Messages

76

Chronos User Discussion / Re: Let's talk LENSES!

« on: July 23, 2017, 04:50:49 AM »

I searched for a bit and I can't find a F to C-mount focal reducer. I guess we need to ask on photography forums if this kind of focal reducer exists.

77

Chronos User Discussion / Re: Let's talk LENSES!

« on: July 22, 2017, 03:45:22 AM »

@Dan Kanes I'll not argue more on the subject and I'll wait to have the camera and some F-mount lenses (already bought a F to C mount adapter) to compare to some real C-mount lenses (actually the Computar 12.5-75 mm and some other small lenses for CCTV) so I'll see by myself who is right.

@ExaltedDuck As said I have the Computar 12.5-75 mm f1.2 which should be perfect for most shots (excepted macro maybe) and I have some small CCTV lenses I was using for CCTV but maybe one of them will do good on the Chronos (or maybe they're all too crappy...)

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Chronos User Discussion / Re: Let's talk LENSES!

« on: July 21, 2017, 12:08:13 PM »

Even without a reducer you can still use it without any problem, you just need to put the camera farther away and/or use lens with a smaller focal length

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Chronos User Discussion / Re: Let's talk LENSES!

« on: July 21, 2017, 04:04:43 AM »

A 50mm lens made for a 35mm camera will offer the same field of view as a 50mm lens made for 2/3" or 16mm.

Actually, no, the "A lens is a lens is a lens, and it doesn’t know what size sensor or film gate is placed behind it." is exactly why we have the crop factor. Please see https://photographylife.com/what-is-crop-factor and https://www.bhphotovideo.com/explora/photography/tips-and-solutions/understanding-crop-factor and https://en.wikipedia.org/wiki/Crop_factor

This means that for our 2/3" sensor the crop factor is almost 4, so a 50 mm lens on 2/3" sensor will have the same effect as a 200 mm lens on a 35 mm sensor, and what ExaltedDuck said is spot on (except the reference sensor isn't 4/3" but 35 mm).

80

Chronos User Discussion / Re: User Manual draft - Comments/suggestions/revew requested

« on: July 14, 2017, 02:33:31 AM »

According to the manual there's a "Safely remove" button in the save menu. I don't know if it's here or if it'll be added later, but you should use it if it's here to properly unmount the storage device.

81

Chronos User Discussion / Re: EV Tables?

« on: July 07, 2017, 04:11:46 AM »

Ok, so to make a very short 101 explanation:

- ISO: is the sensibility of the film (or sensor). Higher ISO means more sensible so less light needed.
- shutter speed: is the time the film or sensor is exposed to the light. Higher shutter speed means less blur on the image but also a darker image (the light has less time to expose the film or sensor).
- aperture or f-stop or f-number: is how open the diaphragm is. Higher f-number means a diaphragm less open so less light but more depth of field.

All of those are independent settings.

NB: with digital camera you only have one sensor so you also have only one ISO sensibility (you can't change the film for another one who is less or more sensible as the film is the sensor...) but you can add gain (amplify) after the image is taken, however it doesn't make the sensor more sensible, it's like the brightness setting in photoshop for example, you amplify the useful signal but you also amplify the noise (example of a noisy image: https://en.wikipedia.org/wiki/Image_noise#/media/File:Highimgnoise.jpg) so you can't add 24 dB of gain and expect a good image quality (but if you're already maxed out on the light, the shutter speed and aperture settings you have no other choice...).

NB²: a rule that can be useful https://en.wikipedia.org/wiki/Sunny_16_rule

I bet there's a lot of tutorials on the web on how to use a camera in manual mode for beginners so you can read those while waiting for the crash course chapter in the Chronos' manual.

82

Chronos User Discussion / Re: EV Tables?

« on: July 06, 2017, 12:05:44 PM »

Ok, so if we take the minimum ISO for the color camera (ISO 320) and this calculator: http://www.scantips.com/lights/exposurecalc.html in manual mode we see you'll have a 3.8 EV difference between the two lens. We also see that with 4.5 you'll need 16.3 EV (very very bright sunny day) and with f/1.2 you'll need 12.5 EV (overcast) for a shutter speed of 1/4000 (= 250 µs, can shoot up to 4 kFPS). You can add gain to up the ISO and shoot at a higher FPS and or use less light, but you'll also add noise if you do that.

With the other lens you can go up to about 1/48000 (20 µs, up to 48 kFPS but the Chronos max out at 40 kFPS anyway) but you'll have a very very short depth of field.

So you can certainly use a f/4.5 lens but you'll not be able to do much higher than 4 kFPS on a very bright sunny day (without adding gain) so it's not the best lens in the world but it's not unusable either

83

Chronos User Discussion / Re: EV Tables?

« on: July 06, 2017, 03:56:19 AM »

It depends on the light level, not the lens (a lens A with with the aperture (f-number) set to 1.2 will let the same quantity of light enter as another lens B with the aperture set to 1.2), so if you want to make a table you need one table per light level which is not very doable (maybe make only one table with the light level of the sun at noon as it's a good standard?).

I guess the best thing to do is tables of depth of field for each lens as a function of the aperture numbers (and zoom levels if it's not a prime lens) so when you want to shoot something you know the lowest aperture number you can set given the lowest depth of field you want; then you set this aperture and you can then set the others parameters after that. This is assuming you want the lowest aperture number possible (which is pretty much always the case with HS cams as you always want more and more light so you can have a decent exposure and shutter speed...).

84

Chronos User Discussion / Re: User Manual draft - Comments/suggestions/revew requested

« on: July 04, 2017, 05:08:40 AM »

Hi,

I must say it's very well written, you've done an amazing job

I saw only a few little mistakes:

* Page 13:
- I'm not sure but I think "Shows the bitrate and frame rate calculated from the bits per pixel setting" should be "Shows the bitrate calculated from the frame rate and the bits per pixel settings"
- I guess "h264 profile | Sets the h264 encoding level." should be "h264 profile | Sets the h264 encoding profile."

* Page 15
- I think this "The black cal is persistent across restarts and will be remembered the next time you use the same resolution." is a bit unclear as I don't know if the next time I select a previously used resolution I need to do a black cal anyway (as mentioned a bit higher on the page) or if it's not needed.

* Page 17:
- The mentioned max shutter speed is 2 µs but on page 11 it's 1 µs (and I've seen a member's test video taken with 1 µs too)

NB: FAT32 is limited to 4 GB per file so I wonder what happens if you try to save more than that?

85

Software Dev / Re: Initial feedback

« on: June 02, 2017, 11:52:49 AM »

Hi,

I didn't received the camera yet but just wanted to say it would be even better to have color histograms (see why here: http://www.kenrockwell.com/tech/yrgb.htm)

Thanks