Category: Photography & Images

Taking & making images.

Machine Shop, Photography & Images, Science

Arducam Motorized Focus Camera: Depth of Field

According to the Arducam doc, their Motorized Focus Camera has a 54°×41° field of view, (roughly) equivalent to an old-school wide(-ish) angle 35 mm lens on a 35 mm still camera. For my simple purposes, the camera will be focused on objects within maybe 200 mm:

Arducam Motorized Focus Camera - desktop test range
Arducam Motorized Focus Camera – desktop test range

The numeric keys are 6.36 mm = ¼ inch tall, the function keys are 5.3 mm tall, and the rows are 10 to 11 mm apart.

The focusing equation converting distance to lens DAC values depends critically on my crude measurements, so the focus distance accuracy isn’t spot on. Bonus: there’s plenty of room for discussion about where the zero origin should be, but given the tune-for-best-picture nature of focusing, it’s good enough.

I set the CANCEL legend at 50 mm and it’s in good focus with the lens set to that distance:

Arducam Motorized Focus Camera - 50 mm
Arducam Motorized Focus Camera – 50 mm

Focusing at 55 mm sharpens the ON key legend, while the CANCEL legend remains reasonably crisp:

Arducam Motorized Focus Camera - 55 mm
Arducam Motorized Focus Camera – 55 mm

Adding another 5 mm to focus at 60 mm near the front of the second row shows the DoF is maybe 15 mm total:

Arducam Motorized Focus Camera - 60 mm
Arducam Motorized Focus Camera – 60 mm

Focusing at 65 mm, near the middle of the second row, softens the first and fourth rows. Both of the middle two rows seem OK, making the DoF about 20 mm overall:

Arducam Motorized Focus Camera - 65 mm
Arducam Motorized Focus Camera – 65 mm

Jumping to 100 mm, near the top of the first function row:

Arducam Motorized Focus Camera - 100 mm
Arducam Motorized Focus Camera – 100 mm

At 150 mm, about the top of the far row just under the display:

Arducam Motorized Focus Camera - 150 mm
Arducam Motorized Focus Camera – 150 mm

I think 200 mm may be the far limit of useful detail for a 5 MP camera:

Arducam Motorized Focus Camera - 200 mm
Arducam Motorized Focus Camera – 200 mm

At 300 mm the DoF includes the mug at 600 mm, but the calculator keyboard is uselessly fuzzy:

Arducam Motorized Focus Camera - 300 mm
Arducam Motorized Focus Camera – 300 mm

At 500 mm, the mug becomes as crisp as it’ll get and the text on the box at 750 mm is entirely legible:

Arducam Motorized Focus Camera - 500 mm
Arducam Motorized Focus Camera – 500 mm

At 1000 mm, which is basically the edge of the desk all this junk sits atop, the mug and text become slightly fuzzy, so the DoF doesn’t quite reach them:

Arducam Motorized Focus Camera - 1000 mm
Arducam Motorized Focus Camera – 1000 mm

I limited the focus range to 1500 mm, which doesn’t much change the results:

Arducam Motorized Focus Camera - 1500 mm
Arducam Motorized Focus Camera – 1500 mm

I could focus-stack a set of still images along the entire range to get one of those unnatural everything-in-focus pictures.

Electronics Workbench, Machine Shop, Photography & Images, Software

Arducam Motorized Focus Camera: Rotary Encoder and Equation

Mashing rotary encoder reading together with the focus-distance-to-DAC equation produces well-behaved camera focusing.

First, set up another test range:

Arducam Motorized Focus Camera - desktop test range
Arducam Motorized Focus Camera – desktop test range

Run the test code:

# Simpleminded focusing test for
#  Arducam Motorized Focus Camera
# Gets events through evdev from rotary encoder knob

# Ed Nisley - KE4ZNU
# 2020-10-20

import sys
import math
import evdev
import smbus

# useful functions

def DAC_from_distance(dist):
    return math.trunc(256*(10.8 + 2180/dist))

# write DAC word to camera I2C bus device
#  and ignore the omnipresent error return

def write_lens_DAC(bus,addr,val):
    done = False
    while not done:
        try:
            bus.write_word_data(addr,val >> 8,val & 0xff)
        except OSError as e:
            if e.errno == 121:
#                print('OS remote error ignored')
                done = True
        except:
            print(sys.exc_info()[0],sys.exc_info()[1])
        else:
            print('Write with no error!')
            done = True

