Replace the 40mm Celeston plossl

[trogre]

Hi all. I have the evolution 8 with standard eyepieces,13 + 40 mm. Not used scope much due to too much cloud. I have read that the 13 mm is pretty naff although having never compared to another eyepiece I cannot confirm this . I will in the future look for an alternative eyepiece to replace the 13 mm but do not know what with as yet.

I have a chance to purchase a second hand Explore Scientific 24mm 68 degree for a very reasonable price and was wondering if it would be a good replacement for the 40mm that came with scope. To me it seems a big jump from 40 to 24 as they are both considered low power. I must admit I have read that a 32mm is a good replacement for the 40mm so maybe a 24 mm is too big a jump.

Must admit wrote a short list of eyepieces to get and it was 32 - 24-17-12 + 9mm . So the 24 is in my list but that does not mean my choice of different eyepieces are correct.I tend not to have a preference in observing the sky so I thought my list would cover all.Thanks for any advice. 

[Roy Challen]

Hi,

If the price is reasonable, I would buy the 24/68 anyway. It'll show about the same area of sky and it will have a darker background because of the higher magnification. If you buy this, you won't need a 30-32mm 1.25" EP either - 24mm in 68 degree format shows just about the maximum amount of sky a 1.25" EP can. Not to mention it is an excellent eyepiece with very good build quality. I had the MaxVision version which is by all accounts the same EP but in a different body.

[Ben the Ignorant]

I assume your scope is a Celestron 8, right? With 2,000mm focal length? Your 40mm Plössl then magnifies 50x, but it has only 40° or 45°, and the Explore magnifies about 80x, albeit with a 68° field. Both show a little less than one degree of sky, but you should snatch the Explore; I have one, it made me give away my 24mm/68° Hyperion to my brother (occasional viewer) because the Explore is sharper over the whole field. I bougth my Ex 24 only because it was on sale, had been ogling it for weeks.

Don't let the Ex 24 go away, it has the widest possible entry lens in 1.25" format, and the widest possible field at the lowest possible magnification. Light is concentrated to the max; another way to put it is the exit pupil is the fattest, but at 2.5mm (hope you know the terms) the exit pupil is not so fat that the sky will be too bright.

[Louis D]

You might still want to hang on to the 40mm to maximize exit pupil on large nebulae.  Especially if you use an OIII filter on them.

[Mak the Night]

4 hours ago, Louis D said:

You might still want to hang on to the 40mm to maximize exit pupil on large nebulae.  Especially if you use an OIII filter on them.

+1

[Mak the Night]

'I have read that the 13 mm is pretty naff although having never compared to another eyepiece I cannot confirm this . I will in the future look for an alternative eyepiece to replace the 13 mm but do not know what with as yet. ' 

I don't know where you read this about the Celestron/GSO 13mm Plossl, you have to remember that opinions can be very subjective in astronomy and most people don't agree on anything. The 13mm Plossl eyepiece usually supplied (accompanied with a 40mm Plossl) by Celestron with various scopes (often SCT's) is a bog standard 1.25" Plossl ultimately manufactured by Guan Sheng Optical. Synta don't source all of their giveaway eyepieces from GSO but many Celestron kits contain GSO Plossls. Both the 13mm and 40mm 'Celestron' Plossls are perfectly decent eyepieces and I would hardly describe them as 'naff'. The build quality is pretty decent and so is the optical glass. 

I have replaced the original aluminium draw tubes on these 13mm Celestron Plossls (above) with chrome plated brass ones sans safety undercuts. Mainly so they will work in my binoviewer which has brass compression rings in its dioptres. The compression rings can cause snags with draw tubes that have safety undercuts, particularly the light aluminium GSO tubes. The 13mm Plossl on the right was a giveaway with my 9.25 Evolution and the other is from a Celestron kit. They are perfectly usable eyepieces. I believe Sky-Watcher (also owned by Synta Optical Technology, like Celestron) sometimes supplies 5mm UWA 'Planetary' eyepieces with some of their refractors. I have read where people have originally assumed that these giveaways are not particularly good eyepieces, until they used them and were surprised just how decent they were.

In fact, these *UWA EP's are manufactured by Barsta (BST) and are eminently usable eyepieces that deliver a bright, crisp image with no discernible light scatter and are very reminiscent of viewing through orthoscopic eyepieces costing much more. As far as I can tell they are a four element Plossl design with a fifth Barlow or Smyth type lens housed in the draw tube. No doubt the learned pundits on SGL will point out where I'm wrong about the construction and make up of these eyepieces, but as I'm not actually Al Nagler, it's difficult for me to be totally objective about eyepiece design and construction.  The very bright and contrasted images these eyepieces give does seem indicative of a basic five element design though.

At the end of the day; not all giveaway eyepieces are worthless rubbish. There's nothing wrong with bog-standard GSO Plossls and some comparatively inexpensive Barsta made eyepieces can be surprisingly good quality.

