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A "Practical" Planetary Eyepiece?

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#1 BillP

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Posted 30 May 2020 - 05:13 AM

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
     
  2. Focal lengths>10mm still spaced close enough for long focal length SCTs without big mag jumps
     
  3. Baffled really well internally to maximize contrast (so also includes a bottom barrel baffle like Vixen HRs)
     
  4. Multicoatings that are tune to the glass indexes again to help the contrast
     
  5. Rather than a super polish as this is way expensive, maybe a higher quality than typical multicoating application would be worth the extra cost so that contamination between layers is near zero which will again aid in contrast
     
  6. We need to keep the number of eyepiece focal lengths down so production costs are frugal, but we also want those 1mm increments, so we need to integrate a Barlow with the set to achieve this -- using a 2.5x Barlow with just 6 eyepiece focal lengths you can achieve both the 1mm increments between 4mm and 10mm, and the close spacing of focal lengths >10mm for our SCT friends
     
  7. Of course want the lens count as low as possible, but do not want terrible eye relief (which the Barlow can solve for us), and also need to be cognizant that from the manufacturing standpoint we want cost effectiveness, so the result IMO is the humble Plossl where the design is tweaked a bit (you know me, this is a big compromise lol.gif )
     
  8. Optical design should be such that on-axis at f/5 the spot is "well" under 1 arcmin, which is the resolution of a good human eye; design should also have an orthoscopic FOV which is important when used for lunar observing as we don't want off-axis RD messing with the shapes of crater walls and rilles and valleys
     
  9. AFOV I am compromising to say 45 degrees mimimum;  While I would like say a 52 degree AFOV, to get an easy to manufacture Plossl that is also orthoscopic have that large of an AFOV is probably impossible and do not want to compromise #8; Could move the design to a 3 element Konig or 4 element Erfle as both these have a tighter on-axis spot than a Plossl (Telescope Optics by Rutten & van Venrooij), but then we complicate the manufacture costs and simplicity
     
  10. For best eye relief the housing would be a classic Volcano that has a strong angle and the eye lens should be no more than 1mm recessed into the housing top; and again the integration of a 2.5x Barlow will help keep the ER more comfortable since for the shortest focal lengths a longer focal length will be Barlowed
     
  11. Integrated Barlow -- since the Barlow is integral to the set, it should be optimized to the eyepieces, so if it needs to flatten the field a little or help correct the off-axis for faster focal ratio scopes then incorporate that into the design, so take advantage that this would be a Barlow for just these eyepieces and not some general-use Barlow; I would also ask that the cost differential be examined for producing the Barlow to possibly a higher than typical level to make it as transparent as possible with any added scatter below the visual threshold
     
  12. Not a necessity but I like my eyepieces to not float away on me so the barrel should be chromed brass so it has some heft

So that's it.  Should be easy to manufacture the optics since the only design needed is for 2 different lenses that are cemented into a doublet.  Addressing #8 might be a challenge but lets see what can be done with the limited degrees of freedom of a Plossl - again, not going for a ZAO set here but a practical one that is good enough and usable across a wide range of apertures, focal ratios, and focal lengths.  Realistically, I think I could compromise down to if these focal lengths were done for Plossls with the build quality of a TV Plossl  if they just added a bottom baffle, changed the design so they did not need a Powermate to produce a non-vignetted view, and of course put it in a volcano top housing loosing the eye guards.  So could be quite happy with that even though it compromises many places.  But if that's all one can get then could settle and drop points 5 and 12, and point #8 could probably relax but it sure would make them special to have that.  So what focal lengths then?

 

2.5x

Barlowed    UN-Barlowed

4.0 mm      10.0 mm

5.0 mm      12.5 mm

6.0 mm      15.0 mm

7.0 mm      17.5 mm

8.0 mm      20.0 mm

9.0 mm      22.5 mm

 

Basically this broad focal length capability can be achieved with just 6 eyepieces so not a lot to manufacture.  The design is also cost effective just being 1 doublet to make for each focal length.  This set will produce non-excessive magnification jumps from 150x to 50x/inch aperture for scopes from 4" to 14" with focal lengths from about 800mm to 3600mm, so it can be a single set that will work with most scopes many people might have.

