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List of Paracorr settings for all brands of EP's

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#151 rprice

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Posted 27 June 2011 - 01:04 PM

Mike,

Thanks for the info. I have the PC1. If I were to use setting "3" and a piece of clear tape to set the focal position of my scope, should I take off the 1.25"-2" adapter? Should I place the tape directly over the top of the Paracorr without the adapter? That's what I would think, but I like to remove all ambiguity.


Yes, when using setting 3 the tape should be placed across the top of the PC1 without the 1.25" adapter.

I'm definitely not buying the PC2. Forgetaboutit. I'm either going to make the PC1 work for me or I'm going to sell it. So far this gizmo is not worth all the trouble.



I will agree with you on this point. My scope is a 24" f/3.65 and I recently purchased a Paracorr2 to see how it compared to the PC1. The short answer is there is no discernable difference between the two Paracorr versions from a visual observing standpoint for my scope. I am sure that if I was CCD imaging over a large field of view I would see a slight improvement in the quality of the star images at the edge of my image with the PC2, but visually there is no difference.

I compared the PC1 and PC2 using a 22NT4 eyepiece in my scope, going back and forth several times carefully evaluating the quality of a star image at center, halfway out, 3/4 of the way from center to edge and right at the field stop. There was virtually no difference between the two Paracorrs.

There have been a few comments going around that the Paracorr2 has better coatings than the somewhat older PC2, so I evaluated limiting magnitude between the two PCs. I looked at several star fields, going back and forth between the PC1 and PC2, and I could see no difference.

In all honesty, I really did not expect to see a difference between the two Paracorrs. If you carefully examine the performance graphs provided by Televue for the PC1 and PC2, while the PC2 performance is completely diffraction limited for my f/3.65 scope, even the older PC1 brings the off-axis spot size for a star at the edge of the 22NT4 field stop within a factor of 2 or so of diffraction limited. This is still a very tight image and its defects would not be visible at the very low power of the 22NT4; you need at least 25 to 30X per inch to start seeing details of the diffraction disc and the 22NT4 is only giving me 5X per inch.

So what's going on?? Well, in a nutshell, coma is not the problem; it is off-axis astigmatism (and a small amount of field curvature) in the long focal length, ultra-wide angle eyepieces that I use in my scope. Many people state that they see lots of coma in their fast Newtonian reflector when they do not use a Paracorr, but I submit they are not seeing coma at all; they are seeing predominantly off-axis astigmatism generated by the eyepiece due to the fast f/#. This was pointed out over 20 years ago in the book Telescope Optics by Rutten and Van Venrooij, and we all know that Newtonians have gotten much faster than the f/5 versions that were evaluated in that book.

Star images appear better when you add the Paracorr not because you have eliminated coma, but because you have slowed the f/# down by 15% reducing the off-axis astigmatism produced by the eyepiece. In my case it changes my f/3.65 scope to an f/4.2 scope. This 15% change may not sound like much, but I believe that the off-axis astigmatism generated by the eyepiece is inversely proportional to the f/# squared, so this would be a 32% difference.

This new generation of ultra-fast Newts is really catching on and I believe rightly so. I love standing on the ground half the time and only going up two short steps to look at an object near the zenith. And my scope is very compact and easy to move in and out of the garage. You just need to be aware that even the best available long focal length (> 20mm), wide angle (>65 degrees AFOV) eyepieces are going to have poor edge performance, Paracorr not withstanding. Shorter focal length / higher power eyepieces work much better because they do not exhibit near the off-axis astigmatism; Pentax XW's 10mm and shorter, Radians 14mm and shorter work quite well at f/3.65 (without PC) with only minor defects in images near the field stop. I am anxiously awaiting the new Delos line from Televue, hoping that they will perform well at these fast f/#s.

Sorry for the long winded reply.

Ron
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#152 Sarkikos

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Posted 27 June 2011 - 01:51 PM

Ron,

Thanks for the "long winded reply." :grin: I am glad to hear that apparently the only observable difference between the PC1 and PC2 is the wider range of in-focus settings for the PC2. That will probably be particulary true in my Newts, which are all f/4.8 and slower. Hopefully I can work around the not-enough-in-focus problem in my PC1 by using the negative profile adapter I ordered last night.

