77 replies to this topic

[MSWcdavis]

I got my hands on a nice F3.7 dob

 

I have a paracorr type 1

 

how quickly should I upgrade to type 2?

 

Immediately?

 

 

 

A paracorr type 1 in an F3.7 would be the equivalen to F-what?

F7? F8?ish

 

Anyone know?

 

Thanks as always

 

Regards

[Vic Menard]

I got my hands on a nice F3.7 dob

I have a paracorr type 1

how quickly should I upgrade to type 2?

Immediately?

Yep.

The difference in my f/4 Dob was readily apparent (including a reduction in field curvature).

...hope you have some good eyepieces too...

[MSWcdavis]

 

I got my hands on a nice F3.7 dob

I have a paracorr type 1

how quickly should I upgrade to type 2?

Immediately?

Yep.

The difference in my f/4 Dob was readily apparent (including a reduction in field curvature).

...hope you have some good eyepieces too...

 

i'll be using my ethos 21, 10, delos 6, and williams optics 100 degree 3.5

 

super excited

 

Thanks

Edited by MSWcdavis, 04 February 2018 - 08:17 PM.

[MSWcdavis]

how much was the type 2 paracorr going for on sale during the sale?

[havasman]

The recommended setting for the 21 Ethos is A on the Paracorr 2. There is no equivalent setting on the P1. That's one reason the P2 was developed.

 

http://www.televue.c...id=61&Tab=_ttop

Edited by havasman, 04 February 2018 - 08:30 PM.

[Pinbout]

I use a p1 on my 8inf3.5 and when I am shorter than 14mm eyepiece I throw the p1 to the side.

[mark cowan]

A paracorr type 1 in an F3.7 would be the equivalen to F-what?

F7? F8?ish

 

would be equivalent to "not so good" hence P2...

 

[Pinbout]

3.7 x 1.15 = 4.255

[Allan Wade]

You might like to consider getting a SIPS unit instead of a P2. I believe at f/3 there’s some benefit to the extra precision that comes from precisely setting the Paracorr to the telescope. Then, there’s the added bonus of not having to adjust settings after changing eyepieces.

[Jon Isaacs]

how much was the type 2 paracorr going for on sale during the sale?

 

I paid $380 plus tax and shipping for mine. I wanted to buy from Don so I was happy to pay the sales tax.

 

Currently I have both the type 1 and type 2. My fastest scope is F/4.06 but most of my observing is done with my 16 inch and 22 inch which are both F/4.4.

 

I'm still deciding which to keep. I know the Paracorr 1's lowest setting is not optimal for the 31 mm Nagler and the 21mm Ethos but to my eye, it still looks very good.

 

The thing about the Paracorr type 2 that bothers me is that with the 31 mm Nagler, I see vignetting at the very edge of the field, right next to the field stop, this happens in all my scopes.I just don't see that with the Paracorr type 1.

 

Since the OP will apparently not be using the 31 mm, this should not be an issue.

 

Jon

[MSWcdavis]

3.7 x 1.15 = 4.255

I know that about focal length but I mean in terms of.visual quality.

From televue paracorr type 1 instructions:
“Paracorr essentially makes an f/4 scope perform like an f/8”

[MSWcdavis]

how much was the type 2 paracorr going for on sale during the sale?

I paid $380 plus tax and shipping for mine. I wanted to buy from Don so I was happy to pay the sales tax.

Currently I have both the type 1 and type 2. My fastest scope is F/4.06 but most of my observing is done with my 16 inch and 22 inch which are both F/4.4.

I'm still deciding which to keep. I know the Paracorr 1's lowest setting is not optimal for the 31 mm Nagler and the 21mm Ethos but to my eye, it still looks very good.

The thing about the Paracorr type 2 that bothers me is that with the 31 mm Nagler, I see vignetting at the very edge of the field, right next to the field stop, this happens in all my scopes.I just don't see that with the Paracorr type 1.

