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List of Paracorr settings for all brands of EP's

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#251 faackanders2

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Posted 29 March 2018 - 07:12 PM

So, finally made it out with my new Paracorr T2.  I borrowed my buddy's 11mm Nagler T6,  as a known starting point (setting "D"), since the correct Paracorr T2 setting is listed on the TV website, to set the primary/corrector distance.  I locked the focuser and noted the tube extension, then put my ES eyepieces in and found focus using the tunable top. 
 
My results: 
ES 30mm 82* = G-H (midway between those letters was best focus, almost at the maximum tunable top extension)
ES 20mm 100* = A-  (had to rack the focuser in slightly, maybe 3-4mm, after dropping to the lowest Paracorr setting, meaning not fully corrected?)
ES 14mm 100* = G
ES 9mm 100* = G
ES 5.5mm 100* = G
 
I plan to experiment a bit more, but those should be pretty close.  I was wowed by the detail that Jupiter showed that evening, all the way across the field of my 100* eyepieces, impressive!

Funny, for ES 20mm 100AFOV I have been using setting H full up, and another post says seting C, and you prefer A- full down.
For ES 5.5mm 100AFOV I have been using setting H full up, and you prefer G.

#252 Starman1

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Posted 29 March 2018 - 07:40 PM

Why?  You only need to know 1 eyepiece and all the others can be found in 1 second by turning the top until the eyepiece is in focus.

 

Explore Scientific says their 20mm 100° eyepiece has its focal plane 15.20mm above the shoulder on which the eyepiece sits.

 

Since the working distance for the Paracorr II is 56mm from lens to focal plane, it is impossible to optimize the 20mm ES 100° because it cannot get close enough to the lens to be at its optimum position.

So, the only thing to do is to use the Paracorr at setting A and realize it is not optimum, but you cannot lower the top from there.

 

ES says the 5.5mm x 100, 9mm x 100, and 14mm x 100 are all parfocal and all have their focal planes 3mm below the shoulders they sit on.

 

Let's see if that makes sense.  TeleVue says setting E is the 0 point for the lens, and is 60mm from the bottom of the tunable top measured on the outside.

That represents the point 56mm from the lens, internally.  So an eyepiece with its focal plane 15.2mm above the shoulder would need 15.2mm of additional in-travel of the tunable top to get to the optimum distance from the lens, but setting A is only 10.16mm below the zero point.  So, I am correct the 20mm ES cannot be moved into an optimum coma correction position in the Paracorr II, and setting A must be used.  At least 90+% of the coma will be removed.

 

The shorter focal lengths of ES 100 will require 3mm more out travel than that due to their focal plane positions, so that would be exactly 0.12" farther out, which is setting F (actually F+0.02").

If you insert one of those eyepieces, move the top to setting F and focus, every other eyepiece in your collection could have its optimum setting discovered merely by focusing the scope using the tunable top instead of the focuser.

 

ES says, "Field stop positions below the end of the (upper) barrel (i.e. shoulder) are positive (because you have to focus outwards), positions above the reference surface are negative (because you have to focus inwards)."  Their focal plane positions are listed on the attached sheet.  It looks like most of their eyepieces are parfocal.

Attached Files


Edited by Starman1, 29 March 2018 - 07:47 PM.


#253 rowdy388

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Posted 29 March 2018 - 08:35 PM

I use a type 1 Paracorr with my ES100 20mm eyepiece so coma correction is even

worse than with the type 2. Does anyone know if the APM (Lunt) HDC 20mm eyepiece

works with a Paracorr better than the ES? 



#254 faackanders2

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Posted 29 March 2018 - 08:58 PM

Why?  You only need to know 1 eyepiece and all the others can be found in 1 second by turning the top until the eyepiece is in focus.
 
Explore Scientific says their 20mm 100° eyepiece has its focal plane 15.20mm above the shoulder on which the eyepiece sits.
 
Since the working distance for the Paracorr II is 56mm from lens to focal plane, it is impossible to optimize the 20mm ES 100° because it cannot get close enough to the lens to be at its optimum position.
So, the only thing to do is to use the Paracorr at setting A and realize it is not optimum, but you cannot lower the top from there.
 
ES says the 5.5mm x 100, 9mm x 100, and 14mm x 100 are all parfocal and all have their focal planes 3mm below the shoulders they sit on.
 
Let's see if that makes sense.  TeleVue says setting E is the 0 point for the lens, and is 60mm from the bottom of the tunable top measured on the outside.
That represents the point 56mm from the lens, internally.  So an eyepiece with its focal plane 15.2mm above the shoulder would need 15.2mm of additional in-travel of the tunable top to get to the optimum distance from the lens, but setting A is only 10.16mm below the zero point.  So, I am correct the 20mm ES cannot be moved into an optimum coma correction position in the Paracorr II, and setting A must be used.  At least 90+% of the coma will be removed.
 
