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Slightly Blotchy Sky

By Tallmanirl
Hi guys!
I use a Canon 5D and 17-40 L lens. Sometimes when I take photos on a bright day the sky,when afterwards viewed at 100% in photoshop can be slightly blotchy. I was wondering what might be the cause of this? It was mentioned to me that it might be just wisps of grey cloud but I was told that people might be better able to view it here rather than in a forum post.

Tags: Sky General Skies SkiesandClouds Skies/Clouds

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banehawi Plus
15 2.1k 4012 Canada
6 Jul 2019 7:49PM
Do you believe this is a typical blotchy example?

Were there wispy clouds when the shot was taken.

Have you recently, or ever, cleaned the sensor?


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banehawi Plus
15 2.1k 4012 Canada
6 Jul 2019 8:11PM
I have uploaded a mod with an area marked; the image has has contrast tweaked. Is the issue you see within this area? Is it anywhere else?

How old is the camera ( images shot to date)

Can you upload an image without any cropping (this is cropped), and at 300ppi please?

dudler Plus
15 877 1496 England
7 Jul 2019 8:19AM
It would be helpful to know what sort of blotches you see, Fergal.

Small dark marks might be dust on the sensor, and will be more visible if you shoot at small apertures.

Larger, light blotches might be the result of flare, especially if the front element of the lens or any filter is dirty, or if you don't use a lens hood.

There's nothing that strikes me in this frame. Are you seeing more in a higher-quality image than shows in this websized one?

Tell us more, and we may be able to tell you more!
Tallmanirl 5 227 Ireland
8 Jul 2019 8:16PM
Hi guys!
My apologies for the delay in replying.
What I'm referring to is that the blue changes colour slightly in patch like formations. If you look closely, you can see lines between them. There are wispy clouds in it alright. I bought the camera in 2009 I think. The sensor has been cleaned but not in a long time. I'll upload the original but how do I upload another photo to this thread?
paulbroad Plus
11 127 1282 United Kingdom
8 Jul 2019 9:10PM
Sounds like compression artefacts to me. The way JPG compression works can cause blotchiness in large expanses of a similar colour. I never save at a compression less than 11. So, I wold doubt the problem is camera/lens related, but just a guess.

dudler Plus
15 877 1496 England
9 Jul 2019 11:29AM
Just add the image as your own Modification - click 'Modifications' and 'Upload Modification'.

Paul may have hit it - if you compress files, you can get something like contour lines on a map, or Newton's Rings appearing. Banding can be a camera artifact at high ISO, but not at 125, I think.

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