erik
telescope surgeon
Reged: 01/30/04
Posts: 24250
Loc: Off Grid in Paradise (Big Isla...
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Feel free to list the optimum paracorr settings for any brand and f/length eyepiece, based on your firsthand experience. To make this thread most useful to those browsing through it, please limit your posts to something like this:
35mm 2" XYZ brand Oober ultra wide eyepiece- Setting "2"
Thanks! 
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-Erik Wilcox
Homebuilt 16" Truss Dob
SV 80mm ED Nighthawk NG on M1 ALT/AZ
Nikon Prostaff 65mm spotter on Trekpod
Konusvue 20x80 binos/Peterson pipemount
Orion 10x50 binos
Homebuilt 80mm f/5 refractor
Mirador 60mm f/12 1960's refractor
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Lawrence Sayre
Abbe Normal
Reged: 10/16/04
Posts: 4736
Loc: N.E. Ohio
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Though it is admittedly only for TeleVue eyepieces, this TeleVue Paracorr tunable top settings chart should make a good opening addition to this thread:
TeleVue Paracorr tunable top settings chart
The chart is about 3/4 of the way down on the linked page.
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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.
Ayn Rand (in the appendix to 'Atlas Shrugged')
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square_peg
Postmaster
Reged: 03/26/04
Posts: 29401
Loc: Maple Valley, WA
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Meade 5K 34mm SWA - Paracorr setting 2
Siebert 34mm Observatory Series - Paracorr setting 1
Meade 36mm QX - Paracorr setting 1
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Tom (Pegster)
DSH-8 (GSO Dob)
15x70 Oberwerks
SVP/ED80
WO 66 Petzval
Sears Discoverer EQ 60/900
8x42 Regals
History is Philosophy teaching by examples.
Thucydides
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ausastronomer
scholastic sledgehammer
Reged: 06/30/03
Posts: 934
Loc: NSW Central Coast (Australia)
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14mm Pentax XW #1
20mm Pentax XW #1
I don't use the paracorr with the 5mm,7mm and 10mm Pentax XW's
Clear Skies
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John Bambury
AS of NSW
AS of Hunter Valley
18"/F4.5 Obsession fully loaded with OMI optics
14"/F4.5 SDM fully loaded with Zambuto Optics
10"/F5 Newtonian with Argo Navis
Lots of Pentax XW's. 12mm & 17mm Nagler T4's, 31mm Nagler T5 & 13mm ETHOS. TV Paracorr and 1.8X TV Barlow and 2.5X TV Powermate
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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Meade Series 4000 UWA:
14mm--5
8.8mm--1
(to be honest, I might have those reversed, but those 2 eyepieces require the extremes when used as 2" eyepieces fully inserted).
Note: The Paracorr has a 43mm lens to shoulder distance at the in-most setting. These two Series 4000 UWAs cannot be used with 1-1/4" filters without hitting the Paracorr's lenses, so the use of these eyepieces in a Paracorr requires the use of 2" filters on the bottom of the Paracorr. If you must use 1-1/4" filters on these eyepieces, use spacers on the 2" barrels to stand the eyepieces out more. This will require different settings on the Paracorr, and the one requiring the most inward position will no longer reach the best position for correction of coma.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Lawrence Sayre
Abbe Normal
Reged: 10/16/04
Posts: 4736
Loc: N.E. Ohio
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14mm Meade Series 4000 UWA, setting #1 when used in 2" mode.
This is purely from memory, and from my recollection that the 14mm Meade requires a bunch of out-travel of the focuser. Or was it my 8.8mm Meade Series 4000 UWA which required all the out-travel??? Hmmm??? I may also have these reversed.
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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.
Ayn Rand (in the appendix to 'Atlas Shrugged')
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asian_hillbilly
super member
Reged: 01/18/06
Posts: 143
Loc: Houston, TX
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Quote:
14mm Meade Series 4000 UWA, setting #1 when used in 2" mode.
Yup, that's the setting I always use. When using the 14mm without the Paracorr, I have to pull the 2" skirt out a bit to be able to reach focus.
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Ted
XT-8
DBA Certified 12"
26T5,17T4,14UWA(4K),10XW,7XW, and Speers 5/8 Zoom
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walt r
Post Laureate
Reged: 02/13/07
Posts: 3458
Loc: Doylestown, PA
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I have worked out an equation for the Paracorr setting.
The setting = (0.365 + adp tk - dim f)/0.12
Where:
0.365 = three combined measurments of the Paracorr.
(I'll explain futher if anyone wishes.)
adp tk = flange thickness of the 1.25 to 2 inch adpter used.
0 if using a 2in ep.
0.16 in for the old style paracorr adapter.
I don't have this dimension for the new style. I'll add it if someone will measure it and send it to me.
dim f = the distance of the eyepiece focal plane (field stop) below the top of the ep barrel (surface that sets of the top of the draw tube).
Positive = focal plane inside draw tube,
negative = focal plane above draw tube.
(see TeleVue ep specs for a drawing, bottom of page).
walt
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Walt
Obsession 18" f/4.45 #1370 AN/SC
MK67 Deluxe 6" f/12 Mak-Cass, Super Polaris GEM, JMI MicroMax DSC
DIY 60mm f/6 Achromat
Cookbook 245 CCD
Edited by walt r (07/31/07 09:15 AM)
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Lawrence Sayre
Abbe Normal
Reged: 10/16/04
Posts: 4736
Loc: N.E. Ohio
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I woke up early this morning and I've been attempting to make a spreadsheet to calculate the ideal Paracorr tunable top setting based solely upon the field stop location of the eyepiece, and although in its present state it appears to give correct answers for all of the 2" TeleVue eyepieces, it gives incorrect answers for all of the 1.25" TeleVue eyepieces. I've attached it here. It was generated in UNIX, and not using Excel, but I saved it in an excel format, so I hope it looks normal on your computer. If not, please let me know. Feel free to massage or alter it at will, as you may find a better solution than I have found, and you may just solve the 1.25" eyepiece problem as well. So far the only way I have gotten 1.25" eyepieces to read correctly is to multiply the added height from the 1.25" adapter by a factor of 3. This modification however is not present in the spreadsheet as given here, as it seems to have no reason for being so.
The only permitted user input is for:
1) Field Stop location in inches (remember to apply the proper +/- sign for this value)
2) 1.25" eyepiece adapters added height in inches (zero for no adapter, as with 2" eyepieces)
Once you have entered these two parameters, read the spreadsheets calculated value for your eyepiece on the extreme right hand side. Then compare this value with the nominal values provided for the various Paracorr settings, and choose the Paracorr setting for which the provided value most closely matches the value as seen on the extreme right for your eyepiece.
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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.
Ayn Rand (in the appendix to 'Atlas Shrugged')
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Lawrence Sayre
Abbe Normal
Reged: 10/16/04
Posts: 4736
Loc: N.E. Ohio
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My first assumption is that the only function of the tunable top is to maintain a more or less constant distance from the eyepieces field stop location to the Paracorr's lens group, with deviation from this optimal distance leading to somewhat less than optimal Paracorr performance. Part of my difficulty in making my spreadsheet (see above post) is that I have sold my Paracorr, and I can not measure this distance, and therefore must guess. I must also guess at the height range provided by the tunable top, and my guess here was 1/2 inch.
TeleVue gives us a chart (reference my first post in this thread for the link) of optimal Paracorr settings, but for 1.25" eyepieces this chart is seriously flawed by the fact that apparently 2 quite differing heights of TeleVue 1.25" to 2" adapter are (or at least were) available for the Paracorr, and the TeleVue table does not specify which adapter they used for the chart. Whichever adapter they used, if you have the other one, then the TeleVue chart is pretty much useless in providing you with the best setting for your 1.25" eyepieces.
