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Using Original Paracorr - tips?

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#1 zakry3323

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Posted 07 December 2018 - 10:21 AM

Long story of kindness and generosity short, a CN member gifted me an original Paracorr to give my dad for Christmas to use in conjunction with his eyepieces on his F/4.5  16" Lightbridge. 

I've been on TeleVue's website...and can only find instructions for the Paracorr Type 1/Type 2. 

The original does not have a tunable top, and I'd like to try to help him figure out how to get the spacings correct for his various EP's. 

If anyone has any tips, or can share a scan of the instructions (Did it come with instructions?), I'd really appreciate it!

Nope, I'm not going to buy the ATT-2125 Tunable Top separately: I'm spending the remaining Christmas budget on some other fun upgrades for him :)

Thanks!



#2 csa/montana

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Posted 07 December 2018 - 10:26 AM

This thread is moving to Equipment for better fit of topic, and more assistance.


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#3 Jon Isaacs

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Posted 07 December 2018 - 11:21 AM

Zakry:

 

I have owned all three Paracorrs (actually 4 if you include the 1.25")

 

This the way I see the original Paracorr without the Tuneable Top:

 

The spacing was designed to correct the coma in the 1.25" TeleVue eyepieces as well as the 2 inch eyepieces of the time.  The 2 inch eyepieces would have been the 20mm Type 2 Nagler, the 32mm and 40mm WFs and maybe the 35mm Panoptics.

 

In any event, these 2 inch eyepieces all require a tall spacing.  With the Tuneable Top, it's nearly fully extended.  Few eyepieces require more extension and for those that require a more inward position, there's not much you can do about it.

 

In terms of 1.25 inch eyepieces, I think the spacing is close for most 1.25 inch TeleVue's.  In my experience, other eyepieces require a little more inward focus, not much you can do about it.

 

So I think the short story is that you just use it and don't worry about it.  It might not be optimal but it will be quite good.  I remember looking up the flange to focal plane spacings for the Explore Scientific eyepieces.  The 20mm 100 degree requires an inward position like the 31mm Nagler, 21mm Ethos but otherwise, they all seemed to spaced outward like the 35mm Panoptic. 

 

Jon


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#4 zakry3323

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Posted 08 December 2018 - 03:04 PM

Zakry:

 

I have owned all three Paracorrs (actually 4 if you include the 1.25")

 

This the way I see the original Paracorr without the Tuneable Top:

 

The spacing was designed to correct the coma in the 1.25" TeleVue eyepieces as well as the 2 inch eyepieces of the time.  The 2 inch eyepieces would have been the 20mm Type 2 Nagler, the 32mm and 40mm WFs and maybe the 35mm Panoptics.

 

In any event, these 2 inch eyepieces all require a tall spacing.  With the Tuneable Top, it's nearly fully extended.  Few eyepieces require more extension and for those that require a more inward position, there's not much you can do about it.

 

In terms of 1.25 inch eyepieces, I think the spacing is close for most 1.25 inch TeleVue's.  In my experience, other eyepieces require a little more inward focus, not much you can do about it.

 

So I think the short story is that you just use it and don't worry about it.  It might not be optimal but it will be quite good.  I remember looking up the flange to focal plane spacings for the Explore Scientific eyepieces.  The 20mm 100 degree requires an inward position like the 31mm Nagler, 21mm Ethos but otherwise, they all seemed to spaced outward like the 35mm Panoptic. 

 

Jon

 

Perfect, this is everything I needed to know! Thanks a lot!!


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#5 Starman1

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Posted 11 December 2018 - 11:53 AM

Long story of kindness and generosity short, a CN member gifted me an original Paracorr to give my dad for Christmas to use in conjunction with his eyepieces on his F/4.5  16" Lightbridge. 

I've been on TeleVue's website...and can only find instructions for the Paracorr Type 1/Type 2. 

The original does not have a tunable top, and I'd like to try to help him figure out how to get the spacings correct for his various EP's. 

If anyone has any tips, or can share a scan of the instructions (Did it come with instructions?), I'd really appreciate it!

Nope, I'm not going to buy the ATT-2125 Tunable Top separately: I'm spending the remaining Christmas budget on some other fun upgrades for him smile.gif

Thanks!

