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UltravioletPhotography

Annisquam River, 340nm


Andy Perrin

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Andy Perrin

This photo is with the Omega 340BP10 Excite FURA 20mm I tested back here. Photo subject is the Annisquam River in Gloucester, Massachusetts (my mother lives on the river, so it's convenient and pretty).

 

We had some nice fog today.

 

 

EL-Nikkor 80mm/5.6 metal, F/10 ISO160 10" + Omega340BP10

Processing: lowered the saturation a lot, removed spots of sensor dust (urgh!), and corrected for vignetting.

post-94-0-90776000-1559411940.jpg

 

Sony FE 55mm/1.8 ZA, cropped, F/6.3 ISO50 1/1250" + BG38 2mm

post-94-0-37907400-1559411958.jpg

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That is a lot of chromaticity for a BP10 filter. I wonder if some out-of-band wavelengths are sneaking through.
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That faint blue looks like IR leak to me. But still a good shot. My 340bp10 also leaks IR, for critical images I stack it with the Baader venus filter. But in many cases the IR leak adds some nice blue color, so I try to remember to use it unstacked first.

 

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Andy Perrin

I was getting blue back here also?

https://www.ultravio...ra-20mm-filter/

 

Okay, Andrea also got blue:

Typically a sunflower can be white balanced on the UV-absorbing areas at the base of the rays. That gave a very strange result here. I'm not sure I consider it a successful WB, but I'm still thinking it over. Some local contrast sharpening was added after resizing.

There is false yellow, blue, green or dark green-cyan and grey in this conversion and the next. That is rather remarkable for such a narrowband filter. Remember, we have all been supposing that there would not be much of a false colour range at all.

https://www.ultravio...__fromsearch__1

 

I think that a white-balanced 340nm filter will show blue sometimes.

 

Wait, are you guys being confused by the fact that I deliberately desaturated the yellow?

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I still think the highly IR reflective trees in the lower right of your image is showing the blue IR leak of the filter.

If you have a baader venus filter, just stack it with that to prove me wrong. But I am sure you have an IR leak there.

You could also stack with an S8612, if you don't have the venus U filter. But it will let through much less at 340nm.

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Andy Perrin
Probably have to wait till Tuesday, I'm out of sunshine and going to be away tomorrow.
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Andy Perrin

So, I did the suggested experiment and stacked with S8612. Pics later when I have a chance to process them, but the preliminary results were interesting. I could see blue in the image itself either way, but what was most informative is that there was a bright blue circular band around the edge of the image that looks like the putty I used to rear-mount the filter is either leaking light itself, or I just didn't fill all the gaps at every location around the filter and light is getting through that way. I think I need a better way to mount this filter.

 

Update

 

Here are the photos. The blue is obvious in both pics.

Settings were F/5.6 2.5" ISO2000 for both. WB was redone for the second photo.

 

Without S8612 1.75mm

post-94-0-54263200-1559691522.jpg

 

With S8612 1.75mm

post-94-0-91262000-1559691551.jpg

 

It gets worse in the second picture mainly because I changed the camera angle slightly and it seems very sensitive to the angle relative to the sun. Also the WB change may have affected it.

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