One of the adapters has a set-screw which fits into a recessed slot, and is thus of a low profile, and the other adapter does not, and is therefore high profile. Both are pictured along with the Paracorr's as seen above the TeleVue website Paracorr tunable top chart.
Most budget after market 1.25" to 2" adapters are of the high profile variety.
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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.
Ayn Rand (in the appendix to 'Atlas Shrugged')
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Lawrence Sayre
Abbe Normal
Reged: 10/16/04
Posts: 4736
Loc: N.E. Ohio
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If my assumption is correct (and it does work to give correct tunable top settings for all TeleVue 2" eyepieces when used in 2" only mode), then I will perhaps never understand why TeleVue chose to place their 1.25" eyepieces where they did upon their tunable top chart. 
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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.
Ayn Rand (in the appendix to 'Atlas Shrugged')
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walt r
Post Laureate
Reged: 02/13/07
Posts: 3458
Loc: Doylestown, PA
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Ok, I think I know where the problem is. Look at the pictures of the ParaCorr parts on TeleVue's web site. They have two different tunable tops with different height 1.25 to 2" adpaters. The old style is 0.16 in thick. The new style is much thicker (I don't have one to measure but it looks to be about 3X the old adapter). In the equation in my post above, the TeleVue ParaCorr setting do work out for all of the 1.24" eyepieces if the adpter thickness is set to 0.37 inch. I did check the above posted equation in a spreadsheet for all of the eyepieces in the ParaCorr Setting Chart (the chart is not correct for 1.25 eps using the old adpter thickness, decrease the setting by 2 is close to correct). Also note that TeleVue states that "set path length from Paracorr flange surface to CCD surface to 55mm ±4mm for best results". ±4mm = ±0.157in, whereas a chenge from one setting to the next = 0.12in. This ± 1.3 settings, so there appears to be a fairly wide tolerance to get the correct setting.
Would you like a copy of my speadsheet?
walt
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Walt
Obsession 18" f/4.45 #1370 AN/SC
MK67 Deluxe 6" f/12 Mak-Cass, Super Polaris GEM, JMI MicroMax DSC
DIY 60mm f/6 Achromat
Cookbook 245 CCD
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Lawrence Sayre
Abbe Normal
Reged: 10/16/04
Posts: 4736
Loc: N.E. Ohio
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Yes, please either attach it here, or PM me. An attachment would let others assist here as well.
I see now that if the 1.25" to 2" adapter which TeleVue actually used to generate their chart is in fact 3 times thicker (higher in profile) than the one I assumed they used (using your provided 0.16" figure, I had assumed the low profile model), then my spreadsheets results are highly accurate just as it is written and attached above for all TeleVue eyepices, and the fudge factor of 3 times the height for the adapter (which I refused on logical grounds to include in my spreadsheet) is in fact unnecessary. The pictured high profile adapter on the TeleVue Paracorr website does indeed look visually to be every bit of a full 3 times thicker than the low profile adapter sitting beside it.
By inference, my initial fundamental assumption is correct, and by further inference, any non TeleVue eyepiece which comes to focus in close proximity to an existing TeleVue eyepiece will thereby share that TeleVue eyepieces recommended (or spreadsheet derived) Paracorr tunable top setting.
Also, since most after market 1.25" to 2" adapters are of the high profile variety, the TeleVue chart is useful for them as well. My spreadsheet will work for all adapter heights, so those with unique adapters need not worry.
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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.
Ayn Rand (in the appendix to 'Atlas Shrugged')
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walt r
Post Laureate
Reged: 02/13/07
Posts: 3458
Loc: Doylestown, PA
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See attached Excel Spreadsheet.
Have fun.
walt
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Walt
Obsession 18" f/4.45 #1370 AN/SC
MK67 Deluxe 6" f/12 Mak-Cass, Super Polaris GEM, JMI MicroMax DSC
DIY 60mm f/6 Achromat
Cookbook 245 CCD
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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Just measured adapter on current Paracorr: 0.379" or 9.69mm.
Hope that helps.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Lawrence Sayre
Abbe Normal
Reged: 10/16/04
Posts: 4736
Loc: N.E. Ohio
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Excellent, thanks a bunch Don!
To all:
I would like to know a few more measurements for specifically the Visual Paracorr model which comes with the taller 0.379" high 1.25" to 2" eyepiece adapter:
CAUTION / WARNING: Whatever anyone willing to undertake these measurements may do to achieve them, please do not scratch your Paracorr in the process.
1) With the Paracorr at setting #1, what is the distance from the top (eyepiece shoulder) to the first (eye) lens element (on axis if possible).
2) Ditto for setting #3
3) Ditto for setting #5
(and ditto with bonus points for settings #2 and #4 if you are brave)
For those less brave (or should I say foolhardy), simply providing the total tunable top span distance from setting #1 to setting #5 would be a great help (I.E. the total travel distance of the tunable top itself, which is the measure of the gain in overall length of the Paracorr). Another great help would be answering if the individual settings gain distance linearly, or non linearly (in which latter case knowing the actual gain in height (length) for each setting would be great).
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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.
Ayn Rand (in the appendix to 'Atlas Shrugged')
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Lawrence Sayre
Abbe Normal
Reged: 10/16/04
Posts: 4736
Loc: N.E. Ohio
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Second plea: I'm now willing to accept much less than before. Will anyone simply measure the total travel span distance (overall height increase from lowest to highest setting) for their modern style (high profile adapter model, the one with no recess slot for the adapters set-screw) Visual Paracorrs tunable top? This is a non-destructive measurement.
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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.
Ayn Rand (in the appendix to 'Atlas Shrugged')
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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Quote:
Second plea: I'm now willing to accept much less than before. Will anyone simply measure the total travel span distance (overall height increase from lowest to highest setting) for their modern style (high profile adapter model, the one with no recess slot for the adapters set-screw) Visual Paracorrs tunable top? This is a non-destructive measurement.
Lawrence:
Height of top of Paracorr w/o adapter, setting 5(low): 1.545"
Height of top of Paracorr w/adapter, setting 5: 1.920"
Length of insertion tube part of Paracorr: 2.39"
Height added to top when adjustable top is in highest position: 0.5" (Setting 5=0", setting 1 =0.5" up), each setting increases by 1/8" on smooth, even ramp. Setting 4=+1/8", Setting 3=+1/4", Setting 2=+3/8", Setting 1=+1/2".
I vaguely recall, when I was using Meade Series 4000 UWA eyepieces in the Paracorr, that the maximum depth of an eyepiece that wouldn't hit the lens in position 5 (the lowest setting) was 43mm (1.7"). I don't recall if that was being conservative so as not to risk the lens or whether or not that was actually the distance from lens center to 2" shoulder in setting 5. I do know that I could not use 1-1/4" filters on the Meade 14 or 8.8 (which had the same height of barrel, though it was the 8.8, I guess, that used position 5) without hitting the lens. So if you have one of those to measure, the distance to lens is definitely larger than that length.
I don't have any way to measure that distance without risking a scratch on the lens. Sorry.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Lawrence Sayre
Abbe Normal
Reged: 10/16/04
Posts: 4736
Loc: N.E. Ohio
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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.
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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.
Ayn Rand (in the appendix to 'Atlas Shrugged')
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Lawrence Sayre
Abbe Normal
Reged: 10/16/04
Posts: 4736
Loc: N.E. Ohio
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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.
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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.
Ayn Rand (in the appendix to 'Atlas Shrugged')
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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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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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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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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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Lawrence Sayre
Abbe Normal
Reged: 10/16/04
Posts: 4736
Loc: N.E. Ohio
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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.
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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.
