Question about Lodestar Live

[HiloDon]

I am new to the Lodestar camera and Lodestar Live s/w. Can a dark frame be saved and imported when needed or does a new one have to be produced every time the program is reopened? Also, should a dark frame be produced for each different exposure time? Thanks for any help or suggestions on dark frames. They do seem to work well in eliminating the noise at longer exposures.

[nytecam]

I am new to the Lodestar camera and Lodestar Live s/w. Can a dark frame be saved and imported when needed or does a new one have to be produced every time the program is reopened? Also, should a dark frame be produced for each different exposure time? Thanks for any help or suggestions on dark frames. They do seem to work well in eliminating the noise at longer exposures.

Hi Don - I take 3 LL averaged darks of say 30s and just this for exp from 10s to 60s and they seem to work fine.  I don't know if they can be saved and reused but as they are camera temperature dependent I think the few second to create them early in the session worthwhile.    I don't [usually] do darks for my e-finder wideangle shot of typically 15s and use 'despeckle' in PSPv4 to remove hot pixel which don't seem to effect the image otherwise.

[HiloDon]

Thanks, Nytecam. I guess I was doing it the right way. You're right, it just takes a few seconds. I didn't think about the potential for temperature change of the sensor.

[Paul81]

Hi Don,

Yep you can save and restore darks, it's the bottom tab when in the Dark acquisition mode. There is a restore button which if you click it will bring up a dialog to chose a master dark FITS file which should be one you have previously saved using the save button on the same tab. You can save after you have captured at least one dark.

As the idea is that you can take a rolling number of dark frames, lodestar live uses a median estimator to yield a median combined dark for your image exposures. In version 0.8, I would recommend you take around 8-10 frames to get a good result (it takes this number for the estimator to converge to a percent or so away from the true median for such a data set). However, in the next version I have vastly improved the estimator so you will only need 3-5 or so.

I recommend you grab darks at the start of an observing session. I do this whilst I align my mount with the camera just sitting on the table with a lens cover on. In this time I get a healthy amount of dark data. I also recommend you switch to darks every 30 mins or so and top it up with say 3 to take into account the camera temperature changing slightly. Of course save the dark before you do that incase you accidently top it up without the scope covered! I've been there and done that!

If the ambient temperature is pretty much the same as a dark you have previously saved, then using the previous will still give good results if you want to get going quicker.

You should take different darks for each exposure length you use. I'd not recommend using say a 60 sec dark on a 30 sec image as you will likely get 'black spots' on your image where there has been too much subtraction!

[HiloDon]

Thanks, Paul. It is much appreciated.