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A "Practical" Planetary Eyepiece?

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#51 lylver

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Posted 01 June 2020 - 04:53 AM

I got two ideas for this type of "serie" project.

First, the eye part could be a symetrical I retro-engineered : I estimated the Tal super-plössl and it is a top eye part due to his high index (>~ 1.66 ) crown.

This glass is much better than the SSK5 (similar index) in the TV plössl. (abbe number greater 55 instead of 51)

I did it with the use of the special CTK3 LZOS glass and their LZOS SF6. I think the color correction is touching the limit for eye color sensitivity like the lanthanum in the Brandon.

The problem is the barlow that is more difficult at f/5 to keep quality with a cemented one.

 

As did Thomas Back with the TMB planetary, an air-spaced one would correct spherical aberration to reach the quality needed at this low f/D.

For the more difficult : the 4mm

for a 43° diffraction limited field at f/5 (50° useable), the 4mm could use a 16mm eye part and a x4 air-spaced integrated barlow. This with approximatively 12mm eye relief.

5mm would keep this barlow and go to 20mm / 15 ER, dioptrix compatible.

Then reducing the barlow for the 6, 7 and 8mm (barlow down to x2.5)

For a 9-10.5-12 a longer again eyepart of 30mm / 22.5 ER

4 barlows / 3 eye part.

 

Second, a modification of the Vixen HR (könig + barlow) is a way to have the 45°-48° field at f/5 by matching the correction of all abberations.

A sort of intermediate with the TMB planetary that is nice at near center but degrades to fast IMO when going on edge. The old TV Radian had more lenses and did the job but induced a bit more scatter.

This would be at least 6 to 8 air-glass surfaces with very good centering tolerance, acceptable/comfortable eye relief we don't have yet.

 

Imo potentially better than the Vixen SLV that has a fixed 25mm "astroplan" eye part for the smallest focal length. I don't now if cheaper.



#52 Astrojensen

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Posted 01 June 2020 - 06:43 AM

How about a pancratic zoom microscope, instead of a traditional barlow and eyepiece? I did some initial experiments yesterday evening and they were extremely promising, but I need to do some more thorough tests and comparisons with more traditional setups. I also need to figure out how to calculate the exact magnifications, so I can match them with my eyepieces for critical evaluation. 

 

A pancratic zoom microscope has a couple of very important advantages:

 

1: The zoom range can be large.

 

2: Baffling is very, very easy and can be superb

 

3: Getting a large eye relief at any magnification is a piece of cake.

 

4: The field can be totally flat and HIGHLY corrected. 

 

 

 

Clear skies!
Thomas, Denmark


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#53 russell23

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Posted 01 June 2020 - 07:28 AM

How about a pancratic zoom microscope, instead of a traditional barlow and eyepiece? I did some initial experiments yesterday evening and they were extremely promising, but I need to do some more thorough tests and comparisons with more traditional setups. I also need to figure out how to calculate the exact magnifications, so I can match them with my eyepieces for critical evaluation. 

 

A pancratic zoom microscope has a couple of very important advantages:

 

1: The zoom range can be large.

 

2: Baffling is very, very easy and can be superb

 

3: Getting a large eye relief at any magnification is a piece of cake.

 

4: The field can be totally flat and HIGHLY corrected. 

 

 

 

Clear skies!
Thomas, Denmark

Sounds interesting but I have no idea what you are talking about. Could you clarify?



#54 BillP

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Posted 01 June 2020 - 07:29 AM

...  The problem is the barlow that is more difficult at f/5 to keep quality with a cemented one. ...

 

...  Second, a modification of the Vixen HR (könig + barlow) is a way to have the 45°-48° field at f/5 by matching the correction of all abberations. ...

Seems like there needs to be many compromises or complications to satisfy the fast Dob market as refractors, especially those designed for planetary, are rarer at the f/5 point.  So why not just separate the field.  Let those who want to have a planetary design for f/4 or f/5 instruments tackle that problem themselves.  Maybe our focus should be on the Apo market first.  AP, TEC, Tak, etc have lots of models on the street that are f/6.3, f/7, f/7.5, f/8.  So maybe move the focal ratio parameter to be f/6.3 or f/6.5 and forget the f/5 nonsense.  That way the majority of the Apo community can have a sleeker design for their needs, then if the faster focal ratio groups want similar, they can tackle that problem with a more complex design.