Ayn Rand (in the appendix to 'Atlas Shrugged')
Edited by Lawrence Sayre (08/08/07 08:39 PM)
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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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.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
Edited by Starman1 (08/08/07 07:38 PM)
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astrodon
Carpal Tunnel
Reged: 04/07/05
Posts: 1804
Loc: Hillsboro, OR, USA
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Thanks for the work guys!
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Putting Tasco Refractors back on their mounts one scope at a time!
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Lawrence Sayre
Abbe Normal
Reged: 10/16/04
Posts: 4736
Loc: N.E. Ohio
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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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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.
Ayn Rand (in the appendix to 'Atlas Shrugged')
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walt r
Post Laureate
Reged: 02/13/07
Posts: 3458
Loc: Doylestown, PA
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Don,
The Spreadsheet I posted does show the optimum setting even if its negative or larger than 5.
walt
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Walt
Obsession 18" f/4.45 #1370 AN/SC
MK67 Deluxe 6" f/12 Mak-Cass, Super Polaris GEM, JMI MicroMax DSC
DIY 60mm f/6 Achromat
Cookbook 245 CCD
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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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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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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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.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
Edited by Starman1 (08/09/07 12:26 PM)
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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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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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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walt r
Post Laureate
Reged: 02/13/07
Posts: 3458
Loc: Doylestown, PA
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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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Walt
Obsession 18" f/4.45 #1370 AN/SC
MK67 Deluxe 6" f/12 Mak-Cass, Super Polaris GEM, JMI MicroMax DSC
DIY 60mm f/6 Achromat
Cookbook 245 CCD
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Lawrence Sayre
Abbe Normal
Reged: 10/16/04
Posts: 4736
Loc: N.E. Ohio
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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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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.
Ayn Rand (in the appendix to 'Atlas Shrugged')
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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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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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Lawrence Sayre
Abbe Normal
Reged: 10/16/04
Posts: 4736
Loc: N.E. Ohio
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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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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.
Ayn Rand (in the appendix to 'Atlas Shrugged')
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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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.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
Edited by Starman1 (08/09/07 04:53 PM)
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Lawrence Sayre
Abbe Normal
Reged: 10/16/04
Posts: 4736
Loc: N.E. Ohio
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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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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.
Ayn Rand (in the appendix to 'Atlas Shrugged')
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Lawrence Sayre
Abbe Normal
Reged: 10/16/04
Posts: 4736
Loc: N.E. Ohio
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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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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.
Ayn Rand (in the appendix to 'Atlas Shrugged')
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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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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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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Or, another way:
5-- 0"
4-- +1/8"
3-- +1/4"
2-- +3/8"
1-- +1/2"
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Lawrence Sayre
Abbe Normal
Reged: 10/16/04
Posts: 4736
Loc: N.E. Ohio
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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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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.
Ayn Rand (in the appendix to 'Atlas Shrugged')
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astrodon
Carpal Tunnel
Reged: 04/07/05
Posts: 1804
Loc: Hillsboro, OR, USA
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Lawrence-
In the photo of the Paracorr with the tunable top you can see that setting 5 is the lowest, for in order to reach that setting the tunable top with the slot in it must descend in order for the set screw to reach that level.
Hope I helped to clear this up, I know it is hard to get just by looking at the image,
~Don
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Putting Tasco Refractors back on their mounts one scope at a time!
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Lawrence Sayre
Abbe Normal
Reged: 10/16/04
Posts: 4736
Loc: N.E. Ohio
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OK, I finally realize that my intuitive view of the 5 being higher in the picture than the 1 was all wet, and I now trust that 5 is the lowest and 1 is the highest setting. Obviously the slide lever has to go up for the tunable top to go down, and visa versa. Thank you Don and Don!!! With that to go on, I've re-worked my spreadsheet once again, and I'm attaching it right here. I'm also now willing to believe that the TeleVue website chart is using the taller adapter for its 1.25" eyepieces. Please kick the tires with this spreadsheet, and let me know if it gives correct tunable top settings across the board.
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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.
Ayn Rand (in the appendix to 'Atlas Shrugged')
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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Lawrence,
It worked for my 31 Nagler and my Type 6 Naglers.
It didn't work for the 17 Nagler, with a field stop to shoulder dimension of -0.03"
The spreadsheet erroneously gives a setting of 5 instead of 3.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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Lawrence,
I accidentally included the adapter height for a 2" eyepiece.
Doh! 
Your calculator works fine.
Don
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Lawrence Sayre
Abbe Normal
Reged: 10/16/04
Posts: 4736
Loc: N.E. Ohio
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Thanks!!!
Whew, you had me worried there for a bit. I was beginning to wonder if I would ever get it right. A sanity tester for sure.
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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.
Ayn Rand (in the appendix to 'Atlas Shrugged')
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Keith
Vendor
Reged: 05/14/05
Posts: 234
Loc: Costa Mesa, CA USA
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for the 30mm 1rpd, setting 3, works suprisingly well. When I later aquired the real deal 30mm widescan III, suprisingly, it wasnt as well correctable with the paracorr, possibly because it has a wider field stop. I kept both eyepieces. Since I also aquired a nice f10 OTA, I use the WSIII with it, and my most recently aquired 31mm nagler with the dob, with or without the paracorr. I have the older photo/visual model, and the vignetting bothers me, so I will likely add the visual model in the future, and keep the other for my 8"f4 for imaging.
my 2c in the 8.8 UWA discussion, I used it in the lowest setting (5) with the included 1.25 adapter in 1.25 mode, like suggested for the 9mm nagler and it worked very well. I dont think I tried it with the 14mm yet, which I aquired more recently.
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Cats (tubes): C11xlt, 8"LX"R". Orion Apex90
Newts: GSO 10"f5dob, Starhoc8-4
APOs: TV101 AT66ED
ACHROS: C102, C80 f11, 60f9, A&F20-60x60
Mounts: G11G, GM8G, CG5-RA, SV M1GG
Apogee U8300M Optec IFW
SBIG: ST1001E, ST7ABG, ST8EABG, Pixcel255
DSIpro DSIc
handfull of binos, 5 cases of EPs
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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I went back and looked for my records:
14mm UWA (used as 2")--setting 1
8.8mm UWA (used as 2")--setting 5
The 31 Nagler would be better corrected at setting 6. The fact there is no setting 6 shows the Paracorr was designed long before the 31 Nagler. I find it "tolerable" with setting 5, however.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Zooball
journeyman
Reged: 02/05/07
Posts: 9
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Thanks Don,
You just saved me a lot of work. I have both of those EPs and a brand new Paracorr PCV-2000 still snug in the box waiting for dark skies.
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sixela
Postmaster
Reged: 12/23/04
Posts: 10848
Loc: Boechout, Belgium
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Quote:
I woke up early this morning and I've been attempting to make a spreadsheet to calculate the ideal Paracorr tunable top setting based solely upon the field stop location of the eyepiece, and although in its present state it appears to give correct answers for all of the 2" TeleVue eyepieces, it gives incorrect answers for all of the 1.25" TeleVue eyepieces.
Probably means you haven't accounted for the extra 9.6mm caused by the Paracorr 2"-1.25" adapter.
Edit: never mind - late to the party...
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400mm f/4.46 self made Dobsonian on Tom Osypowski equatorial platform
Orion Starblast (114mm f/4 reflector, Alt/Az)
Edited by sixela (08/28/07 11:56 AM)
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bkushner
Carpal Tunnel
Reged: 11/26/06
Posts: 1725
Loc: Audubon New Jersey
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What about Ethos?
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Orion XT12i
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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The position of the Ethos' focal plane is only 0.02" different than the Type 6 Naglers. That means setting 4 would be correct--the Nagler Type 6s WITH the adapter, and the Ethos WITHOUT an adapter.
