From: Milton Aupperle <milton@outcastsoft.com>

Date: December 8, 2010 6:43:23 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] 150mm PST Monster Lives!


Hi Ray;


On 8-Dec-10, at 4:47 PM, Ray Byrne wrote:




Hi Milton,


Is this in regard to the use of flat fielding?


Yes.


I may be wrong here but the problem is inherent to the filter itself so a flat field frame would have the same problem and the light source would have to be incredibly bright.



I don't understand!


Flat field corrects for uneven light being collected by the CCD. It doesn't matter if it's uneven from a Filter, or optical issues or dirt or even decreasing sensitivity of the CCD. It corrects the CCD image until it's "flat".


As to exposure, I'm not sure how much one needs using a halogen flood light, but it should not be too long (<3 seconds?).


People shoot with narrow band DSO filters and 150 m refractors all the time and those aren't too much different.


The PST as a filter just has that sweet-spot it seems to me and you live with it or get a bigger filter (at $$$$ more cost)


I don't know much about them, so your guess is as good as mine.



just my two-pen-north


Ray


TTYL..


Milton Aupperle