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#55 BillP

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Posted 01 June 2020 - 07:29 AM

Sounds interesting but I have no idea what you are talking about. Could you clarify?

lol.gif  ... Ditto!


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#56 lylver

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Posted 01 June 2020 - 08:23 AM

Seems like there needs to be many compromises or complications to satisfy the fast Dob market as refractors, especially those designed for planetary, are rarer at the f/5 point.  So why not just separate the field.  Let those who want to have a planetary design for f/4 or f/5 instruments tackle that problem themselves.  Maybe our focus should be on the Apo market first.  AP, TEC, Tak, etc have lots of models on the street that are f/6.3, f/7, f/7.5, f/8.  So maybe move the focal ratio parameter to be f/6.3 or f/6.5 and forget the f/5 nonsense.  That way the majority of the Apo community can have a sleeker design for their needs, then if the faster focal ratio groups want similar, they can tackle that problem with a more complex design.

As I made comparative tests between Radian/pentax XW/Nikon SW /Tmb planetary last days on an AP 130EDF f/6.3

I totally agrees.

A Tal plössl modified 20mm eye part with tuned Smyth/Barlow could do the job.

It needs a better internal cell like the Radian had (internal Delrin or similar low reflective as in classic camera). The cell should be limited to 50-52° maximum : it helps.
I dont know what Explore Scientific had made for the 52° LER but I think it is too simple reading feed back.

The russian lanthanum crown CTK3 is a top tool as the SK5 glass was after WW2. (or equivalent glass)

Used it a sym plössl ou a König 2-1 (or recomputed RKE)

 

As I understand things : TMB are top for f/7 (enough center corrected field at this f/D)

Radian goes to f/4.5 with 5 groups 7 lens (6mm and lower) but restricted a little too much chromatism correction.

 

Simplify stuff : a bit less field and f/6 compatible would fill an existing small gap.



#57 Astrojensen

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Posted 01 June 2020 - 09:33 AM

Sounds interesting but I have no idea what you are talking about. Could you clarify?

It's simply a compound microscope (or, if you like, a normal microscope, with an objective and an eyepiece), where the magnification can be varied by adjusting the distance between the objective (of the microscope) and the eyepiece. 

 

Zeiss has a stereomicroscope with a pancratic zoom in production, with a zoom range of 7.7:1, so the range can be HUGE. This is like going from a 40mm to a 5.2mm eyepiece...! 

 

Can you imagine a 40mm - 6mm zoom with constant 68° AFOV?

 

 

Clear skies!
Thomas, Denmark


Edited by Astrojensen, 01 June 2020 - 09:36 AM.

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#58 SandyHouTex

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Posted 01 June 2020 - 09:37 AM

Every design is a compromise.

Not an eyepiece designed for ONE focal length.



#59 BillP

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Posted 01 June 2020 - 10:07 AM

As I made comparative tests between Radian/pentax XW/Nikon SW /Tmb planetary last days on an AP 130EDF f/6.3

I totally agrees.

A Tal plössl modified 20mm eye part with tuned Smyth/Barlow could do the job.

Are you talking about a 20mm positive followed by a tuned negative group to get all the focal lengths from say 14mm to 3.5mm as was in my original proposal?  If so that negative group would have to pump some significant magnification, from 1.4x to 5.7x!

 

If we are scaling things back to the needs of typical Apos, then if we use the AP 130 f/6.3 as a base and a Tec 180 f/7 as the other end of the spectrum, that means focal lengths (rounded) or 800mm to 1300mm.  If we set the low magnification for planetary at 150x and the high end for planetary being say a 0.4mm exit pupil (450x for the 180mm scope), then the magnifying range of the negative group below the 20mm positive groups of the eyepiece would have be such that the 20mm would operate at anywhere from and 8.6mm eyepiece to a 2.9mm.  Rounding that for simplicity is the negative group would have to magnify the 20mm so it operated from 9mm to 3mm effective, or 2.2x to 6.7x.  That seems excessive isn't it?  Might be better to split it and use two different focal length positive groups, one 20mm and the other a 10mm, that way the negative groups for both would only have to push 1.8x to 3.5x for the 10mm, and 2.2x to 3.5x for the 20mm to get an effective range of planetary focal lengths from 9mm to 3mm (in 1/2mm increments of course).


