Posts Made By: Barry Simon

Ed,

You have a one line statement that the Tfov measured = 3.3 degrees (how did you do that little degree symbol on your keyboard?). I have reported that many wide angle binoculars typically do not have the fields in practical use as what is given in the specifications, but a reduction from 4.5 degrees (what I think is given in the specifications) to 3.3 degrees is significant. Please give us a little more information about your findings here.

Barry Simon

Peter,

Go to http://groups.yahoo.com/group/binocularastronomy/ this is the BinocularAstronomy Yahoo Group and read my full review of the Burgess 20x100's compared to the Miyauchi 20x100's. This was the second pair of Burgess I had to test (the first test was done on the prototype pair back in April. See messages 3734 and 3735.

Barry Simon

Additional Info -

I am posting a 2nd photo. It shows the scopes with a mutually shared sunshade. The sunshade serves two purposes. First it shields your face, while observing, from direct sunlight. This helps tremendously, by putting your face in shadow, the view is enhanced greatly and you are also more comfortable. Additionally you will see the small shadow ring on the surface of the shade concentric with the dewshield and Thousand Oaks filter. When concentric, the Sun is in the eyepiece, thus centering the shadow serves as a finder!

The 1/8" thick by 12" x 24" sheet of Evergreen modeling plastic was obtained at a local hobby shop. It is available in various thicknesses. Much thicker than what I used becomes hard to cut. Having used these shields on all my solar filtered scopes, I find it difficult to observe the Sun without one.

Barry Simon

May be more of a focusing issue. With some scopes (Takahashi comes to mind), it is pretty tough to reach focus with some combos because the tube really is not short enough. Have a straight thru blocking filter and then have to add a regular diagonal behind it and you find that you will have a number of additional telescopes that cannot rack in far enough to achieve focus.

Additionally I bet that doing it straight thru would not have a great impact on cost.

However for those that want the straight thru option, I think it would be a plus. One of the reasons Takahashi scopes are too long is the Japanese like to use them without a diagonal. The extra length is perfect for their use.

Barry Simon

I have looked thru a double stacked 40 and can say that if surface features on a full disc Sun is your goal, go for the Double 40. However in double stacking you will lose some of the limb prominence aspect of hydrogen alpha viewing. Keep in mind to that you mentioned MaxScope, so you would be observing at just 16x with the 25 mm Cemax, and just 22x with the 18 mm. Even a 12 mm with 2x barlow would just give you 66x. At this power the image will be fairly dim with an approximate .5 mm exit pupil.

I believe the concept of double stacking is good, but is really only optimized with the larger aperture Coronado h-alpha filters. I looked thru a double-stacked 90 at the Texas Star Party in 2002 and it was impressive. At the same 66x your exit pupil would be about 1.4 mm making for a much brighter image. To get to that size exit pupil with the smaller 40 mm scope, you would have to drop your magnification to about 29x. (The double 90 would be expensive with a system approaching $10,000.)

I personally have a SolarMax 60 with a BF15. As I prefer prominence viewing over surface filaments, etc., my system works better for me.

Barry Simon

Part II,

note that the original of my first post does look better than the image posted. Any thoughts on getting a more accurate rendition of what I actually have when I post here or to other internet groups?

Anyway, here is a second image.

Barry Simon

Larger aperture filters allows you to go to larger aperture telescopes. With that you can go to longer focal lengths and maintain the same f/ratio keeping images bright with longer focal lengths. I have heard that these filters are optimized for working at a focal length scope at 10x their aperture or f/10 assuming that the aperture of the filter and the scope are the same. (The aperture is dictated by the filter if it is the smaller of the two - filter or telescope objective or it is dictated by the objective or mirror if it is the smaller component). In the later case you would be spending needlessly for some filter area you cannot use.

For the 40 mm SolarMax a 40 mm scope with a 400 mm focal length gives you f/10, and hence with the SolarMax 60, an f/10 focal length is 600 mm and for the SolarMax 90 an f/10 focal length is 900 mm. Once again assuming that the actual focal length is as listed above and the objective size is at least the aperture of the filter. Note - these filters do work very well with faster f/ratios, shorter focal length scopes.

Getting back to the larger filter advantage - the longer focal lengths give you greater image scale and you can drill down using higher magnifications without reducing exit pupil too much. You can go to relatively high power with smaller filters but as the exit pupil is decreased these images are dim and the smaller apertures cannot hold these higher magnifications as well.

Having said that, solar observing with Coronado filters is sometimes done in small blocks of time. I have a multitude of good refractors, both apochromatic and achromatic that I can use with my SolarMax 60. I can get a number of combinations out the kitchen door in just a few minutes for quick looks. If I "upgraded" to the 90 mm filter, my most logical instrument to use would be a Brandon 94 mm apo which would not be quite as portable, the only other logical combo with this filter would be a Vixen 102 mm f/9.8 achromat which is not exceptionally portable either.
So given my current habits in terms of viewing the Sun, the 60 mm filter works best for me and didn't take as big a bite out of my wallet as the 90 mm would have.

Note - a well corrected achromat will do as good a job as a well corrected apochromat. One of my set-ups is using a cheap 60 mm f/11.7 achro tube assembly; I see little difference in image quality as compared to a Takahashi FCT 76 apo tube assembly.

Barry Simon

The image posted in the previous message does not show near the detail of the original. Anyone interested in seeing a better copy can check it out at:

http://groups.yahoo.com/group/DeepSouthAstroImagers/

Go to the Files Section

Barry Simon

What do you want to observe and with what will your telescope purchase be mounted on? Additionally, what do you already have, if anything? While both are relatively small and easy to transport and mount, the 76 is smaller by a fair amount. If the planets will be a major target, Moon too, I would say get the TV 85, if portability is more of a key need, get the TV 76.

Barry Simon

Found a photo. See attached.

Barry Simon