365nm UV Flash?

[colinbm]

Thanks Stefan, that is probably why it looks so good......you get what you pay for ;)

Col

[JCDowdy]

Yes, you do get what you pay for.......

A research grade scanning double grating spectroradiometer setup costs ~$60,000 to ~$120,000 depending on brand.

The single fixed grating diode array/CCD systems have the great advantage of speed and miniaturization. With an understanding of the limitations such systems have great utility. I may try to get a test drive of the INSON "evaluation system in metal housing", it is interesting technology.

[baffe]

If you have the possibility to calibrate it in lambda axis, then a homemade spectrometer can be a very useful instrument! Resolution and accuracy can be higher than that of the MSP1/12 if it is carefully designed and built. And the MSP1/12 is not good enough for basic research either.

[Pylon]

I got a Canon 199A, haven't even had the time to try it yet though.

 

If I were to filter it for UV-only, what thickness should the 34.5 x 59.8 mm Schott S8612 + Schott UG11 filters be? 1mm? 1.5mm? 2mm?

[JCDowdy]

Pylon,

I don't know. The thicker KOPP 3mm KOPP 9863 I tried withstood the flash but Baffle pointed out it has more mass to absorb the heat.

 

The British Museum Technical Research Bulletin 8 (2014) does not give filter thicknesses for the filters on the flash. Consequently, as far as spectral balance I am assuming the same considerations as apply to stacking filters on a lens for reflected UV. I have a 1mm U-360 plus 1.5mm S8612 in 52mm I am adapting to the 199. Consult the Filter Transmission Charts for the best compilation on thickness combinations.

 

The 34.5 x 59.8 mm I mentioned before is the only size of the white plastic diffuser I removed from the 199 wide angle adapter. Figure 2 of the British Museum Technical Research Bulletin shows a homemade slip on adapter for mounting round lens filters which is similar to one Johan has described. Since I already have the 52mm filters that is the approach I will be trying. If that works well then a 34.5 x 59.8 mm frame for a 25 x 50mm half of a standard 50 x 50mm filter might be nice.

[Pylon]

I have the Canon Speedlite 199A. Very easy to modify. No doubt safer to mod as well since you don't have to disassemble as much.

Some have claimed it is more powerful that the Vivitar 285HV, I have not tested that.

The trigger voltage on the two 199A Speedlites I have tested low enough to use safely on my Panasonics.

 

After unscrewing the rectangular frame, the freshnel lens doesn't pop out.. it doesn't seem like it is loose... It feels like it is attached or glued or snapped in there somehow, and don't want to ruin anything by yanking it out and then having a dysfunctional flash... How did you remove it safely? What about discharging it before removing the feshnel lens, is that necessary? If so, how do you discharge it?

[JCDowdy]

It has been a while since I removed mine but I do not recall they were glued. It does snap in with tabs on the sides. I will post a photo as soon as I can fine one of the fresnel lenses so you can see what these tabs look like.

 

As far a discharging is concerned I am no expert. Please refer to some of the various tutorials on other models for precautions. I used the test button to flash the strobe and then immediately removed the battery as shown in this

. However I do not recall getting anywhere near anything that looked like a capacitor because on the 199A you do not have to get inside the unit.

 

Added later:

Here is one of the 199A lenses I managed to find.

 

Please note for me which side is up as I have forgotten.

 

[Pylon]

Please note for me which side is up as I have forgotten.

The side closest to the right side of the JPEG is the top.

 

Figure 2 of the British Museum Technical Research Bulletin shows a homemade slip on adapter for mounting round lens filters which is similar to one Johan has described. Since I already have the 52mm filters that is the approach I will be trying.

I don't have access to this manual, but do you have any information on any slip-on adapters for mounting round lens filters in front of a flash? That would be ideal because I could just use the Baader-U filter I already have. Only slight disadvantage would be that it is slightly smaller than the front of the flash, so you might loose a tiny bit of light output. And you may need to add some heat-absorption filter to protect the Baader-U.

 

One thing I have found when it comes to the SB-140 vs Canon 199A, is that the SB-140 is much brighter than the Canon 199A.

[nfoto]

Interesting. According to these data, SB-140 is approx. four stop brighter than the Canon flash.

