Tuesday, July 15, 2014

Flare reduction and sunshade use in reflected UV ultraviolet photography

Today about flare redction when shooting reflected UV and the dedicated UV transmitting filters, like the Baader-U filter, my "work horse", for that. I'm using here my CERCO 94mm quartz fluorite lens, but in principle this method is applicable for any such lens. However, keep in mind, that quartz fluorite lenses for reflected UV are often single or even uncoated or show hotspotting, so it gets even more important to control flare efficiently, resulting in much higher image contrast and sometimes even removal of the hotspot. All images have been done at identical manual exposure settings, which were tested for correct exposure upfront.

Similar methods using such hoods have been used by others, I'm not claiming anything here, this just documents what I have done to further optimize my own setup.

[click on image to see a larger one]

Test images at nearly infinity (left to right) using (optimized for my camera's sensor size, other sensor sizes will require different sizes)
1) just the UV filter, no sunshade at all
2) a 40mm long sunshade with 50mm free diameter
3) a 50mm long sunshade with 21mm free diameter

The difference gets quite obvious, the longer and narrower the sunshade is, the better flare gets controlled.

Now some closeup shots, using the same method and sequence:

Also here shooting flowers at closeup, it gets pretty obvious, how much flare is present if using no or a simple sunshade, whereas a specilized deep and narrow sunshade results in much improved flare control, hence greatly improved image contrast.

Let me summarize:
Whenever shooting reflected UV (or other multispectral work), make sure to use the deepest and most narrow possible sunshade, that does not vignette, to achieve the best flare control and resulting in best possible image contrast. It is also suitable to control or even remove the effect of hotspots, some of those highly specialized lenses unfortunately show.

I have previously written about filter leakage HERE.

Stay tuned, more will follow on that fascinating subject...

More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos