Click to Enlarge Coronado SolarMax II 60mm Solar Telescope

Introduction

I have previously owned a Coronado Personal Solar Telescope (PST) and became keen enough on solar astronomy to upgrade to a new Coronado SolarMax II scope. I chose the 60 mm single stacked version because it was still light enough to be portable and of a reasonable price (under $2000).

In buying such a scope I was unable to try one out before ordering so I took the punt. It would be nice if one could line up a few models and try them all out before ordering. Anyway my order took longer than expected (3 months wait). I have put together this review to assist others who might be thinking of upgrading.

Details and Specifications

In 2010, the new Coronado SolarMax II 60mm Solar Telescope (previously the MaxScope 60) became available to amateur astronomers who are more serious about solar observing. The scope has a larger aperture than the PST and a lower bandpass (<0.7 A) for observation of surface detail and prominences on the Sun in H-alpha light.

The scope is particularly useful for serious amateurs who are into imaging the Sun (the H-alpha scope is not useful for anything else but observing the Sun). According to Coronado their new SolarMax II models represent a breakthrough in solar observing with the new and revolutionary RichView tuning assembly. This patented system allows direct tuning of the primary etalon filter. The manufacturers claim no other commercially available H-alpha telescope can provide the tuning range and accuracy of the SolarMax II. The scope can be tuned for the highest contrast views of active regions, flares, filaments, and other surface detail, or be quickly and easily re-tuned for prominences on the solar limb.

Specifications of the SolarMax II 60 mm scope :

• Aperture = 60 mm
• Focal length = 400 mm
• Focal ratio = f/6.6
• Bandwidth = <0.7 A
• Weight = 3.0 kg (6 lbs)
• Supplied eyepiece = 25 mm Cemax
• Eyepiece size/magnification:  25 mm = 16X, 15 mm = 27x, 12 mm = 33x, 10 mm = 40x.
• Blocking filter = 10 mm (BF 10)

Blocking Filters

The SolarMax II 60 mm comes with one of three different sized blocking filters. There is a 5 mm or BF5 (similar to that in the PST), a 10 mm or BF10 (this is what I bought) and a 15 mm or BF15.

What’s the difference? A larger blocking filter gives you more blank space around the Sun and allows for further magnification before the image hits the edge of the field of view. Eyepieces with larger field stop diameters can be used without any vignetting in the field of view. A larger blocking filter is more suitable for imaging but the disadvantage is that a larger filter costs more. The price of the scope depends on which blocking filter is ordered. You need to specify which blocking filter you want when ordering, I recommend the BF10.

First Impressions

The scope is very well made – straight away it felt like a very solid instrument and it looks attractive. Although my SolarMax II is labelled 60 mm aperture, it actually measures 70 mm (inside diameter of the objective lens and appears unmasked).

It has:

• a Sol Ranger finder to line up the Sun,
• a clamshell with three 1/4-20 holes for mounting,
• a blocking filter inside the diagonal,
• a 25mm CEMAX eyepiece,
• a standard Coronado drawtube-helical focuser arrangement and
• a travel-storage case.

The etalon is mid-mounted at the end of the main tube and is adjusted via a tensioning screw or stick mounted on the side of the tube. I found I had to shift the tuning stick one notch anti-clockwise to that set by the factory. Once set you only have to move it slightly by a few millimetres (to compensate for varying air pressure etc.) when starting each observing session.

The extra weight of the 60 mm SolarMax (compared to a PST) means you will have to use a stronger mount. The 60 mm also has more weight on the eyepiece side than the objective lens side so is harder to balance. I still use an altazimuth tripod mount as photographs only take fractions of seconds.

Eyepieces and Views

The 25mm Cemax eyepiece supplied is contrast enhanced and made especially for Coronado’s solar telescopes. However I had a 12 mm Cemax from my PST days, and this gives a much larger whole disc view. I compared the image in the SolarMax II with the image in a PST and found the image in the SolarMax is inverted in the N-S plane compared to the image in the PST (but E-W is the same). Must be a different arrangement of the optics.

This single etalon scope easily visually outperforms earlier Coronado double-stacked scopes. It provides excellent images and shows more surface detail and reveals smaller prominences. The larger aperture means higher magnification can be used (compared to the PST).

Like the PST, it takes a while for your eye to become used to the red glare of H-alpha light – the longer you look the more detail you will see. I also found that a polarizing filter or neutral density filter in the eyepiece reduces glare and shows more surface detail (but they also reduce the brightness of prominences). Such filters did not improve the image in a PST. A Barlow lens can also be used with the 60 mm, while it had little value on the PST. I also found I could use my Meade Ultra wide eyepieces in the SolarMax II but I could not in the PST. The larger aperture of the SolarMax II means better resolution and enables higher magnifying eyepieces can be used.

Double Stacking

With a double stack filter the bandpass of the SolarMax II comes down to about 0.5 A. Double stacking improves the surface detail but again the cost is much higher. I would have liked to compare the single stacked with the double stacked but was unable to do so for this review.

Summary

Overall I am very happy with my SolarMax II 60 mm. It shows smaller prominences than the PST and it reveals more surface detail. However the glare of the Sun in H-alpha light is prominent and this reduces contrast in surface detail at least visually. Photographically however, the SolarMax II 60 mm seems much better especially for surface detail than the PST. (Taking photographs is another story).

The SolarMax II 60 mm costs nearly three times as much as a PST (four times if you get a double stacked scope). Is the extra cost worth it? The SolarMax II 60 mm is not three times better than a PST – I would say visually the image is 25-30% better, and photographically perhaps 40%. The main advantages are with the extra resolution and aperture allowing higher magnification to be used and a wider range of eyepieces.

I am still experimenting with my SolarMax – that is half the fun. I like the fact that you can do solar astronomy in the daytime whenever the sky is clear of clouds – it only takes a couple of minutes to set up my scope and I’m away. You do have to do regular observation if you want to be among the first to see flares, amazing prominences etc. Some days the Sun is really active while others it is quiet. But the Sun is always changing and this makes solar observation really interesting and challenging.

Continue reading with Part 2 of my review now available (20-Feb-2012).

Click to Enlarge SolarMax II 60mm Solar Telescope

Review by John Wilkinson (John W). Discuss this review on the IceInSpace Forum.