[Pylon]

That is a pretty big difference :/ I guess I can see now why the SB-140 is better, its just too bad it is inconvenient to use and there are no other alternatives. I should see how it compares to the SB910 w/ visible light, just curious.

 

Are there any studio strobes where a UV-only-pass filter can be placed in front of the UV transmitting light-source, that has even brighter output than the SB-140?

[nfoto]

Sure, but you need additional filtration to get rid of IR.

 

My Broncolors are a few stops "brighter" than the SB-140, by the way.

[Pylon]

What filter do you use? I am assuming it is a large gel?

What broncolor strobe do you have?

[JCDowdy]

The side closest to the right side of the JPEG is the top.

 

Thanks! I will make note of which side is up!

 

I don't have access to this manual, but do you have any information on any slip-on adapters for mounting round lens filters in front of a flash? That would be ideal because I could just use the Baader-U filter I already have. Only slight disadvantage would be that it is slightly smaller than the front of the flash, so you might loose a tiny bit of light output. And you may need to add some heat-absorption filter to protect the Baader-U.

 

I was referring to the links I posted earlier in this thread. One of the papers shows what appears to be a homemade slip on adapter. Johan made his out of black foam core & black tape.

 

One thing I have found when it comes to the SB-140 vs Canon 199A, is that the SB-140 is much brighter than the Canon 199A.

 

I am not to surprised that the SB-140 wins but did not expect that much, what is the guide number comparison between them? Also, what is that you have on the front of your 199A?

[JCDowdy]

I note with wry satisfaction that the bodge way I attach my filters is almost exactly the same as the photo illustrated in the first of the papers.

 

Johan, will you post a photo of it? I thought it looked good.

 

I am taking a different approach and using a 77mm to 52mm step down ring. I will share it when I get finished.

[JCDowdy]

OK, I looked up the answer to my own question. :)

 

The GN for the 199A is 30 (meters @ ASA 100) and the GN for the SB-140 is 32.

source: 199A manual page 5 and SB-140 manual page 27.

 

Of course the 199A GN is no longer valid with the fresnel lens removed.

[nfoto]

The guide number in this case is for visible spectrum? Not very informative for a dedicated UV flash I presume ...

 

For UV the flash head construction itself has a bearing due to the short distances involved. Many flash reflectors don't distribute light well at close range so end up having pretty similar effective output. I experimented a lot with different reflectors and flash-to-subject distances with my Broncolor studio units (Minicom 80 with uncoated Xenon tube, 600 W/s) before settling on a semiwide reflector and a distance of 60 cm. This will give me an exposure for UV around f/16-f/22 at ISO 100 with the flash at full output. I usually deploy 2 and occasionally 3 flash units to broaden the covered field and add fill-in to shadows.

 

With SB-140 replacing the Broncolors, I need to move the flash heads much closer and open to f/8 or so. I have only 2 of the SB-140 so that also limits the versatility of using them in studio. In the field, they are of course much easier to use than any studio unit (I do have portable 220 V A/C pack for them though, however such devices aren't comfortable with the perils of field use).

[JCDowdy]

Bjørn,

 

Yes, of course GN is for visible not UV. I thought it relevant in regard to the discussion of the relative power of two flashes. According to the GNs from the manuals the 199A is very close to the SB-140 at least in the visible.

 

The Nikon manual also gives GNs for UV which are ~50% of the visible but they are for Kodak Spectroscopic Type 103-0 film. I have no idea how to relate that to anything. Your empirically derived <60cm @ f/8 is a GN of <5, if I understand the math, or a GN or <2.5 if one has to divide by the number of lamps. That is with the caveat of also being a different camera and filter assuming your numbers are for a UV-Nikkor lens.

 

I assume the the SB-140 has a properly UV transmitting fresnel where the 199A in Pylon's tryptic above is presumably without it's fresnel. Could the lack of focusing due to removing the lens account for that much observed difference?

 

I had not considered the possibility that the SB-140 may also have better reflector geometry in UV. It could also be that the flash tube of the Nikon is more UV transparent given it's intended function.

 

Six C size batteries does seem a bit arcane and cumbersome by today's standards. One would think something much more field portable could be realized with high capacity Li ion cells such as are used in cordless power tools. The manual does not specify the power output of the SD-7 battery pack.

