macro photography: generating a plane of light?

[dh003i]

Another thing I wonder is this...assuming you have a 6in diameter slit-cylinder around the sample, the circumference is 18.8in or 479mm. You'd need 958 pieces of 0.5mm fiber optics arrayed around it to surround it with a "circle of light". This would probably require pieces of fiber-optics ranging from 2 to 2.5 ft long, and would be pretty expensive (not to mention a pain to assemble). I wonder if the same amount of light focused into fewer pieces of fiber-optics, arrayed in intervals around the slit and pointing to the slit's center, would approximate the effect? Presumably, light exits fiber-optics diffusely, which is why you can see the light exiting them from the sides. Hence, I'd think light exiting one piece of fiber optics should be "seen" by all parts of the sample along the plane.

Another possibility is to use a circline bulb to get light through the slit, but the a lot of light from the circline would be wasted, resulting in exorbitantly long exposures. (if going the fiber-optic route, I'd make a DIY gooseneck illuminator with a bright CFL source and a reflector bouncing most of the light into a fiber-optic bundle).

[Nathan Potter]

A .0005 inch (12um) slit beam width as you suggest needs to be captured by the equally narrow .0005 depth of focus of the camera over the FULL field of view. I don't think any view camera setup can really do this - the alignment adjustments are just too tricky. I had considerable trouble even at 250 um beam width.

When I reduced beam width (IIRC) to about 100 um I removed the back of the camera and mounted the 4X5 film holder onto a tilting stage (see Newport again) with micrometer drives. This Newport stuff is expensive but comes up occasionally on E*ay.

Yes, you perceive the the reduced intensity issue correctly. The halogen illuminators that I used were extended sources so the intensity reaching the first slit is the result of the integral of all points on that extended source. However the second slit eliminates off axis rays as a function of its distance inside the first slit. Use a meter at the first slit then I think you can use geometry roughly to estimate the intensity exiting the inside slit that reaches the sample.

The dashpot deal is ancient technology, as pointed out, but quite inexpensive. I can't remember any significant initial velocity ramp. Of course there has to be, but I think it is small and may have more to do with the compressibility of air than an inertial phenomena. Stepper motors sure are elegant.

Nate Potter, Austin TX.

[dh003i]

A .0005 inch (12um) slit beam width as you suggest needs to be captured by the equally narrow .0005 depth of focus of the camera over the FULL field of view. I don't think any view camera setup can really do this - the alignment adjustments are just too tricky. I had considerable trouble even at 250 um beam width.

When I reduced beam width (IIRC) to about 100 um I removed the back of the camera and mounted the 4X5 film holder onto a tilting stage (see Newport again) with micrometer drives. This Newport stuff is expensive but comes up occasionally on E*ay.

Wow, this is seeming like a very challenging project! Part of my purpose in doing this is to be able to make large enlargements of macro-shots while maintaining DOF...say 5 - 10x enlargements. I don't think a 100 micrometer (0.1mm) slit would allow doing this, except above f/4: e.g., at f/5.6 from 2.7-3x or at f/8 from 2.7 - 6x. There are a lot of Newport manual micrometer tilt stages, do you have a recommendation?

Isn't the 4x5 snap-locking mechanism supposed to position the rear and front standards parallel to eachother? And then the copystand is supposed to position the camera film plane parallel to the stand surface?

Although maybe the issue is the precision of this positioning? But if it is a copystand, it should be pretty precise, right, as perfect parallelism is needed for macro work? In any event, it seems like maybe the weak link would be the positioning of the standards parallel to eachother, the film flatness, and the precision of the alignment of ground glass with film plane when film holder is inserted.

Why not first align the camera as best as possible to be parallel to the stand surface, then align the plane of light to be parallel to the film-plane via some kind of precision tilt stage? This seems like it would be easier than aligning the camera itself.

Yes, you perceive the the reduced intensity issue correctly. The halogen illuminators that I used were extended sources so the intensity reaching the first slit is the result of the integral of all points on that extended source. However the second slit eliminates off axis rays as a function of its distance inside the first slit. Use a meter at the first slit then I think you can use geometry roughly to estimate the intensity exiting the inside slit that reaches the sample.

Thanks, this makes sense.

The dashpot deal is ancient technology, as pointed out, but quite inexpensive. I can't remember any significant initial velocity ramp. Of course there has to be, but I think it is small and may have more to do with the compressibility of air than an inertial phenomena. Stepper motors sure are elegant.

Nate Potter, Austin TX.

Yea, if I can get a precise motor at a reasonable price, I will.

[dh003i]

well combined with your initial idea, you could leave the edges clear and put a circular flourescent light around the edge. You could make the disc of epoxy to custom fit the bulb exactly, and wrap the whole thing except the interior hole in reflective foil. A flourescent bult glows from the edges though, not the center, so a narrow interface with the bulb would be useful. You'd have to have the disc as thick as the circular fl bulb if you wanted to get as much as 1/2 the light from the bulb, and taper it inwards quickly toward the subject. So the disc would take on a concave shape.

are you talking about something like this, with a ballast made around the circline bulb that is attached to the slit-creating cylinders which create the plane of light. The circline and ballast around it are shown in cut-out along the cylinder, with the gray inside the ballast representing a mirror surface.

Attachment 44668

Hence, some of the light not directly in line with the slits might be bounced around so it goes through the slits.

[Nathan Potter]

dh003, the very difficult alignment I was referring to is that of getting the slit beam of light parallel to the film plane at the rear standard, not to mention the front and rear standard parallelism consistent with the extreme shallow DOF you might require for significant enlargements.

