Good quality plossl eyepieces

[Per167]

I have only tried the 15mm version of the GSO Plossl distributed by Teleskop Service in Germany. I have a 130mm f/5 Newtonian scope and the performance of the Plossl was not that good in my opinion. Off-edge unsharpness, a slightly cloudy view and also no distinguished black edge where the field ends. Maybe this is not that important to some people but I found it really annoying. I did not expect wonders out of this eyepiece as it comes at quite a low price but I at least expected it to be better than the default Skywatcher 10mm and 25mm "Super" eyepieces, which I think it was not.

But again, I only tried the 15mm version - maybe the others are different.

[great_bear]

The 15mm GSO is a bit of a weird one I must confess - although I've never had sharpness or cloudiness issues. It's interesting that it's the only one with a strong exterior curvature on the lens, and it's also 16mm, not 15 as labelled.

When you say "No distinguished black edge where the view ends", this is also the case with the 6mm Revelation/GSO as well. Both eyepieces have a field-stop that's either missing or badly misplaced. They've been like this for many years apparently, and so I'm very surprised this issue hasn't been fixed.

[cs1cjc]

They've been like this for many years apparently

It does make one wonder about the quality control on such products. It appears that neither the producer nor the importer is doing any real checking or perhaps that they are happy the product does not have a sharp field stop...

[great_bear]

Quality control is all about consistency - and the 15s have consistently fuzzy field-stops, so they pass

The sad thing is, all it would take is a different type of retaining ring, but it's probably too expensive to machine one up. I did wonder if they got the old one the wrong way around, but experiments revealed this was not the case.

[Moonshane]

is it not more a case of moving the existing ring a little to ensure it's at the point of focus and thus sharp? this is even worse from the maker's point of view though.

[great_bear]

No - I investigated that.

I think - and of course I am only guessing here - that they were probably once OK and then they changed the retaining ring for supply reasons, without thinking through the consequences.

However, WHY on earth GSO left it like this is completely beyond me. I've actually asked them this question in the past - but have never received a reply.

[later] Thinking some more, maybe there was once a little ring underneath the one with the field-stop, then one bright spark said: "We don't need this little retaining ring - what a waste! - the outer ring can hold the lenses in place anyway!". Stranger things have happened