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A "Practical" Planetary Eyepiece?

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#26 BillP

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Posted 30 May 2020 - 12:22 PM

Bill,

 

Interesting concept, and well thought out.

 

a) I think some sort of superpolish is going to be necessary for planetary due to the SP reducing scatter which no coatings can do.

 

b) I think you can pull this off with 3 EPs and 3 Barlows 1.5, 2.25, and 3.35

               1.5        2.25      3.35

17.5      11.67      7.8        5.21

20.0      13.33      8.9        5.96

22.5      15.0      10.0        6.70

Probably right on the polish issue.  We always hear off-hand comments from people about the cost of the next level of polish.  Would be interesting to hear from a current producer of eyepieces how much their costs to the consumer would rise on a particular eyepiece brand it they requested the next level of polish. Would be nice to hear from the horses mount based on current day pricing from their suppliers.

 

On the Barlows, my only issue is having to figure out in the field what BArlow with what eyepiece gets me the next magnification increment.  Right now when I design a series like this I make sure that whatever focal lengths I biring out that after I get to the shortest I just put the Barlow in and it stays in and I recycle through the series in sequence.  So no fuss no muss no thinking lol.gif  So as example, when I bring out the XWs I will often just take the 20, 14, and 10 plus a 2,5x Powermate for 8, 6, and 4.  Makes life easy.  Yours seems to do that but wow...3 different Barlows bigshock.gif


Edited by BillP, 30 May 2020 - 12:23 PM.


#27 BillP

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Posted 30 May 2020 - 12:33 PM

the eyepiece is rarely the bottleneck.

FWIW just the opposite for me, the scope is never the bottleneck and the conditions are never a bottleneck as they just are what they are at the time.  When I go out with an aperture choice from my scopes, into the dark with whatever the conditions are, then it is always operational issues around that aperture that need to be optimized.  Plenty of premium eyepieces out there, none perform all the same on-axis for planetary, not to my eye.  For me personally, no complex widefield, regardless of brand, performs on a planet as good as the more specialty designs and builds for planetaries.  Operationally, none of them have sufficient focal length choices.  So just trying to find a middle ground here that will work.  It will not be for everyone and that is expected and OK as not everyone pursues planetary observing as their primary pursuit.  But for those of us that do, the eyepiece is a most critical component.  Aperture is whatever we decide to bring out at the time so regardless of aperture, the eyepiece always has the final say in the equipment chain. 


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#28 MartinPond

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Posted 30 May 2020 - 01:18 PM

It is possible to have minimal glass ep with eye relief much greater than focal length
https://www.cloudyni...yepiece-design/

Yes and no...

That's a Smyth/Barlow with a Dollond down the road...

  an inboard multiplier.  The afov, to be very sharp, is under 40 degrees..

   From fiddling, I cannot get the contrast to be great.

  

As a note,   I think Jon's "the eyepiece is rarely the bottleneck."

   might partly refer to the chromatics of the scope, very important at

   extreme powers.    An eyepiece cannot really overcome that much bigger

   spread of focal points.  An ED scope helps there, but to avoid staggering

   price escalation, most ED owners also accept an F7 barrel.

 

At that point, I think it's safe to say that any "practical" eyepiece system

    includes a scope length that justifies it, long or  ED/F7.

    Different troubles limit a reflector.  You can Paracorr, but short still hurts. 

 

I think the F7  relief provides a lot better flexibility and contrast, when it

    comes to simpler eyepieces.  Many EP designs can have 

    great contrast by design, so it seems (from experience) that going

   completely minimal on element count ends up with worse contrast,

   by not dispersing out-of-field light as well..  

   I prefer the contrast of a 4-element focal extender to a 2-element Barlow.

   I can't get the field or the contrast out of a Dollond that I get from a

   2,2 Plossl,  1,2 Konig(1) , or a 1,3 Ortho.    It all depends on how the

   designer deflects and absorbs light.   No surprise many love the Delite

   for contrast....at 60 degrees, it has the spare capacity to trade off in

   favor of dumping stray light.

 

Maybe (?):

    ----obsessing about total element count can hurt contrast 

    ----worrying about best-practical-set must refer to a good enough telescope

            that makes a given resolution possible...

           That is, discussing eyepieces without the scope could be a trap.