 

Let me know what you think.  Where does it not hit the mark for you for a "pragmatic" or "practical" planetary set?  What aspects of a planetary specialty eyepiece can you compromise on and not compromise on?  FWIW I pondered the ER issue a lot as we have all those eyeglass wearers out there.  I ended up giving up on trying to incorporate that as would have to move to a positive-negative design then build 12 individual focal length eyepieces and also probably increase the overall internal design to 7-8 elements.  All those things mean production costs, marketability risks, higher unit price, etc. 

 

PS - In the discussion please DO NOT factor in pricing conjectures.  This for me is about what are things folks can compromise on an not compromise on for a planetary set where the goal is to keep the manufacture costs down but also retain enough features that it would be attractive as a planetary option.  Price conjectures will just side-track the discussion into no place productive.  Let's stick to where our expertise is -- in determinimg what we need in terms of features from a planetary set of eyepieces that we would consider not top-shelf like ZAOs but still practically very good and very likely to want if they existed. flowerred.gif


Edited by BillP, 30 May 2020 - 06:14 AM.

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#2 Nippon

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Posted 30 May 2020 - 06:15 AM

I especially like the 1mm increments. So many eyepiece lines jump from 15mm to 10 or 9mm and that is a big jump for long focus SCTs and such. I'd like to see 12 or 13mm as a midway. 


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#3 25585

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Posted 30 May 2020 - 06:36 AM

I use Vixen LVs, the original fold down eyecup design. 2.5, 4, 5, 6, 7, 9, 10. Carl Zeiss Abbe 2x Barlow is excellent.

 

For Tak users, their Q & ED extenders are superb, & allow long FL & eye relief eyepieces to be used for higher magnifications. 

 

But maybe microscope eyepieces, designed for examining minute microscopic detail, are the ideal practical planetary eyepiece, if sized-up for 1.25". I have a Zeiss OPMI, very sharp, flat, contrasty views, and designed for eyeglasses wearers eye relief. 


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#4 db2005

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Posted 30 May 2020 - 06:37 AM

You mention some really great key characteristics for eyepieces!

 

For me the Vixen SLV series hits the mark pretty well already. Optically, they have very good eye relief, and are razor-sharp across the entire field of view, around 50 degrees afov and are reasonably priced considering its good performance. Some have reported problems with a reflective spacer that steals contrast but I have not (yet) noticed this during observation at night. I use the SLVs quite often despite owning several Pentax XWs and a TV Delos 14. The fact is that the lower weight means I can bring out more eyepieces in my coat pockets for an observing session, so low weight and compact form factor are of key importance to me. And it's also important that the end caps (both on the top and on the metal barrel) stay securely in place while not in usde. Actually, the design of the top caps is my main gripe about TV eyepieces: the top cap tends to easily come lose on all their eyepieces, but on my SLVs the caps stay on so I can just put the eyepiece in my pocket and not worry about scratching the lenses if the cap falls off while it's in my pocket. To make the SLVs perfect (without adding cost) I would like to see the top eye lens recessed a bit less and the size of the housing reduced slightly in size.


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#5 junomike

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Posted 30 May 2020 - 08:00 AM

My main OTA's now range from 800mm - 1800mm so for me the TVZ 3mm - 6mm fits all desired magnifications. I added a 2.58XO but rarely needs it.



#6 MartinPond

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Posted 30 May 2020 - 08:25 AM

My favorite is a great Plossl with an excellent focal extender.

I often use a mesa-stripped Mead 4000 (recent, 4-element) 26mm

   with the ES-3X extender.  A Tri-Mag Barlow would give similar results.

   I like the how the ES-3X doesn't aggravate kidney-beaning though. 

   The mesa mounting is just to achieve decent eye relief for glasses.

 

The thing with multipliers is....they can either worsen the contrast,

   or in some cases, make it a lot better.

 

From blowing up images with a 4x monocular, it seems that

Below 20mm,  fine detail on a Plossl can slip a bit for a moderate brand.

   (with a few exceptions)

I'm pondering a TV 15mm, with 3X  extender..

I could even toss in a 17mm knife-edged iris without vignetting,

     for super-contrast.

 

So...to go to the OP,   a package with maybe 3 nice premium Plossls

   and a focal extender would fit my idea of practical-n-perfect.

   And....a razor-edged iris with filter threads.

  For your extremely small effective focal lengths, a 5X extender might be

    the right one.   (like maybe the TV 5X Powermate.)


