[bymy141]

I have to disagree with bert.

the shutter is not fast enough.

Essentually the 1/4000 second shutter speed is not the time the shutter opens or the time it takes to travel top to bottom

That time is more closely 1/180th of a second, i.e. the maximum sync speed.

At speeds beyond 1/180th the shutter is never fully open, only a slit moving vertically and the width of the slit is simply set to give 1/4000 of a second open time, based upon the speed of the shutter blades.

Also, I disagree with the statement that the speed is 1100 feet per second. This is not possible, as it would then be supersonic, (note speed of sound is 1000 feet per second) and the pellet gun would be a lethal weapon, plus it would make a hell of a lot more noise than it does.

Having said that however, it will still be difficult to get timed correctly, even with a photo sensor operated flash.

You would need to consider the field of view of the camera, and the time to traverse the frame, with your field of view and camera to gun distance.

It might be better to do a couple of things differently, first, fire the flash based upon the trigger, and second use the flash in a "strobe mode" perhaps the high speed sync mode, where there are multiple flashes as one might just catch the pellet

Lowell, you are right. I should have quoted:

"Today's modern air guns are typically low-powered because of safety concerns and legal restrictions; however, high-powered designs are still used for hunting. These air rifles can propel a pellet beyond 1100 ft/s (330 m/s), approximately the speed of sound and produce a noise similar to a .22 caliber rimfire rifle. Using lead pellets, many current spring powered .177 pellet guns can break the sound barrier, and one, the Gamo 1250, can reach 1600 fps with these new pellets. Most low-powered airguns can be safely fired in a backyard or garden, and even indoors, with the proper backstop. In some countries, air guns are still classified as firearms, and as such it may be illegal to discharge them in residential areas. Air guns can be highly accurate and are used in target shooting events at the Olympic Games, governed by the International Shooting Sport Federation (ISSF)."
(Wikipedia, the unreliable source...)

- Bert

[bymy141]

Or you can shoot a long exposure shot and use a sensor to trigger a strobe, like this:



He used instructions from High-Speed Visual Imaging to make the trigger and strobe firing assembly.

Now you still have to synchronize the flash with the bullet exiting the barrel.
I hope you can make a flash triggering device that is capable of sync, since the bullet is triggered by mechanics not designed to release within msec resolution.

- Bert

[nanok]

it's good you are not using the pentax, it's a well known fact (tm) that the af sucks, it won't even track properly your common cruise missile in flight when it's coming at you, speeding bullets are also a problem (though nobody lived to tell the whole story so far about either, but "it is known"). sorry, just couldn't help it

i would not even think twice about it: automatically triggered strobe, and open shutter (B). be carefull, nasty things can happen in the dark, when a weapon is also involved. don't even think about using a fast shutter speed, especially that that minolta is horizontal travel shutter, and with a sync speed of about 1/60 iirc (not that it really matters, at those speeds). as was already mentioned, travel-shutters are very sllow, they are only really as fast as their sync speed, anything above it is just a "trick" to manage a local exposure equivalent to the advertised one (more like an aperture than a shutter), the time to take the _whole_ frame with such a shutter is always the sync speed, and an interesting side effect with really slow sync speeds (like 1/60 or 1/30) shutters is that a subject which is fast moving through the frame (not in real life) will be distorted in the shot. but i digress.

one thing that went through my mind reading this is a very cheap triggering system (nowehre near as good as what the others have mentioned, but dead cheap and easy to do a first test with): something like a thin tape on the end of the barrel, covering it, with some thin wire stuck to it, pellet goes out, wire breaks, flash triggers. it _might work_. the dissadvantage is that you have to "rebuild" the triggering system after each try (but it can be set up for the first test in a few minutes). i would start testing with a rather wide field of view, looking perpendicular on the barrel, to see where the pellet is when the flash triggers, whichever the method, doing several tests (it might vary wildly, depending on the method), and finetuning. i think it's bound to be a fun experiment.

enjoy, and be safe

[Lowell Goudge]

it's good you are not using the pentax, it's a well known fact (tm) that the af sucks, it won't even track properly your common cruise missile in flight when it's coming at you, speeding bullets are also a problem (though nobody lived to tell the whole story so far about either, but "it is known"). sorry, just couldn't help it

i would not even think twice about it: automatically triggered strobe, and open shutter (B). be carefull, nasty things can happen in the dark, when a weapon is also involved. don't even think about using a fast shutter speed, especially that that minolta is horizontal travel shutter, and with a sync speed of about 1/60 iirc (not that it really matters, at those speeds). as was already mentioned, travel-shutters are very sllow, they are only really as fast as their sync speed, anything above it is just a "trick" to manage a local exposure equivalent to the advertised one (more like an aperture than a shutter), the time to take the _whole_ frame with such a shutter is always the sync speed, and an interesting side effect with really slow sync speeds (like 1/60 or 1/30) shutters is that a subject which is fast moving through the frame (not in real life) will be distorted in the shot. but i digress.

