Incense

by Bart Arondson

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I'm attempting to do a shot without causing damage to my camera...A hour long exposure of a sunset. I've have used two pieces of welder's glass and got this shot. It caused a purple haze over a good portion of the image. I'm assuming it's infrared or UV light??? If this is the problem, is there a filter like a IR cutoff filter that would do the trick? Or would I need something better? enter image description here

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I can't answer your question but could you please tell me how you mananged to prevent your picture from getting overexposed? What aperture value and ISO did you use? –  shortstheory Sep 4 at 9:29
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@shortstheory as explained in the question...2 pieces of welder's glass. It is a very dark glass, which if you hold up to the light you are unlikely to be able to see anything through it with the naked eye. It's cheap to obtain squares of it. –  laurencemadill Sep 4 at 10:32
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Why don't you try image stacking with shorter exposures, a process used to photograph star trails. A regular ND filter and a short exposure time may be enough then post process in software such as ImageStacker. I never tried it so I can't really provide this as a valid alternative answer. –  Jakub Sep 4 at 16:51
    
Thank you all for the feedback! I've tried the stacking method and still get the same result, just not quite as bad..I didn't think about the fact I had the white balance set to make up for the green tint of the glass, so that's probably why it looks so purplish or magenta. It's actually pretty obvious to me now it's a reflection. I have a couple ideas that may get rid of the reflection I may try out sometime soon. Thanks everybody! –  user32207 Sep 4 at 18:47
    
Random thought only. An intermittent super slow external shutter would allow a lower ND ratio and would at least change parameters which may (or may not) help. eg a 1s on 15s off wheel or sliding mask or ...? would be easyish to implement and should be "easily enough" made to leave no significant artefacts over the time concerned. –  Russell McMahon Sep 4 at 23:14

4 Answers 4

that purple haze is probably a color cast caused by the glass itself; the welders glass often isn't neutral color.

you should be looking at solar filters, or very dark (and probably stacked) ND filters. Thousand Oaks sells solar filters, to name one company.

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IF you're shopping for solar filters; be sure to check if they've got a neutral color balance. Like with welders glass, many of the more inexpensive ones don't. They're acceptable for taking sunspot images through a telescope/long focal length lens; but wouldn't be suitable for what Clint appears to be trying to do. –  Dan Neely Sep 4 at 13:17
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Or you could postprocess with a spectral filter curve opposite to the transmission curve of the welder's glass. –  Carl Witthoft Sep 4 at 14:40

This is just the diffused light going through the welder glass. It comes from two sources:

  • the sky and
  • the two welder glass. (These have coplanar surfaces that allows for bouncing the light for long.)

You cannot do anything with those either. You need to use optical quality filters (ND filters of high value) to achieve this effect, although then you will only have a trace of the Sun and most of the details might get lost.

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Why is there a division? Ie. why is the top of the picture purple and the bottom not, with a fairly sharp division between the two? –  Taemyr Sep 4 at 9:36
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You can get a hint by the trajectory of the sun and there is a weaker, reflected trajectory. The two welder glasses were not completely parallel, e.g. the back one was tilting a bit up and to the right. –  TFuto Sep 4 at 10:45

I never tried it and would probably start with image stacking as opposed to one extra long exposure.

In any case, take a look at IRND filters that are designed to filter out the IR spectrum from some 740nm. The IR pollution causes unwanted color shifts in the images. I don't know if these filters can prevent heat damage, another reason why I would use them for series of short exposures as opposed to one extra long.

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Purple is the welders glass remember welders glass is specially designed to protect our eyes not reduce light transmission as is a nd filter, and is also often seen when stacking cheap nd filters bought from ebay and the like as well.

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