nfoto Posted May 18, 2015 Share Posted May 18, 2015 No filter test in the UV domain can hope to be complete without a few dandelion snapshots. Dandelions are not only the most free-spirited and irresistible of all plants, they also happen to have a rather* well defined UV signature of the classic "bull's-eye" kind. This makes them excellent targets for UV filter experimentation. * there are a myriad of more or less vaguely defined microspecies in the Taraxacum genus, and not all of them have the bull's-eye UV signature fully developed. But all share the presence of UV-darker parts in the centre of the flower head (capitulum). Most kinds of dandelion also exhibit very dark involucre bracts in IR light. I availed myself of a spell of unexpected sunshine to shoot some weedy dandelions using only solar illumination. These plants occurred on trampled grassland thus were prostrate to the ground and less affected by wind movement. All shots done with my broad-band modified Nikon D600 and the ubiquitous UV-Nikkor 105 mm f/4.5 lens. Here is the visible reference (using the Baader UV/IR Cut filter and a custom profile in Photo Ninja), This was my first outing with the D600 this season and of course I forgot to cover the ocular of the finder ... Some stuff goes wrong every year, a kind of UV teething problems I dare say. You won't notice any leakage in the visible range because the scene overwhelms the tiny amount of light spilling past the ocular, but add the Baader U2" filter and all of a sudden the leakage is evident. I used a Zacuto loupe on the rear LCD screen and forgot that the ocular wasn't shielded in any way with this arrangement. Okay, lesson learnt so I covered the ocular to get this UV capture rendered in the typical false-colour 'standard' palette. Now, put the BUG filter (UG5: 1.75 1.5 mm + S8612: 2 mm) stack to the UV-Nikkor, Pushing the hue of the greens makes for an interesting and more informative rendition, Steve Smeed kindly sent me instructions as to massage the BUG output in Photoshop to get an emulation of the look of "UV film", meaning Fuji RTP in the '90s. This is my first try with this emulation technique - not bad. I have to work further to refine the results, though. Link to comment
Alex H Posted May 19, 2015 Share Posted May 19, 2015 The last one is a winner for me! Link to comment
nfoto Posted May 19, 2015 Author Share Posted May 19, 2015 Thanks, Alex. Basically done with a channel mixer adjustment layer in Photoshop. Steve [smeed] sent me his recipe, which can act as a convenient starting point from the BUG output:Red:r+2g+102b-33 Green:r+87g+1b+20 Blue:r+130g-2b+120 You need to tweak this a bit as the reds tend to be too cool and the blues too predominant. But it'll start you on the right track. I labelled this as an action "Fuji RTP emulation", which essentially is the underlying idea. Link to comment
nfoto Posted May 19, 2015 Author Share Posted May 19, 2015 Forgot to put up the IR image, taken with the Wratten 87C. Very evenly reflecting specimens in IR and it is noteworthy that these plant did not exhibit the almost black involucral bracts we tend to associate with dandelions in IR light. Here is the typical IR appearance of dandelions (Fuji S3 UVIR Limited, 1000 mm f/11 Reflex-Nikkor, Wratten 87C filter) There are more between heaven and earth than most places (Norwegian proverb) Link to comment
Andrea B. Posted May 19, 2015 Share Posted May 19, 2015 The bracts aren't black, but they are darker. I note some light leak in the second foto? The bullseye would stimulate the insect's green receptor. The non-absorbing portion of the rays would stimulate the G + UV receptors. So I like the green bullseyes. Link to comment
nfoto Posted May 19, 2015 Author Share Posted May 19, 2015 It's not about "like" but about visual clarity. So I prefer an altered rendition. These are false colours anyway. The text in the first post says there is a light leak in UV .... even old hands forget and have to get the stuff right next season I just showed yours truly wasn't an exception. Using the Zacuto loupe prevents your head from blocking the ocular. That is why there is a light leak. I do wish the D600 had an ocular shutter (except the little plastic thingie that is rapidly lost in the field). Something akin to the shutter found on a D2x or D3-series. Now I have to remember to cover up the finder. Link to comment