one thing that went through my mind reading this is a very cheap triggering system (nowehre near as good as what the others have mentioned, but dead cheap and easy to do a first test with): something like a thin tape on the end of the barrel, covering it, with some thin wire stuck to it, pellet goes out, wire breaks, flash triggers. it _might work_. the dissadvantage is that you have to "rebuild" the triggering system after each try (but it can be set up for the first test in a few minutes). i would start testing with a rather wide field of view, looking perpendicular on the barrel, to see where the pellet is when the flash triggers, whichever the method, doing several tests (it might vary wildly, depending on the method), and finetuning. i think it's bound to be a fun experiment.

enjoy, and be safe

I would take your trigger option to the opposite extreme.

Using a simple concept, and the fact that the pellet is conducting,

Get a hot shoe pick up, with center contact and wire out with a pair of wires to the gun barrel.

one on top, one on bottom (or perhaps close to this but behind so from a slightly behind the muzzle perspective they are hidden)

When the pellet touches both on the way out of the barrel the flash triggers. due to the contact with both wires.

I am not sure one wire would do, but you could try, using the barrel as the other contact, but it may not work.

I propose this scheme because the flash operates by making a connection not breaking it.

[Rick]

This is somewhat indirectly relevant but... air rifles/pistols are not "lethal weapons". Some jurisdictions such as Canada have an energy threshold where the energy of the projectile determines whether the air rifle/pistol is considered to be a firearm or not. i.e. you can get significantly faster velocities out of an air rifle if you use an abnormally light projectile, but there isn't a linear increase in energy to go with those faster speeds as mass is part of the equation for whatever measure of energy you choose to use. You can significantly increase the speed if you significantly decrease the weight of a projectile, but the energy remains somewhat similar Even under Canada's archaic gun control scheme, very few air rifles/pistols are deemed to be firearms. So as photographers we aren't dealing with imminent death here...

Second, in considering the available air rifles/pistols on the market today, some will generate velocities over 1000 fps (which is an arbitrary velocity milestone in itself) but the vast majority do not. Relevant to that, I doubt that the project at hand requires the student to attempt to photograph the fastest air rifles on the market today. The more common (and less expensive) air pistols weighing in at around the 450 - 500 fps mark should be just fine for the technical exercise.

Incidentally, to the best of my knowledge all competitive air rifles/pistols - and .22 rimfire ammunition for competition - is subsonic. Two reasons for this is the instability of the projectile when it is waffling around in the boundary layer during transition leading to instability (thus loss of accuracy), and the fact that bullets travelling at subsonic speeds actually experience LESS wind drift over a given distance than a faster bullet exceeding the sound barrier. This sounds counterintuitive, but if you download any of the freely available ballistics software you can play with this yourself by varying velocity. You have to drive a projectile significantly faster than the speed of sound before you end up with less wind drift than a subsonic projectile.

Pictures of projectiles in supersonic flight, however, make for some pretty cool pictures as you see the shock waves coming off the tip, the heel, and in some instances the beginning of the ogive. Those photos do a lot to help analyze bullet design and so pictures of bullets in flight are pretty common in the ballistics biz. Not hard to figure out which of the following is a more ballistically efficient bullet, eh?






So, getting more back to the subject at hand...

Schemes that depend on the projectile conducting an electrical current aren't going to have much success - pellets are invariably made out of swaged pure lead. Not such a great conductor of electricity.

The earliest methods for photographing bullets - and chronographing their speed - was to have the projectile either break a wire and this starting the clock/triggering the strobe, or passing through conducive paper to the same effect. In fact, if you find some of the earlier photos of bullets in flight, you'll actually see the broken wire just behind the bullet in some of them.

I've never done any of this kind of photography, but I think the solution is going to lie in something like the projectile breaking an electronic beam or wire to initiate a strobe with the camera set on bulb and a dark flat background. Chronographs these days have their timers started/stopped by the bullet passing over a photo eye, and the photo eye detecting the shadow of the projectile. If you could figure out a way to have a chronograph screen initiate your strobe, you'd probably have your technical problem licked.

Addendum: a quick look at the internet suggests that most people using relatively normal gear are using the noise of the gun firing to actuate a strobe in a dark room with the camera on bulb setting.