Edited by BillP, 01 June 2020 - 10:08 AM.


#60 Jeff Morgan

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Posted 01 June 2020 - 10:09 AM

Not an eyepiece designed for ONE focal length.

 

Perfect eyepieces and machines that run forever. An interesting world you live in.

 

Rutten & van Venrooij can get you started on eyepiece trade-offs, and your accountant can tell you about amortization.


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#61 BillP

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Posted 01 June 2020 - 10:43 AM

It's simply a compound microscope (or, if you like, a normal microscope, with an objective and an eyepiece), where the magnification can be varied by adjusting the distance between the objective (of the microscope) and the eyepiece. 

 

Zeiss has a stereomicroscope with a pancratic zoom in production, with a zoom range of 7.7:1, so the range can be HUGE. This is like going from a 40mm to a 5.2mm eyepiece...! 

 

Can you imagine a 40mm - 6mm zoom with constant 68° AFOV?

 

This? http://www.freepaten...com/5825535.pdf

 

PS - I would be happy with a 3mm - 26mm with a constant 60 degrees grin.gif


Edited by BillP, 01 June 2020 - 10:45 AM.

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#62 EverlastingSky

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Posted 01 June 2020 - 02:52 PM

Practical? I'd say TV Delite or a currently available Tak Abbe Ortho are good enough waytogo.gif  I doubt any company is about to start production on any volcano top planet special etc., Don't get me wrong - I'm into the hard to find out of production eyepieces too - having spent a ton to acquire pairs of them for the binoviewer. As an aside... I suspect fantastic glass polish is important and would pay $300-500+ for that extra "option" on any given eyepiece. Not practical though is it? Planet nuts like myself never are grin.gif


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#63 lylver

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Posted 01 June 2020 - 03:04 PM

Are you talking about a 20mm positive followed by a tuned negative group to get all the focal lengths from say 14mm to 3.5mm as was in my original proposal? 

Sorry, I missed something : I was thinking about 4 to 10mm
 



#64 BillP

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Posted 01 June 2020 - 03:50 PM

3.5mm to 9mm would be better for Apos of 800-1300mm FL.  But if 4-10 is what works then close enough!



#65 SandyHouTex

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Posted 01 June 2020 - 03:55 PM

Perfect eyepieces and machines that run forever. An interesting world you live in.

 

Rutten & van Venrooij can get you started on eyepiece trade-offs, and your accountant can tell you about amortization.

I know about all of those things.  And I've worked in machine shops that had 100 year old lathes still working.  The amortization on those went to zero about 80 years ago.

 

You should get out more.


Edited by SandyHouTex, 01 June 2020 - 04:12 PM.


#66 GeneT

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Posted 01 June 2020 - 06:38 PM

"So not talking something at the level of a ZAO or XO in its execution,"

The eyepiece you hanker for has already been invented and produced. The only criteria you mentioned that would not be met is price. Why not reissue ZAO's and XO's? There are always some who will pay for the best possible quality apart from price. I have read dozens of CN reports comparing Explorer Scientific eyepieces to TeleVue and other premimum offerings. It always comes out that if the issue is best value for the money, then ES wins. ES eyepieces in general might be a tad less  performers than Televue and other premimum eyepieces, but why not save a hundred or more dollars per item and go with ES? Yet, people will pay the extra for slightly better performance. If the price point to reissue ZAO's or XO's would be thousands more per item, then most would not pay.  However, reservations could be taken and eyepieces built for as many as subscribed.  



#67 BillP

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Posted 01 June 2020 - 07:55 PM

"So not talking something at the level of a ZAO or XO in its execution,"

The eyepiece you hanker for has already been invented and produced. The only criteria you mentioned that would not be met is price. Why not reissue ZAO's and XO's? There are always some who will pay for the best possible quality apart from price. I have read dozens of CN reports comparing Explorer Scientific eyepieces to TeleVue and other premimum offerings. It always comes out that if the issue is best value for the money, then ES wins. ES eyepieces in general might be a tad less  performers than Televue and other premimum eyepieces, but why not save a hundred or more dollars per item and go with ES? Yet, people will pay the extra for slightly better performance. If the price point to reissue ZAO's or XO's would be thousands more per item, then most would not pay.  However, reservations could be taken and eyepieces built for as many as subscribed.  

