I did a series of images to test the range of ISO values and exposure times to zero in on the ideal settings for my equipment: Canon T3i unmodified camera, Celestron CG-4 mount with RA motor. Because I don't have guiding, my exposure time limit is 30 seconds. At greater than 30 seconds I start getting elongated stars in my images. I also found that my ideal settings are ISO 400 and ISO 800. Lower ISO values require too much exposure time, and higher values introduce image noise. This is a screen shot of the eight good images and the folders containing the experiment images:



Just for fun, I decided to stack the eight test images: ISO 400 @ 15/20/25/30 sec and ISO 800 15/20/25/30 sec. I used RegiStax 6 to stack the images. The output image was in TIFF format. I used GIMP to adjust the contrast and intensity, and also to save them in JPEG format. This first image is very subtly processed, not much different than the output image:


Orion Nebula 01-05-2022 lightly processed image

I this next image I did more intense adjustment, bringing out a lot of the H-Alpha at the expense of blowing out the Trapezium:


Orion Nebula 01-05-2022 more processed image.

I think I'm on to something here. It seems that by taking single frames at various ISO and exposure values and stacking them, I'm capturing a much greater variety of data than when I was taking many exposures at the same settings. The more processed image has good contrast and detail, and shows more features than I have been able to get so far.

It's not time consuming at all to take a variety of single images at various settings. Likewise, it's not a big deal to stack a few images, eight in this case, and then do simple processing. I'm not sure which of these two images I like more, but I do like them both.

Ed D