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Equipment Discussions >> Eyepieces

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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: List of Paracorr settings for all brands of EP new [Re: Lawrence Sayre]
      #1764592 - 08/07/07 08:40 PM

Quote:

Don, Thank you again!

Just to clarify. Are you saying that both the 14mm UWA and 8.8mm UWA when used in 2" mode would safely fit into the Paracorr while at its lowest tunable top setting and without a filter screwed on, but at least one of them (if not both) would most certainly hit the lens of the Paracorr with a filter screwed on?

If this is correct, then can someone who has these eyepieces tell me what their length is from the focuser shoulder to the end of the 1.25" barrel section? Perhaps just standing them up on a table top and carefully measuring from the table top to the focuser shoulder would be the easiest means to accomplish this.



Exactly. The addition of a typical filter (Meade, Orion, etc.) would hit the lens--in the lowest setting of the Paracorr.


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: List of Paracorr settings for all brands of EP new [Re: Lawrence Sayre]
      #1764599 - 08/07/07 08:47 PM

Quote:

One "relatively" safe means to measure the insertion depth of a late model Visual Paracorr while at its lowest height setting on the tunable top would be to simply place a cotton 'Q'-tip down the side until it rests by gravity on the lens element, and then mark it at the shoulder junction. Then remove it, and stand it up (without any downward force applied), and measure from the table top to the mark on the 'Q'-tip.

CAUTION / WARNING: Again, I warn that I would not wish or intend that anyone scratch a Paracorr in attempting to measure it.



Depth is 49mm or 1.93"(about as accurate as I can be) between center of lens and shoulder of 2" insertion barrel, tunable top in place at its lowest setting.
Thanks for the Q-Tip idea--I went ahead and cleaned the lens at the same time. It had a lot of dust on it.


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Lawrence Sayre
Abbe Normal
*****

Reged: 10/16/04

Loc: N.E. Ohio
Re: List of Paracorr settings for all brands of EP new [Re: Starman1]
      #1766582 - 08/08/07 07:08 PM Attachment (486 downloads)

Here (attached) is my final spreadsheet. It assumes that with the Paracorr at a midrange setting of 3 the distance from the eyepiece shoulder flange of the Paracorr to the focal plane of the Paracorr is the ideal 55mm as specified by TeleVue. This plus a bunch of help from Don has taken my spreadsheet out of the realm of empirical, and into the range of being precise in its attempt to choose the optimal tunable top setting which achieves the closest to the ideal of 55mm spacing between the focal plane (FP) of the Paracorr and the focal plane (FP) of the eyepiece. Oddly, though it is in quite high agreement with the TeleVue eyepiece chart for the Paracorr setting of choice (even for the use of the 1.25" adapter), it is not 100% exact. Being quite biased, I'm personally inclined to believe my own spreadsheet in the few areas where it differs from TeleVue's suggestion for the ideal tunable top setting. If you had previously downloaded my earlier attempt at this spreadsheet, please delete it and replace it with this one. The moderators have my permission to eliminate my earlier spreadsheet attachment (post and all if necessary).

As always, please let me know if my UNIX based "OpenOffice" spreadsheet software translates this properly to the Microsoft Excel format. Despite my best efforts to save things in the proper Excel format, sometimes the translation gets a bit jumbled in its formatting, formulas, etc... Excel is not available in UNIX......

As always, kick the tires, and feel free to fix any mistakes I may have made, or improve upon my ideas as you see fit.

Edited by Lawrence Sayre (08/08/07 08:39 PM)


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: List of Paracorr settings for all brands of EP new [Re: Lawrence Sayre]
      #1766628 - 08/08/07 07:36 PM

