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Paracorr a Must have accessory?

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#1 AcTrust

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Posted 02 December 2013 - 10:29 AM

I have been reading about the TeleVue paracorr and have been wondering if it would be a good thing to use for any speed of Dob? From what I have gathered any reflector from F4.5 and less needs one and also that any reflector can benefit from one.

It is a $500 accessory but if it brings a cleaner and sharper image and also reveals stars and objects that you don't see without it I would think all dob owners should have one?

Anyone with some experience on paracorr able to shed some light on this for us nooblets? :help:

Thanks!

#2 brianb11213

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Posted 02 December 2013 - 10:49 AM

The fact of the matter is that Newtonian / Dobsonian reflectors with short focal lengths have severe off axis aberrations, in particular coma, which seriously reduce the useful field of view. The TV Paracorr can be employed to reduce these off axis aberrations to a very great extent, allowing a much wider sharp field of view. Baader also make a coma corrector suitable for "fast" Newtonians, this is considerably cheaper than the Televue product - but the TV Paracorr does one useful thing that the Baader MPCC does not; namely, to increase the focal length by about 20%, giving the eyepiece a much easier tasks (few eyepieces work properly at focal ratios shorter than about f/5 and those that do tend to be very expensive indeed.)

If you want to do wide field viewing or imaging with a Newtonian / Dobsonian faster than about f/6 I would suggest that the Paracorr or MPCC are more or less essential. (Cleaner and sharper images, yes. Reveals stars & objects that you don't see without it, well I think this claim is somewhat exaggerated.) For planets, you can get away without, provided you have very good eyepieces or at least a very good barlow / Powermate to increase the effective focal ratio.

You still need to learn how to collimate your scope properly.

#3 AcTrust

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Posted 02 December 2013 - 10:58 AM

In reading more, it seems like if you want the most from your F6 to F3 reflector that adding this tool is essential. When people are spending $300-$900 on each eyepiece I personally would like to see the best image possible from those eyepieces and from my scope. I am kind of surprised how I have not heard more about this paracorr as it seems like THE accessory to get after you get even one good eyepiece.

Sure it seems like a premium accessory but also seems like once you have used one you won't go back to not using one lol.

#4 Tony Flanders

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Posted 02 December 2013 - 11:04 AM

The TV Paracorr does one useful thing that the Baader MPCC does not; namely, to increase the focal length by about 20%


I actually view that as a downside, not a benefit. Paracorrs mostly seem useful for widefield viewing, and when I want a wide field, I generally want the shortest focal length possible.

If you want to do wide field viewing or imaging with a Newtonian / Dobsonian faster than about f/6 I would suggest that the Paracorr or MPCC are more or less essential.


I'm quite happy without a Paracorr at f/5. Not sure I would be so happy at f/4. Coma is proportional to the inverse cube of the focal ratio, so f/4 is much, much more problematic than f/5.

I wouldn't even consider a Paracorr at f/6.

#5 Achernar

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Posted 02 December 2013 - 11:16 AM

To me they are a must have for users of F/4.5 and faster Dobs who are also using wide and ultra-wide angle eyepieces. However, if you have an F/4.5 or F/5 Dob, you can probably find an original Paracorr with the tunable top on the used market in good to excellent condition for 200 dollars or less. I got one for $150.00 in perfect shape at a star party. The improvement in the views is very noticeable with pinpoint stars all the way to the edge of the field of view.

Taras

#6 GOLGO13

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Posted 02 December 2013 - 11:19 AM

Must have I would say no. But it is a very nice product.

The earlier versions come up for sale used around $200 which isn't too bad.

I'd say if you had a fast reflector and bought a low power wide field eyepiece (like a 26mm nagler or 31mm nagler), then I would certainly say get the paracorr. But if you are mostly using low powers to find something and then going to higher powers for observing it's not needed.

I once had a 26mm nagler and while it was fairly sharp across the field in my F4.7, it wasn't until I got the paracorr that it was completely sharp across the field. However, the two of those products cost me (at the time) about $900. Had to sell both of them unfortunately. However, in my 10 inch I actually like the higher magnifications the most. I do some low power with it, but I focus on the higher powers. I don't usually have issues at the higher powers with coma.

#7 Kevdog

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Posted 02 December 2013 - 11:23 AM

The TV Paracorr does one useful thing that the Baader MPCC does not; namely, to increase the focal length by about 20%


I actually view that as a downside, not a benefit. Paracorrs mostly seem useful for widefield viewing, and when I want a wide field, I generally want the shortest focal length possible.

If you want to do wide field viewing or imaging with a Newtonian / Dobsonian faster than about f/6 I would suggest that the Paracorr or MPCC are more or less essential.


I'm quite happy without a Paracorr at f/5. Not sure I would be so happy at f/4. Coma is proportional to the inverse cube of the focal ratio, so f/4 is much, much more problematic than f/5.

I wouldn't even consider a Paracorr at f/6.


I use my 18" Obsession at f4.5 without a paracorr with ES82 eyepieces. I personally don't find an issue with it. I'm sure others would.

