Can anyone explain this?

[macmaam]

This shot was taken last night, of the CRESCENT moon. I can understand that all of the moon is still there, and dimly lit, and might make a circular image with a long enough exposure, but where did the crescent glare/reflection come from? I have 3 of these, taken within 2 feet of each other, and all have the same glare, in different spots, but all left and down from the moon.

50mm lens, ISO 800, f11, 25 seconds, UV filter. It was a hazy night, and there was a streetlight to my right, but it was a little more than 90 degrees off the front of the lens. Could it have still created a flare?

[FocusingOnFlorida]

Lens reflections from within the elements themselves can cause such things as this. This is a pretty cool effect in this image though.

[metalstorm]

It's lens flare.* All lens have them if the right conditions are present.* Usually mimics the aperture opening in bright light but I suspect since it was so dim, it mimicked the cresent shape of the moon.

http://www.cambridgeincolour.com/tut...lens-flare.htm

[sean_buerger]

Interesting Effect!

I suppose the moon in your picture is blown out. It would be nice to have a histogramme of your picture. The lens flare is an 'under' exposed image, which is within the dynamic range of your imager and therefore does have the correct crescent moon shape (perhaps upside down or mirror image). Since you stopped down to '11' I suppose you were looking for some flare though

That would appear likely to me, but of course it's no more than an educated guess.
Cheers. Sean.

[cyclohexane]

Pull the UV filter off if you don't want the effect. It's an extra surface that can lead to flare.

[macmaam]

Thanks, everyone, for the information.

Here's the histogram. A lot of clipping going on there.
Sean, i don't yet know enough to do ANYthing deliberately! So, a smaller aperture will be more likely to flare? What can a person do to reduce or eliminate it, besides removing the UV filter?

I think i'll do some more test shots tonight, if conditions hold. I feel as though i'm on the verge of understanding something about this process.... maybe. But don't hold your breath waiting. :P

[scoundrel1728]

The ghosting that produced the secondary image of the moon in your shot is the result of reflections within the optics. In this case, two of the curved surfaces of your lens, together with the refractions of the other elements, produced a secondary image that was nearly enough in focus to be identifiable.

Even though special coatings on the elements reduce the brightness of such reflections, they often show up in night shots because these shots often have both massively overexposed bright exposed light sources and large amounts of dark area. This allows these reflections to show up despite their dimness.

[dvdowns]

I suppose putting the moon in the dead centre would make the flare in the centre then you can crop to compose your image ?

[scoundrel1728]

In this instance, cloning out the duplicate image would be no big problem if she wants to get rid of it. Since it is not a zoom lens, the elements won't be moving about a lot with respect to each other and the location of this ghost image is predictable. It can be something of a pain if it shows up a lot though. I have a similar problem with my Nikon E995 for indoor shots when the frame includes exposed light sources. My ghost images have a magenta or green cast rather than a cyan one like macmaam's.

[Jim Jones]

If you want some skylight to silhouette the trees in a Moon shot, shoot while there is enough light left in the sky and give somewhat more exposure than you would for a daylit scene. Don't rely on through-the-lens metering or automatic exposure. The proper exposure for moonshots is sometimes hotly debated. The Earth and Moon receive about the same amount of light from the sun. However, the moon is actually fairly dark, while we expect it to be very bright in a picture. For a full moon high in the sky I use an exposure equivalent to f/8 with the shutter set to the ISO of the film, and bracket. When the Moon is close to the horizon, more exposure may be needed because the longer path through air can considerably darken the Moon. An example of this darkening is sometimes apparent near sunset or sunrise when we can comfortably look directly at the Sun.

[jfrancho]

Ironically, since the moon reflects the sunlight very efficiantly, the sunny 16 rule can be used for determining the exposure. 1/(ISO) seconds @ f/16. Adjust for your preference. I find 1/400 @ f/8 ISO 100 works pretty well.

[macmaam]

Ahh, there's nothing like sitting at the feet of the wise, for incidental learning. I've never heard of this sunny 16 rule; off to do some research.

Thank you all, for all of the information. I may be back with more questions after this batch sinks in!

[scoundrel1728]

Sunny 16 Rule: in bright sunlight, the exposure time is the inverse of the shutter speed when the aperture is set at f/16.

jfrancho is implying that the bright part of the moon is an object lit at about the same intensity as sunlit terrestrial ones, so should be given about the same exposure. I agree with the light intensity argument; nevertheless, some corrections to the Sunny 16 Rule are called for. Moon rock is rather dark and will be rendered dark if exposed according to the Sunny 16 rule. Furthermore, when the moon is in its crescent phase, you can expect long shadows on the moon's surface when viewed from earth, lowering its overall brightness. An exposure increase of a couple of stops is therefore required to render the moon as a bright object. I therefore agree with Jim Jones' "Sunny 8 Rule" as a starting point for a perceptually accurate rendering of the moon's surface, as well as his justification for the rule.

[macmaam]

Thank you. That explains it well, and gives enough background to make a good base from which to make changes.

[jfrancho]

Originally Posted by scoundrel1728

Sunny 16 Rule: in bright sunlight, the exposure time is the inverse of the shutter speed when the aperture is set at f/16.

That should read "inverse of film speed, or ISO." So, at ISO 100, the shutter is 1/100.

[scoundrel1728]

Oops! :-[ You're right.

[macmaam]

Well, i never even noticed... just read it as it was intended. Maybe i know more than i think i do!