Lawrence,
Worked fine. Excel converted the spreadsheet into the latest version of Excel.
I utilized the empirical method to decide the optimum Paracorr setting for each of my TeleVue eyepieces rather than trust TeleVue's spreadsheet that showed the proper setting.
I started at the outmost (1) setting and focused, examined the edge, moved in one setting (2), focused and examined the edge, repeating the process through all 5 settings if necessary.
If two settings seemed to have equal edge correction, I tried the in between setting (e.g.2.5) to see if the correction was better.
All my eyepieces are Naglers now, but I had a Panoptic at the time, and some series 4000 Meade UWAs. My empirical results pretty much agreed with TeleVue's. A couple of the eyepieces' best settings were in between settings, I thought, but the TeleVue recommendations would be fine for their eyepieces in my f/5 scope. At shorter f/ratios, coma correction becomes more critical and residual coma is visible even in a Paracorred eyepiece. In such cases, an in-between setting might become more important.
I put a small marker label on each eyepiece with the proper Paracorr setting, and marked the 1-5 settings of the Paracorr with numbers as well. Now, when I take an eyepiece out of the case, I merely match number with setting--no memory involved.
In the cases where settings 1 or 5 were chosen as the best candidates, I've often wondered if having the tunable top move a little farther in each direction would result in improved coma correction. In other words, I'd have been happier with 7 settings where all my eyepieces' best corrections were settings 2-6. Your spreadsheet could have answered the question if you allowed it to calculate the optimum position rather than the optimum setting.

Edited by Starman1 (08/08/07 07:38 PM)


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astrodon
Carpal Tunnel
*****

Reged: 04/07/05

Loc: Portland, OR, USA
Re: List of Paracorr settings for all brands of EP new [Re: Starman1]
      #1766645 - 08/08/07 07:43 PM

Thanks for the work guys!

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Lawrence Sayre
Abbe Normal
*****

Reged: 10/16/04

Loc: N.E. Ohio
Re: List of Paracorr settings for all brands of EP new [Re: astrodon]
      #1766771 - 08/08/07 08:50 PM

OK guys, I really hate to do this to you, but I just changed my spreadsheet once again to fix a glitch, so if you downloaded a copy of my "final" version prior to my 8:39 PM today revision time as listed in my above post with the attached spreadsheet, please go to that same post above and download it from there once again.

One interesting thing I discovered is that in its final (I hope) form, I can now definitively conclude that the spreadsheet/chart output which TeleVue has posted on its website is in fact for the much older version of the Visual Paracorr which came with the much lower profile 1.25" to 2" adapter (which is 0.16" high). Therefore in its current form, the TeleVue chart on their website is not usable for 1.25" eyepieces in conjunction with the higher profile adapter models (which I believe may have came about when the compression ring was added to the adapter). This makes sense, as the chart has been around for a good while, and the compression ring adapter is the new kid on the block so to speak.


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walt r
Post Laureate


Reged: 02/13/07

Loc: Doylestown, PA
Re: List of Paracorr settings for all brands of EP new [Re: Lawrence Sayre]
      #1767558 - 08/09/07 10:10 AM

Don,
The Spreadsheet I posted does show the optimum setting even if its negative or larger than 5.
walt


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: List of Paracorr settings for all brands of EP new [Re: Lawrence Sayre]
      #1767803 - 08/09/07 12:08 PM

Lawrence,
I have a question about your spreadsheet:
On the TeleVue site, TeleVue shows the setting for the 1-1/4" Type 6 Naglers as setting 4. It also shows that the field stop for each of these eyepieces is 0.25" below (toward the field lens end) the eyepiece "shoulder" (where the inserted eyepiece sits).
Do I enter this as a positve (as TV shows on their site) in your calculator, or as a negative?


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: List of Paracorr settings for all brands of EP new [Re: walt r]
      #1767817 - 08/09/07 12:16 PM

Quote:

Don,
The Spreadsheet I posted does show the optimum setting even if its negative or larger than 5.
walt




Walt,
Your calculator showed the proper setting for the Type 6 Naglers as 4.11 with the new adapter. My empirical test done with the 13 showed setting 4 as the best setting.
So there's a general agreement between your formula and what I see at the eyepiece for these 1-1/4" Naglers.

Lawrence's calculator showed setting 2 or 1 (depending on how the field stop distance from the shoulder is input), which didn't match with what I see.

