Eyepieces for SW Heritage 150P Dob

[DhamR]

I'm starting to think about eyepieces for my SW 150P Heritage, probably won't bite the bullet for a little while, but want to start a bit of research.

I'm surprisingly happy with both the 25mm and the 10mm that came with the scope.  More so the former. But from comments prior to purchase I was under the impression I'd hate the 10mm and it doesn't seem to be that bad (although I've nothing to compare it to).  I've had issue with my eyelashes applying grease marks to the upper lens of it (I'm not a lady, just a man with pretty eyes ) so the eye relief is one complaint.

Another is that it's not par-focal with the 25mm, and because I'm a novice, I like switching from one to the other as I move around the sky to help find objects.  Whilst I've got go-to in the Virtuoso mount, I'm trying to encourage myself to find things manually where possible (Orion's Neb is/are easy enough with the RDS, but I've enjoyed star hopping to the Andromeda galaxy).  Also the beauty of the scope is that it's grab-and-go and I don't always want to spend time aligning it, especially on partially cloudy days.  So what I'm currently doing is focusing the 25mm flush to the bottom of the focuser, and then suspending the 10mm part-way in the focuser, however when holding it in with the two thumb-screws, there's a little play, and I'm always wary I'm fixing it at a slight angle, which I'm guessing makes more and more difference the shorter the f/l. 

I've started looking at threads on here, including Warthogs excellent "Bare Minimum" thread.  I noted that because the scope is an f/5 dob, I should consider using a barlow and a 6-8mm EP to hit higher powers, so I was looking at the below for rough numbers:

- good 2 x Barlow
- 6-8mm for High Power with above, and Med-High without.
- 10mm Med-High (I have a 10mm so can leave this for now)
- 15-20 Med-Low
- 25mm low (which again, I already have - although at 35 years old, is it worth maybe eeking a bit more exit pupil out of my eyes before they get old?)

I'm a glasses wearer, but I'm only mildly shortsighted, and have a mild astigmatism.  I prefer viewing without my glasses as my eyes/brain seem to work around the astimatism after a minute or two, and focus is handled by the scope.  But as the focuser on the Heritage is, frankly, a bit annoying and sloppy, I'd love my EPs to be par-focal - is this even possible?  Does a barlow mess this up?

Happy to be punted to other good threads on the topic if that's easier!

Edited January 17, 2022 by DhamR

[wulfrun]

Just to throw in another idea, have you considered a zoom? Most zooms are close to parfocal* as you change the focal length. Downsides are that they have the narrowest AFOV at the longest FL, opposite to what would be desirable. Extra downside with the Hertage's helical focuser is that you'd need to hold the zoom's body stationary as you alter the FL. That could get annoying.

* opinions vary, my experience suggests it's no worse than a "tweak"

EDIT: re a Barlow...did you mean will an EP be parfocal with/without it? No, because it'll shift the focal point. A focal extender (such as the Explore Scientific 2x, for example) has far less shift. If two EPs are parfocal without a barlow/FE, they should still be close with one (I think!).

Edited January 17, 2022 by wulfrun
typo

[cajen2]

I have no idea of your budget....but I asked a similar question about the same scope when I got it:

and a more specialised one about short focal length EPs later: 

You should find some ideas in those threads. As a summary, I think the idea of a zoom is good, to give you clues as to the best mag for a particular target (I use the OVL Hyperflex), a good Barlow ( mine's only a cheapish Svbony 2x ......i'm waiting for an ES to be delivered). The Pentax XW range is excellent if you can stretch to them: I have the 5mm and 14mm. They give a wide FOV, good eye relief and a clear image.

A good option for a low-power EP is a Vixen NPL - I use a 30mm.

 

 

 

Edited January 17, 2022 by cajen2

[Guest]

I will add another vote for a zoom eyepiece.  I use Orion's 8 to 24mm and I have put it in a 2x and 3x barlow.  You can get some wonderful views with this set up.

[Louis D]

Buy some rubber O-rings with an inner diameter no bigger than the outer diameter of the 1.25" insertion barrel.  Measure how many millimeters you're off between the 10mm and 25mm eyepieces, divide that by the thickness of each O-ring, and slip that number of O-rings on the 10mm (which seems to focus farther out), pushing them up to the shoulder (wide part) of the eyepiece.  Hopefully, there's still enough lower barrel to secure the eyepiece in the focuser.  Below is an image of how I parfocalized my Tele Vue 12mm Nagler T4.  I needed to add a 20mm long, 2" barrel extension to the 2" skirt to have enough barrel to insert it into the focuser.  Each of the O-rings is 4mm thick times 5 rings to raise the eyepiece 20mm.

