• Ultraviolet Photography
  •  

Ringflash: new flash tubes intended for UV

UV Lighting
9 replies to this topic

#1 Mark

    Member

  • Members(+)
  • 479 posts
  • Location: Massachusetts, USA

Posted 21 April 2019 - 01:42

I have an AlienBees ringflash which I've tested on more than one occasion and found it to be a surprisingly low performer for UV illumination, at least as compared to some of my clunky old hot-shoe flashes. Now, I understand this is actually a good thing as far as the intended design of the unit (VIS imaging), so I contacted the manufacturer and purchased a set of replacement flash tubes which I was told are uncoated. To test the improvement in UV of using these uncoated flash tubes I took a set of images before and after exchanging the old tubes for the new, uncoated tubes.

My subject is a Kiwi fruit, photographed with equivalent camera setting in all four images. The first two images (top row) were taken with the old, stock flash tubes, at 1/32 then 1/4 flash power. The bottom row repeats the top row, only after exchanging the tubes for the new ones.
Attached Image: 2019-04-20_ABR800_tubereplacements_pre-v-post-post.jpg

So - I'd say these tubes either are not actually uncoated tubes, or the tubes I originally had installed are already uncoated. If the former is true, then I'm going to be upset that I was sold something which is not what I was told it is. If the latter is true, then this flash is remarkably weak in UV - especially surprising for such large flash tubes (I just assume they would put out 'a lot of light').

I'm not sure which it likely is. I am sure though, that what I have (using either set of tubes) is, in the end, not so useful for UV imaging. What do you think?

#2 nfoto

    Former Fierce Bear of the North

  • Owner-Administrator
  • 2,232 posts
  • Location: Sørumsand, Norway

Posted 21 April 2019 - 07:14

Assessing the performance would be easier if you tell us the camera, lens, aperture, and ISO settings ...

My Broncolor 800 or 1600 Ws units require 1/16- 1/32 power and f/11-16 at ISO 100 when used fairly close (~30 cm). The flash tube and the dome protection are both quartz and look crystal clear to the eye. When I do visible-light work, I put on a coated dome that steals a lot of the UV output. That dome has a yellowish-brownish cast to it.

#3 JMC

    Member

  • Members(+)
  • 641 posts
  • Location: London, UK

Posted 21 April 2019 - 08:12

Mark, also, does it have a protective clear ring that goes over the flash, and if so was it installed for both sets images? If it does, and if it was installed, then depending what it is this could be robbing a lot of UV too.

Using my Bowens GM500, going from coated glass to uncoated glass got me about a 1.3 to 1.5 stop improvement, for imaging with Baader U and using a Rayfact 105mm lens with my modified EOS 5DSR.

#4 Alaun

    Member

  • Members(+)
  • 268 posts

Posted 21 April 2019 - 10:00

Mark, you might also take UV-pictures of the bulbs, illuminated by a UV-torch. You would see differences and you would see, if there is a coating or if the glass of the bulb is clear in UV.

By the way: Happy Easter!
Werner

#5 Mark

    Member

  • Members(+)
  • 479 posts
  • Location: Massachusetts, USA

Posted 21 April 2019 - 11:50

Hi all,

As I said above, the images after exchanging the tubes are a repeat of the first set... I apologize - to be clear, the shooting and development settings are exactly equivalent, so this is simply a relative test regardless of the exact shooting settings. And to the point, the before and after images are, relatively, essentially the same. Also to note, there was no cover used on the the flash (bare bulb only, before and after).

@Alaun: That sounds like a good idea to me. I'll try that later today.

And happy Easter :)

#6 nfoto

    Former Fierce Bear of the North

  • Owner-Administrator
  • 2,232 posts
  • Location: Sørumsand, Norway

Posted 21 April 2019 - 12:35

'Bare bulb' is often highly ineffective for close-ups. One really needs an efficient reflector. For my studio flashes and UV I tend to use a fairly broad reflector (wide-angle reflector) that softens the shadows for close-ups.

#7 Mark

    Member

  • Members(+)
  • 479 posts
  • Location: Massachusetts, USA

Posted 21 April 2019 - 13:09

I agree, close-up imaging with a flash tends to exacerbate harsh lighting/shadows. To ameliorate that effect I pointedly chose this flash format (ring flash).

@Alaun: I tried your suggestion. This UV image shows both the original tube and the new tube. In order not to bias anyone's judgement of which is which, I'll not say for the moment, because, to the point, I think at least it is evident that these are both effectively equivalent.
Attached Image: 2019-04-21_07-11-59_ABR800oldvsnewtubes_post.jpg
Illumination source: 4 x 18" T8BL-B + FL-02 glass
Lens filter: Asahi 0340

#8 nfoto

    Former Fierce Bear of the North

  • Owner-Administrator
  • 2,232 posts
  • Location: Sørumsand, Norway

Posted 21 April 2019 - 13:29

If there is a difference, it is not evident in the glass transparency in UV :(

#9 Alaun

    Member

  • Members(+)
  • 268 posts

Posted 21 April 2019 - 13:50

With comparison to the tubes here: http://www.ultraviol...page__hl__ad200 your tubes look quite transparent.

Edited by Alaun, 21 April 2019 - 13:51.

Werner

#10 Mark

    Member

  • Members(+)
  • 479 posts
  • Location: Massachusetts, USA

Posted 28 April 2019 - 10:10

I finally just got word from the manufacturer that the flash tubes I had originally installed in the unit were already non-UV-coated tubes. In fact, for this flash unit they only offer non-UV-coated flash tubes. This at least explains why I saw no difference in my before/after photos.

Is it just me, or does it seem a bit misleading that when I contacted them to specifically request non-UV-coated tubes for my flash they didn't bother to mention that the flash tubes I already have are, already non-UV-coated...? (yes, I was very specific in several emails and phone calls with them to be sure they were sending me non-UV-coated tubes in particular.)

I guess technically they sold me what I was asking for, so I can't fault them for that. But it still seems a bit shady to me. I think I just lost respect for that business.