Celestar Manual
improved upon dramatically if several 30-60 second exposures are added together using the Track and
Accumulate™ feature.
When imaging some objects like planetary nebula (for example M57, the Ring Nebula) and small galaxies
(M104, the Sombrero Galaxy), larger image scale is needed to resolve finer detail. These objects are better
shot at f/6.3 or even f/10.
IMAGING AT F/6.3 (MEDIUM SIZE TO SMALL GALAXIES)
F/6.3 imaging gives you finer resolution then at f/1.95, but the slower f-number will usually require you to
guide the image while you are taking longer exposures. Guiding can be accomplished by using an optional
Radial Guider or a piggyback guidescope. The exposure times are about 10 times longer but the results can
be worth the extra effort. There are some objects that are small enough and bright enough that they work
great at f/6.3. M104 (the Sombrero Galaxy) can be imaged under dark skies with a series of short
exposures using Track and Accumulate. Ten exposures at 15 seconds each will yield a nice image and is
short enough that you may not need to guide the exposure at all. For f/6.3 imagining the optional f/6.3
Reducer/Corrector is needed. (see Optional Accessory section at the end of this manual).
IMAGING AT F/10 (LUNAR OR SMALL PLANETARY NEBULAE)
f/10 imaging is more challenging for long exposure, deep sky imaging. Guiding needs to be very accurate
and the exposure times need to be much longer, about 25 times longer than f/1.95. There are only a select
few objects that work well at f/10. The moon images fine because it is so bright, but planets are still a bit
small and should be shot at f/20. The Ring nebula is a good candidate because it is small and bright. The
Ring Nebula (M57) can be imaged in about 30-50 seconds at f/10. The longer the exposure the better.
IMAGING AT F/20 (PLANETARY OR LUNAR)
f/20 is a great way to image the planets and features on the moon. With the PixCel CCD camera and
optional Color Filter Wheel, it is easy to take tri-color images of planets also. When imaging the planets,
very short exposures are needed. Many cameras have trouble taking images under .1 seconds. The PixCel
camera can image at .01 seconds exposures due to the design of the CCD array. The exposure lengths
range from .03 to .1 seconds on planetary images. Focus is critical as is good atmospheric conditions.
Generally you will take one image after another until one looks good (see AutoGrab feature in the PixCel
Operating Manual). This is do to the atmospheric "seeing" conditions. For every 10 exposures you might
save 1. To image at f/20 you need to purchase a 2x Barlow and a T-adapter or Radial Guider.
Figure 8-4 M27 – The Dumbbell Nebula
4 exposures of 30 seconds each!
Figure 8-5 M51 – The Whirlpool Nebula
9 exposures of 60 second each.
