Have I got this right?

CMC68

20

Have I got this right?

« on: 17 / August / 2009, 14:11:04 »

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Hi,

I stumbled across CHDK and this site a couple of days ago whilst searching around High Speed Photography. It is completely new to me but as a keen amateur photographer who also loves 'tinkering' I was intrigued. SO I have spent the last couple of days absorbing what I can and considering the potential CHDK can offer me.

One area I love messing about with is high speed photography - bursting balloons, smashing eggs/lighbulbs etc. hence the searching. Currently I use a Quaketronics controller (triggered by sound or beam interruption) to fire a remote flash gun (a vivitar 283) whilst my DSLR is set on bulb in a completely dark environment. Its pretty effective as the flash can be forced down to 1/30,000th of a second but the need to be in complete darkness does cause limitations to potential subjects (I'd like a shattering bulb with the filament glowing for example) and makes some shooting trickier.

So I have a few questions before I jump in with both feet. Mainly just looking for confirmation of what I think I understand from my searching (bear in mind electronics and programming are not my strong points, I'm more of a mechanics person).

Could I really have a high speed shot in daylight at or above 1/30000"? If so is the DoF workable or does the aperture required to allow enough light effect this
If so, is it theoretically possible to use my controller which obviously outputs a signal (I guess I need to measure it) in conjunction with a USB trigger, and using some sort relay, to fire the camera's shutter? If so would the delay in this be minimal (the USB side)
Is motion detection a potential trigger option too? I.e. response times quite quick and or a delay programmable?
Are there any other triggering options bearing in mind it may need to be sound based or beam tripping. Needs to react quickly and have variability of delay

I have also had a hankering to try KAP for a while. If I have to buy a small camera and get additional functionality from CHDK this could be the ideal opportunity to give it a go. I seem to have narrowed options to either the A590, 650 or 720 Are there any pro's and cons to any of these models based on my two potential uses?

So many questions...

Chris

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CMC68

20

Re: Have I got this right?

« Reply #1 on: 20 / August / 2009, 06:06:27 »

Did I post this in the wrong place? Or ask an obvious/dumb question? Please someone let me know if I did.

Anyway, some more research has narrowed down the answers to the questions I posed.

Re-reading the wiki article on high speed it seems there's flash involved in all examples to some degree. Although that still allows some ideas not possible with my current set up. Id be interested if anyone has examples of high speed shots without any flash employed. There is a Casio camera that has a theoretical 1/40,000 shutter speed out of the box but feedback I've seen has suggested it really isn't that workable due to the lighting requirements.

The question about using my sound/light trigger via USB was really just about whether there is any delay when firing via USB (signal to shutter operation), does anyone know this?

I've found the comparison which includes motion detection times and see 150ms as a figure suggested for the A series cameras I'm looking at. By my rough maths, a typical object dropped from 5 metres will take about one second, in .15 of a second it will go 75cm (more I know as it will be the end of the fall, but this is rough theory). So if the camera see's the falling item at (slightly above) 75cm the shot should capture the impact. Have I made any stupid assumptions and/or can anyone fine tune my maths to make this a more accurate estimate?

I'd still be interested if anyone else has used any techniques to trigger the shutter for high speed shots.

Camera selection wise, I am definitely going to have a crack at KAP too. So for now cheaper seems to make more sense and the A590 is top of my list as combining KAP and high speed potential. No reasons not to go down that route is there? The thinking being that once I have a hang of flying a KAP rig I could upgrade if I think I need to.

Cheers.

Chris

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Microfunguy

4037

Re: Have I got this right?

« Reply #2 on: 20 / August / 2009, 07:32:33 »

Quote from: CMC68 on 20 / August / 2009, 06:06:27

Did I post this in the wrong place?

It does no harm to post again in the 'Creative uses of CHDK' section.

Do not be seduced by the absurd claims of very high shutter speeds.
This has been discussed here (somewhere) and the fastest speed is nothing like 1/40,000 sec.
If it was, how would you get enough light.
If you are using flash, it is effectively setting a very short duration at macro distances.

Quote

The question about using my sound/light trigger via USB was really just about whether there is any delay when firing via USB (signal to shutter operation)

I only know about SDM ... if you are in prefocus mode (a brief on/off click of the switch), it will take a photo when USB goes low.

In so-called FAST mode, it triggers as soon as the USB goes high.
You will have to measure that delay yourself, if you have suitable equipment.

There is another way .. the pulse after prefocus blanks the screen and waits for switch release.
It will time-out after ten seconds.
If your circuitry can pull the signal low during that time the response will be very fast.

Quote

I am definitely going to have a crack at KAP too.

This is the group to join http://steel.ced.berkeley.edu/kap/discuss/

CHDK forum member Zeno is also a member of that group.
I imagine he has not seen your post here.

