Making a scanner with a DSLR

[Peter De Smidt]

These are great ideas. This project has the greatest chance of success if we get lots of good input.

Right now, I'm procrastinating about going out into the unheated shop to finish my first reasonably complete prototype.

Regarding a collimated light source, would the following work? Take a piece of aluminum flashing, such that it'll cover the front of a flash. Make a round hole in the flashing directly over the front the flash reflector such that light is only let out that hole. Would that be a possible replacement for a halogen light in Nathan's sketch?

Another option would be to use an LED. A high intensity 3w Cree would probably produce enough light.

[Ben Syverson]

One thing to keep in mind when it comes to light sources... Ideally the color temperature of the light will closely match the "native" WB of the sensor. For most sensors, I think this is close to daylight. As you move to other color temperatures, you increase noise in the color channels.

Another option for color negative is to gel the light until the orange base of the negative is photographing as a neutral gray. That way you're not having to subtract the mask digitally. The less you have to push the image around digitally (whether in-camera via WB or on the computer via Photoshop), the better.

[Bob Salomon]

At Peters suggestion here is a concept drawing for a DSLR scanner that I posted in another thread. Clearly this is where there is activity on this, so here it is. No big deal, but this is how I might approach this in a vertical configuration.

To maximize contrast I suspect that one needs to use a collimated light source. Drum scanners essentially do that by applying the transmitted light through a narrow angle as seen by a detector, typically a lens and thence to a PM tube. For the ultimate in S/N ratio they may use an integrating sphere with a PM attached, although I don't know if any actually use that technology - possibly unnecessary or awkward in the scheme of things.

In my sketch it may be desirable to move the plano/convex condensers up under the X/Y stage for a sort of upside down D2 configuration. I've assumed about 75 mm diameter condenser lenses (Edmund Scientific @ $75 ea.). The point source might be on the order of 6 to 10 inches from the condensers. I've used this arrangement for other purposes with considerable success (it drastically reduces light scattering in the emulsion).

The support system needs to have the stability of an industrial quality microscope and of course exact planarity between stage and sensor is a must since the DSLR wants to be utilized at near maximum aperture. Obtaining a stage with a 4X5 minimum window is a heck of a problem but I was thinking of that from say a Nikon comparitor as used in machine shops - say a junk piece.

This is really a pretty simple lash up if the parts can be obtained. The ultimate problem will be with the collimated light source and the precise imaging of defects and dust that will be a plague. While of no concern for experiments and proof of concept the final version will need a sealed optical path with access for an occasional cleaning.

With luck herewith is a drawing:


SCANNER-3jpg by hypolimnas, on Flickr

Nate Potter, Austin TX

Now look at any Kaiser copy stand + The Novoflex CASTEL CROSS Q + a NOVOFLEX CASTEL COP DIGI and a Gepe Pro Daylight Illuminator or the Kaiser Scan box and you will see what you just designed are off the shelf items and don't need any condensors. Just screw them all together. And, if you use either of the illuminators above you can eliminate the CASTEL COP DIGI.

[Peter De Smidt]

Bob,

I appreciate the suggestions.

The Kaiser Prolite Scan Lightbox 17"x19" looks very nice, which it should be for $2000!
http://www.adorama.com/KRPSLB.html

The Gepe Pro 8" x 18" Slim Pro Illuminator Light Box with A/C Adapter, 1.5" Thick is more reasonably prices at $165, but I don't know how even it's illumination is. See: http://www.adorama.com/GPLB818.html

[Mike Anderson]

Bob,

I appreciate the suggestions.

The Kaiser Prolite Scan Lightbox 17"x19" looks very nice, which it should be for $2000!
http://www.adorama.com/KRPSLB.html

The Gepe Pro 8" x 18" Slim Pro Illuminator Light Box with A/C Adapter, 1.5" Thick is more reasonably prices at $165, but I don't know how even it's illumination is. See: http://www.adorama.com/GPLB818.html

Seems like there's 2 ways to go with respect to evenness of illumination:

1. expensive hardware to provide even illumination
2. cheap hardware with uneven illumination and correct it in software

[Peter De Smidt]

I'm hoping for:

3. cheap hardware with less than 1% variation in light intensity.

I'm close now. It shouldn't be that hard to achieve.

[Nathan Potter]

Peter, a pinhole intercepting light would work but the intensity reduction would be extreme since most of the illumination flux is intercepted by the area outside the pinhole. The way to get around that is to use a double condenser system when using a broad area light source such as a non point incandesant or electronic flash. The setup would use a condenser closest to the flash to focus as much light as can be grabbed from the flash to a point (called a virtual point source) then recapture all that flux further on using a second condenser to correct the rays to infinity corrected (parallel rays as shown in the diagram). The idea is to capture and preserve as much of the original flux as possible through the optical train. While more complicated and difficult to work out experimentally from a uniformity angle using a flash appears to have a big advantage in the way of color fidelity (as Ben says) but also high speed exposure for vibration mitigation.

Hadn't thought about an LED source which could be interesting to investigate; although the spectrum of those show some high narrow band peaks which I believe are difficult to color balance well. In fact the tungsten source would need a CC filter to balance to the recommended color temperature for the particular DSLR sensor - but that should be straight forward.

BTW it would actually be informative to see results from both a diffusive light source and a collimated light source so I wouldn't want to discourage both approaches for a feasibility experiment. Geez, I wish I had some time to fool around with this.

Nate Potter, Austin TX.

[Peter De Smidt]

There's some Cree LED fixtures that are over 90 CRI. I'll look up the link later. Here it is: http://www.cree.com/products/modules_lmh2.asp
See also: http://search.digikey.com/us/en/prod...0TW-ND/2524694


Sawing thick hard maple by hand is tiring. I need a break. Whew!

[peter ramm]

Peter, here are a few links you may find interesting. This stitching system is for microscopy, but discusses some general issues.

http://www.mcid.co.uk/applications/montaging.asp

This macro equipment link is just to show an illuminator that is stable (important because you will be acquiring images over time and don't want brightness variation) and even.

http://www.mcid.co.uk/hardware/map/

The illuminator was about $3000 new but they come up used. For example (no idea what they want for it):

http://www.usedlabequipment.com/lab_...n+light&ManId=

Moving the film is the problem. Ideally, you would just tape it in place on the illuminator and then move the whole thing under the camera on an XY translation table. Some precision is required because any angular errors will kill your correction software. There are gliding stages that you could mount an illuminator on, but expensive I think. eg

http://www.solino.com/cms/index.php?...id=178&clang=0

Don't know if something like this would work.

http://www.visionaid.co.uk/product_view.php?pid=80011

Theoretically, as has been pointed out, a collimated light source is better but implementing one that doesn't actually make things worse takes some skill. Diffuse is easier. Generally, we match collimated sources to scanning optics and diffuse sources to area arrays. A mask can help the flare somewhat, especially if you pick a lens that focuses very close to the film. My favorite lens for this type of thing was the 55 MicroNikkor, which is pretty cheap used I think.

I am enjoying following your progress.

[Peter De Smidt]

Hi Peter,

Thanks for the links. I'll check them out.

I'll be using a 55mm Micro Nikkor for my first tests.