Effective Aperture=Nominal Aperture x (magnification +1)
Originally Posted by BetterSense
So, in your case (above) EA=22(1+1)=44
The Z stacking is superior but as David points out this is an analogue site, so instead the OP could use a psuedo stacking technique developed long before digital shenanigans. That would be all analogue scanning photomicrography. The idea is simple and obvious but devilishly difficult to execute. The trick is to illuminate the subject with a sheet of light of a thickness equal to approximately the depth of field of the lens while simultaneously focusing the lens at that illuminated sheet. The subject is then moved thru the sheet of light while the shutter is open, exposing the entire subject during its transit thru the plane of best focus and illumination. Since the shutter is open during the extended exposure time (typically 10 to 30 sec.) the room needs to be darkened to avoid extraneous light fogging the film. The key advantage is that if the plane of light can be made as thin as the depth of field of the lens at a moderate aperture - say f/8 or 11 - pretty decent resolution can be realized over a large distance. The subject needs to be translated thru the focus plane at a uniform velocity to avoid banding of the lighting uniformity. One can use either a stepper motor or even gravity thru a dashpot connection for translation. I have done this in a vertical setup with translation in Zaxis and dual slit illuminators horizontally positioned in an X and Y plane. Lots of setup here but it gets the job done with superlative results.
Nate Potter, Austin TX.
Ok guys, lets get it right. It's Photomacrography not Macro Photography.
Right, now...since we're on an analog forum....
Forget Z stacking & look up "light scanning photomacrography". Simple.
Yes, you need to find, or build the equipment, but the results can be stunning...especially on LF.
Sorry, should have read the previous post first
Nice to see someone else has enjoyed this technique Nate!
Last edited by Philip Taylor; 04-24-2013 at 06:22 AM. Click to view previous post history.
I use a Nikon 55/3.5 at that ratio quite a bit, and keep the lens at f:4 which means f:8 working aperture. You're working at f:45, and diffraction is giving you mush. Your lens is limited to 33 lp/mm at that stop (assuming the film is recording everything the lens gives it), when you enlarge it to 8x10 that becomes about 4 lp/mm on the print.
Originally Posted by BetterSense
Sounds interesting, but I'm slightly confused. Surely if you're moving just the subject (with illumination plane, camera and focal plane all stationary) then you're just going to get a smear unless the shape of the subject is extremely constrained so that no two parts at different depth image onto the same part of the film?
Originally Posted by Nathan Potter
Wouldn't it be more accurate (obviously more difficult) to slide the focal plane and the illumination plane through the subject while keeping the subject/lens distance fixed? It'd mean that the light and film back go in the same direction but at different speeds unless the magnification is 1:1 and doesn't vary much through the depth of the subject.
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You're still making a 2 dimensional image of a 3D object, so as you say, no two parts of the object are exposed onto the same piece of film. If light hits a part of the object underneath another which has already been imaged, the first piece is blocking the now illuminated part (from lens viewpoint), so it is never imaged.
Originally Posted by polyglot
There are some issues with the technique:
Because camera, light sheet (& focus) are all set, and the image is only made at that plane as the object passes through it, magnification is constant, and therefore perspective doesn't work as it normally would. "Leading lines" no longer exist, and objects look a bit flattened.
A sphere would lose it's expected shape, I imagine.
To create a light sheet, often two boards in the shape of a donut are sandwiched 1 or 2mm apart from each other (we used brass spacers), then 3 lights are placed 120deg from each other around the edge, directed into the centre.
This works well, but if the object has holes or depressions in it, they may not be illuminated as it passes through the sheet - the end result is an object with a deep shadow in the said depressions.
But, for a sphere, this isn't an issue.
Not sure if that makes things any clearer or worse.
Yeah, that helps; thanks. As you say, there is a loss of the perspective and my concern is that the change in projection could cause overlaps. Can't as I know for sure though.
My Sinar 4x5 has 28 inches of bellows, so I'd just grab the thing and be done with it. It would faster than reading thru all the foregoing.
Drew, there's no way that either of us, with our antiquated gear, can get the infinite depth of field at any magnification that confocal techniques do. That said, confocal techniques can't be used in the situations where I've shot at high magnification.
Originally Posted by DREW WILEY
Around the turn of the century, one of my collaborators who was also chairman of a college biology department, scraped up $250 k and bought a shiny new confocal microscope. He remarked to me that his professors had better get a lot of good publications with it.
What you need Dan is a scanning electron microscope - no good for color, however. I don't think a mere
250K will buy one of those, however ... perhaps a used one.... And confocal techniques per se won't resolve critical diffraction issues. Apochromaticity at high magnifications requires a very specialized kind
of hybrid correction, way out of my $ league. I'd be happy just to have one of those Zeiss research microscopes like I used in college, along with a sheet film holder. They're common, but still in demand
enough to be expensive. The Polaroid holders could be adapted to standard sheet film I think. Or the
Sinar system itself can be adapted to high magnifcation work - you just need a very stable base column
and a lot of rail sections and bellows. I don't really understand all this fuss, however ... unless someone needs 1:1 or some other fixed scale of reproduction, the larger film at smaller aperture will
give better results, and in something printed small like publication, it won't matter anyway. Sometimes
it's fun to look at images on Nikons "Small World" site. Most are false color and taken with expensive
gear from their medical imaging division.