Edited by MartinPond, 30 May 2020 - 08:31 AM.


#7 russell23

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Posted 30 May 2020 - 08:45 AM

It seems like you have found a really nice concept if someone was starting from scratch.   I think if you wanted to approximate this with what is already available then the TV DeLite line with a 1.6x Nikon barlow and a 1" extension tube gets pretty close.  With the 1" extension tube in my 1.6x Nikon barlow the magnification factor with the 18.2mm DeLite was 1.86x and with the 13mm DeLite was 1.85x.  So lets just call it 1.85x for with the DeLite's

 

Here would be the line:

 

18.2mm

15mm

13mm

11mm

10mm --> 18.2 DeLite w/1.85x = 9.8mm

9mm

8mm --> 15mm DeLite w/1.85x = 8.1mm, or 13mm Delite w/1.6x = 8.1mm

7mm

6mm --> 11mm DeLite w/1.85x = 5.9mm

5mm

4mm

3mm

2.5mm -->  4mm DeLite w/1.6x = 2.5mm

2mm --> 3mm DeLite w/1.6x = 1.9mm

 

Also worth noting:

 

13mm DeLite w/1.85x = 7.0mm

11mm DeLite w/1.6x = 6.9mm

9mm DeLite w/1.85x = 4.9mm

 

So you could substitute out some of the shorter FL if you wanted.

 

Recall that the 1.6x Nikon barlow had the lowest scatter in that series of laser tested barlows.

 

Personally, I find the DeLite's with the Nikon barlow to be excellent for lunar/planetary.


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#8 lylver

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Posted 30 May 2020 - 09:22 AM

By order of appearence

 

3. Baffled really well internally to maximize contrast (so also includes a bottom barrel baffle like Vixen HRs)

Mandatory. This is a failure encountered in the Long Perng SPLER and rebranded and in first version of the TMB Planetary. Remember : the higher AFOV, more difficult is to design the baffling.

 

4. Multicoatings that are tune to the glass indexes again to help the contrast

If needed to cancel ghost (aka internal reflexions) : lens by lens decision. single Mgf2, 4 layers BBAR, or real multi-layers. Heavy number if coating induces scatter, should be used wisely.

 

5. Rather than a super polish as this is way expensive, maybe a higher quality than typical multicoating application would be worth the extra cost so that contamination between layers is near zero which will again aid in contrast

Needed in the integrated barlow (explaination further : there is IMO no simple combination good enough at f/5). Beware, for the barlow, of some glass that cannot be melted with highest homogeneity. This is where light is the most concentrated.

 

 

6. We need to keep the number of eyepiece focal lengths down so production costs are frugal, but we also want those 1mm increments, so we need to integrate a Barlow with the set to achieve this -- using a 2.5x Barlow with just 6 eyepiece focal lengths you can achieve both the 1mm increments between 4mm and 10mm, and the close spacing of focal lengths >10mm for our SCT friends

Heavy magnification barlow (over x3) are hard to be done. Low magnification barlow (< x2) are also non efficient. Short barlow length... idem

We can have 2 (more possible) versions for the eye part, because at low exit pupil (<1mm), aberration of the eye have little importance and under 0.6mm can be completely neglected : no corrected lenses needed. Except for strong astigmatism or ... dioptrix like compatibility over these exit pupil size.

 

So at f/5 design : lower eye relief for 4, 5, 6 mm focal length would help design performance (from TV Radian experience : the lens added add scattering).  Dioptrix compatibility implies 14mm eye relief minimum for all. At 7mm you can increase this directly to 23mm for all eyeglasses users.

Eventually reduces ER to 12mm for the 4mm fl (near complete canceling of eye astigmatism)

 

 

7.Of course want the lens count as low as possible, but do not want terrible eye relief (which the Barlow can solve for us), and also need to be cognizant that from the manufacturing standpoint we want cost effectiveness, so the result IMO is the humble Plossl where the design is tweaked a bit (you know me, this is a big compromise lol.gif )

I would specify 6 or 8 air-surfaces maximum, depending on field wanted. Burried surfaces causes less issues.

