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.