northern lights - weird thing - DPChallenge Forums

11/08/2004 12:00:05 PM · #1

i only took a couple shots of the northern lights last night.
but in this photo what is the ring in the middle from?

canon 50mm f:1.8 - f:22 - iso200 - tripod - long exposure. focused manually

it's a brand new lense - and the other two photos taken with the same settings, varying times, did not have that ring effect? i will add that it's an older UV filter on the lense.

hopefully they will be out again tonight so i can see if it happens again.

is it the lense or what?

scalvert

Canon EF 24-105mm f/4.0L IS

11/08/2004 12:03:23 PM · #2

Looks like your UV filter is touching the glass on your lens and creating the pattern. Not a good thing.

mrorange002

Canon EOS-5D

Canon EF 16-35mm f/2.8L USM

11/08/2004 12:06:30 PM · #3

it's the aliens

frumoaznicul

Canon EOS-20D

Canon EF-S 18-55mm f/3.5-5.6

11/08/2004 12:09:53 PM · #4

Originally posted by ericlimon:

it's the aliens

or god :))

11/08/2004 12:12:34 PM · #5

shouldn't be - i'll check it out.
EDIT: at no focus point does the lense touch the UV filter - they move together.

i am wondering if it was condensation - it was pretty cold out.

scalvert

Canon EF 24-105mm f/4.0L IS

11/08/2004 12:13:20 PM · #6

Ring-type USM on the lens. ;-)

Canon EF 28-135mm F/3.5-5.6 IS USM

11/08/2004 12:15:05 PM · #7

what gets me is that this is the middle photo - and the first and last dont have this pattern, but have some foreground elements in them. this one didn't

EDIT: another reason why this lense is a good value..

Originally posted by scalvert:

Ring-type USM on the lens. ;-)

Message edited by author 2004-11-08 12:17:05.

siggi

Canon EOS-10D

11/08/2004 12:19:49 PM · #8

Clean the lens, its your fingerprint! :P

11/08/2004 12:24:47 PM · #9

Very strange. It looks like a circular wave-interference pattern, but I can't imagine why it's showing up in your photo. How long was this exposure compared to the others you took, where the effect did not appear?

Just for fun, shoot a darkening evening sky sometime (after sunset, before completely dark) with the same exposure and same settings and see if you can duplicate it.

What were your exact settings, BTW (exposure and f-stop)?

giega

Canon EF 16-35mm f/2.8L USM II

11/08/2004 12:30:04 PM · #10

You bumped your head. I don't see anything ;-D

11/08/2004 12:31:54 PM · #11

the shot settings are posted in my initial post, and the same for all three photos. they are all from the same location - looking in different directions.

edit: i lightened this with levels a bit to bring out the color - but the rings were visible in the unmodified file.

this ( middle ) exposure was 420 seconds ( oddly enough )
the first exposure was 338 seconds
the the last exposure was 504 seconds

Message edited by author 2004-11-08 12:33:42.

11/08/2004 12:34:09 PM · #12

the lense, and filter are clean.

11/08/2004 12:38:58 PM · #13

Why such long exposures? All of mine were shot with 5-30 second exposures at ISO400-800. I would say that at such a long exposure, you were getting some optical defect in the lens to show up, but that doesn't explain why it only showed on your middle image. Was the aperture wide opened or stopped down, and did you change the aperture between the photos?

Originally posted by soup:

11/08/2004 12:43:09 PM · #14

it was not long enough as these needed levels adjustment to brighten them... the effects last night were not overly bright, you wouldn't have noticed it with out specifically looking for it.

stopped down to f:22 for all of them.

Gauti

11/08/2004 12:53:47 PM · #15

It's captain kirk going into hyperdrive, how dense can you earthlings be :)

Why did you stop down to f:22? With NL you usually want to get all the light awailable, so I stop up to the lens max (1.4 on my 50mm or 4 on my 17-40) and add iso to maybe 400 and time to 2-10 sec
with more than 6 sec you start to get all kinds of strange colours in clouds (well, really it starts at 4 sec)

11/08/2004 12:59:41 PM · #16

My guess is that you've rediscovered one of the odd manifestations of the wave-particle duality of light. If you hurry, the Nobel prize committe may still be taking nominations for next year.

With your aperture stopped down so far, you basically had photons trickling through all that glass for several minutes, allowing time for an "airy disk" to become evident. If your exposure had been even longer, the image might have brightened enough to overwhelm it. If you had a bigger aperture, likewise. I bet if you go to your other two images and crank the contrast way up, the same effect is in those as well, just not noticeable at first.

I'm not positive that this is what you're seeing, but it looks VERY much like illustrations in physics/optics texts that deal with such things. Google "airy disk" and browse the results. Though I'm not a physicst, I think your small aperture was close enough to point source for the diffraction effects to produce the characteristic "ripple pattern" you saw.

BTW, for aurora, or other faint celestial targets (constellations, the milky way, etc.), open the aperture up all the way or nearly all the way. For faint displays like that, you want all the light you can get, as quickly as you can get it.

11/08/2004 01:06:56 PM · #17

usually i do use a wider aperture for this kind of thing - was kind of a rush job last night setting up, and i wasn't really thinking.

11/08/2004 01:09:59 PM · #18

i would say it's airy discs.

well that clears that up - thanks.

kirbic

Canon EOS R5

Canon RF 24-70 f2.8 L IS

11/08/2004 02:12:38 PM · #19

After looking closely at it, I still believe it is "Newton's rings", that is, interference pattern. Is the filter possibly two layers that might be in contact at the center? If there are two layers, it's possible that exposure to cold temperatures could generate compressive stress on the glass elements from the aluminum ring, and force them to contact at the center.
An airy disc, as I understand it, requires a point source of light. there is none at the center of the pattern.

11/08/2004 02:27:18 PM · #20

Kirbic's explanation makes much more sense, so I retract all my blathering about the airy disc. It was a long-shot anyway. Besides, Fritz is an electrical engineer and has certainly had more physics classes than I have (a psychologist!).

Originally posted by kirbic:

11/08/2004 02:59:07 PM · #21

hmm - well i don't actually know if it's two layers.
but i suppose that's possible - it was pretty cold out.

the filter is an older one - made by canon skylight filter 1A - circa late 80's.

i'll try it with out the filter if it clears up for tonight, and also maybe with a different filter.

still doesn't explain why it was only apparent in the one photo though.

thanks,

Originally posted by kirbic:

--------------------------------------------------------------------------------
After looking closely at it, I still believe it is "Newton's rings", that is, interference pattern. Is the filter possibly two layers that might be in contact at the center? If there are two layers, it's possible that exposure to cold temperatures could generate compressive stress on the glass elements from the aluminum ring, and force them to contact at the center.
An airy disc, as I understand it, requires a point source of light. there is none at the center of the pattern.

11/08/2004 05:11:49 PM · #22

After further reflection Fritz, if it is an example of Newton's rings, why would it be in focus at the level of the sensor? If it was part of the old filter that Soup used, it wouldn't show up so sharply in the photo. I have heard that the bonding of the filters to the sensor is handled differently in the 300D. It's just as likely that it's an interference effect between layers on the sensor itself, maybe set in motion by dropping ambient temperatures or by heat generated in the camera itself as a result of the long exposures.

scalvert