I don't believe you could get the Ethos close enough to the Paracorr lens if used with a 1-1/4" adapter.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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sixela
Postmaster
Reged: 12/23/04
Posts: 10848
Loc: Boechout, Belgium
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Can't. In 1.25" mode in a 2"-1.25" adapter, it doesn't insert with the 1.25" barrel completely seated in the adapter, because the 2" barrel contacts the adapter.
When used this way, the focal plane is much too far from a Paracorr lens, even with a zero-length adapter.
Ethos: 2" mode, top fully pulled out.
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400mm f/4.46 self made Dobsonian on Tom Osypowski equatorial platform
Orion Starblast (114mm f/4 reflector, Alt/Az)
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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It works fine in a TeleVue "High-Hat" 1-1/4" adapter, but, in general, the Ethos should be used as a 2" eyepiece in 2" focusers. And in the Paracorr too.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Mr. Bill
Post Laureate
Reged: 02/09/05
Posts: 3147
Loc: Just passing through.....
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Anybody know offhand what the settings for the 14, 10.5 and 7 mm Pentax XLs is?
I say "is" because they are all parfocal.
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10x50 Fujinon binos + 16x70 Fujinon binos + UA UniMount
Oberwerk BT100 45 degree +24mm Pans + Hercules fork mount
120mm f/5 Orion achromat + Moonlite focuser
130mm TMB 130SS f/7 APO refractor
140mm f/5.7 Vixen NeoAchro Petzvel refractor
150mm f/8 homemade achromat
8 inch newt with f/5 Swayze mirror
10 inch f/4.7 Orion newt + Paracorr
15 inch f/5 Discovery "Galactic Cannon"
Member IDA
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sixela
Postmaster
Reged: 12/23/04
Posts: 10848
Loc: Boechout, Belgium
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Quote:
It works fine in a TeleVue "High-Hat" 1-1/4" adapter,
That doesn't fix the issue either, because the reason it works is because the high-hat adds extra length.
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400mm f/4.46 self made Dobsonian on Tom Osypowski equatorial platform
Orion Starblast (114mm f/4 reflector, Alt/Az)
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Mr. Bill
Post Laureate
Reged: 02/09/05
Posts: 3147
Loc: Just passing through.....
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Quote:
It works fine in a TeleVue "High-Hat" 1-1/4" adapter, but, in general, the Ethos should be used as a 2" eyepiece in 2" focusers. And in the Paracorr too.
That's what TV's Ethos instruction sheet plainly says....
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10x50 Fujinon binos + 16x70 Fujinon binos + UA UniMount
Oberwerk BT100 45 degree +24mm Pans + Hercules fork mount
120mm f/5 Orion achromat + Moonlite focuser
130mm TMB 130SS f/7 APO refractor
140mm f/5.7 Vixen NeoAchro Petzvel refractor
150mm f/8 homemade achromat
8 inch newt with f/5 Swayze mirror
10 inch f/4.7 Orion newt + Paracorr
15 inch f/5 Discovery "Galactic Cannon"
Member IDA
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Starkler
scholastic sledgehammer
Reged: 11/04/05
Posts: 782
Loc: Australia, Melbourne
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Quote:
Anybody know offhand what the settings for the 14, 10.5 and 7 mm Pentax XLs is?
I say "is" because they are all parfocal.
The Pentaxs appear to perform best with the tunable top set to the highest setting (which requires the max amount of focuser in-travel). I had to cut 15mm from my truss poles to accommodate but its worth it
I find the paracorr works wonderfully as a field flattener, nicely mitigating the often criticised field curvature in the 14 and 21mm pentaxs
A note of caution! A friend handed me an OIII filter to try on my 31nagler. Dont try it as it hits the paracorr lens
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Geoff
15" SDM truss dob | Vixen r130sf | GSO 10" dob
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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Quote:
A note of caution! A friend handed me an OIII filter to try on my 31nagler. Dont try it as it hits the paracorr lens
Ouch.
Note: 2" filters should be threaded on the bottom of the Paracorr for safety's (and convenience's) sake.
And don't use 1-1/4" filters on the bottom of the dual 1-1/4"/2" eyepieces when used as 2" eyepieces either. The filter will hit the lens if a lower setting is used.
If you use a Paracorr, it is safer to use all 2" filters and thread them on the bottom of the Paracorr.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Olivier Biot
Amused
Reged: 04/25/05
Posts: 16319
Loc: 51°N (Belgium)
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For that reason I'm designing a 2" filter wheel that goes right below the ParaCorr.
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Prediction is very difficult, especially about the future. Niels Bohr
Tal-200K (#199) with JMI NGF-Mini2M focuser on GEM3 • Astro-Tech AT80ED • Orion Sirius EQ-G with wireless EQDIRECT • Astro-Tech Voyager • Celestron Regal LX 10x42 • Helios 15x70
ATM 14" f/5 (redesigning) • ATM 10" f/6 Portable Truss (polishing) • ATM 10" f/25 Dall-Kirkham (optics)
AstroForecast
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Shawn H
Carpal Tunnel
Reged: 05/16/07
Posts: 2954
Loc: Southern France 43°56'N-4°50'E
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Lumicon sells thier coma correcter for about 100 euros less than TV's paracorr in France, I'd love to hear if anyone has done a side by side comparison!
Shawn Haggerty Avignon, France
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18" David Lukehurst truss Dobson with Sky Commander flash 4 DSC's & Moonlite CR2 focuser & Astrocrumb filter slide
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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The Lumicon has a full-aperture lens, so it won't vignette, but adjusting the eyepiece focal plane to lens distance will require the use of spacers, because there is no adjustment there. The Lumicon was designed as a photographic accessory where the distance from the camera's focal plane to the lens is set once and forgotten. Unfortunately, different eyepieces have their focal planes in different spots and some method of adjusting the lens to focal plane distance is needed.
Because of the lens design (it's a Ross), there will be more spherical aberration on axis, though somewhat better coma correction at the edge of the field.
But note: even if not perfect, applying coma correction, whether dialed in or not, to the image in a short focal ratio newtonian will result in better images than without it.
For visual use, nothing beats the Paracorr. But if you're correcting the image for imaging, the Lumicon, Baader, and TeleVue will all work wonders. And all are better than nothing.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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V.A.
sage
Reged: 05/14/05
Posts: 281
Loc: Ontario, Canada
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what image degradation will happen if the 55mm distance between the paracorr lens and the eyepiece field stop is not maintained?, if there are eyepieces with focal planes that will increase or decrease the 55mm distance beyond the 55 +\- 4mm tolerance coma correction won't be optimal, but what about other abberiations, such as spherical abberiation?
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10" binocular telescope
Oberwerk 7x50 Mariner
tv 24pans , plossl's and 12mm t4s
6.5 mag. dark skies
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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Coma correction will be less, and spherical aberration will be added. However, a less-than-optimum setting still works OK. Nagler's own 31mm Type 5 requires a setting 1/8" farther in than the Paracorr can be set, yet the correction is still superior to the eyepiece by itself. What small amount of spherical aberration that is added is a small price to pay for such a significant amount of coma reduction and some field flattening.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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backwoody
Pooh-Bah
Reged: 01/08/07
Posts: 1114
Loc: Idaho USA
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I recently purchased a Paracorr for my f4.8 dob, and really appreciate this thread. I'm working to find the best settings with various EPs, with no problem for most of them. But I am having a hard time finding field stop data for some, and thus, can't run the calculations -- although I will likely discover the best Paracorr settings by trial-and-error.
Anyone have personal knowledge of Paracorr settings for Vixen LVW 17mm and Pentax XF 12 and 8.5mm? 
Thanks in advance,
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woody
a parsec farther out...
12.5" f/4.8 custom truss dob, EQ platform
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Denimsky
sage
Reged: 01/21/07
Posts: 254
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Thank you Lawrance.
