A Coronado Personal Solar Telescope (PST) & eyepiece shootout

Solar SIG!a NOVAC Solar SIG Observing Report

Jim Richberg and Ed Seward

Saturday Jim Richberg and I got together with our Coronado Personal Solar Telescopes (PSTs). There were two tests we wanted to test: a side by side comparison of the two PSTs and to conduct a PST eyepiece shootout.

As a starting point, we rated the seeing today as average.

The side by side scope comparison is due to the superb detail that Jim has seen since purchasing his PST and that was validated in an observing session with NOVAC’s solar guru – Grep Piepol. Based on the excellent chromosphere detail that was observed it was estimated that Jim’s PST was resolving at < 0.7 angstroms, and was consistently besting his more expensive but identical aperture Coronado Maxscope/SolarMax 40 telescope. Coronado denies that this high unstacked resolution is physically possible, but it’s now been seen by a total of three NOVAC members and on two PST’s.

Today both of our scopes showed excellent resolution and contrast across the entire disc of the sun *and* the limb features (prominences). In prior testing we’d discovered that neither scope’s resolution appeared to be improved appreciably by “stacking” a Solarmax 40 filter onto the PST. Based on the serial numbers, our PST’s are close in the production run (~300 units apart). Possibly Coronado had a particularly good batch (these PST’s were probably manufactured about two weeks apart) or their production process is producing quality that significantly exceeds their expectations.

We were fortunate in that there were a number of prominences, filaments and spicules visible today. It is so much fun to watch a prominence change over a relatively short period of time! As Jim put it, the sun is so dynamic that by comparison the reining speed champ of the night sky –Jupiter– is a sluggard! The result of this quick scope comparison suggested that there was no discernable performance difference between these two PSTs.

We spent the bulk of our time doing a side by side comparison of the following eyepieces: 3-6mm Nagler zoom set at 6mm, TMB Super Monocentric 6mm, 7mm Type 6 Nagler, 9-21mm Nikon zoom, and Cemax 12mm with and without the Cemax Barlow.

While a 5mm is the ‘theoretical’ smallest eyepiece for the PST, the 6mm seemed to push the seeing envelope for today. In fact, Jim felt that none of the four 6/7mm combinations– TMB, Nagler 3-6 zoomed out, Cemax 12mm barlowed, and Nagler 7 T6– was reaching its full resolution potential given the windy conditions and so-so seeing. What we *were* able to test was contrast, light grasp (ability to detect the faintest prominences) and focus.

First the negatives. We were not happy with the results of the Cemax Barlow when used with the Cemax 12mm. We could not get a crisp focus. While the 7mm Type 6 Nagler showed great detail its seven elements dimmed prominences so much as to lose detail and even the ability to discern the faintest proms at all.

Of the eyepieces we used today, the Nagler 3-6mm zoom, the TMB Super Monocentric 6mm and Nikon 9-21mm were the best. All three provided bright crisp viewing with excellent contrast. The Cemax 12mm also did extremely well and was comfortable to use due to its 18mm eye relief. It appeared to be comparable to the Nikon zoom in performance, but the more comfortable eye relief would make it a winner for eyeglass wearers.

Besides the eyepiece rankings and scope comparison, we have recommendations for tips and techniques we’d like to share:

1) Use a bellows-style eyecup. We moved one between two eyepieces and it GREATLY improved the apparent contrast! (Orion Telescope and Edmund Optical make these; Orion’s are much less expensive)
2) At least for solar observing (and consider it for those very faint fuzzies as well) use eyepieces with no more than five elements. We’re not sure why the five element Nagler zoom was able to keep up with the one element TMB monocentric in performance, since “less should be more” in solar as well as planetary observing. (Both the Nagler and Nikon zooms have 5 elements.)
3) Do not use the Cemax Barlow.
4) Consider a mount with slow motion controls.
5) If you are going to use a tripod (which one of us does), be sure it is sturdy and try to get one with very smooth head movement.
6) If you wear transition type glasses (darken in the light), you should remove them.
7) Even if you use a decent rubber eyepiece cup, wear a broad brimmed hat or (better yet) make a cardboard shield you can use to block additional sunlight from the eyepiece. There is at least one commercial after-market product available for the PST to do this. A shield plus the bellows style eyepiece cups heightened the contrast remarkably when compared to “low rider” (Televue, Meade, etc.) eyepiece rubber and cupping your hand to block extraneous light.

—–Original Message—– From: Jim Richberg
Sent: Saturday, November 27, 2004 3:01 PM
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