Long exposure artefacts

Those with long memories may remember I posted a set of long exposure 'cock ups' about this time last year, the causes of which were clear and from which I learned a great deal .

However, I took some long exposures last month on vacation which show an odd artefact which I can't explain... so any help identifying the problem would be appreciated.

An example of the artefact
(103 secs, f16, ISO100, 21 Ltd, B&W F-Pro 10 stop ND filter, Marumi DHG circular polariser, K5)




Note the red-ish horizontal banding in the bottom third of the frame. Anyone know what has caused this ????? Is it something to do with using a 10 stopper and a circular polariser at the same time? I took a series of shots earlier in the trip with just the 10 stopper which do not show the artefact.

Long exposure with just the 10-stopper (no polariser, no artefact!)





Thoughts?

I don't see any obvious red banding (on 2x calibrated IPS screens), if you are seeing it at full resolution it may be the way the sun, water droplets and the reddish rock acting in concert during a long exposure, maybe give us a look at a higher res file.

On the other hand, banding or not they are couple of cracking shots

I can see the band - it curves down towards the centre and is most obvious on the second rock from the left in the foreground.

Given the curvature, I would guess it is connected with a possible reflection off a filter rim.

Is it possible you could try taking similar images without the polariser, then with polariser in front of the 10 stop and then behind the 10 stop.

And where is the report on your Singapore trip?

Looking at the first image, I would guess that is one of the first.

Where was the sun in relation to the camera?

Sun shining into the view-finder?

Thanks all

More or less overhead (taken at 11am in Malaysia... facing due South)... but thinking about it I'm not sure I remembered to cover up the viewfinder for these shots (doh and double doh!). So you're probably on to something. Could well be some sort of (reflected?) light getting in through the viewfinder.



Yup. Still working through the shots . Many slightly dull record shots of the hols, but I'll post some of the more interesting stuff when I find it/get a chance .

Found this;

link

You need to cover your viewfinder during long exposures to prevent light leakage.

Yup... Almost certainly stray light through the viewfinder... The brighter it is, and the more direct the sunlight through the back of the viewfinder, the worse it tends to be in my experience... Any way you can find to block it will do (I use a cut out piece of an old credit card)...

Best

I usually find that rubbing some black shoe polish (about
0.1mm thick) around the finder, not only makes it look good,
but also makes it tacky enough to hold a small piece of
card in place for the duration of the exposure

Mystery solved - thanks All.

Real schoolboy error I've used black tape for covering the viewfinder in the past but not this time. I did have the viewfinder cover with me but simply forgot to use it. Senior moment ahoy.

Any particular make of shoe polish :

Kiwi's the best!.... It's waterproof and hard to wash off!

the old black eye telescope updated for the DSLR age eh?

the old ones are the best!