Aluminized Mylar vs. Baader Astrofilm

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Review

I thought it would be in the nature of this forum to discuss, or rather review, the differences between the less expensive forms of solar filters. There are other types and price ranges of filters, and there are glass filters as well, but I wish to limit the review to two types that are relatively alike in form.  Aluminized Mylar is a plastic and so is the Baader filter material. I used them on a home-built aperture mask that fits over my 203mm reflector telescope. It was made with cardboard and duct tape, so the investment was very minimal. To start with, my telescope is a Meade 8" f/6 reflector. I was using a 26mm super plossl eyepiece with a 1-1/4" barrel diameter. Until I had the right amount of filter material to be safe, I used a Celestron variable polarizing filter set in front of the eyepiece. The mask was a good fit onto the end of my telescope objective, and has a 3" (76mm) off-axis aperture.

The aluminized mylar filter material was acquired through Apogee, Inc. of Union Illinois USA. It is delivered in 18"x30" sheets in a protective mailing tube. The packaging was very good with a well protected box outside of the canister. The delivery was on time and in good condition. The material was surprisingly light and flexible. I had imagined it to be like aluminum foil, but it was more like plastic food wrap, but a lot less sticky. I held it up to a 60 watt light bulb and it showed light pretty easily. The next unexpected impression was when I tried to cut the material for my mask. It was fairly tough to cut with a pair of household scissors. After careful cutting, I had a square that I simply taped to the outside of the mask over the aperture opening. As I said before, I used a polarizing filter set adjusted to a very dark setting ahead of my eyepiece. 

The Sun was difficult to find right off because the entire view field was glowing and I couldn't tell whether I was looking in the right direction or not. Finally after moving around a bit I had the out-of-focus Sun in the view. I focused in as well as I could before I realized I had a washed out view even though I had a polarizing filter. Very little sunspot detail was available. I cut another piece of filter and added it to the first one. At this point I noticed a difference between one side and the other of the filter. One side was shinier than the other. I flipped the shiny side out on both. When I looked again, I was pleased at the contrast. I removed the polarizer filter set and noticed the image was still a bit brighter than I had expected. After adding even more filter material, I decided the view was becoming grainier and dimmer, so I reverted to the two layer filter setup. The sunspot detail was pretty nice, but everything was a bright blue with a hint of yellow in the Suns' disk. The image reminded me of a cue-ball in the daytime sky. The space around the Sun was sky blue. No appreciable granularity of the Suns' surface was noticeable even after I boosted the power to 260x with a Meade 4.7mm Ultra Wide plossl eyepiece. The sunspot images were there, but nothing to get excited about. The 
sunspot penumbra were muddled and showed no real structure.Upon conclusion, I decided the filter material was usable, but lacked something of a visually appealing manner.

The Baader AstroSolar (TM) filter material was acquired from Draco Productions, Inc. of Pensacola Florida USA. It came in a mailer envelope and was mounted in between two paper sheets. I ordered the 3" size to match my aperture mask. The package also included a receipt of sale and a white sheet giving a full description of how to build your own filter cell, and how the AstroSolar filter was designed. The package came on time and was in good condition. The company also e-mailed me with a delivery confirmation after I ordered. Nice touch.

As before, I noticed the light weight feel of the material. I did notice the material had a streaked or smudged area on both sides. I was a bit concerned about whether I might have received a part of the end of the roll or it had been damaged in assembly. I held it up to the 60 watt bulb again and noticed the light transmission was a lot less. I was hoping I would only need one layer because I only bought this one piece. I opted to use the polarizing filter set ahead of the eyepiece again, just in case. I also noticed that both sides of the film were shiny. I suppose that is due to the fact that they coat both sides. I was comforted in this as it is a safety feature as well. Any hazardous scratches would have to be on both sides to matter. Nevertheless, I inspected it closely as any solar filter should be before use.

The Sun was right in the line of view when I first looked through the eyepiece. As luck would have it, I was even in focus. I didn't need the polarizer set, so I removed it straight away. I couldn't believe the difference in the view. The sky around the disk was jet black. The disk was round looking and three-dimensional. There were at least half a dozen sunspots visible. The striking thing was the 
clarity of the penumbra on each of the sunspots. I quickly switched up to the 4.7mm eyepiece, and noticed a great deal of detail in the sunspots. There was no glare from the disk to the background sky and a hint of granularity was truly exciting to see. This left me wishing I was looking at this with a nice APO refractor. As I panned through the solar field, I was left breathless.

This filter was very pleasing and leagues above the former. The lack of color is the only curious drawback, but not important enough to worry about. If a good look at our host star is the quest, then this material is the order of the day.

In summation, I would certainly recommend the Baader over the Mylar. The noteworthy difference being the price. You can buy the Mylar for half the cost of the Baader, and there is ten times as much. On the other hand, if the view is less, then what is the advantage?

Submited by - David Ryle

Aluminized Mylar from Apogee, Inc. Phone(815)568-2880
http://www.apogeeinc.com/

Baader AstroSolar (TM) from Draco Productions Phone(850)484-1152
http://www.dracoproductions.net/