Low power eyepiece for F/5 telescope ( BST vs Vixen )

[soojooko]

Hi all

I have a Heritage 130p ( F/5 ) and wanted to add a low power eyepiece. I wanted something to give be a reasonable bump in quality and viewable area over the 25mm ( 52° ) that comes with the scope.

I'm looking at these right now:

• BST Starguider 25mm / 60°
• Vixen NPL 30mm / 50°

Both offer similar viewable area and are at the max end of my budget. ( £50 )

I've spoken to somebody I know who owns the NPL, and was told its a very good EP, but the person who told me this uses an F/8 scope. I was told it might not be quite so good with a fast telescope like an F/5 and that a wide view 25mm might be better. Hence the BST 25mm. Is this sound advice?

Can anybody offer some insight into the above two EPs in an F/5 telescope? Are there other eyepieces I should be considering? I almost bit the bullet on a Skywatcher 32mm plossl, which is a bit cheaper than the above two, but then heard about issues with fast telescopes so decided to hold back for now.

Thanks

[Zermelo]

I use the 30mm NPL in an F/5 scope and I really like it. It gives me sharp stars and preserves colour differences well. It has a large eye lens, generous eye relief and no blackouts, so is very comfortable to use. The body is a bit plasticky and doesn't feel as substantial as the BSTs. I've not used the BST 25mm, but it has been discussed a few times on the forum and some have found that the edges aren't as good in fast scopes, compared with the others in the Starguider range. I do sometimes see some distortion at the field edge in the NPL, but I suspect that's my own astigmatism. The longer focal length EPs, irrespective of make, do give lighter background skies. Both eyepieces will give pretty much identical true fields of view (as would the 32mm Plossl), because they're hitting the limit of the 1.25" barrel format.

[Zermelo]

You might also be interested in these discussions:

https://stargazerslounge.com/topic/377846-25-mm-bst-or-something-else/

https://www.cloudynights.com/articles/cat/user-reviews/24-26-mm-eyepiece-comparison-r2651

 

[soojooko]

4 minutes ago, Zermelo said:

I use the 30mm NPL in an F/5 scope and I really like it. It gives me sharp stars and preserves colour differences well. It has a large eye lens, generous eye relief and no blackouts, so is very comfortable to use. The body is a bit plasticky and doesn't feel as substantial as the BSTs. I've not used the BST 25mm, but it has been discussed a few times on the forum and some have found that the edges aren't as good in fast scopes, compared with the others in the Starguider range. I do sometimes see some distortion at the field edge in the NPL, but I suspect that's my own astigmatism. The longer focal length EPs, irrespective of make, do give lighter background skies. Both eyepieces will give pretty much identical true fields of view (as would the 32mm Plossl), because they're hitting the limit of the 1.25" barrel format.

Thanks for the insight. Nice to hear the NPL doesn't suffer from blackouts like most other 32mm plossls. To be honest, Ive not heard a bad word about the NPL. It seems very well regarded.  One question: can the eyecup be removed? I would like to be able to attach my smartphone adapter to whichever EP I go for. I know it can be removed on the BST, but the NPL doesn't look like its possible. Assuming it cant be done, can you give me an idea of the eyecup diameter please? I can fit up to ~50mm in the adapter, so it might work even with the eyecup on.

[Mr Spock]

The NPL will be much better at f5. Another one great at f5, if you can find one used, is the Meade 4000 series 32mm Plössl - a very crisp eyepiece.

[Zermelo]

4 minutes ago, soojooko said:

One question: can the eyecup be removed? I would like to be able to attach my smartphone adapter to whichever EP I go for. I know it can be removed on the BST, but the NPL doesn't look like its possible. Assuming it cant be done, can you give me an idea of the eyecup diameter please?

The eyecup twists up and down, but to remove it you need to lever apart the silver ring from the black plastic ring immediately below it. The two are glued together, so you need a spot or two of superglue when reassembling. I've done it once when I wanted to do a full clean, but you wouldn't want to be doing it regularly.

The diameter at widest part of the eyecup is around 48mm, certainly under 50.

[soojooko]

20 minutes ago, Mr Spock said:

The NPL will be much better at f5. Another one great at f5, if you can find one used, is the Meade 4000 series 32mm Plössl - a very crisp eyepiece.

Thats 2 for the NPL! Thanks for you input. As far as the Meade goes, is it any different to the Skywatcher/Celestron/GSO 32mm plossls. They all look much the same - with the 'super plossl' 4 element design. I was warned that these designs are the ones that dont work well with fast scopes. Is the Meade any different?

13 minutes ago, Zermelo said:

The diameter at widest part of the eyecup is around 48mm, certainly under 50.

