June 22, 2018, 10:53:24 PM

Author Topic: Proof of concept: UV-reflectance stacking with MP-E 65  (Read 21069 times)

scyrene

  • Canon EF 300mm f/2.8L IS II
  • ********
  • Posts: 2036
    • My Flickr feed
Re: Proof of concept: UV-reflectance stacking with MP-E 65
« Reply #30 on: February 17, 2017, 05:26:48 PM »
I'm currently sort-of experimenting with this myself. I don't have a modified camera or proper filter, but I've found the results with an astro light pollution filter quite good even if I'm crossing streams, so to speak :) Here's my first direct comparison (few flowers here at this time of year!), it's the rear underwing of a swallow-tailed moth, Ourapteryx sambucaria, in visible vs filtered UV light. Focus stacks using the MP-E and Affinity Photo. Surprisingly few moth specimens I've tried show much in UV but this one was interesting enough to persist with.
Neat. I think what you are doing is essentially a blue channel image. There are some faint yellow lines visible in the first image, and those are black in the second. Yellow = no blue, so those yellow areas will be dark. Compare the blue channel information from the first image with the second, and I would think they will be very similar.

To image UV light, you cannot get around a modified camera body.

If I follow you right, you're saying that desturating the green and red channels in the visible light image should give the same result, is that correct? I don't think that can be quite right. As a comparison, using this technique made green leaves bright red. That would not be the case if I did what I think you are suggesting.

I agree a modified camera must be better, but UV filters are sold for a reason - and not just to protect the lens's front element! The sensor must be sensitive to some UV, or otherwise to fluorescence in UV? I'm no scientist, so apologies if I'm way off :)
Current equipment: 5Ds, 5D mark III, 50D, 24-105L, MP-E, 100L macro, 500L IS II; 1.4xIII + 2x III extenders; 600EX-RT.
Former equipment includes: 300D; EOS-M, EF-M 18-55, Samyang 14mm f/2.8, EF 35 f/2 IS, 70-200L f/4 non-IS and f/2.8L IS II, 85L II, Sigma 180 macro, 200L 2.8, 400L 5.6

canon rumors FORUM

Re: Proof of concept: UV-reflectance stacking with MP-E 65
« Reply #30 on: February 17, 2017, 05:26:48 PM »

Zeidora

  • EOS 5D Mark IV
  • ******
  • Posts: 639
Re: Proof of concept: UV-reflectance stacking with MP-E 65
« Reply #31 on: February 17, 2017, 06:33:19 PM »
You're right, something else is going on. So most likely fluorescence, i.e. UV light is shifted into visible light wavelength.

All sensors are UV sensitive to around 320 nm, but there is filter in front of the sensor that cuts off UV at around 400-420 nm. That filter is taken off when a camera is converted, and replaced with a UV transparent filter. In order to take UV images, you need to exclude all visible light, and also the IR. Sensors are less sensitive to near UV than to visible light, so you need to exclude ALL visible light. If you look through your filter against a bright light source and you see anything, then it is not suitable for UV reflectance imaging. Hope that helps a bit.
5D2 full spectrum, 5DsR, a bunch of Zeiss (some other) primes, for documentary natural history, macro, and micro.

scyrene

  • Canon EF 300mm f/2.8L IS II
  • ********
  • Posts: 2036
    • My Flickr feed
Re: Proof of concept: UV-reflectance stacking with MP-E 65
« Reply #32 on: February 19, 2017, 11:32:06 AM »
You're right, something else is going on. So most likely fluorescence, i.e. UV light is shifted into visible light wavelength.

All sensors are UV sensitive to around 320 nm, but there is filter in front of the sensor that cuts off UV at around 400-420 nm. That filter is taken off when a camera is converted, and replaced with a UV transparent filter. In order to take UV images, you need to exclude all visible light, and also the IR. Sensors are less sensitive to near UV than to visible light, so you need to exclude ALL visible light. If you look through your filter against a bright light source and you see anything, then it is not suitable for UV reflectance imaging. Hope that helps a bit.