# set up focus distances

closest = 50            # mm
farthest = 500
nominal = 100           # default focus distance

foci = [n for n in range(closest,nominal,5)] \
     + [n for n in range(nominal,250,10)]  \
     + [n for n in range(250,1501,25)]

# compute DAC equivalents for each distance

foci_DAC = list(map(DAC_from_distance,foci))

focus_index = foci.index(nominal)

# set up the I2C bus

f = smbus.SMBus(0)
lens = 0x0c

# set up the encoder device handler
# requires rotary-encoder dtoverlay aimed at pins 20 & 21

d = evdev.InputDevice('/dev/input/by-path/platform-rotary@14-event')
print('Rotary encoder device: {}'.format(d.name))

# set initial focus

write_lens_DAC(f,lens,foci_DAC[focus_index])

# fetch I2C events and update the focus forever

for e in d.read_loop():
#    print('Event: {}'.format(e))

    if e.type == evdev.ecodes.EV_REL:
#        print('Rel: {}'.format(e.value))

        if (e.value > 0 and focus_index < len(foci) - 1) or (e.value < 0 and focus_index > 0):
            focus_index += e.value

        dist = foci[focus_index]
        dac = foci_DAC[focus_index]

        print('Distance: {:4d} mm DAC: {:5d} {:04x} i: {:3d}'.format(dist,dac,dac,focus_index))

        write_lens_DAC(f,lens,dac)

Because the knob produces increments of ±1, the code accumulates them into an index for the foci & foci_DAC lists, then sends the corresponding entry from the latter to the lens on every rotary encoder event.

And then It Just Works!

The camera powers up with the lens focused at infinity (or slightly beyond), but setting it to 100 mm seems more useful:

Arducam Motorized Focus Camera - 100 mm
Arducam Motorized Focus Camera – 100 mm

Turning the knob counterclockwise runs the focus inward to 50 mm:

Arducam Motorized Focus Camera - 50 mm
Arducam Motorized Focus Camera – 50 mm

Turning it clockwise cranks it outward to 1500 mm:

Arducam Motorized Focus Camera - 1500 mm
Arducam Motorized Focus Camera – 1500 mm

The mug is about 300 mm away, so the depth of field extends from there to infinity (and beyond).

It needs more work, but now it has excellent upside potential!

Oddities, Photography & Images, Science

Chestnut Parasites

I spotted this little gadget chugging steadily across a table in the living room:

Chestnut parasite larva - detail
Chestnut parasite larva – detail

Nearby, two of its friends / siblings / clones remained near their landing craft:

Chestnut parasite larvae - overview
Chestnut parasite larvae – overview

They’re about 5 mm long and, although there are no larva-size holes visible in the chestnuts tucked inside the burr, that’s definitely where they started their journey.

A few hours later, the rest of the crew bailed out:

Chestnut parasite larvae - irruption
Chestnut parasite larvae – irruption

The exit hole must be on a nut under the curve of the husk, but they’re sufficiently squishy to wriggle their way out. The little brown dot over on the left belongs to the top larva of a pair queued in the exit corridor:

Chestnut parasite larvae - exiting husk
Chestnut parasite larvae – exiting husk

I lost count at 18. There’s surely more where they came from, so I replaced the plate with a bowl to reduce the quantum tunneling probability.

In an ideal world, they’d grow up to be chestnut weevils, but I put them out near the suet feeder and, a few hours later, my offering was accepted.

Electronics Workbench, Machine Shop, Photography & Images, Science

Arducam Motorized Focus Camera: Focusing Equation

The values written to the I²C register controlling the Arducam Motorized Focus Camera lens position are strongly nonlinear with distance, so a simple linear increment / decrement isn’t particularly useful. If one had an equation for the focus value given the distance, one could step linearly by distance.

So, we begin.

Set up a lens focus test range amid the benchtop clutter with found objects marking distances:

Arducam Motorized Focus camera - test setup
Arducam Motorized Focus camera – test setup

Fire up the video loopback arrangement to see through the camera:

Arducam Motorized Focus test - focus infinity
Arducam Motorized Focus test – focus infinity

The camera defaults to a focus at infinity (or, perhaps, a bit beyond), corresponding to 0 in its I²C DAC (or whatever). The blue-green scenery visible through the window over on the right is as crisp as it’ll get through a 5 MP camera, the HP spectrum analyzer is slightly defocused at 80 cm, and everything closer is fuzzy.

