CHDKPTP: S90 Primary Focal Plane Configuration - hacking out the CCD - page 3 - Creative Uses of CHDK - CHDK Forum supplierdeeply

CHDKPTP: S90 Primary Focal Plane Configuration - hacking out the CCD

  • 704 Replies
  • 140550 Views
Re: CHDKPTP: S90 Primary Focal Plane Configuration - hacking out the CCD
« Reply #20 on: 20 / October / 2012, 09:47:41 »
Advertisements
A circular shutter for the S90 CCD has to have a clear aperture of at least 10.0 mm.

Well, in this message http://chdk.setepontos.com/index.php?topic=8613.msg90637#msg90637 you said "The architecture of my instrument is not the usual you'd expect, so I don't need a small aperture."

The implication being that you do not need an aperture at all (as you did not say that you need a large aperture).

Anyway, the shutter I use has a 4.5mm aperture http://www.optics-online.com/OOL/CMT/CMT-SHT934.pdf
« Last Edit: 20 / October / 2012, 10:03:07 by Microfunguy »

*

Offline SticK

  • *****
  • 779
Re: CHDKPTP: S90 Primary Focal Plane Configuration - hacking out the CCD
« Reply #21 on: 20 / October / 2012, 10:18:31 »
You have a good memory!  Yes, that's because the diagonal of the S90 sensor surface in 9.5 mm and in my case, I put the shutter directly in front of the CCD, thus it needs a 10 mm clear aperture.  It also has to fit in a 30 mm space and be as thin as possible.  In your case, you must have a lens arrangement where you place your shutter at the tightest convergence point in your light path, farther from your CCD.  In the S90, the shutter sits sandwiched right against the exit pupil of the zooms lens aggregate, which is 5.0 mm, so its shutter clear aperture is 5.5 mm.

The Sunex part is less than 1/10th the cost of the Uniblitz, but unfortunately for my application, the 4.5 mm is the only one they carry.

Re: CHDKPTP: S90 Primary Focal Plane Configuration - hacking out the CCD
« Reply #22 on: 20 / October / 2012, 10:26:54 »
The shutter also has to close VERY quickly.

Just how quickly I think depends on light intensity.

At relatively low illumination from a microscope I used a tiny pager motor that operated a shim steel vane.
The shim was from spark plug feeler gauge set.
Ideally, it should be blackened.

You can move a very lightweight vane very quickly over 9.5mm, especially if it as the end of a long lever.
It has to crash into something absorbent like foam plastic.

It can also be very thin.

*

Offline SticK

  • *****
  • 779
Re: CHDKPTP: S90 Primary Focal Plane Configuration - hacking out the CCD
« Reply #23 on: 20 / October / 2012, 10:49:07 »
The feeler gauge is a very good idea to build one's own with.  For me it would be impractical to build a shutter mainly because of the space limitation: to swing a 10 mm single vane requires a 15 mm radius minimum leaving no space for housing construction.  A multi-vane does not have that impediment.  For example, the 4-vane DSS10 is 27 mm diameter including the housing.  The standard option is Teflon black-impregnated vanes.  They also have a metallic one-side reflective option for laser applications.  If I recall, their shutter has a 3 ms reaction time for all vane options.  Overall, shutter reaction speed should be theoretically independent of light flux falling on the CCD.  The most important timing characteristic is the close operation after the shot has been taken: that has to happen before data readout begins.


Re: CHDKPTP: S90 Primary Focal Plane Configuration - hacking out the CCD
« Reply #24 on: 20 / October / 2012, 11:16:10 »
shutter reaction speed should be theoretically independent of light flux falling on the CCD.

Presumably a fixed parameter related to CCD readout.
It would be in the datasheet, except you cannot get one.

Quote
  The most important timing characteristic is the close operation after the shot has been taken: that has to happen before data readout begins.

Well, you get some interesting, unwanted results if it does not.

There is another way, but it involves some light reduction and the introduction of a non-precision optical element.

Quite simply, it is one of the 'lenses' (not really) from an old pair of 3D active shutter glasses.
You drive these with a symmetrical waveform that has no DC component.
They are very thin, very fast and take-up minimal depth.

I do have a possibly working demo in a box somewhere.

More information here  http://www.liquidcrystaltechnologies.com/tech_support/drivingshutter.htm

However, there are problems http://www.liquidcrystaltechnologies.com/tech_support/LCDShutterConsiderations.htm

The only other solution, if your application allows it, is to use a flash as light source.

If none of them are acceptable, you are stuck with the Multiblitz.

« Last Edit: 20 / October / 2012, 11:42:19 by Microfunguy »

*

Offline SticK

  • *****
  • 779
Re: CHDKPTP: S90 Primary Focal Plane Configuration - hacking out the CCD
« Reply #25 on: 20 / October / 2012, 16:57:26 »
Quote "Presumably a fixed parameter related to CCD readout. It would be in the datasheet, except you cannot get one."