Edited by MartinPond, 30 May 2020 - 01:20 PM.

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#29 BillP

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Posted 30 May 2020 - 03:55 PM

I think the F7  relief provides a lot better flexibility and contrast, when it

    comes to simpler eyepieces.  Many EP designs can have 

    great contrast by design, so it seems (from experience) that going

   completely minimal on element count ends up with worse contrast,

   by not dispersing out-of-field light as well..  

   I prefer the contrast of a 4-element focal extender to a 2-element Barlow.

   I can't get the field or the contrast out of a Dollond that I get from a

   2,2 Plossl,  1,2 Konig(1) , or a 1,3 Ortho.    It all depends on how the

   designer deflects and absorbs light.   No surprise many love the Delite

   for contrast....at 60 degrees, it has the spare capacity to trade off in

   favor of dumping stray light.

I'm pretty much fixed at f/8 and f/9 for my scopes.  So I prefer the longer focal ratios.  When you have a moment would like you to elaborate on exactly what you mean about dispersing out of field light and either deflecting or absorbing it.  And also what is meant by the DeLite having "spare capacity" so it can dump the out of field light instead of absorb it. 



#30 25585

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Posted 30 May 2020 - 04:58 PM

As food for thought, here is an article on microscope oculars     https://www.olympus-...natomy/oculars/

 

The part describing which gives best view as a combination of eyepiece and objective is interesting. 

 

Given that planets & Moon are very small, with tiny detail, they can be seen in the same vein as lab samples, but observed under much less ideal environments than carefully illuminated & positioned glass slides. Telescopes are microscopes on the cosmos.

 

Having a need for long FL, long eye relief eyepieces, I have longer FL scopes (with extenders where necessary) for planets etc. The combinations work well. Rather than fewer elements more finely polished, the materials used and optics design can determine how good a view is. 

 

Perhaps the design of a planetary eyepiece, needs to be re-thought from the ground up, for build, optics,  practicality, and end desired result, rather than constant re-treading of conventional, historic models.           


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#31 BillP

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Posted 30 May 2020 - 09:03 PM

As food for thought, here is an article on microscope oculars     https://www.olympus-...natomy/oculars/

 

The part describing which gives best view as a combination of eyepiece and objective is interesting. 

 

Given that planets & Moon are very small, with tiny detail, they can be seen in the same vein as lab samples, but observed under much less ideal environments than carefully illuminated & positioned glass slides. Telescopes are microscopes on the cosmos.

 

Having a need for long FL, long eye relief eyepieces, I have longer FL scopes (with extenders where necessary) for planets etc. The combinations work well. Rather than fewer elements more finely polished, the materials used and optics design can determine how good a view is. 

 

Perhaps the design of a planetary eyepiece, needs to be re-thought from the ground up, for build, optics,  practicality, and end desired result, rather than constant re-treading of conventional, historic models.           

It really does.  How an eyepiece behaves is very much tied to the main objective design.  In the book Telescope Optics they lay out the ray trace results for several eyepieces, then several main objectives, then when they are combined in Chapter 16.7.  Amazing how the synergy changes things.  So it is clearly NOT the case that a given eyepiece will work the same in various scope designs.  But, if you design an eyepiece to be scope-type specific, you really limit your market.  Had a long discussion on that topic with Tom Back many years ago.  Plus no easy task to try to correct what might be going on from the main objective right near the end of the light cone.  Where the eyepiece sits is the worst place to try to for change.

 

Actually reworked the concept I put forward here with an interested party so that the short end of the Barlowed focal lengths are at 1/2mm increments.  Would provide much smoother magnification jumps which is important for planetary.  Also did it to incorporate a 2x Barlow instead as makes the math much easier for the user.  It would be interesting to have this as operationally there is no eyepiece set that gets one this, and it is funny as it is such a sought after thing by many planetary observers so they build disparate collections so they can get to the smoother less large magnification jumps.  So now have it going at 1/2mm increments from 3.5mm to 7mm, then 1mm increments from 7mm to 14mm.  Covers the needs of SCTs well too.  Threw a 28mm in there for a finder focal length (and to get to 14mm).  8 focal lengths total and the 2x of course.  Would make for some great capability from those focal length choices that don't have now, and then be able to service lots of different scopes well.  Will see what happens.

