Are planetary Plossls worth the short eye relief?

[Stonius]

Last time I used a short (4mm) Plossl, was with the 60mm Tasco Refractor I had as a kid, and I remember it being quite an uncomfortable experience.


Now to be fair, that scope wasn't built for that kind of magnification, and without a tracking mount it was an exercise in futility that has scared me off Plossls ever since. There was also something incredibly annoying about having your eyelashes hit the lens every time you blink.



But the 'less glass' thing makes sense to me, plus they're fairly cheap, but the TV ones only go up to focal lengths of 8mm with 6mm eye relief.


Yes you can barlow it, but then you might as well use a Nagler because you're introducing more glass anyway, but if you don't then, 8mm isn't really *all that* short, is it? If conditions suffice, wouldn't you *want* shorter focal lengths?


I also struggle to understand the use for a 50mm Plossl for? My understanding is that wouldn't even work in a binoviewer. Surely at those focal lengths it's outperformed by other EP's with similar field of view?


So I guess what I'm asking is whether my FOMO is justified? People who have tried / own them, was it a slight incremental improvement, or was it an 'Aha' moment?


So far I've been pretty happy with my Pentax XW's, but maybe my memories of that 4mm in my tiny refractor are making me unfairly biased?


Markus

[AstralTraveller]

Markus,

I have a UO 7mm ortho which is optically great and I can handle the eye relief. However I find the 5mm too short for comfort and never used it much. FWIW I have a 7.5mm Celestron silver top plossl from the 70's which I used to think was OK. The UO ortho eats it. If I was going to go for less glass my preference would be towards orthos.

[glend]

The problem with short focal length EPs in general is that conditions rarely support their use. I hated spending money on anything shorter than 9mm. If I though I could use more magnification I simply Barlow a longer fl EP., say like a 9mm down to 4.5mm. Longer focal length EPs are generally more user friendly.
Of course the scope your using the EP on is a big factor.
If your already using a longer fl scope, say like a Cassegrain, sticking a short fl EP on them is almost guaranteed to make seeing much worse.

[Camelopardalis]

Markus, the XW are up there. I prolly wouldn't be wanting to trade-in their qualities for anything less than a very fine replacement.

fwiw, they do a 3.5mm XW :lol:

[Stonius]

Yes, I've got it, but rarely use it. Usual story - typically conditions won't allow. Maybe when we're allowed to have star parties again I can find someone kind enough to volunteer a Plossl for a little EP comparison testing.

[glend]

Star Parties?..tell him he's dreamin!
:lol:

[mura_gadi]

Hello,

If the question is about ER, buy a $20 4mm plossl from ebay or similar. If you find the eyelash feedback not so bad, you can look at a higher quality investment.

Your evaluating the ER not the EP after all.


Steve
Ps. 32mm Plossl on my 8" SW (f6) is 1.3+ degrees, fairly wide view, very little glass.

[astro744]

A 50mm Plossl is useful in long focal length telescopes with slow focal ratios. At f10 you get 5mm exit pupil for brighter images. The Tele Vue 55mm Plossl has a 46mm field stop diameter which is the same as the 41mm Panoptic. The Panoptic will give 4.1mm exit pupil at f10 but has a wider 68 deg apparent field and the 55mm Plossl will give 5.5mm exit pupil at f10 with 50 deg apparent field.

Note the Clave Pic Du Midi observatory Plossl series had 30, 35, 40, 45mm all with 48 deg apparent field in 50mm or 50.8mm barrels. Also in same barrels but with smaller true fields (deg) were 55mm (42), 65mm (37) and 75mm (32).

A good quality Plossl is not just for planetary also for deep sky to tease our the faintest detail or even just pick up the faintest galaxy. Such contrast boost possible from the superb polish on all glass surfaces that make up a good Plossl eyepiece not just the reduced number of elements in its makeup.

On the subject of eye relief with short Plossls, you will find it considerably more comfortable if you are tracking the target with an equatorial mount. You can turn away to rest your eye and return to the view without losing the target.

I did a test with Jupiter one night using a 6mm Clave Plossl, 6mm Brandon and 6mm Tele Vue Radian on my 10.1” f6.4 Newtonian on an equatorial platform. Each time I changed the eyepiece I thought I saw some new detail I didn’t see before. The view I enjoyed the most was with the Radian simply because of the comfortable 20mm eye relief. If seeing was better that night perhaps one eyepiece would show more than another more consistently but not that night.

I still enjoy my Plossls and one absolute gem is the Tele Vue 8mm Plossl which gave me superb lunar views one night through my Newtonian. I do also enjoy the Nagler Zooms (4-2mm and 6-3mm) for their ability to change magnification at a reasonably generous 10mm of eye relief. My all time favourite combination is the Clave 10mm Plossl with Clave 2x Barlow for an absolutely exquisite 5mm eyepiece.

Note to see the difference a quality Plossl gives requires the best of seeing and most nights simply wont offer that opportunity. Note too there are many modern alternatives such as Tele Vue Delos or DeLite but not having used any I cannot comment on their performance.

[N1]

I have (and enjoy using) many short-eye relief low-glass eyepieces. For planets at least, I find the eye relief issue pretty much irrelevant because I observe the centre and simply don't need to see all of the field (stop) at all times. My XP3.8 has less than 3mm of eye relief yet is perfectly useable for small targets like planets. It's also much smaller and lighter than the 3.5 Nagler it replaced, ideal for a grab and go kit.

I sold my 7mm Nagler after discovering that a 7m Plössl from the same maker beat it on just about everything that happened within 25° of the optical axis, i.e. where it matters Yes, it was sharper and had more contrast. I've also had good results with barlowed Plössls. A decent quality combo would be no worse on planets than say Naglers but at a fraction of the cost.

