Friday, 1 June 2012

Focus stacking wild orchids

Monkey orchid flower head: D300/ 90mm Tamron f/2.8. Focus stacked with Helicon Focus.
Orchids in the landscape. D300/Sigma 10-20mm f/4-5.6
As a follow-up to Martin's last post on photographing wild orchids, here are a couple of mine from this week.

The evening when Martin and I went to see the orchids was very still, so it looked like a good time to photograph them: even though the light was quite dim, the orchids were not moving in any wind, so slow exposures were possible. The sky was also quite bright, which gave the opportunity to open up the shadows in the orchid flowers by using a small reflector positioned at the base of the orchid plant.

I wanted to be able to get some close-up pictures of the flowers where the background was suppressed by being defocussed. The problem with this is that the orchids were in quite dense foliage, so to get an out of focus background means using quite a wide aperture. Correspondingly, there is then the problem of depth of field across the flower. As I have blogged previously, one solution to this problem is to use focus stacking. In this, a series of images is taken by changing the focus point through the subject, and then the images are combined in software (I use Helicon Focus) to produce a sharply focused image across the depth of the subject. The background is still so far out of the plane of focus that stacking does not change its smoothness.

We met Martin's friend Steve at the site, who was also out photographing the orchids. He is another Nikon user, and he offered to lend me his Tamron 90 mm f/2.8 macro lens to use on my D300. The picture at the opening of this blog post (upper picture) is a stack from one of the resulting series of images with his lens (thanks, Steve!). The images were all taken at f/5.6, which I chose to give a sufficiently smooth background, but with enough depth of field within the flower so that the individual planes of focus did not have to be impossibly close to each other. I set the camera onto manual control (aperture, shutter speed and focus), and then used the smallest possible movements of the focusing ring between shots to move the plane of focus across the subject.

Back home, I simply exported 16-bit ProPhoto RGB Tiffs from Lightroom, and popped them into Helicon.  As a first go at focus stacking orchids in the wild, I think it is not too shabby, and the Tamron lens seemed to live up to its very high reputation.

I had taken my own 60 mm micro-Nikkor: although that is a great studio-type lens for flowers, on this occasion I really feel that the extra focal length of the 90 mm was very helpful. It would also have been nice to be able to control the camera using automation to ensure even and small steps. Helicon Remote does this very well, but you need to run it from a laptop, and I have enough to carry without schlepping a laptop on countryside shoots! I see on their forums that Helicon are finding it difficult to adapt Helicon Remote to the iPad: I hope this can be sorted because I think that controlling focus stacking from an iPad in the field would be a very powerful approach.

I went back with Gina a couple of days later. She was also keen to see the orchids, and was an uncomplaining assistant with another shot. The evening we went back it was too breezy for focus stacking -- the orchids were waving around far too much. But the overall light was nicer, so I tried some pictures to show the orchids in their landscape setting (lower image, above).

My idea was to try to show the orchids (really quite small flowers) and the slope of the valley they are growing in. As I've mentioned previously, I have a predilection for using an ultrawide lens; I thought that by getting down to the level of the flowers, and as close to them as possible, with the Sigma 10-20mm lens set at 10 mm on the D300, it should be possible to show them in their context.

Several difficulties came up with this, not the least being that while the lens needed to be set on very close focus for the orchids, but I also wanted to show the extent of the valley. The simplest way to get the required depth of field was to use f/22. If you read the forums, you will be told in no uncertain terms never to stop down this far because diffraction effects will ruin the picture. And there is no question that this setting does nothing for the ultimate sharpness of the image. In general terms, it might have been possible to use focus stacking to achieve the extreme depth of field I wanted, but with the flowers waving in the wind I didn't fancy effects of ghosting. The other problem was with the range of brightness between the side of the valley where the flowers were and the sky that I wanted to include. The brightness range was in excess of four stops. So to get everything on scale with a correct exposure overall in a single image, I put a three stop graduated neutral density filter over the sky (which also impinges on the tree line), and then lit the foreground by firing in a flash through a large diffuser. The flash helped give the orchid colours a bit of pop. I am reasonably happy with the resulting image: it required minimal post processing, and just for tidying up. I suppose I could have HDR’d it, or blended several exposures by hand in Photoshop, but I’d actually prefer not to.

Thinking about it, I think these two pictures illustrate the way I prefer to work. I’ll assemble a picture in post-processing when I need to (there’s no better way to get the first picture than by focus stacking), but I enjoy the challenge of getting a picture in a single raw file if I possibly can, even if it means using a combination of ultrawide lens, tripod, remote release, flash and wireless trigger, diffuser and ND grad. Nothing’s simple!

Lots of fun, and thanks to Martin for getting us there in the first place.

No comments:

Post a Comment