Hmm... 48mm is cutting it really tight. I just measured my adapter again and its just under 50mm max. I may have difficulty squeezing it in. Shame - this may be a deal breaker. The particular phone adapter I use is really good. Works far better than all the others I've tried, so its kind of important that whatever EP I go for fits.

[cajen2]

+1 for the NPL. It's my standard EP for low mag but not just for star hopping - I find the image super-clear and consistent across the FOV. I've used it in both my Heritage 150p f/5 dob and my new SL 200 f/6 dob with no issues in either.

[Zermelo]

9 minutes ago, soojooko said:

Hmm... 48mm is cutting it really tight. I just measured my adapter again and its just under 50mm max. I may have difficulty squeezing it in. Shame - this may be a deal breaker. The particular phone adapter I use is really good. Works far better than all the others I've tried, so its kind of important that whatever EP I go for fits.

OK, the reply above was from a ruler measurement. With the digital calipers, I get:

45.8mm on the outer end (the upper surface of the black rubbery part)
48.1mm at the widest part of the silver ring, which is the end furthest from the eye. That maximum dimension is 20.4mm from the top of the eyecup, of which 9.9mm is the depth of the black ring.

So both the black top ring and the silver ring have a slight taper, narrowing towards the eye. Success or otherwise for your phone holder will depend on where it needs to locate on the eyepiece. I have a holder that I don't really use, but I found it impossible to grip on any of my BSTs because of the taper and length of the guard. As you say, it's easily removed on the BSTs, but I only found that out after I stopped experimenting.

[Mr Spock]

53 minutes ago, soojooko said:

Thats 2 for the NPL! Thanks for you input. As far as the Meade goes, is it any different to the Skywatcher/Celestron/GSO 32mm plossls. They all look much the same - with the 'super plossl' 4 element design. I was warned that these designs are the ones that dont work well with fast scopes. Is the Meade any different?

The NPL is also a Plössl  Not all designs are the same. My Meade works well at f4.8, though any 32mm at that focal ratio will have a large exit pupil.

[soojooko]

54 minutes ago, Zermelo said:

OK, the reply above was from a ruler measurement. With the digital calipers, I get:

45.8mm on the outer end (the upper surface of the black rubbery part)
48.1mm at the widest part of the silver ring, which is the end furthest from the eye. That maximum dimension is 20.4mm from the top of the eyecup, of which 9.9mm is the depth of the black ring.

So both the black top ring and the silver ring have a slight taper, narrowing towards the eye. Success or otherwise for your phone holder will depend on where it needs to locate on the eyepiece. I have a holder that I don't really use, but I found it impossible to grip on any of my BSTs because of the taper and length of the guard. As you say, it's easily removed on the BSTs, but I only found that out after I stopped experimenting.

Ok - that sounds promising. It might just fit. There is around 8mm depth in the adapter eyepiece holder - but it grips pretty tight. It should be able to grab hold of the tapered rubber eyecup.

  

20 minutes ago, Mr Spock said:

The NPL is also a Plössl  Not all designs are the same. My Meade works well at f4.8, though any 32mm at that focal ratio will have a large exit pupil.

Indeed. But in the case of the meade/GSO/celestron etc, they all look very similar. Identical aside from color. And they all seem to have that super plossl 4 element design. Whereas other 32/30mm like the TV or the NPL have very different looking designs, which lead me to believe they are different optically.

 

I posted the exact same question on the CN forum - but the few responses I've had over there talk up the BST. And yet here, there seems to be more love for the NPL. I cant say it's helping my decision making here!😖

Edited February 27, 2022 by soojooko

[Zermelo]

1 hour ago, soojooko said:

I posted the exact same question on the CN forum - but the few responses I've had over there talk up the BST. And yet here, there seems to be more love for the NPL. I cant say it's helping my decision making here!

SGL will (usually) provide you with input to your decisions, and possibly some convergence towards a conclusion. But there are very few purchasing questions that are so clear-cut as to result in unanimity.

In the sub-£100 market both the NPLs and Starguiders/Paradigms are thought of favourably on here. The differences between them are probably small enough that subjective preferences will play a large part in recommendations. If you're looking for a first purchase to upgrade from the Skywatcher stock eyepieces, I doubt that you would be disappointed with either choice.

[Pixies]

4 hours ago, soojooko said:

The particular phone adapter I use is really good. Works far better than all the others I've tried, so its kind of important that whatever EP I go for fits.

What type is it? Are you talking about the Celestron NexYZ? If so, I have one and also an NPL 30mm - so I can test it out for you, if you like.

[soojooko]

28 minutes ago, Pixies said:

What type is it? Are you talking about the Celestron NexYZ? If so, I have one and also an NPL 30mm - so I can test it out for you, if you like.

