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The Road to Perfection - What to buy next for my Dobsonian?

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#1 earlyriser

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Posted 11 September 2019 - 01:47 PM

The next optical trinket I plan to buy is a Televue Paracorr Type-II. However, I have read posts from members wiser than I that the tolerances for collimation when using the Type-II are quite stringent. I would even call them intimidating.

 

Currently, I use a cheapy combination sight tube/Cheshire to collimate my Dobsonian. I also have a cheapie laser collimator that came with the scope which I use to check the secondary alignment. With these tools, I believe I am achieving good collimation for visual use. On nights of good seeing, stars are very sharp in the center of the field. On one miraculous morning of exceptional seeing, Jupiter was stunningly sharp, albeit at only 208X.

 

So, the question is, should I hold off on the Paracorr until I have better collimation equipment, get the Paracorr next, or keep saving for that Zambuto mirror?


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#2 photoracer18

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Posted 11 September 2019 - 02:10 PM

Zambuto mirror will not fix coma. Nor will it improve your collimation.

My opinion, having owned fast Newts for the better part of 35 years, is to learn how to collimate better (improve your tools if needed however I have done all my scopes with the old Astro-Systems 3-piece collimation tools and an occasional laser, I own a Hutech holographic one mainly because I own cats also). I ended up with a Parracor by accident a few years ago. Before then I owned a 28mm Pretoria coma-correcting eyepiece. Big difference. I would vote for the Parracor if you had no collimation issues.


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#3 areyoukiddingme

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Posted 11 September 2019 - 03:58 PM

I'd say get the paracorr, even if collimation is still somewhat of an issue. It sounds like it must be close, otherwise you'd not be getting particularly good views of Jupiter.

 

Even if your tools aren't perfect, they can at least get you in the ball park.

 

After that you can always collimate your primary on a star at high power.



#4 Jon Isaacs

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Posted 11 September 2019 - 08:25 PM

Hi:

 

Looking at your eyepiece collection, I'd say go for the Paracorr.. You have some very nice eyepieces, they deserve a Paracorr.

 

Jon


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#5 turtle86

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Posted 11 September 2019 - 08:42 PM

I agree that your collimation tools must be doing the job if you’re able to get a really sharp view of Jupiter like that.  At some point you might want to get Farpoint, Astrosystems, etc. tools to get the best possible collimation so I too vote for a Paracorr.  You might even consider a Paracorr I on the used market, which goes for about half the cost of a Paracorr II and does a fine job.



#6 DavidC

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Posted 11 September 2019 - 09:38 PM

I use an older parracor type-1 after I collimate the best I can. I use a laser to center the secondary, then cheshire/sight tube to center the primary. When I'm done, then I insert the parracor and I get pinpoint stars. I read somewhere the parracor adds about 15% to the magnification to the EP's you use..



#7 havasman

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Posted 12 September 2019 - 12:43 AM

It was the 31T5 that made the P2 necessary. The A position on the P2 is not available on a P1. That is the setting for a 31T5 and the longest Ethos. Since you have a 31T5, it is your decision whether you can be pleased with the cost savings buying a P1 would bring while knowing the performance of your critical widefield eyepiece cannot be maximized.

 

You may likely find, based on your observations, that your primary mirror is just fine. And it sounds like you can collimate your scope. Coma seems the best target. It's pretty dramatic to see in a 10" Dob when you 1st get a corrector into the path, definitely a WOW moment for me.



#8 Jon Isaacs

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Posted 12 September 2019 - 09:02 AM

Regarding the Paracorr 1 and the 31 mm Nagler:

 

The optimal position for coma correction was not available but the correction was still very good. In a f/4.4 or greater scope, the biggest difference between the 1 and the 2 is the Tuneable Top.  With the 1, the top is effective but I could not adjust it with a heavier eyepiece in place, I had to adjust off and insert the eyepiece.

 

That changes with the 2. The Tuneable Top on the 2 is really a smooth, fast helical focuser. That lets me insert an eyepiece and focus it with the Tuneable Top and only do the fine focusing with the focuser. I don't need to know the settings if I'm starting with an eyepiece with a known setting.

 

Jon



#9 earlyriser

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Posted 12 September 2019 - 10:34 AM

Regarding the Paracorr 1 and the 31 mm Nagler:

 

The optimal position for coma correction was not available but the correction was still very good. In a f/4.4 or greater scope, the biggest difference between the 1 and the 2 is the Tuneable Top.  With the 1, the top is effective but I could not adjust it with a heavier eyepiece in place, I had to adjust off and insert the eyepiece.

