Gareth

Horizontal line across clear sky!

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Posted (edited)

I wonder if there's anyone who can shed any light on an issue I'm having with clear, blue skies?

 

There appears to be a fairly straight, single line running horizontally at about the upper third, across my images of cloudless blue skies.

I don't think it's banding, since it's evident straight out of the camera as an unprocessed RAW. And isn't banding a processing artifact?

I really hope it's not a defect on my cameras sensor - it's a Canon 7d mk2 - I've tried to find out if it's a particular problem with this camera, but the evidence is inconclusive.

I've managed to blend an overlay in photoshop to mask it on some images (feels like cheating!), but this is proving to be an awful lot of work when it interferes with buildings etc.

 

Short of avoiding shooting anything with clear skies (I don't want to do this), I don't really know what to do.

 

Here is a recent image - just basic JPEG processing from the original RAW.

 

6mMZz1v.jpg

 

(I know about the dust spot on the right before anyone says!):D

 

Any help would be gratefully received, thanks.

 

Gareth

Edited by Gareth

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No streaks on the sensor from the last cleaning?

- Breathe lightly on the open sensor. Lightly.

8 bit or 16 bit?

Is it always in exactly the same place?

- Put a fair lot in layers and turn them on and off.

Is it really straight? One row of pixels is affected and the next one not?

- On your example this is not clear: too many blotches of different tones and lots of jpg artifacts. Test this on a full size tiff.

Is it only in one channel?

- Look at the different channels. Turn them off and on one by one.

 

wim

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10 minutes ago, wiskerke said:

No streaks on the sensor from the last cleaning?

- Breathe lightly on the open sensor. Lightly.

I've never had it professionally cleaned, I just use a puffer gently for dust spots - maybe I should get it properly done.

13 minutes ago, wiskerke said:

8 bit or 16 bit?

16 bit

13 minutes ago, wiskerke said:

Is it always in exactly the same place?

- Put a fair lot in layers and turn them on and off.

Yes - can even be seen on the back of the camera.

16 minutes ago, wiskerke said:

Is it really straight? One row of pixels is affected and the next one not?

- On your example this is not clear: too many blotches of different tones and lots of jpg artifacts. Test this on a full size tiff.

Seems pretty straight.

It is a tonal change though - seems to abruptly change from the darker tone above to the lighter tone below, over maybe a 10 pixel range when zoomed right in.

Sorry about the blotchyness - no other processing/NR done!

22 minutes ago, wiskerke said:

Is it only in one channel?

- Look at the different channels. Turn them off and on one by one.

I never thought of this - definitely worth a look.

 

Thanks Wim.

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26 minutes ago, Gareth said:

I've never had it professionally cleaned, I just use a puffer gently for dust spots - maybe I should get it properly done.

16 bit

Yes - can even be seen on the back of the camera.

Seems pretty straight.

It is a tonal change though - seems to abruptly change from the darker tone above to the lighter tone below, over maybe a 10 pixel range when zoomed right in.

Sorry about the blotchyness - no other processing/NR done!

I never thought of this - definitely worth a look.

 

Thanks Wim.

 

I would still do the light breathing.

And go back in your files to see if you can find where it started. Gradually? Abrupt?

Vertical/Horizontal?

 

wim

 

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Forgive my ignorance, but wouldn't breathing on the sensor possibly leave moisture on it?

Or is that the point?

Would this 'mist' it up in order to highlight a smear?

I must admit, I've always been (perhaps over-) careful about exposing the sensor, never even looked closely at it for fear of getting it dusty!

 

I have only recently begun to shoot landscapes - and it's only been during this recent hot weather that I've been able to shoot clear skies - it doesn't show on cloudy skies....I suppose I should at least be thankful for the changeable weather here in the UK lol, should be back to clouds and rain anytime now!

 

I first noticed it a few weeks ago, but buried my head in the sand like an idiot!

But yes, I will go back through my files, there must be at least one with a clear sky....the weather can't have been that bad!

 

Oh, and it's horizontal.

 

Thanks Wim.

 

Gareth

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There's a very good possibility your skies over there in Norfolk just look like that.

A controlled test will involve an even piece of blue paper and even lighting.

 

The light breathing indeed fogs it up slightly. Hold the camera in front of you at about eye level, while there's a light or the sun shining on the shutter. Now open the shutter (using the menu setting for it) and breathe lightly so that there's a very thin fogging visible for just a second or so. It will reveal streaks if they are there.

You're right that it's not a good thing in general. Because it makes dust cling to the surface somehow.

 

wim

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10 minutes ago, wiskerke said:

There's a very good possibility your skies over there in Norfolk just look like that.

Ha ha! I really hope you're right Wim!

I haven't yet dared submit one without being 'fixed' first - wouldn't want a failure due to 'banding' and I'm not sure Alamy would believe me!

15 minutes ago, wiskerke said:

A controlled test will involve an even piece of blue paper and even lighting.

Good idea, thanks - looks like tomorrow (or rather later today) will be a testing day for me.

