80 and 85mm Plossls

[Bigzmey]

Just saw 80mm and 85mm 2" Plossls on sale on Astromart. You don't see those every day.

https://astromart.com/classifieds/astro ... -eyepieces

Something to consider if you own a scope slower than F11 and live under dark skies.

[Lady Fraktor]

The 85mm would give me a 5.5mm exit pupil with my f/15
I imagine these are Russel Optics Plossl?

[notFritzArgelander]

The 85mm would give me a 5.5mm exit pupil with my f/15
I imagine these are Russel Optics Plossl?

So it would appear.

[DeanD]

The eye relief would be interesting: general for a plossl it around 80% of the FL: so ~ 60-65mm!

Good luck keeping your head in the right spot and steady with that ER!

[notFritzArgelander]

The eye relief would be interesting: general for a plossl it around 80% of the FL: so ~ 60-65mm!

Good luck keeping your head in the right spot and steady with that ER!

I've used and owned some of Gary Russell's long focal length Plössls. I didn't find the long eye relief that difficult to get accustomed to. (I have good fine motor coordination. It's my big moves that have me falling on my face. ) I can easily see that if fine motor coordination is not your strong point, it might be an issue.

The main difficulty I found is that the lenses (on the ones I bought) were NOT coated at all. So the main trick to using them is to have absolutely dark surroundings other wise stray reflections can be annoying. Since I sometimes observe in suburban settings that's easier said than done. So investing in a flat black hoodie or draping a towel over your head is something to consider.

[The Happy Parrot]

What is the ideal use for this type of eyepiece?

[notFritzArgelander]

What is the ideal use for this type of eyepiece?

You have a long slow scope day f/12 or f/15 and you want to choose a larger exit pupil to detect a faint fuzzy or lower magnification to frame a larger TFOV.

[Lady Fraktor]

What is the ideal use for this type of eyepiece?

With my Antares 105mm f/15 the magnification range is from high power using a 7.5mm (210x) to low power using a 105mm (15x)

A 105mm 25° AFOV eyepiece would give me a 7mm exit pupil and a TFOV of 2°

[Bigzmey]

The eye relief would be interesting: general for a plossl it around 80% of the FL: so ~ 60-65mm!

Good luck keeping your head in the right spot and steady with that ER!

My longest FL EP (56mm Plossl) has eye relief about 40mm. I have made an extra long eyeguard, which lets me observe quite comfortably.

It is not the long eye relief per se, but inadequate eyeguards what make observing uncomfortable.

[Lady Fraktor]

Eye relief of a 105mm eyepiece would be in the 85mm range though (3.3") if a Plossl design

[The Happy Parrot]

What is the ideal use for this type of eyepiece?

With my Antares 105mm f/15 the magnification range is from high power using a 7.5mm (210x) to low power using a 105mm (15x)

A 105mm 25° AFOV eyepiece would give me a 7mm exit pupil and a TFOV of 2°

Very interesting, LF. I had no idea such long eyepieces existed, but it makes sense.

[Lady Fraktor]

Long focal length eyepieces are a niche product, Russel Optics and Siebert Optics in the USA make quite a few different ones.
In the EU I can order them through ATC in Czech Republic.
Most retailers have something in the 42mm to 55mm range but not full lines, they usually go 35mm, 42mm, 50mm, 55mm.

[DeanD]

Long focal length eyepieces are a niche product, Russel Optics and Siebert Optics in the USA make quite a few different ones.
In the EU I can order them through ATC in Czech Republic.
Most retailers have something in the 42mm to 55mm range but not full lines, they usually go 35mm, 42mm, 50mm, 55mm.

There is always this one too: https://agenaastro.com/masuyama-3-inch- ... -80mm.html - and it is on special!

- although it might be bigger than some scopes! 212mm long x 110 wide, and weighs ~ 1.7kg...

[Lady Fraktor]

Yes but most people do not own 3" diagonals Dean
Though there is the 2" 60mm eyepiece in the series.

[DeanD]

Yes but most people do not own 3" diagonals Dean
Though there is the 2" 60mm eyepiece in the series.

Here ya go: https://agenaastro.com/kokusai-kohki-3- ... gonal.html -it has a 3" to 2" adapter too, so you just need to add a 2" to 1 /4" to cover all bases! (and a 3" focuser...)

Should look good on my TV76, although I might get confused about which end to look in, and the 12.7mm exit pupil for the 80mm eyepiece might be a bit of overkill...

[Lady Fraktor]

I noticed earlier that Agena says discontinued but APM lists it as on request though for a higher price.
https://www.apm-telescopes.de/en/optica ... ystem.html
but they do sell the Explore Scientific 3" for the same price as the KK from Agena?
https://www.apm-telescopes.de/en/optica ... 2mm-3.html

Masuyama eyepieces are designed to work at f/7 or longer, at f/6.3 you will see a soft edge.

[DeanD]

I noticed earlier that Agena says discontinued but APM lists it as on request though for a higher price.
https://www.apm-telescopes.de/en/optica ... ystem.html
but they do sell the Explore Scientific 3" for the same price as the KK from Agena?
https://www.apm-telescopes.de/en/optica ... 2mm-3.html

Masuyama eyepieces are designed to work at f/7 or longer, at f/6.3 you will see a soft edge.

I am not even considering it Gabby! This was all tongue in cheek.

It might be nice on my friend's 8" f18 (I think) home-made refractor though...

[Lady Fraktor]

I figured that since the mirror would be larger than the focuser

[Bigzmey]

Yes but most people do not own 3" diagonals Dean
Though there is the 2" 60mm eyepiece in the series.

Here ya go: https://agenaastro.com/kokusai-kohki-3- ... gonal.html -it has a 3" to 2" adapter too, so you just need to add a 2" to 1 /4" to cover all bases! (and a 3" focuser...)

Should look good on my TV76, although I might get confused about which end to look in, and the 12.7mm exit pupil for the 80mm eyepiece might be a bit of overkill...

Exit pupil is overrated. I believe any self-respected astronomer should have 3" EP to go along with sextuplet APO.

[MistrBadgr]

If it will not go with your refractor, you could always take it to an ant hill in the daytime and burn ants! :cool: :Pirate: