Analog focus stacking techniques

[Michael R]

Agreed - I should have been clearer - the kind of thing I was imagining would necessarily require a lot of masking-type work. As I think about it I’m realizing in the end it would really be more of a compositing exercise than anything else so it isn’t novel anyway - and has pretty much nothing to do with focus stacking.

Think about it - for any given distance in the image field, you'd be recording or printing multiple layers of fuzz on top of a single layer of in-focus. I'd expect the fuzz to dominate. Maybe if it was just two exposures, you'd have two planes that look sort of in-focus, but even those at least somewhat blurred by a haze of OOF stuff. The effect might be pleasing or not, depending on your taste.

It works in the digital domain because the stacking software is in effect filtering out the OOF stuff.

[ic-racer]

You can use a slit light source to illuminate each focal plane of the scene one wishes to expose. If it was easy and worked well, it would be a standard technique, but it is not easy and does not work well.

Most LF photographers use the oldest trick in the books, and adjust the focal plane so the most important parts of the image fall in the plane.

[nolindan]

...something I've always wanted to try (and will sometime soon) - is continuously adjusting focus over the duration of a time exposure. Resulting image will probably look really weird and/or be completely unusable...but who knows? Anybody here try this?

I've done it. It's not really applicable to LF work, though.

You need to use a zoom lens. As a lens is focused it changes it's effective focal length, so as the lens is focused the lens also has to be zoomed to compensate.

The results are underwhelming. Or they were when I tried it. It's very hard to get the correct zoom/focal-focus length relationship. If you want to try it I would set up point-source focusing targets - probably using laser pointers.

[nolindan]

There are three rather related analog techniques: structured light, confocal optics and 2/3 photon imaging.

The plane illumination technique mentioned by IC racer is one of several 'structured light' methods. These find primary use in industrial inspection. The plane illumination technique focuses a camera and a plane of light that stay stationary while the object is brought through the illumination. I played around with this using a razor blade slit in a slide projector for the light plane source - it proved a real PITA. There was a Pop Photo magazine article on the subject showing work at RIT in the mid/late 80's - I think it was called 'confocal photography'.

Confocal microscopy https://en.wikipedia.org/wiki/Confocal_microscopy is used for imaging the interiors of semi-transparent items like cells and cell matrices.

2 (and 3) photon imaging is another microscopy technique used to image the distribution of florescently tagged molecules in biological samples https://en.wikipedia.org/wiki/Two-ph...ion_microscopy I was peripherally involved when I was working in non-linear optics. I was amazed at what a deep dive into the rabbit hole I took when trying to wrap my head around the 'simple' photon.

[Dugan]

In a similar vein...
In college, we were given an open assignment to photograph a chair.
My initial concept was Cubistic...to photograph a chair in the studio with a 4x5.
My plan was to set up a basic studio shot of a chair, and do multiple exposures on one sheet of 4x5, each one with a maximum movement..front tilts, rear tilts, front swings & rear swings.
Interesting idea, but underwhelming... I ended up doing something else.
I probably would have gotten a good grade for the Cubistic concept attempt, but I went a different direction and nailed both concept & execution.

[John Layton]

Just remember...never stop trying the "improbable/impossible" stuff (and do ignore those naysayers!) - because you'll always learn something...and amazing things can happen!

[pkr1979]

True. The naysayers do make sense, but I have some film I can try this with. I'll give it a go.

[John Layton]

"do ignore those naysayers" - in other words, yes, ignore them!

Obviously I always pay attention to well informed suggestions/advice...but even then, I'll often go right ahead and repeat others "mistakes," because...I just want to verify results for myself - and to learn how I might tweak things to make them work (for me).

[newt]

I can recall times when I was much younger when I made bracketed exposures, yet they all were too thin, and I put the 2 negs together in register to make up for the density. Can't recall which images I might have done that on though. Can't say that is analog focus stacking either.

[John Layton]

Newt on the surface of things that might be difficult...due to the necessary vertical separation of accurate focus planes within the enlarger's negative carrier, although I guess this might also depend on subject matter, print size, and desired visual "effect."

Then again...if one were to employ a combination of very thin emulsion films (likely slightly underexposed to accommodate later density build-up) and/or massively stopping down the enlarger lens in the attempt to acquire enough depth of (enlarger) focus to accommodate the focus planes - well?

Or...pin-registering the negatives so that they could be printed in sequence on a single piece of photo-paper (which would also allow a bit of extra headroom for negative densities)?

But oh dear me...there would still be those darned OOF areas rearing their heads! Then again, if the "donor negatives" are both kept to a minimum (in numbers - two or three max) and if each of these can be exposed at tiny apertures to maximize depth within them (to heck with diffraction!)...then just maybe something resembling success could be achieved!

Bottom line...sounds like fun!