 

Of course a 7-14 zoom with a 2x would provide the same capability.  But then the lens count increases and more difficult to effectively baffle it and the lenses as they move will mean less than fixed-precise alignment and an overall not as precise view as is capable from a fixed focal length (as we have seen in the several zoom attempts to date).  So a lot of new ground to blaze for a planetary zoom...more straight forward and established what to do for fixed focal lengths.



#32 MartinPond

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Posted 31 May 2020 - 01:20 AM

Ahh.  I see.  You are probably correct, but then again this concept I floated needs to make compromises so there is production efficiencies in place to keep overall costs down.  If we were discussing the "perfect" planetary build then no holds anywhere smile.gif

Indeed...nothing is perfect..

 

Compared to many glass minimalist designs, though,  (ball, Dollond alone, etc,.. ),

    35-40 degrees or so is pretty generous.   

For the long-positive-negative-achro's design, I don't think you would need to worry much  about production

   in general....other than being forced to buy hundreds to get a deal..

 The design is very generous in terms of working fine away from the perfect optimum..

  Your idea could be called 'minimalist-long-eye-relief' to emphasize the unique combination.

   If the long interior were baffled and threaded right you would have super contrast.

 

    I would need 2-negative-achro  and 4-eyepiece achro.  So...6 is more than 4..

      6 air-glass surfaces to, not 4 .   

 

     I suppose I could use a 1,2-Konig to get rid of one piece of glass.

     It offers more eye relief than the Plossl (at same top fl)

      or any other simple EP, and performs tops in a 

      3X---5X or more scheme..   And 50 to 55 degrees crisp (multiplied)... 

      At least that gets me down to 5 elements for a very high power with long 

     eye relief.  It has assymetric stray light deflection like the ortho, too.

     An overlooked gem.. 

 

     Plossls can be manufactured with looser tolerances all around though,

      and still perform extremely well.. I suppose that is a factor in their

      taking over the low end. 

 

       

     The Burgess monocentric seems like your cup of minimalist tea, air-interface-wise.

     But there is a too-big problem.   The longest fl is 10mm..... you would want maybe 25mm

     for glasses-level eye relief before multiplying.   

     Easier to get: a Hasting triplet.  It wants F10....easy with your small-net-fl  approach.



#33 BillP

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Posted 31 May 2020 - 10:25 AM

I agree the 1-2 Konig is a great design.  It is not overlooked either as I see it working its way into designs, like the Tak LE in 5mm and 7.5mm have around an 11mm 1-2 Konig-like design in the upper housing, and the negative field doublet supplying at least magnification if not more below that in its own removable housing.

 

I am not overly stressing on the number of elements here, just wanted to start with a positive-only design since Barlowing is in the mix.  The most important thing trying to achieve is a system-approach to the focal lengths produced so they yield planetary magnifications with small focal length separation between the eyepieces so can best tune to what the seeing is allowing.  So this would be a well thought out system of eyepiece focal lengths and Barlow(s) so the offering is comprehensive.  And since Apos and the many 1200mm focal length production Dobs need fine focal length increments between 3-8mm for planetary, while the SCT crowd need it in the 7-20mm focal length range, it is a hard problem to solve if want to embrace all the scope communities.  AFOV can't be too small too as as a rule the amateur astronomy market does not take very well to under 50 degrees, and seems to have an abhorrence of under 40.  So need to consider both production efficiencies and marketability.  Need them to perform too of course on planetary, but thinking might be easier and more cost effective to increase their contrast through careful choice of optical design and baffling rather than paying for excessive polishing.

 

Anyway, it is an interesting exercise, and have come across a few makers that are at least showing casual interest.


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#34 SandyHouTex

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Posted 31 May 2020 - 11:44 AM

Probably right on the polish issue.  We always hear off-hand comments from people about the cost of the next level of polish.  Would be interesting to hear from a current producer of eyepieces how much their costs to the consumer would rise on a particular eyepiece brand it they requested the next level of polish. Would be nice to hear from the horses mount based on current day pricing from their suppliers.