[Louis D]

1 hour ago, Mike Q said:

I will add another vote for a zoom eyepiece.  I use Orion's 8 to 24mm and I have put it in a 2x and 3x barlow.  You can get some wonderful views with this set up.

How well does it work in a helical focuser?  Unless it's super low resistance, it will require two hands to zoom to avoid changing focus.

[Guest]

6 hours ago, Louis D said:

How well does it work in a helical focuser?  Unless it's super low resistance, it will require two hands to zoom to avoid changing focus.

I don't know about helical focusers, I know it works well with a Crayford.  I can say that the adjustment on the eyepiece does have some resistance, but it is steady all the way through and turning it with one hand is not an issue at all. The Baader I believe has positive stops at each power setting.  The Celestron and Orion are just a smooth twist.  All three claim to be parfocal and more or less they are. 

Edited January 18, 2022 by Guest

[wulfrun]

6 hours ago, Louis D said:

How well does it work in a helical focuser?  Unless it's super low resistance, it will require two hands to zoom to avoid changing focus.

Correct, two-handed operation. I have used a Hyperflex in my Heritage 150, it does require the barrel to be held while the zoom ring is turned. How annoying this is is somewhat down to the individual user.

[bomberbaz]

I would not bother with the supplied 25 if you can afford to buy another. Although the idea of buying a 30mm plossl is perfectly feasible, I would also pass this over in favour of a Explore Scientific 26mm 62 Degree eyepiece as your main finder, low power viewing eyepiece, here's why.

25mm supplied EP with 50D FOV gives you x30 with a true field of view of 1.67. A 30mm plossl by 50D FOV gives you x23 by 2.13 tfov. A 26mm ES by 62D FOV gives you x29 by 2.15 TFOV.   So the ES gives you a better magnification, so darker background than a 30mm plossl and at the same time a better tfov than either of the other eyepieces. The 30mm plossl on paper might have a slightly more contrasty view but this will probably be lost with the darker background of the 26mm EP.

I ran some other focal lengths through a calculator and and 12 plus 8 combined with a barlow would cover your remaining needs. I shall do a table below of how it all pans out for you.

26mm = x29 plus 2.15 tfov  (low power/finder)

12mm = x63 plus 0.96 tfov  (mid range)

8mm = x94 plus 0.63 tfov (mid range)

6mm = x125 plus 0.48 tfov (mid range)

4mm = 188 plus 0.32 tfov (high power)

Combo achieved with the ES eyepiece, plus BST 12mm, 8mm and the short barlow. I have the BST short barlow, only played around with it as yet but dos look a quality bit of kit. 3 decent eyepiece and a barlow should cover most of your viewing needs, the existing glass would become redundant and the cost for everything £248 from FLO. (feels like this post is turning into an advert) 😂

You could add a 3.2 BSt later for those evenings when the conditions allow you to push the boat out (x236)

HTH

[cajen2]

52 minutes ago, bomberbaz said:

I would not bother with the supplied 25 if you can afford to buy another. Although the idea of buying a 30mm plossl is perfectly feasible, I would also pass this over in favour of a Explore Scientific 26mm 62 Degree eyepiece as your main finder, low power viewing eyepiece, here's why.

25mm supplied EP with 50D FOV gives you x30 with a true field of view of 1.67. A 30mm plossl by 50D FOV gives you x23 by 2.13 tfov. A 26mm ES by 62D FOV gives you x29 by 2.15 TFOV.   So the ES gives you a better magnification, so darker background than a 30mm plossl and at the same time a better tfov than either of the other eyepieces. The 30mm plossl on paper might have a slightly more contrasty view but this will probably be lost with the darker background of the 26mm EP.

I ran some other focal lengths through a calculator and and 12 plus 8 combined with a barlow would cover your remaining needs. I shall do a table below of how it all pans out for you.

