DSLR Scanner: Light Sources

[Serge S]

Standard light boxes aren't ideal for two reasons. First, most have very noticeable hot spots. My Porta-Trace one certainly does. Second, at these magnifications vibration can be a real problem. If you have a Canon with the EFSC shutter mode (See: http://krebsmicro.com/Canon_EFSC/index.html), then you can probably do what you like, but if you don't have that super-low vibration shutter, then you probably want to avoid timed exposures in the 1 second to 1/15th of a second range. Using flash correctly minimizes the problems with vibration, but there might be issues with consistency, although that hasn't been a problem for me so far.

Thanks Peter. I am planning to upgrading to the 5D2 at some point. I see that it has that shutter you are referencing
Sounds like the Illumitran Idea was not half bad, as it is electronic flash

[rdenney]

I just managed to score a nice Illumitran, with the contrast device. I'm thinking a mirror might be a useful thing with that and my setup. I'll know more when it arrives.

Rick "who recently put eyes on some old work with 35mm Kodachrome that will see action again" Denney

[ludvig friberg]

The uneveness is not a big issue at least not for me. I have done some testing where I take a picture of the lightsource and use to divide the uneveness from the lightsource. This also takes out any vignetting and dust on sensor. If I have a piece of the film with no exposure I can also divide out all colorshifts from the lightsource in combination with the orange mask. I haven't tested how important CRI is yet. I have one some exposures with a Canon speedlite flash and some LED sources but I don't know the CRI rating of any of them. Xenon bulbs is far from perfect I believe and LED even worse most of the time. I get pretty decent results anyway. I am going to try out sunlight when it stops raining and see if there is any big difference. Sunlight of my test neg should provide a nice perfect reference. I have looked at some new halogen bulbs called solux that have a very good CRI and are used by kodak in the Pakon line of scanners.

[Peter J. De Smidt]

On an email list, Ernst Dinkla, a very knowledgeable scanner, printer and tinkerer, said that with BW film his Coolscan does best using only the blue LED. (Using Vuescan he can turn off the red and green leds.) He theorized that due to the shorter wavelength the scanner could capture more detail than when using all of the leds. He posited that with a dslr scanner using green light for BW film might be best, as most dslrs have twice the number of green sensors than blue or red, and it would avoid the longest wavelength, i.e. red. Since I wanted our scanner to work in color, I've been working with a white source. I also thought that getting info to all of the camera's sensors might be a good idea, but Ernst's idea is definitely worth looking into for BW scanning.

[ludvig friberg]

I have done quite a lot of testing on color neg lately. I have tested different LEDs, flash, sunlight, tungsten in my dslr scanner up against a hand tuned scan in Nikon coolscan 8000ed. With handtuned I mean I have dialed in the orange mask by changing the exposure of the red, green and blue LEDs in the scanner to get the best possible AD conversion from the sensor. This is my gold standard right now. I get pretty good separation between the cyan, magenta an yellow inverse dyes from the Nikon butI have never scanned on anything better than the NIkon so I dont know how good separation I should try to achive. I have no idea what wavelenghts the leds in in the 8000ed has but I assume it is as wide as possible to cover the very varying dyes in different films.

The conclusion of my tests so far is that tungsten is by far the best artificial lightsource for negative color film. This is quite obvious if you think about it, tungsten is full spectrum so it covers all parts of the dyes. With the LED and flash I get much poorer separation between C,M and Y. It is of course much to warm(Kelvin) so I use full CTB filter, this takes a lot of light so I need a lot of Watt. Either that or one exposure for the red channel and another one for the green and blue. Probably I will need something like 1500 lumen from the lightsource. I will have a relay so it turns the light on only for a second or so when its exposing. Also any fans will turn off a second before exposure. And then dimmed for setting focus and general setup, the live view autoexposes and shows a nice image with some more iso and full aperture. I will try in the future to do the Infrared too and then tungsten is very handy, lots of IR is emitted.

Another solution I have looked at is seperate leds in a matrix and a diffusor. Either rgbleds plus IR or led in a pattern of: red, blue, green, IR, red, blue etc. Here you have to really choose your wavelenghts with precision I think most leds are quite narrow.

This one is a cheap and very customizable platform for something like this.

http://evilmadscience.com/productsmenu/tinykitlist/75

or this one for a smaller lightsource like mine
http://evilmadscience.com/productsmenu/tinykitlist/157

I have built the first stage of motion now and I have solved all the programming and control of the machine. Are working on the negative holder now, waiting for parts to finish the stage.


best regards

Ludvig

[Peter J. De Smidt]

It's great to hear about your progress, Ludvig. Nice work! Are you using an Arduino to control the motion? (Although we should probably switch threads if we discuss that aspect of the project.)

[Daniel Moore]

Very exciting developments, Ludvig. Please tell us more about your design so far.

[Peter J. De Smidt]

Heat reflecting or heat absorbing glass could be helpful with a tungsten source, ala many enlarger heads. If someone goes this route, using a real enlarger head could be a very viable alternative, especially if they have one laying around.

[cosmicexplosion]

i have absolutely nothing to contribute to this fred, except maybe a bit of cheering from the side, GO YOU MAD BASTARDS!!!!!

[Peter J. De Smidt]

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