Hi,

This isn't necessarily a CCDAP question, but I'm hoping maybe someone out there has some thoughts...

In between exposures, when CCDAP dithers, it instructs MaxIm to do a full-frame exposure with the guide camera so it can reposition the guide star. Periodically (last night it happened twice out of 10 exposures), MaxIm will choose an area of the field where there is no guide star at all, I'm guessing from some transient event like a cosmic ray hit that happens to be brighter than the real guide star. When this happens, the system then attempts to guide on camera noise. Frequently the "guide error" will by chance fall within the range that CCDAP is looking for, so it happily starts exposing.

Can anyone think of a way to keep this from happening? I've lost a surprising amount of shots because of it. Obviously it's more likely to happen with a faint guide star.

Could it even be something that CCDAP could look for? Perhaps a reasonability test for how much the guide star moved from the last exposure or something?

Thanks!

Bob

Bob,

You are not alone. This happens to me all of the time. 2 in 10 images seems about right.

Lately, I have added an AO-8 to my imaging train. Because the exposure time is between .1 and .4 seconds, the guide stars are quite dim and the loss of images is higher.

I loose about 25% to 33% of my images using the AO.

If it is a cosmic ray, then perhap spatial filtering will elimate the cosmic ray effect.

I have a Starfish camera for off axis guiding when I am not using the AO. The driver has a hot pixel filter and two kernal filters that can be invoked prior to download. I will have to experiment with this autoguider to see if Maxim still has trouble.

I also suspect the star detection algorithm used in Maxim has a problem. During Autoguider calibration with the AO using bright stars, it routinely misses the detection. This is particularly frustrating since the cal star is the brightest star in the field by 2 to 4 magnitudes.