 

On the Barlows, my only issue is having to figure out in the field what BArlow with what eyepiece gets me the next magnification increment.  Right now when I design a series like this I make sure that whatever focal lengths I biring out that after I get to the shortest I just put the Barlow in and it stays in and I recycle through the series in sequence.  So no fuss no muss no thinking lol.gif  So as example, when I bring out the XWs I will often just take the 20, 14, and 10 plus a 2,5x Powermate for 8, 6, and 4.  Makes life easy.  Yours seems to do that but wow...3 different Barlows bigshock.gif

I’ve never understood why leaving a lens on a machine for twice as long to get a high level of polish adds that much cost. Eyepiece lenses are small and made on mandrels with 10 of them at once.  Being polished by a machine means one person can monitor multiple machines at once.  So where’s the cost?  Not in the consumables, water and polishing agent, not in labor, and certainly not in utilities, water and electricity.


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#35 MartinPond

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Posted 31 May 2020 - 01:41 PM

If you are willing to use the generous and rich

   Konig 1,2 .... it occurs to me:

 

----just have a telescoping section with a mild negative,

     like the Burgess OCA (says 1.9x, but that's for the nose

     of a binoviewer).   I make a supreme 2X  by swapping that onto

     the nose of an Orion  Tri-Mag (very nice baffling in there)..

     better contrast than the 3X they sell, great as it is.

----then make a marked 'mild zoom' out of the 1,2  so you can get (just guessing)

     something like 20mm, 18, 15, 13, and 12 (or finer steps) out of a 25mm  1,2.

          

----next comes a higher power:   maybe a 15mm  1,2 up top, but now you need

     a stronger Barlow with a special light trap, and it needs 3 elements (sorry about that)..

     ...and that would be the 3X  X-Cel LX.   So that would give you something like: 

       12, 10, 8, 7, 6, 5 mm, 4 and maybe 3 if you stretch it.  You can do 3X with 2 elements

       but a stronger nose zooms more.

 

A little nicer shaping on the 1,2-Konig, and considering the multiplication always

   being 1.2 or more, you would have 55 degrees, clean across at F6 or more.

   Perfect ED companions.

 

At the least, a mild zoom Barlow would chop your parts count way down for the set.

The longer-fl one might not cover the range I guessed at without mechanical

   complications, but you get the fine steps and ep-qty reduction for sure.


Edited by MartinPond, 31 May 2020 - 01:43 PM.


#36 emilslomi

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Posted 31 May 2020 - 02:05 PM

Ever smaller increments between eyepieces and use of a Barlow sound like a zoom to me. I would jump on a constant field 4-12 or even 4-10 in an instant. With those focal length, even a constant field may still be practically possible. May be a variable entrance baffle would be possible too. And instead of polishing and coating expenses for top quality umpfteen times, you only have them once. I have the TVZ 3-6. It's just a bit much to be truly useful to me.

 

Emil



#37 MartinPond

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Posted 31 May 2020 - 02:51 PM

Ever smaller increments between eyepieces and use of a Barlow sound like a zoom to me. I would jump on a constant field 4-12 or even 4-10 in an instant. With those focal length, even a constant field may still be practically possible. May be a variable entrance baffle would be possible too. And instead of polishing and coating expenses for top quality umpfteen times, you only have them once. I have the TVZ 3-6. It's just a bit much to be truly useful to me.

 

Emil

Some interesting stuff there!

 

"

  I would jump on a constant field 4-12 or even 4-10 in an instant.

"

...Problem is, a constant field plus 2:1 or 3:1 zoom always leads to many more elements..

Practically possible, but as messy and hi-count as a camera zoom of the same range,

    all those elements moving on different spiral tracks inside..

....But a mild zoom (1-1.5x  or 1.8x) ... makes it easy to use the top set at uniform afov. 

 

 

"

May be a variable entrance baffle would be possible too

"

...Actually, a nice variable iris works super-well, usually just inside, behind the 1st group.

When I do it, though, it's held together with a lot of glue. A sadly missing component,

  variable-iris in proper 1.25 and 2 inch formats. 

 

 

  "

And instead of polishing and coating expenses for top quality umpfteen times,

  you only have them once.

"

...Yes, AND  you also get the benefit of a large base FL up top, which for the same

    level of polish and mech-spacing tolerance, gives you finer edges in the end.

     Note how favorites in simple EPs are

      "18mm BCO.....26mm Super-Plossl...32mm GSO Plossl,  28mm RKE....etc"

     Making a premium 10mm ortho finish is a lot harder than making a premium 25mm..

