Exposure and light

Hi, I’m going to realize a continue scanner for 8mm.
Since I’m planning to scan at least 5 frames per second, what exposure time should I use and how many lumens do I need? What light source do you suggest to use?

My scanner is stop motion, so take the information as theoretical.

Suggestion on how to unpack the question.
As you may have seen in the forum, the lens best sharpness and resolution for the typical lenses used for 8mm is between f4 and f5.6. That’s set.

Film speed motion will give you the camera exposure time, since you need to freeze the movement. A global shutter sensor (search the forum for more info of global vs rolling shutters) will be required.

The lens aperture (set) + exposure for freezing + sensor sensitivity = light required.

Good quality white LED. You will need a lot of light in a short time. You may need to flash it to avoid overwhelming the sensor. This posting provides some info. His scanner is a great example of continuous motion.

Hi, thank you for you reply.
Yes, I planned to buy a global shutter camera → USB 3.0 Camera | 3 Megapixel IMX265 Color | MER2-302-56U3C

I’ve seen these leds that have a very high CRI → YUJILEDS® CRI 98 5W COB LED - 135XL - 5pcs — YUJILEDS High CRI Webstore

When picking up LED, the Spectral Distribution Graphs are an important item. The 3200 K looks fairly smooth, and may be a good option.

I don’t know enough about these cameras. Decide early if that resolution is enough. You can find in the forum both sides of the argument regarding resolution (more is more vs less is more), there are some valid use cases on both sides.

To determine an approximation of how much light you need, check the camera sensor specifications. There is usually some information there. For the particular camera above is the IMX265. Not sure if is this specific version, but let’s use the data for illustration.

In the remarks for the sensor characteristics, it provides the testing conditions: 3200 K, 706 cd/m2,
1/30s accumulation.

The camera specs indicate 56 fps @2048 × 1536 resolution.

Think in photography. When you halve the exposure, you need to double the light. If the sensor needs 3200 K, 706 cd/m2, 1/30s accumulation, to maintain the level at 56 fps, it probably needs double that. And if you are going to flash the light (and it may be required in this case) the time of the flash will determine the light intensity.

Sorry I don’t really have practical experience with global shutter to provide more insight. Hope the information is helpful.

You’ll want at least 3-4 of those LEDs to get enough light. I used the same ones with the same sensor size.
I’d put even more light in there than you need, particularly for very dense, underexposed film
I can’t remember what shutter speed I was using sorry.

The helicoid/extension tube loses a lot of light when setup for 8mm.

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Thanks for your helpful infos.
What if I get something like this? It has integrated fans, it’s dimmerable, and looks to have high CRI

Has anyone tried using these for making integrating spheres.


I have not personally constructed an integrating sphere. Here are some examples from others using cake molds or bath bomb molds. I would be concerned about the interface between the 2 halves (see the 3rd link.) Do the 2 halves form a perfect sphere or form an ellipsoid? If ellipsoid, how does the deviation affect light uniformity?




@justin: that is probably rather irrelevant. I have seen integrating “spheres” realized as a simple styrofoam box. Some enlargers which were used in the old days of analog photography worked with that principle.

More important should be that the coating inside the sphere is lambertian (ideally). That lambertian reflectance realizes the desired random mixing of light inside the sphere by multiple reflections. Small form deviations from the spherical form will not make a too much difference than.

Finally, the openings of the sphere should be sufficiently small with respect to the sphere’s diameter in order to get an evenly distributed light intensity out of the ports.

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@agus35monk I am using 55mm ping pong (oversized) ball, which is decent for an 8mm target. No coating was used, I did select that the visible portion does not have the hemisphere seam or the injection mark.

@justin thank you for sharing these references. The last reference uses this interesting aluminum cake molds, which are available in various sizes. The part looks like a promising half sphere, perfect for light sanding and coating. As mentioned by @cpixip, the relation between the diameter and the port size, and the reflecting surface are critical.

As mentioned prior, imageJ is a great tool to measure the resulting flatness of the illuminant+reflector+lens+sensor+library and provides a great visual representation to confirm the system is flat.