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Posts Made By: John Centala

July 1, 2003 09:14 PM Forum: Solar System Observing


Posted By John Centala

For a free copy of the latest issue of The Strolling Astronomer, go to Then scroll down to the bottom and click on FreeJALPO45-2.pdf. This issue has a lot about Mars.

John Centala

April 13, 2003 02:06 PM Forum: Equipment Talk

Celestron CGE Mount

Posted By John Centala

I just tried out my friend's new CGE1400 last Thursday. The mount is similar in gear and shaft size to a Losmandy G11. I would estimate that it is a little more rigid than the Losmandy, but of course could not make a side by side comparison. The mount is a little small for the 14 inch, but is OK visually, certainly better than typical fork mounts. I would want a bigger mount for photography with the 14 inch, since I routinely bump the eyepiece when guiding. I'm not too sure about the Go To feature. It seemed to work, but also occasionally went off on its own. The instruction manual does not have enough detail to learn how to operate the mount properly.

John Centala

May 24, 2003 09:44 PM Forum: Astro Binoculars


Posted By John Centala

I have seen all the Messiers, including M109, with my 20 x 100 Vixen binoculars. Walter Scott Houston claimed that all are visible in a 1 inch refractor at 40x.
John Centala

June 9, 2003 06:36 PM Forum: Solar System Observing

Mars Magnification?

Posted By John Centala

For the best view of the south polar cap in 1988, the last good Mars opposition, I used 480x with my 8 inch refractor. The polar cap is a high contrast feature and can tolerate lots of power. For the best view of the dark areas, I found 325x to be optimum. Of course the seeing must be reasonably good. Here in Iowa we occasionally have very good seeing. The minimum magnification I use on the planets (Mars, Jupiter, and Saturn) is 230x. If the image is fuzzy at this power, I close up the observatory.

July 6, 2003 05:38 PM Forum: Film Astrophotography - Imaging and Processing

Photographic Magnitude Limits

Posted By John Centala


With my 8 inch refractor I have been able to barely see a 14.7 mag star, using 325x. In a 15 min exposure on Kodak Royal Gold 400 at prime focus (F/12), I got to about 17.0 mag on orange stars, and 16.5 on bluish white stars. In my experience, E200 slide film is noticeably slower than Royal Gold 400.

John Centala

August 19, 2003 07:00 PM Forum: Equipment Talk

Star Atlas - Greek letter confusion

Posted By John Centala

Obviously you did not study Greek in high school. For the letter theta, the "O" with a line thru is the printed or typed form, while the one with the curl on top is handwritten or script.

September 2, 2003 07:59 AM Forum: Film Astrophotography - Imaging and Processing

Help : OM-1 Shutter is stuck

Posted By John Centala

I had a similar problem with my old original OM-1 (not MD). I took it to a repair shop, and the problem was a bent shutter button plunger, a small shaft just below the release button. It was probably caused by using too much force on the cable release. Since then I have been very careful not to push any harder than needed on the cable, just enough to trip the shutter, and the problem has not recurred. I don't think that this problem can occur unless a cable release is used.

September 2, 2003 08:06 AM Forum: Film Astrophotography - Imaging and Processing

Mars photo question re: exposure?

Posted By John Centala

At f/170, a 0.5 sec exposure is about right on 400 speed film. This is equivalent to 1/500 sec at f/11.4. As already noted by John Boudreau, your image scale is much too small to get much detail. I am using a focal length of 34,000 mm!

September 5, 2003 06:40 PM Forum: Solar System Observing

Martian moons

Posted By John Centala

Early this morning (1:10 to 1:40 am CDT) I saw Phobos with my 8 inch refractor. I used 270x with an occulting bar. I could still see it when only half of Mars was obscured by the bar, but could not see it when Mars was in full view. I used the same equipment to view Phobos during the 1988 opposition. I did not look for Deimos this morning since it was not well placed.

April 11, 2004 09:26 PM Forum: CCD Imaging and Processing/Solar System

First light: SBIG one-shot 2MP color camera

Posted By John Centala

A good picture, except that the color seems extremely subtle. Note that all the bright stars in globular clusters are orange giants. A picture taken with most color films shows this very well. Is it possible to increase the color saturation? Can you test the camera in daylight to see how well it reproduces color? I was thinking about getting this camera, but now I'm not sure I want it. The SBIG website picture of M33 shows better color, maybe just a bit weak compared to normally processed color film.