Purple dicloration on the edge of night picture

[dr4gon]

http://www.dcresource.com/forums/attachment.php?attachmentid=38304&stc=1&d=1217197158
DSLR-A300 w/ Tamron 17-50mm F/2.8 DI-II - 22.0mm (35mm equivalent: 33mm) - Exposure: 30.000 s - Aperture: f/2.8 - ISO equiv: 800 - White Balance: Auto - Metering Mode: Spot - Exposure: Manual - Exposure Mode: Manual


So I took this picture of the milky way last night and it's a nice picture, but it had a purplish/pinkish tinge in the upper right and left corners. I took one right after in a different part of the sky in a portrait orientation (exact same settings) and it wasn't on any of the corners. Out of the ~40 pictures, this was the only one that had it. If it's kind of hard to see on your monitor, you might need to look at it from a different angle on some LCDs.

While looking at the pictures in lightroom, I clicked "auto-tone" out of curiosity to see what lightroom would do with it and several other pictures had the same purple show up. It just wasn't evident in the raw pictures (without making PP adjustments).

This can't be normal. So, how can I fix it? Is the lens bad?

[toriaj]

I can't see your picture.

[dr4gon]

oops, fixed. anyone know?

[DonSchap]

Well, here's a night exposure I took ... one foggy night ... and I got colors I never thought of in it.

1) It was a school image that I needed to complete the course,
2) the world looked a bit weird looking toward the expressway and O'Hare airport
3) I've only shot the moon and the lunar eclipse, since.

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Thirty-seconds is a long, long exposure. You've got all sorts of things baking themselves onto your wide-open sensor. Admittedly, this was NOT a SONY sensor, so there will be some differences ... and I have not done any 30-second work with the SONY to offer a comparison.

EDIT: I did a couple indoor test shots at 30-sec exposure and there are no lighting issues I could find, so it may just be the lens ... but I would be reluctant to conclude that until you shoot through another lens, under similar conditions.

By the way, your metering mode might better set to Multi-segment, and not SPOT.

I suppose it could be "light pollution" reflecting off your lens sheild or filter edge. The corner of the frame is just close enough to the edge of the image circle to start picking it up. There is a definite source of it in the lower right hand area of the frame.

[dr4gon]

Hey thanks. I'm thinking it was a combination of the heat and my UV filter (I think it was on for this one) :o. As for metering, it was in the M manual mode at F/2.8 at 30 seconds so I'm not sure if changing the metering would help would it?

The reason for the high ISO is that my shutter release broke and the max I could do was 30 sec which wasn't giving enough light at 100 ISO, so to make the best of a bad situation.

Thanks for your picture and your help, I'll these the next time I go out.

[DonSchap]

As far as metering goes, it is a matter of correctness in your shooting. You stated the type of metering used, so it would be prudent to use, perhaps, the best one for the style of shot, regardless of the other issues.

30-seconds of light is a substantial amount, of that you can be sure. Pushing the sensor past ISO-800 is asking for other issues, beyond light, to be introduced into the image. Some cameras also have a long-duration noise-reduction setting just for this purpose. I have not investigated this aspect for the SONYs, but you might.

[dr4gon]

It does have an option of long duration noise reduction, it was enabled. But next time I will take some dark frame shots at identical exposures and subtract it out with photoshop. I will also recheck all my settings and set them to multi metering, manual focus, SSS off, wide af? (not that it matters?), AF-S? (not that it matters), and DRO off.

[DonSchap]

AF-S?

Okay, wise guy. :rolleyes:

[dr4gon]

? I was kind of asking lol... I read about it and forgot what it did.

I think AF-C always focuses continuously(no half way to hold)
AF-S is single (half to hold?)
AF-A is automatic? not sure what's the difference, does it pick what to focus on? But that's AF area.

[DonSchap]

This aspect of AF is a little complicated to get your mind around, so forgive if I do not explain it perfectly, but hey ... YOU asked.

When the AF-lever is set to "AF-A" (the default setting), it will toggle back and forth between "AF-C" (Continuous) and AF-S (Single) if it detects movement from the subject. What complicates things is the AF-Area setting (Wide, Spot and Local) and an advanced feature setting in the menu system.

First, there is a technique descibed, in the manual, that allows you to "lock focus" on off-center subjects (believe me, this happens a lot more often than I care to remember) using the multiselector joystick. Also, the advanced lenses have a "lock focus" button on the side of them that allow you to get the subject in focus, then quickly reframe your image and shift the subject to one side or another for the shot.