If the perfect position for 1.25" eyepieces requires they be closer to th lens, then 2" to 1.25" adapters currently exist that allow the eyepiece to actually sit BELOW the 2" surface at the top.

We'll call them "Drop-in" adapters.  So you can get many 1.25" eyepieces up to 1/2" closer to the lens than the top of the 2" socket.

And, in the opposite direction, 1.25" adapters exist that raise the eyepiece as much as 5/8", so there is quite a range of 1.25" eyepiece positions available.

It's a little more difficult for 2" eyepieces.  You can slide them out a bit, safely, and tighten them down if you need out focus, but you can't get than closer to the lens.

 

A simple investigation might show the best way to use the coma corrector:

--stick and eyepiece in, and focus the scope.  Look at the edge of the field, just inside the field stop.  Still see some coma (radial flaring of the star)?

--pull the eyepiece 1/8" out of the coma corrector and tighten it in place.  Refocus the scope.  Look at the edge.  is coma reduced?  Great, repeat the procedure until coma is gone.

Is coma worse?  Then you have an eyepiece that will not be optimized but which will have to be used fully inserted and just accept the coma correction that does occur (and it will be a lot more than zero).

--let's assume that coma correction improved and that you found a position (maybe pulled 1/4" out of the Paracorr top) that eliminated coma.

Freeze the focuser at that point.  You won't use the focuser to find the optimum position of any other eyepiece.

--Take every one of your eyepieces and insert the eyepiece into the Paracorr, pushing it in and pulling it out until it is in focus.  THAT is the optimum position for that eyepiece.

You can add a parfocalizing ring to the eyepiece if you want so that every time it's reinserted it stops at that point.  Rubber o-rings work as parfocalizing rings if you don't have the aluminum kind.

FOR EVERY EYEPIECE THAT NEEDS TO MOVE FARTHER IN TO GET IT TO FOCUS, YOU WILL USE THAT EYEPIECE FULLY INSERTED.  PERFECT CORRECTION WON'T BE OBTAINABLE

BUT IT WILL STILL BE A SIGNIFICANT IMPROVEMENT.

 

By optimizing one eyepiece, you found the correct place for the Paracorr in the light cone from the primary mirror.  All other eyepieces are optimized by focusing them by adjusting the distance between the eyepiece

and the Paracorr, essentially parfocalizing your eyepiece set.  But, as mentioned, you may find eyepieces that need to be closer to the lens than the insertion barrel allows. Those you will simply use fully inserted

and refocus the scope with the focuser, knowing that you are moving the Paracorr away from its optimum position in the light cone.  But if you have even one eyepiece that you have optimized, then youknow

what the correct position for the Paracorr is.

 

There is another way to optimize the eyepieces/Paracorr relationship:

--place a couple pieces of translucent scotch tape over the opening of the Paracorr in an X shape (no eyepiece inserted) and put it in the focuser.

--point the telescope at the moon and focus the moon on the tape.  You have found the optimum position in the light cone of the scope for the Paracorr.

[this same technique works with the current Paracorr model in setting E].

--insert any eyepiece, with or without adapter, and slide it in and out of the Paracorr until it's in focus.  That is the optimum position for that eyepiece relative to the Paracorr.

Remember that some eyepieces may need to be closer, and those will require focuser movement. (in practice, you'll always need a couple milimeters of focuser travel because different people have different vision

and because you may not find 'perfect' focus by sliding the eyepiece in and out of the Paracorr.

 

Hope all that helps.


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#6 Jon Isaacs

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Posted 11 December 2018 - 02:17 PM

Don:

 

Having owned the original photo visual Paracorr, I believe there are essentially no eyepieces requiring the eyepiece be slid outward.  The spacing is designed around eyepieces like the 35 mm Panoptic. 

 

The 1.25 inch adapter is inset negative profile and is designed around eyepieces like the 4.8 mm Nagler which is parfocal with the Type 6 Naglers.

 

Jon


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#7 Starman1

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Posted 11 December 2018 - 02:27 PM

Jon,

There are some 2" eyepieces with focal planes deep in the 2" barrel that require a fair amount of outfocus, like the TeleVue 55mm Plössl, with a focal plane 1.16" (!) below the shoulder.