With your spreadsheet, I could calculate the tunable top positions for my eyepieces.
Pentax XW 7: setting 1
Pentax XW 20: setting 1
Speers-Waler 5-8 variable: setting 1
Pentax XL 40: setting 3.
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DH
Edited by Denimsky (01/27/08 12:06 PM)
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Pete Laky
journeyman
Reged: 02/11/08
Posts: 8
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Looking for a sanity check...
I worked through the spreadsheet but want to check out the results (might be locked up). I get setting 5 for a TV new model paracorr with the stock 1.25" adaptor and my 14mm Meade 5k UWA?
Took the advice on filters, ended up using my O-III filter laid over the top of the eyepiece...need to acquire some 2" filters...
Thanks in advance...
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V.A.
sage
Reged: 05/14/05
Posts: 281
Loc: Ontario, Canada
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i was looking at the parrcorr about that issue your having with the 31mmt5 not reaching it's optimal position. there's a ridge on top of the tunable top that the eyepiece rests on, it's about .2" tall, right above the brass ring. it could be machined down by .125" to bring the 31t5 to it's optimal position. this would make the #5 setting to #6 and you would loose the #1 position (or do i have the numbers backwards?) , but it seems like it will work fine and it's a very simple modification.
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10" binocular telescope
Oberwerk 7x50 Mariner
tv 24pans , plossl's and 12mm t4s
6.5 mag. dark skies
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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Yes, the lip of the tunable top could be machined down.
I have eyepieces that use 1-5 now. I'd have to extend the tunable top's slot to allow more movement up to make that modification, though.
The correction may not be perfect, but it is fine for the low power use in my f/5 scope. Were my dob larger and faster (generating more magnification for the 31 and more coma to correct), position 5 might not be adequate. But, though it is 1/8" away from the perfect position, it certainly works OK for that eyepiece.
I have a machinist friend who might be able to make a tunable top for me with the necessary travel and shape, and I'd love to get rid of the compression ring and have a nice snug fit instead with a 1/4" nylon screw eyepiece tightener.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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V.A.
sage
Reged: 05/14/05
Posts: 281
Loc: Ontario, Canada
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i think i may have overlooked the antireflection threads inside the parrcarr, it seems like the eyepiece barrel might hit the threads before it will go down any further, so the modifications are a little more extensive than i first thought, the antireflection threads would need to be machined down a little as well.
on a diffrient note, i noticed when holding the parrcorr in front of my eyes and looking through it ,the parrcorr seems to have a positive focal lenght, i can actually place an eyepiece in front and it will form an image. how does it extend the focal lenght by 1.15x when it appears like it would act as a focal reducer? there must be some optical principals i'm unware of.
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10" binocular telescope
Oberwerk 7x50 Mariner
tv 24pans , plossl's and 12mm t4s
6.5 mag. dark skies
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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Well, in the aggregate, it has to perform like a slightly negative lens in order to have a positive magnification effect.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Mike Foreman
super member
Reged: 04/06/07
Posts: 122
Loc: Texas
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Does anyone know the in focus of a Paracorr?
With the 26nT5 I can focus without it but can't focus with it.
I am trying to calculate how much to trim off my truss tubes.
BTW I am using an 18" f:5.
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18" f:5 DOB
TV101
CAT's:C8 and a 14 pound female black and white named Cookie
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walt r
Post Laureate
Reged: 02/13/07
Posts: 3458
Loc: Doylestown, PA
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An update on using a N12T4 with the barrel extension.
Note: I have an older Paracorr with the tunable top.
Check this procedure using the technique of starting with an EP that has a known setting. Then without moving the focuser, change to the N12T4 and adjust the Paracorr until focused.
When the barrel extension is installed on a N12T4 the extension will bottom out inside the Paracorr and not on the tunable top. This means that the tunable top's setting is meaningless if one just inserts the N12T4 into the Paracorr.
Through experimentation I discovered how to get the proper Paracorr setting on the N12T4 with the barrel extension.
1) The starting setting of the Paracorr is really unimportant but I usually have it at setting three, the mid-setting.
2) Insert the N12T4 into the Paracorr until the barrel extension bottoms in the Paracorr.
3) Tighten the thumb screw to lock the N12T4 to the tunable top.
4) Loosen the Paracorr tunable top lock.
5) Rotate the tunable top to the right (extending the top outward) one setting (or move to the next setting on the left). From setting 3 to setting 2 for example.
6) Lock the tunable top.
The Pararcorr is now set for the N12T4.
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Walt
Obsession 18" f/4.45 #1370 AN/SC
MK67 Deluxe 6" f/12 Mak-Cass, Super Polaris GEM, JMI MicroMax DSC
DIY 60mm f/6 Achromat
Cookbook 245 CCD
Edited by walt r (06/13/08 02:45 PM)
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Mike Foreman
super member
Reged: 04/06/07
Posts: 122
Loc: Texas
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Thanks Walt.
So if I am understanding correctly once the Paracorr is set relative to the telescope then it is a matter of getting the eyepiece set to the Paracorr?
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18" f:5 DOB
TV101
CAT's:C8 and a 14 pound female black and white named Cookie
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walt r
Post Laureate
Reged: 02/13/07
Posts: 3458
Loc: Doylestown, PA
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Thats correct Mike. The Paracorr specs are a set distance from the Paracorr lens to the focal plane in the EP. It is the EP's focal plane to external dimensions that differ from EP to EP.
Translated, the Paracorr lens is to be at a fixed distance inside the original focal plane of the primary mirror.
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Walt
Obsession 18" f/4.45 #1370 AN/SC
MK67 Deluxe 6" f/12 Mak-Cass, Super Polaris GEM, JMI MicroMax DSC
DIY 60mm f/6 Achromat
Cookbook 245 CCD
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Starkler
scholastic sledgehammer
Reged: 11/04/05
Posts: 782
Loc: Australia, Melbourne
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Quote:
Thanks Walt.
So if I am understanding correctly once the Paracorr is set relative to the telescope then it is a matter of getting the eyepiece set to the Paracorr?
Once you have the correct position for one eyepiece sorted and focused, you can lock your focuser and focus other eyepieces with the tunable top and it will be correct 
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Geoff
15" SDM truss dob | Vixen r130sf | GSO 10" dob
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Astrolabe
super member
Reged: 07/08/07
Posts: 116
Loc: sydney Australia
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Thanks to everyone for the work done in the relation to the Paracorr settings. I recently bought a paracorr but I have no problems with the settings as all my eyepieces are made by Televue.
An observing mate wants to try the Paracorr with his Meade 5000 32mm - 2" Plossl and his 21mm Orion Stratus. I haven't any more information on these eyepieces so I cannot use the spreadsheet. I will be gratefull if someone could tell me the paracorr settings for these two eyepieces.
Thanks in advance and regards
George (astrolabe)
Sydney Australia
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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Quote:
Thanks to everyone for the work done in the relation to the Paracorr settings. I recently bought a paracorr but I have no problems with the settings as all my eyepieces are made by Televue.
An observing mate wants to try the Paracorr with his Meade 5000 32mm - 2" Plossl and his 21mm Orion Stratus. I haven't any more information on these eyepieces so I cannot use the spreadsheet. I will be grateful if someone could tell me the paracorr settings for these two eyepieces.
Thanks in advance and regards
George (astrolabe)
Sydney Australia
It's easy, mate.
Set the Paracorr for one of your TeleVue eyepieces and focus.
Remove your eyepiece and install his. Refocus using the tunable top and look at the setting. That's the setting for that eyepiece. Write it down. REmove the eyepiece and install the other one. Focus using the tunable top. Note the setting. You can do this for a whole box of unknowns.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Astrolabe
super member
Reged: 07/08/07
Posts: 116
Loc: sydney Australia
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Don
Your opinion and advice is always valued and appreciated, thank you for the prompt reply.
