Posts Made By: Ed Zarenski

Personally, I find every galaxy looks different than the others. I suggest you go over to the Equipment forum and read Jim Gleason's post "Learning to See" 4-25-03.

edz

Mark, these brief book reviews may help you make your decision. 25 book reviews in one article.

Luginbuhl and Skiff is a good book, just data, no charts.

Believe it or not Binocular Astronomy by Crossen is full of descriptive data and since it crosses the boundary, has data, charts and detail, an excellent choice.


http://www.cloudynights.com/books/books-general.htm

edz

NOW COMES THE QUESTION:
!!!!!!!EDITED 5-3-03!!!!!

In my research of the Airy disk formula, I noted numerous well-regarded astronomy references and several websites that have published astronomy related formulae referring to a shortened form of the formula for calculating the Airy disk radius. That shortened form in all cases was given as A = 1.22/D where it is stated that A = arcsec and D = scope diameter in meters.

This has been proven to be innaccurate. The correct formula is theta = 1.22 lambda/D. This formula does provide results for the radius of the Airy disk in radians that must be converted to arcseconds. The results are nearly equivalent to the results one would get using Rayleigh criteria as 5.45/D.

Numerous reference books and websites, some by noted authors, have explanations for Dawes Limit, Rayleigh Limit and how these relate to Airy disk. Many of these references are incorrect.

An excellent source is http://www.licha.de/AstroWeb/articles_fullsize.php3?iHowTo=16

Neither Dawes nor Rayleigh indicates a condition where two stars are completely separated. Rayleigh indicates somewhat greater separation than Dawes. Neither is equivalent to the diameter of the Airy disk.

The distance between the centers of two point sources that appear completely separated needs to be at least twice the value determined by the wavelength formula. This would be approximately equal to twice the value determined by the Rayleigh Limit formula 5.45/D.

If you need further information
You may contact me at [email protected]
Thank you,
Ed Zarenski
Cumberland, RI

The viewer who originally stated he was able to split 75Her 4.1" with his 20x60 Pentax has since corresponded with me to let me know he was not able to do this upon retry. I have since used my TV85 and determined the lowest magnification I could split 75Her 4.1" was at 43x. The results (for me) is an apparent separation of 176 arc seconds.

Milt, yDel is listed as 9.6" in Skycataloge 2000.0, my bible. You split it with 18x50s and that results in an apparent separation of 173 arcseconds. Inge has sent me some results that reflect significantly greater acuity. Once he has seen a split at a higher power, he is able to go to lower power. He is getting down into the 120-130 arcsecond range on the best occasions, although these are the exception and not the rule.

No one, with any binocular has yet reported that they are able to split Castor 4” or Algeiba 4.4”. 75Her at 4.1" fits perfectly in with this group. I'd like to hear from someone with 25x or 30x binoculars that would attempt these three splits. Also refer back to the original post for a few easier doubles in the 6" to 14" range.

edz

10mm radian. 9mm UO ortho. 8.8mm Meade UWA.

The best deepsky eyepiece I have in that range is the Meade 8.8mm UWA. It provides 12% more mag than the 10mm radian and about a 40% greater Tfov. (Correction = It has 40% greater Afov BUT provides about 22%-23% greater Tfov than the radian). Sees much more than the 10mm radian (because of the aditional magnification) and is absolutely pinpoint sharp right off the edge.

On planets the UO9mm is better.

The UWAs and the Radians sell for the same prices 240$new or $180used.

edz

http://www.cloudynights.com/breviews/4way-2.htm

edz

These are some of the differences in what was seen with the 15x70 Oberwerks 2002 (15Ob02), Oberwerks 2003 (15Ob03) and the Fujinon 16x70 (16Fuj). All viewing from mounted parallelograms not touching binocs except to acquire and fine focus. 6-6-03, by 1:00 A.M. Cygnus Milky way was just faintly noticable.

Mizar 2.3-4.0/14.4” - in 16Fuj can easily see split, in the 15Ob03 it was suspected, in the 15Ob02 it is not seen or elongated.

100Her 5.9-6.0/14.2” – in 16Fuj remarkably easy, in 15Ob03 seen easily, in 15Ob02 just barely seen.

yDel 4.5-5.5/9.6” – suspected split in 16Fuj, definite thin elongation in 15Ob03, no elong in 15Ob02. yDel was just barely seen in TV85 with 27Pan at 22x.

M13 easily seen but no resolving in any. M13 not resolved in TV85/27Pan at 22x.

St1 o.c. in Vul (40*, 24* to mag 9.5 in 60’) – 34* seen in 16Fuj, 33* seen in 15Ob03, 27* seen in 15Ob02.

M39 o.c. in Cyg (30* in 32’) – 22* seen in 16Fuj, 20* in 15Ob03, 18* in 15Ob02. 24* seen in TV85/27Pan at 22x.

North America nebula in Cyg near Deneb - NW section of neb (the northeast quarter/half of US and Canada) seen with 16Fuj, not seen in any other instrument.

Fujinons showed nearly as much faint star background light as TV85/27Pan. Fujinons were able to focus double stars to a much finer point of light than either of the Oberwerks.

edz

Leif, M24, the Star Cloud, is so large you would need a 2° to 3° fov eyepiece to surround it. It is easy to be right on it and not see the boundaries so you wouldn't know you are in the middle of it. I think it is best seen with binoculars.

edz

Agreed. I own the G5. My favorite high power eyepieces in this scope are a 9mm and the 7.5mm Ultima. edz

Sounds right if both the barlows are operating at the rated factor. My Ultima barlow varies from about 2.2x to 2.4x in my SCT. It's 2.2x in my refractor.

edz