I am evaluating CCDInspector for possible purchase and spent about 3 hours last night trying to use the tool to collimate my C-11.

I was getting solutions with around 215-220 stars and averaging using 3-5 images with 30 sec exposures. The resulting collimation errors were fluctuating from 8.2" to 39.5" over several image runs without any adjustments being made to the scope. I attribute this to the seeing conditions (?). Several times I got the message "stars not widely space enough". A few nights ago I was getting "not enough stars".

The tool seems to be fairly picky when it comes to settings and seeing conditions. Can someone please provide a list of tips and pointers for using CCDinspector to collimate? What kind of star fields is it looking for?

Thanks,
KW

Hi KW,

What image scale is your setup? With a C11 at F/10, you are going to get better results if you bin your camera 2x2 and keep the scope close to perfect focus.

If you have to average 5 images to get to 200 stars, you are probably not pointing to a rich-enough star cluster. Ideally, you should see that many stars in a single 15-20 seconds exposure, especially if you bin 2x2. Look for dense star fields, usually these are easier to find near the Milky Way arms.

Variation from 8.2" to 39.5" is much more than the seeing conditions should be able to cause (unless you are doing this in a hurricane )

Variation in the 4-5 arcsecond range is possible with poor seeing.

Here are some tips:

1. Make sure you use auto-dark subtraction when collimating
2. Bin 2x2 when well-sampled (your setup is)
3. Use clear or no filter
4. Focus well before collimating. If you change collimation by more than just a touch, you may want to fine-tune the focus
5. Find a rich star cluster that covers most of the field of view with stars
6. If you make an adjustment, allow CCDI to take a few readings after the adjustment, as the scope may still be shaking from you touching it.
7. Increase the "images to average" setting only if nothing else helps produce enough stars

Regards,

-Paul

Hi Paul,

I am imaging with an SBIG ST-7XME using a f/6.3 focal reducer on my C-11.

I was pointing near an open cluster in Cassiopeia, binned at 1x1, no filter and autoguiding (I get trailing in RA over 20 sec). The seeing was definitely an issue due to some occasional wind gusts that were coming and going - when it was calm it was great. My scope is protected by a dome, but the wind was still causing me some problems.

Can you give more information on the "stars not widely spaced enough" message? I was getting that most of the time.

Thanks,
KW

Hi KW,

Stars not spaced out enough message usually means that there are enough stars, but there are portions of the image where there aren't any stars or are too few to measure.

CCDI will try to interpolate star sizes for the areas where there aren't any in the image, but this interpolation is not as precise as measuring real stars, and can lead to the large variations you are seeing.

Unfortunately, guiding, drifting, and wind will all interfere with CCDI measurements as they all tend to distort star shapes in ways that have nothing to do with collimation of the system. If the tracking error is not large in a 15-20 seconds exposure, I would try to go unguided and see if you get better results.

Regards,

-Paul

OK. I will give it another shot tonight. Maybe the seeing will be better.

--- KW