Since the OP will apparently not be using the 31 mm, this should not be an issue.

Jon

Wow Jon - so you are on the fence at F4?

This comports with another tremendously experienced observer I know that the differences were minor. But others I know just won’t have it.

Edited by MSWcdavis, 05 February 2018 - 06:13 AM.

[Jon Isaacs]

Wow Jon - so you are on the fence at F4?

This comports with another tremendously experienced observer I know that the differences were minor. But others I know just won’t have it.

 

 

I haven't really has the time to decide. The F/4.06 was down getting the primary recoated so I've only used it a couple of times and very little with the 2.

 

It's kind of a hassle making an proper A-B comparison, it takes away from observing time.  We used them all those years at F/4 and no one complained.

 

In your situation, at F/3.7, I'd be trying to borrow a Type 2 or somehow get a long enough look to see.

 

But.. you can probably buy a type 2 for $400,  you sell your type 1 for $200 if you prefer the type 2. The 2 is only $200 to you and at F/3.7 that's what it was made for.

 

Jon

[MSWcdavis]

Yea. I’m going to do it.

Regards all

[Starman1]

 

3.7 x 1.15 = 4.255

I know that about focal length but I mean in terms of.visual quality.

From televue paracorr type 1 instructions:
“Paracorr essentially makes an f/4 scope perform like an f/8”

 

Since coma is eliminated completely (visibly) at f/3.7 over a 40mm field using the Paracorr II, it's the equivalent of converting the scope to f/13.3, where coma is concerned.

[a newtonian of f/13.3 would also have no coma over a 40mm field]

see: http://televue.com/p...2_spotsizes.pdf

The Paracorr 1 does a bit better than your quote.  It essentially eliminates coma over the 40mm at f/5.2 and longer.

[Allan Wade]

Out of curiousity I spent some time observing without a Paracorr in my f/3.3. Wow, what a mess. But, there was still enough usable field at the centre of the eyepiece to produce pin point stars. I was able to pick out all the faint little proto stars in the Orion Nebula, including the ones inside the Trapezium.

[Bob S.]

Allan and Don, Since Colin, the OP, has much younger eyes than most of us, I suggested to him that he consider taking a bit of time and doing some A/B comparisons with his current ep's and a Paracorr 1 and Paracorr 2 and report the differences he may see in the 80-100% outer regions of the FOV with his f/3.7 new-to-him intermediate size (16.5") Newtonian.

 

I know that everybody's sensitivity to coma is different based on their own physiology/receptor systems but remember in the early days of the Paracorr 2 introduction that the improvements in coma correction between the two correctors was a bit less than some had hoped for. IIRC, the efficacy of the two correctors was pretty highly dependent on the ep designs, where for example the Nagler T4's and T5's seemed to have a less dramatic improvement than the Ethos ep's that were coming into favor at the time. Of course, Colin has to take into account that beyond a certain focal length of the ep's that the efficacy of Paracorr coma correction becomes less effective with higher mag ep's. There seems to be a half-hearted consensus that 14mm and higher power ep's require less coma correction for pleasing views. 

[Starman1]

Bob,

I've always found that, regardless of focal length, apparent field was the deciding factor for the visibility of coma (apparent coma, not linear coma),

i.e. the wider the field, the more visible was coma.  That makes sense given that wider apparent fields extend further into the coma zone of a newtonian mirror.

So, when correcting coma, a higher level of correction is always going to be more noticeable in wider fields.

I tried my 3.7mm Ethos (110° field) one night without the Paracorr.  OMG.  I had forgotten how much coma could be seen at f/5!

It seriously makes me wonder how anyone could use an f/4 scope without a coma corrector.

Of course, if the eyepieces have narrow fields........

 

I'll be curious about the comparison of P1 and PII.