Andrea B. Posted May 19, 2015 Share Posted May 19, 2015 I'm totally agreed that any of these cameras should have a viewfinder shutter.I so badly want to convert my D810 - which has a vf shutter - yay! Link to comment
Andrea B. Posted May 19, 2015 Share Posted May 19, 2015 Well then I won't have a "good" camera anymore. Link to comment
nfoto Posted May 19, 2015 Author Share Posted May 19, 2015 You still have the Df .... Link to comment
colinbm Posted May 20, 2015 Share Posted May 20, 2015 Hi Bjorn"The BUG filter (UG5: 1.75 mm + S8612: 2 mm) stack to the UV-Nikkor".Could you explain your CWB method here please ?Col Link to comment
nfoto Posted May 20, 2015 Author Share Posted May 20, 2015 The usual UV-white PTFE (Teflon) disc. Just checked my BUG filter and it's actually UG5: 1.5mm, S8612: 2 mm. So my memory has to be recalibrated as well. I have corrected my original post. eBay seller 'uviroptics' delivers the BUG filter in various configurations. I wanted the thinner version of the UG5 to allow a bit more of the visible range to pass through. Link to comment
colinbm Posted May 20, 2015 Share Posted May 20, 2015 Thanks BjornSilly me, I thought there was more to this 'witches brew' ;)Col Link to comment
nfoto Posted May 20, 2015 Author Share Posted May 20, 2015 If you look at the first BUG picture, you'll notice the lower right square of the CC Passport is neutral dark grey. Just like it is on the Bader U2" example. Both have white balance set in the same manner and both agree on this small target (elsewhere they obviously differ tremendously). The visible-light reference is also colour balanced in the same manner. Link to comment
colinbm Posted May 20, 2015 Share Posted May 20, 2015 Thanks BjornI'll spend some time over the next few days & try & replicate this.Col Link to comment
nfoto Posted May 20, 2015 Author Share Posted May 20, 2015 That will be interesting. The filter itself holds no secrets regarding the spectral properties, but its usage on actual subjects still can make surprising results. Link to comment
Andrea B. Posted May 20, 2015 Share Posted May 20, 2015 Apropos, I hope, of BUG filters - here is an example of a shot made with the Baader 435 Blueband filter which does gives somewhat buggy results in spite of this restricted test I made (way back in 2009). D200BB + Noflexar 35/3.5 + Baader 435 Blueband + Nichia 365nm UV-Ledf/? for 6" @ ISO-400 The buggy look emerges after some white balance trickery. The raw file looks like this. I did have to brighten it up a bit by pulling in the white point. There isn't much contrast. I took a sample of the raw data on the flower and made the histogram because I was curious how this filter was recording. First the raw sample strip, then the histo for it. It seems strange that this is a Blue bandpass filter which records the flower parts mostly in the red channel. Here is the transmission chart for the Baader 435 Blueband. I was the one who coloured it underneath the curve. I don't have any data on how serious that red/IR leakage is. I don't think I recorded much of that using the UV-Led indoors. Link to comment
msubees Posted May 21, 2015 Share Posted May 21, 2015 Nice looking shots. I have experimented with S8612+UG5 also last year. Right now I have a cheaper alternative QB21(~S8612 so I thought, but Steve tells me it is more like BG38) + ZWB1 (~UG11). It seems to give similar UV photos so far, but I have not seen the nice green (when it is totally black with S8612+UG11, S8612+UG5 usually gives a nice green) yet with QB21 + UG5, which is strange. Maybe it is not strange, now that Steve says QB21 is not the same as S8612 but more like BG38. BG38 leaks some IR near the end. I use 2 QB21 (2 mm + 1.6 mm). This plus UG5 should me green color at UV dark areas, but I am not reproducing that. Link to comment
Andrea B. Posted May 22, 2015 Share Posted May 22, 2015 It could be a matter of changing the white balance or simply turning the colour wheel in the converter/editor?? I don't know those filter prefixes: QB or ZW. Who makes that glass?? (Thanks.) Link to comment
msubees Posted May 22, 2015 Share Posted May 22, 2015 These are made in China...but I have not figured where their initials come from what Chinese characters yet ;)ZW could be from ziwai (UV). QB? not sure what. It could be a matter of changing the white balance or simply turning the colour wheel in the converter/editor?? I don't know those filter prefixes: QB or ZW. Who makes that glass?? (Thanks.) Link to comment
Recommended Posts
Please sign in to comment
You will be able to leave a comment after signing in
Sign In Now