A Confusing method of light control - explain this one if you can!

[Overread]

Ok I've tried to work this one out and failed and tried a few experiments and failed with them as well (though I'll admit my setup was very crude and might have hindered getting the proper result).

The basic approach is something I found a guy working on where he has a stactic camera, static focal point and a stactic thin beam of light. The subject is then move through the beam of light very slowly whilst the camera take a shot in bulb mode - the result being a shot with increased depth of field after the subject has moved through the light beam.

However I've tried to recreate this (using a flash rather than constant light source, but the single strip of light remains the same) and got what I expected - a messy mess of a shot (ok so I might have to work on the exposure part a little more). But even just considering the concept I can't see how it works as to my mind the subject should end up with blurr as the focal point remains the same whilst the subject moves through it.

So does anyone here have a better understanding that might explain why this works and how?
For additional refrence the original source I found this method on: my set up for long exposure scan | Flickr - Photo Sharing!

I spoke to the photographer in question and he said this:

"You would think that things could merge but it doesn't happen as far as I can tell. Light on a part of the object behind that has part of the object closer to the lens is hidden from the sensor by that part so that the part already recorded on the sensor remains intact - if that makes sense."

though it still leaves me confused as to how it works. Be interesting if anyone can recreate the effect - might be then that we start to understand the process a little better.


Also just to repeat - this is a Single shot (in bulb mode) and not the result of multiple shots stacked with software - the stack shot used is only to move the subject with a constant speed through the light beam

 

[tirediron]

You owe me a bottle of aspirin!!!

 

[Garbz]

No he's right. The subject would not be a blur providing a sufficiently thin lightbeam is used. Effectively as the subject moves through the continuous beam towards the camera. Try this in bulb mode quickly take a 1 second photo while moving the camera forward. Notice that the middle remains reasonably sharp and the blurry things are the ones moving past the camera on the edge of the frame? Now remember we're talking macro, and often long focal lengths. There's nothing moving past the camera only towards the camera.

If the camera wasn't dead on front to the subject you'd get some fierce blurring.

That said all of this has a major downside. The photo has effectively zero perspective. It's the equivalent of taking a photo from infinitely far away with an infinitely long telephoto lens. Everything appears to be at exactly the same distance from the camera. Arty, creative, but personally I think it looks like arse and far prefer the focus point stacking methods in photoshop to achieve incredible depth of field.

 

[Overread]

You owe me a bottle of aspirin!!!

You'll have to wait your turn I'm afraid

If the camera wasn't dead on front to the subject you'd get some fierce blurring.

Ahh now I think I know why my test shots at this failed to work as I was trying it at an angle rather than head on.

Thanks for the explanation as well I think I now sort of understand it a little better and at least know the one thing I was getting wrong so I might have another go tonight and see I can recreate it. I agree its tricky method as far as light and exposure control go so its probably not something I'll make a big use of, but I like knowing of its existence and it might have a place/use in some circumstances.

 

[dylanstraub]

You could also change when th flash fires. Mine allows you to change it to second curtain which seems to help with the blur sometimes.

 

[bazooka]

Dylan, he is firing multiple flashes during a single exposure while moving the subject between each flash, closer or further away. Motion blur is irrelevant because there is no motion captured by the sensor.

Interesting idea... are there any examples?

 

[Overread]

The only examples I know of are in the flickr stream that I link to in the first post - which is where I discovered the method.

Also talking to some others who've used this method with microscope photography apparently you gain no depth of field for the working aperture over just a single exposure. So whilst it clearly has a use it might be more limited to specific microscope work .

 

[Garbz]

Well no you don't gain depth of field. You effectively gain flattening of the entire field into the depth of focus.

It's sharpness but not increased depth of field.

 

[dylanstraub]

You owe me a bottle of aspirin too.