Secondly, you can also do "Direct Manual Focus" (DMF), without having to slip into MF mode, using the AF/MF button. Normally, when you use AF, you are stuck with whatever the camera is focused on, at the moment, until you do a refocus cycle. But, SONY has given us the option to override this "feature", by going to Recording Mode Menu 3 ... selecting "AF-A setup" ... switching it to "DMF".

When you do this, what will happen is that when you now AF-A on your subject ... by pressing down halfway, you get your normal AF lock ... but, now you can use the focusing ring on your lens and adjust the focus manually to tighten up the focus for ... like an f/2.8-shot where the Depth of Field (DOF) is not quite where you want it. Now, you can press the "preview" button and move it, by turning the lens' focus ring.

Oh, hey .... it's a trifle complicated and requires you actually think about what you are doing ... but, after a dozen or so tries ... it should be pretty well understood. Personally, if you do not use a wide-aperture lens ... this procedure may have limited use, but it beats hitting your head against the wall when your AF is fighting you in a shot.

Okay, okay ... I know. Added 'control' means added 'responsibility.' It is a little tricky and that is why it is considered an advanced feature. Most people don't even know it exists ... they just give up on the shot, complaining that the AF wouldn't cooperate.

Also, I have found that toggling between MF and AF, using the AF/MF button can be dangerous for subsequent shots. Please, indulge me here.

1) You've got you subject sighted in, using AF-S (Single), AF-A, or AF-C (Continous) mode.
2) You press to use AF, but the camera just cannot lock the focus and keeps locking onto another "subject" that's close by, but in the way.
3) You press the AF/MF button and momentarily slip out of AF mode.
4) You refocus, manually, using the lens focus ring and get the image. :D
5) Oh yeah, your still in MF ... for your next shot! :eek: You forgot to toggle back ... not only that, because that button is active (yes, it can be toggled on and off from the menu) ... it can be activated accidentally (even though it is detented ... it is right next to the thumbwheel ... and I am "all thumbs", sometimes, when I am in a hurry) and you may not notice the lens is not automatically focusing (ambient noise levels are too loud to hear the camera focus) until several shots (misfocused) have been taken. :mad:

Personally, I find this a little problematic. Call me "forgetful", accident-prone or whatever, but you can lose shots to this type of procedure. The DMF technique is precisely where this can help.

After selecting the AF-A setup -> DMF operation, the procedure now becomes:

1) You've got you subject sighted in, using AF-A mode only.
2) You press (halfway) to use AF, and the camera locks the focus onto another "subject" that's close by, but in the way.
3) (Because your are using DMF from AF-A setup) the focus ring of the lens has been released (you do need to maintain that half-press of the shutter release during this).
4) You refocus, manually, with the len's focus ring and get the image. :D
5) You turn to take another image ... and AF-A instantly snaps back on and accurately focuses on the new subject ... and the subsequent shot is not missed or mis-focused. :D :D :D

No forgetful AF/MF-button nonsense. ;) Well, that's my story and I'm stickin' to it. There are significant benefits to shooting an A700 over the other models. I know this is a lot to absorb, but if you have read this ... it could solve some issues you may have been having. I know it has for me.

Good luck and I sincerely hope that settles the "AF-A" question. LOL

[DonSchap]

By the way, it does not hurt to have a manual focusing grid in your camera, too. You can live w/o one ... but, why not make things easier on yourself? It's your camera! :D

[dr4gon]

Now I wish I had an a700! darn.... because I don't have the DMF and AF-A menus in my a300. It sounds really useful for composing things exactly how you want it. I'd like to be able to manipulate the focuser after it's auto focused in on the subject. Guess I'll be the one stuck toggling AF/MF! :mad:

What is the manual focusing grid you are talking about. I didn't see it in any of the menus. (must be another a700 feature :rolleyes:)

[DonSchap]

What is the manual focusing grid you are talking about. I didn't see it in any of the menus. (must be another a700 feature :rolleyes:)

It's the Katz-Eye.

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Use this LINK (http://www.katzeyeoptics.com/cat--Pentax-DSLRs--cat_sony.html)


I had it installed about two months back. It is only for the A700 ... so quit cursin' what you have and sell that darn camera of yours ... then step up to the big boy toys. LOL

[dr4gon]

Yeah I thought it was something like that. It's in an old Canon SLR that I have.

[DonSchap]

Before Autofocus ... and the Dark Side.