David

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Anaglyphic

129
Anaglyphic lives!

Re: Have I got this right?

« Reply #3 on: 20 / August / 2009, 14:56:26 »

Hi.

Quote from: CMC68 on 20 / August / 2009, 06:06:27

* Could I really have a high speed shot in daylight at or above 1/30000"? If so is the DoF workable or does the aperture required to allow enough light effect this
* If so, is it theoretically possible to use my controller which obviously outputs a signal (I guess I need to measure it) in conjunction with a USB trigger, and using some sort relay, to fire the camera's shutter? If so would the delay in this be minimal (the USB side)
* Is motion detection a potential trigger option too? I.e. response times quite quick and or a delay programmable?
* Are there any other triggering options bearing in mind it may need to be sound based or beam tripping. Needs to react quickly and have variability of delay

* CHDK and high shutter speed overrides is debatable. I don't know if any camera actually pulls 1/30000th.
* USB firing delay when using the falling edge (=sync) is fairly consistent and < 60ms for most cameras.
* While you can add delay to the motion detection reaction, it is probably not the best choice here.
* Your best bet for triggering when sub-second accuracy is required is to use an external trigger.

Quote from: CMC68 on 20 / August / 2009, 06:06:27

There is a Casio camera that has a theoretical 1/40,000 shutter speed out of the box but feedback I've seen has suggested it really isn't that workable due to the lighting requirements.

Quote from: Microfunguy on 20 / August / 2009, 07:32:33

Do not be seduced by the absurd claims of very high shutter speeds.
This has been discussed here (somewhere) and the fastest speed is nothing like 1/40,000 sec.
If it was, how would you get enough light.

But it's so seductive! :b Doing the "dremel speed test" some people have measured very high overrides, so you can get high shutter speeds on certain cameras; I know I can shoot 1/15000th on the SX100, and probably shorter. But as you both point out, how in the world are you going to light the scene? Here's a picture of the noon day sun with clouds: SX100, ISO80, f/8.0, 1/16000th, so even @ f/2.8... multiple PAR64s? 500w halogens? 1000w metal halides? Your set will be melting.

Quote from: CMC68 on 20 / August / 2009, 06:06:27

I've found the comparison which includes motion detection times and see 150ms as a figure suggested for the A series cameras I'm looking at.

Here's the problem - the MD shot latency isn't static. LCD display buffer selection is round-robin... this method tightens up the shot-to-shot variance over the previous method, but it's still variable. For my CHDK-capable cameras it varies 5ms-40ms. I'm not sure, but it doesn't seem this would be sufficient for the accuracy required. I would use that external trigger to fire via voltage drop on the USB +V pin.

Quote from: CMC68 on 20 / August / 2009, 06:06:27

I am definitely going to have a crack at KAP too. ...

Crack. Interesting choice of words. :b Just consider the camera disposable, and the choice is clear. Cheapest! I'm sure experienced KAP veterans have sent $1000 rigs into the dirt/water at "ludicrous speed"... but if you're just starting kite flying in general and flying a DIY picavet off a small delta, your chance of a catastrophic crash & burn is an exercise in statistical probability. Most of these PowerShots are not durable; impact on an extended lens at even the slowest speed (or just dropping from your hand to the floor) can misalign the gear teeth on the lens motor, or worse...

I'm fascinated by KAP; not so much the images produced as the dedication and obsessive nature of the KAPpers themselves; it draws you into their world with wide eyes and a big grin. CHDK/SDM & KAP are made for each other.

Not for nothing, but you sound like someone who's going to have much more fun with a CHDK/SDM-capable Canon than a Casio. Just sayin'.

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Since we cannot know all that there is to be known about anything,
we ought to know a little about everything. -- Blaise Pascal

zeno

891

Re: Have I got this right?

« Reply #4 on: 22 / August / 2009, 07:55:23 »

The A590 (and before that the A570) is very popular with KAPers and not just because of CHDK/SDM. One useful feature is the ability to fit a lens 'hood' on these cameras which protects the zoom lens in the event of a rough landing. I speak as one who got the dreaded E18 error with a Canon Ixus in just such an accident. See here: Canon A570 fitted with a 37mm adapter

The G9 is also a popular KAP camera - see Windwatcher's photos here: http://www.flickr.com/groups/kiteaerialphotography/

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A570, S100, Ixus 127
Author of ASSIST, STICK, WASP, ACID, SDMInst, LICKS, WICKS, MacBoot, UBDB, CFGEdit

CMC68

20

Re: Have I got this right?

« Reply #5 on: 23 / August / 2009, 06:57:21 »

Thanks everyone for taking the time to reply.

High speed wise, even though the lighting issue is as I thought, a very fast shutter combined with the flash still opens up some situations my current set up doesn't allow due to needing darkness. I'm going to have some fun playing.

