The story behind my gallery shot.
Originally inspired by preperation for macro in combination with Combined ZM focus stacking program. Early trials are in this thread
http://www.worldphotographyforum.com...ead.php?t=3337
While doing those tests I realised that I often faced problems getting adequate dof on other still life shots not of the macro variety. The D2X becomes diffraction limited at f11 and tests showed image softness sets in beyond f13. The abiity to stack a series of images taken at optimal f8 to achieve whatever dof is required is therefore of great interest.
Each summer we have had filming for the TV series Kingdom here, and quite a bit of time has been spent watching the camera crew and in particular the focus puller. No auto focus kit used here. In essence the focus puller measures out and places tape on the ground as markers for the various points of focus. These point are marked on the white wheel on the follow focus mechanism on the camera. The camera lens focus being driven by gears from the follow focus through to the geared ring on the lens itself. Through gearing a small movement of the lens is magnified at the follow focus, so giving greater precision of view than from the lens barrel engraving. As the scene is being filmed the focus puller uses the control wheel on the unit to change the point of focus. See attatched pic for explanation.
Nothing like that on SLR lenses, experimented with various options before I found that one particular Qualcast lawn mower drive belt was a good match for the ribs on my Nikon lenses. Now I just needed a means of driving and gearing it. All a bit trial and error when it came to gearing it. Maths boffins could probably do it on the back of a fag packet but for me its trial and error and it takes ages to plane the teeth for just one gear. If I had a wider bit of metal then I may well have added a fast wheel to give finer view of near infinity lens movement. If I do a MKII then I probably will take time to make the addition just cos. I even thought of making a cam and linked to a 1 thou graduated workshop clock, but sanity and simplicity finally prevailed, hence the choice of using a standard clock face marked at hour and 1/2 hour positions.
So how does it work. Two explanitory pics attatched to show basic construction and how it goes together etc.
With the subject framed, focus is made on the front point of required focus. Its position on the clock face is noted. Next focus is made on the rear point and its position on the clock face noted ( sector arms may be added later ). Focussing can be by way of the lens, or the fine focussing knob on the unit. Precise focus is easier with the units fine focus knob. A series of images for stacking can now be taken without the need to confirm new point of focus through the viewfinder. Invaluable if I am in the workshop, and my softbox, when in position, is cutting out half the available light.
Don
PS: Ooops just realised I forgot to add the link.
