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Mace · 09-28-2010, 04:28 AM

Hi,
I took some shoots last night of aurora borealis.

If you have a look at the picture below you will see some nasty rings in the centre of the picture. Whats the reason for that and how to avoid this in the future?

Thanks a lot,
Mace

Picture infos:
Camera K-7
Lens SMC DA 18-55 at 18mm
f5.6
iso 400
30sec
0ev

Rawformat DNG
opened with Aperature Software

Attached Images

Attached Files

Matze - 000430 - 2010-09-27.jpg.zip (643.8 KB, 128 views)

kyramas · 09-28-2010, 04:33 AM

Maybe its heat related
Do you get them in normal shots ?

Mace · 09-28-2010, 04:42 AM

Temperature was only -2°C. Usually I don't get them in normal shots at these temperatures.

Col · 09-28-2010, 04:42 AM

Try googling: "colour banding in sky" or if you insist: "color banding in sky". Generally related to converting to 8bit jpg... just not enough subtlety for sky shades. You should see my early LCD TV!

Mace · 09-28-2010, 04:51 AM

The color banding is not the problem. I have the same effect in the raw DNG file.

It looks more to me like a radial lens disturbance. It has definitely to do with the lens or the sensor.

Mace · 09-28-2010, 04:52 AM

If you check the zipped file and zoom to the center you will see what I mean.

Col · 09-28-2010, 05:04 AM

Beginning to think its a "rounding" beat pattern from the dark frame subtraction.

Nitrok · 09-28-2010, 05:15 AM - **1 Like**

I had this same problem long time ago with Minolta D7Hi. In the end I found that it was the UV-filter which caused those rings. So if you are using a filter, try removing it first.

Mace · 09-28-2010, 05:28 AM

hm, I am indeed using a skylight filter for lens protection. That could be an explanation.

**Digitalis** · 09-28-2010, 05:31 AM - **1 Like**

I agree with Nitrok, those look like newton rings. Do you have a filter/polariser on the lens? I recommend that you take it off.

Col · 09-28-2010, 05:40 AM

Originally posted by Mace

hm, I am indeed using a skylight filter for lens protection. That could be an explanation.

Simple (and cheapest) solution! I don't use "clear" filters for protection so never crossed my mind. I don't know about your country but here a decent filter costs more than the kit lens! (Poor under appreciated glass)

Nass · 09-28-2010, 05:42 AM

Useful thing to learn. Thanks.

thazooo · 09-28-2010, 05:59 AM

Try using a different RAW Converter, sometimes images get interpreted differently.

**Digitalis** · 09-28-2010, 06:09 AM

Originally posted by thazooo

Try using a different RAW Converter, sometimes images get interpreted differently.

i'm doubtful of that, Newton rings are a known optical phenomenon. To suggest that the demosaicing algorithm produced an artefact that looks exactly like one is very far-fetched.

Mace · 09-28-2010, 06:10 AM

Its the same in every RAW converter.

The filter seems to be the most reasonable explanation of the problem, unless the lens itself causes it.

I guess I'll do my longterm exposures in future without a filter.
Still, living in a very rough, rocky and dusty environment, I prefer to have a protection filter on my lens on a regular basis.

09-28-2010, 05:40 AM	#11
Col Veteran Member Join Date: Apr 2007 Location: Stansted Essex Photos: Gallery Posts: 614	Still like the image. Originally posted by Mace hm, I am indeed using a skylight filter for lens protection. That could be an explanation. Simple (and cheapest) solution! I don't use "clear" filters for protection so never crossed my mind. I don't know about your country but here a decent filter costs more than the kit lens! (Poor under appreciated glass) Last edited by Col; 09-28-2010 at 05:47 AM.

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09-28-2010, 04:33 AM	#2
kyramas Junior Member Join Date: May 2007 Location: Athens Photos: Gallery Posts: 37	Maybe its heat related Do you get them in normal shots ?

09-28-2010, 04:42 AM	#3
Mace Forum Member Join Date: Sep 2010 Photos: Albums Posts: 56 Original Poster	Temperature was only -2°C. Usually I don't get them in normal shots at these temperatures.

09-28-2010, 04:51 AM	#5
Mace Forum Member Join Date: Sep 2010 Photos: Albums Posts: 56 Original Poster	The color banding is not the problem. I have the same effect in the raw DNG file. It looks more to me like a radial lens disturbance. It has definitely to do with the lens or the sensor.

09-28-2010, 04:52 AM	#6
Mace Forum Member Join Date: Sep 2010 Photos: Albums Posts: 56 Original Poster	If you check the zipped file and zoom to the center you will see what I mean.

09-28-2010, 05:04 AM	#7
Col Veteran Member Join Date: Apr 2007 Location: Stansted Essex Photos: Gallery Posts: 614	Beginning to think its a "rounding" beat pattern from the dark frame subtraction.

09-28-2010, 05:15 AM - 1 Like	#8
Nitrok Veteran Member Join Date: Sep 2008 Location: Finland Photos: Gallery Posts: 1,275	I had this same problem long time ago with Minolta D7Hi. In the end I found that it was the UV-filter which caused those rings. So if you are using a filter, try removing it first.

09-28-2010, 05:28 AM	#9
Mace Forum Member Join Date: Sep 2010 Photos: Albums Posts: 56 Original Poster	hm, I am indeed using a skylight filter for lens protection. That could be an explanation.

09-28-2010, 05:31 AM - 1 Like	#10
Digitalis Site Supporter Join Date: Mar 2009 Location: Melbourne, Victoria Photos: Gallery Posts: 11,694	I agree with Nitrok, those look like newton rings. Do you have a filter/polariser on the lens? I recommend that you take it off.

09-28-2010, 05:42 AM	#12
Nass Veteran Member Join Date: Aug 2009 Location: The British Isles Photos: Gallery Posts: 2,402	Useful thing to learn. Thanks.

09-28-2010, 05:59 AM	#13
thazooo Pentaxian Join Date: Sep 2006 Location: Mississippi, USA Photos: Gallery Posts: 854	Try using a different RAW Converter, sometimes images get interpreted differently.

09-28-2010, 06:09 AM	#14
Digitalis Site Supporter Join Date: Mar 2009 Location: Melbourne, Victoria Photos: Gallery Posts: 11,694	Originally posted by thazooo Try using a different RAW Converter, sometimes images get interpreted differently. i'm doubtful of that, Newton rings are a known optical phenomenon. To suggest that the demosaicing algorithm produced an artefact that looks exactly like one is very far-fetched.

09-28-2010, 06:10 AM	#15
Mace Forum Member Join Date: Sep 2010 Photos: Albums Posts: 56 Original Poster	Its the same in every RAW converter. The filter seems to be the most reasonable explanation of the problem, unless the lens itself causes it. I guess I'll do my longterm exposures in future without a filter. Still, living in a very rough, rocky and dusty environment, I prefer to have a protection filter on my lens on a regular basis.

K-7 Aurora long time exposure gives rings in the picture

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