[nfoto]

Most flash units have a "GN" (in visible) corresponding to about f/11-f/16 at 100 ISO when used closer than 20 cm from the subject. This is due to the inefficiency of the flash reflector plus the fact that in the near range, the light no longer can be considered a point-light source so the inverse square law no longer applies.

 

The Broncolor heads are awkward to position this close and in fact, you get about the same exposure with them approx. 50 cm away. Do note that by changing the reflector type, you can easily lose 1-2 stops compared to the optimum one, and by using a "bare bulb", ie. no reflector at all, in the manner of high-resolution photomacrography of the '60s, you lose even more. So instead of f/22, you find yourself at f/5.6 or f/8.

 

Yes, I was refering to the use of a UV-Nikkor or Coastal 60 APO lens. These are my work horses for studio shooting in UV.

[Pylon]

With the Baader-U attached to the end of a big step-down ring stack, you can take the rectangular cap off of the 199A and then wedge the largest step ring around it and it stays. 77-82mm. Only thing left to do is somehow block the open bit around the largest ring so light doesn't escape out the other direction. I hope that exposing the filter close to a UV light source would not deteriorate the filter at all.

[JCDowdy]

Very similar to the approach I am taking.

 

I am using a 77mm to 52mm step down ring and Nikon K rings to move my 52mm filter stack to a safer distance from the source. I bought a set of metal 77mm filter stack caps and after a bit of Dremel work should have a rectangular hole the size of the front of the 199A. A couple of 90° tabs on the back and some peel and stick Velcro so it wont fall off and break expensive filters will finish mine. The space between the stack cap and the 77-52 step down ring could trap something a couple of mm thick also.

 

I kinda like the looks of your conical snoot, did you do the black newsprint smoke test at the distance of your filter?

[Pylon]

Very good ideas!

 

I should do that newspaper test, thanks for bringing that up!

 

I'd like to see a photo of what you have made when you are done with it :)

[JCDowdy]

Sure, I will post a photo when I finish.

 

One other caution, or rather question, what is the trigger voltage of the SB-140 and is it compatible with your camera?

[Pylon]

I don't know what the voltage is, so I put a wein safe sync on the end of the PC-Sync cord, and then a wireless trigger attached to the wein safe sync. For some reason it only fires about 1/3rd of the time, donno where the problem lies. Is the Canon 199A below 5V (anything below 5V I read is safe for all new dslrs)?

[JCDowdy]

What constitutes safe flash trigger voltage varies with the camera.

 

The ISO standard for photography ignition circuits was established in 1992 (ISO 10330:1992) so modern digital cameras are supposed to conform to that standard although some may not. ISO 10330 specifies 24V but Canon allegedly specifies 6V.

 

Older flash units can run much higher voltages upwards of several hundred volts. I have an old ring flash that measured at 200V which works fine on a WEIN Safe Sync. The internet abounds with statements that 5V is the safe limit but I never found supporting evidence that is correct, other than unverified comments that Canon digital cameras supposedly should use 6V.

 

To answer your question, I just happened to put fresh batteries in a 199A and it measures 5.4V. I seem to recall the other one, which I do not have at hand, was slightly lower. These flashes have functioned reliably on Lumix G3 and G5 for me for a good while now, but I only use them in M manual mode.

 

I have never measured trigger voltage on an SB-140 or SB-14. In the recently posted photo of Bjørn he is using some sort of PC adapter but I cannot tell if it is a voltage regulator or not. Perhaps he will enlighten us.

[baffe]

Never had any Problems with Camera defects using WEIN Safe sync. Even the Radio Transmitters (several types) live definitely longer when I use them between Reciever and my Phillips Flashes.

 

I only had problems when I used the WEIN (or equivalent) together with a flash unit with very low trigger voltage. Problems were delay in trigger and long recovery time.

 

My Canon EOS/Rebel 300D fell into an "ERROR mode" several times when the trigger voltage was more than about 6 volts. The only way (I found) to reset the cam was to remove the battery. So I don't ecceed 6V now with EOS/Rebel's.

 

Opposite my Pentax SFXn (analogue Cam). The SFX went defective and can't fire any flash now. Even the internal flash doesn't work now.

 

Checking trigger voltage is very easy and takes 1 minute. The instrument is cheaper than ANY damage to a cam.