 

 

8.Optical design should be such that on-axis at f/5 the spot is "well" under 1 arcmin, which is the resolution of a good human eye; design should also have an orthoscopic FOV which is important when used for lunar observing as we don't want off-axis RD messing with the shapes of crater walls and rilles and valleys

9.AFOV I am compromising to say 45 degrees mimimum;  While I would like say a 52 degree AFOV, to get an easy to manufacture Plossl that is also orthoscopic have that large of an AFOV is probably impossible and do not want to compromise #8; Could move the design to a 3 element Konig or 4 element Erfle as both these have a tighter on-axis spot than a Plossl (Telescope Optics by Rutten & van Venrooij), but then we complicate the manufacture costs and simplicity

 

Yes 1 arc minute in center as said Rick Blakley (Techniques of Designing Eyepieces using ®ATMOS) with complement.

High strehl (>0.95) for +/-12.5° off axis, non tiring. This is the pocket book reading angle : 11cm wide writing at 25cm.

Diff. limited at +/-21.5° : over this limit, only color hue is usefully discriminated. Eye turning in his orbit decreases much vision resolution (cornea quality and muscles/bones induced aberration on the eye optic)

By reviewing many designs : it is very hard to reach this at low f/D.

Clave asym. plössl is near that around 10mm fl and f/D 16, but eye relief is not fulfilled.

 

 

10. For best eye relief the housing would be a classic Volcano that has a strong angle and the eye lens should be no more than 1mm recessed into the housing top; and again the integration of a 2.5x Barlow will help keep the ER more comfortable since for the shortest focal lengths a longer focal length will be Barlowed

Efficient X cornered eyecup protecting from external light. (Pentax & Clave "Pic du Midi" concept not bad from this point of view).

 

 

11. Integrated Barlow -- since the Barlow is integral to the set, it should be optimized to the eyepieces, so if it needs to flatten the field a little or help correct the off-axis for faster focal ratio scopes then incorporate that into the design, so take advantage that this would be a Barlow for just these eyepieces and not some general-use Barlow; I would also ask that the cost differential be examined for producing the Barlow to possibly a higher than typical level to make it as transparent as possible with any added scatter below the visual threshold

F/5 eyepieces : cannot be avoided. Should be seen as Smyth Barlow : global correction.

Flatness of exit pupil should be preserved from negative 25cm (10") curvature of field (~C8) to fast 200mm f4 newton.

This is easy for 4-10mm eyepiece.

---------------------

General consideration : eye relief is difficult for low number lens eyepieces. Goes from 0.7 to 0.9 in general.

This also has a relationship with the sharpness of the eye part of the formula.

When I consider 12mm eye relief for a 4mm it helps to tame the barlow magnification and by the way his size.

 

Best eye part formula seems to have 6 air-surfaces today (astroplan 2-1-2, konig 1-2-1, konig 2-1-1). They can be pushed to 55-60°

Some old recipee still worked with high f/D : TMB planetary (könig 2-1), asym plössl like Clave and abbe duplet like Brandon. But field is limited around 50°.

 

So going down to f/5 with a maximum x3 barlow : you need a very good eye part that work at f/15 as I wrote like written at §8 & 9 and have a minimum 12 mm eye relief.

Not easy.

a) The König eye part of the TMB works well for the job (over than 1.f eye relief) but had chromatism to be corrected by the Smyth/Barlow and enhanced Spherical aberration (sharpness) by adding an another air-space in the barlow, complexifying it. Hard to baffle, hard to collimate, be lucky on Smyth/Barlow optical quality, not sure to have sharpness criteria at all fl.

b) Vixen HR let it simple but reduced field and the eye relief. (42°, 10mm, can go to f/4)

So what ?

sol_818143_pic2_2.jpg vixen-HR16.jpg


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#9 izar187

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Posted 30 May 2020 - 09:22 AM

Consider options here perhaps. 

Available already, and IME very well working.

 

https://www.sieberto...rtho page).html

 

https://www.sieberto...eces-ultra.html

 

https://www.sieberto...cs-barlows.html

 

Outside my experience, but perhaps an option.

 

https://www.sieberto...s.com/Mono.html


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#10 BillP

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Posted 30 May 2020 - 09:24 AM

I think if you wanted to approximate this with what is already available then the TV DeLite line with a 1.6x Nikon barlow and a 1" extension tube gets pretty close. 

