Focus Stacking Rail.

[Jim Ford]

I'm starting to put together a few ideas for a focus stacking rail.

Rather than move the object utilising the positioning system from a DVD drive (as has been recently shown in a thread), I want to do it 'properly' by moving the camera.

I envisage driving a platform on a lead screw with the camera mounted on it, through pulleys driven by a stepper motor. The motor will be controlled by a microcontroller (Arduino).

I'll do a 'proof of concept' using a plain nut on the leadscrew and plain pulleys, but if it looks like a 'goer', finally fit a ballscrew and toothed belt and pulleys for better positional accuracy.

I anticipate that the user will only need to enter the lens aperture, focal length, subject near distance and subject far distance, for the software to calculate the camera step size and number. As this will be a one-off (or zero-off, if it doesn't get completed!), the circle of confusion size (for my camera) will be hard coded - at least initially.

The only thing I'm currently undecided about is what sort of range am I likely to need? I'm thinking 50mm should easily cover it. I'd welcome some input here.

Does anyone have any further ideas that may be worth considering? What are the 'long felt wants' of you photographers who currently do manual focus stacking?

Jim

[nightshade]

I like the idea of using a machine table, they have good mass and accurate
repeatable movement (Axminster tools)

[Jim Ford]

Originally Posted by nightshade

I like the idea of using a machine table, they have good mass and accurate
repeatable movement (Axminster tools)

Probably too heavy to carry in the field and too expensive. Also I only need movement in one axis, not two.

Jim

[Bruce Williams]

Jim,

Cognisys Inc have developed an automated focus stacking rail (StackShot) that may well meet your requirements. It comes with a computerised controller and is available in two rail lengths. See: StackShot - Focus Stacking Macro Rail

It's well reviewed and there is quite a lot of info on the web. If you check out the Equipment Discussion forum of the Photomacrography Forum you'll find quite a bit of user feedback. See: www.photomacrography.net :: Index

The focus stacking package, Zerene Stacker has recently been modified to work with this unit.

I don't believe there are any UK suppliers as yet and I know from various forum comments that it can be quite costly to buy from Cognisys. However, at the very least you may get some useful ideas by reading up on the StacShot spec and related forum comments.

Bruce

[Lancashire Lad]

Originally Posted by Jim Ford

....I want to do it 'properly' by moving the camera....

Surely Jim, doing it "properly" would entail producing a system which was able to critically alter the lens's focus, without moving either camera body or the subject being photographed.

I say this because when either the camera/lens or subject being photographed is moved in relation to the other, the effects of "image perspective" are destroyed.

For example, (and because I'm struggling to think of a suitable way of explaining this ), let's say we are using a 1:1 macro lens, and that we are photographing a pencil, of diameter 10mm, with the pencil point slightly below, but towards the lens, and the blunt end away from the lens.

In a single shot photo, with the lens at closest focus on the pointy end, the diameter of the sharp end of the pencil as recorded will be 10mm, but the blunt end of the pencil would be recorded on the sensor slightly narrower, due to perspective.

Now, let's say we are going to do a focus stack of the full pencil length.

If focus was not altered, but the camera/lens assembly is incrementally moved in order to provide sharp focus further and further down the pencil, then the diameter will be recorded as 10mm for every shot - thus destroying proper perspective. The same would occur if the camera/lens remained static, but the subject was moved towards the lens.

However, if the camera, lens, and subject all remain static, and only the lens focus is altered between shots, the perspective "narrowing" effect will be recorded correctly.

So, to do it "properly", the camera/lens/subject should be static, and only the lens focus should be altered.

Regards,
Mike.

[DorsetDunk]

I agree Mike better off with the camera tethered to the laptop and using dslr bracketeer (freeware) for the lens focus movement
photomacrography.net.as Bruce mentioned is the place to go for info on technical macro and micro techniques and rail construction if you still wish to go down that route Jim

just thought i better add dslr bracketeer is only compatible with CANON cameras

[Lancashire Lad]

Originally Posted by DorsetDunk

I agree Mike better off with the camera tethered to the laptop and using dslr bracketeer (freeware) for the lens focus movement....

That looks like a very interesting possibility for Canon users. - Unfortunately I use Nikon so can't give it a try. (However, I'm getting reasonable results when stacking by simply manually adjusting focus).

I originally found that spherical objects were the hardest to get good stacks from, but I've adjusted my technique and can now get usable stacks without discernable digital artefacts. - A perimeter crop being all that is needed.

This is a 27 shot manually focussed stack from yesterday, with a front to back depth of about 12mm: -
230711-02 - Wild About Britain Pics

Regards,
Mike.

[Bruce Williams]

Re: automated focus control for focus stacking:

For Nikon DSLRs with liveview capability there is also ControlMyNikon - available for download for $9.95. ControlMyNikon

I use this software to produce computer controlled focus stacks using my Nikon D300 + Nikon 105mm Macro lens. The software enables you to specify a step size and the number of slices required. It controls both focus and shutter release and also enables you to specify a pause between shots to allow for mirror slap and recharge of flash heads if used. It displays the liveview image on screen and enables you to input various camera settings via the laptop (eg, shutter speed, aperture, flash settings etc).

I have to say that for such a cheap product the results have been surprisingly good.

I use Zerene Stacker to create the focus stacked image.

I should add that I use both methods of focus stacking (camera movement and lens focus ring) and haven't really noticed much difference in the quality of the end product. Subjects have varied in size from the head of a fly to the skull of a badger with stack sizes from as few as 10 to well over 100 slices.

*Nice clean stack Mike.

Bruce

[Hobjob]

I'm not sure that I fully understand this subject, but would a focussing rail for a tripod be suitable?

Kirk FR-1 Focusing Rail (FR-1) - Warehouse Express

I have a manfrotto one which helps with macro work, and I hope this winter is going to help with slide copying.

[Jim Ford]

Originally Posted by Lancashire Lad

Surely Jim, doing it "properly" would entail producing a system which was able to critically alter the lens's focus, without moving either camera body or the subject being photographed.

I understand what you're saying.

To minimise the problem of the apparent size of the subject changing with the camera being moved, I intend to use a long focal length lens eg 150mm. With the subject (say) 1 meter away, a change of distance of (say) 10mm shouldn't make much difference.

Jim