Reply to: Mini digital cameras: An engineering challenge

[DS23]

i think you need a different source of expertise. what about someone from this lot:

http://www.bpc-cave.org.uk/

http://www.rrcpc.org.uk/

http://www.eldon.org.uk/

or try this forum:

http://ukcaving.com/board/index.php/board,1.0.html

[realityhack]

Good idea, although they won't be bright enough. Not unless you fill the place with them.

[teclo]

For a light source you might want to get a bunch of those plastic light sticks. The ones filled with liquid that light up when you snap the glass inside.

If the place is filled with water they should float, so bung a ton down the whole and it might give enough ambient light for you.

As for a camera, I recently bought a Nikon Coolpix s210. It is small, compact has a metal body and can be set to take a picture every 30 seconds. It has a special low light mode where the iso ramps up to 3200. Also it's quite cheap about £100.

[xoggoth]

Not sure what 400 iso means so probably quality would not be adequate for your main purpose but for initial survey maybe a cheap CCTV camera, under 40 quid.

It should just fit if you unscrew the mount, can easily be supported by the cable with bit of tape on the plugs and plugs into video socket of a TV. Quality is fairly low but has wide range of focus and has built in infra red LEDs for operation in dark. Recently got a system from this lot:

http://www.sctltd.co.uk/acatalog/DiyDvr_CCTV.html

[realityhack]

That is my major worry, I was thinking that if I can get the ISO up to about 800 then that would solve the problem, the caverns wil range in size but we really don't know what is down there and the dimensions involved.

But then I don't know of many small cameras where you can modify the sensitivity, or one that will take an external flash which would help.

A flare has been mentioned as a second light source but I don't know where you buy them.

Even ISO800 isn't going to get you close.
Re: flash strengths - I have a top of the range Metz that, at full output, would only illuminate objects at 80' max on ISO3200 stock at 1/60th and f2.8. You might have more luck with infrared film and flash, but the easiest and cheapest way to capture a viable image in these circumstances would involve a long exposure with lighting. You'd need multiple, dispersed light sources to avoid massive shadows, and a secure mount for the camera.

As an example:
ISO800 at f2.8 would require a 15sec exposure at ev -6 (night, away from light pollution, starry sky).
Flares or halogen lighting would bring this up to ev-1 (dim artificial lighting in a large space), which would require ISO3200, f2.8 and 0.5 sec exposure.
Without lighting this really isn't feasible, as the ev would be sub -6.

For a 'normal' camera, like a disposable, you'd be looking at ISO800, f5.6 and a subsequent exposure of +4min (aprox) with flares/halogen. Approximate because exposure times over 10 seconds will encounter reciprocity law failure, where the relationship between aperture, speed and exposure starts to behave unpredictably, and colour & contrast tolerances will be outside the film stock's range.

I'd find the smallest second-hand camera I could with a bulb setting and the fastest lens possible, secure it to a rod, with a long cable-release mechanism, and try using high-rated films with flares dropped down other pipes into the cavern... I'd have to think a bit more on this - let me know what you're planning and I might be able to advise.

[minestrone]

At that size a cavern getting a picture from a small camera simply won't work, it won't have the focus and it would need to be very steady for a long enough exposure. You will need one hell of a good light source too a camera flash won't help much.

I took a lot of pictures in large monuments over the summer and where there was only limited daylight the results were poor. In a totally black cavern with a relatively limited light source you're not going to get much if anything.

In the past when I used to be something of a spelunker some of my colleagues were keen photographers. They relied on looooong exposures and tripods or people lugging in what amounted to floodlights to get any pictures at all, caverns aren't easy to photograph.

That is my major worry, I was thinking that if I can get the ISO up to about 800 then that would solve the problem, the caverns wil range in size but we really don't know what is down there and the dimensions involved.

But then I don't know of many small cameras where you can modify the sensitivity, or one that will take an external flash which would help.

A flare has been mentioned as a second light source but I don't know where you buy them.

[TykeMerc]

Na, it's filled with water mainly, just under 1 million tonnes of the stuff. That gives you an idea of the size if. The caverns are about 40 meters high.

At that size a cavern getting a picture from a small camera simply won't work, it won't have the focus and it would need to be very steady for a long enough exposure. You will need one hell of a good light source too a camera flash won't help much.

I took a lot of pictures in large monuments over the summer and where there was only limited daylight the results were poor. In a totally black cavern with a relatively limited light source you're not going to get much if anything.

In the past when I used to be something of a spelunker some of my colleagues were keen photographers. They relied on looooong exposures and tripods or people lugging in what amounted to floodlights to get any pictures at all, caverns aren't easy to photograph.

[minestrone]

That'd be interesting if it's an old mine & full of gas...


Even a xenon flash is a bit doubtful under those circumstances...

Na, it's filled with water mainly, just under 1 million tonnes of the stuff. That gives you an idea of the size if. The caverns are about 40 meters high.

[d000hg]

You could even drop a flare down first if you really need a proper amount of light.

[minestrone]

What is it, an old mine? Can't you actually get inside?

pretty much, the entry points are filled in, there is however a series of test holes over the site which we want to use.

[expat]

Thought about going for the mini webcam but we want to use the pictures for printing and quality could be an issue. The cavity is massive and I mean the size of St Paul's cathedral massive so there really needs to be a decent amount of light.

d000hg> the pipe is man made and is about 15 meters long, thickness of a bottle of beer.

What is it, an old mine? Can't you actually get inside?

[minestrone]

Thought about going for the mini webcam but we want to use the pictures for printing and quality could be an issue. The cavity is massive and I mean the size of St Paul's cathedral massive so there really needs to be a decent amount of light.

d000hg> the pipe is man made and is about 15 meters long, thickness of a bottle of beer.

Quite like the timer on a disposable camera idea, I could just drop the thing down on a rope although I wonder if the thing will stop moving around by the time the camera goes off.

I'm thinking that I could drop some kind of light down on a rope first and then drop the camera in.

[realityhack]

Of course, the advantage of a webcam is you'll be able to see that you're photographing the whole area. I'd go for a high quality webcam with a super bright LED array, lower and slowly sweep 360, then adjust the angle and repeat.

[dang65]

Digital cameras almost invariably have a delay timer built in. Shouldn't take long to lower a camera down a ten metre pipe, so just put the timer on and start lowering. Sure, it'll only take one pic at a time, but probably be quicker and certainly less destructive and expensive than breaking the camera and attaching remote control wires to it.

[TykeMerc]

Well web cams or for that matter security type cams have a decent resolution if you buy the right one, they're also small and have no housing to chop about. Illumination is a trivial problem with the pencil sized LED torches available at any market for a quid.
The solution I suggested allows for taking as many pictures as you like as the viewfinder would be at operator level which would be a major issue for a stills camera on a stick/wire.