Best regards
George (astrolabe)
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cyberhedz
sage
Reged: 07/29/08
Posts: 200
Loc: 38.16N, 76.28W
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since we have a bunch of paracorr users here, it seems rather fitting to ask, even if only an opinion, I'm getting a 12" dob f/4.9 and was wondering how necessary paracorr was. i do plan to get an antares 1.6 barlow and some hyperions EPs with it and plan to save up for a 2x powermate and an ethos.
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Sam
-CPC 1100, stock for now-
-Celestron 15X70 skymaster binocs-
-Celestron 2x barlow-
-Hyperion 13mm, 24mm-
Baader O-III filter
wishlist:
-Antares 1.6x barlow-
-Baader UHC,Skyglow & moon-
-lumicon or baader H-beta-
-DGM Optics NPB filter-
-Hyperion 3.5, 5, 8, 17, 21, Aspheric 31 & 36-
-Meade 5000 or WO 40mm super wide, maybe some lower powers, have to find some first -
-Antares Sentinel 80mm Semi-APO-
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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Varies. I found coma severe enough at f/5 to require a Paracorr. Other observers don't use one at f/4.5.
Here's a question: Do you want the stars at the edge to be as tight as the center? You'll need a Paracorr.
Don't care about the edge? Probably won't need one.
Don't know the answer?
Look first, buy later. There's no shortage of Paracorrs.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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See the following posts for why this post has a mistake in logic...Don
Ethos Paracorr Settings:
TeleVue's recommended settings are incorrect, according to both my eye and the two excellent calculators on this thread.
Here's what I found:
Used as 2" eyepieces in the Paracorr:
13mm Ethos--Setting 1, with the eyepiece pulled out of the Paracorr 1.5mm
8mm Ethos--Setting 1, with the eyepiece pulled out of the Paracorr 12.5mm (not practical unless a 2" skirt is added to the eyepiece)
Used as 1.25" eyepieces in the Paracorr:
13mm Ethos--Setting 4
8mm Ethos--Setting 1 with the eyepiece pulled 2.5mm further out.
It seems TeleVue's recommended settings may have been calculated using pre-production design specs. TeleVue says that the 1.25" settings for the Ethos are 5(13) and 4(8) respectively, and that isn't even close on the 8mm.
I used the empirical method of actually looking at the edge-of-field star images, and the settings I derived agreed with the 2 calculators on this thread.
The focal plane of the 8mm is 0.7" (17.78mm) below the 2" shoulder, or 0.43" (10.9mm) lower in the barrel than the 13.
If the 13 uses setting 1 in the Paracorr in 2" mode, the 8mm is going to need to be at least 10.9mm farther out than setting 1. If used with a Paracorr, there's no way around a lot of infocusing on the eyepiece/Paracorr combination. I caution any potential buyers to look at their focuser position for the 13 before you buy an 8mm--you will need around a half inch of additional in-focus.
My recommendations:
Use the 13 Ethos as a 2" and use setting 1.
Use the 8 Ethos as a 1.25" and use setting 1 and pull the eyepiece out about 2mm. This will require a LOT of infocusing.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
Edited by Starman1 (08/07/08 01:52 AM)
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Tigerider
Vendor (Televue Rep)
Reged: 02/21/06
Posts: 305
Loc: Torrance, CA.
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Quote:
Ethos Paracorr Settings:
TeleVue's recommended settings are incorrect, according to both my eye and the two excellent calculators on this thread.
<snip>
My recommendations:
Use the 13 Ethos as a 2" and use setting 1.
Use the 8 Ethos as a 1.25" and use setting 1 and pull the eyepiece out about 2mm. This will require a LOT of infocusing.
Wow thats quite a statement...
Let's see : The TV website recommends the #1 setting for the 13 Ethos also,
so how are we incorrect there ?
As for the 8 mm: Your's & our settings are 12 mm apart, which 1.25 adapter are you using on the 8 mm Ethos ?
We recommend the "lower" adapter that comes with the Paracorr.
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John Rhodes (TV Rep.)
TeleVue: NP 127is,101is,101
102,85,76,60is,60 all EP's+
Flat Field Imaging from F/4.2 - F/8.1
360mm - 990mm Focal Lengths
Celestron CGE mount
Celestron Ultima 11 & C-5
Meade Research Grade 856 (1970's)
Celestron 20 x 80
Canon 20 Da {*;*} DSLR
Canon "is" Binoculars: 10x30 & 15x50
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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John,
Yes, the 13Ethos works great at setting 1 (2").
I'm using the standard 1.25" adapter that comes with the Paracorr.
Here's the math:
The focal plane is 0.70" below the shoulder, per TV's chart.
The 1.25" adapter is 0.379" tall (calipers measurement).
That combination results in a focal plane to optimum Paracorr lens distance of 2.76mm too low for the 8mm Ethos when the Paracorr is set to setting 1, that is the 8mm eyepiece needs to go up another 2.76mm to achieve the optimum 55mm distance from focal plane to lens.
Have I missed something?
I could be wrong, but the calculator shows setting 4 would be 12.28mm too low, and that setting 1 is 2.76mm too low.
I'm forgetting something--see below
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
Edited by Starman1 (08/07/08 01:54 AM)
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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John, et al.,
My wife just pointed out how much of a bonehead I was. It took her to show me the error in my logic.
Now I eat crow....
The focal plane of the 8mm Ethos is 0.7" below the 2" shoulder.
When I put the eyepiece in the adapter, it automatically raises the eyepiece by the length of the 2" skirt (1.04"). Hence, the focal plane of the eyepiece is now 1.04-0.7 ABOVE the adapter (or 0.34"). So long as I also take into account the thickness of the adapter, the calculator should work fine.
According to the TeleVue website, that means the focal plane is above the reference surface (the bottom of the 2" skirt the eyepiece is resting on).
That means I should be able to plug the 0.34" figure into the calculator and get the proper setting for the Paracorr.
OK. I get setting 3.
It gets setting 4 for the Type 6 Naglers (agreeing with TeleVue), and setting 5 for the 22T4 (again agreeing with TeleVue), and setting 3 for the 17 T4 (same as TeleVue).
But I get setting 3 for the 8 Ethos (no agreement there--TV says 4) and setting 3 for the 16T5 (where TV says 4), but the difference is now 1 setting (0.125" or 3mm).
That says the 8mm Ethos is best used as a 1.25" eyepiece in the Paracorr.
So, John, is my math now better? Or have I overlooked something else?
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
Edited by Starman1 (08/07/08 01:56 AM)
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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Plugging the focal plane positions from TeleVue's website into Walt's calculator (and compensating for the skirts on the 12mm T4 and Ethos eyepieces), I get the following optimum(55mm spacing) settings for the Nagler eyepieces(1.25 eyepieces use adapter):
31T5--6 (there is no 6, so use setting 5)
26T5--3.3
22T4--5.2
20T5--1.7
17T4--3.2
16T5--3.7
13T6--4.0
12T4--3.9 (with 1.25" adapter)
11T6--4.0
9T6--4.0
7T6--4.0
5T6--4.0
3.5T6--4.0
2.5T6--4.0
13 Ethos--.8 (as 2")
8 Ethos--4.2 (as 1.25")
Rounded off to the nearest whole number, the settings seem to agree with TeleVue's chart.
It should be noted that TeleVue says +/- 4mm is an acceptable margin for error on the setting. Since the settings on the Paracorr are 3.2mm apart, that means there is quite a bit of leeway in the setting of the Paracorr (i.e. that if optimum is setting 4, good correction can be anywhere from setting 3 to setting 5).
