Sunday, November 25, 2012

A little backlit fern photography

It's been horrible weather the last few days.  Rain, gale force winds - not the sort of environment for field photography even on the few occasions when the sun has broken through.  And, of course, I was looking for subjects to test out the cheap Opteka SB-15 flash diffuser I'd just purchased to give me softer lighting for macro and semi macro plant and insect photography.  Even in South West England there aren't too many plants in flower or insects on the wing in mid November - and especially not when the gales are blowing a hooley straight off the Atlantic.

In a few brief respites from the prevailing awfulness I wondered around the garden with my Canon 600D/Tamron 90mm/430EX/Kirk flash bracket/Opteka diffuser combination and even managed to get a few shots in before the heavens re-opened.  The lighting is definitely softer than with the Stofen Omnibounce diffuser that I've used previously, hardly surprising as the effective light source is considerably larger.  On the other hand the flash recycle time is longer, even when the light source is close to the subject on the bracket.  There is always a trade off.

One of the shots interested me and gave me an idea.  I grow a large tree fern, Dicksonia antarctica, in the rear garden.  It's currently sporing, with sporangia - the little capsules the cover the ripening spores in ferns - dotting the frond edges on the older fronds.  Here's the shot:

Dicksonia antarctica sporangia - Tamron 90mm macro, 600D, 430EX diffused flash on bracket
It's not too bad for a hand held shot but it lacks that little sparkle.  The lighting, though soft, is a little flat.  Fern fronds are thin enough to be translucent with strong backlighting but that means balancing ambient light with fill flash.  I'm never going to achieve that given the blustery conditions. 

So I gather fronds from some of the evergreen ferns I grow and move indoors.

And light breaks through yonder window.  Low angled, mid November sunlight.  Which can be used as backlight if I set up a quick studio on a suitable support.  It's very simple.  The fern frond is held vertically using an improvised clamp in a position where the sun will shine through the frond.  I angle it in such a way that I will have a dark background when I get the front of the lens parallel to the subject.  I mount my recently acquired (cheaply) Sigma 180mm HSM macro on the 600D and position the bracket mounted flash and softbox at the end of the lens.  Mirror lock up and remote release was used to produce the best sharpness on shots taken at around 0.5sec.  A couple of test shots suggests values of -1/3 exposure compensation for both metering and flash exposure using AV metering, the fill flash illuminating the front of the fronds and the sunlight providing the backlit translucency.  The difference from direct frontal flash is obvious.  Compare these two shots of the hardy maidenhair fern, Adiantum venustum:

Adiantum venustum - direct frontal flash
Adiantum venustum - backlit with fill flash
The second, with the thin halo of light around the fronds and illumination of the body of the fern and sporangias, to my eyes, far more interesting.

A few shots later and I have some backlit examples to show the different sporangia arrangements on four more of my ferns (I grow about a dozen but some have already retreated below ground and others had no suitable material for photography).

Athyrium onopordon 'Okanum'

Dryopteris erythrosora

Polystichum polyblepharum

Polypodium vulgare 'Cornubiense'
Each one is different in shape, number and arrangement of the spore cases and spores.  Indeed they are a feature used for fern identification.  And they do make good subjects for indoor shooting in wild and windy November.

There is one problem.  Fronds are not flat.  Even at f11 the depth of field is insufficient to have everything in focus.  So I tried focus stacking using Combine ZM software.  I'm still getting to grips with this and really need a focusing rail to produce the sequence of differently focused shots needed for the software to combine into a single image with far greater apparent depth of field.  I'm probably not taking enough shots for a really successful merge as I still get edge artifacts in the finished product.  Noticable at 100%, less so in a shot resized for the web.  Even so the results can be very interesting.  Adiantum venustum again, 5 shots stacked.

Adiantum venustum, 5 shots stacked using Combine ZM software
Definitely a technique to work on.  But well worth working on - the results can be spectacular.

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