 

That changes with the 2. The Tuneable Top on the 2 is really a smooth, fast helical focuser. That lets me insert an eyepiece and focus it with the Tuneable Top and only do the fine focusing with the focuser. I don't need to know the settings if I'm starting with an eyepiece with a known setting.

 

Jon

I'd rather have the P2 for this feature alone, but I'm tempted to get a P1 since they are so much cheaper on the used market. I figure I could always sell the P1 for close to what I paid for it and get a P2 later if I want the tunable top badly enough. My current telescope is f/5, and I doubt I'll ever have a telescope faster than f/4, so the optical advantages of the P2 aren't as imperative as they might be for someone with a really fast mirror.


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#10 areyoukiddingme

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Posted 12 September 2019 - 01:16 PM

I have both the P1 and P2. I find the performance very close for the most part, and really don't see any difference for the 31 Nagler and 21 Ethos.

 

I've never heard anyone complain that they can see a difference like this. I've only seen 'theoretical' statements b/c of the knowledge that the correction is not quite optimal in the P1 for these eyepieces.

 

The P1 also allows me to use my Pentax XW 40 and shows no vignetting. The P2 shows so much vignetting that I find it practically unusable knowing how much better the P1 is.

 

However, for high power on planets, I think the P2 is a little sharper than the P1, but the difference is small and subtle.



#11 Pierre Lemay

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Posted 12 September 2019 - 06:35 PM

I have both the P1 and P2. I find the performance very close for the most part, and really don't see any difference for the 31 Nagler and 21 Ethos.

OK, that's kind of useful. But, specifying the telescope's focal ratio would be much more informative.

 

When we discuss how well our eyepieces and/or coma correctors work it is always best to specify the optical system those accessories are used with.

 

In the example above, if the coma corrector is used with an f/6, of course there won't be much difference between the P1 and P2. But if it's an f/3, that's another story!


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#12 areyoukiddingme

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Posted 12 September 2019 - 07:19 PM

That's tested at 12.5" F5 and 8" F7

 

(edit: the 12.5 is F5, not F6).

 

I'll also add that seeing coma at F7 is very easy. For deep sky the paracorr is clearly a benefit.

 

For planetary at moderate powers for that scope (~200x) the coma correctors give a tighter image at the edges of the field. On average, a benefit. The P2 is better than P1 to my eye at that.

 

At high 200/300, it's starts to get harder to tell whether the coma corrector is worthwhile or not.


Edited by areyoukiddingme, 13 September 2019 - 11:44 AM.


#13 Adun

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Posted 12 September 2019 - 08:26 PM

You can add a Barlow to your laser, and try the Rear View Barlowed Laser method


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#14 turtle86

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Posted 12 September 2019 - 09:51 PM

I'd rather have the P2 for this feature alone, but I'm tempted to get a P1 since they are so much cheaper on the used market. I figure I could always sell the P1 for close to what I paid for it and get a P2 later if I want the tunable top badly enough. My current telescope is f/5, and I doubt I'll ever have a telescope faster than f/4, so the optical advantages of the P2 aren't as imperative as they might be for someone with a really fast mirror.

 

 

If your scope is an f/5, the P1 is really all you need for purposes of coma. Many observers even claim not to need a Paracorr at all at f/5, though I’m not one of them.  Just want to add that the tunable top of the P1 is not bad at all, though the one on the P2 is very nice.


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#15 Jon Isaacs

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Posted 12 September 2019 - 10:08 PM

That's tested at 12.5" F6 and 8" F7

 

Very few even bother with a coma corrector at F/6, even fewer at F/7.  The Paracorr 2 was designed to provide coma correction down to F/3 and below.  At F/6 with the Paracorr 1, the diffraction limited field should be 28.5mm with the Paracorr 1, at F/7, it should be 45mm.   That would be difficult to see at F/6.. 

 

I'd rather have the P2 for this feature alone, but I'm tempted to get a P1 since they are so much cheaper on the used market. I figure I could always sell the P1 for close to what I paid for it and get a P2 later if I want the tunable top badly enough.

 

I believe the last Paracorr 1's used the same Tuneable Top as the Paracorr 2.  Maybe someone can verify this.

 

Jon



#16 areyoukiddingme

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Posted 13 September 2019 - 11:46 AM

Very few even bother with a coma corrector at F/6, even fewer at F/7.  The Paracorr 2 was designed to provide coma correction down to F/3 and below.  At F/6 with the Paracorr 1, the diffraction limited field should be 28.5mm with the Paracorr 1, at F/7, it should be 45mm.   That would be difficult to see at F/6.. 

 

I believe the last Paracorr 1's used the same Tuneable Top as the Paracorr 2.  Maybe someone can verify this.

