why does this happen ?

fwellers · Jul 8, 2009

This is like an 80% crop of a picture I took this morning of the moon.
I was on iso 800 f3.5 1/60 handheld.

Using a D90 and the nifty fifty. I wonder why the red ring is around the moon. I have another image ( having a hard time getting that crop uploaded ), and it has a greenish yellow ring around the moon that's visible when fully cropped.

I thought this was chromatic abberation, so I tried to get it out with nx2. That correction did absolutely nothing for it.
Is this something I'm doing wrong, or is it because of the lens or something else ?

Thanks,
floyd

smadab · Jul 8, 2009

I'm not sure - my guess would be the overexposed moon causing some "pixel bleed". Especially combined with the higher ISO.

DemonAstroth · Jul 8, 2009

Chromatic aberration?

JerryPH · Jul 8, 2009

Thats what CA is supposed to look like.

Josh66 · Jul 8, 2009

fwellers said:
I thought this was chromatic abberation, so I tried to get it out with nx2. That correction did absolutely nothing for it.

I have never used nx2, but - I have never been able to get rid of CA with the adjustments in Lightroom.

I don't even bother trying anymore, every time I do there is no noticeable difference. So, it doesn't surprise me that your software didn't do anything for it...

You could try selectively desaturating just that color.

Joves · Jul 8, 2009

Well with the moon being that overexposed you would see some chroma. And it would change color depending on the angle it hits the galss at any one point. You are shooting at a direct reflected light source, shoot one test pic then adjust your aperture to compensate for the moon. What was the main subject anyhow because that is what is effecting how the moon turns out.

fwellers · Jul 8, 2009

Thanks for the replies.
Joves, the main subject was the moon. I guess I overexposed it. I was in kind of a hurry. I thought the meter was centered, and maybe it was, but with that light source I guess it may have tricked the meter a bit.
Live and learn.

Thank you all.

Joves · Jul 8, 2009

The moon is a pain. Depending on what lens you are using. A tripod is your friend in these shots.

fwellers · Jul 8, 2009

Yea one of these days I'll get a tripod and start making some sharp pictures.

I was thinking about it. I bet I just didn't meter correctly, since the moon was such a small part of the frame. The rest of the frame was darker so that would make the meter want to overexpose the moon.
Yea that's it.
the other shot didn't turn out too bad. ( for me ).

musicaleCA · Jul 8, 2009

O|||||||O: You really haven't been able to remove CA in LR? I've always been able to remove it. Sure, the edges are left soft but there's nothing to be done about that.

Josh66 · Jul 8, 2009

musicaleCA said:
O|||||||O: You really haven't been able to remove CA in LR? I've always been able to remove it. Sure, the edges are left soft but there's nothing to be done about that.

The cases I'm trying it on are probably too far gone to be saved.
If it's minor, I don't really worry about it too much.

KmH · Jul 8, 2009

Joves said:
The moon is a pain. Depending on what lens you are using. A tripod is your friend in these shots.

Oh ya. There is quite a bit of dynamic range between bright young Tycho and the dark old Mare.

How about an HDR of the moon, Joves. Haul out your big mirror.

Hummmm, maybe a digital Schmidt Camera?

Dwig · Jul 8, 2009

Judging from the EXIF data, the moon in the first shot is something like 8 or 9 stops overexposed. I'm sure what you are seeing is, to a large degree, pixel bleed.

It can't sensor caused CA, the type that can be corrected in post processing, unless the moon is perfectly centered in the image. Sensor casued CA always displaces one color radially outward and its compliment inward. The colored ring would be one color on one side and its compliment on the other. This ring is uniformly red.

astrostu · Jul 9, 2009

HDRs of the moon itself are unnecessary. The DR of it is easily capturable with today's CCD/CMOS sensors.

Sachphotography · Jul 9, 2009

Hey,
Ive done a lot with astrophotography and CA is one of the biggest issues when shooting. The moon is by far the easiest thing in the world to shoot due the fact it is soooooo bright. FYI never shoot it when it is full. IF you shoot it at about 50% full you will notice the shadows add a world of detail and interest to your picture. Also try not to over expose it. Your best bet is to take 2 to 4 shots ans stake them. Kinda the same idea as hdr but but not really I guess. Astrophotography is all about staking images. I have a buddy who shoots 30-60 pictures ans stacks them allowing for low noise high detail images. A tripo will help a lot as it eliminates the shaking. Also use the delay function on our camera press it and step away from it while it fires.
Good luck