EF 300/4L IS USM + 420EZ Flashgun combination? (1 Viewer)

EF 300/4L IS USM + 420EZ Flashgun combination(on a EOS 5)?

Hello,
I am a starter with using flash :h?: .......and want to use it for fill flash.
Now the question:
If I put on my 300/4 lens, and a 420 EZ flashgun on my EOS 5, is it then still usefull? What i mean is, the flash can zoom in from 24mm up to 80mm(or more, don't know now), So if i put om my 28-135IS lens it zooms with it up to the maximum zoom it can handle.
But what now if i put on the 300mm lens? Say the object is 20meters away, or maybe 40meters, will the flash reach the object? What SETTINGS must i use? Where do i put the zoom on on the flashgun?

Can someone please give me some help?
I don't think it wil not work, but how it WILL work, i don't know.....

Hope you can give me good advice!
Thanks so far

Sarel
Want to specially use it in South Africa next month.

Sarel said:

Hello,
I am a starter with using flash :h?: .......and want to use it for fill flash.
Now the question:
If I put on my 300/4 lens, and a 420 EZ flashgun on my EOS 5, is it then still usefull? What i mean is, the flash can zoom in from 24mm up to 80mm(or more, don't know now), So if i put om my 28-135IS lens it zooms with it up to the maximum zoom it can handle.
But what now if i put on the 300mm lens? Say the object is 20meters away, or maybe 40meters, will the flash reach the object? What SETTINGS must i use? Where do i put the zoom on on the flashgun?

Can someone please give me some help?
I don't think it wil not work, but how it WILL work, i don't know.....

Hope you can give me good advice!
Thanks so far

Sarel
Want to specially use it in South Africa next month.

Click to expand...

Hi Sarel,

I am no expert on flash, but I think you're asking too much of your 420 to reach 20m. Is there not a chart for the flash gun giving the exposure settings you need at various distances / ISO ratings ? If not, there is a standard rating system for flash guns (can't remember what it is called). I'd guess your's is either 42 or just possibly a 420 depending on what scale is being used now. Search the web or ask a local photographer, there should be standard charts for your rating. Look at those charts and I think you will find 20m is way off the chart :-(

Generally, light intensity reduces according to the square of the distance it has to travel. Light from a flash has to travel from the camera, to the subject and back again - in this case 20m there and back or 40m.

So if your 420 can light a subject nicely at 4m for your 28-135, your base "index" is the square of 4 times 2 - i.e. 64. At 20m your "index" will be the square of 20 times 2 or 1600. Roughly, you will need a flash 1600/64 or 25 times the intensity.

What can you do about this ?

I said "generally". Lasers focus the light so that this "square law" does not hold. If your flash was similarly focussed, the loss between camera and subject would not be so bad. However, the return path to the camera would not be focussed like a laser, so the square law would apply.

A more practical method is to place the camera and flash nearer the subject. Eric Hosking was a master at this, devising all sorts of innovative ways of firing the camera so he could be well away from the owls he wanted to photograph. you do need to be able to predict where your subject will be !

The flash alone can be moved closer, but that only achieves part of the benefit - the light has to travel back to the camera. In the example above, if the flash could be 2m from the subject, the index would be the square of 20+2 or 464. That requires a flash of roughly 7.5 times the intensity - quite an improvement on 25 times. One way to achieve this is to buy a "slave" flash or unit. A slave flash is triggered by the flash from your main flash, but they tend to be low power, not really suitable as main lighting. A unit does the same job, firing flash gun(s) attached to it. One worry in this case is that at 20m the slave might not be sensitive enough to detect the flash from your camera.

I hope this will trigger people who really know to give you better info,
Mike.

Mike,
Thanks a lot! Does help a bit, and i hope someone else has got some info as well!

Yes, thought 20m was to far and the 40 even out, but if you don't know anything of flashes, you startto quess! Ind i think that is where the problem starts.......

[I'd guess your's is either 42 ]
Yes, it is 42.