That's why I'm doing this for your community on the side along with my application ... exactly because there is no datasheet.

Some comments on LCD shutters.  For high-performance imaging they are almost useless.  They polarize light and introduce attenuation, my guess 1 EV or more.  Worst of all, are the interconnects across the FoV that cast shadows when open, and when closed they leak pretty badly.  They're cute because they have no obvious moving parts, but I would not recommend them in the least.

*

Offline SticK

  • *****
  • 779
Re: CHDKPTP: S90 Primary Focal Plane Configuration - hacking out the CCD
« Reply #26 on: 21 / October / 2012, 00:22:00 »
DEFINITION of the S90 SHUTTER CONTROL SIGNALS and an EXTERNAL SHUTTER CONTROLLER

OVERVIEW

One of the great advantages of a PFP-configured CCD optical instrument especially for low light photography such as astronomy I haven't discussed yet, is the removal of the lens increases flux by the speed of the lens you remove.  For example, the S90 has an f/2 lens.  By taking all the glass out from an S90, you go from f/2 to f/1, giving you a +2EV immediate flux advantage.  Also, in a telescope you typically remove the eyepiece optics and position the CCD on the telescope's focal plane, further improving signal strength.

In a camera lens, the exit pupil diameter defines the minimum diameter a shutter can be.  In the S90, the exit pupil is 5 mm diameter, hence the shutter clear aperture in this camera is 5.5 mm diameter.  This is about half the size of the CCD itself and cannot be used in the PFP architecture.  Most often, the lens in your instrument will be larger than a camera lens.  Therefore the complete solution is an external shutter that has a clear aperture larger than the diagonal of the sensor area.  For a 1/1.7" CCD that is 9.6 mm, hence to be safe and have some installation tolerance, a minimum 10 mm shutter is required.

CAMERA SHUTTER SOLENOID DRIVE SIGNALS

The S90 employs a bistable shutter that is used for CCD data readout and dark frame acquisition when enabled, as discussed earlier.  This means that the shutter changes state with a brief application of current polarity reversed pulse generated by an H-bridge driver on the main board, and stays in that state mechanically until excited again.  Figure 1 shows the two states.  The left panel shows the OPEN->CLOSE transition pulse, and the right panel is the CLOSED->OPEN pulse.  The drooping tail is inductive back-EMF.  The pulses are 6.1 and 1.3 ms with a voltage of 4.9V.  Thus the native H-bridge is capable of delivering +/- 550 mA into 9 ohms. 

DEFINING an external SHUTTER

In terms of timing your own shutter, the OPEN->CLOSE reaction is the more important of the two.  That's because after closure either data readout begins or dark frame acquisition begins.  Hence to guarantee imaging quality is not subject to deterioration by stray light, your shutter has to close at least as fast as the Canon shutter.  According to the measurement in Fig 1, we can comfortably make the assumption that firmware operations (readout or dark) will not start any earlier than 6.1 ms after the rising edge of this pulse.  Because of hardware latency, this time could be longer than 6.1 ms.  The right way to get the firmware start-operation time mark is to actually measure the Canon shutter with a photodiode, which I have not done as of this writing.  Staying with the first assumption for now, after you detect the rising edge, you have 6 ms to make sure your shutter is closed, all told ... signal detection, level translation, drive, solenoid energization, and mechanical settling time.  Therefore the shutter you select or build, has to meet this specification.

SPECIFYING an external SHUTTER CONTROLLER

If your shutter can be driven by 5V at less than 550 mA, then you can wire it directly to the Canon native H-bridge.  However, because more mass has to be moved over a larger distance for a 10 mm aperture, it is likely the external shutter will need more power to change state.  Figure 2 shows a very flexible general-purpose shutter controller that you can use to drive your bistable shutter.  It can deliver up to +/- 1.5A from a DC supply of +4V to +13V, and you can set the open and close pulse widths from 1 ms to 23 ms independently.  All you need to do is connect the input to the 2-wire points on the Canon shutter, and run the circuit at the rated voltage of your shutter.  The circuit has an auxiliary output that stays latched in the open or closed states.  For example, you use this signal to enable an illumination lamp during the open state and disable the lamp during the closed state, simulating an external shutter if your camera is in a completely dark environment.  The lamp cannot be an incandescent type such as a halogen because of thermal lag.

CIRCUIT FUNCTIONAL DESCRIPTION

When interfacing your own powered equipment with camera electronics, it is prudent to use optoisolators, as I've done here.  There are two independent symmetrical paths in this circuit that split up at the TLP2160 input and recombine at the Si9986 H-bridge output.  A Canon open or close pulse turns ON one of the two LEDs in the TLP2160.  The -ve going output of the TLP2160 gets inverted by the 74HC00 and clocks the D flipflop (74HC74) to generate a -ve going TRIGGER pulse to the LMC555.  The LMC555 output goes HIGH to begin its timeout.  Its output is connected to 3 nodes:
   1) D-flipflip PRE pin inverted via 74HC00.  The LMC555 LO->HI transition immediately resets the D flipflop.  This retriggerable feature allows the shutter excitation signal (to the TLP2160 LED) to persist longer or shorter than the set delay in the LMC555, guaranteeing that the external shutter will always get its prescribed pulse width regardless of input excitation pulse width; 
   2) SR flipflop.  The LCM555 output changes the state of NOR-gate (74HC02) SR flipflip which drives the state LED indicators and is connected to the lamp enable/disable output;
   3) Si9986 H-bridge.  Drives the H-bridge for the timeout period in the corresponding current polarity.
The RC network on the 74HC00 is PUP reset.