The shorter focal lengths of ES 100 will require 3mm more out travel than that due to their focal plane positions, so that would be exactly 0.12" farther out, which is setting F (actually F+0.02").
If you insert one of those eyepieces, move the top to setting F and focus, every other eyepiece in your collection could have its optimum setting discovered merely by focusing the scope using the tunable top instead of the focuser.
 
ES says, "Field stop positions below the end of the (upper) barrel (i.e. shoulder) are positive (because you have to focus outwards), positions above the reference surface are negative (because you have to focus inwards)."  Their focal plane positions are listed on the attached sheet.  It looks like most of their eyepieces are parfocal.


OK Paracor Seting A (full down) for ES 20mm 100 AFOV (and I was previously using incorrect H full up).
Hopefuly this will make stars more like pinpoints, because this is my worst eyepiece for that and why I got the Paracorr II for my 17.5" f4.1 Dob.

OK I will use setting F for ES 5.5 100AFOV (previously incorrectly used H full up).

Don, What are you using for ES 9mm 120 AFOV?

#255 Starman1

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Posted 30 March 2018 - 12:36 AM

Setting E if I pre-set it.

Usually, though, it follows something else, and I just dial in the focus with the tunable top.

Technically, it's perfect setting is 0.04" in from setting E, but setting D is 0.10" in from E, so it's closer to E than D.

It looks pretty good at that setting.

 

I use the 10mm Ethos most of the time, though.  The 120° field is a bit too wide for much of my observing, but I find the 203x magnification excellent on many targets.



#256 faackanders2

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Posted 30 March 2018 - 11:17 AM

Setting E if I pre-set it.
Usually, though, it follows something else, and I just dial in the focus with the tunable top.
Technically, it's perfect setting is 0.04" in from setting E, but setting D is 0.10" in from E, so it's closer to E than D.
It looks pretty good at that setting.
 
I use the 10mm Ethos most of the time, though.  The 120° field is a bit too wide for much of my observing, but I find the 203x magnification excellent on many targets.

I prefer the 10mm 100AFOV Ethos also due to sharpness and not much smaller AFOV.

Thanks setting E for 9mm 120AFOV ES.

#257 jtrezzo

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Posted 08 June 2019 - 12:16 PM

I have been perusing this thread for starting points as I don't have a Tele Vue EP to do the known reference point.

 

I think some people are getting the T1 numbers backwards, as I was looking at Pentax XW settings in here and they said Type2 was A and Type1 was 1, which would be the complete opposite ends.

 

Setting A on T2 should equal setting 5 on a T1. It goes from 5 to 1, in to out on the T1. 



#258 Starman1

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Posted 08 June 2019 - 01:10 PM

I have been perusing this thread for starting points as I don't have a Tele Vue EP to do the known reference point.

 

I think some people are getting the T1 numbers backwards, as I was looking at Pentax XW settings in here and they said Type2 was A and Type1 was 1, which would be the complete opposite ends.

 

Setting A on T2 should equal setting 5 on a T1. It goes from 5 to 1, in to out on the T1. 

Correct.  What might confuse people is that TeleVue reversed the 1-5 order in an illustration on information on their site concerning the Paracorr 1 without reversing

the settings information for the eyepieces. TskTsk.

I brought that to their attention and they fixed the "manual" for the Paracorr 1:  http://www.televue.c...nstructions.pdf

That is now correct.

But they had the numbering wrong for years.

 

The thing abut the Paracorr, or any coma corrector, is that you CAN empirically find the correct setting for any eyepiece by merely starting with the out-most setting, insert the eyepiece,

focus the scope, and inspect the stars at the edge.  When coma disappears, you have the correct setting for that eyepiece.  Every other eyepiece follows from that one: insert the eyepiece

and focus with the top of the Paracorr instead of the focuser.  When the eyepiece is in focus, that is the correct setting for that eyepiece.

AND, if you take the time to parfocalize all your eyepieces, when you find the correct setting for one eyepiece, ALL your other eyepieces will use the same setting.

 

The only caveat to the empirical method is if the eyepiece has a lot of astigmatism at th edge of the field, or a strongly curved focal plane.  The other issues with stars at the edge may make the determination of the absence of coma somewhat difficult.  Coma is easier to identify in dark skies (the other parts of the star image are more visible), so I recommend this procedure in a dark sky if possible.

I find it interesting that when I tried the empirical method with my TeleVue eyepieces, many of the "best" settings were as much as 1/2 setting away from the recommendations in TeleVue's list,

and eyepieces they called "parfocal" weren't--close, but not exact.


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