26mm = x29 plus 2.15 tfov  (low power/finder)

12mm = x63 plus 0.96 tfov  (mid range)

8mm = x94 plus 0.63 tfov (mid range)

6mm = x125 plus 0.48 tfov (mid range)

4mm = 188 plus 0.32 tfov (high power)

Combo achieved with the ES eyepiece, plus BST 12mm, 8mm and the short barlow. I have the BST short barlow, only played around with it as yet but dos look a quality bit of kit. 3 decent eyepiece and a barlow should cover most of your viewing needs, the existing glass would become redundant and the cost for everything £248 from FLO. (feels like this post is turning into an advert) 😂

You could add a 3.2 BSt later for those evenings when the conditions allow you to push the boat out (x236)

HTH

All this is true, BB, but there are a couple of practical problems:

- the ES is double the price of the Vixen 

- the ES  range is unobtainable at the moment. I've had an ES Focal extender on order for two months without success.

 

[bomberbaz]

14 minutes ago, cajen2 said:

All this is true, BB, but there are a couple of practical problems:

- the ES is double the price of the Vixen 

- the ES  range is unobtainable at the moment. I've had an ES Focal extender on order for two months without success.

 

Yes well to be fair I didn't say it was cheaper, just from my perspective it would be the way I would go. Just a difference of preferences. 

TBF not much can be got these days without a wait. I am still waiting a pair of EP's for my bins, they have been on back order for a while too.

[cajen2]

.....and the Vixen 40mm is available immediately from Flo, with the 30mil in 2-4 days. The Vixen is a fine EP too! 👍😄

Edited January 18, 2022 by cajen2

[DhamR]

Wow, a lot to read through and digest here:

- I think a zoom might be an annoyance with the helical focuser if I'm honest, the focuser really is the worst part of this scope, and I haven't had much success with ptfe tape, even a single layer makes things too stiff, and causes shredding so I cleaned it all out. (I don't want tape falling down my tube).

- All that info from @bomberbaz is really interesting, I hadn't figured that you could get more mag AND wider FOV from the same lens.  Will definitely bear that EP in particular in mind, as I'm happy to spend a bit more for better quality up to a point, but especially if it reduces the need to buy an additional EP.

- I guess this is what I meant by having nothing to compare things too.  I am straining to get close enough to both EPs, so more eye relief and wide FOV would probably make things a lot more comfortable, particularly when showing things to others.

Thanks everyone.  Sounds like the BSTs are highly regarded in the other FLs, but if anyone has alternatives worth looking at that would be great.

[wulfrun]

35 minutes ago, DhamR said:

Wow, a lot to read through and digest here:

- I think a zoom might be an annoyance with the helical focuser if I'm honest, the focuser really is the worst part of this scope, and I haven't had much success with ptfe tape, even a single layer makes things too stiff, and causes shredding so I cleaned it all out. (I don't want tape falling down my tube).

- All that info from @bomberbaz is really interesting, I hadn't figured that you could get more mag AND wider FOV from the same lens.  Will definitely bear that EP in particular in mind, as I'm happy to spend a bit more for better quality up to a point, but especially if it reduces the need to buy an additional EP.

- I guess this is what I meant by having nothing to compare things too.  I am straining to get close enough to both EPs, so more eye relief and wide FOV would probably make things a lot more comfortable, particularly when showing things to others.

Thanks everyone.  Sounds like the BSTs are highly regarded in the other FLs, but if anyone has alternatives worth looking at that would be great.

Just to offer another route...OVL Nirvana 16mm, 7mm and Barlow, plus the ES 26mm. The Starguiders are well regarded and excellent value but the OVLs are 82-degree, which means less nudging with a Dob. Depends if your budget stretches enough though. I can vouch that the 16mm works really well in the Heritage 150P, I'd expect the 7mm to do equally well.

Regarding the zoom, I can understand the reluctance and I threw the suggestion in in case you hadn't thought of it.

EDIT: on reflection, the 16mm + Barlow is a bit close to the 7mm, possibly think about this a bit more carefully.

Edited January 18, 2022 by wulfrun

[Carbon Brush]

Regardless of the eyepeices you choose, here is a simple way to make then parfocal.

https://www.firstlightoptics.com/adapters/astro-essentials-parfocal-rings.html

[Louis D]

3 hours ago, bomberbaz said:

A 26mm ES by 62D FOV gives you x29 by 2.15 TFOV.   So the ES gives you a better magnification, so darker background than a 30mm plossl and at the same time a better tfov than either of the other eyepieces.