I wasn't considering the Casio for this just aware of its theoretical shutter speed, I may come back to is at some time though as it offers 1000fps video capture as well. I've go enough to do for now though!

Anaglyphic, I guess you were saying the motion detection delay varies from shot to shot. That's going to make things very random and not at all practical

My key challenge now then is to link my current trigger to a USB firing device. I need to measure the output from my trigger and presumably match it up to a relay with a 5v supply attached. I'll probably have to come back and ask for some advice when I get to it as I'm not an electronics person.

I've just picked up a camera on ebay, an A720IS. Cheap enough, light enough for KAP use and (thanks Zeno) can take an extension tube. All being well it will give a reasonably fast shutter speed too.

I had found the KAP forum, its a fantastic resource with many references to CHDK. I'm going to be spending a lot of time both on there and here over the coming weeks. First off is to absorb the CHDK users guides and the MAC users instructions.

Thanks again.

Chris

« Last Edit: 23 / August / 2009, 13:18:59 by CMC68 »

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Anaglyphic

129
Anaglyphic lives!

Re: Have I got this right?

« Reply #6 on: 23 / August / 2009, 13:19:14 »

Quote from: CMC68 on 23 / August / 2009, 06:57:21

Anaglyphic, I guess you were saying the motion detection delay varies from shot to shot. That's going to make things very random and not at all practical

Indeed it does, and indeed it is. It's actually less random than if you got here 6 months ago, but for that specific application, it's too wide-ranging to be of use.

Quote from: CMC68 on 23 / August / 2009, 06:57:21

My key challenge now then is to link my current trigger to a USB firing device. I need to measure the output from my trigger and presumably match it up to a relay with a 5v supply attached. I'll probably have to come back and as for some advice when I get to it as I'm not an electronics person

This is actually very easy. There's no reason to use a expensive and mechanical relay, just 10 cents worth of parts. Since your dSLR trigger fires by going high, you'll wire up a transistor as an inverter and take the output off the collector. It can be powered off a separate +5V voltage if needed, and then just tie the base to the trigger's output through a limiting resistor. Attached a quick xschematic in case I explained it poorly. Obviously you'll also need a USB Mini-B cable to sacrifice to "the cause". :b

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Since we cannot know all that there is to be known about anything,
we ought to know a little about everything. -- Blaise Pascal

CMC68

20

Re: Have I got this right?

« Reply #7 on: 24 / August / 2009, 05:15:16 »

Quote from: Anaglyphic on 23 / August / 2009, 13:19:14

This is actually very easy. There's no reason to use a expensive and mechanical relay, just 10 cents worth of parts. Since your dSLR trigger fires by going high, you'll wire up a transistor as an inverter and take the output off the collector. It can be powered off a separate +5V voltage if needed, and then just tie the base to the trigger's output through a limiting resistor. Attached a quick xschematic in case I explained it poorly. Obviously you'll also need a USB Mini-B cable to sacrifice to "the cause". :b

That's fantastic, much simpler than I imagined. Thanks.

Can I just confirm my understanding as I am not very strong on electronics and circuit design. The transistor acts as the switch, switching the +5v supply when triggered by the flash trigger and also turning the flash trigger's output from off -> on to on -> off. Looking at your schematic the 1k resistor is fixed but the 10k resistor may be something else which I need to asses by measuring the output from my trigger, and selecting a resistor which will match that output to the input for the transistor.

If I have got that right I need to measure the output. Any tips? I tried connecting to my multimeter and measured at all current and voltage ranges but picked nothing up - could it be too quick. Could it be standard? It is to trigger any flash gun via a pc cord - is that a standard voltage/current?

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fbonomi

469
A570IS SD1100/Ixus80

Re: Have I got this right?

« Reply #8 on: 24 / August / 2009, 05:47:22 »

Quote from: zeno on 22 / August / 2009, 07:55:23

One useful feature is the ability to fit a lens 'hood' on these cameras which protects the zoom lens in the event of a rough landing. I speak as one who got the dreaded E18 error with a Canon Ixus in just such an accident.

zeno, that is quite simple and brilliant... I never thought about that.

If I understand correctly, you are speaking of just using a lens adaptor without any lens so that it protects the real lens.

but won't the 37 mm give some vignetting? ... maybe not.

anyway, I just ordered this
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280346668428
for $9.99 shipped worldwide, it's a good insurance on your camera :-)

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zeno

891

Re: Have I got this right?

« Reply #9 on: 24 / August / 2009, 09:29:49 »

I bought the adaptor to try the two add-on lenses I had (the Nikon fisheye was bought for doing KAP VR like this one Totnes Panorama with an old second-hand Nikon 4300).

Just using the adaptor as a protector does not result in any vignetting that I can see - I never ever take it off so all my pictures are taken with it. The one you bought is very similar to mine (which actually came with a couple of filters I don't use).

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A570, S100, Ixus 127
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