I have been reading a good bit of articles online pertaining to astrophotography, in preparation for me travelling out to western PA next month to photograph the Milky Way.
With that said, these are the two lenses I have in my bag: 17-40L and 24-105L. As you all are aware, the max aperture for both lenses is f/4. For those of you who are more experienced in astrophotography than I am, will this lens lineup work? I was specifically looking to use the 17-40 over my 24-105. Should I possibly rent a WA lens with a smaller aperture? (ie. 16-35L) Or will my current lens lineup suffice?
I have personally gotten up to 30 sec. sharp astro exposures with a 18-70mm f3.5-5.6 lens. From what I have read when I was looking into it, f4 is adequate depending upon focal length used.
Douglas
"Adequate" is a matter of how picky you are. For my tastes (I have lots of very fine astronomy-specific equipment, which tracks for hours to tiny sub-pixel accuracy, so I'm pretty picky), a 30-second image of the Milky Way, with DSLR on a tripod, generally shows far too much star movement (depends to some extent on focal length and where in the sky you're pointing, obviously), even using the 16-35.
The longer your focal length, and the farther from the Polaris you're imaging, the more star movement will show. You'll have to play with your system, determining what you're happy with, but if you're considering renting a lens for this, I'd be thinking about one as fast as I could get (while still being sharp), and as short a focal length as I could get.
You also should consider testing with your camera and your 18-70 to see if, even at 18, you can get enough of the sky to make you happy; you'd be surprised how much you have to get to have a compelling photo of the Milky Way.
The place I'm going to is 5 hours away, so I want to make sure I go there with the right equipment since I'm not going to be in my backyard where I can just go inside and get another lens that may work better.
I considered renting the 15mm f/2.8 since I would be able to take advantage of my 5DII being FF.
Realistically speaking, I know I'm not going to see the Milky Way as clear as I would if I were in Arches National Park or somewhere remotely out west.
So long as you have a tracking platform you should be ok. Unguided it will be tough to get much. I tried my 24-70 at the wide end and started to see star trails at 15 seconds. Light pollution will dictate your exposures as well. Western PA sounds like it could have some dark skies but it probably depends on how far away Pittsburg is to your location.
Sorry mate, I'm clueless about it as well. I don't even know what the gadget is called. All I know is that it helps you track the star or constellation so that you can do long exposure without getting the star trail.
We're just gonna have to wait for StarNut to shed some light on this. I'm quite interested in Astrophotography as well, after seeing some rather remarkable photos.
I have the AstroTrac. It's small and very portable. There are also others. Do a search to see. The AstroTrac runs around $600ish. I agree with StarNut and others. For any exposures longer than 30 sec or so you would need a tracking device unless you want trails.
Tracking platforms adjust for the rotation of the earth. They are usually polar aligned with a special scope with etchings on the lens so you can line it up with local stars or just Polaris (Northern Hemisphere) for a rough alignment for wide lenses. They range in cost and portability. AstroTrac is a popular one that gets fairly good reviews and is very portable.
Another noob here so please pardon my ignorance, but would it work if you were to take several 15sec exposures and then stacked them? Other than the extra steps in post, for what other reason(s) would a f/2.8 lens be better?
I'm also interested in astrophotography and like Nick (nburwell) my biggest aperture is f/4.
BennyR wrote:
That's a different animal. Larger and heavier and I don't believe it tracks at the sidereal rate which is what you need.
Sorry, I wasn't very clear. What I meant was, since I will only be doing it occasionally, I find it hard to justify $600. So if I was to spend that much money, I'd be looking at Gigapan panohead as well (for a totally different non-astrophotographic use).
I've tried my hand at unmounted astrophotography a few times with mixed results. At f/4, you'll get some stars, but you won't get a ton of astonishing details; though you'd be surprised how many more stars will show on your sensor than show up by eye. I'd suggest renting a faster lens if you can. I've done it a few times with my 35L wide open, and even then I wish I could squeeze more out of it. I think I ultimately could use a tracker.
For those inquiring regarding mounts and whatnot, I'm no expert, so I defer. But I would point you to a few places that will illustrate what's being talked about. Basically, they're referring to a mounted, generally motorized device that slowly moves your camera to account for the rotation of the stars (or, more appropriately, the rotation of earth thereby making the stars appear to rotate).
If you've ever just pointed your camera up at a dark sky and snapped extended exposure shots, you'll notice that, upwards of 8-15 seconds, the image starts to blur. This is because the stars appear to rotate around Polaris. Professional astrophotography shots (where you can see galaxies and whatnot) require very long exposures. However, if you can't account for the stellar rotation, you end up with a star trail shot like this: http://asa100.com/blog/wp-content/uploads/2010/10/figure2v21.jpg
Accordingly, pro-astrophotographers used motorized mounts to offset the rotation, thereby keeping the stars "constant" insofar as the camera sensor is concerned. This enables highly detailed long exposure shots of "still" stars.
Like I said, I'm no professional astrophotographer, so take what I say with a grain of salt pending a more comprehensive explanation. Anyway, I hope that helps.
I only know serious astrophotography (with equipment that makes "normal" photographic equipment look cheap; my mount alone--not including astronomy-specific camera or telessope, among other necessities for serious imaging--sells for $14,500), so I can't really add much to a discussion of photographing the night sky with a DSLR.
But I've played a bit, in dark skies, with my 5D2 on a photographic tripod (no tracking), and found unacceptable star trails even in 20-second exposures, at 16mm focal length.
I do see nice night photos here, showing the Milky Way. I don't know if, at a larger scale, these show star movement.
As to stacking individual exposures, that won't help without guiding/tracking.
If you are a DIY type of person there are all sorts of websites that explain how to build a simple barn door tracker for very little. Just depends on how much effort you want to put into it.
So to stack 10sec exposures to get 10mins worth, you're gonna need 60 shots. Not to mention the stars would've "moved" which means you'll need to align the frames.
