dark sky astophotography, equatorial mounts, and distant faint objects - Dath Valley

Jzazzi

We have a trip planned to Death Valley in a couple weeks and I want to make use of the "darkest place in the US" for some awesome night sky captures. I have two goals: replicate a pano of the milky way band like in the below photo (credits here), and to capture some very distant and faint objects like a nebula or similar. You know, the kind of stuff I can't do from home with all the light pollution nearby.

I'm just starting to research this and it looks like I need an equatorial mount with a motor and very precise polar alignment for any kind of long exposure (ie the nebula or distant, faint captures). I might be able to find a proper mount or rent one, that should not be a problem. But for something like this pano of the sky, I'm hoping a vanilla tripod would be enough with a mild exposure of less than a minute, does that sound right?

To capture something as dark as the milky way and all the wonderful stuff seen in this photo, what kind of exposure should I be expecting? I plan to use my 17-55mm f/2.8 wide open and a max 400iso, with many captures to stack to reduce noise. Any ideas on shutter times for this?

Deathvalleysky_nps_800px.jpg

kdog

Take a look at Samir's website. He's got tons of milky way and deep sky photos taken with a variety of equipment. He gives lots of detail on focal lengths and exposures. http://www.samirkharusi.net/

I would also peruse some of the more specialized astrophotography forums.

Good luck!
-joel

codrus

I don't have any personal experience with this, but from various things I've read on the net I've gotten the impression that equatorial mounts are no longer really necessary. Historically they were important because it was easier to add mechanical complexity in the mount than logical complexity in the motor/controller, but now that computers are so cheap the pendulum is swinging the other way.

--Ian

Jzazzi

kdog:
Great link, that's helpful. He takes what I'm trying to do to the extreme, but good learning material nonetheless. It looks like all the awesome deep-sky captures I have in mind are best done with some decent gear which both costs money and takes up space. I don't have a bunch of money to spend for this one-off trip, nor do we have lots of room for gear our car. But! it's great stuff to read though, thanks for the link.

codrus:
I think you are right in that respect, technology and computing power are really catching up. Auto-aiming telescopes are becoming really inexpensive and can be found very easily. It looks like these scopes track objects just fine, but don't counter the spinning motion of the stars from the rotation of the earth. So while one star might stay centered, the rest of the sky will be moving. Not sure if that makes any sense, it's kinda late and I just finished a workout so I might be a little dumb (I once took my cell phone into the pool with me after a workout, it was still in my hand).

All in all, I should be able to make a panorama of the milky way bands like the photo above using a vanilla tripod and medium-high ISO with fast glass, then stacking multiple exposures using one of the widely available scripts to reduce noise. This is the plan so far, but I'll keep plugging away anyways.

-J

codrus

Jzazzi wrote:

It looks like these scopes track objects just fine, but don't counter the spinning motion of the stars from the rotation of the earth. So while one star might stay centered, the rest of the sky will be moving.

Yeah, I was thinking about that afterwards, so I went and did a bit of googling. Looks like the alt-azimuth mounts are used for pro telescopes because they're more stable, and they use software to fix the rotational problem. Obviously that's harder to do with a DSLR, although you could theoretically do it in post-processing if you turned up the frequency on your individual captures so that no individual frame had more than some minimal amount of blurring due to rotation.

--Ian