• Ultraviolet Photography
  •  

Testing a UV-flash

UV Lighting
8 replies to this topic

#1 Nico

    Nico Chalwatzis

  • Members(+)
  • 121 posts
  • Location: Bensheim, Germany

Posted 07 July 2013 - 22:19

So far, I’ve been doing UV-photography with daylight only. However, it was frequently quite difficult, often tedious, and sometimes even impossible to get reasonably sharp images, especially with subjects that have a weak UV-reflexion and with (more or less) constantly moving subjects.
Therefore, I’ve been considering a UV-flash for some time. There are not too many choices on the market and the choices are narrowed further if one wants to avoid significant costs for international shipping on top of the flash price.
I finally found two offers within my country (Germany). Both dealers were willing to send me a unit for tests, which I thankfully accepted.
All tests were done with the broadband-modified Panasonic Lumix G1, the EL-Nikkor 80 mm, f5.6 and the Baader U-filter 2”.
The first flash that I received didn’t meet my expectations. Even with my EL-Nikkor 80 mm wide open (f 5.6) the images were pretty dark with a yellow cast if I was using my regular UV-processing (first image). Most of the time I would have to use ISO 800 with that flash at f5.6 which doesn’t yield reasonable results with my Lumix G1:

A selection of garden flowers ISO400, f5.6, 1st flash
Attached Image: NCH_P1080628_130519.JPG

The second flash that I’m still testing is this one:
http://www.kohlrusch...hre-Kamera.html
The results that I get at ISO 200 or 400 with the latter flash look reasonable to me. The colours are very close to the results I get with sunlight. I would wish the flash was another 1-2 stops faster, but it is already usable and I think I can get better images with it than I got before with just daylight.
Please let me know what you think!

Oenothera biennis, ISO 400, 1/30s, f8, “UV Flash it”
Attached Image: NCH_P1090696_130702.JPG
Image reference: NCH_P1090696_130702

Silene vulgaris, ISO 400, 1/30s, f8, “UV Flash it”
Attached Image: NCH_P1090705_130702.JPG
Image reference: NCH_P1090705_130702

Campanula rapunculoides, ISO 200, 1/160s, f8, “UV Flash it”
Attached Image: NCH_P1090833_130705.JPG
Image reference: NCH_P1090833_130705

#2 Andrea B.

    Desert Dancer

  • Owner-Administrator
  • 5,266 posts
  • Location: USA

Posted 08 July 2013 - 15:20

Thanks for the review, Nico.
Is this an LED flash?
*****

A couple of useful tips for UV-flash photos.

Hand-hold the UV-flash to get the proper distance. Very UV-dark flowers usually require holding the flash closer in order to cut exposure times. Very UV-bright flowers might require the flash be at a longer distance. Hand-holding the flash also allows you to direct it towards a feature of particular interest on a particular flower.

Contrast will likely be increased in flash photos, so use some shadow lifting in your editor. Brush the edit only onto any dark-shadowed flower parts while leaving the background dark. (Lifted backgrounds are usually very noisy, so I leave them alone.)

In the UV-studio or outside when the breezes are still, set a long exposure time and fire the flash manually two or three times from different positions to even out any dark shadows. You have to be careful not to brush against the flower and not to waft any air towards it while moving the flash, else you will record motion blur.

Don't flash the same flower too many times or it will fry from flash heat and UV !!
Andrea G. Blum
Often found hanging out with flowers & bees.

#3 nfoto

    Fierce Bear of the North

  • Owner-Administrator
  • 1,873 posts
  • Location: Oslo, Norway

Posted 08 July 2013 - 16:04

Well, the flower can sustain quite a lot of UV [flash] if you keep the flash head at a distance. Most battery-powered flashes then will have too weak output and you are forced to move them in closer, creating all sorts of issues with heavy shadows, wilting, etc. Flashing several times in a single exposure is feasible only in a darkened room and there is a real risk of the plant slowly re-orientating itself when repeatedly flashed.

My preferred studio setup is using 2 or 3 units of 600 or 800 Ws studio flash heads with uncoated Xenon flash tube. They run off the mains so can recycle very quickly and being powerful you can move them say 40-60 cm away from the subject so overheating [of the subject] is minimised. Flower can tolerate up to 200 times full flash output before movement becomes severe. Darkening the room is not required. A further advantage of the studio flashes is that their UV output quite closely mimic the sun spectrum.

Depending on the subject you can get exposures down to f/22 [nominal] at ISO 100 at 1:1 magnification. So throttling the flash output if often mandatory when you perform focus stacking and may want to use a wider aperture.
Bjørn Birna Rørslett

#4 Andrea B.

    Desert Dancer

  • Owner-Administrator
  • 5,266 posts
  • Location: USA

Posted 08 July 2013 - 16:28

Well, I've fried the occasional flower on much less than 200 flashes. :D But we get the point.
Andrea G. Blum
Often found hanging out with flowers & bees.

#5 Nico

    Nico Chalwatzis

  • Members(+)
  • 121 posts
  • Location: Bensheim, Germany

Posted 08 July 2013 - 17:06

Andrea and Bjørn,

Many thanks for your input!