Well it violates a few things... First off we are moving a bit away from keeping the glass count and scatter down as you would be placing probably a 6 element 4 group eyepiece then adding a doublet again for the Nikon Barlow.  Second you are making individual eyepieces in all focal lengths which for that choice makes it over a $2,500 option!!!  I think I would prefer the smaller form factor, and having half the line with only 4 elements, and overall price probably well less than half of the DeLite concept.  I mean I could take most any complex wider AFOV line and work it to be "close" to what I am suggesting, but hardly would be considered a planetary specialty eyepiece then.  Nice try though cool.gif
 



#11 BillP

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Posted 30 May 2020 - 09:37 AM

Needed in the integrated barlow (explaination further : there is IMO no simple combination good enough at f/5).

I think you misunderstood my "integrated" Barlow.  I meant integrated as a separate component to the set, not placed into the eyepiece to make a positive-negative design.  So no issues with any magnification as it is a separate Barlow that is also tuned to work best with this particular set (if any tuning needed).  And it is quite easy to get an on-axis spot less than an arcmin at f/5.  The standard 3 element Konig does it and the standard Plossl does it per the spot diagrams in the book Telescope Optics.  Interestingly their ray trace of the Nagler design does not come near.  At any rate, these are initial conditions.  If it turns out that it can be done but just have to relax from f/5 to f/6 then fine.  Definitely want nothing to do with a positive-negative design here. 



#12 BillP

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Posted 30 May 2020 - 09:43 AM

Consider options here perhaps. 

Available already, and IME very well working.

 

https://www.sieberto...rtho page).html

 

https://www.sieberto...eces-ultra.html

 

https://www.sieberto...cs-barlows.html

 

Outside my experience, but perhaps an option.

 

https://www.sieberto...s.com/Mono.html

I've had the SS and Ultras before.  Nice but not close to what a good Abbe can do.  And the internal baffling is wanting in these,  Finally the price becomes a bit high for an ATMed looking build and can only build in the short focal length range as none of them at >15mm were as good IMO of similarly priced production stuff.

 

The reason I started the base of the concept with a Symmetrical Plossl (or an Abbe or Konig also fine), is because these have proven themselves as very capable classical minimum glass, low scatter, high contrast planetaries when their build/baffling is good and real attention to tuning the coatings.  I've yet to find a complex design come very close (perhaps the DeLite but it was close and not there).  So don't need to settle when these classic designs already excel in this role over other designs.  So now let's just give attention to the build and focal length choices and packaging with a dedicated Barlow and the set can really cover all the planetary bases for the majority of common scope apertures and focal lengths. 

 

And as a general side note -- the concept is not meant to deal with f/4 Dobs and things like that.  Very fast optics exact a toll on the eyepiece and all other scopes don't need to suffer because of them.  If they want a good planetary I think they have the best they can use, which would be an Ethos or Delos.  But the rest of us can get a more rerfined planetary given or more relaxed focal ratios.


Edited by BillP, 30 May 2020 - 09:50 AM.

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#13 lylver

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Posted 30 May 2020 - 10:13 AM

I think you misunderstood my "integrated" Barlow.  I meant integrated as a separate component to the set, not placed into the eyepiece to make a positive-negative design.  So no issues with any magnification as it is a separate Barlow that is also tuned to work best with this particular set (if any tuning needed).  And it is quite easy to get an on-axis spot less than an arcmin at f/5.  The standard 3 element Konig does it and the standard Plossl does it per the spot diagrams in the book Telescope Optics.  Interestingly their ray trace of the Nagler design does not come near.  At any rate, these are initial conditions.  If it turns out that it can be done but just have to relax from f/5 to f/6 then fine.  Definitely want nothing to do with a positive-negative design here. 

I don't agree with you on the subject, it is not a misunderstanding. This because I said having either a fixed eye part or a fixed Smyth barlow part is non efficient.

Pentax understood this when they did the XW. But IMO they forgot about the scatter induced by increasing the number of lenses and keeping a big AFOV of 70°.

XW.jpg

 

For solar H-alpha observation, I was discussing this two days ago, on two refractors : Starfire 130EDF f/6.3, Scopetech ST80L (certified .98 on C ray)

We used a 90mm ERF filter + double stack

Having edge of sun with a 55° AFOV works good/better.