Don't want a ZAO-level eyepiece.  Or a overly complex overly scatter burdened one either.  Just a good quality classic design like an Abbe, 1-2 Konig, or Symmetrical that is available in 1/2mm increments from 3.5mm to at least 8mm (if just satisfying the Apo market and some of the production Dob market - i.e., tailored for scopes with 800mm to 1300mm focal lengths).  So that is the parameters as they evolved in this thread from the original posting.  No one has made anything like that. 

 

Would not want to do this with ZAOs or XOs because at those production cost levels 10 eyepieces would cost what? $5,000!  No thank you.  Now something on the level of a Tak Abbe which come in around $150 would be much more doable.  Or something of the quality of a TV Plossl which comes in around $100 for the mid-range focal lengths.  So 10 of those would be $1,000 which is much more manageable for something that is not available from anyone else.

 

But actually, I can beat this by integrating some Barlows to bring down the number of eyepieces needed.  So if we say what we want is to only make 6 eyepieces, all in the longer focal lengths as these have better eye relief than trying to use a 3.5mm Plossl as example.  And integrating the Barlows will mean the ER will be pushed out to more comfort still.  So if you make these little potentially $100 quality Plossls in 12, 14, 16, 18, 20, and 22mm, then also make 2 Barlows for the set in 4x and 2x, then from those 6 focal lengths you will get 18 focal lengths that are 2mm apart in the bottom third, 1mm apart in the middle third, and 1/2mm apart in the top third giving smooth magnification increases of many times just 20x to 40x jumps for scopes with focal lengths of 800mm all the way up to 3600mm (i.e., a C14)!  So if those special eyepieces with their classic even Symmetrical design come in at $100 each (that would be a TV-level pricing, so $600, then say $150 for each Barlow for $300 total, then we again have this Planetary package for $1,000 and it can service every scope from a 4" Apo to a 14" SCT with a smooth range of small magnification increments from 150x all the way up to a 0.4mm exit pupil and smaller!  Yes not ZAO performance, but as good and probably better than TV Plossl or Tak Abbe performance since the parameters are not for these to operate at f/5 and go out to 50 degrees but instead f/6.3 and 45 degrees so the on-axis can be optimized more (and even better if a 1-2 Konig is used instead sine this has the best on-axis spots of the three designs). 

 

So that is my take.  Then we have lylver's take where he wants the Barlow element internal to each eyepiece so would be making 3.5mm to 8 or 9mm in 1/2mm increments or 10-12 eyepieces.  That concept does not need separate Barlows but again if the build and optic quality is similar to a TV Plossl would imagine these could come in for another $50 since the Barlow is integrated so let's say $150 each.  More expensive at $1500-1800 but then no Barlow to manage.

 

Finally we have Thomas who came up with the out of the box suggestion to just make a constant AFOV zoom over a much larger focal length range, maybe 3mm to 30mm, using the Zeiss concept called a Pancratic Zoom which they have already fielded in the microscope world!  That would be mind-blowing!!

 

Anyway, nothing out there today does this with a view quality (crispness and contrast) on par with say a Tak Abbe Ortho or even a TV Plossl (which no wide field offering is up to for planetary) and small sub 1mm focal length increments over the 3.5 to 8mm or 9mm range. 

 

PS - the inspiration for this multi-Barlow aproach came from a private PM discussion with CNer RFeaster. waytogo.gif

 

Planetary Magnification Chart.jpg


Edited by BillP, 01 June 2020 - 09:50 PM.

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#68 RFeaster

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Posted 02 June 2020 - 12:01 AM

I like it and would be a buyer.  I would think the manufacturers would like it too as consumers would be more likely to buy the entire set with matching barlows as opposed to cherry picking EP's from different lines/manufacturers as a lot of people (including me) do now.  Plus, they could tune the barlows to this specific set of EP's and not try to accommodate every other EP made.  Dump the undercut barrels and put a single nylon tip screw in the barlows and we have a winner!