Thanks for clarifying :) I wonder what the precise cutoff for the in-camera UV filter is? My light source is rated at 395nm so very close, but just under 400. I guess I'll have to get an appropriate filter and see if anything is visible in just that light. I rather like some of the images I've taken with the current setup, however, so maybe it's worth pursuing for its creative merits in any case. Thanks!
Current equipment: 5Ds, 5D mark III, 50D, 24-105L, MP-E, 100L macro, 500L IS II; 1.4xIII + 2x III extenders; 600EX-RT.
Former equipment includes: 300D; EOS-M, EF-M 18-55, Samyang 14mm f/2.8, EF 35 f/2 IS, 70-200L f/4 non-IS and f/2.8L IS II, 85L II, Sigma 180 macro, 200L 2.8, 400L 5.6

Zeidora

  • EOS 5D Mark IV
  • ******
  • Posts: 639
Re: Proof of concept: UV-reflectance stacking with MP-E 65
« Reply #33 on: February 19, 2017, 12:48:11 PM »
395 nm is very close to visible. It is essentially the "Disco" light for glowing cloths. There are 365 nm flashlight, and I am currently working on modifying a flash for UV photography: remove yellow plastic UV filter, and replace with UG11. If you are interested in this, look at the http://www.ultravioletphotography.com/content/ forum. UV is hazardous, so take appropriate precautions.
5D2 full spectrum, 5DsR, a bunch of Zeiss (some other) primes, for documentary natural history, macro, and micro.

Zeidora

  • EOS 5D Mark IV
  • ******
  • Posts: 639
Re: Proof of concept: UV-reflectance stacking with MP-E 65
« Reply #34 on: December 30, 2017, 07:39:40 PM »
Here's am update on my experiments, with which I am quite happy.

Set-up: Canon 5D2, Lens Nikon EL 80 mm f/5.6, Baader U-Venus filter on lens, cheap Russian M42 bellows in between; various adapters all throughout. Illumination with Metz 45 CT1, removed plastic front shield and replaced with cheap Chinese UG11 equivalent filter. Aluminum foil on opposite side brightens right side of image. Metz is triggered via FlashZebra slave, with Canon MT26 EXRT connected to 5D2, firing single head at 1/512 power. The whole rig on Cognisys Stackshot. Have to put 10s firing delay in program, so that the flash can re-charge between firings. Flash head gets quite warm after 60-100 shots.

Processing through DxO with Premium noise reduction removing all color artifacts. No more messing with gaussian blur masks in AffinityPhoto. Easier, but takes a lot of time on computer. Then in AffinityPhoto, steepened a and b curves in Lab space quite bit (lower corners moved halfway to middle, so doubled slope). Plus a bit of fine tuning so that black background is neutral in color.

Biggest problem is low power of flash. Have to go to ISO 400-1600 at full power of flash to get enough UV through the system. May get two Metz 60 flashes, so that should get me in ISO 100-400 range.

Still no pattern on flowers, but there is some differentiation between flower and rachis. About 2.5:1, some 70 frames at f/5.6 and 100 ┬Ám steps.
5D2 full spectrum, 5DsR, a bunch of Zeiss (some other) primes, for documentary natural history, macro, and micro.

danski0224

  • EOS 5DS R
  • ******
  • Posts: 1070
Re: Proof of concept: UV-reflectance stacking with MP-E 65
« Reply #35 on: December 31, 2017, 10:03:02 AM »
Wow, pretty darn impressive.

privatebydesign

  • Canon EF 800mm f/5.6L IS
  • ***********
  • Posts: 6891
  • Would you take advice from a cartoons stuffed toy?
Re: Proof of concept: UV-reflectance stacking with MP-E 65
« Reply #36 on: December 31, 2017, 12:08:33 PM »
So you are using a $1,000 flash as an optical triggering device to trigger an underpowered $20 flash? I don't see that as making any sense, why not just plug the Metz into the PC port on the camera?

But a simple 'studio' light is going to give you way more bang for the buck anyway and get you to the power output you need rather than mess around with AA batteries.
Too often we lose sight of the fact that photography is about capturing light, if we have the ability to take control of that light then we grow exponentially as photographers. More often than not the image is not about lens speed, sensor size, DR, MP's or AF, it is about the light.

canon rumors FORUM

Re: Proof of concept: UV-reflectance stacking with MP-E 65
« Reply #36 on: December 31, 2017, 12:08:33 PM »