Unless the observer is experienced at evaluating eyepieces, it can be difficult to distinguish among coma, astigmatism, field curvature, etc. I don't presume to have the level of expertise as some of the experts on CN. If the image looks better to my eyes, I am happy. Also it should be kept in mind that at low power, the observer may start seeing whole eye astigmatism, which we cannot blame on the scope, the eyepiece or the Paracorr. FWIW, I've noticed that sometimes SCT users, who might not be accustomed to wide exit pupils, are surprised at the level of astigmatism that can be seen in Newts at low power, whether from eyepiece or eyeball or both.

Mike

#153 Starman1

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Posted 27 June 2011 - 02:32 PM

I evaluated both older and newer Paracorrs in my f/5 scope.
My findings were totally expected:

31 Nagler and 21 Ethos had improved edge-of-field stars in the Type 2 because of the lower setting possible on the Type 2. The Type 1's lowest setting wasn't low enough for optimum edge correction.

I saw no other obvious differences (I didn't expect to at f/5 because f/5 was fully-corrected by the Type 1 Paracorr).

Whereas Ron is mostly right about many inexpensive 2" eyepieces and astigmatism, the Nagler he compared, and my Ethos eyepiece set, has no edge-of-field astigmatism. The design is free from that problem down to f/4.

In my case, f/5 is not short enough to induce any form of astigmatism at the edge of the field in the Ethos eyepieces, yet, without the Paracorr, all my eyepieces display what is, to my eye, horrible coma. The star images are probably 10X as long, radially, as they are circumferentially. With the Paracorr, the stars at the edge are small points.

You see, coma is a linear problem that starts in the center and gradually increases toward the edge. The linear size of a comatic star depends solely on the distance from the center of the focal plane of the scope.
But the apparent size of the comatic star image depends on magnification.

So, for example, a 100 degree 21mm eyepiece will have the same magnification as a 21mm 50 degree eyepiece, but because the radius of the field will be twice as large in the 100 degree eyepiece as in the 50 degree eyepiece, the linear AND apparent size of the comatic star images at the edge of the field in the 100 degree eyepiece will be twice as big, and appear worse.

Double the magnification but keep the apparent fields the same, and the 50 degree eyepiece will see a comatic star image at the edge which has half the linear size, but at twice the magnification. Hence, the comatic images at the edge will appear the same as at half the power. The same is true of the 100 degree eyepiece. The comatic star images appear twice as wide as the 50 degree eyepiece, and it displays the same difference with the 50 degree eyepiece as at the lower power.

So the visibility of coma is related to the apparent field of the eyepiece: Wider = More coma at the edge.

And if the eyepiece is fully corrected for astigmatism at the f/ratio you are using, you will see coma, and perhaps de-focusing caused by field curvature, at the edge, but not astigmatism. Of course, field curvature, which might cause the stars to bloat, may make coma appear worse than it is.
I had an eyepiece that had horrible coma at the edge that the Paracorr corrected, leaving small, out-of-focus, star images due to that eyepiece's inherent field curvature. I dealt with it by focusing at the 50% field point and letting my vision correct for the center and edge. That worked because it was a low-power eyepiece.

I found myself surprised at how bad coma actually appeared at f/5. I thought, and still think, that a coma corrector is essential at f/5 to produce good star images over the entire field of view. Looking at the correction charts on the TeleVue site corroborates what I see.

But Ron is right that if the eyepiece has substantial astigmatism, correcting the coma will not be sufficient to correct the star images at the edge of the field. If you're trying to correct an Erfle eyepiece, for instance, the star images at the edge after coma correction will still appear non-stellar.
But, the best-corrected eyepieces of today will have star images tight enough at the edge, if corrected by a coma corrector, to see a globular cluster exit the field with the core still completely resolved. I am certain of that--I've seen M15 exit the edge of my 13 Ethos with the core still resolved into tiny pinpoint star images.
The correction at f/4 won't be as perfect, but the difference will not be that bad. The coma-corrected f/4's star images are still WAY better than the non-coma-corrected f/5's.

#154 rprice

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Posted 27 June 2011 - 04:55 PM

Don,

Whereas Ron is mostly right about many inexpensive 2" eyepieces and astigmatism, the Nagler he compared, and my Ethos eyepiece set, has no edge-of-field astigmatism. The design is free from that problem down to f/4.



That is an interesting statement; the word "no" is pretty absolute. I would appreciate your referring me to where this is stated in Televue literature or elsewhere.


