[Filter Test] Raw Colour Differences in 6 UV-Pass Filters

[Andrea B.]

I made raw composites of photos made with each of 6 different UV-pass filters to illustrate how the RGB channels respond. This experiment is not definitive, merely one illustration taken from one subject. However, there is a trend shown here which reappears in other photographs I have made with these filters.

 

Equipment [D600-broadband + UV-Nikkor 105/4.5]

Exposure [f/8 @ ISO-100. Exposure times vary as needed]

 

The UV-Pass Filters (in alphabetical order)

• AndreaU MK-I [Aug 2021: No longer sold by UVR Optics.]
  
• BaaderU
  
• PrecisionU, thin mount [Aug 2021: No longer sold by UVR Optics.]
  
• PrecisionU, thick mount [Aug 2021: No longer sold by UVR Optics.]
  
• StraightEdgeU, Red [Aug 2021: No longer sold by UVR Optics.]
  
• U360 (2.00mm) + S8612 (1.75 mm) Stack [UvirOptics (Ebay: uviroptics)]
  

The 'Magenta' UV-Pass Filters

This is my designation for those UV-pass filters which record predominantly in the Red and Blue channels.

They also record in the Green channel. We know from transmission charts that both these filters record more between 380-400 nm than do other UV-pass filters (that I know about).

• AndreaU MK-I
  
• StraightEdgeU
  

The 'Orange' UV-Pass Filters

This is my designation for those UV-pass filters which record predominantly in the Red and Green channels.

They also record in the Blue channel. These filters have transmission peaks between 360 - 370 nm, approximately. For the filter stack, the transmission peak is shifted off 360 nm to the right by the S8612 IR-blocker.

• BaaderU
  
• PrecisionU, thin mount
  
• U360 (2.00mm) + S8612 (1.75 mm) Stack
  

The 'Orange-Yellow' UV-Pass Filters

Also records predominantly in the Red & Green channels, but seems to have an Orange tending towards Yellow. Also records in the Blue channel.

• PrecisionU, thick mount
  

Raw Photo Crops

These crops were made from the original photos to which the same sky saturation and sky brightness (except for the cloudy areas) were applied for better comparisons.

 

I caution you not to read into these raw colours too far because when converting and editing, there is a lot of range available for setting the final false-colour appearance of photos made with these filters. Look over the other recent Filter Tests for the StraightEdgeU to see what I mean.

 

Again, these are in alphabetical order.

 

 

 

 

 

 

[aphalo]

Nice and useful examples. Thanks!

Do you now how much these channel responses depend on the camera model and make?

Did you use the Coastal Optics objective for these examples?

[Andrea B.]

I had forgotten to add the gear and exposure info. Done now. I used the D600-broadband set to ISO-100 and the UV-Nikkor 105/4.5 set to f/8.

 

Do you now how much these channel responses depend on the camera model and make?

That is an excellent question. And I should produce an experiment to illustrate this. I currently do not have a definitive answer.

 

What we do know is that we obtain similar white-balanced photos when using different cameras with a dedicated UV lens. This would indicate that the raw response is about the same from different cameras. But I have not specifically compared raw extracts across platforms when shooting the same subject with the same lens.

 

I'm going now to put this experiment on the list: http://www.ultravioletphotography.com/content/index.php/topic/1950-test-list-and-sowhat-should-i-test-now/page__view__findpost__p__14010

 

I have these broadband: Pentax K5, Lumix GH1, Sony a7R and the Nikon D600 to experiment with.

This will be fun !!!!!