WARNING – NEVER VIEW THE SUN WITHOUT PROTECTIVE SOLAR FILTERING. THIS INCLUDES NAKED EYE VIEWING, THROUGH BINOCULARS, OR TELESCOPES. IT ALSO INCLUDING FINDERSCOPES, RED DOT FINDERS AND TELRADS.
Always check your filters by holding them up to a bright light and viewing the light with your bare eyes through the filter to identify scratches, tears or holes. Do not use a damaged filter until it can be determined to be safe. It just isn’t worth the risk.
With the upcoming Mercury transit I thought it was about time I purchased some form of solar protection for viewing and imaging the event. The big question was “What sort of solar filter should I get?”
After looking around the net and asking a few questions of knowledgeable people and viewing through a couple of types of filters, I came up with either the Baader Solar Film or the Thousand Oaks type 2+ filter. But I wasn’t sure which one to get. I liked the colour and feel of the Thousand Oaks, but the Baader film gave a nice clean white image.
Well you know how it is. When in doubt, get both. And I did. So here is my highly subjective, unscientific first day appraisal of these two items. Please note. I am a newbie when it comes to filters so these are only my first hand experiences and impressions.
First a bit of a description for other solar newbs like myself.
I saw the Baader film last year at the Qld Astrofest, so I was familiar with what I would be receiving. (It looks like a tough sheet of alfoil.) I ordered an A4 sheet of Baader from Aquila Optical and Electronics for $45 plus $6 postage (An A3 sheet was about $110 so unless you want to cover a humungous mirror and you need heaps you will get three sheets of A4 delivered for a bit more than the A3
). A couple of minor delays, but the film was delivered the following week by Express Post (Tuesday I believe). So that night was filter making night. Instructions included with the sheet and very easy to follow. I decided to go for full aperture filters for a pair of binoculars, my ED80 and HE-102 refractors (same diameter dew shields so only one filter needed) and a couple of finders (8x50 and 6x30). So for $51 I had 4 sets of solar filters, 5 if you count the binos as separate filters. No bad.
The film is amazingly tough. The express package, when it arrived, looked like one end had been stuck under a pallet of bricks and someone had tried to reef it out. The whole end had been torn off the envelope and the protective top layer of quarter inch cardboard had a great chunk torn out. I was quite concerned about this, but after inspecting the film VERY carefully I could not find a hole anywhere. This incident ended up giving me more confidence in the durability of the film and relieving concerns over punctures and tears.
While going through this process I had also been in contact with Steve Massey from Myastroshop about the availability of Thousand Oaks glass filters. As luck would have it Steve was in the process of arranging a new order the following week. I considered getting another filter for the ED80, but ended up deciding on one for my 8” SCT. This would make more sense for those rare days when hi rez imaging of sunspots would be possible. I had looked through an 8” glass filter before at Astroron’s but I didn’t really remember what it looked like as it was quite a few months previous. So I was buying blind really. Steve was great and we emailed quite a bit until we were sure I was ordering the right size.
The 8” Thousand Oaks filter is more expensive than the Baader film, but the quality of manufacture is excellent and the glass arrived blemish free. But be warned, don’t look at the glass. For one thing it is a mirror that doesn’t lie, and another just looking at it puts smudges one it
. (Consider getting a new dob mirror and trying to keep marks off it.) It is also much heavier than a home made Baader filter, but fits very snuggly over the end of the scope with the supplied adhesive felts for inside the filter rim. One of the concerns I had with the Baader was making sure the filters were tight enough that they didn’t blow off. As a consequence I need to be careful putting them on as they are tight. They probably don’t need to be that tight, but I’m not using anything to secure them. On the other hand the TO filter is very unlikely to blow off.
So now for the big test, how do they look……..through.
The Baader, in a word is, bright. The image through my ED80 at 40x was razor sharp and clean and white. But it is still bright. Removing my eye from the eyepiece I had symptoms of “Full moon viewing blindness”. It was by no means as bright as a full moon, not as disruptive, but there was a definite halo to my vision as I looked away from the eyepiece. Apart from that though it was a sweet view. There was one group of very small sunspots that snapped into focus and were easily resolvable. There was also considerable granulation around the area, though this wasn’t quite as obvious.
Unfortunately, the seeing was lousy and anything more than 60x magnification caused the view to start to deteriorate. This was a shame as I don’t have an eyepiece of sufficiently long focal length to achieve this low magnification with my 8” SCT. The best I could achieve was 62x with a 32mm eyepiece. Also being of larger aperture it was more affected by the seeing than the ED80.
The Thousand Oaks filter gives a much more comfortable view and there was no after viewing halo. The light is a soft orange red similar to a number 21 orange filter. (In fact by placing that filter inline with the Baader film on the ED80 the two filters appeared very similar in colour.) The same sunspot was easily visible in this filter, but not as well resolved, simply because of poor seeing. Also the contrast appeared less though the effect felt more “natural”. The area of granulation was however more clearly discernable as was the overall granulation of the surface. It wasn’t like looking through a pure Ha filter, but it did give that impression.
One interesting affect I noticed was, with the number orange 21 filter on the Orion, individual elements of the sunspot group were more distinct. I put this down to the light not being as bright and swamping the smaller group elements. If this is any indication then in good conditions the Thousand Oaks filter should be a cracker for finding smaller sunspots etc.
I tried a number of filters inline on both solar filters. I used a green number 56, a pale green/blue(?) Number 58A, an orange number 21 and a yellow number 12.
The orange made little if any difference to the TO filter, but as mentioned above did improve the resolution in my ED80. The 56 and 58A worked moderately well in the ED80 though I found the green unnatural to view through and didn’t appear to provide any improvement in resolution over the light blue 58A. The 58A certainly subdued the brightness and improved overall resolution significantly, comparable to the orange 21. In the TO, again I didn’t like the green filter though it did improve resolution as did the 58A but I found that the granulations were harder to discern. The main advantage seemed to be in increasing contrast between already high contrast objects. The 56 and 58A also made the overall appearance of the sun look slightly “muddy”.
For me the stand out was the yellow number 12 in the ED80. I felt it gave a significantly higher contrast and resolution using the Baader film, with possible exception to the orange 21. It didn’t dim the view as much as the orange, but it tamed the brightness enough not to leave strong afterimages in the eye. I also feel there may have been a slight improvement with the TO filter as well, though the image didn’t appear yellow as it did in using the Baader.
So what was the outcome? At this stage it’s too early to tell. I don’t feel that the seeing allowed me to fully explore the potential of the Thousand Oaks filter, though I do have a feeling that when conditions are right, it is going to be a great viewing and imaging filter. I do like the natural colour and it is very easy on the eyes in terms of brightness and contrast. I also felt it allowed me to see more surface detail than the Baader film without filters.
Similarly with the Baader filter. I wasn’t able to push the limits with this filter in the ED80, so that while it performed well at low magnifications I can’t judge at higher magnifications at this time. At these low magnifications it supplied great contrast, especially in conjunction with some colour filters, but without the filters I found it tended to be a bit bright and swamped some fine details. Do I consider it value for money? If you are handy with scissors, glue, tape and cardboard to construct the frames – Definitely value for money. I still have some concerns, though minor now, regarding durability of the film and resistance to puncture. But these are only personal concerns and the film has a good reputation for resilience.
I guess the only real ways to answer these issues is to wait for a day of much better seeing or buy another sheet of Baader for my 8” and get a Thousand Oaks for the ED80 and try again.
Or I can make an aperture mask to go over the 8” to stop it down to reduce the effect of seeing. Could be a job for another day
View Safely.
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