Sunday, February 1, 2015

Comet Lovejoy (C/2014 Q2) with DSLR on Motor EQ-1 Mount

I'm getting better at polar-aligning my motor driven EQ-1 mount, and increasing the total exposure length I can achieve without star trails. However, now I'm running up against another barrier - I'm getting to the point where my sky conditions have too much light pollution to even merit longer exposures.

long exposure without star trails DSLR
My longest single frame without star trails (left) straight from the camera. I love the aqua color of the comet without any processing! Stacking always seems to make it a dull green.
ISO 1600, 300mm, f/5.6, 20 seconds, Canon T5i on motor driven EQ-1.

With the sky beginning to wash out even after 20 seconds, you can tell that my techniques are advancing up against another ceiling, the sky conditions themselves. Even if I did have a super fancy tracking mount, would it even be worth it if I can only get exposures of 20 seconds?

comet lovejoy DSLR 300mm
Comet Lovejoy C/2014 Q2 with Canon T5i on EQ-1 mount
Stack of 31 light (ISO 1600, 300mm, f/5.6, 13 sec), 21 dark, 23 bias, and 15 flat frames
Processed in DSS

comet lovejoy DSLR 300mm
Comet Lovejoy C/2014 Q2 with Canon T5i on EQ-1 mount
Stack of 31 light (ISO 1600, 300mm, f/5.6, 13 sec), 21 dark, 23 bias, and 15 flat frames
Processed with layers from both DSS and Photoshop

And yes, I'm using flat frames like a good boy! Every time I learn something new it seems to make my imaging procedures longer not shorter! Flats make a big difference though, it's like the "eating your vegetables" of astrophotography. I used the same technique I talked about in this previous post.

Flats should be gray, not white. Below is a sample of one of the flat frames (left) and that same frame with the contrast turned WAY up (right) to show that there really is some gradient and vignette information there even though to the naked eye it just looks like an even gray wash. The purpose being that the image processor, such as Deep Sky Stacker, will remove the hot spot gradients and corner vignettes.

flat frame compare with contrast gradient
One of my flat frames with contrast boosted on one side to show gradient information hidden within. Adjust exposure time until you get a good histogram just to the left of center. This one happens to be ISO 1600, 300mm, f/5.6, 1/640 seconds.

take flat frames with computer screen
Taking flat frames with DSLR - I actually took them hand-held as close to the screen as possible while moving the camera around to make sure I didn't get a dust spot in the same place each time.

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