Saturday, March 2, 2013

Filter leakage in reflected UV ultraviolet photography - unsuitable UV vs Baader-U filter III

Today again about IR leakage in reflected UV photography and how to deal with it. I have posted about that before here.

So what I wanted to show to today is, how different reflected UV images look like with and without IR leakage, so to enable a potential UV shooter to detect that. Images are presented in a side-a-side waqy, to make comparisons easier.

[click on image to see a larger one]

Here now the comparison with a commercially available UV filter, that not only leaks IR but also some blue vs the Baader-U 2" filter, Winter Aconite as target:

So here another example for very strong IR leakage (left), vs correct UV recording using a Baader-U 2" filter (right) using a strongly IR reflecting spring crocus as a target:

Same situation, but different angle and different crocus:

here in bw version, that shows that exposure was identical, but the pattern and structure is completely washed away by that IR leakage::

This following last example now shows the results of two different UV transmitting astro filters, left one with just a little IR leakage, but still enough to render the result useless, right the currently best filter for reflected UV in my opinion, the Baader-U 2", again using Winter Aconite as target:

Well, it was my goal to bring the attention to an often overlooked, but very important fact: IR leakage in reflected UV photography. Often beginners try to experiment with cheap UV transmitting filters, hoping to get some useful results. Unfortunately due to the very high IR sensitivity of modern sensors, just the tiny fraction of 0.1% leakage leads to useless results. So there is no way other than using highest quality UV transmission filters to secure useful results. Demand at least a IR suppression of OD3 from any UV transmitting filter, better even OD4!

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

More info on this very interesting field may be found on my site