Homemade lens tests at 313nm

[dabateman]

I just looked at a quick test with some of my home made lenses using two ExoTerra UVB lamps, U330WB80 Improved filter and 313bp15 filter on the lenses.

 

All shot on Full spectrum converted Olympus EM1mk1

 

Fused silica group lens with 3 elements to be 35mm equivalent:

 

ISO 200 Fully open (the element maximum is 20mm), 15 seconds:

 

ISO 200 slightly closed down using aperture ring, 15 seconds:

 

Fused silica single 39mm element

This is closed down 15 seconds, ISO 200:

 

SvBony 0.5x focal reducer mounted in 25mm filter ring with helicoid and aperture control ring

15 seconds fully open, ISO 200:

 

Slightly closed down ISO 800, 15 seconds:

 

PMMA Fresnel 35mm focal length 50 mm in diameter and only 2 mm thick mounted close to camera

Fully open 15 seconds, ISO 200. there isn't room behind for adjustable aperture ring, but I could add a fixed stop:

 

PMMA, Fully open, 8 seconds, ISO 200:

[colinbm]

You got to the magic green,,,Stefano will be pleased

[dabateman]

The last two images are using the exact same lens. The angle seems to effect the Fresnel effect, the colors change a little on you.

 

My PMMA flashlight curve lens was just too soft to bother posting and dark.

 

I quickly tried the igoriginal 35mm lens with this set. But in hindsight I was too close to the subject an thus was out of focus. Also very dark.

[Andy Perrin]

How does the KSS do?

[Stefano]

You got to the magic green,,,Stefano will be pleased

Yes indeed, green is my goal now.

 

David started this topic also because I wanted to know how good the SvBony 0.5x focal reducer is used as a lens in UVB. I can capture 310 nm images with the Soligor, but the exposure times are very long.

[JMC]

Nicely done David. So were these all with the same filters? Just wondering as the last 2 are very different colours. I don't know anything about the performance of fresnel lenses, and just surprised to see such a change.

[Stefano]

David, if you can, can you photograph your SvBony lens at 313 nm? Like a transmission test with a uniform background to see how transparent it is. Thanks.

[dabateman]

Nicely done David. So were these all with the same filters? Just wondering as the last 2 are very different colours. I don't know anything about the performance of fresnel lenses, and just surprised to see such a change.

 

Yes all same filter set. The Fresnel lens is kind of funky. It had one ok distance with similar colors (the first image), then I moved it around and went either super red or green. Must have to do with the filter being dichoic and the interference pattern of the fresnel lens to get its focal length.

 

[JMC]

Interesting thanks David. Looking forward to seeing more with the fresnel lens as you get chance to play with it.

[dabateman]

This is the 50mm diameter Fresnel PMMA lens now with a 8mm cut out of black paper behind it to give F4 approximately

15 Seconds exposure F4, ISO800:

 

20mm fused silica element with 3mm hole cut out of black paper behind the element to give approximetely F6

15 seconds exposure F6, ISO 800

 

KSS lens (real lens) at F4, ISO 800, 15seconds exposure

 

 

Boy what a difference a real lens makes.

 

But the SvBony is still usable as a UVB/UVA lens for those that want something cheap.

[Stefano]

Interesting tests David. Your fused silica lens with three elements at the beginning is not comparable to the KSS, but has a nice quality.

[Andy Perrin]

Is the F4 on the KSS because of the incorrect aperture markings?

[Andrea B.]

Cool beans, David !!

 

Of course, I want to know what are the raw colors. What white balance was the Oly set to? Is that WB reflected (so-to-speak) in the posted photos?

[dabateman]

All white balance settings are the same and my favorite golden profile that I set in camera as custom 2.

 

Andy I tighten it up to F4 when I had it apart to fix my loose ring problem. F4 is the setting on the ring. I rarely shoot it differently. I think in reality though due to the internal baffle, that the F4 setting might actually be F8. But I will have to measure the opening for that to correctly know.

 

Stefano,

I agree, I did a decent job in the design of that lens and corrected it okish. Its not super sharp, but it is 35mm Fused Silica focal length and cost me an order of magnitude less than the UKA optics 35mm in m43rds mount. So I am happy with it.

 

The single element 20mm UV optimized coated lens is a bit of a letdown. But it was cheap. I need to figure out the best stop to place behind it. This will mostly be used with my Pi camera monochrome HQ sensor. So will have to work out what best for it.

 

This post hopefully also lets people know not to waste their money on PMMA lenses.

 

But the SvBony element is an option as long as they continue to make it out of K9 = bk7 glass.