BST Starguider 3.2mm with 4" ED refractor

[Davesellars]

Well, I plan on something a touch higher power that the 4mm I currently have - this is mainly for lunar observation and some planetary later on once they've risen sufficiently.  I currently have a 4mm TMB clone which works fine giving 179x.  I think the 3.2 will give 224x so a reasonable step.

So I like the price and particularly that it's 60 degree apparent FOV (for manual driven mounts).  My 4mm gets a tonne of use actually in most of my scopes.  The 3.2 may be restricted a bit more to seeing conditions but I think will get a reasonable amount of use for lunar observation particularly and double stars.

Question is...  what is the EP actually like?  Is there light scatter?  Reflections or other abberations?  Would this be a good choice?  I don't particularly have the budget to go up to buying a Delite at the moment (unfortunately), but perhaps next year...

[Louis D]

I have the entire line except for the 3.2mm.  The 5mm, 8mm, and 12mm are all very good.  The only comment from an experienced observer about the 3.2mm that I've read is from Jon Isaacs over on CN:

At F/5-F/7, the 25mm and the 18mm show significant off-axis astigmatism. I still use them but the views are not optimal.  Probably better at F/10.

The 12mm, 8mm, and 5 mm are quite sharp across the field even at F/5.  

The 3.2mm, it's a little weird off-axis at F/5, I haven't quite decided about it.  

[Davesellars]

Thanks Louis.  It's a bit difficult finding any information about someone using it with an f/7 ish refractor.  f/5 is gets into the realm of many eyepieces not being ideal off-axis.

[Louis D]

I would probably look for a quality Barlow or telecentric magnifier myself and just reuse my existing eyepieces at higher powers.

[Davesellars]

You're probably right... I have the 7mm and 5mm Pentax XW so a 2X Barlow would give 3.5mm and 2.5mm.  I'm not keen on extending the optical train, but this may well be the better solution.

Edit...  Or even a 3X barlow with the Delos 10mm giving 214xmm (useful) and with the 7mm Pentax 306x (useful for double stars and Mars / Saturn?)

Edited March 16, 2022 by Davesellars

[Louis D]

I have the 3.5mm Pentax XW and find myself using it only a few times a year, such as during Mars oppositions.  It's super sharp and with no obvious flaws.  However, I've found that at high powers, I see much more on planets with binoviewers.  My floaters become much more manageable, and two eyes process the image much better than one.

[Don Pensack]

7 hours ago, Davesellars said:

You're probably right... I have the 7mm and 5mm Pentax XW so a 2X Barlow would give 3.5mm and 2.5mm.  I'm not keen on extending the optical train, but this may well be the better solution.

Edit...  Or even a 3X barlow with the Delos 10mm giving 214xmm (useful) and with the 7mm Pentax 306x (useful for double stars and Mars / Saturn?)

If you get a decent 1.25" barlow of the type where the lens unscrews from the tube, then you have 4 magnifications from one barlow:

threaded to the eyepiece ~1.5x

in its tube under the eyepiece-2X

threaded to the front of the star diagonal--2.5x

in its tube in front of the star diagonal ~3x.

You would have to do star timings to determine the actual magnification factors in each position, but the idea is one barlow adds 4 additional magnifications.

 

If you have a 2" diagonal, then the 4 positions are: threaded to the 1.25" adapter, in its own tube under the adapter, threaded to the front of the diagonal, in its own tube in front of the diagonal.

[Davesellars]

Thanks Don. that may be useful.

Do you have any recommendations on such a 1.25" barlow where the lens unscrews from the tube?

[Don Pensack]

1.25":

https://www.firstlightoptics.com/barlows/astro-essentials-125-2x-barlow-with-t-thread.html

https://www.firstlightoptics.com/barlows/celestron-2x-universal-125-barlow-old.html

2":

https://www.firstlightoptics.com/barlows/stellalyra_2x_2_barlow.html

https://www.firstlightoptics.com/barlows/skywatcher-ed-deluxe-2x-two-inch-barlow-lens.html

 

[Louis D]

My favorite is the vintage, Japanese made Meade Series 400 #140 APO 2x Barlow.  They come up used on this side of the pond all the time for $40 to $65.  I have several in different usage configurations.  One is as a Barlow for 2.4x, one is as a binoviewer GPC/OCS/OCA to reach focus and boost magnification by 3x, and one is combined with a 0.5x reducer and 45mm of spacer tubes to achieve 1.0x with the binoviewer when used in a Newtonian.  They're highly versatile.  I've even put the nosepiece on the front of a 1.25" diagonal and the 0.5x on the binoviewer to get to a vignetted 0.7x power.  Screwed onto an eyepiece yields 1.6x.  All the measurements were taken with a 14mm Pentax XL that focuses at its shoulder.

I have the GSO 2" ED 2x that's also sold as Stellalyra and many other brands.  Look for the Taiwan label to distinguish it from the Chinese variants.  It is very good and compatible with the TV Panoptic Barlow Interface to make a poor man's Powermate.  It yields 2.1x natively.  I haven't measured the other usages' magnifications.

@John usually recommends the Baader Q-Turret 2.25x Barlow, especially as used with a 7.2mm - 21.5mm zoom.  However, because of the way it screws into filter threads, your eyepiece can't have its field lens down near to bottom of the insertion barrel.

[Mr Spock]

I'd second the Meade 140 - there's one currently on ENS' website. And the 2" ED - I have an older version.

You can play with these. With the 2" you can unscrew the end, screw it into a 35mm extension (StellaLyra) to make x1.85, which is what I use in my 102mm. With a 6mm eyepiece I get x220.

The Meade measures at x2.35, the nosepiece attached to an eyepiece, x1.5. I also have a Svbony 70mm extension tube which with the Meade attached gives x2.1 and the benefit of a compression ring fitting.

[Davesellars]

Thanks guys!  That Meade 1.25" 2x barlow looks OK but also tempted by the new Stellalyra 2" ED - looks to be a bargain for £59.

[Franklin]

I had a full set of BSTs a while ago and the 3.2mm worked just as well as the rest. Great eyepieces for their price point.

[ScouseSpaceCadet]

Owning a 4" ED refractor, I had a similar decision to make and due to eye floater issues, decided not to buy eyepieces with focal lengths less than 4mm. Luckily I picked up a 'like new' GSO 2.5x 3 element barlow very very cheap on *bay. It's very good indeed paired with an OVL ES-Nirvana 7mm. Although there is some debate whether this barlow is closer to 2.2x, in reality it does the job admirably and is used regularly. One of my better bargain basement purchases.

[rwilkey]

Hi Dave, I have the 3.2 StarGuider and use it in my C100ED in particular on the Moon and find it very satisfying, no light scatter etc, I haven't tried it on double stars though as I use my Nagler zoom for that.  I do not believe you will be disappointed, it's good for the Moon but not much else in my humble opinion.

[Louis D]

21 hours ago, rwilkey said:

I do not believe you will be disappointed, it's good for the Moon but not much else in my humble opinion.

I was able to use my 3.5mm Pentax XW on Mars during the last opposition to good effect.  However, as I've said before, the view was much better with two eyes through my binoviewer at similar powers.  That's why I've felt zero need to pick up a used 3.2mm BST/Paradigm just to see how it performs.  It's a one or two trick pony as you say.