Experimentally, the low byte of the I²C word written to the DAC doesn’t change the focus much at all, so what you see below comes from writing a focus value to the high byte and zero to the low byte.

For example, to write 18 (decimal) to the camera:

i2cset -y 0 0x0c 18 0

That’s I²C bus 0 (through the RPi camera ribbon cable), camera lens controller address 0x0c (you could use 12 decimal), focus value 18 * 256 + 0 = 0x12 + 0x00 = 4608 decimal.

Which yanks the focus inward to 30 cm, near the end of the ruler:

Arducam Motorized Focus test - focus 30 cm
Arducam Motorized Focus test – focus 30 cm

The window is now blurry, the analyzer becomes better focused, and the screws at the far end of the yellow ruler look good. Obviously, the depth of field spans quite a range at that distance, but iterating a few values at each distance gives a good idea of the center point.

A Bash one-liner steps the focus inward from infinity while you arrange those doodads on the ruler:

for i in {0..31} ; do let h=i*2 ; echo "high: " $h ; let rc=1 ; until (( rc < 1 )) ; do i2cset -y 0 0x0c $h 0 ; let rc=$? ; echo "rc: " $rc ; done ; sleep 1 ; done

Write 33 to set the focus at 10 cm:

Arducam Motorized Focus test - focus 10 cm
Arducam Motorized Focus test – focus 10 cm

Then write 55 for 5 cm:

Arducam Motorized Focus test - focus 5 cm
Arducam Motorized Focus test – focus 5 cm

The tick marks show the depth of field might be 10 mm.

Although the camera doesn’t have a “thin lens” in the optical sense, for my simple purposes the ideal thin lens equation gives some idea of what’s happening. I think the DAC value moves the lens more-or-less linearly with respect to the sensor, so it should be more-or-less inversely related to the focus distance.

Take a few data points, reciprocate & scale, plot on a doodle pad:

Arducam Motorized Focus RPi Camera - focus equation doodles
Arducam Motorized Focus RPi Camera – focus equation doodles

Dang, I loves me some good straight-as-a-ruler plotting action!

The hook at the upper right covers the last few millimeters of lens travel where the object distance is comparable to the sensor distance, so I’ll give the curve a pass.

Feed the points into a calculator and curve-fit to get an equation you could publish:

DAC MSB = 10.8 + 218 / (distance in cm)
        = 10.8 + 2180 / distance in mm)

Given the rather casual test setup, the straight-line section definitely doesn’t support three significant figures for the slope and we could quibble about exactly where the focus origin sits with respect to the camera.

So this seems close enough:

DAC MSB = 11 + 2200 / (distance in mm)

Anyhow, I can now tweak a “distance” value in a linear-ish manner (perhaps with a knob, but through evdev), run the equation, send the corresponding DAC value to the camera lens controller, and have the focus come out pretty close to where it should be.

Now, to renew my acquaintance with evdev …

Oddities, Photography & Images, Science

Monthly Image: Chestnut Burrs!

Much to our utter astonishment, this appeared on the driveway:

Chestnut burr
Chestnut burr

We’ve since found half a dozen chestnut burrs in the yard, which means at least two trees (it takes two to cross-fertilize) are growing in the immediate area.

We originally thought they were American Chestnuts, but Mary (being a Master Gardener) found enough references including comparative burr pictures to convince us they’re Chinese Chestnuts.

We’ve seen squirrels carrying the burrs in their mouths from the trees to wherever they bury their food supply, as shown by this gnawed spot on the other side of the burr:

Chestnut burr - gnawed section
Chestnut burr – gnawed section

I regard this as conclusive proof that squirrels either have no sense of pain or no lips, because I can’t imagine carrying that thing in my hand, let alone gnawing through it to extract the nuts inside.

Each burr contains three nuts, although this empty husk shows some nuts can fail to fill out:

Chestnut burr - interior with failed nut
Chestnut burr – interior with failed nut

We don’t know where the trees are, but the squirrels seem to carry the burrs across our yard from north to south, so they can’t be too far from us or each other.

Despite our conclusion, it’s faintly possible they’re American Chestnuts, in which case they’re definitely survivors!