[turtle86]

Bob,

I've always found that, regardless of focal length, apparent field was the deciding factor for the visibility of coma (apparent coma, not linear coma),

i.e. the wider the field, the more visible was coma.  That makes sense given that wider apparent fields extend further into the coma zone of a newtonian mirror.

So, when correcting coma, a higher level of correction is always going to be more noticeable in wider fields.

I tried my 3.7mm Ethos (110° field) one night without the Paracorr.  OMG.  I had forgotten how much coma could be seen at f/5!

It seriously makes me wonder how anyone could use an f/4 scope without a coma corrector.

Of course, if the eyepieces have narrow fields........

 

I'll be curious about the comparison of P1 and PII.

 

It's even worse at f/4.3!    I've also experimented with the 3.7 and 4.7mm Ethos eyepieces without a Paracorr II, and quickly came to the conclusion that the Paracorr II is best seen as an essential part of the scope.

[Vic Menard]

...I'll be curious about the comparison of P1 and PII.

I did an A-B comparison a few years back at the Winter Star Party with Al Nagler and his personal eyepiece collection (Nagler, Ethos & Delos). We were using my 22 f/4 on star fields and DSOs deep in the southern "winter" Milky Way. Even Al admitted that he was surprised that the Type 2 ParaCorr delivered such obvious improvement (at f/4) over the original Type 1. Admittedly, the real takeaway was the image performance gains when the Ethos & Delos eyepieces were combined with the Type 2 ParaCorr. I don't doubt for a minute that we were seeing the synergy of Paul Dellechiaie's optical design, since he's responsible for all three (Ethos, Delos & Type 2 ParaCorr).

 

Edit: For the record, the Type 1 ParaCorr delivered round stars to the edge of the field of view, although at the edge, the stars could be focused to smaller round stars, but then the center of the field wasn't perfectly focused. With the Type 2, center to edge, the stars were smaller and focused.

Edited by Vic Menard, 07 February 2018 - 01:36 PM.

[Mike Lockwood]

I did the comparison back in 2009 in my 20" f/3.0 and 14.5" f/2.55, and there was no comparison.  Greatly improved field curvature with the P2 (as Vic describes above) was the main difference that I noticed, along with much improved coma correction in fast telescopes.

 

I talked about the P2/SIPS in my Okie-Tex 2009 article:  http://www.loptics.c...kietex2009.html

Edited by Mike Lockwood, 07 February 2018 - 10:15 PM.

[Bob S.]

Colin, Based on Vic Menard's time with Al Nagler and the FULL range of TeleVue ep's, it looks like it would be best if you just sold your Paracorr 1 and didn't waste anymore time with a comparison. Both Al and Vic really know what they are doing and had all of the ep's necessary to ascertain what was what with the two iterations of the Paracorr. I know that you just got the Paracorr 2 so that should be your "axe" of choice IMHO for your fast mirror. Clear skies with that new scope of yours and I am sure you are going to have a ball with it! Bob Schilling

[mark cowan]

Al said when the P2 was just some preliminary design work of Paul's that it should be best used with the Ethos line - which was just being rolled out at the time.  As I recall he commented that the latest Ethos (probably the 13 then) had a design SA of about 1/100 wave central field.  So it was going to complement that and does. Only sensible.

[Jon Isaacs]

Question:

 

Does anyone else see vignetting at the very edge of the field with the 31mm Nagler and the Paracorr II?  I see it in all my scopes, my friend Jeff saw it.

 

I discussed it with Paul at TeleVue and he said that there was some vignetting at the very edge of the Paracorr 2, 

 

I don't see it with the Paracorr 1.

 

Jon

[areyoukiddingme]

Yep, I see light drop off with P2 and 31 Nagler. But I didn't think it was vignetting, just an under-sized secondary.

 

I also talked with Paul who mentioned the vignetting. Interesting to hear that the P1 doesn't show it. I tried to buy one the other day--cough, hint, hint--but will go for a GSO or similar if I can't find a P1.