Thanks for the offer. No, I don't have the Celestron, although I do have access to one. Mine is considerably cheaper, but it works very well. 

https://www.amazon.co.uk/gp/product/B07QLB16Y9

Don't let the price fool you - it really does work. I've tried a few different adapters in the past, and this cheap model is the best I've found.

 

I'm leaning slightly towards the BST, for this reason alone; being able to remove the eyecup so I can easily attach the adapter. It sounds like they are both good EPs. I would likely go with the NPL if I knew it would fit - but its so close that it is risky. The slokey website says 45mm max and the NPL looks like its around 46-47mm.

[Pixies]

Just measured it. It's 45mm at the narrowest part (soft rubber top) and 48mm at the widest part (the bottom of the plastic section)

[soojooko]

2 hours ago, Pixies said:

Just measured it. It's 45mm at the narrowest part (soft rubber top) and 48mm at the widest part (the bottom of the plastic section)

Thank you. That's really helpful. To be 100% clear, is that 45mm at the low edge of the eyecup? Basically, the border where the eyecup and the silver body meet?

Edited February 27, 2022 by soojooko

[Pixies]

2 minutes ago, soojooko said:

Thank you. That's really helpful. To be 100% clear, is that 45mm  basically at the low edge of the eyecup? Basically, the border where the eyecup and the silver body meet?

Nope.  It's 45mm at the top end:

[Pixies]

Just found that the soft rubber top can come off!

43mm across and 4mm deep

[soojooko]

35 minutes ago, Pixies said:

Just found that the soft rubber top can come off!

43mm across and 4mm deep

Thanks again for the info. I see you called the eyecup 'soft rubber'. I keep seeing reports online of people calling the eyecup hard plastic. Has there been different versions over the years?

[Zermelo]

I'm not sure about previous versions, but I have the same one as @Pixies.

I'd say that the black top ring might be a harder rubber or a softer plastic. It's certainly not as soft as the eyecups you can fold down on themselves.

If the question behind your question is "would it be firm enough to be gripped by my camera holder?" then I would think your best bet would be to remove the black part and attach it to the grey plastic, if 4mm relief is sufficient.

[maddogharper]

I have a Skywatcher Skyliner 300P Synscan.

I have a few eyepieces, I like Explore Scientific but if your on a budget I also have a 24mm Skywatcher LET LER which is ok, a 9mm Plossl which is as you'd imagine.

I also have a 68 degree SVBony 15mm UW long eye relief, seriously bang for buck those SVBony eyepieces are brilliant, I was shocked, especially at the price point.

If you looked through it, you would not believe it cost so little. Highly recommended and within your budget.

 

[soojooko]

7 hours ago, Zermelo said:

I'm not sure about previous versions, but I have the same one as @Pixies.

I'd say that the black top ring might be a harder rubber or a softer plastic. It's certainly not as soft as the eyecups you can fold down on themselves.

If the question behind your question is "would it be firm enough to be gripped by my camera holder?" then I would think your best bet would be to remove the black part and attach it to the grey plastic, if 4mm relief is sufficient.

Haha! That was exactly the question behind the question! I dont think I would be comfortable removing the eyecup over and over again. If I could just grip the eyecup, that would be my preference.

@maddogharper Thanks for the suggestions. But right now I'm only interested in a low mag wide view EP.

 

There's one thing I would really like to understand. What are the practical differences between a 25mm 60° and a 30mm 50° eyepieces? When using https://astronomy.tools/, both seem to have exactly the same viewable area. But in use, I expect there to be some differences. Can anybody elaborate?

Edited February 28, 2022 by soojooko

[Louis D]

The higher power, wider field eyepiece will show objects at a larger image scale with a darker background leading to better contast.

On the other hand, at a given price point, the higher power, wider field eyepiece will generally be less well corrected edge to edge.

The 25mm BST Starguider is not sharp to the edge at f/6, let alone f/5, in my experience.

[Louis D]

Here are comparison images through some of my eyepieces using a phone's camera in those focal length ranges to give you some idea of what the resultant image looks like.  The telescope used was a 72ED f/6 refractor.

The 25mm Paradigm is the same as the BST Starguider and the 32m Plossls will look very similar to the 30mm NPL.  Open them at full image scale to get a better idea of the differences since the pixel scale is the same at that point.  Notice how much sharper the Plossls are at the edge compared with the 25mm Paradigm/Starguider.  Also notice that the former are showing slightly more true field of view than the latter.  You would need to move up to a 24mm APM UFF to get similar true field and edge sharpness as the 32mm Plossls.

Edited February 28, 2022 by Louis D

[soojooko]

@Louis D whoa - that's really useful. Thank you. The big surprise for me is the GSO super plossl. That wasn't even on my radar, but looking at your images, its sharpness across the field is really impressive. So much so that I find it hard to believe! Can such a cheap 32mm EP really be that good on fast scopes?

Edited February 28, 2022 by soojooko