Re: Calculation from scratch; practical measurement
boxerman wrote:
OutsideTheMatrix wrote:
I just noticed something really curious. 13 seconds is acceptable if you're talking about stars near the center of the field. But when those same stars drift towards the edge of the field, the star trails appear to blend close stars together. I wonder if stars trailing more near the edge of the field could be caused by lens distortion or perhaps a lower resolution near the edge of the lens?
That sounds right to me. I have read that lens coma, which gives you elongated images for points, is especially critical for astrophotography. So, that's a thing to look for. I don't think it's just lack of resolution, but maybe that contributes, too.
I'm thinking lens distortion too- I know Sequator "fixes" it (somewhat) but I don't see a fix for star trailing or stars blending together LOL
What I noticed was that with my level of light pollution, the sky turns to a light brown if I go over 13 sec at ISO 800 or over 8 sec at ISO 1600. So in addition to star trailing, light pollution becomes another consideration. By the way, when is the best time to image, plus or minus 5 days from a Full Moon? I normally look for a time when the moon isn't above the horizon, but not sure if the moon matters much as long as it's not in the same part of the sky as the target.
I can't tell you from experience. And, it probably depends on the level of pollution and dust. Obviously, if there's more of that, then the moon's light will scatter and be more of a problem. If the atmosphere were completely clear, I doubt there's any effect, as you say, as long as the moon is not in the frame, or close enough to exploit a lens defect ("flare").
I think I might want to stop using auto white balance and use that 4000K setting you use. I just worry that it will throw off the stars' colors. But the thing is, sometimes (even in the same night), the sky turns brown a lot sooner than it does at other points- thus the same settings can result in brown skies that earlier in the night gave me nice contrasty black skies! I can't figure out why- the moon wasn't even out when I first noticed this.
I want to get an equatorial mount; the computerized mount I have for my telescope is Alt Az. The fear I have about equatorial mounts is polar alignment With computerized mounts you have to slew to three different stars to make it accurate.
Probably too much work for my uses, too. But, I imagine even if you are not very accurate for general night sky shooting, it'd help a lot. Now, if you're shooting with a long lens, or have very long shooting times, that's a different story. If it reduces streaking by a factor of 2 or 4, you and I would be quite happy, I'd think.
The next advance that happens from Olympus, I want them to do what Pentax did, where they are using sensor shift to account for the earth's movement- thus you can take trail free images with shutter speeds up to 5 minutes with their GPS accessory.
How are the Rockies? I talked to a fellow from Utah named Jay who swears by the Rockies (as long as you're under 10,000 ft elevation- when hypoxia starts to set in.)
I would think it'd be pretty good, but I really don't know the specifics. Since I grew up there, I'm not afraid of altitude, though I've been careless and gone up too quickly, with no acclimatization. Awful headache. But, your body does adjust fairly quickly. Not sure whether it's a day or a few. No more than that.
What do you set Saturation, Contrast and Sharpness to in-camera? Just the default 0,0,0 settings (natural picture mode?)
I shot jpeg for my first tries Botswana and Kalahari. Next time, surely it will be RAW after I saw the PP was really necessary, at least if you want to shoot not to blow out the stars and still be able to boost to see Milky Way. I was shooting for colored star trails, so knew I was going to be boosting saturation a lot. So, that setting was not relevant to me.
My default safari setting is vivid (VERY little chance of getting, in nature, the kind of unrealistic color you get in civilization (lots of pure colors around), or even with flesh tones. I also keep sharpness and noise reduction down, generally. Again, I'm not recommending (except to shoot RAW to preserve options), just saying what I did with jpeg settings.
Interesting- did you find that vivid makes the noise more prominent? I imagine it might have an effect with areas of high pollution too. I usually stick to default settings and then boost saturation and contrast in post.
How do you manual focus your lens? I suspect you just set it to infinity?
I have seen a lot of talk about this, but it was really completely easy and foolproof to use manual focus. The thing I looked for was that any amount of blur makes faint stars disappear. So you just adjust until you get a very palpable "locking in" on the fainter stars. Autofocus is useless. Most lenses are not accurate enough with adjustment to try to go by any markings or the like. I think all m4/3 lenses actually focus electronically, so there's not even a stop to go by.
People have other tricks (e.g., use a flashlight on a distant terrestrial object, but I don't know why you would bother when the starts themselves, especially per the faint star trick, are so easy to use.
In my case unfortunately, I've had to use hyperfocal techniques because I don't see any stars (but Sirius) in my live view. I see them after I take the picture lol. I use the AF-L button to lock focus on a distant street light (about 200 ft away) and then keep that setting through the entire session.
... Question- do you use any special techniques to shoot star trails?
Yes, I used something called StarStax.
There's a piece of software called "Starry Landscape Stacker" that helps you align and stack while still preserving an terrestrial objects you have in the image.
Thanks, I'll look up this software!
I wish you well and hope to see how you do pursuing this. It will probably take another safari for me to get serious again. Just being focused on things I WANT to do, rather than work, makes a lot of difference.
Indeed- that's the difference between work and hobbies!