 

 

"

I have the TVZ 3-6. It's just a bit much to be truly useful to me.

"

The Televue 3-6mm Nagler?    

'A bit much' could mean many things...   but the element count is high, and the price.

It is a uniform 50 degrees, to be sure.  At 3-5mm, or 6-10, many simpler things can do that.

If you mean "a bit much hassle",   the small power steps and huge range

    make that 'a bit much' whatever you do ;-)

I'm happy with ~30-40% jumps.  


Edited by MartinPond, 31 May 2020 - 02:52 PM.


#38 Jeff Morgan

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Posted 31 May 2020 - 05:39 PM

I’ve never understood why leaving a lens on a machine for twice as long to get a high level of polish adds that much cost. Eyepiece lenses are small and made on mandrels with 10 of them at once.  Being polished by a machine means one person can monitor multiple machines at once.  So where’s the cost?  Not in the consumables, water and polishing agent, not in labor, and certainly not in utilities, water and electricity.

 

Any machine has a limited lifespan at which point it is un-economic to rebuild/maintain.

 

I don't know that that number might be, but it does not matter. Take twice as long to polish and over the life of the machine only half as many eyepieces can be produced for the cost of the machine.

 

Operator supervision and whatever the consumables are (cerium oxide, electricity) goes on top of that.


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#39 SandyHouTex

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Posted 31 May 2020 - 05:45 PM

Any machine has a limited lifespan at which point it is un-economic to rebuild/maintain.

 

I don't know that that number might be, but it does not matter. Take twice as long to polish and over the life of the machine only half as many eyepieces can be produced for the cost of the machine.

 

Operator supervision and whatever the consumables are (cerium oxide, electricity) goes on top of that.

In most manufacturing environments I worked in, provided you did the scheduled preventative maintenance when you were supposed to, the machines never wore out.



#40 BillP

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Posted 31 May 2020 - 06:03 PM

Ever smaller increments between eyepieces and use of a Barlow sound like a zoom to me. I would jump on a constant field 4-12 or even 4-10 in an instant. With those focal length, even a constant field may still be practically possible. May be a variable entrance baffle would be possible too. And instead of polishing and coating expenses for top quality umpfteen times, you only have them once. I have the TVZ 3-6. It's just a bit much to be truly useful to me.

 

Emil

The moment someone figures out how to make a zoom that presents a crisp enough view, high enough contrast view, and orthoscopic view to be considered as a serious planetary contender, then I of course would be interested and it would solve many issues.  But to date no one has figured out how to have a zoom that even rises to the level of a "good" Abbe fixed focal length eyepiece.  But if they could, I would see them being in 3 ranges and only double magnification -- need to not push things so sub-arcmin spotsize and contrast can be retained.  2.5-5mm, then 5-10mm, and 10-20mm.  That would be quite nice.  While constant AFOV would be nice, if it varied from 45-55 degrees, so not an excessive amount, that would be fine for me as well.



#41 BillP

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Posted 31 May 2020 - 06:05 PM

I’ve never understood why leaving a lens on a machine for twice as long to get a high level of polish adds that much cost. Eyepiece lenses are small and made on mandrels with 10 of them at once.  Being polished by a machine means one person can monitor multiple machines at once.  So where’s the cost?  Not in the consumables, water and polishing agent, not in labor, and certainly not in utilities, water and electricity.

The only way I can make sense of it would be if the polisher was in a state of being nearly backed up in orders.  So if they needed to polish twice as long for the upgraded polish, then that means they are losing money as a complete other order could have been completed.  So you get charged 2x to make up for that loss.



#42 Astrojensen

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Posted 31 May 2020 - 06:57 PM

The moment someone figures out how to make a zoom that presents a crisp enough view, high enough contrast view, and orthoscopic view to be considered as a serious planetary contender, then I of course would be interested and it would solve many issues.  But to date no one has figured out how to have a zoom that even rises to the level of a "good" Abbe fixed focal length eyepiece.  But if they could, I would see them being in 3 ranges and only double magnification -- need to not push things so sub-arcmin spotsize and contrast can be retained.  2.5-5mm, then 5-10mm, and 10-20mm.  That would be quite nice.  While constant AFOV would be nice, if it varied from 45-55 degrees, so not an excessive amount, that would be fine for me as well.

