Televue plossl patent - what we can learn on paper?

[great_bear]

I'd hope that we can pay more attension to the technical parts of this patent.

Is there something left that you'd like clarification on?

[YKSE]

Is there something left that you'd like clarification on?

Well, just a couple of questions

e.g. the patent claims that it corrects coma, is there any negative impact if we use it in a coma-free scope, your 180 Mak e.g.?

[michael.h.f.wilkinson]

It corrects coma of the EP itself, not coma in the scope.

[YKSE]

It corrects coma of the EP itself, not coma in the scope.

Can we draw reference that other plossls introduce (more) coma to the optical chain, then?

[russ.will]

It corrects coma of the EP itself, not coma in the scope.

And yet we hear TV Plossls are better in faster Newts because they are better able to handle the coma of the scope. Is it just that there's less total coma and they're as prone to the scope's coma as any other EP?

Russell

[YKSE]

Then the lesser correction of TV plossl on aberrations at the exit pupil, as stated in the patent, this aberration is not good for daytime viewing, so the natural question is: how does this aberration manifested itself when using a TV plossl for daytime viewing? if we ignore the effect of pincuchion distortion so to speak.

[John]

And yet we hear TV Plossls are better in faster Newts because they are better able to handle the coma of the scope. Is it just that there's less total coma and they're as prone to the scope's coma as any other EP?

Russell

I thought it was because TV plossls show less astigmatism in faster scopes than other plossls ?. As 50 degree AFoV eyepieces plossls will show less of the scopes coma than, say, a 68 degree eyepiece because there is less of the off axis field visible but they, as far as I'm aware, don't actually correct the coma.

In rare cases an eyepiece can introduce coma of it's own, but I believe that is very unusual.

[great_bear]

I thought it was because TV plossls show less astigmatism in faster scopes than other plossls ?.

That's right - the only eyepiece that corrects telescope coma by design is the Klee Pretoria.

[RikM]

This does back up the reasons why some prefer to use EPs with better correction for distortion rather than field curvature. The EP tradeoffs are by design and do match what we, as observers, notice about the different EPs.

[ollypenrice]

The English teacher in me is intrigued by this sentence:

It is another object of the invention to provide a Plossl type eyepiece having improved coma and astigmatism aberrations at the edge of the field of view. (My emphasis.)

Now what does it mean to improve an aberration? I know what it would mean to reduce an aberration but is there not a slight ambiguity here?   Suppose Johnny Depp went to his make-up artist and said, 'I want you to improve the scar on my face...' wouldn't that mean make it look worse?

Hehheh.

Olly

[Merlin66]

Re Patents.....

In my research for the book on digital Spectroheliographs, I found that Meade had obtained a US patent (2007) on a design which was already in the public domain and being used by amateurs since at least 2003!!!!

How can that be!

[Psychobilly]

Re Patents.....

In my research for the book on digital Spectroheliographs, I found that Meade had obtained a US patent (2007) on a design which was already in the public domain and being used by amateurs since at least 2003!!!!

How can that be!

Dodgy prior art search....

Peter...

[slickfonzy]

The English teacher in me is intrigued by this sentence:

It is another object of the invention to provide a Plossl type eyepiece having improved coma and astigmatism aberrations at the edge of the field of view. (My emphasis.)

Now what does it mean to improve an aberration? I know what it would mean to reduce an aberration but is there not a slight ambiguity here?   Suppose Johnny Depp went to his make-up artist and said, 'I want you to improve the scar on my face...' wouldn't that mean make it look worse?

Hehheh.

Olly

It could also be improved coma, and astigmatism aberrations (I added the Oxford comma for emphasis) - the patent attorney in me was equally intrigued     It seems this was drafted in the US, where the grasp of intricacies of the English language (and sometimes the basics) amongst some patent folk is, sadly, not so good.  Rest assured, I'm sure any UK patent attorney would hang their head in shame if they'd made such a schoolboy error 

Ian

[YKSE]

Sure we can put much time to find the not-so-exact or even ambiguous descriptions in this patent. I would prefer to understand optical impact of this patent.

[John]

I was looking at some optical diagrams of the Meade 3000 and 4000 series plossls. If they are accurate (they were on Meade's website) they indicate that the 3000 series use flat surfaces on the outward facing sides of the two lens groups while the 4000 series seem to adopt the concave profile that is in the Tele Vue patent. Whether the radaii of the Meade 4000 series surfaces follow the Tele Vue prescription I don't know because the Meade diagrams are illustrative only. The Meade 3000 plossls did not use blackened lens edges wheras the 4000 series do.