In my case, f/5 is not short enough to induce any form of astigmatism at the edge of the field in the Ethos eyepieces, yet, without the Paracorr, all my eyepieces display what is, to my eye, horrible coma. The star images are probably 10X as long, radially, as they are circumferentially. With the Paracorr, the stars at the edge are small points.



What you are describing does not sound like coma; the comatic blur does not have a 10 to 1 aspect ratio like that. If you place a bright star at the edge of the field and focus in and out, you will probably find that the very long radial image will cross over into a circumferential one - this is what I see at the edge of the field with long focal length /wide field eyepieces and it is astigmatism, not coma.

Your description of coma as varying linearly with field is correct. And since coma varies linearly and if you keep the AFOV the same over a range of magnifications, then the coma will appear roughly the same at all of the different magnifications. But it is common for fast Newtonian users to employ a Paracorr with their lowest power eyepieces, but feel they do not need it with shorter focal length eyepieces.

For example, I always use the PC when using my 22NT4 or similar focal length, wide angle eyepiece. But when I switch to higher power, I don't use the PC. For example, I can use 10, 7, 5 and 3.5 XW's, or short fl Nagler T6s without a PC and the field looks sharp except for the very edge, where the image degrades somewhat. This is possible because very high quality short focal length eyepieces are well corrected for off-axis astigmatism at fast f/#s, so in this case all I am seeing is coma, and nothing else. The problem of off-axis astigmatism at fast f/#s is only present at the long focal lengths and ultra wide fields. Off-axis astigmatism scales linearly with eyepiece focal length; a 20mm eyepiece of a given design will have 4 times as much as a 5mm eyepiece of this same design.


But, the best-corrected eyepieces of today will have star images tight enough at the edge, if corrected by a coma corrector, to see a globular cluster exit the field with the core still completely resolved. I am certain of that--I've seen M15 exit the edge of my 13 Ethos with the core still resolved into tiny pinpoint star images.
The correction at f/4 won't be as perfect, but the difference will not be that bad. The coma-corrected f/4's star images are still WAY better than the non-coma-corrected f/5's.


The first part sounds perfectly reasonable at f/5. With the PC in place the Ethos eyepiece is working at almost f/6 (f5.75), so its performance should be superb. You did not state what focal length the Ethos is, but the shorter the better. I also see a similar view when using the 10mm or 7mm XW without a PC; I let a bright globular drift across the field and it stays resolved to the core up until the last 5 degrees of apparent field.

My point in all this is that a specific group of eyepieces - 20mm and longer focal length with AFOVs of 70 degrees or more - exhibit off-axis astigmatism with sub f/4 primary mirrors. And I am not talking about war surplus Erfles, I am talking about the best eyepieces money can buy in this group. Extrapolating the performance of these long focal length ultra-wide angle eyepieces at f/5 to what happens at f/3.65 and faster (f/3.3 scopes are in production now) is simply not valid.

And I am not trying to be critical of the eyepieces that are available; the Nagler, Ethos and Pentax XW eyepieces are fantastic and better than anything that has been available to the amateur in the past for low power wide angle view through fast Newtonians. My comments are intended to be informational and to assist others that may own or intend to purchase one of these ultra-fast Newts.

Clear skies,

Ron

#155 Starman1

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Posted 27 June 2011 - 06:41 PM

Ron,
Al Nagler himself has stated that all their eyepieces are tested at f/4 to have no extra aberrations added due to the fat light cone with its oblique angles. The only design he admitted they have produced that did have astigmatism at the edge of the field were the original Widefields.
He told me that the Panoptic line was developed after the introduction of the Paracorr where, when coma was corrected, the residual astigmatism became visible in the Widefields. After that, their design goal was zero astigmatism.
[and zero angular magnification distortion, but that's another story].

The comatic blur is shaped more like a narrow V that has a faint extension beyond the V shape. It is not astigmatism because it does not change from radial to circumferential on the other side of focus. I suspect many people do not view in skies dark enough to reveal the full extent of the comatic star image. 10X as long as wide might be a slight exaggeration, but it is not unusual for the star image to be many times as wide as the Airy Disc if coma is present.
Coma does not end with the edge of the visible image--it extends to fainter than the eye can see. The camera can capture it, though. Here is a good example of what I see without a coma corrector:
http://www.astronomy...telescope99.jpg Would you not describe that as 10X as long as wide when the star image is at the point?
I would.

