]

9 hours ago, 0rcrest said:

just reading this ,about to choose between the 12/15/18 bst  starguider  i already have the 25mm and 3.2 on f5 130p struggling with the 3.2 but moon and saturn good though on a good night 25mm lovely

I used to own 25, 12, 5 and 3.2 BSTs. The 12mm was definitely the best of the bunch, very crispy views. The others were fine eps also, better than stocks but not quite on par with the more expensive equivalents. I had the problem with ghosting on bright targets using the 5mm (very prominent when looking at Mars or Jupiter), not sure if it was just my particular sample.

The 3.2 on your 130p newt will yield 203x mag which would be useful for the moon and planets only under very good seeing condition.

[Louis D]

9 hours ago, 0rcrest said:

just reading this ,about to choose between the 12/15/18 bst  starguider  i already have the 25mm and 3.2 on f5 130p struggling with the 3.2 but moon and saturn good though on a good night 25mm lovely

The 12mm is the best corrected to the edge of those three.  I would add the 5mm and/or 8mm next.

1 minute ago, KP82 said:

I had the problem with ghosting on bright targets using the 5mm (very prominent when looking at Mars or Jupiter), not sure if it was just my particular sample.

I haven't looked for ghosting in my Paradigm/BST samples.  I suppose I'll have to explicitly look for it sometime.

[NGC 1502]

On 07/09/2021 at 04:31, 0rcrest said:

just reading this ,about to choose between the 12/15/18 bst  starguider  i already have the 25mm and 3.2 on f5 130p struggling with the 3.2 but moon and saturn good though on a good night 25mm lovely

Of course, it’s your call. But if you have the 25mm BST, then for me the 18mm would be too close in magnification. I’d go for the 12 or 15.  I prefer a larger jump from low to medium power, then closer with increasing power.

As always, your mileage may vary…..

Ed.

[Pitch Black Skies]

On 07/09/2021 at 04:31, 0rcrest said:

just reading this ,about to choose between the 12/15/18 bst  starguider  i already have the 25mm and 3.2 on f5 130p struggling with the 3.2 but moon and saturn good though on a good night 25mm lovely

An 8mm or 12mm would be closer to the 2mm exit pupil sweet spot of 2mm, with the 8mm being 1.6mm and the 12mm being 2.4mm. I'd go with the 8mm or 12mm but if you just Barlowed the 25mm, you have 12.5mm effectively.

(Apologies to the OP)

[NGC 1502]

2 hours ago, Pitch Black Skies said:

An 8mm or 12mm would be closer to the 2mm exit pupil sweet spot of 2mm, with the 8mm being 1.6mm and the 12mm being 2.4mm. I'd go with the 8mm or 12mm but if you just Barlowed the 25mm, you have 12.5mm effectively.

(Apologies to the OP)

Good thoughts.  I’d go 25/12/8/5 myself…….but there’s so many ways to do this…….I’ve had a scope since 1979. Over the years I’ve swapped eyepieces and changed my mind so many times.  It’s easy to get hung up over minute details about eyepieces and forget the magnificence of the universe we see through our eyepieces and scopes. Fussing over our equipment can rob us of the joy of……looking 🙄

Ed.

[0rcrest]

thanks for the input guys,i went for the 12mm and 5mm ,as a newb i'm still juggling ep's all night but i have noticed a considerable uplift in performance now i've had some clear nights to test ,good eye relief and f.o.v .will try them in my 114/900 f8 as well soon and compare.i might get an 8mm next looking at vixen npl or bst?

Edited September 23, 2021 by 0rcrest

[Pixies]

The BSTs are a little wider than the NPLs  (which are Plossls). BSTs are 60degs and NPLs are 50degs.

Both are similar quality. The NPLS are lighter and at 8mm has pretty tight eye relief, as well as a much smaller lens:

[ScouseSpaceCadet]

5 hours ago, 0rcrest said:

thanks for the input guys,i went for the 12mm and 5mm ,as a newb i'm still juggling ep's all night but i have noticed a considerable uplift in performance now i've had some clear nights to test ,good eye relief and f.o.v .will try them in my 114/900 f8 as well soon and compare.i might get an 8mm next looking at vixen npl or bst?

Good choices. I've had the 8mm BST for a couple of years now. It's just fine. Comfy to use like the rest of the line. It may actually be the best BST. 

Don't worry about 'juggling eps'. Seeing conditions can change minute to minute so it's not unusual to swap. I have 4,5,6,7,8 and 9mm for that very reason. Wide field is less demanding, so bigger gaps; 12, 16 and 24mm.

[NGC 1502]

12 hours ago, 0rcrest said:

thanks for the input guys,i went for the 12mm and 5mm ,as a newb i'm still juggling ep's all night but i have noticed a considerable uplift in performance now i've had some clear nights to test ,good eye relief and f.o.v .will try them in my 114/900 f8 as well soon and compare.i might get an 8mm next looking at vixen npl or bst?

As you already have the 12mm and 5mm BSTs if it were me I’d fill the gap with the 8mm BST.  The Vixen 8mm is a good eyepiece but I think you’d miss the wider field and good eyerelief of the BSTs.  I’m blown away by the price and decent performance of the BSTs.