Pentax XW 14 does the Job, Nav SW 14 does the job, but better was University König 16mm (on center for Starfire and all on the high f/D) and finally Zeiss GF-PW 16x 16 (57-58°) for global view on all two scopes

Contrast on monochromatic was the criteria.

The low scatter of the Z beats the sharpness on the 25°+ off axis.


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#14 sanbai

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Posted 30 May 2020 - 10:25 AM

I would welcome something new, but just some thoughts:

How much improvement do you expect from existing eyepieces?

At this point, wouldn't be most scopes actually the bottle neck? (See recent thread about planetary scopes) the "scope" means quality of mirror/lenses, thermal management, (easy of) collimation...

Not to say seeing as a factor number one for many if not most observers

And comfort is also key. Some compromise on top optical quality for better comfort (AFOV, eye placement, eye relief...) may be worth, delivering actual better experience.

My gut feeling is that there is little to win, only for the best connoisseurs, with excellent scopes, under best seeing skies.

I would like to avoid the feeling some may have when reading this type of threads, that their eyepieces may be their bottle neck and they are clearly underperforming for planets/moon. I believe most eyepieces (sets), especially premium ones, can deliver near-best possible experience.
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#15 lylver

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Posted 30 May 2020 - 10:30 AM

My gut feeling is that there is little to win, only for the best connoisseurs, with excellent scopes, under best seeing skies.
 

I disagree. Made a test few days ago with two others highly active astronomers (I am not).

6mm TMB planetary Burgess brand, rebaffled versus 6mm TV Radian.

On Moon, it was obvious over Theophilus

80mm long f/D 12.5, EQ, hand moved : TMB wins highly, center mounts popped with their shadow side and the little crater inside the edge     # scatter

130mm Short f/D=6.3, EM200 mount : Radian 6 win, TMB 6 equals only when centering                                                                                      # field astigmatism correction

I will not speak about other eyepieces we have. ( 6 mm ortho, XW 7, ethos 6 already out of challenge), the challenge was on comfortable eyepieces.

To conclude : use eyepiece adapted to your scope.

------------------

and scope adapted for the observation.


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#16 russell23

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Posted 30 May 2020 - 10:34 AM

Well it violates a few things... First off we are moving a bit away from keeping the glass count and scatter down as you would be placing probably a 6 element 4 group eyepiece then adding a doublet again for the Nikon Barlow.  Second you are making individual eyepieces in all focal lengths which for that choice makes it over a $2,500 option!!!  I think I would prefer the smaller form factor, and having half the line with only 4 elements, and overall price probably well less than half of the DeLite concept.  I mean I could take most any complex wider AFOV line and work it to be "close" to what I am suggesting, but hardly would be considered a planetary specialty eyepiece then.  Nice try though cool.gif
 

I'm just saying that I like your concept and this is the closest you can get with what is available on the market.  I don't think you can get the kind of performance you want for less than half the price of a DeLite.  The Brandons provide the closest starting point to what you are looking for. They are made in the USA and cost $235 each.   The Vixen HR's also are on that caliber and cost $279 each. 

 

The DeLite line with the Nikon barlow would allow you to hit all the focal lengths you desire and you will get excellent sharpness and comfort.

 

Maybe you could cobble something together using multiple lines because the Brandon line lacks the needed FL.  I really wish there were 20mm and 10mm Brandons.  At one point I thought I had Don Yeier convinced to make 10mm, 20mm, and a 2" 36mm Brandon.   He said he had the specs worked out.  But then he sold the business.

 

What would you get If you took the 16mm, 12mm, and 8mm Brandon's and added in the Nikon barlow with extension tube - assume 1.6x and 1.9x for the barlow and barlow with extension tube?

 

16mm

12mm

10mm -->  16mm x 1.6

8.4mm --> 16mm x 1.9

8mm

7.5mm --> 12mm x 1.6

6.3mm --> 12mm x 1.9

5mm --> 8mm x 1.6

4.2mm --> 8mm x 1.9

 

That is not the idealized situation you are proposing and there is a lot of close duplication around 8mm.  However, since the idealized situation not exist this would be a decent alternative to the DeLite lineup options I mentioned.  Total cost would be $920.


