Flats, Darks, and light leaks

Hi, I am recently doing imaging of galaxies and clusters using my AT10 RC, STT8300M and with Moonlite focuser. When making flats and darks should particular care be taken to not allow light to leak into the image train? I searched the forums for leaks, but nothing related to astronomy (just politician leaks on the political forum!)

Two light leak sources I have found (using LED flashlight and looking down OTA) is through the fans to back of mirror, and the gap between the draw tube and body of the focuser. If taking flats at dusk, can enough light leak in to give incorrect flats?

My imaging location is not particularly dark, ie near streetlights. If some light gets to the back of the scope I think it will affect the imaging. If I cannot cancel the nearby lights, then will it help to seal over the fans and drape the focuser with dark cloth?
Thanks for your help and advice!
Roger

Hi Roger,
You should work to eliminate sources of stray light, if you can see it with a flashlight its an issue. The sources you describe will be variable during light frame exposures and flats. This will cause variations in the background from frame to frame as the telescope position changes during your imaging session, and from night to night as you image more difficult objects.

While there are sophisticated algorithms to reduce the impact of random nonuniform illumination sources, Signal to Noise is always traded and adversely impacted. In astro imaging its all about bringing out details, signal, as close to the noise as possible.
Regards,
Dave