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
Edited by Starman1 (08/07/08 02:27 PM)
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Zoomit
sage
Reged: 12/04/06
Posts: 282
Loc: Tehachapi, CA
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Quote:
Used as 2" eyepieces in the Paracorr:
13mm Ethos--Setting 1, with the eyepiece pulled out of the Paracorr 1.5mm
8mm Ethos--Setting 1, with the eyepiece pulled out of the Paracorr 12.5mm (not practical unless a 2" skirt is added to the eyepiece)
Don, if you would...can you confirm this is still accurate?
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Brandon
Newts: 18" f/4.6; 7.4" f/6.4
EPs: TV 26Nt5, 13E, 3-6NZ; Antares 2" 1.6x, Paracorr
Bino: 15x70, 12x50, 6x30
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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WEll, not quite.
I'm sorry if it wasn't clear.
Close, but not exact.
I was slightly mistaken in how to measure the eyepieces with a skirt.
The Ethos 13, if used as a 2", requires setting 1 (all the way out). That is close to the optimum setting. If used in the 1.25" mode, setting 5.
The Ethos 8mm, if used as a 1.25" eyepiece with the standard Paracorr adapter, requires setting 4. It is not usable in a 2" mode unless a barrel extension is added to the eyepiece, in which case the eyepiece would be pulled out 12.4mm from the Paracorr, with the PC in setting 1. In other words, this eyepiece requires the use of the 1.25" adapter in setting 4. I wouldn't bother to try to use it as a 2" eyepiece in the Paracorr. Just remember that this requires some in-focus movement of the focuser.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Fireball
sage
Reged: 03/24/06
Posts: 347
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Can somebody help me with the Meade 5000 UWA ?
I have 6.7 - 18 - 31mm.
What about Hyperion, e.g 13mm ? Or QX26mm ?
TIA
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20x90 Bino
12" Lightbridge
Meade UWAs, TV Ethoi, Pentax XW, Hyperion, AT Titan.
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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It might be helpful to review how to pick a proper setting for the Paracorr:
1) If you have a TeleVue eyepiece, set the Paracorr for that eyepiece (from the TV website) and focus. Remove the eyepiece and insert another. Focus using the tunable top on the Paracorr, not the normal focuser knobs. Note the setting, write it down, because that's the setting for that eyepiece.
2) If you don't have a TeleVue eyepiece, start in setting 1 (tunable top all the way turned out), and put the eyepiece in. Focus. Evaluate star images at edge of field. Still flared in a radial direction slightly? Move Paracorr to setting 2. Refocus. Star images at the edge better or worse? Worse? Setting 1 is your choice. Better? Move Paracorr to setting 3 and focus again. Evaluate stars at the edge. Worse? Go back to setting 2. Better? Continue to setting 4. Etc.
You will find one setting that is the best for that eyepiece. Write it down. Return Paracorr to that setting.
Remove that eyepiece, insert other eyepieces one at a time, and focus using the Paracorr tunable top instead of the focuser. Note the setting for each eyepiece where it is in focus--that's the Paracorr setting for that eyepiece. In this way, you can do a whole collection of eyepieces with experimentation only on the very first eyepiece.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Robert Provin
professor emeritus
Reged: 08/14/06
Posts: 691
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Quote:
It might be helpful to review how to pick a proper setting for the Paracorr:
1) If you have a TeleVue eyepiece, set the Paracorr for that eyepiece (from the TV website) and focus. Remove the eyepiece and insert another. Focus using the tunable top on the Paracorr, not the normal focuser knobs. Note the setting, write it down, because that's the setting for that eyepiece.
2) If you don't have a TeleVue eyepiece, start in setting 1 (tunable top all the way turned out), and put the eyepiece in. Focus. Evaluate star images at edge of field. Still flared in a radial direction slightly? Move Paracorr to setting 2. Refocus. Star images at the edge better or worse? Worse? Setting 1 is your choice. Better? Move Paracorr to setting 3 and focus again. Evaluate stars at the edge. Worse? Go back to setting 2. Better? Continue to setting 4. Etc.
You will find one setting that is the best for that eyepiece. Write it down. Return Paracorr to that setting.
Remove that eyepiece, insert other eyepieces one at a time, and focus using the Paracorr tunable top instead of the focuser. Note the setting for each eyepiece where it is in focus--that's the Paracorr setting for that eyepiece. In this way, you can do a whole collection of eyepieces with experimentation only on the very first eyepiece.
Don, your posts here have been very helpful, thank you! 
BTW, it was nice meeting you up at Mt. Pinos last weekend.
Robert
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peter k
super member
Reged: 02/03/07
Posts: 172
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Quote:
It might be helpful to review how to pick a proper setting for the Paracorr:
1) If you have a TeleVue eyepiece, set the Paracorr for that eyepiece (from the TV website) and focus. Remove the eyepiece and insert another. Focus using the tunable top on the Paracorr, not the normal focuser knobs. Note the setting, write it down, because that's the setting for that eyepiece.
2) If you don't have a TeleVue eyepiece, start in setting 1 (tunable top all the way turned out), and put the eyepiece in. Focus. Evaluate star images at edge of field. Still flared in a radial direction slightly? Move Paracorr to setting 2. Refocus. Star images at the edge better or worse? Worse? Setting 1 is your choice. Better? Move Paracorr to setting 3 and focus again. Evaluate stars at the edge. Worse? Go back to setting 2. Better? Continue to setting 4. Etc.
You will find one setting that is the best for that eyepiece. Write it down. Return Paracorr to that setting.
Remove that eyepiece, insert other eyepieces one at a time, and focus using the Paracorr tunable top instead of the focuser. Note the setting for each eyepiece where it is in focus--that's the Paracorr setting for that eyepiece. In this way, you can do a whole collection of eyepieces with experimentation only on the very first eyepiece.
This is a very useful post--thanks, Don. However, there seems to be something I'm missing. The above quote suggests (to me) that for a given scope there is a single, fixed point of best focus for the Paracorr, and once this is established, focus is obtained for different eyepieces by use of the tunable top, leaving the focuser untouched, regardless of eyepiece. This does not seem consistent with earlier posts, including Don's just a couple up, which states that additional in-focus is needed for the Ethoses. Can someone (Don?) clarify?
Thanks much.
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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Sure.
There is one distance from the paracorr lens to the eyepiece's focal plane that results in the best coma correction.
But how do you find it?
Answer: correct the coma completely for one eyepiece. You have found that eyepiece's lens-to-focal plane distance.
Insert another eyepiece and focus using the Paracorr top. Note that while doing so, you are effectively moving the eyepiece in and out to adjust the eyepiece position relative to the focal plane of the telescope plus Paracorr. This is really no different than you would do adjusting the focus of the eyepiece in the focuser without the Paracorr, only instead of moving the focuser, you're moving the Paracorr's top.
What it implies, and it would be true, that there is only one position for the focal plane of the telescope, whether the Paracorr is used or not. The Paracorr moves the focal plane position slightly, but the idea is the same as having no Paracorr--you are moving the focal plane of the eyepiece to the focal plane of the scope in order to focus.
The Paracorr does not focus, per se, so you are not focusing the Paracorr, merely putting it into the system to modify the focal plane slightly.
Now, if your eyepiece's focal plane is low in the eyepiece, you will have to move the eyepiece back relative to the Paracorr's lens in order to maintain the correct distance to the lens for best correction. But that means the focal plane of the system is now higher than before. In order to bring the focal plane of the paracorr plus eyepiece to be coincident with the focal plane of the telescope, you will have to move the Paracorr plus eyepiece in to make the focal planes coincident.
So, eyepieces with low focal planes require more out travel with the Paracorr and more inward movement of the focuser.
In a sense, that's no different than an extension tube. Add an extension tube to the focuser, and you will have to move the focuser in to get to focus: eyepiece goes out, focuser goes in.
