Raspberry Pi Camera Guide Scope

[Darren Poulson]

Made a bit of a start on my guide scope. Plan is to use it in conjunction with kstars/indi.

Started with a 9x50 finder, and currently in the process of modding that. Just finished the first part which is a Pi camera to 1.25" adapter. Laser cut mount, with an eyepiece tube from a spare 2x barlow.

Need to decide if I can (or want to) adapt the finder scope, or just by an adapter for standard 1.25" fittings from Modern Astronomy.

[NickK]

Have you tried the camera in darkness yet?

I have a couple of CMOS cameras attached to blackfin 537s with enough ram to act as a frame buffer. Only issue is I think the rate/exposure time is limited.

Instead I'll probably stick to the OAG for tracking but as a sensitive wide field I have a 300mm f4 camera lens that I'll looking to add on to the system too. Not sure if I'll use a old ATIK camera or use one of these CMOS instead. These cameras are the OV9655 colour IIRC.

 

Sensitivity 1.1 V/(Lux • sec) 
	S/N Ratio 42 dB 
	Dynamic Range 50 dB 
	Scan Mode Progressive 
	Maximum Exposure Interval 1050 x tROW 
	Gamma Correction Programmable 
	Pixel Size 3.18 μm x 3.18 μm 
	Dark Current 15 mV/s at 60°C 
	Well Capacity 10 K e 
	Fixed Pattern Noise <0.03% of VPEAK-TO-PEAK 

 

I see the RPi camera is an omnivision OV5647 so the data sheet shows:

Sensitivity 680mV/(lux-sec) (ie 0.680V/lux-sec compared to above)

S/N Ratio: 36dB

Dynamic range: 68dB

Scan Mode/Shutter: rolling/global

Max Exposure Interval:  1968*tROW

Pixelsize: 1.4um x 1.4um

Well capacity: 4.3 K e

Dark Current: 16 mV/sec @ 60degC

Fixed Pattern Noise: <1% Vpeak-to-peak

It does have 2x2 binning and ... if you look at the data sheet (http://cdn.sparkfun.com/datasheets/Dev/RaspberryPi/ov5647_full.pdf) you can control the exposure time if you switch off the auto-exposure/gain system (section 4.5).

Only thing is 4.3 Ke is a little low.. and 1.4um is really really small.. With 2x2 binning (assuming hardware and not software binning) will give you 2.8um * 2.8um which is probably better.

[NickK]

Actually looking at the OV9655 it's possible to perform a manual frame grab rather than a video-based repeating feed using the B_RESET pin which is modified behaviour (becomes exposure) if some of the registers are setup correctly. That would then cause it to perform a capture manually.

So in short it's doable if the same behaviour is true of the RPi camera.

In fact with the blackfin it would be possible to create a static stacking camera as it has 32MB of RAM and 4MB of flash. That method would help keep the noise level lower in the final image.

I'll be setting up an odroid c2 with ubuntu/kstars/ekos/indi.

 

Looking at the old SRV (the rover pictured above) firmware (it runs on bare metal) the register setups for 0xA1 set the exposure times for the AEC. On your camera look at section 4.5.1 and the exposure registers (once setup) 0x3500 etc.

I helped the original developer of the SRV-1 create a stereo vision (the prototype on the rover above) hence have some experience of the OV cameras and embedded