To optimize an eyepiece like that, it WILL be pulled out of the Paracorr's top.

And there are eyepieces that are the other way, like the 31mm Nagler, with a focal plane 0.38" ABOVE the shoulder.  Those two eyepieces focus 1.54" apart!

Many 2" eyepieces will require some in-travel, however, and will simply be used fully inserted.

And some 1.25" eyepieces have focal planes well above the top of the barrel (like the 35mm Ultrascopic and several others) that may require negative profile

adapters that use setscrews on the eyepieces, like the TeleVue AIT or the Astrosystems ultra low adapter.

The point is that other than those 2" eyepieces needing more in-travel, there are creative ways to parfocalize the eyepieces.



#8 Jon Isaacs

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Posted 11 December 2018 - 04:33 PM

Don:

 

Few will be using a 55 mm Plossl with a Paracorr in an F/4.5 Dob.  

 

My point is that from a practical point of view,  there are very few eyepieces that will benefit from moving them outward of the existing configuation of the original Paracorr .

 

Looking at the Paracorr type 1 settings , I believe the original is configured in the 2 inch mode at Setting 1, full extension . In the 1.25 inch mode , it would be Mark 4, one step outward from bottomed out .

 

Of the 1.25 inch eyepieces I own and have used in my type 1 and type 2 Paracorr's , I can think of none that required a further outward setting than the TeleVue 1.25 inchers at Mark 4.

 

Jon



#9 Starman1

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Posted 11 December 2018 - 05:07 PM

Don:

 

Few will be using a 55 mm Plossl with a Paracorr in an F/4.5 Dob.  

 

My point is that from a practical point of view,  there are very few eyepieces that will benefit from moving them outward of the existing configuation of the original Paracorr .

 

Looking at the Paracorr type 1 settings , I believe the original is configured in the 2 inch mode at Setting 1, full extension . In the 1.25 inch mode , it would be Mark 4, one step outward from bottomed out .

 

Of the 1.25 inch eyepieces I own and have used in my type 1 and type 2 Paracorr's , I can think of none that required a further outward setting than the TeleVue 1.25 inchers at Mark 4.

 

Jon

The Zero setting on the Paracorr Mk 1 tunable top was setting 3, the center.  Since most of TeleVue's 1.25" eyepieces have their focal planes below the shoulder by 0.25", they used settings a bit farther out, like setting 1.

However, the 1.25" adapter had about 3/8" height, requiring 3 settings farther in, or setting 4, as you mention.  Each setting was 1/8" apart.  Setting 4 was 1 setting away from all the way in.

That is assuming setting 1 is all the way out and setting 5 all the way in, which is how they described it early on.

 

TeleVue changed that on the final versions of the Paracorr 1 spec sheet: http://www.televue.c...nstructions.pdf  i.e. they reversed the numbers for the settings.  5 became 1 and vice versa.

But only in the picture, which you can see was renumbered.

However, they forgot to change the settings in the eyepiece lists, which are numbered for the reverse order, where 5 is the in-most setting.  Otherwise, the eyepiece list makes no sense.

The eyepieces with the focal planes above the shoulder (e.g. 31 Nagler, 22 Nagler) used settings farther in (those 2 eyepieces used the maximum IN setting, whatever number you called it).

I advise people to NOT use that instruction sheet unless they renumber the 1-5 as 5-1.


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#10 Jon Isaacs

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Posted 11 December 2018 - 07:03 PM

Don:

 

Thank you for the clarification.  I knew the locations of the proper settings for my type 1 Paracorr but the settings themselves were worn off years ago and I didn't actually know their designated name so I looked up the settings on the chart .

 

The technique you describe will provide the best possible spacings.  My point is that unfortunately there are only a few eyepieces that would benefit from the effort. 

 

At one time,  I think you could buy a Tuneable Top for the original Paracorr but it would probably not be cost effective today. 

 

Jon



#11 Stardust Dave

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Posted 12 December 2018 - 04:17 AM

Having the Paracorr type one with tunable top, now a little confused.

 

I was blindly following the chart that is referenced in post #9.

Found myself using the 35pan in low position , and the 12nag T4 in 5 position.

