Paracorr

casstony · #1 15-05-2007, 10:12 AM

I used a Paracorr for the first time last night in my 10" f/5 dob. I was expecting a subtle improvement after reading about this device but the improvement was very obvious. The edge of field was cleaned up in both the 22 Nagler and Pentax XW14, to the point where I now have no thoughts of selling the XW14mm. I put the XW in after using the Nagler at Paracorr setting 5 and the view was not good, but changing to setting 1 fixed that.

It's hard to draw conclusions after just one observing session, but the Paracorr looks like it will be staying in my eyepiece collection.

I'm curious to hear what setting others use with the XW14 and Paracorr?

Starkler (Geoff) · #2 15-05-2007, 01:31 PM

Its interesting in that the paracorr is designed for coma correction, but it does things other than that. The xw14 wouldnt be seeing coma in that scope and if the pracorr makes an improvement it would appear that it could be flattening the field.

casstony · #3 15-05-2007, 02:06 PM

I'm not sure of my ability to separate the types of aberration or whether there are other factors that come into play, which is why I stuck to a generic "cleaned up the EOF" description. The EOF in the XW14 did look comatic to me though, so I suspect there's coma correction and field flattening occurring. I used the wishing well cluster as my main test subject as it has a nice spread of medium brightness stars across the field.

MortonH · #4 15-05-2007, 11:09 PM

Here's a line from the Paracorr page on the TV website (under 'astrophotography' but presumably applies visually as well).

"Edge-of-field sharpness is further enhanced since Paracorr also acts as a field-flattener."

Morton

ausastronomer (John Bambury) · #5 16-05-2007, 08:45 AM

Hi Tony,

I also found that the paracorr does an excellent job of cleaning up the EOF in both the 14mm and 20mm Pentax XW's using #1 or #2 setting. Setting 1 is better but requires me to collimate the mirror very low to reach focus. The paracorr also cleans up the EOF nicely in both the 12mm and 17mm Nagler T4's. The dominant aberration in both the 14mm and 20mm Pentax XW's is field curvature. While the paracorr is not specifically designed to fix this, it does a remarkable job on it.

The 14mm and 20mm Pentax XW's don't show the same degree of field curvature in a larger scope with a longer focal length but the paracorr still improves them.

CS-John B

casstony · #6 16-05-2007, 09:54 AM

I've been waiting for your input John, but I see in your ethos thread you have a good excuse for being a little tardy - you've been off enjoying yourself too much

. Performace with the Paracorr certainly casts a new light on ownership of the XW14 and 20. Now that I can stop hyperventilating over EOF imperfections I feel I have a near perfect eyepiece set (Paracorr, Nagler 22, XW's 14 &10). It's convenient that the 14 and 22 just happen to use the two extreme Paracorr settings - no need to look at settings in the dark. Brighter nebulosity looks quite stunning through the XW14.

Thanks for your info too Morton.

StarLane · #7 18-05-2007, 11:50 PM

I have a Q that doesn`t relate to the original post, I`m hoping someone can kindly answer.
Does the Paracorr have a 2inch filter thread on the bottom???

Much appreciated.
Cheers.

casstony · #8 19-05-2007, 12:33 AM

Starlane, just went and had a look for you and the Paracorr does have a 2" filter thread.

MarkN · #9 19-05-2007, 11:57 AM

Tony:

Very interested to read your post. Did you have any balance issues using the Parracorr with the 22 mm?

I've been considering a Parracorr for a while now as I'm becoming less and less tolerant of EOF distortions.

Mark.

casstony · #10 19-05-2007, 12:43 PM

Hi Mark, I didn't have any balance problems with the Nagler 22 and Paracorr, but the tube wasn't pointed at lower altitudes either. I never use the altitude springs as I don't like to apply unnecessary friction to the bearing. I keep a stack of 3 or 4 speaker magnets on the eyepiece rack that can be easily applied to the rear of the scope if necessary, so I don't run into any balance problems anyway.