 

Jon

I had a typo . . . F5 in the 12.5, not 6.

 

Are there different P1 tunable tops? I find the P1 and P2 tops really aren't far off. Both are poor as far as focusing goes, but obviously preferable to having no such ability.



#17 turtle86

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Posted 13 September 2019 - 11:54 AM

I had a typo . . . F5 in the 12.5, not 6.
 
Are there different P1 tunable tops? I find the P1 and P2 tops really aren't far off. Both are poor as far as focusing goes, but obviously preferable to having no such ability.


I believe so. IIRC, the PVL-2008 P1 (with white lettering) added an extra thumbscrew.

#18 Jon Isaacs

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Posted 13 September 2019 - 12:30 PM

I had a typo . . . F5 in the 12.5, not 6.

 

Are there different P1 tunable tops? I find the P1 and P2 tops really aren't far off. Both are poor as far as focusing goes, but obviously preferable to having no such ability.

 

I find the P2 Tuneable top effective for coarse focusing, close enough that I only need minor tweaks with the two speed for sharp focus and even then, it's often just to make sure. In the 22 inch, i go from the 13 mm Ethos at about 215x to the 8 mm Ethos at 353x. These both have barrel extenders so the standard settings don't apply.

 

I just put the 8 mm in the focuser and use the Tuneable Top to focus, It's basically all the way in to nearly all the way out. I get a good focus if not perfect focus. That's at F/4.4. 

 

Jon



#19 25585

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Posted 14 September 2019 - 01:33 AM

My first trinket was a PC2 but should have been better collimating kit. Eventually I bought a Howie Glatter laser and most importantly a Tublug. I chose his laser as its own collimation is assured, the Tublug 2" makes primary collimation painless compared to a Cheshire. Recently I have got a TS Concenter for secondary mirrors.

 

Collimation analysis and solving is the big bugbear of Newtonians. My 10" F6 thus gets used most. 



#20 earlyriser

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Posted 16 September 2019 - 06:35 AM

Evidently, you can buy the tunable top that comes with the Paracorr Type-2.

 

https://www.highpoin...adapter-att2125

 

I'm curious if anyone has tried to retrofit this to a Paracorr Type-1? Even if you can, at $155 it would probably make more sense for anyone who owns a Paracorr Type-1 to sell it and buy a Type-2, but it would be good to know if this option exists. 


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#21 Spartinix

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Posted 19 September 2019 - 11:59 AM

My first trinket was a PC2 but should have been better collimating kit. Eventually I bought a Howie Glatter laser and most importantly a Tublug. I chose his laser as its own collimation is assured, the Tublug 2" makes primary collimation painless compared to a Cheshire. Recently I have got a TS Concenter for secondary mirrors.

Collimation analysis and solving is the big bugbear of Newtonians. My 10" F6 thus gets used most.


Isn't some astigmatism hidden by coma, so that it's better to collimate with the Paracorr in the chain?

#22 earlyriser

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Posted 19 September 2019 - 12:07 PM

Isn't some astigmatism hidden by coma, so that it's better to collimate with the Paracorr in the chain?

If you are using a star to collimate, you center the star in the field of view to assess collimation. Since there should be no coma in the center of the field of view even without a Paracorr, I wouldn't expect a Paracorr to help with this.

 

As for collimation using a laser or Cheshire, the Paracorr would get in the way.


Edited by earlyriser, 19 September 2019 - 12:16 PM.

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#23 turtle86

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Posted 21 September 2019 - 09:38 AM

Evidently, you can buy the tunable top that comes with the Paracorr Type-2.

 

https://www.highpoin...adapter-att2125

 

I'm curious if anyone has tried to retrofit this to a Paracorr Type-1? Even if you can, at $155 it would probably make more sense for anyone who owns a Paracorr Type-1 to sell it and buy a Type-2, but it would be good to know if this option exists. 

 

Since a new Paracorr 2 now goes for close to $500, retrofitting the top to a Paracorr 1 would make sense if that would work.  


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#24 junomike

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Posted 21 September 2019 - 11:33 AM

Since a new Paracorr 2 now goes for close to $500, retrofitting the top to a Paracorr 1 would make sense if that would work.  

If you're happy with the PC1 this makes sense however I've believe the PC2 corrects better in a fast OTA for eyepieces with the FS further up in the housing (31T5).



#25 SteveG

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Posted 21 September 2019 - 03:27 PM

To the OP, adding a Paracorr type 1 (tuneable top) was the best optical mod I've ever done with a 10" f5. Highly recommend it. I paid $230 for mine used.


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