Upgrade my Plossls?

[Mak the Night]

Actually I suspect the opposite is true, back in the day when I was watching this sort of thing closely, Telescope House always seemed to sell out of the 8 and 11mm TVP first. That could be due to not keeping many of them in stock though.

TV Plossl pricing is odd. I had to recently choose to buy another Plossl to make a Bino pair. It came down to between a TV 11mm, 15mm or a Celestron Omni 15mm. Although the Omni had the better eye relief I went for the TV 15mm as it is, to my eyes, noticeably better quality and in a direct comparison with the Omni gives a larger, sharper and brighter image. The Omni seems more like the 17mm Celestron Plossl and in fact highly resembles it. Although more expensive than the Omni the 15mm TV was around a tenner cheaper than the 11mm. Oddly, when I priced Omni Plossls the 15mm was cheaper than the 12mm Omni.

[Mak the Night]

Below are four eyepieces. From left to right: A 15mm TeleVue Plossl, 15mm Celestron  Kellner, 15mm Celestron Omni and a 17mm Celestron Plossl.

The TeleVue is physically the smallest eyepiece and has the smallest subjective lens. The Kellner has the largest subjective lens and the largest AFOV (unsurprisingly). Only the TeleVue features a typical TeleVue slightly tapered barrel undercut with the other Plossls utilising standard 90° undercuts and the Kellner is a 'smoothie'. The 15mm Omni and the Standard 17mm Celestron Plossls are virtually identical in size, weight, field stop, AFOV, ergonomic design and subjective lens size. The Omni has a silver finish whereas the 17mm is black, both have identical rubber barrel grips. In daylight comparison tests in the same 102mm Maksutov Cassegrain telescope  (a distant Church steeple) the TeleVue gives the most magnified*, brightest and sharpest view. The Kellner has the largest AFOV and the views between the Omni 15mm and the 17mm Plossls were very similar, the 15mm Omni giving a slightly more magnified image as would be expected over the slightly longer f/l 17mm Plossl. The Kellner image appeared to be magnified to the same size as the 15mm Omni.

*Image is noticeably larger than the other 15mm eyepieces.

[John]

The Tele Vue tapered lower undercut edge is a relatively new development. Most of my TV eyepieces have a conventional, albeit it shallow, undercut.

[Mak the Night]

The Tele Vue tapered lower undercut edge is a relatively new development. Most of my TV eyepieces have a conventional, albeit it shallow, undercut.

Yes, I know it's relatively new. I'm fairly sure TeleVue redesigned the tapered lower undercut edge as a direct response to repeated customer  whinging complaints feedback. lol

[John]

Yes, I know it's relatively new. I'm fairly sure TeleVue redesigned the tapered lower undercut edge as a direct response to repeated customer  whinging complaints feedback. lol

It would be nice to think that

All my TV's were bought used and only one, the 21mm Ethos, has the "new" undercut style. Not that I find the old style an issue.

[phil125]

Thanks Mak the Night, I find direct comparisons like this really interesting. I'd not thought of doing daylight comparisons, but I support this make sense.

[John]

Odd that the other 15mm's image scale did not match the Tele Vue's

TV's specs are generally pretty much spot on so it suggests that the other brands offerings are a little shy of 15mm in focal length.

[Mak the Night]

Thanks Mak the Night, I find direct comparisons like this really interesting. I'd not thought of doing daylight comparisons, but I support this make sense.

You're welcome. I just get really curious at times lol. It was the wide angle views with that 15mm Celestron Kellner that influenced me to eventually buy specialised wide angle eyepieces. Since then my TV Plossls have been used less frequently.

It would probably still make one half of a good bino pair but I don't think Celestron market them outside of their kits.

My William Optics bino's came included with two of their 20mm SWAN 72° eyepieces and I added a pair of 9mm SWAN's. Both work well in the bino and give me the bino's max FOV of 66°. My favourite eyepieces in the bino however are the 50° 15mm TV Plossls though. 

[Mak the Night]

Odd that the other 15mm's image scale did not match the Tele Vue's

TV's specs are generally pretty much spot on so it suggests that the other brands offerings are a little shy of 15mm in focal length.

This is what puzzled me. The Celestron Omni 12mm Plossl is actually 12.5mm according to Celestron's own site, yet it quite clearly claims 12mm on the side of the barrel. 

It makes me wonder how Celestron calculate or round up their magnification ratios. I suspect, with possibly less expensive optical glass than that used by TeleVue employed, they try to achieve a balance between magnification and eye relief. The TV 15 Plossl is a tightish 10mm (like the Nagler 16mm T5). I believe the 15mm Omni has a 13mm ER. It is weird though. The overall similarities between the 15mm Omni and bog standard Celestron 17mm Plossls are remarkable. 

[Mak the Night]

It would be nice to think that

All my TV's were bought used and only one, the 21mm Ethos, has the "new" undercut style. Not that I find the old style an issue.

I think most of the problems with undercuts were when they interacted badly with brass compression rings from differing manufacturers. 

[John]

Variations from published specifications are quite common in the astro world I've found. Some scopes are not quite what is printed on their side and some eyepieces and barlows differ from spec as well.

[Mak the Night]

Variations from published specifications are quite common in the astro world I've found. Some scopes are not quite what is printed on their side and some eyepieces and barlows differ from spec as well.

It could be that some hardware has specification changes or is modified during the manufacturing process. Or possibly a bit of pork pie factory, as that's not unknown in advertising especially. Celestron claim a lot things for many of their low end scopes. Mostly their stuff is pretty good but I suppose the market is quite competitive these days. All in all I think the Omni range is pretty good, but I chose the TV 15mm for a bino pair in preference to the Omni, even though the TV has 3mm less ER.

[phil125]

Just bought a TV 32mm and 15mm Plossl second hand, should arrive tomorrow. Lets see which gives the best view of the clouds!

[Mak the Night]

Just bought a TV 32mm and 15mm Plossl second hand, should arrive tomorrow. Lets see which gives the best view of the clouds!

Excellent choices for cloud viewing. I actually saw Orion for five mins between the clouds last night. Alas, no time to get a scope set up! I believe, one night, there will be no clouds ... I believe, I really do ...

[spike95609]

Just bought a TV 32mm and 15mm Plossl second hand, should arrive tomorrow. Lets see which gives the best view of the clouds!

Both of those have worked very well for me. I hope you feel the same!