Focus Stacking with a Raspberry Pi – First Focus Stacked Image
After various false starts I have now hit on a method of lighting the photo specimens. Two IKEA JANSJÖ LED lights are mounted below the level of the stage shining upwards into a light box. I had tried various methods of attaching diffusers to the lights themselves but that did not work mechanically or from the viewpoint of achieving well diffused lighting. The idea of the light box came from a paper published by the USGS Bee Inventory and Monitoring Laboratory (BIML) describing how it takes photographs of insect specimens in the lab. They seemed to use a polystyrene box (very sophisticated – Polystyrene is a great diffuser material) – my lightbox is made of foam-board which is rigid and lightweight.
Anyway, it works very well, and leaves me with a spare lamp unit which is handy to have, as I had bought three. At £10 each, they are good value for money.
Inside the light box there are a couple of reflectors made from kitchen foil to direct light internally and to ensure it doesn’t land directly on the front of the lens. It will also be possible to put reflectors or absorbers inside the box to achieve unbalanced lighting should this be required. At the back of the box there is a rectangular 2:3 aperture revealing the backdrop behind. The backdrop is a matt black board to which coloured backdrops can be attached and illuminated by led stalk lights.
To facilitate the bottom up lighting arrangement the camera and stage have been elevated each by two thicknesses of aluminium channel to give clearance for the lamps and their flex stalks.
So, today I took my first stack. I had collected a few dead insects found on windowsills at the end of last year when I thought I might need something to practise on. A couple of small moths, a butterfly, a house fly and some other indeterminate insect (I shall have to get better at identification!) It was time to wheel one of these out. None were in very good condition. The small moth was chosen as a test sample mounted on the end of a cocktail stick with superglue and attached to the stage with plasticine. I used an Otamat 20mm lens on a 62mm extension tube. I decided to shoot a detail of the wing mounted at an oblique angle to the lens as this would not be too demanding.
Working out the DOF was not so easy and I decided on a 50 micrometer focus increment which required a 98 image stack – rather in at the deep end. My software predicted 27 minutes for the shoot and it was quite accurate. The images were uploaded into Lightroom and exported into Zerene where I did a PMax and DMap stack. The Dmap looked the best and that is the one shown here post LR processing and a light dose of Topaz detail.
Overall, happy so far.
