Eyepiece regrets

[JeremyS]

11 hours ago, jetstream said:

Im in the same boat.

In that case we both might sink 🫣

[Don Pensack]

20 hours ago, Highburymark said:

This is exactly what I need now - a pair of 1.25” 50/55mm plossls, though I have the excellent TV40s. Why? Because I have a solar Ha filter that needs as slow a light beam as possible to show surface detail well - so ideally I’d stick a 2x extender in front of the 3x barlow/extender built into the filter. Trouble is, that would still give me far too much magnification with my TV40s in a binoviewer. A pair of 55mms would be perfect - though not even I am demented enough to try two TV55s in a 2” binoviewer. 
Yet there may be a solution. I believe Russell Optics in Vermont does a 50mm 1.25” plossl. But I’m sure they would be extremely challenging with eye relief. Don’t know if Louis or Don have any experience with Russell, or even more unlikely, with such an unlikely eyepiece?

Apols for diverting the thread anyway….. I liked your story John

My advice is to achieve the longer f/ratio with a 25-26mm Plössl and a 2X Barlow instead.

You will still have a 45-50° apparent field instead of a 28° apparent field (55mm 1.25" Plössl)

[Highburymark]

2 hours ago, Don Pensack said:

My advice is to achieve the longer f/ratio with a 25-26mm Plössl and a 2X Barlow instead.

You will still have a 45-50° apparent field instead of a 28° apparent field (55mm 1.25" Plössl)

The problem is to achieve the very lowest magnification possible through a binoviewer, through this frankly ridiculous optical path:

ERF - 120mm refractor - 2x extender - solar filter incorporating 3x barlow - binoviewer - eyepieces.

Even 40mm plossls are too much. If some enterprising designer could make a pair of 1.25”, 100mm lightweight eyepieces, with 15mm eye relief, a decent AFOV, and minimum glass, that would be perfect…… It’s a question for another thread, or perhaps another universe.

[Don Pensack]

45 minutes ago, Highburymark said:

The problem is to achieve the very lowest magnification possible through a binoviewer, through this frankly ridiculous optical path:

ERF - 120mm refractor - 2x extender - solar filter incorporating 3x barlow - binoviewer - eyepieces.

Even 40mm plossls are too much. If some enterprising designer could make a pair of 1.25”, 100mm lightweight eyepieces, with 15mm eye relief, a decent AFOV, and minimum glass, that would be perfect…… It’s a question for another thread, or perhaps another universe.

There is a 100mm 1.25" eyepiece from Vixen.  I read it has an 11° apparent field, but I think that is overstated on that one.

The apparent field in 1.25" eyepieces is directly related to focal length:

Here are theoretical maxima in simple eyepiece designs:

24mm--68°

32mm--50°

40mm--43°

55mm--28°

70mm--22°

100mm--15°

So what you want is not physically possible in 1.25".

If you expand that to 2", 100mm maxes out at 26°

If you expand that to 3", 100mm maxes out with 40°.  That's about the same as 1.25" in 40mm, but, of course, 3" eyepieces and binoviewers don't match.

Edited April 25, 2023 by Don Pensack

[Highburymark]

On 25/04/2023 at 18:58, Don Pensack said:

There is a 100mm 1.25" eyepiece from Vixen.  I read it has an 11° apparent field, but I think that is overstated on that one.

The apparent field in 1.25" eyepieces is directly related to focal length:

Here are theoretical maxima in simple eyepiece designs:

24mm--68°

32mm--50°

40mm--43°

55mm--28°

70mm--22°

100mm--15°

So what you want is not physically possible in 1.25".

If you expand that to 2", 100mm maxes out at 26°

If you expand that to 3", 100mm maxes out with 40°.  That's about the same as 1.25" in 40mm, but, of course, 3" eyepieces and binoviewers don't match.

Looked up the Vixen - and my goodness you’re right. I’d seen this eyepiece once before and dismissed it as an April fool joke (the CN thread discussing it just happened to be at that time of year). A binoviewing pair would be quite something, though I’d have to take the cross wires out as it’s a finder eyepiece.