 

*Although often marketed as 'UWA' (possibly ultra wide angle) they actually have a 58° field of view, which is only 8° greater than most Plossls.

[Moonshane]

What Louis and Roy said.

[Louis D]

7 hours ago, Mak the Night said:

5mm UWA 'Planetary' eyepieces

A bit of history, these were designed by Thomas M Back as low cost, higher quality, wider FOV, longer eye relief eyepieces.  They were originally sold under his TMB label.  It didn't take long for his design to be sold under various generic names, possibly by other manufacturers, most likely without the permission of his estate.  As a result, I would try to buy the official TMB version to support his estate.

[John]

21 minutes ago, Louis D said:

A bit of history, these were designed by Thomas M Back as low cost, higher quality, wider FOV, longer eye relief eyepieces.  They were originally sold under his TMB label.  It didn't take long for his design to be sold under various generic names, possibly by other manufacturers, most likely without the permission of his estate.  As a result, I would try to buy the official TMB version to support his estate.

We had a long thread on this a while back which is worth a read for those interested:

https://stargazerslounge.com/topic/134974-tmb-planetary-originals-vs-type-iis/?hl=tmb+eyepiece#entry1983180

This discussion pre-dated the introduction of the Skywatcher branded versions but I guess is applicable to those as well ?

 

[Mak the Night]

47 minutes ago, Louis D said:

A bit of history, these were designed by Thomas M Back as low cost, higher quality, wider FOV, longer eye relief eyepieces.  They were originally sold under his TMB label.  It didn't take long for his design to be sold under various generic names, possibly by other manufacturers, most likely without the permission of his estate.  As a result, I would try to buy the official TMB version to support his estate.

AFAIK the Sky-Watcher UWA's aren't TMB clones which were six element rather than the five element wide angle 'Plossls' made by Barsta. They look very influenced by TMB's though. The Barsta UWA's are also sold under the Olivon label in the US. They look identical to the Sky-Watcher eyepieces.

These (above) are six element and are probably TMB clones. Whether they're BST, Synta, GSO or other is debatable. I have no idea who the OEM is and they aren't featured on the Barsta site.

[Mak the Night]

16 minutes ago, John said:

We had a long thread on this a while back which is worth a read for those interested:

https://stargazerslounge.com/topic/134974-tmb-planetary-originals-vs-type-iis/?hl=tmb+eyepiece#entry1983180

This discussion pre-dated the introduction of the Skywatcher branded versions but I guess is applicable to those as well ?

 

I'm not so sure the SW UWA's are TMB clones. On the box it states 'WA Plossl'. Although that could mean almost anything.

[John]

29 minutes ago, Mak the Night said:

I'm not so sure the SW UWA's are TMB clones. On the box it states 'WA Plossl'. Although that could mean almost anything.

Who knows for sure unless we start taking them apart ?. Skywatcher don't seem to commission their own eyepiece designs though, at least based on the ranges they have had over the past few years.

Back in 2013 there was a review on here of 4 of these types of eyepiece in the 4mm focal length. One was the Skywatcher version:

https://stargazerslounge.com/topic/179997-four-4mm-planetary-eyepieces/

 

[Mak the Night]

5 minutes ago, John said:

Who knows for sure unless we start taking them apart ?. Skywatcher don't seem to commission their own eyepiece designs though, at least based on the ranges they have had over the past few years.

Back in 2013 there was a review on here of 4 of these types of eyepiece in the 4mm focal length. One was the Skywatcher version:

https://stargazerslounge.com/topic/179997-four-4mm-planetary-eyepieces/

 

Thanks John. George from Astronomy Connect told me that the Agena BST Planetary Eyepieces weren't actually TMB clones but had virtually identical housings. I know there's been much discussion about the 'clones' versus the originals. I'm guessing the Barsta/SW/Olivon EP's are very influenced by the original TMB design but are not outright copies.

[John]

Somewhere I read that the BST Starguider / Explorer range are closer to the original Burgess / TMB Planetary eyepieces in optical design than most of the so called clones are.

Again, without dissection or X-rays, one can't be sure.

Just using the same elements in the same arrangement doesn't necessarily mean a clone either. The glass types, precise element spacing, coatings, lens edge blackening (or not), interior barrel baffling and lens retaining mechanics can all influence the end performance.

If we look through them and like what we see then thats what counts !

[Mak the Night]

7 minutes ago, John said:

Somewhere I read that the BST Starguider / Explorer range are closer to the original Burgess / TMB Planetary eyepieces in optical design than most of the so called clones are.

Again, without dissection or X-rays, one can't be sure.

Just using the same elements in the same arrangement doesn't necessarily mean a clone either. The glass types, precise element spacing, coatings, lens edge blackening (or not), interior barrel baffling and lens retaining mechanics can all influence the end performance.

If we look through them and like what we see then thats what counts !

Yeah, you never know what's actually inside these EP's unless you take them apart. Something I doubt I'll ever do  purposely (I've come close to it accidentally lol).  I'm just surprised how good the Sky-Watcher UWA's are for under 40 quid.