Also, the lens group pairs do not seem identical with the 4000 series (different radaii for the internal facing elements) wheras the 3000's do seem to be symmetical. Maybe the diagrams are not too accurate though ?

Here are links to the relevent web pages:

http://www.meade.com/catalog/meade_4000/OLD%20files/meade_series_4000_04.htm

http://www.meade.com/catalog/meade_4000/OLD%20files/meade_series_4000_01.htm

[great_bear]

The trouble with Meade Series 4000 Plossls is they're so hard to pin down. Gone are the days when you could ascribe a certain meaningful vintage to them - today, the individual components are second-sourced, and so a unit produced on one day might be quite different to the construction of one produced the next.

What I can tell you though, is that out of all the Series 4000 plossls that I have disassembled (which is quite a few of different generations, SP, LP, but not the infamous DS version) I have never come across a single one where the achromats are anything other than perfectly identical. I did however note with interest that the best-performing one of the lot was not the "Japan Smoothside", or the non-pseudo-masuyama Japan version, but a run-of-the-mill Chinese version. I find it disappointing that people assume any optic not made in Japan must be inferior - especially since Tele Vue eyepieces are "Made in Taiwan" anyway.

Collecting Series 3000 Plossls is a little indulgence for me. Whilst they have plano exterior lenses, there must be *something* special going on (glass type?), since - for me - they are the best-performing Plossl I've tried so far. It doesn't matter that they don't have "blackened lens edges": A renowned eyepiece commentator on CloudyNights told me that when he dismantled an eyepiece a while back and manually blacked all the lens edges with paint, when he re-assembled it, he found it made no difference whatsoever. This should not surprise any optical designer - the only thing that unblackened edges should affect is the darkness of the area around the field-stop, and not the image within its bounds...

[great_bear]

The only thing that unblackened edges should affect is the darkness of the area around the field-stop, and not the image within its bounds...

*clarification - the above statement applies to lenses *above* the field stop - Smyth lenses, Barlows etc. which lie below the field stop are another kettle of fish entirely...

[John]

I agree with you re: the Meade 3000's Jeremy. I've really liked the ones I've owned.

I think Tele Vue use both Taiwan and Japan based manufacturers, based on whats written on mine anyway.

[great_bear]

Yes - I don't think Tele Vue change country of origin once production had started - "what happens in Japan stays in Japan" :-)

[RikM]

I borrowed a 16mm Meade 3000 and loved it. I bought a 24 or 25 mm hoping it would be the same only to be very disappointed.

[russ.will]

Yes - I don't think Tele Vue change country of origin once production had started - "what happens in Japan stays in Japan" :-)

Which I suppose begs the question; Who else's EPs are made in those factories and which manufacturers are they?

Russell

[John]

I borrowed a 16mm Meade 3000 and loved it. I bought a 24 or 25 mm hoping it would be the same only to be very disappointed.

I only used the 16mm, 5mm and 40mm Meade 3000's, They were the Japanese made ones and were pretty decent plossls. The 16mm and 40mm seem to be the best of the range. I don't normally like 40mm 1.25" eyepieces but the Meade 3000 seemed more immersive than others that I've tried.

[Moonshane]

a relative of mine runs an abattoir. animals vary in quality (usually meat to fat ratio etc.) and they assign certain animals to certain buyers as they come in, based on quality. they know that if they send animals of substandard quality to the most discerning customer, they will lose the business; other buyers are not too bothered and quantity is as important as quality. I suppose it's no different with eyepieces which seem similar and all made in the same factory.

[YKSE]

Anyone would like to comment on the impact of small undercorrected field curvature? or larger aberration of exit pupil in daytime use?

[great_bear]

Anyone would like to comment on the impact of small undercorrected field curvature? or larger aberration of exit pupil in daytime use?

The field curvature means the outer edge of field requires different focus than the middle. Younger eyes may not notice, but older eyes - if the problem is severe enough - may struggle to focus. I don't think that's the case here though, since the problem is probably still small enough to be masked by residual astigmatism. I've not been bothered by field curvature on Televue eyepieces, and my focussing abilities are as weak as a kitten these days...

The exit pupil aberration means that the eyepiece is more likely to kidney-bean under daylight conditions.