As for why newtonian users do not employ coma correction at higher powers, I am mystified. I see the exact same coma with my 8mm Ethos barlowed as with my 21 Ethos by itself. I have not see a high enough magnification that the coma was not present. Which is why I use a coma corrector at all magnifications and with all eyepieces. I see it in f/6 scopes, too. It's a matter of expectations: I want center-of-field images at the very edge. I don't get that, but it's close at f/5 with a coma corrector.

I am very familiar with aberrations in eyepieces, and I've owned over 300 of them. I know exactly what astigmatism looks like. One of the ironies of eyepiece design is that leaving positive angular magnification in the eyepiece and solving for rectilinear distortion, as is done on many eyepieces designed for terrestrial use, results in a smaller apparent size for the comatic blur at the edge of the field. That's the case for the Pentax XWs, which have less RD, but as a result, more AMD. Excessive AMD (on a wider design) is probably one of the reasons Pentax did not go wider than the 70 degree field (that, and the fact their spotting scopes don't illuminate a field much wider than that).

One thing I have experienced is that a lot of longer focal length eyepieces have more field curvature than shorter focal lengths (the Pentax XWs are an exception--it is the 20mm and 14mm that have the most field curvature). This tends to bloat the star images at the edge of the field, and exaggerate both coma and astigmatism. The worst "coma" I've seen in a scope was an f/4.3 newtonian without coma correction, using such an eyepiece. The scene in Star Wars when they go to superluminal speeds and you are looking at the stars from the bridge of the Millenium Falcon is only a *slight* exaggeration of what I saw (and some small scopes have star images that look like that all the time).

#156 rprice

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Posted 28 June 2011 - 12:32 AM

Hi Don,

Your conversation with Al Nagler is interesting, but I am not able to dismiss the studies and evaluations that Rutten and Van Venrooij did in their book, and there are others that are more recent. And more importantly, the notion that Nagler and Ethos eyepieces are "perfectly" corrected for f/4 and faster cones is difficult to believe when I see something different in the eyepiece. It would be wonderful if Televue would provide performance graphs or spot diagrams for the long focal length Naglers and Ethos eyepieces showing how they performed at incremental f/ratios from f/5 to f/3. I commend them for providing the performance graphs for the PC1 and PC2.

Regarding your description and picture of coma, that is all quite reasonable. However, what I see at the edge of the field in my 24" f/3.65 with the 22NT4 and PC2 is not coma. It is a blur that goes from radial to circumferential in appearance and is predominantly astigmatism. Without the PC2, I see basically the same thing, only more severe.

As others have pointed out in some of the "fast scope" discussion threads, many have jumped onto the sub f/4 Newtonian bandwagon before all of the details and nuances of these scopes have been proven out, myself included. I am convinced, though, after using my new scope over a hundred times this past year that it is a resounding success and will give me a lifetime of viewing pleasure. But I am also convinced that the unique issues of eyepiece performance in f/3.65 and faster scopes is still being 'shaken out', especially the lowest power, ultra wide field eyepieces.

The fact of the matter is probably that neither the PC2/Nagler or PC2/Ethos combination performs "perfectly" with the sub f/4 Newtonians, but I believe these two are the best choices you have right now at any price. I, too, want center-of-field images at the edge. So, one has to decide if it is worth spending $1000 to $1300 for a low power wide field combo that gives you significantly improved but not "perfect" performance, or wait until something better comes along.

Thanks for your comments.

Clear skies,

Ron

#157 photiost

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Posted 08 February 2012 - 08:08 PM


This being a super long thread ..

I would just like to ask if anyone has finally compiled a table showing the Paracorr setting(s) for different eyepieces.

#158 Sarkikos

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Posted 23 February 2012 - 02:37 PM

I am slowing determining the settings for my eyepieces. A few days ago I found that the setting for an ES 82 deg 30mm eyepiece is about 2.25. This was in my Paracorr I. I was using a 10" f/4.7 Dob. I primed the Paracorr and focuser with my ES 100 deg 9mm at setting 2.

A setting of 2.25 for the ES 82 30mm produced sharp stars across the FOV. The Double Cluster looked especially nice. I recall seeing a little grouping of reddish stars within the following cluster. Very sharp, good color rendition.

Mike

#159 Richard Low

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Posted 09 May 2012 - 09:20 AM

This being a super long thread ..

