Digitalising slide-film with magic lantern

[natschil]

I've been working on a machine for digitalising slide film for a while, and it has reached a point where it is working very well, so I thought I would share

Here is a video of the machine in action https://drive.google.com/file/d/1HwVwULBRlTh9yDRKbw87FjLXRVLTpz3j/view


I'm using an EOS M, together with a modification of ML where I've mapped certain PTP commands to take a picture and adjust exposure times. Because slide film has such a high dynamic range, a single exposure time would not have worked well. I therefore look at the histogram and adjust exposure for each image. If the image is still too dark, I increase the exposure time, take another picture, and then combine both pictures with the enfuse utility. The lens is a 100mm Canon FD macro lens, together with some teleconverters.

I've digitalised several thousand pictures at this point, here is one https://drive.google.com/file/d/1cbxvvk_QhnVmxhfcxLwNyc8-gOdHBt_e/view?usp=sharing

What is slowing things down quite a bit is that setting the exposure time isn't instantaneous. A large chunk of time is spent waiting just to be sure that the exposure being set has been set. Nevertheless, the whole thing is still *much* faster than using a slide film scanner that scans the slide "line by line". The sharpness of the images is limited by the grain of the slides.

This project would not have been possible without ML, thanks a lot to everyone who has worked on ML over the years!

[Luther]

This is great @natschil !
I've been looking to get into film again, but the price of quality scanners is pretty high, such as these ones from Plustek OpticFilm.

What is slowing things down quite a bit is that setting the exposure time isn't instantaneous. A large chunk of time is spent waiting just to be sure that the exposure being set has been set.

Have you tried to do multiple exposures using advanced bracketing and merge them later using HDRMerge or similar software? That way you woudn't need to measure exposure, just do 2 f-stops above and bellow and let the software decide the optimal exposure for each area of the image...
What are you using to precess the image? Rawtherapee added this very nice feature to invert film scans recently: http://rawpedia.rawtherapee.com/Film_Negative

[natschil]

@Luther: That's an interesting idea I hadn't thought of. The downside is that I have to wait between taking pictures also, and doing it this way means every frame need several shutters openings when previously I only take 2 pictures when necessarily.

Note also that I'm not digitalising "normal" analog film but analog film slides (wikipedia says "reversal film") meaning I don't have any negatives. I only really do minimal processing with imagemagick in order to remove black edges, I'm not using something like Rawtherappe because (a) white balance is done in camera as using large raw files would add some more time when transferring the image via usb and (b) I'm using this for fairly large numbers of old film slides (probably more than 10K) where I want to as little manual processing as possible.