Focus Stacking Rail.

[Jim Ford]

Originally Posted by Bruce Williams

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.

Very interesting - thanks Bruce. It's pretty much what I have in mind. I'll check it out further.

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.

The price quoted is $525, which would translate to £525 if it gets imported into 'Rip-off Britain'! I already have to hand much of what I need to make mine and hope that the total cost will be well under £50.

However, at the very least you may get some useful ideas by reading up on the StacShot spec and related forum comments.

That's what I intend to do!

Jim

[Lancashire Lad]

Originally Posted by Jim Ford

...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....

Hi Jim,

I'm confused as to what sort of subjects you would intend using with this set up, as with anything like these sorts of parameters, I don't think there would be any need for stacking. (Since it only really comes into its own when the depth of focus cannot be achieved in one shot).

The fully in focus depth of field of a 150mm lens set at f11, and focussed at 1m would be in the region of 20mm - so any subject thinner than 20mm wouldn't need stacking. (And by using smaller aperture, substantially thicker subjects wouldn't need stacking).

Focussed at around 1m, a 1:1 macro lens would be giving images at best of about 0.3:1 magnification ratio, so such a set up would only be of use for relatively large subjects.

I've done stacking on fairly large fungi at that sort of distance, and three/four shot stacks at f11 (which are very easy to do manually and certainly wouldn't warrant an automated slide), usually get the full mushroom in good focus front to back.

Regards,
Mike.

[Jim Ford]

I've had a look at the Stackshot page.

It's interesting that in spite of the degree of automation, the user has to enter the "number of motor steps or distance".

The distance made by each step is dependant on the depth of field, which is dependant on the focal length of the lens, the lens aperture, the distance to the nearest point of the subject and the diameter of the circle of confusion. The number of motor steps is dependant on the step size and the distance to the furthest part of the object.

With the Stackshot all the above has to be calculated by the user. Why haven't they made the software do this, so the user only has to enter the lens data and subject near/far distance, as I propose doing?

Jim

[Bruce Williams]

Jim,

StackShot provides an "auto-distance" mode where the user first enters the step size (ensuring some overlap) then uses the StackShot controller (FWD and BACK buttons) to move the camera to the nearest point of focus (press button to store position) then uses the controller to move camera to furtherest point of focus (again presses button to store position).

Stackshot will then calculate the number of steps required. On initiating capture, StackShot will control camera and rail to raise-mirror/pause, fire shutter, move reqd step distance, pause (user set time) and repeat for calculated number of slices.

Using this method the only work the user has to do is calculate the step size (selecting nearest and furtherest position obviously can't be automated any further).

However I agree by inputting lens info greater automation would be possible.

Bruce

[nightshade]

Originally Posted by Jim Ford

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

Jim

I have just made a macro/stack table from a couple of fotomate rails, so I was locked in with that type of idea.
Anyway I seemed to remember an interesting project using Lego gears.
Lots of it on You Tube, enjoy ‪Remote Follow Focus Concept Testing‬‏ - YouTube
http://www.youtube.com/watch?v=it8ij1hFrFE
Now imagine the fotomate being driven with the lego g/box
http://www.supaprice.co.uk/p/result....&q=lego+motors

[nightshade]

A manual Kinex system ‪DIY Follow Focus using K'nex‬‏ - YouTube