Aspects of image scale and technique for UV captures

[Bjørn Rørslett]

[ Posted 21 August 2013 - 09:14 With permission Bjørn Rørslett ]

A question newbies as well as old-timers ask is how much improvement can better gear bring in our UV photography. This is not an easy question to answer as so many variables come into the equation, and we always have to remember what purpose the final outcome is thought to serve. With that in mind, read the following account of my photographic journey exploring a common sunflower.

On a recent trip, I pulled over to shoot this specimen of Sunflower (Helianthus annuus; Asteraceae) on a road verge. This is a typical habitat for sunflowers in my country. The species is easily introduced, but being annual it rarely persists on these locations as seeds only occasionally ripen. So virtuall all occurrences are of a transient nature.




A close scrutiny (100% crop) showed plenty of interesting detail, amongst them several pollinator calling on the capitulum. The outer ring of disc flowers in their first, male stage, is clearly visible and we can see the style pushing through the anther tube.




Time spent for this first shot was < 10 secs. Essentially it was a snapshot from the hip so to speak, done with my Nikon 1V1 camera and its 10 mm f/2.8 lens. Nothing spectacular in terms of image quality, but it sets the framework for the remainder of this post.

Now, time for some UV. The field kit usually comprises a Panasonic GH-2 (broad-band modified) with the Coastal Optics 60 mm f/4 APO lens, or a Nikon D3200 (modified with internal Baader U2 filter) and a 35 mm f/3.5 Noflexar lens. I also bring an old yet still highly functional Nikon SB-140 UV/IR flash.

This time, the Nikon D3200 and the Noflexar were brought to bear on the sunflower. Hand-held so precise alignment is tricky. I used settings of f/16 and ISO 400 with the SB-140 at full power.




One usually shoots a few frames to get the UV capture right. Including processing time, time spent for this capture was < 2 min.

The overall UV signature of the sunflower head is well captured by the Noflexar. The UV dark patches on the ray flowers extend about half way to the ligule tips. Also seen (in the 100% crop) is the UV pale blue pollen mass and the long thread-like epidermal cells on the perianth of the disc flowers. Pollen grains are not  fully resolved despite the 24 MPix resolution of the sensor. Magnification was 1:3.





Next step is taking the specimen into the studio and set it up for closer photographic scrutiny.

Here I have used a broad-band modified Nikon D600 (24 MPix sensor on FX format) and again the Coastal optics 60 mm f/4 APO lens. Magnification of detail is 1:3 and lighting was provided by two Broncolor studio flashes with uncoated Xenon tube. I used setting of f/16 and ISO 160 and cut down output from the Brons by -2EV in order not to blow highlights.




This studio capture differs from the hand-held field shot in several aspects. Firstly, in a studio setting up to get properly aligned subjects is a breeze; secondly, you get much better control of the overall lighting of the scene. Price to be paid of course is the setting up takes much more time. As this was an easy subject, I spent probably no more than 10 minutes including post processing, though.

So, what could the better optically speaking lens (Coastal vs Noflexar) produce in detail? Actually, as shown below in a 100% crop, a lot.




Do note that this is not a very scientific comparison as both lenses and cameras differed. Yet it serves to illustrate what can be squeezed out of a subject with improved technique.


The final point is seeing what we can achieve by increasing magnification and add focus stacking in an attempt to recover the depth-of-field lost by higher magnification.

To this end I used again the Nikon D600, Coastal 60 APO lens at f/16, but now working at 1:1.5 (adding extension), a StackShot automated macro slider, the Bron flashes, and the very same sunflower specimen. I shot a sequence of N=80 frames.

Here is the overall capture,




It is obvious that we learn nothing new about the sunflower's UV signature when the entire frame is seen as a whole. The UV signature appears identical despite the technique is quite different.

However, going to the 100% crop, a new world of added detail becomes available. Please view large (right-click to bring up the View menu) to appreciate this fact.




The steep price to pay for this additional detail is a massive increase in time spent. The setting up and actual shooting took about 1 hour to accomplish, the computer churned 20 minutes on the files in PhotoNinja, the stacking software (Zerene Stacker) required another good 30 minutes (using two different stacking methods), and painstakingly retouching the final outcome to mitigate stacking artefacts took nearly 1 hour. So at least 3 hours of my time were used to hike the image quality another notch.

Was it worth the efforts? The purpose of the shoot will, hopefully, provide the correct answer. Suffice it to say that one should have a good reason to enter into such endeavours and they can never be a daily routine simple because of time constraints.
 
(first published on www.ultravioletphotography.com. Minor editorial changes for NG)

[Bjørn Rørslett]

[ Posted 21 August 2013 - 12:51 Published by written agreement ]

We have indeed come a long way. The quality improvement as far as rendition of detail is concerned is remarkable over the last decade. Concomitantly we have seen image resolution of our UV cameras rise from 2.7-4 MPix (Nikon D1H, D2H) to today's 24 MPix (Nikon D600). As the lenses such as the UV-Nikkor largely remain unchanged, we can attribute much of the increase in observed UV quality to the higher resolving cameras of today. Plus improved filtration plays an important role. Perhaps a tiny bit can be credited to learned experiences over the same time period as well.

To illustrate, here is a Sunflower in UV anno 2002 (taken with UV-Nikkor on a D1H). There is contrast loss due to IR contamination, an aspect scarcely recognised at that time but later shown to be of critical importance to the overall UV rendition. At the time a sunflower was considered to lack a "UV signature". We know now how unjustified that assertion was.

(100% crop)

[Frank Fremerey]

Asphalt. The white stripe. The sun flower. A very convining composition with a high visual impact for my taste. Thank you for sharing. The technical aspects I will digest and comment later. Thank you.

The 3 hours of work reveal fascinating details.

I experience the same with visual light and the D600 compared to the D3. The D3 was already a big leap forward from the D70s. With the D600 I can count the hair of bees in handheld non stabilized shots.

Add all aspects of studio work like strudy stabilisation and reliable lighting of high contrast and color fidelity and the real potential of the lenses is revealed. Some are maxed out but exceptional optics like Bob Friedmans printer lenses or the Otusses or my Schneider APO Digitar are not.

in this sense your UV findings go in parallel to the visual lighting development.

Gear is as important as technique and training.

Gear means potential
Technique means living up to the potential
Training means to get much faster with setup and editing.

F.

[Jørgen Ramskov]

Thanks for reposting these, they are quite fascinating to read. The money is not there currently but I think I will HAVE to get an UV and/or IR camera at some point. Will have to do some research first...and earn some money for it.

[Erik Lund]

Jørgen, IR is much easier to get into than UV.

An old D200 and a new cover glass is all it takes!

It's a lot of fun - Highly recommended indeed

[Andrea B.]

May we please have this on UVP??

[Jørgen Ramskov]

Thanks Erik, that was the gist of what I had understood by reading a bit on Bjørns site and on the UVP site. Unless I win the lottery, a cheap used camera + lens will certainly be how I will eventually go forward.