I would just like to ask if anyone has finally compiled a table showing the Paracorr setting(s) for different eyepieces.



Here is a working list, perhaps someone could review on its accuracy. Kindly add or edit where necessary.

Paracorr setting 1
Meade QX 36mm
Meade Series 4000 UWA 14mm
Pentax XW 14mm, 20mm
Speers-Waler variable 5-8mm
Siebert Observatory Series 34mm
Televue Ethos 10mm, 13mm in 2" mode
Televue Nagler T5 20mm, 31mm
Televue Nagler T2 20mm
Televue Nagler 13mm (original) in 2” mode
Televue Panoptic 41mm, 35mm, 27mm,
Televue Panoptic 22mm in 2” mode
Televue Widefield 32mm

Paracorr setting 2
Explore Scientific 100° 9 mm, 14 mm
Meade 5K 34mm SWA
University Optics 40mm MK-70

Paracorr setting 3
1rpd 30mm
Pentax XL 40mm
WO UWAN 28mm
Televue Nagler T4 17mm
Televue Nagler T5 26mm

Paracorr setting 4
Televue Ethos 3.7mm, 6mm, 8mm in 1.25" mode
Televue Nagler 1.25” originals, T5s, T6s – all in this series
Televue Radians – all in this series
Televue Panoptic 15mm, 19mm, 24mm
Televue Zooms – all in this series
Televue Plossls 8-32mm

Paracorr setting 5
Explore Scientific 100° 20mm
Explore Scientific 82° 4.7mm, 14mm
Meade Series 4000 UWA 8.8mm in 2” mode
Televue Ethos 17mm, 21mm
Televue Ethos 10mm, 13mm in 1.25" mode with TV Hi-Hat 2”-1.25” Adaptor
Televue Nagler T5 31mm
Televue Nagler T4 22mm
Televue Nagler T4 12mm in 1.25" mode
Televue Nagler T2 12mm, 16mm in 1.25" mode
Televue Nagler 9mm (original) in 1.25" mode

----------------

Paracorr Type 2

Paracorr setting A
Pentax XW – all in this series
Televue Ethos 17mm, 21mm
Televue Nagler T5 31mm
Zeiss Abbe Orthos – all in this series

Paracorr setting B
TV Ethos 6mm, 8mm in 1.25" mode
Televue Nagler T4 22mm

Paracorr setting C
Explore Scientific 100° 20mm

Paracorr setting D
Televue Ethos 3.7mm in 1.25” mode
Televue Nagler T6s – all in this series
Televue Nagler T4 12mm
Televue Nagler T5 16mm
Televue Radians – all in this series
Televue Panoptic 19 & 24mm
Televue Nagler Zoom 2-4mm, 3-6mm
Televue Plossls 8-32mm

Paracorr setting E
na

Paracorr setting F
Televue Nagler T4 17mm
Televue Nagler T5 26mm

Paracorr setting G
Televue Nagler T5 20mm
Televue Panoptic 35mm

Paracorr setting H
Televue Ethos 3.7mm, 6mm, 8mm in 2” mode
Televue Panoptic 41mm, 27mm
Televue Plossl 40mm

#160 nevy

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Posted 21 July 2012 - 11:52 AM

Does anyone know the best setting for a tv 55mm plossl ( smoothside) for the Paracorr type2 ?

#161 nevy

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Posted 25 July 2012 - 10:30 AM

Does anyone know the best setting for a tv 55mm plossl ( smoothside) for the Paracorr type2 ?

No need to answer this question, I tried it last night at f5 and it doesn't need one , it's pretty sharp at the edges ,( at F10 it's superb) ;-/

#162 Starman1

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Posted 25 July 2012 - 11:07 AM

Since that eyepiece produces an 11mm exit pupil in your dob, do you notice the shadow of the secondary? Generally people who have f/5 dobs rarely go longer than about a 31-35mm eyepiece focal length.

#163 nevy

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Posted 25 July 2012 - 11:47 AM

Since that eyepiece produces an 11mm exit pupil in your dob, do you notice the shadow of the secondary? Generally people who have f/5 dobs rarely go longer than about a 31-35mm eyepiece focal length.

No I didn't , I didn't expect too much from it in the dob as I bought it mainly for the C11 but I was quite surprised at how good it performed in the dob , I like it alot. The only problem I had was that I needed to pull the eyepiece right to the top of the focuser to achieve focus ,so for safety I will put the tv barrel extender on it next time.