I'll try the breathing trick too - if I can keep my nerves in check!....at least I'll be able to see if my sensor needs professionally cleaning.

 

Thanks for your help and advice Wim.

 

Gareth

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Sorry Wim, DO NOT breathe on your sensor.  There's a chance fungus could rear its ugly head.  Get the gear to wet clean your sensor, I do my own and it's a very easy task, as long as you clench your cheeks!

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Posted (edited)

When you get a similar sky again (next year? ;) ) or find an evenly toned subject. Take a picture again and also one with the camera tilted. If it is a sensor issue it will remain horizontal, if it stays parallel to the horizon it may be a haze effect, shouldn't appear at all if it is of an artificial even toned subject (painted wall for example).

Edited by Martin P Wilson
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I think your 'dust spot' is way too big to be a dust spot. It looks more like an oil spot to me. I get these a lot on my 5D2. I'm very suspicious of the fact that the spot is exactly in line with the streak... you can see where I'm going with this, can't you?

 

Alan

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1 hour ago, Inchiquin said:

I think your 'dust spot' is way too big to be a dust spot. It looks more like an oil spot to me. I get these a lot on my 5D2. I'm very suspicious of the fact that the spot is exactly in line with the streak... you can see where I'm going with this, can't you?

 

Alan

 

Agreed, especially as the streak seems to be wider at the dust spot side. Have you tried taking a portrait picture?

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If you open the image in Photoshop and darken it to exaggerate the effect*, the top quarter of the frame is slightly darker then the rest.
 

Perhaps you have a sticky shutter blade?

 

* For example, set levels to 17, 0.2, 215

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You need to try and replicate it. Set your camera to it's lowest ISO, lens to f16 or f22 and try and get a shutter speed of slower than 1/15th with the metering showing about 1/3rd of a stop underexposed. Then set the focus to manual and turn it out of focus. Photograph the sky with the camera at a 45 degree angle while panning quickly. If the effect isn't there then your original post is showing a cloud formation. If the stripe is there then it's a camera issue.

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44 minutes ago, AndrewP said:

You need to try and replicate it. Set your camera to it's lowest ISO, lens to f16 or f22 and try and get a shutter speed of slower than 1/15th with the metering showing about 1/3rd of a stop underexposed. Then set the focus to manual and turn it out of focus. Photograph the sky with the camera at a 45 degree angle while panning quickly. If the effect isn't there then your original post is showing a cloud formation. If the stripe is there then it's a camera issue.

 

Holding it still at 90 degrees would be enough ;-)

 

wim

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If I were you I would get the sensor professionally cleaned rather than mess about. If it is still bad after that then you might have a more serious problem. Your sky in that pic is quite a mess when viewed in PS with a strong s-curve and I am not sure it is just down to jpeg artefacts - it would be necessary to see the raw really. Fixation in London are authorised Canon repairers and do excellent while you wait sensor cleaning. They are owned by WEX in Norwich if that is convenient to you although I don't think they do sensor cleaning in Norwich but I expect you could drop the camera in there.

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Posted (edited)

Thanks to everyone for all the advice.

 

I've been trying to replicate the phenomenon today, with no success - cloudy skies here today.

Tried to shoot a plain surface with flat light....no line but the 'dust/oil' spot shows clearly.

I've checked some earlier images from when I first noticed it, but I can't seem to find any problems with them now!

Am I going mad?! Feels like it!!

I don't have any of the original RAWs either....I convert to DNG as soon as I get them out of camera (I'm using older software which doesn't recognise the 7dmk2s CR2 files)

 

The image I posted above seems to be the only (worst by far) image I have, so maybe it's a strange, haze effect when shooting directly away from strong sun into a clear blue sky.

 

@Colblimp I haven't done that, (sorry Wim, nerves got the better of me!!)

 

@Inchiquin & @BobD Yes, I see where you're going.

 

@Sprocket I was shocked when I did that....

 

7yrErCG.jpg

Probably not worth trying to salvage this image....but it does illustrate the problem....hmm....is there any way to pull this from QC before it's evaluated?

As for a sticky shutter blade....could heat affect the shutter action? On the few occasions I've noticed it, it has been very hot....at least 25°C, and in direct sun it felt a lot hotter - the camera felt pretty warm too.

 

 

@AndrewP Thanks, I tried this, and was not able to see any issue....which is somewhat comforting.

 

@wiskerke I did that also, no line I'm relieved to say.

 

@MDM I agree, in fact I think I'm on my way now, I'm not far from Norwich, and indeed Wex is where I buy most of my gear, so I know them pretty well.

I hope it is just a simple clean that is necessary, and not something more serious.

 

Fingers crossed!

 

Thanks again everyone that took time out to respond with advice.

 

Gareth.

Edited by Gareth

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Posted (edited)

If the shutter were sticky the shadow presumably wouldn't be dead sharp, but we can't tell if it's an abrupt line, as Wim said, which IMO would make it a camera problem.

If it's dirt, it's a very neat bit of dirt. Wet cleaning a sensor isn't very scary- I've been doing it for years- but it's fair enough if you don't fancy it.

