Monday 28 July 2014

Colour - More on UV Imaging

Having now had a couple of weeks with my bespoke Near UV camcorder, trying to perfect the method and checking out UV reflectance and absorption patterns, I can report some more useful results and conclusions.

Camera Setup and Method

I put together a simple bracket to connect the VIS and UV camcorders and keep them close together.  Not only does this help to create near identical VIS and UV footage for comparison purposes, I also find it easier to keep both cameras steadier when lashed together.  The Xacti is giving trouble unfortunately so I have switched to an older Panasonic camcorder (SDR-H60).

I think there is a big advantage in dual VIS and UV because it can be very hard to locate and track a subject in monochrome UV, especially if both the subject and background are similarly UV absorbing/reflecting.  With the target zone roughly pinpointed through the view-finder of the UV camera I can glance at the VIS LCD screen with my other eye and locate the subject then back to the UV to lock on, focus and compose the footage.  Takes a bit of practise but I am now fairly well able to capture decent UV footage, even some moving targets.

 Protecting the UV Filter

The Baader-U filter is not cheap so you might want to consider protecting it from scratches and marks.  At the moment I am just using a rubber O-ring to give it some protection.  Most photographers use UV clear glass filters to protect their lenses.  When I placed a UV filter over my Baader-U, I was expecting the UV filter to block out all remaining light to the sensor.  I thought something was a miss when the camera 'saw' right through the filter like it wasn’t even there (see below).  My UV filter it turns out is filtering UV beyond the range of sensitivity of the camera sensor.    Many cheap UV filters don’t really filter Near UV (300nm – 400nm) all that well it transpires, so they can be used as a lens / Baader-U filter protector without any detectable loss of UV transmission in this instance.  Of course the more expensive UV filters will probably filter some Near UV light so will need to be avoided.  For more see HERE and HERE

UV days, good and bad

UV light is of a lower intensity than VIS light (thankfully, as it is highly damaging to life on earth).  As I have been out and about with my UV camera I have been keeping an eye to what is happening with the UV Index.  The UV Index (HERE) was first put into use in the 1990’s as a way to measure and gauge UV exposure risk.  There is an excellent website ( that provides daily and weekly UV Index forecasts for everywhere on the planet.  I have used it to gauge what days might be good for UV imaging and what days might suck.  UV varies throughout the day, tending to peak around lunchtime (handy for a spot of UV imaging during break time).  The website tracks the predictive UV index throughout the day and displays it in a neat little movie.  Well worth checking out.  

With the kit I have I am finding that High UV index is desirable for bright images, but not totally necessary.  I have managed to get some reasonable images when the UV index is moderate to high.  So I would be hopeful that I will be able to continue to create UV images in spring and autumn, and possibly even on a bright winter's day.  But that all remains to be tested.

More Results

Before I get on to birds, I took my camera to a nearby garden centre and they were gracious enough to let me walk around inspecting and filming their flower collection, looking for Nectar Guides.  There were some real beauties on show but the one that really caught my eye was this aptly named Arctotis called "Hope".  It really is impossible to guess which flowers will reflect and which will absorb UV, or what their exact Nectar Guides will look like.  It is both fascinating and exciting taking a look into this hidden world inhabited by the bee and the flower, and for me this has been reason enough to take the plunge into UV imaging.  

Needless to say, the garden centre staff had been unaware of UV Nectar Guides beforehand and some of the other patrons were equally bemused!  I hope to plant my garden with flowers that can be appreciated in both the VIS and UV.

But there is lots more to come…

The birds havn’t been too cooperative of late.  It is high summer and many of the more colourful passerines are keeping a low profile it seems.  So far the images which I have obtained are not very inspiring.  The best way to describe UV absorption and reflection in birds is, it is VERY subtle.  I am in the process of putting together the videos which I have managed to capture and will post them up in the next couple of weeks together with some thoughts.  For now I have been making the most of the time of year and in particular the abundance of butterflies to take a look at a phenomenon almost as well known as the UV Nectar Guide.  I am referring to Butterfly UV communication.  Having been fortunate to capture 10 of Ireland's paltry 33 Butterfly species over the last week, I found there were some real surprises in store.  Hope you enjoy the video below.  For more on ultraviolet communication in butterflies see HERE.

No comments:

Post a Comment