Hi Chuck, Looks like most are saying to go full aperture so please do that if possible. I went over to SPOC last evening and took a picture and got some measurements. Taking the picture got me a good look at the objective and reminded me that it really needs to be cleaned. http://users.wirelessbeehive.com/~paw/temp/BOGDAN.JPG The diameter of the glass is 200mm. The outside diameter of the cell is 250mm. That, BTW, surprised me as I machined the cell to fit the piece of irrigation pipe that now serves as the scope's dew shield. I figured that since I bought the pipe here in Utah it would have been manufactured in American units. But, no, it's exactly 250mm. Speaking of American units, anyone care to guess the significance of this display of American units (image taken in my truck yesterday)? http://users.wirelessbeehive.com/~paw/temp/almost20.JPG But back to the filter, thanks for doing that Chuck. Much appreciated. patrick On 15 Mar 2013, at 08:21, Chuck Hards wrote:
On Fri, Mar 15, 2013 at 3:39 AM, Patrick Wiggins <paw@wirelessbeehive.com>wrote:
Chuck Hards was kind enough to offer to make a custom fitted white-light solar filter for SPOC's Bogdan refractor so I brought that up at last evening's SLAS board meeting.
There was some discussion about whether any such filter should be make of mylar or glass (to be determined) but one thing that I'd like discussed here is the size of the filter itself.
Usually when it comes to telescopes I think "bigger is better" but in this case I'm wondering if it would be better to go full aperture (200mm) or would we really gain that much by going full aperture over something smaller.
Opinions?
Patrick, I was thinking about the aperture question, myself.
Mornings are usually the best time for large, full-aperture solar viewing. By afternoon, daytime seeing almost always degrades to the point where large apertures don't result in increased resolution. Also, 5 or 6 inches of aperture is usually enough for high-powered views of small solar detail. So I would recommend a solar filter of about 6 inches for the Bogdan refractor, but I could easily make it full-aperture if desired.
As to mylar vs. glass, my offer is for a Baader filter only. If the board wants a glass filter, they will have to purchase a commercial one using SPOC funds, or have one donated by someone else.
I own both types. I use Thousand Oaks glass as well as Celestron glass, but I prefer the Baader filter material. The sun is "white" to our eyes, and only the Baader filter is a true "neutral" density filter. I consistently see finer detail with the Baader filter than through the orange-tinted glass filters (or any color glass filter, for that matter). Baader solar film is the best made, is true optical-quality mylar, and is 100% safe. I know some people don't like mylar but it's come a long way since Tuthill's "Solar Skreen"- which was utter crap, no offense intended to the late Mr. Tuthill. It also lasts a long time if properly taken care-of. I just replaced the mylar on one of my filter cells that was 15 years old. Glass filters with their evaporated metal coatings are delicate too. If dropped, they shatter, and are just as susceptible to pinholes in the coating. If damaged, you buy a whole new filter and have to wait for it. A Baader filter can be replaced the same day. I'll even donate an extra piece of filter material that can be kept in a large envelope in the SPOC equipment bay, and will show the telescope operators how to replace it in the field if it's ever necessary.
I have to laugh when people state that an orange-tinted sun looks more natural. They are responding to a lifetime of conditioning, from art and photographs taken through tinted filters. We evolved under sunlight and to our eyes, the sun is most definitely "white", or neutral in tint, spectral classification aside.
If the board wants to take me up on my offer, I will also make a filter for the refractor's finder.