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UltravioletPhotography

Aspects of image scale and technique for UV captures


nfoto

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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 annus; Asteracea) 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.

 

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A close scrutiny (100% crop) showed plenty of interesting detail, amongst them several pollinators 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.

 

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Time spent for this first shot was

 

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 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.

 

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

 

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 resolved despite the 24 MPix resolution of the sensor. Magnification was 1:3.

 

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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 D600 (24 MPix sensor on FX format) and 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.

 

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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.

 

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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 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 same sunflower specimen. I shot a sequence of N=80 frames.

 

Here is the overall capture,

 

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It is obvious that we learn nothing new about the sunflower's UV signature when the entire frame is seen as a whole.

 

However, going to the 100% crop, a new world of added detail becomes available. Please view large to appreciate this fact.

 

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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 were used to hike the image quality yet 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.

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  • 1 year later...

That last stacked photograph is excellent, Bjørn.

Quite amazing.

 

It is great to see the Stack Shot in use once again.

Maybe someday I'll give that another go.

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