Focus Staking with a Raspberry Pi – first stacked insect image


    Here is an image I took a few weeks ago. This little chap was about 1mm wide. It was processed in Zerene from a stack of 111 images at 45micron intervals taken with my Sony NEX7 camera with an Otamat lens on extension tubes. I am quite pleased with the result though I still need to sort out the backdrop lighting which I think is too dark. I also need to perfect my retouching technique as I do not like the halo effect visible around the legs.

    Focus Stacking with a Raspberry Pi – test stack of 148 images of a fly

    Today I made another test run with a stack of 148 images at 40 micron intervals using the Otamat 20mm lens, this time on a 42mm extension tube. The subject was another of my old insects forraged last year for trial purposes. I have been waiting to see how these tests go before getting hold of various bits of entomological equipment – forceps and the like – as well as acquiring the necessary chemicals for relaxing the insects, stilling, drying etc, and plastic/glass tubes and containers for processing the specimens and keeping them clean. The work by Johan J Ingles-Le Nobel on his website – Extreme Macro – has been an inspiration and a huge help in working out what to do.

    test specimen - not in the best of conditioning - no prep other than mounting for the stack
    Test specimen – not in the best of conditioning – no prep other than mounting for the stack

    So this specimen is a bit ugly in many respects, is missing some key components with many bristles broken off, and it could do with a wash and brush up!  But it has served its purpose. I am satisfied that if I can prepare a passable specimen, then I can make a passable macro image. After a number of test stacks I am now sure that the kit works as envisaged, and that the lenses are OK; we are good to go to the next stage.

    There are some minor software changes to be implemented to make things a little easier; I am accumulating a list and at some point will do an integrated update. I intend to make another light box, much larger, to accommodate larger specimens in a diorama form for 1:1 macro work; for this I will need to improve the method of positioning and lighting the backdrops as the current arrangement doesn’t really do what is required – back to the drawing board here.

    Finally I need to decide on my stacking software. At the moment I am using a trial version of Zerene. I am quite happy with the results so far but will probably have a look at Helicon Focus too.

    Focus Stacking with a Raspberry Pi – First Focus Stacked Image

    Moth wing detail showing scales
    Moth wing

    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.

    Focus Stacker set up to take the moth wing image
    Focus Stacker set up to take the moth wing image

    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.

    The two IKEA LED lights. The aluminium stage slides along the slot in the base of the light box.
    The two IKEA LED lights. The aluminium stage slides along the slot in the base of the light box.

    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.

    Camera set up
    The stalk pointing at the camera contains the IR trigger for the camera shutter.

    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.

What’s it all about?

Here are my jottings about my photographic projects and activities. I have been working on a focus stacking macro photography rig. There are quite a few posts about that. In addition I write about other photographic activities as and when!


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