324 replies to this topic

[erik]

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!

[Lawrence Sayre]

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.

[square_peg]

Meade 5K 34mm SWA - Paracorr setting 2
Siebert 34mm Observatory Series - Paracorr setting 1
Meade 36mm QX - Paracorr setting 1

[ausastronomer]

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

[Starman1]

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.

[Lawrence Sayre]

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.

[asian_hillbilly]

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.

[walt r]

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

[Lawrence Sayre]

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.

Attached Files

•  1757078-Paracorr Setting Calculator.xls   85.5KB   1382 downloads

[Lawrence Sayre]

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.

[Lawrence Sayre]

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.

[walt r]

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

[Lawrence Sayre]

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.

[walt r]

See attached Excel Spreadsheet.
Have fun.

walt

Attached Files

•  1758433-ParaCorr.xls   18KB   1713 downloads

[Starman1]

Just measured adapter on current Paracorr: 0.379" or 9.69mm.
Hope that helps.

[Lawrence Sayre]

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).

[Lawrence Sayre]

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.

[Starman1]

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.

[Lawrence Sayre]

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.

[Lawrence Sayre]

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.

[Starman1]

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.

[Starman1]

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.

[Lawrence Sayre]

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.

Attached Files

•  1766582-Paracorr Setting Calculator.xls   47KB   910 downloads

[Starman1]

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.

[astrodon]

Thanks for the work guys!