I've only had one chance to use the Paracorr so far, but it's very nice to be able to leave the scope still for longer and see a sharp image as an object moves across the field. I suspect the Paracorr is only worth having if you are using premium eyepieces, with astigmatism overwhelming other aberrations in cheaper eyepieces. As soon as I get a clear night I'll test that theory out with my Andrews 30mm UWA.

skies2clear · #11 19-05-2007, 04:04 PM

Tony,

very interesting thread. I'm very interested too about your further tests with the Paracorr. I've been toying with the idea of getting one, but haven't made the plunge yet, still wondering if it's the only option, or something else available too (that doesn't magnify the image like a Paracorr?). Maybe the Paracorr is the only game in town?

Clear Skies
Nick

casstony · #12 19-05-2007, 04:42 PM

Nick,
there are other options, that I haven't seriously investigated, but which are cheaper and don't magnify. My brief impression was that if you have only one eyepiece to correct for, seriously consider one of the other coma correctors. If you want to use a number of eyepieces with corrector, get the Paracorr as it is the only one that allows convenient adjustment of the distance between the eyepiece and the correcting lens assembly. Also the Paracorr corrects the field curvature issue in the XW14&20 which is a big deal if you want to use those eyepieces - I don't know if the others do that.

I don't mind the 15% magnification increase as I was considering swapping my 22mm Nagler for a 17mm - now I have an 18.7mm Nagler when used with the Paracorr. The 22mm also has 2mm more eye relief than the 17mm, so I'm happy how things have worked out.

MortonH · #13 19-05-2007, 07:24 PM

Although I don't own a Paracorr (yet), I think it is the only option that is convenient to use in the field, i.e. you don't need to unscrew something each time you change eyepieces (as you would with the MPCC, for example). As Tony said, there are four(?) different height settings with the Paracorr, and you need to figure out the optimum position for each eyepiece you own, but this isn't really a big deal.

All things considered, I think a slight magnification increase is aceptable for the improvment in performance. I'm sure if it was possible to make a similar item with no magnification, Al Nagler would have done it!

Morton

StarLane · #14 19-05-2007, 08:59 PM

Quote:

Originally Posted by casstony

Starlane, just went and had a look for you and the Paracorr does have a 2" filter thread.

Thanks for that Tony.

Cheers, Paul.

MarkN · #15 20-05-2007, 09:59 AM

Thanks for all that Tony. Hmmm...now where's that piggy bank?

Mark.

skies2clear · #16 22-05-2007, 08:43 AM

Thanks everyone for commenting. I probably wouldn't use the Paracorr just for one eyepiece, but possibly for the XW14 XW20 and a couple of others too, all longer FL's. While I find the XW14 fine (very slight curvature), the XW20 performance is great in some scopes but in my smaller newts (FL = 900mm to 1000mm), field curvature is noticeable. In longer FL's it's not a big issue at all for me. From what you say, the Paracorr will noticeably improve things.

Having to disassemble would be a pain, so while I had thought of the MPCC, it looks seriously like the Paracorr is the best option,

Thanks again

CS
Nick

Satchmo · #17 22-05-2007, 10:31 AM

Quote:

Originally Posted by skies2clear

I've been toying with the idea of getting one, but haven't made the plunge yet, still wondering if it's the only option, or something else available too (that doesn't magnify the image like a Paracorr?). Maybe the Paracorr is the only game in town?

Nick , there is the Lumicon2" Photo-Visiual Coma Corrector for $345 at Bintel, and it doesn't magnify. I know a guy in Adelaide who owns an 18" F4.5 and uses one and he says it works really well.

Mark

skies2clear · #18 23-05-2007, 12:26 PM

Thanks Mark,

I'll look into the Lumicon too. This is cheaper than the Paracorr I think?

Cheers
CS
Nick

ausastronomer (John Bambury) · #19 24-05-2007, 03:00 AM

Nick,

It won't work properly for visual I dont think. It is more an imaging unit. The advantage of the Televue one is that it is adjustable and you use all five of those adjustment positions depending on the eyepiece used. This is why Televue make both a visual and photographic Paracorr.

I have the Televue Visual and it is superb.

CS-John B

skies2clear · #20 27-05-2007, 09:51 PM

Thanks John,
I'll give the other options a miss and look at the Paracorr. The flexibility and ease of use as well as optical performance is important. When you're tired and you want to drag the scope out, you want life as easy as possible!!!

Cheers and clear skies,

Nick