Some Introduction To My Solar Imaging

 

Welcome to my solar imaging page! I started solar imaging in 1988 by using my trusty old department store 50mm f/16 refractor with Density 5.0 Solar Skreen mylar solar filter. I first began imaging the whole disk which was only about 800mm f/16 with my small scope then after a few more tries, then started going into positive projection imaging of interesting sunspot group. Since the original alt-azimuth mount was a little bit shaky. I piggyback the refractor into my homemade 6" f/9 dobsonian reflector. My setup was using 8mm Kellner eyepiece using positive projection giving me an effective focal length (EFL) of 5450mm f/109. With that setup my exposure was very slow at 1/60sec with Agfachrome 100 slide film. So what I did was to use just one of the thinner of the 2 sheet of Solar Skreen which gives me density 2.5 and with this new setup plus an orange filter, I was starting to use 1/1000sec which gives me some good images. You can see some of these images at my old Sun page which is still active till now but will be using the new solar image page starting now.

In 1997, I save enough money to get myself a Televue TV-101, a 101mm f/5.4 apo-flourite refractor. My first plan was to get the Astrophysics 105mm Traveler because it is much shorter and compact than the TV-101. But the problem was that the waiting time for the AP105 is around 1 to 2 years so I cant wait that long and thus acquire the TV-101.

I set up my TV-101 on a Super Polaris Mount (I have sold this mount already and replace it with SP mount's bigger brother, the Great Polaris  Deluxe (GP-D) which has a greater payload capacity of about 10kgs against 6kgs capacity of SP mount) with Vixen Sky Sensor 2000 and tried various solar filters in the market such as Solar Skreen, Thousand Oaks Glass filters Type 2+ and 3+, Baader AstroSolar Filter 5.0 and the 3.8. Of the above the Baader gives a better contrast than the rest but the problem is that the Baader filter, whether 5.0 or the 3.8 are good only for whole disk imaging at high speed and is not very suitable on my setup as I need exposures that is faster than 1/1000sec. With the need to have a high speed exposure camera, my budget that time was to get a Canon EOS 50E camera body which has a top speed of 1/4000sec which is very useful on my setup.

My problem was solved when I got a chance to acquire a 2" INTES Herschel Wedge set. A Herschel Wedge is a professional tool for the serious amateur to view the Sun in white light. The original set includes the wedge itself and high quality B+W Schneider Neutral Density (ND) filters 3.0, 1.8 and 0.9. I also ordered a B+W Linear Polarizer and ND 0.6 to complete my set. This cost me around $600 to acquire them. But to use a Herschel Wedge, proper understanding on the danger of viewing the Sun is at its maximum. Below are some warnings:

  1. It requires responsible handling and should never be used by anyone who is not completely familiar with its construction and use. Prevent that unexperienced observers or children use this instrument on their own, without expert supervision.
  2. Never remove the 1:1000 (ND3.0) Neutral density glass filter from the eyepiece (or the 1.25"/2" adapter) except for eyepiece projection photography.
  3. Do not look into or allow anyone to look into the Herschel Wedge from the wrong side (do not look into the mirror.)
  4. Always keep the reflected beam of excess sunlight pointing toward the ground.
  5. For visual observation, use both the neutral density filters, ND3.0 and ND1.8 or Polarizer, threaded together into either the eyepiece or the reducing adapter.
  6. The total transmission of the Herschel Wedge without the neutral density filter is 5%, still very bright to use without the said filters.
  7. When focusing for the eyepiece projection photography, always hold the ND0.9 filter between the camera and the eye to avoid irritating brightness.
  8. Never attempt to view the Sun with this instrument unless you have checked and are absolutely sure that it is properly setup to reject harmful excess sunlight!
  9. Never use the Herschel Wedge with a catadiotropic telescope such as Schmidt-Cassegrain or a Maksutov or reflectors such as Newtonian and Cassegrain as it can damage the mirror coatings and inside baffling and should be best used with a refractor or schiefspieglers.
  10. Never thread the ND filters into the focusing barrels in front of the Herschel Wedge Unit. Thisn could damage or break them. Use the ND filters only behind the Herschel Wedge and threaded into the eyepiece barrel or the reducing adapter.
  11. NEVER LEAVE THE TELESCOPE UNATTENDED OUTSIDE DURING THE DAYTIME. THIS APPLIES TO ANY TELESCOPE, WHETHER OR NOT FITTED WITH THE HERSCHEL WEDGE.

 

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