#164 Sarkikos

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Posted 15 August 2012 - 06:57 AM

Last Sunday night I took my family to a dark site for the Perseids. To save room in our vehicle, I brought along my 5" f/5 Dob instead of the 10".

While I was there, I tried my Baader Hyperion Zoom in the Paracorr Type I to determine the best setting. I had attempted the Zoom in 1.25" mode before, but of course there was not enough in focus.

I thought I had attempted 2" mode with my 10" Dob and it had not worked (not enough in focus). But this time I made sure to prime the 5" with a TV Plossl 25mm in the Paracorr, and to change the Zoom to 2" mode.

I discovered that the Baader Zoom would indeed come to focus in 2" mode at setting 1. The stars were nice little points of light from center to edge. They were still in focus - or very nearly so - whether the Zoom was at 24mm or 8mm or anywhere in between. Only a very small tweak of the focuser was needed, if at all, at 8mm vs 24mm.

The next time I take my 10" Dob to the dark site I'll retest the Zoom in 2" mode in my Paracorr, being sure to prime it first with the TV Plossl. I'm pleased that the Baader Zoom works well in the Paracorr, since that is the eyepiece that sees the most sky time in my Dobs.

Mike

#165 Sarkikos

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Posted 15 August 2012 - 07:22 AM

Recent updates for eyepiece settings in Paracorr Type 1 - the good, the bad and the ugly!

Baader BGO 9mm: not enough in focus
Sky Watcher Super Plossl 9mm: not enough in focus
Edmund RKE 12mm: Setting 4.75
Baader BGO 12.5mm: not enough in focus
Brandon 16mm: Setting 4
Baader BGO 18mm: not enough in focus
Surplus Shed WF Kellner 19.9mm: Setting 2.5 (for what it's worth :grin:)
LOMO Ortho 20mm (12.5x microscope EP): Setting 4.5
Russel RK 20mm: not enough in focus
Faworski Super Abbe Ortho 24mm: Setting 3.75
Sterling Plossl 25.1mm: not enough in focus
Baader Mark-II Zoom (2" mode only): Setting 1 (for all focal lengths)
ES 82deg 30mm: Setting 1.5
Orion Ultrascopic 35mm: not enough in focus
Vixen Ortho 40mm: Setting 3.5

Mike

#166 Starman1

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Posted 15 August 2012 - 10:14 AM

Mike,
Since most of these are 1.25" eyepieces, what you need for the ones that require more infocus is an adapter that allows the eyepiece to move substantially closer to the Paracorr's lens.
Here is what you need:
http://www.astrosyst...ieceadapter.htm
For a lot of eyepieces, it's worth its weight in gold.

#167 Sarkikos

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Posted 22 August 2012 - 08:20 AM

Yes, thanks, Don. I already purchased one of those awhile back. In fact, I think it may have been you that gave me the advice at that time!

The only downside to the adapter is that you need to use a little hex key to secure or remove the eyepiece. I guess I could buy multiple adapters for all my 1.25" eyepieces that won't come to focus any other way in the Paracorr. But that would cost some serious money for me.

:grin:
Mike

#168 Sarkikos

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Posted 22 August 2012 - 08:26 AM

Update on the Baader Hyperion Zoom: It will also work in my 10" f/4.8 Dob with Paracorr Type 1 Setting 1, as it did in my 5" f/5 Dob. (I primed the Paracorr with my TV Plossl 25mm.) That is what I expected. The particular Newt that the Paracorr is in should not matter.

However, the Baader Zoom must be in 2" mode in order to come to focus.

Mike

#169 Starman1

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Posted 22 August 2012 - 09:37 AM

Yes, thanks, Don. I already purchased one of those awhile back. In fact, I think it may have been you that gave me the advice at that time!

The only downside to the adapter is that you need to use a little hex key to secure or remove the eyepiece. I guess I could buy multiple adapters for all my 1.25" eyepieces that won't come to focus any other way in the Paracorr. But that would cost some serious money for me.

:grin:
Mike

Adjust the small setscrew in the adapter so the fit of the eyepiece is tight enough you have to "rotate it in" and "rotate it out". Then, every 1.25" eyepiece can be placed in and removed from the adapter without having to snug down the setscrew on each one.

