Archived posting to the Leica Users Group, 2006/12/17
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Leonard, Having just done a bit of research on the B+W 403, it passes UVA in the range 320-385nm. Given what you said about the enlarging lens having a capability down to about 350nm. That seems to imply that the light that you used is probably predominantly in the region 320 - 340nm or so (presumming that the response of the enlarging lens drops off as it approaches the upper limit). As the 403 is designed as a bandpass filter those cutoffs must be pretty abrupt. Seems that you've concocted a filter with a bandpass of about 20nm! Interestingly B+W say that the filter factor is VERY sensitive to the emulsion and to the illumination with a factor of BETWEEN 8 and 20. That is probably enough to explain the varying responses for the various sensors in the cameras. The D2X presumably has a colour gamut wide enough to reach that far into the IR To get a look at the gamut curves and so on for a few cameras including the D200, lok at http://www.luminous-landscape.com/tutorials/prophoto-rgb.shtml but you'll need to open it in somrething other than Netscape to get the interactive effects. Whatever the details, the photos make intriguing viewing. Keep them coming! Peter Dzwig Leonard Taupier wrote: > Peter, > > Thanks for your comments and interest. Let me try to answer some of > your questions with my limited knowledge of the subject of ultra-violet. > > I have not looked into the response curves of the Nikon digital cameras > I use. I can only comment on the results I've gotten with different > cameras. > The D2X has good UV response, much better than the D1H I use for IR. > The D1H gives very noisy photos. > The D1X has much better IR response than the D2X. > The D200 has no sensitivity to either UV or IR. > > That brings us to the frequency spectrum of light from UV through > visible light to IR. > The Ultra-violet light we are concerned with in photography has a > wavelength from about 200nm to 400nm (nano-meters) > Visible light is from about 400-450nm for violet to about 600-750nm for > red. Photographic lenses are designed to pass visible light from 450 to > about 800nm (into the IR zone). > > Nikon made a UV 105mm Micro lens for the F series some years ago. The > lens was made of fluorite glass and had a response between 200nm to > 900nm. This lens is still being produced today (not by Nikon), but is > too expensive for the casual user. That brings us to the next best > available lenses for UV. That is the enlarging lens which has a > response down to about 350nm. My guess then is that the area where the > photos were taken were between 350nm and 500nm which includes the > purple area of visible light. > > I did, by mistake, take photos without the filter but using the black > light. The photo became much lighter (same exposure as with the filter) > but now other colors entered the picture. The dark room background > became blue and the center of the flower had little yellow growths > which came out yellow. The main petals were still a light shade of > violet. This tells me that the black light has visible light components > up into the yellow area which has a wavelength of about 580nm. > > I have tried other lights called black light bulbs but found they were > only painted incandescent bulbs with nearly no UV content. What really > produces UV is the ionization of Mercury vapor, like a florescent light > tube. I looked into getting Mercury vapor bulbs but they are expensive, > require a special fixture, and are too dangerous to be exposed to. > > I hope this answers some of your questions and is not too much > information. > > Regards, > Len > > > On Dec 17, 2006, at 7:58 AM, Peter Dzwig wrote: > >> Leonard, >> >> Wow! Very, very interesting, and very creative too. None of that IR >> stuff ;-. You must be near the limit of the camera's response. I >> guess that the D200 just doesn't have the response in that part of >> the spectrum. >> >> Have you looked at the response curves for the camera? >> >> Any idea where in the UV the picture was taken? >> >> What happens if you don't use the filter? Dies the extra light make >> much difference? >> >> Peter Dzwig >> >> Leonard Taupier wrote: >> >>> The flowers were exposed with Ultra-Violet light from a black light >>> in an otherwise totally dark room. >>> <http://gallery.leica-users.org/v/LeonardT/UV/UV_1.jpg.html> >>> <http://gallery.leica-users.org/v/LeonardT/UV/UV_2.jpg.html> >>> Please comment on what you think. >>> The camera was a D2X at 20 sec exposure >>> Lens an El-Nikkor 105mm f5.6 at f11 mounted in a Nikon PB4 bellows >>> with a homemade F to LTM adapter >>> Focus was in incandescent light. >>> Exposure black light only, using a hot mirror filter and a B+H 403 >>> UV bandpass filter. >>> No attempt was made to color correct. The 403 filter is a nearly >>> black, red filter. >>> I tried the same setup using a D200 and even with a 6 stop exposure >>> increase no image was produced. Totally black. >>> As a retired engineer I can't stop experimenting. I just think it's >>> fun. Hope you enjoy it. >>> Len >>> _______________________________________________ >>> Leica Users Group. >>> See http://leica-users.org/mailman/listinfo/lug for more information >> >> >> >> _______________________________________________ >> Leica Users Group. >> See http://leica-users.org/mailman/listinfo/lug for more information > > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information > >