Calculations and Explanations

 This thread started when, on the night of August 18, I finally got a chance to do some imaging. That night, the targets were going to be Jupiter and Saturn. With my setup, those are relatively quick targets; no flats and darks, if any, taken at the same time as the lights. The results were....amazingly poor. I usually blame results this bad on the seeing, atmospheric turbulence. In this case, I'm sure that was the major player. But, as I understand more about the telescope and camera, I can see that its not just that (even if, as we will see, it appears to be the major player). First, though, the “final” images.

Jupiter

 

 

 

 

 

 

 

 

 

 

 

 

Saturn

 

 So, what can I learn from this.

1. First thing is to find out what the scope is capable of. This is often reflected (no pun intended, but not bad anyway) in the Dawe's limit. This is a calculation that puts a number on the resolving limit of a telescope. Resolution is the ability of the scope to “resolve” to objects that are next to each other into the two separate objects. In other words, how close together can, say, two stars be and I'm able to tell they are two stars, not just one fat one. For an 8 inch SCT, which is what I have, that limit is 0.57 arc-seconds. Anything closer together than that can't be separated.

2. Camera “resolution”. This is something I've known and worked with for a long time and I (mostly) understand the factors involved. For the images above, the relevant information is scope... 8”, F10, and camera... 3.75micron pixels,1290x960 chip. This calculates to a resolution of 0.38 arc-seconds per pixel.

3. If the image seems blurry, it is not because the image is smeared over too many pixels, since the camera can “see” better than the scope can deliver (0.57 scope vs 0.38 camera), it must be something else like focus or seeing.

What can I do to improve my planetary images.

1. Move to an area of the country with better skies, ie, less water vapor (clearer), and better seeing. Not likely to happen in my lifetime.

2. Get a faster camera. The air turbulence causes motion blur. A faster frame rate has the possibility of “stopping” the motion to get clearer frames. This is possible, especially since the company that makes my camera has several versions that are faster, with faster download speeds (which is usually the bottleneck).

3. Get a bigger telescope, say a 14 inch SCT. This would allow the Dawe's limit to be the limiting factor in resolution. Really not likely to happen in my lifetime.