Zeiss made a 10-25mm zoom with constant 50° AFOV. I think it was later also made by Docter Optics. Have you tried it?

 

 

Clear skies!
Thomas, Denmark


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#43 SandyHouTex

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Posted 31 May 2020 - 07:36 PM

The moment someone figures out how to make a zoom that presents a crisp enough view, high enough contrast view, and orthoscopic view to be considered as a serious planetary contender, then I of course would be interested and it would solve many issues.  But to date no one has figured out how to have a zoom that even rises to the level of a "good" Abbe fixed focal length eyepiece.  But if they could, I would see them being in 3 ranges and only double magnification -- need to not push things so sub-arcmin spotsize and contrast can be retained.  2.5-5mm, then 5-10mm, and 10-20mm.  That would be quite nice.  While constant AFOV would be nice, if it varied from 45-55 degrees, so not an excessive amount, that would be fine for me as well.

A carry-over from the camera lens world - Zooms can only be optimized for ONE focal length.  So if you design say a 70-200mm zoom, you optimize it for 135mm.  Then when it zooms, everything but that focal length is a compromise.



#44 vahe

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Posted 31 May 2020 - 08:14 PM

A carry-over from the camera lens world - Zooms can only be optimized for ONE focal length.  So if you design say a 70-200mm zoom, you optimize it for 135mm.  Then when it zooms, everything but that focal length is a compromise.

 

The one and only single advantage that zoom offers in camera lens world is the convenience, all else is compromise, including zooms optimized focal length, even that is a compromise due to large number of elements that are piled up in the light path compared to a fixed focal lens of the same focal length.

.

Vahe 


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#45 BillP

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Posted 31 May 2020 - 09:01 PM

Zeiss made a 10-25mm zoom with constant 50° AFOV. I think it was later also made by Docter Optics. Have you tried it?

 

Never even heard of it!!



#46 RichA

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Posted 31 May 2020 - 10:59 PM

I have been mulling over, OK lamenting, how few manufacturers make classic planetaries, and when they do that they miss the mark in many ways.  So I was pondering what would be an easy to manufacture concept for a planetary eyepiece line that still retained some of the more necessary attributes.  So not talking something at the level of a ZAO or XO in its execution, more relaxed so less costly, but something that is still "special" in enough ways that I would probably feel it is a "keeper" for planetary.

 

So what are the attributes I felt were important?

  1. 1mm focal length increments from 4mm to 10mm

Only ones I know that might meet that criteria these days are the TMB Planetary eyepieces floating around on Ebay.  You can get them in something like (claimed) 8 focal lengths from 2.8 to 9mm. 



#47 MrJones

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Posted 31 May 2020 - 11:19 PM

Practical hmm. My planetary eyepieces over the years have become the BCO 10mm and 18mm and Nikon 20x/12 microscope for 12.5mm and Nikon 15x/14 that seems to be about 16mm. I use them with a Baader 2.25x and X-cel 2.0 Barlows. I've been through a lot of EP and Barlows (BGOs come to mind) and tired of the pinholes and/or scatter wound up with these. The BCOs are multicoated and I assume the Nikons are single coated but know little about them other than they are incredibly sharp with flat fields and very little scatter.

 

I've kept my TMB Planetary II 5mm and Meade 5.5mm UWA because I like them but the BCO 10mm and Nikon 20x/12 Barlowed are still better.

 

Not everyone's thing I guess but especially the Nikon 20x/12 that can be had for ~$50 used is pretty amazing.

 

https://www.ebay.com...pe/362590858178

 

 

nikon.jpg


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#48 Jeff Morgan

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Posted 31 May 2020 - 11:38 PM

A carry-over from the camera lens world - Zooms can only be optimized for ONE focal length.  So if you design say a 70-200mm zoom, you optimize it for 135mm.  Then when it zooms, everything but that focal length is a compromise.

 

Every design is a compromise.


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#49 Jeff Morgan

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Posted 31 May 2020 - 11:40 PM

Never even heard of it!!

 

https://www.cloudyni...25mm/?p=3497292


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#50 25585

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Posted 01 June 2020 - 04:01 AM

Best "zoom" is a turret of close FL prime eyepieces.


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