BST Planetary Eyepiece

[russ.will]

Actually, that's not quite right. Yes, the original Meade Super Plossls did have an extra singlet between the two achromatic doublets, but the extra element in a Super Plossl is adjacent the eye lens group, whereas in an Erfle it is closer to the field lens group. I saw somewhere that the Meade Super Plossls were closely related to the Masuyama EPs of the '80s and both were made in Japan at that point. I don't know if this was coincidental, or not.

Regardless and Erfle is only suitable for longer FL EPs because it suffers too much astigmatism below 20mm, suffers unacceptably short ER at short FL and has a native 60deg plus aFOV. The Super Plossls only eeked aFOV out to 52deg.

In later years, the 5-element Super Plossls were dropped and latterly, the name only really came to mean that the Plossl had a rubber eye cup. Super indeed!

Russell

[great_bear]

Actually, that's not quite right. 

Sorry Russ, I'm 100% right. The information you are quoting relates to Meade S4000 Plossls.

The (60 degree) Meade S5000 "Plossls" (of which I own several) are known to be Erfles - it's not a matter of opinion..

[russ.will]

Don Pensack would seem to think otherwise.

Russell

[alan potts]

Dr Hamzonia,

TeleVue Plossl eyepiece are I believe based on the original design however Mr Nagler did change it enough to get a patent out on his design, as to what was changed I have no idea.

Dude with,

I was really just saying that TV Plossl eyepieces are sharp in a fairly fast scope where as the Meades 14mm SP are not, I though I made it clear, sorry if I didn't. However the full set of Meade's  7 S Pl's eyepieces work very well in a slower scope at F 10.

With regards to the 14mm Meade eyepieces from the Su Plossl Series 5000 range it is optically not as good as the TV 15mm Plossl albeit with a smaller field of view. On the other point I too thought these were the Erfle design eyepieces as well.

Alan

[great_bear]

Hi Russell.

The 60-degree, Meade Series 5000 Plössl lens stack consists of:

1. A small bi-convex cemented achromat, resting inside a shouldered ring
2. A bi-convex lens, resting on top of another ring
3. A larger convex/concave cemented achromat, resting on the retainer

This arrangement is commonly described as an Erfle II

Is there any part of this information that you wish to dispute?

[great_bear]

With regards to the 14mm Meade eyepieces from the Su Plossl Series 5000 range it is optically not as good as the TV 15mm Plossl albeit with a smaller field of view.

Interesting - I found the opposite in my Mak - so I sold my TV15mm Plössl pair and kept the Meade 14mm Series 5000s instead. I don't know whether the Mak's F15 focal ratio is responsible for this or whether other parameters come into play - since the S5000s also easily fought off a pair of 16mm Brandons - which is something that I really wasn't expecting at all.

I've made several attempts to replace the Series 5000 Plössls with something else - but my Mak just seems to like them, so I've given up now and just enjoy the view they give me in that particular scope.

[alan potts]

Jeremy,

Interesting findings. I have the same type of Mak as you and the 14mm was indeed very good in this scope and I did use it a fair bit while I had it on loan. The 15mm TV though I have not tried in this scope but now it will be on my to do list if it stops snowing, weather!

alan

[great_bear]

The William Optics Binoviewer that I use might also have a role to play in the equation...

[russ.will]

Hi Russell.

The 60-degree, Meade Series 5000 Plössl lens stack consists of:

1. A small bi-convex cemented achromat, resting inside a shouldered ring
2. A bi-convex lens, resting on top of another ring
3. A larger convex/concave cemented achromat, resting on the retainer

This arrangement is commonly described as an Erfle II

Is there any part of this information that you wish to dispute?

Oh! Now it's an Erfle II! You'll have to hold that target still if you want someone to shoot it!   I checked it out and I stand corrected re the difference between S4000 (to which I was referring) and 5000.

Mind you, in checking it out, it lead onto many interesting sojourns, not least of which was the 6 element Erfle...

Did you try the S4000 v 5000 in the F6 Dob? Okay, it's not exactly a sub F5 test, but one would expect *from what you read* that the Series 5000 SP would look distinctly dodgy at the edges if they're Erfles (and they're short ones at that) without a reduced field stop to hide the outer FOV?

I read your comments with respect to binoviewing in the Mak with interest, especially now I've joined the SCT club and already have a decent short frac. It's something I'd like to try, without going to too much expense (initially) and the S5000 SPs, from what you say, look like they're good enough to be very good, but unfashionable enough to be cheap. I've seen nice binoviewing comments re the HD-60s too - Have you tried them?

Russell

[great_bear]

one would expect *from what you read* that the Series 5000 SP would look distinctly dodgy at the edges if they're Erfles

They're famously poor at the edges, and I found the 26mm unserviceable even in a slow scope, as did EdZ on CloudyNights.

The central zone is nice though, especially on moon and planets...

I've seen nice binoviewing comments re the HD-60s too - Have you tried them?

Yes, but I dislike field-stops at infinity and beyond; and Meade's "Plössl" ranges(3000/4000/5000) all have near-focus field stops, so even if you're short-sighted like me they are razor-sharp and satisfying.

[Charic]

Did someone mention TV Plossl......Ooooops! See how subjective eyepiece selection can be.

What ever you buy, it can always be sold on if it does not fit or satisfy your requirements properly. Dont feel let down if someone suggests a lens that doesnt feel right while you use it. I have tried a TV and a TMB and did not like them during first light testing? Buy with instinct, or just a gut feeling that it will be ok, and either keep or move them on.

[Moonshane]

One of the main benefits of buying used is that you can buy, try and sell on for little or no loss.

[Dr Hamzonian]

Lots of valuable information here guys! and a tad bit of interesting off-topic discussion

Thanks everyone!