[Stonius]

Good thoughts all. I suspect that I wouldn't be able to detect much difference between a planetary Plossl EP and my XW's given my aging eyes and level of observing abilities and if that's the case, I'm pretty happy. Still would be good to try one day.


Cheers


Markus

[gregbradley]

I have a few XWs, optically pretty perfect. A little bit sensitive to eye placement.

Super cheap TMB planetary 11 eyepeices are remarkably good performers for their low cost ( $55).

Get them on Ebay.

Morpheus, Pentax XW, APM 12.5 Hi FW with barlow or XWA with barlow would be what I would reach for.

Greg.

[Don Pensack]

The "less glass" idea only works if the optics are equal.
I think the idea got started by people comparing cheap 3 and 4 element eyepieces with cheap 6 and 7 element eyepieces.
If, on the other hand, the lens polish and coatings are superior on the multi-element eyepiece, it might be the case, and I've seen this, that the multi-element eyepiece might actually yield a better image. My TeleVue Delites yield a better planetary image in my 4" apo than Plössls do.

Add to that the fact that most eyepieces are pretty much the same on axis, i.e. yield a spot size smaller than the Airy disc, and the differences are largely outside of the on-axis view.
That would matter a lot if you use a non-tracking mount and want to watch the planet or Moon image as it drifts across the field. If you do that, then there are definitely some 70° eyepieces that are better than the "less glass" types.

The light loss through an 8 element eyepiece might be as much as 1-2% more than a simple 4 element eyepiece, and that is unnoticeable to the eye and hard to measure in a lab, so we can ignore that difference. It simply won't matter.

So, stick to your XWs (the eyepieces Daniel Mounsey on cloudynights.com called the "best widefield planetary eyepieces" in a couple reviews a few years ago.[He's a hardcore planetary and double star observer].
4mm and 5mm Plössls are best used as telescope "dustplugs".

[Renato1]

I bought a cheap 4mm Plossl from Andrews Communication years ago.

The eye-relief was terrible - I couldn't see the entire field......that was a useless purchase I thought.

But then I had a bright idea - I pulled off the rubber that ran around the top of the eyepiece, and then I could see the entire field, and the eyepiece was actually pretty good - and I bought two more.

My understanding of the "less glass" thing from something I read decades ago, is that it's a hangover from before WW11, when multicoatings on glass surfaces were generally unavailable. Less glass gave the best images back then, but that ceased to be the case afterwards when more glass could be used.
Regards,
Renato

[Stonius]

I had always assumed (probably wrongly) that the 'less glass' thing came from the fact that any lens is made to a tolerance and the errors accumulate with each refractive surface. The more refractive surfaces, the more accumulated errors you'll have. It made sense to me but I have to admit it was all based on supposition, so could be entirely wrong.


Markus

[astro744]

There’s more to it than just less glass otherwise Huygens would be highly sought after. They are good eyepieces if you have a refractor of f20 or more and observe on axis with tracking.

Surface accuracy and a high degree of polish makes the most difference to teasing out those low contrast features. Multi coatings help but I believe Brandon still use single coating and they are amongst the finest eyepieces out there when contrast is paramount. Clave too have a high degree of polish but theses have been discontinued many years ago.

[yoda776]

The only thing I would watch for in Brandons (as I have owned a set of them) is they benefit from F8 or slower scopes. Really nice eyepieces though. Claves you will be paying through the nose for them if you can find someone that will part with them and then if they do in good nick. I have a 30mm Clave and it is a fantastic eyepiece. I like the fact the sides are high enough to act as an eyeguard.

[yoda776]

I agree with your earlier statement though Markus - nothing worse than having eyepieces where your eye lashes are touching the glass or having to hold your eye open look away and blink. The Pentax XO 2.5mm I had was like that - great views though but always tensely avoiding contact with the lens. Had someone in the Ukraine who bought it and was believe it or not going to binoview with them!

Pentaxs outside the above are good for viewing and have known Vixens with good eye relief too. The Meade Ultra wide 5000 series I had with the twist up eye guards were also good and my viewing buddy also has a Meade 4.7mm UW 5000 series he regularly uses and enjoys with his not so great eyesight.

[Culford]

I love plössl eyepieces but am not a big fan of them below 10mm. The exception are my 7.5 mm Halloweens.

For planetary views I often use a 6mm Fujiyama ortho when using my 80mm frac but on my 8" Dob a 7mm Delite presents an awesome, comfortable view.

[ausastronomer]

Hi Markus,

A bit late here. I have 5mm and 7mm Pentax XW's and 5mm and 7mm UO HD Orthoscopics. I've spent quite a bit of time comparing them side by side over the last 15 to 20 years. I'm yet to really pick much of a difference, if any, in terms of planetary detail visible. Sometimes you think you see something in one that you don't see in the other. Then you revisit the same feature with both shortly after, and it's there in both, or gone in both and obviously the previous difference you saw was seeing related. The UO HD orthos are very good and probably the optical equal of any plossl I've ever used. If you went to the top level of orthos to say Zeiss Abbe, Pentax XO or Nikon, I think you would detect a slight advantage in favour of the orthos, but I'm yet to find a plossl that can run at that level.

On the basis that the Pentax XW's have a big advantage in terms of Eye relief, comfort, AFOV and EOF correction the orthos only get used with my spectroscope, as it needs a small eyepiece to attach to.

Cheers
John B

[Stonius]

Thanks John. That makes sense :-)


Markus

[MortonH]

Agree. A few years ago I acquired a Tele Vue 7.4mm Plossl and it was super sharp. Subsequently sold it but wouldn't mind having another one.