Flats with dewshield on or off?

[RikM]

My newt is prone to dewing so I have a camping-mat dewsheild on it which helps no end. To take sky flats should I leave the dewshield on or take it off?

From what I have read on here I should reduce the exposure of the flat frames compared to lights and darks right? What should I reduce it to? I am after M27 tonight and plan on about 60 lights and 10 darks: 30s at ISO800. I am unguided and have to rely on the in-camera timer anyway so can't run longer subs. What should I be looking for for flats exposure times? Does this seem like a reasonable strategy?

Thanks

Rik

[jgs001]

Rik, my frac's have a fixed dew shield, not a problem with the flats. Are you using and slr ( li don't get to see your sig on this app) as you mention iso800 I'd think so, in which case put the camera in Av mode and let it work it out. That works great for me, and puts the trailing histogram, with the peak on about the 70% Mark on the display.

[RikM]

Thanks John, I will give it a go and see how it turns out. I am using a borrowed stock 300D for now. Not sure it has histogram features. Nothing ventured....

Rik

[jgs001]

Not sure, the display shows the histogram, but the setting should provide the same result... Use aperture priority (Av mode) and just fire away... The exposure meter in the camera will calculate the correct exposure for the lighting conditions and capture the flat for you.

As far as I can tell.. the 300d has a histogram display... when viewing a captured image, press the display button... it'll probably pop up... it's not really needed though... for astro work anyway... I turn that off on my slr, and only use it for daytime use.