I might try one someday if I can get one used, but I'd prefer the Baader as well as I don't need an increase in focal length!

#8 AcTrust

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Posted 02 December 2013 - 11:45 AM

I should have researched a little more but I found this on CN. Paracorr was used on a F5.9 dob...


"last night i was feeling lazy since i have been working 70-80 hours a week for 7 weeks. it was the first night that i have been able to observe in that same amount of time. anyway, i was going along scanning the milkyway in my z8 (i was too lazy to get the Z12 out) and i just decided to try my paracorr.

it was a good decision. faint stars that were not there before became visible. the views were very refractorlike maybe apo like because the stars were the right colors. i have decided that this deserves more exploration. the other decision is that i think i have become a reflector guy. the images were so beautiful that they would cost a fortune to get similar results with a refractor.
sorry, got sidetracked there. anyway, this exceeded my expectations and i was seriously just playing with my equipment. all this being said, i would not buy a paracorr for an f6 scope. if you have a paracorr already, give it a try. to be clear, don't buy a paracorr for your f6 scope. if you have a faster scope and you want one, buy one. if you plan on buying a faster scope, buy one. you do not need s paracorr at f6, it just makes stars prettier and tighter."


He says at the end I wouldn't buy one for an F5.9 telescope. Yet he mentions almost all the key improvements from paracorr usage. He notes during his experience, faint stars that were not there are now there, the color of the stars have been corrected, tighter and more pretty stars making the reflector perform like a refractor or APO-like...

That all sounds pretty darn good to me lol.

#9 GeneT

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Posted 02 December 2013 - 12:52 PM

'm quite happy without a Paracorr at f/5. Not sure I would be so happy at f/4. Coma is proportional to the inverse cube of the focal ratio, so f/4 is much, much more problematic than f/5. I wouldn't even consider a Paracorr at f/6.


I generally agree with this. Due to some issues, I can't accommodate a Paracorr with my 12.5 inch, f5 Portaball. Conventional wisdom that I subscribe to puts an F5 mirror at the break point for a Paracorr. My views are excellent two thirds of the field of view. Faster optics need one, in my opinion. However, people owning F3+ optics have posted that they don't need a Paracorr.

I don't know about refractors and using a Paracorr. All my experience is with reflectors. Refractor owners--does a Paracorr fit in with your viewing experience, and if so, what parameters for the optics?

#10 Starman81

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Posted 02 December 2013 - 01:00 PM

Some eyepieces show the mirror's coma a bit more than others. The 22T4 is one and so is the 17.3 Delos (I have both). I've had the 22T4 for some time and though a ParaCorr helps, I usually forget to use it in m 8" f/5.9 dob. Any perceived coma in the 22T4 is usually not enough to remind me to use the PC.

In the f/5 Omni XLT 150--yikes! IMHO, PC definitely needed for the 22T4, Pan 35 etc. Shorter focal length eyepieces can
probably get by though.

In the f/4.3 STS 11, I might as well have the PC fused to the focuser!

On a side note: the main reason I picked up a PC was to use in the f/5.9 dob (before I got the STS), ironically. Specifically though, for use with two eyepieces--Pentax XW 20 and 14. For field flattening purposes, of course.

#11 brianb11213

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Posted 02 December 2013 - 01:05 PM

I don't know about refractors and using a Paracorr. All my experience is with reflectors. Refractor owners--does a Paracorr fit in with your viewing experience, and if so, what parameters for the optics?

Newtonian reflectors & refractors (of various designs) have completely different off-axis aberrations. The Paracorr (& MPCC) are designed for use with parabolic mirrors & are far more likely to degrade the performance of any other type of scope than improve it.

In any case few refractors have a short enough focal ratio to make a Paracorr necessary, and those that do either have dedicated field flatteners or have off-axis correction built in (e.g. the Televue NP101 & NP127 quadruplets).

#12 esd726

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Posted 02 December 2013 - 01:24 PM

I never felt it was worth the money and sold it the next day, so IMO no it's not a "must have". Just didn't make that big of a difference to me to justify the $.

#13 mayidunk

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Posted 02 December 2013 - 01:44 PM

Using a 13mm Ethos in a 10", f/3.9 Newtonian astrograph, I was very surprised at how well corrected the views out to the edges of the FOV actually were! While coma was apparent at the outside edges, it was very mild (to me, anyway), and the views away from the edges were coma free! Now that was just with the 13mm. As I recall, I didn't check any of the other Ethos' as it was first light for the scope, and so I wasn't really testing the EPs.

My advice would be for you to determine for yourself if the views through your scope, using your EPs, are bad enough for you to invest in a paracorr. I think this is a case where YMMV really applies! For me? I'm starting to think that I may never find a need for my paracorr, but since I've already made the investment I'll just hang onto it.

#14 David Knisely

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Posted 02 December 2013 - 01:48 PM

Tony Flanders wrote:

Quote:
The TV Paracorr does one useful thing that the Baader MPCC does not; namely, to increase the focal length by about 20%



I actually view that as a downside, not a benefit. Paracorrs mostly seem useful for widefield viewing, and when I want a wide field, I generally want the shortest focal length possible.


