Re: Calculation from scratch; practical measurement
boxerman wrote:
OutsideTheMatrix wrote:
boxerman wrote:
Seems like we have converged fairly well to a nice benchmark. Consistent with your and my experience.
OutsideTheMatrix wrote:
So I did a test run tonight and found that 10 sec is perfectly fine, even with the LCD 14x magnification. 13 sec is questionable; in some frames I could clearly see two separate stars, while in others it looked like a single streak. 15 sec and above at 14mm was definitely not acceptable on the E-PL6, by my eyes anyway.
The formula we acquired earlier to find the shutter speed equivalent to the E-520 was SQRT(1.6) I believe, which comes out to 1.265, so 15/1.265=11.86 sec. So my pinpoint 15 sec exposure at 14mm with the E-520 would be 11.86 sec on the E-PL6, in terms of star trail equivalency anyway. Sounds like the "eye test" of the tipping point being somewhere between 10 sec and 13 sec proved to be correct. How much of a star trail do you get with 13 sec exposure at 14mm? I think I'll keep it to 10 sec just to stay on the right side of tolerance.
Sorry, haven't done this specific test, and it's not too likely that I will in the near future. (I have two lenses that I use for night sky shots. My "old favorite" is my 20 mm Panasonic 1.7. My 12-40 Olympus f/2.8 (at 12 mm) is about 3/4 of a stop less efficient (needs more ISO), so I seldom use it.But, I'm confident enough in the "theory" now that I'd go by the benchmark we've come to.
Oh I meant that since 10 sec at 14mm results in a 5 pixel star trail, how many pixel star trail would 13 sec at 14mm cause?
Mental math: 13 seconds is like 1/3 more than 10 seconds, so about 7 pixels. Or did I misunderstand?
No that's right. 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?
13 sec seems to be closer since doing the actual calculation of horizontal pixels of the E-PL6 (4608) divided by the horizontal pixels of the E-520 (3648), gives a result of 1.263. 15/11.263 yields 11.875 sec.
Not 100% sure I'm tracking you, but, indeed, 13 secs calculates to 5 pixels for the 10 mpx sensor. If I said something else, it was probably mental math error. With these calculations, I do rough calculations sometimes since it usually doesn't make a huge difference. Famous last words...
Does increasing the shutter speed
you mean duration?
Yes, sorry about that.
keep capturing more stars or is there a point of diminishing returns, which is governed by light pollution?
Well, when ambient light gets to around the brightness of stars, I imagine you just can't see any more stars. So, I'd expect, as you say, that you just can't see "more stars" after you're down to stars that are less bright than the ambient sky. But, you're pushing me to first principles, since I have no practical knowledge of this.
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.
Using 13 sec on the 16 MP sensor as our guide, we get a 180 rule (or 360 rule for FF).
Or is the limit more a result of star trails spreading the light of dimmer stars over a larger area, thus making them too dim to discern in the image? I've always wondered about that.
I have wondered about this too. It seems clear that spreading the light over multiple pixels limits the accumulation in one pixel (properly, "sensel"). So, my "time over which the image moves one pixel" is a basic parameter of exposure, as well. But, I haven't explored this idea theoretically or practically. The essence can't be wrong, though. Like squirting water by moving a hose across multiple containers. Each container gets water limited by the time the hose is over that container.
How do you feel about the 45mm f/1.8 Olympus prime? I was thinking of getting that, because of its nice aperture. I see B&H offers a package where you can buy the 45mm f/1.8 and 75mm f/1.8 together.
1.8 is a nice aperture, for sure. The problem is, of course, that you're in more serious difficulty if you want trail-free images, limiting shutter duration. More than likely, you'll be best served by getting an equatorial motor mount to correct. I understand they are not expensive.
My other problem is that I don't know what celestial structures fit nicely in the 45 mm field of vision. Just ignorance. Most people seem to prefer wide star views, in part for the star trails problem. If you WANT star trails, again big vistas seem nicest.
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.
... The Kalahari Desert is one of the least light polluted areas in the world! I read that the best sites are 1)The outback of Western Australia, 2) Namibia (Kalahari Desert), 3) Mauna Kea, Hawaii, 4) Atacama Desert, Chile, 5) Dome C, Antarctica, 6) Nebraska, U.S.
Sounds right. I knew the Kalahari was in that list, Mauna Kea (like 13000 ft; not much atmosphere left, in addition to being away from light pollution), and had heard about Chile. Nebraska sounds a little counter-intuitive because altitude is not that high, and the mid-West suffers high levels of particulate pollution, if not light pollution (I grew up in Colorado). It was our trip to the Kalahari that got me to actually do night skies in the first place.
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.)
How many images did you stack? I typically stack from 7-15 images using a combination of DSS and Sequator and then tweak contrast and saturation using Irfanview.
I haven't stacked, yet.
Yes, the DR range is extremely high and I've found if the DR of the setting that are used is less than 10 stops, star colors suffer (which is why I keep the ISO less than 3200 if at all possible.) Using the settings above you were able to expose for colored star trails and get decent images of the Milky Way too? That's very impressive!
Well, truth in advertising, the colored trails emerged mainly after a lot of added saturation.
What do you set Saturation, Contrast and Sharpness to in-camera? Just the default 0,0,0 settings (natural picture mode?)
I think you might like the prime lenses I mentioned above, they're some of the best Olympus has.
I had my eye on wider angle lenses. There's a cheap Rokinon f/2 at 12 mm. Manual focusing is a non-issue for night skies. Some other manual focus, not-too-expensive wide-angle lenses are appearing.
How do you manual focus your lens? I suspect you just set it to infinity?
I love those images- did you just use standard postprocessing software?
Thanks so much! As I recall, I just used Olympus viewer. Did a lot of curves fiddling, in addition to brightness and contrast to get the Milky Way.
... Question- do you use any special techniques to shoot star trails?
Yes, I used something called StarStax. Actually, nice software for nearly free, as I recall. There's some brilliant good stuff coming out of the amateur astronomy community. Their software design is often quite good, getting the easy/important things, and with very few bells and whistles. My taste. I also made some videos---time-lapse. My piece de resistance showed a still image of my initial shot and then the trails spread out gradually, and then finally shrinking down to the final image I took in the sequence. I had to do some tap dancing to get single images (trails) of subsets, in time sequence AND reverse time sequence, of my 150 shot night. But, it was great fun, and the result is pretty impressive, if I do say so myself.
Theres 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. It's on my list to try, if I get to that kind of shooting.
Thanks, I'll look up this software!
I see the newer Olympus cameras have a feature to make star trail shooting easier.
Yes. Anxious to try this out. My next camera.
But I don't have a True Pic VII sensor camera- no matter how much Olympus wants to insist otherwise
I'm not sure it's critically processor dependent. I think it's pretty simple algorithm. But maybe the earlier processors are not capable enough. I thought it was just a new feature, not worth implementing on older cameras.
