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SvBony 0.5x Focal reducer is good for UV but not magical.


dabateman

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Part of the fun of using an Olympus camera with a four thirds sensor is that only the center portion of the lens is captured by the sensor. Thus a focal reducer can be used and the common ones are only 0.71x. I have the Metabones one which trades off Exposure for field of view. As in the 1 stop of light gained due to focal reduction is lost due to the 6 elements of the lens. But its maximum usage is just to 370nm.

 

However, there is a cheap alternative. The SVBony 1.25 inch 0.5x focal reducer which is used mainly for telescopes. Using a Micro four thirds to dual C-mount/ M42 mount adapter (adds 6mm) you can mount C-mount lenses in the center and then add a M42 focusing helicoid. Using a 5mm C-mount extension tube taped to an empty 1.25 inch filter housing, I was able to screw the SvBony focal reducer close to the sensor and then use a 17-31 helicoid connected to my Quartz 85mm UAT f4.5 lens for some test. This also works with an extra 5mm extension still filling the frame, so you can push close to a 0.4x crop on the lens and still cover the sensor.

 

First using a single 365nm LED light filtered with 2mm ZWB1 glass:

 

UAT only filtered with U330WB80 and 370bp15, needed ISO 200, F8 20 seconds:

post-188-0-23633300-1583484020.jpg

 

UAT 0.5x reducer with U330WB80 and 370bp15, needed ISO 200, F8 4 seconds:

post-188-0-58688700-1583484044.jpg

 

UAT 0.5x reducer with in camera 2x Magnification with U330WB80 and 370bp15, needed ISO 200, F8 4 seconds:

post-188-0-94683900-1583484068.jpg

 

UAT only filtered with U330WB80 and 370bp15, needed ISO 200, F8 5 seconds:

post-188-0-10249100-1583484087.jpg

 

A 2 stop improvement in UV light captured and increase field of view.

 

Second using 2 ExoTerra UVB lights:

 

UAT only filtered with U330WB80 and 313bp25, needed ISO 1600, F8 8 seconds:

post-188-0-68129400-1583484110.jpg

 

UAT 0.5x reducer with in camera 2x Magnification filtered with U330WB80 and 313bp25, ISO 400, F8 25 seconds:

post-188-0-39242500-1583484128.jpg

 

UAT 0.5x reducer filtered with U330WB80 and 313bp25, ISO 400, F8 25 seconds:

post-188-0-45916500-1583484149.jpg

 

Only about a 1/3 to 1/2 stop of light gained, but still get the wide field of view.

 

Third Using single tube 302nm light:

 

UAT only filtered with U330WB80 and 313bp25, needed ISO 800, F8 6 seconds:

post-188-0-84594200-1583484169.jpg

 

UAT 0.5x reducer with in camera 2x Magnification filtered with U330WB80 and 313bp25, ISO 800, F8 6 seconds:

post-188-0-27822800-1583484190.jpg

 

UAT 0.5x reducer filtered with U330WB80 and 313bp25, ISO 800, F8 6 seconds:

post-188-0-26155800-1583484235.jpg

 

Again slightly brighter image with the focal reducer and wider field of view.

 

UAT only filtered with U330WB80 and 303bp10, needed ISO 800, F8 30 seconds:

post-188-0-90202000-1583484256.jpg

 

UAT 0.5x reducer with in camera 2x Magnification filtered with U330WB80 and 303bp10, ISO 800, F8 30 seconds:

post-188-0-49584600-1583484272.jpg

 

UAT 0.5x reducer with U330WB80 and 303bp10, ISO 800, F8 30 seconds:

post-188-0-79008400-1583484286.jpg

 

I have 4 of these reducers now and for fun stacked two on top of each other. Not very useful:

post-188-0-40775900-1583484814.jpg

 

All four of mine behave similarly. So I am confident to say that this reducer is UV capable.

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This poorly shot series shows the gain in field of view. However I did miss focus so you can't draw too many conclusions other than the field of view.

 

UAT only UVB light 313bp25 filter:

post-188-0-82409400-1583485738.jpg

 

UAT 0.5x reducer UVB light 313bp25 filter:

post-188-0-12092200-1583485762.jpg

 

UAT 0.5x reducer with 5mm extension UVB light 313bp25 filter:

post-188-0-11238700-1583485780.jpg

 

I now have a C-mount to 1.25" adapter that is only 10mm total, similar to my C-mount to 1.25" taped ring. So this will allow for more stable images. It also might just be at 0.5x. So my total distance from film plane would be 19.25 +6+10 = 35.25 to the back of the focal reducer. Adding 5 mm extension places it at 40 mm. So I am not sure exactly where the best location of the reducer would be, but it clearly doesn't need to be 55mm away like other Astro focal reducers.

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  • 1 year later...

Update on using this focal reducer. Its mounted for an eye piece of a telescope.

So its backwards.

If you want to use this with a camera it needs to be flipped so the concave surface side faces the sensor. This dramatically improved the image quality.

All of these above photos are taken at its worst in the wrong orientation.

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  • 5 months later...

Updated to show the SvBony apart and an attempt at the through filter test image.

 

So this is the single element (positive meniscuses lens) that is inside the SvBony 0.5x focal reducer. I have 4 and they all look like this:

post-188-0-01113600-1629955385.jpg

 

post-188-0-86449800-1629955391.jpg

 

It can be mounted into a 25 mm filter ring, and needs to be flipped anyway as its backward with the concave side up.

 

This is my attempt at a through the glass image. I don't like these as there is shadow confusing it and there is bulb reflection. But this is what I think people wanted to see.

There is PTFE sheet up in the back. The elements are a 75mm quartz in C-mount ring, then the SvBony in 25mm ring, then some 2mm UV glass filter I found on my bench.

On the camera is a KSS 60mm quartz lens set at F4, with U330WB80 improved filter and the 313bp25 Omega filter.

 

post-188-0-90340000-1629955641.jpg

 

Funny many of the cheap Chinese UV filters that I buy to pop the glass out and use for just the ring actually had good UV transmission down to UVB. I wonder how may "UV filters" are really B270 glass.

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David, thanks for the test. Yes, that looks good. You can see some difference between the quartz and the SvBony, but it's not much.
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