New user having black speck problems

[blave549]

Hi,

Another noob has landed!

For my first foray into PI, I'm working with a set of 10 ten-minute luminance subs of the Pelican Nebula, along with a master dark that is based on 25 dark subs. These were taken with an Atik 428EX at 0c.

My integrated result coming out of BatchPreprocessing has black specks all over it. I've tried to research this but haven't come up with any "a-ha!" information. Initially I had created the master dark in Nebulosity, but this morning I recreated it in PI and tried using that, and still have the issue.

The specks are related to the master dark somehow, but I cannot figure out what I'm doing wrong or what's going on. I've tried multiple passes with differing options in BatchPreprocessing but no luck so far.

The attached image shows the integrated result next to the dark, with corresponding areas circled.

Thanks for any insight!

cheers,

Dave B.

[sreilly]

Are your darks working in other programs? Sometimes mismatched temps/times can give less than stellar results. Are you using Bias frames as well?

[blave549]

Are your darks working in other programs? Sometimes mismatched temps/times can give less than stellar results. Are you using Bias frames as well?

I just tried integrating the subs/master dark in Nebulosity. In some cases I can see dark specks on the result, but it's not nearly as pronounced as in PI.

The darks are the same time and temp as the L subs -- 10 minutes at 0 degrees C.

re: bias frames -- no, I'm not. I will try that next.

thanks,

Dave.

[blave549]

followup about using bias frames: I've never used them before. The Nebulosity documentation says this:

If you’re using Dark Subtraction, keep in mind that your dark frames already have the
bias current in them. You will not typically use both darks and biases as a result. If you
do, you’ll end up removing the bias twice (which injects the inverse of the bias back in).
So, don’t do that.


and the MaximDL docs say this:

It should be mentioned that bias is also included in dark frames. As such, it actually is possible to perform accurate calibration without using bias frames. That said, you should always use bias frames if either of the following are true:

    You are using exposure scaling to match dark frames to light frames

    You are using flat-field frames but are not using matching dark frames ("flat-darks")

Since my darks are at the same exposure time and temp as the luminance subs, and I'm not using flats, it sure sounds like I shouldn't be using bias frames.

Comments?

thx,

Dave.