Edited by RFeaster, 02 June 2020 - 12:10 AM.


#69 TG

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Posted 02 June 2020 - 03:20 AM

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


I also have a pair of 20x Nikons and they are incredibly sharp. I think they are either a 3 or 4 element design because they suffer from astigmatism toward field edge but center of field they are one of the sharpest eyepieces I have used.

Tanveer
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#70 Second Time Around

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Posted 02 June 2020 - 03:32 AM

How about a pancratic zoom microscope, instead of a traditional barlow and eyepiece? I did some initial experiments yesterday evening and they were extremely promising, but I need to do some more thorough tests and comparisons with more traditional setups. I also need to figure out how to calculate the exact magnifications, so I can match them with my eyepieces for critical evaluation. 

 

A pancratic zoom microscope has a couple of very important advantages:

 

1: The zoom range can be large.

 

2: Baffling is very, very easy and can be superb

 

3: Getting a large eye relief at any magnification is a piece of cake.

 

4: The field can be totally flat and HIGHLY corrected. 

 

 

 

Clear skies!
Thomas, Denmark

This looks very interesting. I look forward to the results of your further testing.



#71 BKSo

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Posted 02 June 2020 - 03:50 AM

One reason why premium planetary eyepieces are so expensive (and clones are so cheap). The manufacturer expects low volume of sale, so the gross profit must be higher to recover the R&D and startup costs.


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#72 SandyHouTex

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Posted 02 June 2020 - 08:59 AM

I have always wondered why Televue doesn't make and sell Orthos.  Surrendering that entire market to Japanese manufacturers seems curious to me.



#73 csrlice12

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Posted 02 June 2020 - 10:31 AM

Only Al knows.... Lord knows the idea has been beat to death.


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#74 CrazyPanda

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Posted 02 June 2020 - 10:52 AM

The most practical planetary eyepiece would be a reasonable quality 8-24mm zoom + barlow. The Baader zoom w/2.25x barlow fits the bill.

 

It lets you dial in the magnification to match seeing conditions perfectly, and its optical quality is going to be good enough that it should meet the definition of "practical" - especially for those who do not own expensive optics and live under Pickering 8+ skies most of the year.

 

Now, if your standard is the sharpest, highest contrast possible from an ocular because all else in the light path is already as good as it can be, then I'm not sure we're still in "practical" territory.

 

> I have always wondered why Televue doesn't make and sell Orthos.  Surrendering that entire market to Japanese manufacturers seems curious to me.

 

My guess is there's no real market for them when you have DeLites. If a TV Plossl is $100, and a DeLite is $250, and a Takahashi Abbe Ortho is $150, and a Fujiyama HD Ortho is $100, where does a TV ortho fit in, in terms of quality and value proposition?

 

The whole selling point of a TV Abbe Ortho would have to be *extreme* sharpness, contrast, and scatter control (which is NOT a given just because of its design). This means lots of time spent on shaping, polishing and special alignment of the optics, with high quality glass, and special considerations made for baffling and blackening. This would make them expensive. So if they were say, $200, then why wouldn't people just buy a TV DeLite? Would TV's answer be "because optically it's not quite as good", thereby disparaging one of their own eyepiece lines?


Edited by CrazyPanda, 02 June 2020 - 11:02 AM.

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#75 Jeff Morgan

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Posted 02 June 2020 - 11:18 AM

One reason why premium planetary eyepieces are so expensive (and clones are so cheap). The manufacturer expects low volume of sale, so the gross profit must be higher to recover the R&D and startup costs.

 

And it is not just a small astronomy market. It's a small slice of that small market - dedicated planetary observers.

 

Today half the markets are Dobs. I'm not implying anything about the Newtonian design as a planetary scope, but rather the owners of those scopes. They specialize in the deep sky, "planetary observing" means an occasional two minute jaunt to Jupiter - when it won't interfere with dark adaptation. And most of them do manual tracking. Keeping a planet centered in the eyepiece for extended periods? Not happening. They emphasize AFOV for drift.

 

For such an observer, a Delos or XW is a very passable planetary (despite the fact that a $150 ortho will best it). So why spend $500+ on a set of dedicated planetary eyepieces? 

 

All things considered, we're lucky to have the choices in planetary eyepieces we have.


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