Your formula is easy to use for an eyepiece whose field stop position can be determined. But many new eyepieces don't have such information available. The old empirical method would seem to be the only choice in those cases.

However, on the 2" Naglers, the results from your calculator are diffierent than TeleVue's claims, but I understand why. For example, I get a setting of greater than 6 for my 31 Nagler, which makes sense, I guess. The field stop of that eyepiece is 0.38" ABOVE the shoulder, which means the field stop-to-lens distance is 58.65mm in setting 5. Since the optimum is 55mm, the 31 Nagler should go 3.65mm further into the barrel to achieve the optimum setting (i.e.an imaginary setting 6). Setting 5 is just the best the Paracorr can do for that eyepiece.

I like the calculator. It works.

Edited by Starman1 (08/09/07 12:26 PM)


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: List of Paracorr settings for all brands of EP new [Re: Starman1]
      #1767860 - 08/09/07 12:37 PM

One more point about Walt's calculator:
The divisor should be 0.125 instead of 0.12
It defines the difference between each setting in inches, and I measured 0.125" between settings, not 0.12".
The results are the same, so I'm being persnickety.


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walt r
Post Laureate


Reged: 02/13/07

Loc: Doylestown, PA
Re: List of Paracorr settings for all brands of EP new [Re: Starman1]
      #1768077 - 08/09/07 02:19 PM

Don,
I forgot that you got the 0.125 measurement for the new style ParaCorr. I have the old style and measured a difference of 0.48 inch from setting 1 to 5. That's 0.12 inch per setting.

My best guess is that there are some dimensional differences between the old and new style ParaCorrs beside the diffence in the 1.25 to 2" ep adapter.

walt


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Lawrence Sayre
Abbe Normal
*****

Reged: 10/16/04

Loc: N.E. Ohio
Re: List of Paracorr settings for all brands of EP new [Re: Starman1]
      #1768155 - 08/09/07 03:12 PM

Quote:

Lawrence,
I have a question about your spreadsheet:
On the TeleVue site, TeleVue shows the setting for the 1-1/4" Type 6 Naglers as setting 4. It also shows that the field stop for each of these eyepieces is 0.25" below (toward the field lens end) the eyepiece "shoulder" (where the inserted eyepiece sits).
Do I enter this as a positve (as TV shows on their site) in your calculator, or as a negative?




Don,

Below is positive, and above is negative. This is the same as TeleVue's convention.


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: List of Paracorr settings for all brands of EP new [Re: Lawrence Sayre]
      #1768193 - 08/09/07 03:31 PM

Lawrence,
Then something isn't working in your calculator.
Example:
55mm (2.165") is the optimum field stop-to-lens distance on the Paracorr.

The depth of the Paracorr is 49mm (1.929") and the height of the 1-1/4" adapter is .379". That would be 2.308" at setting 5 (all the way in). A setting of 4 (+0.125") would yield 2.433".

The Type 6 Naglers have a field stop 0.25" into the 1-1/4" lower tube, so I subtract that from 2.433" to yield 2.183", only 0.018" from the perfect location.

TeleVue's website says position 4 is optimum for the Type 6 Naglers.

Your calculator derives a setting of 2 for those eyepieces. Walt's derives a setting of 4, like TeleVue's recommendation.


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Lawrence Sayre
Abbe Normal
*****

Reged: 10/16/04

Loc: N.E. Ohio
Re: List of Paracorr settings for all brands of EP new [Re: Starman1]
      #1768271 - 08/09/07 04:28 PM

Starman,

The distances are what they are, and all of this is really quite simple (being nothing but straightforward distance addition and subtraction). I've already explained that the chart on the TeleVue website dates to the older pre-compression ring Paracorr with the low profile adapter. For this adapter it gives the proper setting of position 4 for all of the 1.25" eyepieces with the field stop 0.25" below the focuser shoulder. This is a natural outcome of my finally having done it right.