I don't remember what lens you are using but given that the maximum aperture would be about f/4 then the Depth Of Focus (DOFo) would be about 100 um at infinity and would double at 1:1 mag. to 200 um (8 mils). Your resolution would be determined by your slit of 12 um but my point is that all of that 12 um slit of illumination would need to fall within the 200 um DOFo over the whole 4X5 frame, and preferably centered within it. Very tough setup to confirm, let alone adjust to - hence tilting stage for the film plane. I had our machine shop hog out the center region of a large tilting stage to 4X5 dimension then slapped the holders against the back side of the stage. Focusing with a dummy machined holder with a GG at proper distance from the stage surface (0.191 inch IIRC).

The specific stage I can't recall but I'm guessing it was about 8 inch in x and y.

Nate Potter, Austin TX.

[dh003i]

Nathan,

I'm having a Micro-Nikkor 55/2.8 and Tokina AT-X 90/2.5 rigged by S.K. Grimes to reverse mount to a 4x5 board, with a Polaroid MP-4 shutter mounted on the subject side. These are 35mm lenses, so I've calculated that I'll need 2.8x or greater to cover 4x5 (163/43 - 1 = 2.8). I'd be working with enlargements of up to 7x or so..

According to my calculations...at 7x, assuming a 5x enlargement and 5 lp/mm for the final print, DOF at stated f/5.6 (effectively f/45) for a symmetrical lens (micro-nikkors are "nearly symmetric") is 0.073mm (73 µm). f/5.6 is the largest stated f-stop at 7x that can be used and give a 5x enlargement. At 2.8x, things are easier and a 5x enlargement can be obtained even at stated f/11 (effectively f/42) and DOF is 0.427mm (427 µm).

I wonder if the zig-align system can help with aligning the standards at the macro level?

In any event, as you've suggested, seems like quite a challenge.

I think that perhaps the entire dashpot + light focusing slit assembly could be placed on a Newport dual-axis tilt stage like one of these (they support 15 lbs), with a rigid metal platform screwed onto the stage. They have a precision of 2 - 11 arcseconds (2/3600 to 11/3600 of a degree).

Then the other difficult thing would seem to be film holder fidelity to position of ground glass and film flatness :-( If the film isn't flat in the holder, that's a big problem. I haven't noticed any problems with my film flatness on my Graphic film holders or with the holder positioning not being precisely aligned with the ground glass... but flatness and precision have a different meaning at >1:1 than at landscape magnification ratios.

[dh003i]

dh003i, to answer your questions from above.

1. I used a Newport XY stage single section with a connection to the dashpot piston directly below. The dashpot has an air bleed valve that adjusts the rate of descent of the free falling stage. Travel was about 4 inches for the stage and dashpot.

Thinking out loud, I think that the Velmax A1506D-S1.5 ($236) or Velmax A2509D-S2.5 ($346) may fit the bill. They have a worm-drive that is disengage-able ("Rapid advance") by a kind of clutch-like mechanism. Haven't been able to find any long enough free-falling Newport stages. They'd just need to be stood up perfectly perpendicular to the ground by some mechanism, and a perpendicular stage mounted to the sliding stage.

[Dr Klaus Schmitt]

To re-invent such an old system surely makes a lot of fun, just for the experience of doing it!

When it is about achieving high resolution macros with extended DOF, modern stacking techniques have left these older methods way behind. An excellent source to see that at work (incl. lots of technical discussions) may be found here: http://www.photomacrography.net/forum/

[Nathan Potter]

Klaus, many thanks for the photomacrography site alert. I was not aware of the stacking technology, but I can see the technique is a logical development of digital capture and computer software. Especially the Zerene Stacker software discussed seems quite highly developed.

At the resolution that dh003i is talking about (say 12 um slices) a one inch DOFo equivalent is 2000 slices, certainly requiring automated stepping with digital camera sync. He appears a serious fellow so should certainly evaluate this technique, since the lighting challenge would be greatly simplified.

Nate Potter, Austin TX.

[dh003i]

Thanks for the reference to image stacking. I've heard of stacking techniques before, and actually have a program, KImageFuser (uses enfuse) that is capable of stacking. It is certainly great for any format where you have a digital sensor. But There are no sensors for 4x5 (only >$6K scanning backs) which can take 1-5 min to scan...at 2000 slices, that's a lot of time! Even with digital, it is a lot of time. I don't know if there are reducing backs for digital MF, but digital medium format is >$20k.

I am seriously interested in photography...as a hobby. I'd like to get a website up for my work eventually, but the equipment for digital macro on a 4x5 just isn't feasible for me. I'm trying to keep this project under $1k :-). So-far, that seems feasible (well, especially if I dissociate the SK Grimes fab cost of reverse mounting a Micro-Nikkor 55/2.8 and Tokina AT-X 90/2.5 to a board...as that can be for 4x5 macro in general).

I do have an Olympus E-3, and stacking is of course feasible with that, and because I need much less magnification with my E-3 to fill the sensor, maybe manual focus stacking is more feasible.

Btw, if you use a precise Velmax positioning rail or something to control the focus stacks, I'm not sure that automated stepping with digital camera sync is necessary. For my E-3, I could just attach a remote shutter, advance the stage, take a picture, repeat...many many times. (ok, so automated stepping would save a little bit of time and be a lot more convenient...I figure it'd save a second or two for each slice and would of course allow me to do other things in the meantime).