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UltravioletPhotography

Filter stack orientation on UV converted flash.


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Hi I was wondering if filter orientation matters or not so I ran a test. First image is made with the Hoya U-340 on the outside of the stack and the Schott S8612 on the inside facing the bulb. Second image is with the filters the other way around. The images are SOOC have only been reduced in size absolutely no other editing at all done to them. Is there a specific way to put the filters? Testing was done with exact framing and focus exact same settings and as close to exact position of light source trying not to move the light stand while changing flashes over. Each flash had fully charged batteries. Unless one of my flashes is brighter than the other I see a fair difference here.

 

 

 

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I figured out why one is brighter than the other and now feel a tad bit silly about it but i will share. The one with the schott filter facing out has more of the filter covered by tape and foil hence has less total output than the other one. So I guess orientation doesnt matter then ?
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Orientation on a light shouldn't matter.

 

However orientation on a camera can matter depending on internal reflection within a lens and camera.

 

The flocking material, internal paints and metal baffles aren't always designed for our desires into deep UV or far IR. So hotspots, glare and loss of contrast can occur. Even a lens design for UVC, like our 60mm macro lens on the forensics imager, has a highly reflective paint coating on the lens barrel, killing contrast.

 

I like to always have the darkest flat filter side face the sensor side. This sometimes helps to reduce loss of contrast. If you have a filter that is shinny like a mirror on one side and mat black on the other, than the black should face the sensor and the mirror side should face away towards the subject.

So look at your filters, you may see one side slightly shinier on one side, that do the same.

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That was a good summary David.

 

On the camera one more thing might be considered for UVIFV.

Some long-pass filters are made of filter glass with fluorescence.

If you want to limit the UV and violet impact with a filter like a GG420 it is a good idea to place it behind a filter that cuts some of the UV.

Beside some obsolete rare filter materials from Schott, also most (all?) Tiffen filters lack strong fluorescence. A Tiffen UV Haze 2A or 2E is a good candidate for that.

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