#170 Sarkikos

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Posted 22 August 2012 - 10:09 AM

Thanks, I'll try that.

#171 Busguy

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Posted 22 August 2012 - 12:12 PM

Anyone input the Delos line into the settings?

#172 Starman1

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Posted 22 August 2012 - 03:31 PM

Anyone input the Delos line into the settings?

All the Delos eyepieces except the 17.3 and 14 will use setting "D" with the Paracorr's supplied 1.25" adapter.
The 17.3 and 14 will require setting "A" for right now, also using the 1.25" adapter.
There may be another, lower-profile, 1.25" adapter for the 17.3 and 14.0 a little later on, as the "perfect" correction for those two will require a setting a little farther in than setting "A".
But "A" will still correct a lot better than no Paracorr, in the same way that the original Paracorr didn't completely correct the 31 Nagler or 21 Ethos but they still were improved a lot over no Paracorr.

#173 miguel gonzalez

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Posted 16 September 2012 - 03:31 AM

Hi all..

I have TV paracorr type 1.

And I have Docter/Zeiss 12.5mm UWA and Nikon Nav Sw 10 mm eyepieces.
What settings should I use in the Paracorr?

Thanks

#174 Starman1

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Posted 16 September 2012 - 01:28 PM

Let's review how to set the Paracorr when you don't know the correct setting and you have no TeleVue eyepieces (if you have a TeleVue eyepiece, use their prescribed setting for that eyepiece and all the other eyepieces will follow--instructions follow:)

Start with the out-most setting of the Paracorr. Focus the telescope and examine the edge of field stars. Still see coma? Move the Paracorr in one setting and refocus. Still see coma, but it's improved? Continue in one more setting.
With trial and error, you will find one setting that produces the least coma at the edge of the field. If aberrations are not fully corrected, it's likely the eyepiece has some residual astigmatism at the edge of the field that the Paracorr won't correct.

Once you have the proper setting for that eyepiece, write it down so you can return the Paracorr to that setting before using that eyepiece the next time.

Now, how to set the other eyepieces once you have a perfect setting for that one eyepiece:
Put the second eyepiece in and focus using the tunable top of the Paracorr. When that eyepiece is in focus, look at the tunable top setting. That will be the setting for that eyepiece. Write it down so you can go to that setting before the next use of that eyepiece.

In that manner, you can do an entire collection of eyepieces without knowing in advance what the settings for those eyepieces are.

As you can see, the tunable top makes all your eyepieces parfocal--only the movement in and out of the tunable top before you insert the next eyepiece is required, plus, perhaps, a tiny bit of refocusing. But the movement of the focuser will be tiny as long as the Paracorr is used.

What if you cannot correct the coma of an eyepiece because the Paracorr's settings don't extend far enough to fully correct that eyepiece?
Well, that's not unusual. The 31 Nagler and 21 Ethos were in that category on the original Paracorr. And the 17.3 and 14 Delos are in that category on the Paracorr II.
Don't worry about it. If the eyepiece is close to the ideal coma correction setting the images will still be improved significantly over no Paracorr at all.
BUT, don't use that eyepiece to determine the settings for your collection. Use an eyepiece that has its best coma correction among the settings of the Paracorr. And, to make sure you have a good starting point, use your eyepiece that has the widest apparent field of view because coma will be more visible in that eyepiece than in narrower field eyepieces.

After you have determined the correct settings for all your eyepieces, even those whose correction is not ideal at one extreme or the other of the Paracorr settings, hopefully you will have written down the settings. If, like me, you don't want to resort to a list before inserting the eyepiece, use a label maker to put the Paracorr setting on the side of the eyepiece so you don't have to remember.

There is an alternative to this, and I admit to using it when I'm using an eyepiece briefly and then inserting another eyepiece: Having the setting absolutely perfect for one eyepiece, I insert another and simply focus using the tunable top. Then, I touch up the focus a tad with the main focuser. That way, I don't even have to read the label on the eyepiece to find the correct setting for the next eyepiece. It helps if you have eyepieces that all use extreme settings (most of mine use one extreme or the other) and your less-often-used eyepieces use an intermediate setting.

So, as you can see, the purpose for this thread is a little unnecessary. All you need to do is take the time to get one eyepiece dialed in and all the rest follow.

#175 miguel gonzalez

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Posted 16 September 2012 - 02:24 PM

Thank you very much, Don.


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