Electronics Workbench, Machine Shop, Photography & Images

RPi HQ Camera: 4.8 mm Computar Video Lens

The Big Box o’ Optics disgorged an ancient new-in-box Computar 4.8 mm lens, originally intended for a TV camera, with a C mount perfectly suited for the Raspberry Pi HQ camera:

RPi HQ Camera - Computar 4.8mm - front view
RPi HQ Camera – Computar 4.8mm – front view

Because it’s a video lens, it includes an aperture driver expecting a video signal from the camera through a standard connector:

Computar 4.8 mm lens - camera plug
Computar 4.8 mm lens – camera plug

The datasheet tucked into the box (!) says it expects 8 to 16 V DC on the red wire (with black common) and video on white:

Computar Auto Iris TV Lens Manual
Computar Auto Iris TV Lens Manual

Fortunately, applying 5 V to red and leaving white unconnected opens the aperture all the way. Presumably, the circuitry thinks it’s looking at a really dark scene and isn’t fussy about the missing sync pulses.

Rather than attempt to find / harvest a matching camera connector, the cord now terminates in a JST plug, with the matching socket hot-melt glued to the Raspberry Pi case:

RPi HQ Camera - 4.8 mm Computar lens - JST power
RPi HQ Camera – 4.8 mm Computar lens – JST power

The Pi has +5 V and ground on the rightmost end of its connector, so the Computar lens will be jammed fully open.

I gave it something to look at:

RPi HQ Camera - Computar 4.8mm - overview
RPi HQ Camera – Computar 4.8mm – overview

With the orange back plate about 150 mm from the RPi, the 4.8 mm lens delivers this scene:

RPi HQ Camera - 4.8 mm Computar lens - 150mm near view
RPi HQ Camera – 4.8 mm Computar lens – 150mm near view

The focus is on the shutdown / startup button just to the right of the heatsink, so the depth of field is maybe 25 mm front-to-back.

For comparison, the official 16 mm lens stopped down to f/8 has a tighter view with good depth of field:

RPi HQ Camera - 16 mm lens - 150mm near view
RPi HQ Camera – 16 mm lens – 150mm near view

It’d be nice to have a variable aperture, but it’s probably not worth the effort.

Electronics Workbench, Photography & Images

Arducam Motorized Focus Camera Control

Despite the company name name, the Arducam 5 MP Motorized Focus camera plugs into a Raspberry Pi’s camera connector and lives on a PCB the same size as ordinary RPi cameras:

Arducam Motorized Focus RPi Camera - test overview
Arducam Motorized Focus RPi Camera – test overview

That’s a focus test setup to get some idea of how the control values match up against actual distances.

It powers up focused at infinity (or maybe a bit beyond):

Arducam Motorized Focus RPi Camera - default focus
Arducam Motorized Focus RPi Camera – default focus

In practice, it’s a usable, if a bit soft, at any distance beyond a couple of meters.

The closest focus is around 40 mm, depending on where you set the ruler’s zero point:

Arducam Motorized Focus RPi Camera - near focus
Arducam Motorized Focus RPi Camera – near focus

That’s the back side of the RPi V1 camera PCB most recently seen atop the mystery microscope objective illuminator.

Pondering the sample code shows the camera focus setting involves writing two bytes to an I²C address through the video controller’s I²C bus. Enable that bus with a line in /boot/config.txt:

dtparam=i2c_vc=on

If you’re planning to capture 1280×720 or larger still images, reserve enough memory in the GPU:

gpu_mem=512

I don’t know how to determine the correct value.

And, if user pi isn’t in group i2c, make it so, then reboot.

The camera must be running before you can focus it, so run raspivid and watch the picture. I think you must do that in order to focus a (higher-res) still picture, perhaps starting a video preroll (not that kind) in a different thread while you fire off a (predetermined?) focus value, allow time for the lens to settle, then acquire a still picture with the video still running.

The focus value is number between 0 and 1023, in two bytes divided, written in big-endian order to address 0x0c on bus 0:

i2cset -y 0 0x0c 0x3f 0xff

You can, of course, use decimal numbers:

i2cset -y 0 0x0c 63 255

I think hex values are easier to tweak by hand.

Some tinkering gives this rough correlation:

Focus value (hex)Focus distance (mm)
3FFF45 (-ish)
300055
200095
1000530
0800850
Arducam Motorized Focus Camera – numeric value vs mm

Beyond a meter, the somewhat gritty camera resolution gets in the way of precise focusing, particularly in low indoor lighting.

A successful write produces a return code of 0. Sometimes the write will inexplicably fail with an Error: Write failed message, a return code of 1, and no focus change, so it’s Good Practice to retry until it works.

This obviously calls for a knob and a persistent value!