Actually, it is more like about a 15% increase in the focal length, which is fairly small. If you had a maximum true field of view of one degree, you would only be down to 0.85 degrees in true field. As for a "benefit", at certain f/ratios, the focal length extension can indeed be a benefit. In my case for example, my 14 inch f/4.6 goes up to an f/5.29 without having the scope be physically any longer. Many eyepieces tend to show a bit of a drop-off in outer field performance when used in f/ratios at or below f/5, so that increase in f/ratio can indeed be somewhat helpful. I noted this immediately with the silly 2-inch 3-element eyepiece Orion sent with my scope. It shows really horrid astigmatism over the outer half of the field of view, but with the Paracorr in-place, the astigmatism dropped notably, although it was still there. There is indeed something of a minor benefit to the slight focal length extension provided by the Paracorr (as well the obvious significant reduction in coma). As for being a "must-have", it isn't a requirement, but I would say if your scope has an f/ratio at or below f/5, a Paracorr is definitely worth getting. Clear skies to you.

#15 AcTrust

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Posted 02 December 2013 - 03:14 PM

Long story short is I am going to pick a TeleVue PC up and see if the claims are true both from the poster I quoted and also from the TeleVue website. I have trusted Uncle Al this far so may as well go all the way! When I do get one and it actually stops snowing I will post the perceived results. If it doesn't do anything I will take it back to the shop I buy TV from and have $500 credit towards another eyepiece there.

Sounds fun, now stop snowing!!!

#16 backwoody

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Posted 02 December 2013 - 03:27 PM

Must have? Probably not. I have one, but only use it occasionally.

With my f4.8 reflector, many EPs don't seem to require it; notably 24mm Panoptic, 17mm Vixen LVW, Pentax XF 12 and 8.5mm. For wider FOVs, like Pentax XW or Pano 36mm I sometimes dig it out. It adds weight however, creating another need - rebalancing the dob.

You might try borrowing one to try with your favorite EPs before buying. In any case, shop the used market. Many are barely used.

#17 AcTrust

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Posted 02 December 2013 - 03:42 PM

I would love to borrow one to try but I think I am the only Astronomer in the city lol. If I do run into someone who does observe they are just minimalists with a fun scope and look every so often.

When I do buy my Obsession it will be the only one here for sure :D

#18 AcTrust

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Posted 02 December 2013 - 05:13 PM

As for any observing tonight I believe it will be tough. No paracorr can fix this!!

Attached Files



#19 backwoody

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Posted 02 December 2013 - 05:20 PM

Holy hawkeye...better wait a bit! At least until the snow stops...

#20 Scott Watson

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Posted 02 December 2013 - 09:13 PM

My opinion is <f5, a Paracorr is required. Between f5 and f6, a Paracorr is optional. Above f6, a Paracorr is almost never worth it. YMMV.

#21 obin robinson

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Posted 02 December 2013 - 10:22 PM

It is a $500 accessory but if it brings a cleaner and sharper image and also reveals stars and objects that you don't see without it I would think all dob owners should have one?


$500 for a visual accessory? And people say astrophotography is expensive.

obin :roflmao:

#22 SpooPoker

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Posted 02 December 2013 - 11:10 PM

I am tempted to get a Paracorr/Coma Corrector for a 6" f/5 I have. One issue? My focusser is 1.25" and companies do not make these devices in 1.25" barrel size.

#23 SteveG

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Posted 03 December 2013 - 04:25 PM

My Paracorr type 1 with tunable top lives in my f5 dob. I picked it up used for $200. With wide-field eyepieces, my reflector now gives refractor-like views.

#24 Feidb

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Posted 03 December 2013 - 10:34 PM

I've compared them side by side with and without, in the same model scope as mine, (a friend had one in the same model next to mine) same magnification, or almost since the Paracorr gives a slight boost, and though it did improve the image, I didn't think it was worth the very steep price. Plus there's the issue of having to tune it to different eyepieces, catching dust, another optical element in the way, another attachment... I didn't think the improvement was worth either the price or the extra hassle. That's why I'm also not in the market for the Baader or one of the other cheaper alternatives either. I'd rather get another filter.

#25 csrlice12

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Posted 04 December 2013 - 08:31 AM

I am tempted to get a Paracorr/Coma Corrector for a 6" f/5 I have. One issue? My focusser is 1.25" and companies do not make these devices in 1.25" barrel size.


Sorry to hear that, but considering that the largest actually "useable" 1.25" eyepiece is a 32mm plossl(the 40 if you like soda straws), or the 24mm 68* or shorter f/l eyepieces are better corrected and the coma may not be as noticible. The other option is to upgrade to a 2" focuser, but that could get expensive as you may have to replace the secondary mirror as well. The paracorr really was designed for the large f/l widefield eyepieces, which you really aren't going to get into much with a 1.25" focuser.

Was there ever a 1.25" Paracorr??? Doubtful, but they do include a 1.25" adapter with it. Maybe BillP might know if Televue ever put one out (if they did, it would be a rare collector's item indeed).






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