Star trails

[Raikyn]

Okay I'm looking to take some shots without star trails.

At 50mm at 10sec it seems you can get a pretty sharp star.
What I'm wondering is if the crop factor of the camera makes a difference.

To my logic 50mm is 50mm. It won't matter if it is a 1.3 or 1.6 crop you can use the same settings on each and stars should still be sharp. Just on the 1.3 crop the field of view would be wider.
Correct?

[watchtherocks]

I think the longest shutter speed you can go without star trails is 9 seconds.
Theres a WHOLE heap of crap associated with star photography. It's very very technical.
But yeah, the lower the crop the wider the lens.

[Jim G]

The crop factor doesn't affect the lens at all; you'll just get a wider field of view with a 1.3x or FF sensor. In that sense for the same framing you'd need to use a wider focal length and thus would be able to have longer exposures without star trails but 50mm is 50mm, you're entirely correct.

[Raikyn]

I think the longest shutter speed you can go without star trails is 9 seconds.
Theres a WHOLE heap of crap associated with star photography. It's very very technical.
But yeah, the lower the crop the wider the lens.

9 seconds with the 50mm before it shows??
Technically you get trails at any focal length unless you are tracking.

By lower the crop the wider the lens I assume you mean wider the field of view. This shouldn't have an effect on trails though should it?

[Raikyn]

The crop factor doesn't affect the lens at all; you'll just get a wider field of view with a 1.3x or FF sensor. In that sense for the same framing you'd need to use a wider focal length and thus would be able to have longer exposures without star trails but 50mm is 50mm, you're entirely correct.

Ah thanks, just wanted to make sure my logic was correct. Best lens I have to shoot astro is a 50 1.4
Whether I use it on a 1.3 or a 1.6 camera wouldn't have any effect on the length of exposures I can shoot before trails emerge.

[E-K]

Crop size will indirectly impact when trails emerge to some extent when viewing/printing the images at the same size. The apparent motion on the sensor will be the same but you have to enlarge the higher crop camera which will make the trails a little more apparent.

e-k

[primoz]

I think the longest shutter speed you can go without star trails is 9 seconds.
I think this goes for Moon. For stars you can go much longer. Of course we are talking now about visible trails. Otherwise it's true as someone wrote, that with any exposure, even if it's 1/8000sec you get trails. But they are so short you can't notice them :)

[watchtherocks]

Hmm, yes, now I think about it the 9 seconds was about the moon.
I was put off astrophotography ages ago from reading a thread on photo.net. It was so long and so full of calculations and I just gave up then and there:D

[Stocky]

Crop size will indirectly impact when trails emerge to some extent when viewing/printing the images at the same size. The apparent motion on the sensor will be the same but you have to enlarge the higher crop camera which will make the trails a little more apparent.

e-k

Agreed. Its the same as the crop factor effecting your camera shake since in both cases all you are measuring is the motion between the camera and the object.

[PhotosGuy]

I think this goes for Moon. For stars you can go much longer. Of course we are talking now about visible trails. Otherwise it's true as someone wrote, that with any exposure, even if it's 1/8000sec you get trails. But they are so short you can't notice them I agree. Here's what you can expect from a 20mm, ISO 400, f/4, 64 seconds.
Perseids 2007 (http://photography-on-the.net/forum/showthread.php?p=3815285)

[E-K]

I agree. Here's what you can expect from a 20mm, ISO 400, f/4, 64 seconds.
Perseids 2007 (http://photography-on-the.net/forum/showthread.php?p=3815285)

That's a good example too of how it also depends on where in the sky you are pointing the camera. Trails will be greatest at the celestial equator versus the poles.

e-k

[Raikyn]

Well results so far

http://img401.imageshack.us/img401/1165/milky3800x533jn8.jpg

30 shots + 20 dark frames stacked and aligned with deep sky stacker

50 f1.4

Shots at 10 sec f2.2 iso 800

[Nighthound]

Good results Raikyn.

Be careful with the black point. By clipping it you loose a lot of faint data in the dense dust areas and in the areas mostly void of dust. This is important in processing all deep sky images but even more so when shooting such short sub exposures. I'd love to have the 50/f1.4 for piggy back widefield shots, very nice.

[John_TX]

Well results so far

30 shots + 20 dark frames stacked and aligned with deep sky stacker

50 f1.4

Shots at 10 sec f2.2 iso 800

Quick question, when you do shots like this, with the intent of stacking them, do you re-frame after x number of shots due to the Earth's rotation?

Or do you simply crop out what drifted into the frame/drifted out of the frame?

Also, how does Deep Sky Stacker deal with this?
Does it do any type of automatic cropping? Or do starts that drift into a couple of frames just appear fainter than the rest?

[Wazza]

I was going to suggest stacking, but you've already done it :)
9/10 seconds will still show a slight trail.

http://www.warrenwilliams.co.nz/2008/FEB_2348.jpg
That's just 1.3 seconds, high ISO. Orion's Nebula on top left -

Another way to shoot is mounted on the screw on top of a scope, which is fitted with an equatorial mount, which has a motor to track the stars.

[Raikyn]

Quick question, when you do shots like this, with the intent of stacking them, do you re-frame after x number of shots due to the Earth's rotation?

Or do you simply crop out what drifted into the frame/drifted out of the frame?

Also, how does Deep Sky Stacker deal with this?
Does it do any type of automatic cropping? Or do starts that drift into a couple of frames just appear fainter than the rest?

DSS will rotate/align all the shots taken, and I didn't reframe at all. It left the final shot with darker bands on the outside due to the rotation. Obviously this way the longer you shot(either focal length or time) the more you have to crop at the end.

I was going to suggest stacking, but you've already done it :)
9/10 seconds will still show a slight trail.


That's just 1.3 seconds, high ISO. Orion's Nebula on top left -

Another way to shoot is mounted on the screw on top of a scope, which is fitted with an equatorial mount, which has a motor to track the stars.

I've the equatorial mount(EQ5), but no motors :(