Exposure time range

What should be exposure time for rpi high resolution build?
By default it was above 32000, is it ok? I had to reduce illuminator led pmw < 10%
Is it any guid showing how to setup the height of the illuminator, go correctly go through optic calibration process.
Thank you in advance

any change to increase depth of filed?

The exposure time should be reset to its minimum when you run through the auto-calibrate routine for the camera (this is available in the “settings” tab). I have usually found it’s fine a bit below the 32ms maximum imposed by the 30fps video stream, though you can decrease the video frame rate (also in settings) if you need more.

In general, unless you have an extremely sensitive sample, you’re probably better reducing the exposure time rather than reducing LED brightness with PWM - though if you are using a Sangaboard 5 I believe the PWM frequency is high enough that you shouldn’t see any flickering.

We need to improve our documentation on aligning the condenser - the simple answer is that if you hold a piece of paper underneath it, you should be able to find a spot (~1mm across) where the light focuses. The aim of aligning the condenser is to place that spot on your sample.

To increase depth of field of the illumination you could reduce its numerical aperture - the easiest way to do that is to remove the condenser lens (or, if you’d rather not risk damaging it, print a new condenser without a lens). That will give much greater depth of field, at the expense of resolution.

To increase depth of field of the microscope objective you’d either need to sacrifice resolution or use Z-stacking (which is my preferred option).

Thank you for your help.
It looks like exposure time value is not update on UI after calibration till system reboot.
Anyway, it seems to be working.
As far as i undestood the LED PWM should be set to 100% before auto calibration ?
And one more thing, what is CC slider for on Sangaboard extension screen? I keep it set to 30% but not sure what it does :slight_smile:
Thank you in advance.

What you set the lamp to for calibration depends on how you would be using the microscope. Set to 100% there is nowhere to go if you have a dark sample, but there is of course the auto exposure function to adjust the gain and shutter speed for that. Set a bit lower to start with you can use the lamp to adjust up or down for the image brightness.

The extension controls will need @filip.ayazi to explain. I think the CC and PWM relate to different pins in Sangaboard v0.5.

Thank you.

As William said the CC and PWM sliders refer to different illumination option. The Sangaboard has a built-in programmable constant current driver (CC) which is used to control illumination brightness when using the LED board from the illumination kit or if wiring an LED directly. This will provide 0-100mA of current.

For higher power LEDs, there are two PWM channels, with larger MOSFETs and 1.5 Ohm series resistors for current limiting, which for typical LEDs results in ~1A of peak current, so with PWM this can results in 0-1000mA for the LED (a heatsink is strongly recommended for high power).

So depending on your wiring you want to use one of the three sliders to control brightness.

Thank you for explanation. So it means that when I use the LED illumination kit i bough together with the sangaboard, i should connect the led to cc pins, instead of PWM1 as it done now.

Yes, that is correct, it should be plugged into the CC pins on the LED header.
The LED on that board can only take 150mA continuously, the PWM system will drive it a lot harder than that at full power (hard to say how high the peak current will be due to the increase in forward voltage, probably 400-600 mA).

Thank you.

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