The conclusion which I have reached is that for the newer model Paracorr and adapter the optimal 1.25" TeleVue eyepiece setting is in fact setting 2 (for all of their 0.25" below the shoulder FP position 1.25" eyepieces). The reason for this is straight forward. Add 1/4" to the height of the adapter, and the FP of the 1.25" eyepiece is thereby moved 1/4" farther away from the 55mm optimal. To counter this, the Paracorr must be screwed in 2 full notches to make it 1/4" shorter. Of course none of the 2" eyepieces are affected by any of this.


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: List of Paracorr settings for all brands of EP new [Re: Lawrence Sayre]
      #1768310 - 08/09/07 04:49 PM

Lawrence,
If you read my post, you will see I used the dimension from the newest adapter, with the .379" thickness to show that the Type 6 eyepieces optimally use setting 4 of the Paracorr, which is what TeleVue suggests. My Paracorr's instructions even have a cross-section of the Paracorr pictured, showing the new adapter.
Simple arithmetic shows setting 4 is correct for these eyepieces with the new adapter.
My empirical test also showed setting 4 produced the best correction.
Hence, there is an error somewhere in the calculator if it suggests setting 2 is optimum.

By the way, if the newer adapter is thicker than the older adapter, that would raise the eyepiece away from the lens, necessitating a closer setting of the Paracorr with the thicker adapter. If the thinner adapter used setting 4, the new adapter would require a setting 6 in order to get close enough to the lens. So your contention that the older, thinner adapter used setting 4 and the newer thicker one setting 2 is illogical.
Remember, setting 1 is the farthest from the lens.

Rereading your post, I see we are talking about the same direction, and that you have merely reversed the order of the settings. 5 is closest, and 1 is farthest, not the other way around.

Edited by Starman1 (08/09/07 04:53 PM)


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Lawrence Sayre
Abbe Normal
*****

Reged: 10/16/04

Loc: N.E. Ohio
Re: List of Paracorr settings for all brands of EP new [Re: Starman1]
      #1768329 - 08/09/07 05:06 PM

Starman, is not 5 the highest (longest) setting, and 1 the lowest (shortest) setting, or am I looking at the Paracorr completely backwards? If the eyepiece is lifted 1/4" "more" away from the Paracorr by the new adapter, then to erase this 1/4" increase in the distance between their respective focal planes the Paracorr itself must contract in length by 1/4".

Obviously the TeleVue website chart of Paracorr settings can only be correct for one of the two possible adapters. Does anyone recall this chart suddenly changing at some point?


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Lawrence Sayre
Abbe Normal
*****

Reged: 10/16/04

Loc: N.E. Ohio
Re: List of Paracorr settings for all brands of EP new [Re: Lawrence Sayre]
      #1768394 - 08/09/07 05:43 PM

I sold mine awhile back. Will anyone who currently owns a Paracorr with a tunable top tell me which numeral (setting) corresponds to the shortest overall length of the Paracorr, and which corresponds to the greatest overall length?

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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: List of Paracorr settings for all brands of EP new [Re: Lawrence Sayre]
      #1768484 - 08/09/07 06:49 PM

Lawrence,
5 is the lowest setting, with the tunable top screwed in to make the Paracorr shortest.
1 is the highest setting, with the tunable top screwed out to make the Paracorr longest.
Since the screw doesn't move, the leftmost slot position is 1 and the righthand slot position is 5. The slot tilts uphill toward the right, allowing the tunable top to come in (down) as a higher number is dialed.
Don


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: List of Paracorr settings for all brands of EP new [Re: Starman1]
      #1768486 - 08/09/07 06:51 PM

Or, another way:
5-- 0"
4-- +1/8"
3-- +1/4"
2-- +3/8"
1-- +1/2"


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Lawrence Sayre
Abbe Normal
*****

Reged: 10/16/04

Loc: N.E. Ohio
Re: List of Paracorr settings for all brands of EP new [Re: Starman1]
      #1768497 - 08/09/07 06:56 PM

Don, somehow I don't intuitively get that from looking at this photo:

Paracorr with tunable top

And how can anyone explain that the spreadsheet gives correct output for 2" eyepieces, while not working for 1.25" eyepieces? The laws of optics are the same for both, so the math which works for one must work for the other, no?


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