Hope that makes it clearer.
--------------------
Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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interalia
newbie
Reged: 10/15/07
Posts: 3
Loc: Space Coast, Florida
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A formula I have found useful for finding paracorr settings (in the newer paracorr) when the distance to the focal plane from the eyepiece seat is known is:
8(13/40 - f) or, what is equivalent, 8(0.325 - f)
The attached chart illustrates where the eyepieces in the TeleVue table lie along the range of motion available and the settings best for them. It is from the two constraints that the range of motion is known to be half an inch and that all the eyepieces TeleVue gives settings for must find those settings correctly that the above formula is derived.
Hopefully it may be of some use, and the chart be helpful.
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Stephen
18" Le Dob - télescope provenu de Montréal très compact avec miroir de Pegasus
plateforme équatoriale fait par Osypowski
17mm, 13mm, 8mm Ethoses
Pentax XW's, Nagler t4's
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llanitedave
Humble Megalomaniac
Reged: 09/26/05
Posts: 12932
Loc: Amargosa Valley, NV, USA
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I just got a chance to play with the Paracorr settings for my 8mm and 17mm Hyperions. For both, the best setting seems to be 1.
I was looking not so much for coma correction, which seems to be pretty good at all the settings, but the you can definitely tell a difference in the on-axis star images as you adjust.
I also tried different setings for the Hyperion 31mm Aspheric, and it seems to be giving me the tightest images at setting 5. However, it's not very sensitive to the Paracorr setting, and I might have to try it a few more times to be sure.
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"Since the process of science generates more mysteries than it solves, I predict that we'll never learn everything: and we'll continue to generate new ignorance at the speed of knowledge."
"S.O.E." (Sauron's Other Eye), with 16" Royce conical mirror: A permanent work in progress.
10" Homebuilt dob, old Coulter mirror
Under Construction: The "Eye of Sauron" Observatory!
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phanfave
Pooh-Bah
Reged: 08/21/06
Posts: 1436
Loc: Pioneer Valley
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Reread this thread again. First of all thanks to everyone! It's a must read for using a Paracorr and a fast scope. I've got a few Ethos and the shorter ones I have the 2" barrel extension skirt. Is this going to give me too much distance away from the top lens? Can I use these in setting 1 and get good correction? I'd really like to use them as 2" eyepieces with the skirt if possible. Thanks for your input.
Sean
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IDA Member
Astro League At-Large Member
Amherst Area Amateur Astronomer Association
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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Quote:
Reread this thread again. First of all thanks to everyone! It's a must read for using a Paracorr and a fast scope. I've got a few Ethos and the shorter ones I have the 2" barrel extension skirt. Is this going to give me too much distance away from the top lens? Can I use these in setting 1 and get good correction? I'd really like to use them as 2" eyepieces with the skirt if possible. Thanks for your input.
Sean
The 13 and 10 Ethos use setting 1 as a 2" eyepiece, but the 8 and 6mm Ethos use the 1.25" adapter and setting 4. You unfortunately cannot use these two as 2" eyepieces in the Paracorr because the correct position for them would be with the eyepieces pulled 1/2" out of the Paracorr and using setting 1. It's actually more secure to use them as 1.25" eyepieces with the Paracorr.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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phanfave
Pooh-Bah
Reged: 08/21/06
Posts: 1436
Loc: Pioneer Valley
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Thanks Don. That makes sense. But it also makes me wonder if the 2" extension skirt would work too since the eyepieces will be further out from the Paracorr compared to using in the 2" mode (or even 1.25" mode with the adapter or the high hat). I picked up the 2" extension this past weekend at NEAF (and they have been slightly redesigned...black anodized now) and have them on the 13,10,8, and 6. I'll get to try them all out tomorrow with the skirt and the Paracorr and will report back here. I'm hoping they work well enough to keep them on.
Here's a pic with the extension on and off:
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IDA Member
Astro League At-Large Member
Amherst Area Amateur Astronomer Association
Edited by phanfave (04/22/09 10:34 AM)
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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Yes, with a 2" extender, you should be able to use the 8 and 6 Ethos as 2" eyepieces in the Paracorr. As I read the calculator, use the paracorr in setting 1, then pull the eyepiece out until the "shoulder" of the upper eyepiece sits 1/2" above the top of the Paracorr(leaving 1/2" of the silver 2" skirt showing).
The 13 and 10 don't need the extender because the length of the extender will prevent them from fully seating in the Paracorr. You would use them without an extender, in 2" mode, at setting 1.
If you are thinking about using the 2" extender to use 2" filters, don't worry--2" filters thread directly to the bottom of the Paracorr. And since the Paracorr doesn't have a "safety undercut", it's easily removable from the focuser to attach a filter to its bottom.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
Edited by Starman1 (04/22/09 11:37 AM)
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phanfave
Pooh-Bah
Reged: 08/21/06
Posts: 1436
Loc: Pioneer Valley
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Thanks again! It would have been nice for simplicity sake to use the 13 and 10 with the 2" extension but as you pointed out it's neither necessary nor possible.
Sean
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IDA Member
Astro League At-Large Member
Amherst Area Amateur Astronomer Association
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jonstarrysky
sage
Reged: 01/03/09
Posts: 225
Loc: England, U.K.
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try using one of these stops to precisely position the Ethos if using the extension barrel:
http://www.cloudynights.com/ubbthreads/attachments/3092105-2009%20Apr%2028%20007%20small.jpg
http://www.agenaastro.com/Baader-Hyperion-2-Finetuning-Stopring-p/paar-bp-hyp-stop.htm
My thinking is as above. E13=#1 (2" mode). E8=#4 (with 2-1.25" adapter). I may leave the paracorr 2-1.25" adapter on my E8 permanently. Simlifies swapping between eg E8, E13, 26T5. Or to use the barrel extension as indiccated.
2" filters at the bottom of the paracorr ? Yes, but youre taking off/ on a mighty train of glass, you dont wanna drop it.
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Orion XT10i
Televue eyepieces :-)
Assorted binoculars
Astro-Systems (U.K.) FG-1 6" reflector
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deSitter
Carpal Tunnel
Reged: 12/09/04
Posts: 2925
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Here's a handy (for me at least) Paracorr trick - defocus so that the shadow of the secondary is clearly visible but not too large - and tune the Paracorr so that the pattern is symmetrical in the out-of-focus center stars as well as the out-of-focus edge stars. Coma will make a lopsided pattern with the shadow close to the inner edge.
-drl
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JoshH
member
Reged: 11/07/08
Posts: 47
Loc: Jefferson City, MO
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Anyone have any suggestions for the proper setting on the University Optics 40mm MK-70? I tried this eyepiece for the fist time in my 16" F4.5 dob along with the Paracorr and I was quite happy with the performance. There was still some coma present, but it made a totally un-usable eyepiece in my dob into an eyepiece I will probably use often. The sky background was a bit too gray for my liking in what I would call pretty good skies, but it made a nice view for large objects like the double cluster as it gave a 1.3 deg FOV. The exit pupil is a bit large but I never saw the shadow from the secondary. I found that position 2 seemed to give the best view, any other comments?
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16" F4.5 Astrosystems Telekit, Galaxy Optics Primary
Meade LX-50 8" F10 SCT Magellen II DSC (For Sale)
Intes Micro MN-56 Maksutov Newtonian
Orion 100mm F6 Achromat
Orion ST-80 F5 Acrhomat
Unistar Alt-Az Mount
Celestron CI-700 Mount
UO 40mm MK-70, 26mm Nagler, 20mm Pentax XW, 13mm Ethos, 8mm Ethos, 4.7mm 5k UWA, TMB Planetary Set, Paracorr.
Modified Canon 400D
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