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Urbex Ninja

Purple blobs with long exposure?

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When I was doing some long exposure earlier today, I came across a problem. My camera started producing these wierd purple blobs and crosses across the picture, I had been doing it for about 10-20 minutes previous without problems until this happened.

oDPI4T0.jpg

pAuvSmz.jpg

I'm using a Nikon D3100, 18-55 VR Kit Kens, with a Variable ND Filter set to 10.

Anybody got any suggestions/remedies? Thanks

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Looks like a shadow/reflection to me, from the shape, could it have been light reflecting off anything, even the camera? Someone told me once that you should cover the eyepiece as light can be reflected in this way and onto the image, not sure how/where that applies though! Knowing what you/environment were doing differently when they started, though guess you've been through that. I'm no expert but that's my suggestion! :)

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Looks like a shadow/reflection to me, from the shape, could it have been light reflecting off anything, even the camera? Someone told me once that you should cover the eyepiece as light can be reflected in this way and onto the image, not sure how/where that applies though! Knowing what you/environment were doing differently when they started, though guess you've been through that. I'm no expert but that's my suggestion! :)

I'll keep that into consideration for next time! thanks :)

hot spots?

I used to get spots on m old son when I did a lot of long exposures close together

The sensor heats up and distorts slightly

Could have been that actually, a friend suggested it was the sensor heating up. Any way to combat this other than a better camera?

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I'm going to suggest it is the variable ND filter causing this, because of the way they work (2 polorising filters which rotate against each other) they are not the best filters, particularly if they are cheaper ones. Things which look fine and are not picked up by a faster exposure can suddenly become a problem when you do longer exposures.

I know you said you didn't have problems previously mind, but is it still doing it and does it make any difference when you remove the filter?

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I haven't tried since to be quite honest, problem is if I remove the filter I wont get any pictures at all, it'll be all white!

Edit.

Just tried to re-create the problem playing about just shooting constant long exposures at the settings I was using previous. Tried both with and without the filter and couldn't get it to re-create. Thing is it's never done it before, I've had the filter on the lens for a while now and done some long exposures without issues; so maybe it was due to overheating? Which would be weird because it was fairly cold out and I've never had that problem before, even shooting extremely long star trails. :s

Edited by Urbex Ninja

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Variable ND filters are known to produce a dark X in the shot when turned up high (you can find loads of threads on the forums about this). I think this happens more on UWA lenses. I had one for a brief time which I used on Tamron 10-24 and I saw the same issue so I returned it. Basically they dont work very well (I had this issue on Hoya filter so its not just an issue on cheap variable ND filters). You may find this less of an issue if you shoot at longer focal lengths.

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100% certain it is the variable ND filter, that's what you get when you turn it exactly to max :)

I used to use 2 linear polarisers as a DIY ND filter, and that's what it does.

thing is the sweet spot should be rather narrow, turn it half an inch to either side and blob should be gone!

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