How well did the ES-62 work at f/5 for you?  I have it's predecessor, the Meade 5000 Plossl 40mm.  It's a five element super plossl (Zeiss Astroplan) design opened up to 60 degrees from 50 degrees.  At f/6, it falls apart beyond about 50% to the edge, so I can't imagine it's actually better at f/5.  Since it's a scaled design, the ES-62s should all perform the same across focal lengths.  I'll admit it's very sharp in the central 50% with low distortion across the field, so the moon doesn't distort into an egg shape as it drifts across the field.

Here's a comparison image showing the Meade stacked with other eyepieces at f/6 in a field flattened 72ED scope:

It's serviceable for an $80 eyepiece, but not for a $180 eyepiece.  I would just get the 25mm BST Starguider and call it a day:

It's not perfect, but it's no worse than the Meade 5000 Plossl/ES-62, and it's a lot cheaper at £49.

There's also no shame in a 32mm Plossl.  Sure, it won't be perfect to the edge either, but they're only £29.

[KP82]

If the OP has the budget for an ES62 26mm, he might as well go a bit further for ES68 24mm or APM 24mm UFF. The latter two provide max tfov in 1.25" format and better edge performance on a f/5 scope.

Edited January 18, 2022 by KP82

[DhamR]

I'd say spending upwards of £100 on one eyepiece would need a lot more thought about it than £50 even if in real terms it just means budgeting to upgrade over a longer period.

Is there a particular EP which it's worth spending more money on?  I assume from conversations it's the wider end, but worth asking? 

Edited January 18, 2022 by DhamR

[bomberbaz]

2 hours ago, KP82 said:

If the OP has the budget for an ES62 26mm, he might as well go a bit further for ES68 24mm or APM 24mm UFF. The latter two provide max tfov in 1.25" format and better edge performance on a f/5 scope.

Good point well made. aS @Louis Dpoints out the ES 62 degree version are not well corrected in an F5 scope, the 24mm UFF, of which I own and can confirm for the extra few quid would be a much better buy. 

APM 24mm UFF are available in uk from widescreen centre, there is a wait though. 

Edited January 18, 2022 by bomberbaz

[Louis D]

The 24mm APM UFF is also sold as the Altair Ultraflat, Celestron Ultima Edge, Meade 5000 UHD, and Orion Ultra Flat Field.  I may have missed some European-only versions, so check around.  Point is, there's a good chance someone has it in stock at a decent price.

Short of a 24mm Panoptic, it's about as good as it gets at f/5, especially if long eye relief is important.

[bomberbaz]

Celestron are quite a bit more expensive than the APM version though. 

The others are not available in the UK as far as I can tell although I may be wrong.

[Second Time Around]

The Altair ones are, Steve.  Here's a link to their website and a review:

https://www.altairastro.com/altair-24mm-ultraflat-eyepiece---precision-barrel-stainless-steel-237-p.asp

https://www.skyatnightmagazine.com/reviews/eyepieces/altair-ultraflat-eyepieces-review/

Had I not had the now discontinued 22mm Vixen LVWs I'd been tempted myself.

Edited January 18, 2022 by Second Time Around

[cwis]

31 minutes ago, Second Time Around said:

The Altair ones are, Steve.  Here's a link to their website and a review:

https://www.altairastro.com/altair-24mm-ultraflat-eyepiece---precision-barrel-stainless-steel-237-p.asp

https://www.skyatnightmagazine.com/reviews/eyepieces/altair-ultraflat-eyepieces-review/

Had I not had the now discontinued 22mm Vixen LVWs I'd been tempted myself.

Interesting - now £125! The AA 24mm UFF was £135 when I bought one 18 months ago. Must be responding to the introduction of the Svbony UFF clones. - they don't do a 24mm yet though.

I really rate my 24mm UFF (not that I have much experience!) 

Edited January 18, 2022 by cwis

[Zermelo]

1 minute ago, cwis said:

the introduction of the Svbony UFF clones. - they don't do a 24mm yet though

I was just looking for that, and you've explained my lack of success. Svbony have been selling the other two (SV190) for quite a bit less than Celestron (£53 vs £142 for the 10mm). If they brought out a 24mm it would be popular.

[DhamR]

Thoughts on the Nirvana 18mm?  I've seen a used one and thinking of snapping it up.

According to the various field of view visualisers it'll give a very similar field to my 25mm, but I assume it'll be a large step up in quality and ease of viewing