Edited by spacecadet
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8 hours ago, Colblimp said:

Sorry Wim, DO NOT breathe on your sensor.  There's a chance fungus could rear its ugly head.  Get the gear to wet clean your sensor, I do my own and it's a very easy task, as long as you clench your cheeks!

 

Of course I do my own wet clean, but also pay for a professional cleaning now and then.

For the rest: don't spit on it. If you read closely you'll see I'm not advocating the glasses cleaning method of heavy breathing repeatedly. Just a light breathing to reveal possible streaks. By holding the body way higher than your mouth the amount of moist will be minimal. Just enough.

What do you think is in the different cleaning fluids? Even the ones containing pure alcohol are not 100% pure. Some sensors must be cleaned with water based fluids though. Like my Sony. Well officially anyway.

I have never heard of fungus on a sensor, but I won't rule it out. I even had a snowflake blowing inside once in late summer on a mountain pass near Denver somewhere.

You got me scared though. I will be googling all evening for all strange horrors that can befall my wee sensor.

Like the pit in one of mine put in by a very good and professional service station after that snowflake. Just even with a professional service stuff happens. It's about 2 or 3 pixels and in the end I just left it.

Some music to go with my googling.

 

wim

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Posted (edited)

I would be suspicious of a software problem in conversion to DNG, I would check the original raw, if you manage to replicate the problem. You need to get as close to the original sensor data as possible and track the problem step by step from there. Also has it happened on more than one memory card, it could be data corruption (even just one bit) on the card?

 

Has your DNG conversion software been updated recentlY?

Edited by Martin P Wilson
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@spacecadet Just checked again, and it is indeed dead straight and quite sharp....maybe a pixel or two....not looking good....I'm worried now!

Annoyingly I can't really compare it to the horizon since I must have levelled it quite well....they're both parallel!

Missed Wex today, they shut at 5pm....I'll take it in tomorrow for an assessment and/or clean - not brave enough to do it myself!

 

@Martin P Wilson I found the original RAW file - it was still on my memory card....for once I'm thankful for being lazy!!

However, it's still there in the RAW....doesn't show up clearly until I do some tweaks though.

I don't think it's a software issue unfortunately, I'm up to date, or at least compatible with my Camera Raw and Photoshop versions (ACR 6.7, PS CS5)

 

I'll change out my memory card for another too, maybe eliminate that as an issue.

Haven't had any success replicating the problem today though....I'll keep trying.

 

By the way, is there a trusted way for me to upload a RAW file anywhere, for anyone who wants to take a gander?

 

Gareth

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The darker image looks like a graduated filter has been applied with any feathering. Certainly doesn't look like a cleaning problem.

 

 

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16 minutes ago, BobD said:

The darker image looks like a graduated filter has been applied with any feathering. 

Yes, but I didn't apply one....honest!

19 minutes ago, BobD said:

Certainly doesn't look like a cleaning problem.

I have to agree....now I'm really worried!

 

What's infuriating though, is that I can't seem to replicate it today.

All the sky or plain background shots I've taken today show nothing! (Except that blimming dust/oil spot!)

 

Anyway, it's just gone through QC, so I suppose my 'fix' was decent enough - not sure I'll put it on sale though.

 

Gareth.

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I'm thinking that two pixels has got to be a camera or card issue. Card first, much cheaper.

The only time I had a card failure the image went to pieces horizontally, much worse than yours though.

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54 minutes ago, spacecadet said:

I'm thinking that two pixels has got to be a camera or card issue. Card first, much cheaper.

 

Just popped back to the location in the image (only a 10 min drive from where I live) to recreate the conditions, took a spare card also.

Couldn't replicate the heat on that particular day, but took some shots, same settings/composition etc, and nothing - no line, just a nice, clear blue sky....and that ruddy church....sick of it now actually! lol

Tried it with the old card onto which I shot the original, same deal, nice and clear!

 

I've updated to the latest DNG converter also just in case, but I don't think it was the problem since it's in the RAW file, before it gets anywhere near any processing.

 

The only thing I can think of now is that it was some sort of freak atmospheric condition, or maybe the heat....I just don't get it!

It's such a neat line right across the top third....if it's an intermittent glitch, I may have to just live with it and attempt to plan around it when (if?) there's anymore sunny, clear days this year.

 

Oh well, I think I've managed to satisfy myself that while it's annoying, it hasn't wrecked any other images so far, but I'll be taking it in for a sensor clean tomorrow anyway.

 

Many thanks to everyone for your kind advice.

 

Gareth

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Posted (edited)

It looks like it could potentially be a shutter blade problem to me. At very short exposures the first and second curtain are supposed to transit in same time to create a constant width slit that moves across frame creating a uniform exposure. It looks like one of the blades hasn't quite transitioned smoothly causing the slit width (and hence exposure) to change part way across the frame. I once had a film SLR that would do something similar. This could well be temperature dependent and intermittent.

 

Mark

Edited by M.Chapman

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