I would say it is a classic xenon flash tube. It is probably uncoated so that it provides a good UV output.
I considered modifying a flash myself but I think that removing the coating from the tube is a bit tricky and electrical safety is also an aspect. So, since it is available for purchasing it looks like a reasonable solution to me.
The flash here was at least 10-20 cm away from the subject. I am looking for a portable (battery driven) solution, since I want to be able to use it in the field.

Best regards,
Nico

#6 Alaun

    Member

  • Members
  • 172 posts

Posted 08 July 2013 - 19:31

Nico,

you might try to get one of the older Metz 45CT-1 with the yellowish plastic cover (rather easy and cheap to get, as they were once very popular. Usually the batteries (Akkus) are down, instead of Akkus (rechargable batteries) you can use one time batteries (extra cage, to fit them in, with different positions of contacts, so the flash knows it gets a higher voltage).

The bulbs are uncoated, you have to remove the plastic covers. If you do not like the exposed bulb, you can replace it with fused silica glass (quartz glass) or with some plastic, which does not holds back UV (e.g. the plastic, which is used to hold the neck of a new shirt or from other packaging like from the boxes sd-cards are sold in).

You do not necessarily need the UV-pass filter (the sun also has no UV-pass filter ;-) ), but if you like, you can buy some filter glass e.g. from Edmund Optics (they sell from Germany).

I also use a rather cheap (and old) Vivitar 285 (also with once a yellow plastic cover !! so no coating on the bulb, now replaced by quartz glass). With the old Vivitar flashes, you have to test the Trigger voltage, some are working with low voltage, some with high voltage (just measure the voltage on the two Pins to make the flash shoot. High voltage would kill the camera electronics (probably), but there are special Adapters available, to also use theses type of flashes).

The Vivitar is less powerfull than the Metz.

A problem I have not solved yet is, with the removed plastic covers, the flash light is more focused,as the dispersion effect (Streuscheibeneffekt) is missing. So the flash light produces rather hard shadows and the flash has to be directed precisely onto the subject.

I got my flashes on camera flea market events ("Kamerabörse") and found them in the trash boxes.

When you open a flash to remove the plastic cover, be carefull with the capacitor. If you have tested the flash just prior to opening, it probably holds some high voltage charge (can be released by a shortcut with a high Ohm resistor and some good insulated wires).

It takes some more time, to get these things together than buying a ready made flash, but it makes fun, is cheaper and the Metz is already rather strong.
Werner

#7 Andrea B.

    Desert Dancer

  • Owner-Administrator
  • 5,266 posts
  • Location: USA

Posted 08 July 2013 - 22:19

Thanks for the info about the UV-Flash-It Xenon tube, Nico.

There didn't seem to be anything about that on the website. When I read there that this flash's peak was around 365nm, I started thinking it might be some kind of LED flash. And my experience is that the 365nm UV LEDs aren't broad enough to give a sunlight-like flash (which I prefer).

Does the UV-Flash-It sit in the hotshoe?

My SB-14 UV-mod requires a hotshoe adapter and (long) sync cord. But it has proven to be a good thing to be off the hotshoe because I can vary the flash distance for proper effect. This is only way to control the amount of flash with my particular gadget. :D Now I have gotten to like that hand-holding control because I can move the flash all around the flower as needed.

I will likely add your UV-Flash-It to our UV Sticky after you try it out a bit more and feel satisfied with it. Be sure to let us know whether you find a battery pack for it.
Andrea G. Blum
Often found hanging out with flowers & bees.

#8 Andrea B.

    Desert Dancer

  • Owner-Administrator
  • 5,266 posts
  • Location: USA

Posted 08 July 2013 - 22:27

Werner, thanks for your UV flash info. Very nice to know of inexpensive UV flashes for Do-It-Yourself modification.

The hard shadow effect can be mitigated somewhat by UV-flashing at a distance during a longer exposure which gathers some of the available UV in the sunlight. This method, of course, puts you back in danger of blurred photos if there are breezes and the exposure starts to go much over 1/2". Indoors, however, next to sunny windows, I've gotten some very nice, almost shadowless, soft-light UV still life photos this way. (My windows are about 50 years old, so they do let in some UV.)
Andrea G. Blum
Often found hanging out with flowers & bees.

#9 JCDowdy

    JCDowdy

  • Members
  • 1,019 posts
  • Location: Arlington, TN

Posted 12 October 2013 - 17:50

Nico,
Sorry for the late comment.

I looked at the link you posted for the “UV Flash it”. My German is not so good but thanks to Google Translate I can it seems obvious that this is a filtered flash. At 564 Euro a rather expensive one at that!

My understanding is that the filter on the flash is normally only required when you are photographing UV-induced fluorescence. This is where the UV excitation wavelengths are passed by the filter on the flash but blocked by the filter on the lens. As in fluorescence microscopy the filter on the camera transmits only the fluorescent emission wavelengths. The Baader-U filter on your lens makes the filter on the flash redundant. In your application the filter on the flash is probably reducing the UV output of your flash by 20-30%. I suggest you try some photos with the filter removed from the flash if you can and see how much faster it is then.