CALIBRATION and USAGE

When you first try your circuit, it is possible that you may experience swapped behavior, such as the GREEN LED turning ON after a close signal.  Simply swap the input terminals.  Likewise, if your shutter is operating in reverse, swap its terminals.  You don't need a scope to set the delays.  If you use a 10 or 11 turn trimpot, delay will be ~2 ms/turn, starting at 1 ms fully CCW.  You can test your circuit directly with the native shutter on the camera by setting the operating voltage to +5VDC:
  a) disconnect the ribbon cable from the solenoid, attach the 10 ohm resistor as shown,
  b) connect the ribbon pair to INPUT, and
  c) connect OUTPUT back to the solenoid. 
Set OPEN to 1.3 ms and CLOSE to 6 ms.  The device should work identically to the native Canon connection.  Always PUP the controller first, then the camera. Then take one dummy shot to allow it to set itself into its correct standby initial state.

BOM - DigiKey
1X  296-1187-1-ND   SN74HC00DR   IC QUAD 2-INPUT NAND GATE 14SOIC
1X  296-1188-1-ND   SN74HC02DR   IC QUAD 2-INPUT NOR GATE 14-SOIC
1X  SI9986DY-T1-E3CT-ND   SI9986DY-T1-E3   IC BUFFERED H-BRIDGE 8-SOIC
1X  TLP2160(F)-ND TLP2160(F)     ISOLATOR 2.5KVRMS 2CH TOTEM SO8
1X  296-17360-1-ND   LP2981-33DBVR   IC REG LDO 3.3V .1A SOT23-5 (can be soldered too)
2X  SM-42TW204CT-ND   SM-42TW204   TRIMMER 200K OHM 0.25W SMD (11 turn SMD)
2X  LMC555CMXTR-ND      LMC555CMX/NOPB    IC OSC MONO TIMING 3MHZ 8-SOIC
2X 478-1239-1-ND   0603YC104KAT2A   CAP CER 0.1UF 16V 10% X7R 0603   

BOM - Mouser
2X  Schmartboard 204-0004-01

Resistors LEDs and other capacitors are your choice.  It is advisable to disconnect the Canon solenoid and replace it with the 10 ohm resistor to prevent false triggering due to the inductive kickback.

See also: http://chdk.setepontos.com/index.php?topic=8801.msg92704#msg92704
« Last Edit: 02 / November / 2012, 01:56:04 by SticK »

Re: CHDKPTP: S90 Primary Focal Plane Configuration - hacking out the CCD
« Reply #27 on: 21 / October / 2012, 06:42:40 »

You are honoured with my post numbered  (int)10000/3.

Excellent.

However, you do not have an external shutter so is this theoretical or have you built it ?

Quote
By taking all the glass out from an S90, you go from f/2 to f/1, giving you a +1EV immediate flux advantage.


+2EV immediate flux advantage.
« Last Edit: 21 / October / 2012, 09:40:23 by Microfunguy »


*

Offline blackhole

  • *****
  • 868
  • A590IS 101b
    • Planetary astrophotography
Re: CHDKPTP: S90 Primary Focal Plane Configuration - hacking out the CCD
« Reply #28 on: 21 / October / 2012, 09:01:07 »
Quote
One of the great advantages of a PFP-configured CCD optical instrument especially for low light photography such as astronomy I haven't discussed yet, is the removal of the lens increases flux by the speed of the lens you remove.  For example, the S90 has an f/2 lens.  By taking all the glass out from an S90, you go from f/2 to f/1, giving you a +1EV immediate flux advantage.  Also, in a telescope you typically remove the eyepiece optics and position the CCD on the telescope's focal plane, further improving signal strength.
I think that the 'f' will be like on optics of telescopes, if I well understood what you wanted to say.
Another issue is the diameter of the exit pupil which often leads to vignetting which can be solved by positioning of sensors but it often leads to the inability to focusing because there is not enough long gait on the focuser.

Re: CHDKPTP: S90 Primary Focal Plane Configuration - hacking out the CCD
« Reply #29 on: 21 / October / 2012, 09:29:37 »
That's why I'm doing this for your community on the side along with my application ...
After 385 posts on this subject,  I think you are now allowed to refer to this as "our community"   8)
Ported :   A1200    SD940   G10    Powershot N    G16

 

Related Topics