ozimax wrote:...Does anyone know of which settings for D70 and kit lens would be good for photographing the moon and stars. I realise that you can't hold the lens open too long because all the heavenly bodies move quickly.
Full Moon overhead is lit by the same light source (the Sun) as Earth, and from the same distance, so exposures of the surface are going to be pretty close to what you would use for terrestrial photographs, in theory. You might find the Moon looks a bit dark in places if you use the same exposure as for a sunny landscape- thats because the moon's albedo is about the same as a lump of coal! it should be dark. So at the D70's ISO 200 a good starting point will be 1/250 @ f/11, when its overhead.
However, since you are photographing it as it rises, you are looking through as much as 40 Earth atmospheres, which is going to remove much of the light that was heading your way. So you are going to have to use longer exposures and or wider apertures. How much? well that all depends on exactly how much dust/water/aerosols/pollution (not much at Woopi!)/smoke/cloud etc is in the air.
Exposures for the stars are going to need to be much longer than for the moon, since they are much fainter.
Also important is that they will record proportionally to the actual aperture of the lens (not the f/#) . A 200mm @ f/2 will record a lot more stars than a 50mm @ f/2 in the same time. Thats because the stars are essentially point sources of light, increasing the magnification doesn't increase their size, so they record proportional to the area of the lens, (square of the radius X pi). Extended objects ( pretty much everything except the stars) that are magnified by longer folcal length will still record the same at f/2 though, no matter what focal length, neglecting lens transmission losses etc.
Now if you want to record the moon rising and theres a lot of haze around, you're in luck, because the landscape/seascape may be of similar brightness to the moon, so you can expose for the scene and the Moon wont be overexposed by much, if at all. You need to catch it low for that to work though.
In twilight this will sometimes be the case. If the moon rises when its dark, this isnt going to work very well, unless you have a brightly lit cityscape. You may want to do 2 seperate exposures and
PS the properly exposed moon in later. You can use a longer focal length for the moon, and paste a larger than real moon in for effect too.
As Earth rotates, the Sun, Moon and stars appear to move across the sky, but the Moon actually moves more slowly than the others, due to its orbital motion around Earth. However, this wont save you from trailing when doing time exposures without an equatorial driven mounting.
A general rule of thumb for 35mm cameras to keep trails unnoticeable is:
600/focal length = exposure in seconds. So for a 50mm lens, this is 8 seconds. This is for the equatorial sky, you can get away with longer exposures towards the poles. At 60 degrees south in the sky (Southern Cross, pointers etc) the sky moves at half the speed, so you can double your exposure time to 16 seconds.
In practice you can use a bit longer, it depends on how much you plan to enlarge, and how sharp your lens is. However with the 2/3 size sensor in the D70, using 400/focal length may be safer... Experiment!
With the D70 for astro imaging I generally use 200 and up to 500. Beyond that the images are just too noisy with bands across them that cant be removed easily.
OK, that should have everone soundly sleeping
Gordon
Posted: Mon Jan 16, 2006 5:38 pm