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#17 MitchAlsup

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Posted 30 May 2020 - 10:38 AM

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



#18 sanbai

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Posted 30 May 2020 - 10:39 AM

I disagree. Made a test few days ago with two others highly active astronomers (I am not).
6mm TMB planetary Burgess brand, rebaffled versus 6mm TV Radian.
On Moon, il was obvious.
Long f/D 12.5 : TMB wins highly
Short f/D=6.3 : Radian 6 win
I will not speak about other eyepieces we have. ( 6 mm ortho, XW 7, ethos 7), the challenge was on comfortable eyepieces.
To conclude : use eyepiece adapted to your scope.

But these are existing eyepieces. They are discontinued, but the can be bought second hand. I'm talking about something really new very optimized for planetary.

And I'm not denying that some existing eyepieces are better than others. It's one's job to get what it works best for their equipment from current offerings (including used ones).

Edited by sanbai, 30 May 2020 - 10:41 AM.


#19 BKSo

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Posted 30 May 2020 - 10:57 AM

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

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Posted 30 May 2020 - 11:03 AM

Maybe you could cobble something together using multiple lines because the Brandon line lacks the needed FL.  I really wish there were 20mm and 10mm Brandons.  At one point I thought I had Don Yeier convinced to make 10mm, 20mm, and a 2" 36mm Brandon.   He said he had the specs worked out.  But then he sold the business

 

Nothing wrong at all with the "mix and match" concept. 

 

If the new owners did the 20mm and 36mm Brandon my credit card would leap out of the wallet.



#21 Jon Isaacs

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Posted 30 May 2020 - 11:24 AM

I disagree. Made a test few days ago with two others highly active astronomers (I am not).

6mm TMB planetary Burgess brand, rebaffled versus 6mm TV Radian.

On Moon, it was obvious over Theophilus

80mm long f/D 12.5, EQ, hand moved : TMB wins highly, center mounts popped with their shadow side and the little crater inside the edge     # scatter

130mm Short f/D=6.3, EM200 mount : Radian 6 win, TMB 6 equals only when centering                                                                                      # field astigmatism correction

I will not speak about other eyepieces we have. ( 6 mm ortho, XW 7, ethos 6 already out of challenge), the challenge was on comfortable eyepieces.

To conclude : use eyepiece adapted to your scope.

------------------

and scope adapted for the observation.

 

And the scope adapted to the location and the observer.

 

Bill's eyepiece proposal is not practical for me..

 

I would like to avoid the feeling some may have when reading this type of threads, that their eyepieces may be their bottle neck and they are clearly underperforming for planets/moon. I believe most eyepieces (sets), especially premium ones, can deliver near-best possible experience.

 

 

I like this.. the eyepiece is rarely the bottleneck. 

 

Jon


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#22 alnitak22

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Posted 30 May 2020 - 12:09 PM

Good grief. If I couldn’t find excellent planetary performance among the offerings available today it would tell me one of two things. I should find a new hobby or I just want to grouse about something online.


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#23 BillP

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Posted 30 May 2020 - 12:16 PM

I don't agree with you on the subject, it is not a misunderstanding. This because I said having either a fixed eye part or a fixed Smyth barlow part is non efficient.

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


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#24 BillP

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Posted 30 May 2020 - 12:17 PM

If the new owners did the 20mm and 36mm Brandon my credit card would leap out of the wallet.

lol.gif


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#25 SteveC

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Posted 30 May 2020 - 12:18 PM

And the scope adapted to the location and the observer.

 

Bill's eyepiece proposal is not practical for me..

 

 

I like this.. the eyepiece is rarely the bottleneck. 

 

Jon

Every observing aspect is a bottleneck. Location is often dictated,  not by mechanics and physics,  but by the bottleneck called life. The observer is often ruled by bottlenecks such as  comfort, aesthetics, and perfection. Tuning a scope mechanically to fit those needs is a bottleneck. What we minimum glassophiles ask for, is not a one size fits everybody solution, not the elimination of widefield/good ER  production, but something that appeals directly to what we perceive as a bottleneck. Like you, we have our eyes and location determined by life. We have chosen our scopes, diagonals,  and mounts though years of viewing experimentation. Now we're tackling the eyepiece issue. What's not practical for you is practical for us orthophiles to explore and pay for.

 

I know you're finished with eliminating your bottlenecks and so am I. I have everything I need, eyepieces included, but some are still searching because ZAOs and monocentrics are out of reach for many orthophiles. Bill is lobbying for an affordable solution.


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