Another night with the telescope this saturday. Continuing to test out the homemade telescope mount - this time with some images.

After improving the backlash on the telescope mount last week it was time to test again with some longer exposures.

The testing needed to see if I had improved the guiding in declination (DEC) with my mechanical adjustments. I also need to test the CCD camera. I'd had the camera apart a few days ago to clean the sensor and hopefully cure a noise problem. I've also made some mechanical adjustment to the telescope mirror cell, so I need to check the field illumination.

When we are this close to summer solstice, the nights are very short. It never really gets properly dark, and the sky glows brightly all night. For this reason a hydrogen alpha filter has been used for all testing. The Ha filter only lets through light at the extreme red end of the spectrum. The sky is blue - therefore this filter helps block out the skyglow. Another advantage is that the longer wavelength of light are less effected by the turbulence in the atmosphere.

First target was a shot of M13, a large bright globular cluster in Hercules. This image is two exposures of 300s which have been combined. Total integration time is 10 minutes. Obviously such a puny integration time is going to give a very noisy image, but it would appear I'm better focused than on previous tests, and guiding looks improved.

Click on the images for the full sized version.

I then moved across the sky a bit to the Elephant Trunk Nebula region and did a single 1200s exposure. Again, everything seemed to be working about right.

Now it was getting on for midnight, and about as dark as it was going to get, so I moved back to the same pelican region I'd use on the previous test. I managed to stay awake long enough to complete 3 x 1800s exposures.

I've tried to do some further post processing on this dataset but the it seems that the sky glow has really washed out the contrast. The moon being around didn't help either.

Moving on to the other tests. During twilight I pointed the telescope at the sky and took a few very short exposures to so how the flat field was looking. The answer would appear to be "quite good". Although there is some dust and scratches, plus a smudge, there is hardly any classical Newtonian vignetting.

flat field frame

Finally, I've been suffering some some nasty diagonal banding on my images from the CCD camera over the last couple of years. The camera is a kit build Artemis 285 with a Sony ICX285 sensor. This camera became the Atik 16HR. The bias frames used to be very good, but deteriorated a few years ago. I think I've pinned some of the problem down to a dodgy earth on the 5v regulator.

Below is a before and after image of a cropped region of the bias frame. The one on the left is before and the one on the right is after. The diagonal banding is still visible on the right hand image, but is much reduced.

ccd camera bias frame