Had to remove the paracorr 12mmT4, ran out of in-focus. Right on the verge of being able to get in focus but not quite.

 

Guess the levelers backed out a few turn bumpy ride up the ridge. Might have increased the FL by up to a centimeter.

Out of lack of understanding of the paracorr ,other than it flattens the field and increases mag by 1.3X? And racking focuser a lot.

 

The settings on the tunable top I though could effect exit pupil and the contrast perhaps.

No complaints really, scope gathers a lot of light. I see most what Im looking for.

 

Don or John ,  my lineup is short a few items but goes 35pan 22nagler T4 12mm T4 and 7mm nagler.

 paracorr T1 tunable top.    

 I have an old TV 1.8 barlow I use when need more the naglerr 40X and above per inch when viewing permits. 

 

Can you explain on why TV says don not focus by sliding in the paracorr. Ive tried different settings-   to focus without a lot of racking and looking at my objects. Exit pupil , illumination ect?

 

Open for advice  (without spending money)lol.gif


Edited by Stardust Dave, 12 December 2018 - 05:31 AM.


#12 Starman1

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Posted 12 December 2018 - 10:16 AM

Dave,

 

22 T4 Nagler--lowest setting of top--all the way down (or in, if you prefer)

35 Panoptic--highest setting--all the way up (or out, if you prefer)

12 T4 Nagler--(using as 1.25" eyepiece and using Paracorr adapter)--lowest setting--all the way down (or in, if you prefer)

7 Nagler--(using Paracorr 1.25" adapter) whether type 1 or type 6--setting one tick up from all the way down (or in, if you prefer)

 

You don't focus the scope by sliding the Paracorr up and down in the focuser, but you can come close to focus by using the tunable top as a focuser.

It doesn't move finely enough to actually use the tunable top as a focuser, but it'll get you in the ballpark.  You can use the focuser for a fine adjustment.

 

The adjustment of the top is supposed to bring the focal plane of the eyepiece to the focal plane of the Paracorr.  Essentially, the tunable top parfocalizes all your eyepieces.

If TeleVue is right about the settings for the eyepieces listed, you should have very little (maybe a couple mm) refocusing to do when switching eyepieces.

 

The presence of the Paracorr eliminates a lot of coma.  Dialing in the setting gets the little bit that's left.

My advice has always been to use your eye to evaluate whether or not coma is gone.

My empirical findings have generally agreed with TeleVue's recommended settings, though some eyepieces seem best when off by a half setting.

After all, "parfocal" in eyepieces only means "within a couple millimeters of exactly parfocal".


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#13 Starman1

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Posted 12 December 2018 - 12:46 PM

Take another look on the TeleVue site at the manual for the Paracorr 1 visual unit:

TeleVue has corrected the image to match the text.

http://televue.com/p...nstructions.pdf



#14 Stardust Dave

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Posted 12 December 2018 - 03:18 PM

Thanks Don for the input.

 

 "doesn't move finely enough to actually use the tunable top as a focuser, but it'll get you in the ballpark.  You can use the focuser for a fine adjustment."   I get that ,got the word sliding and turning-tuning mixed up 

 

I was inserted fully in the focuser with the paracorr but was unaware the purpose of tunable top was to parfocalize the ep.



#15 Starman1

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Posted 12 December 2018 - 04:57 PM

You see, there is only one position for the Paracorr in the light cone of the scope that yields good coma correction.

The coma corrector lens system has a focal length and, therefore, an image plane.  Bringing the field stop of the eyepiece to be coincident with that image plane

puts the eyepiece in the best coma-correction position.  Since eyepieces have focal planes at different places in their barrels, some means of

freezing the coma corrector in place in the telescope's light cone and moving the eyepiece in and out to focus is necessary.

Hence, the tunable top.

Were it a fine helical top, you could probably just focus with it.  But it's a bit coarse for that.  It'll get the eyepiece close to perfect focus, but you'll still need a millimeter or two of focuser adjustment for the finest of focuses.

By "pre-setting" the tunable top to a position where the eyepiece is close to ideal, VERY little focusing of the focuser will be required.

I think my focuser could literally have 3mm of focuser travel and satisfy me and all my nearsighted friends.  So much for needing 2" of focuser travel.


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