I have been reading about support images; bias, darks, and flats.  I am no expert and I am probable at the level of just knowing enough to be dangerous. Since my old brain’s signal to noise ration is about like my cameras’ I figure I need to go over this stuff 9 to 16 times to get a clear picture. You are my Ginny pigs.  We always have Patrick to straighten us out.   Bias Bias frames record the signal from the low-level charge that naturally occur on CCD or CMOS sensors and are added to every image taken .  I shot a picture with the lens cap on, at room temperature; at the fastest speed my camera would go 1/4000 of a second.  If I was doing this for real and planed on using it I would have to do this at the same temperature I would be imaging at.   Looking at the image: http://www.slas.us/gallery2/main.php?g2_itemId=1306   It looks like a perfect black field.  But taking the image into PhotoShop we see on the threshold display a little bit of dribble on the left side that represents the Bias. http://www.slas.us/gallery2/main.php?g2_itemId=1309&g2_imageViewsIndex=1   Then moving the threshold slider over under the dribble we begin to see the bias: http://www.slas.us/gallery2/main.php?g2_itemId=1312&g2_imageViewsIndex=1   Then sliding the threshold slider all the way to the left we really see the bias noise: http://www.slas.us/gallery2/main.php?g2_itemId=1315&g2_imageViewsIndex=1   With the eyedropper active I was seeing values from 10 to 80 that are added to every image I take including dark frames.   Flats A flat-field frame is a picture of the optical system's in the condition you are about to shoot your image including peculiarities, such as vignetting, uneven illumination, and dust shadows.   I got a hair brained idea for making a flat-field thingy instead of a light box.  The light nbox I believe would be superior but one of its drawback is bulk.  Someone probably thought of this before, but for me it just popped into my head. My idea cuts down on the bulk and is versatile enough for other things including Flat-fields mask, Hartman or Bahtinov masks, and crosses for diffraction spikes for stars. Oh, and the price is right.   The basic materials are shown here: http://www.slas.us/gallery2/main.php?g2_itemId=1318 Yep, embroidery hoops with 2 ply of t-shirt material for flats, some vinyl for Hartmand or Bahtinov masks or what ever. Here is the flat-fild hoop for my 100mm ED http://www.slas.us/gallery2/main.php?g2_itemId=1321   Here is the flat-field hoop for my 12.5” dob: http://www.slas.us/gallery2/main.php?g2_itemId=1324   Here is the flat-field hoop in action: http://www.slas.us/gallery2/main.php?g2_itemId=1327   and this is what the flat looks like: http://www.slas.us/gallery2/main.php?g2_itemId=1330&g2_imageViewsIndex=1   I will probably take these images off this galary after a week or so.   A word about bias.  Although we have shown what bias looks like and we can see that it will be included in our images, what I read is that for DSLR imaging in subtracting regular dark frames you are also subtracting bias to some extent.  It may be different for LRGB imagers; ask Tyler of Patrick for that.  For scientific grade stuff you would probably be concerned about bias. For general deep sky imaging and especially if you are trying to learn the entire process of deep sky imaging, I wouldn’t worry about bias until you get down the road a ways.  Know that it is there, and don’t completely ignore it. But, feel comfortable with you polar alignment, focusing, collecting 16 darks & flats or making a dark library and processing images.  Then if you images need some improvement, look at bias as source of improvement.   Jim