Probably a very stupid question...

Hi, I apologise in advance but hopefully someone will take pity on me rather than laugh!

Say I want to take a picture of a nudibranch at 15m in UK waters (so it's not veyr light down there) and I want the background to be black. I set the F stop to around F22 yes? But then I may have to open the shutter speed so much so that the shot becomes blurred (ok I know they don't move fast but you get my gist)

Do I just set myself a minimum shutter speed that links to my strobe and rely on manual strobe settings to give enough light, adjusting as I go along, or is there a better / right way to get the effect I want?

Once again apologies, I really am very much learning!

Hi, I apologise in advance but hopefully someone will take pity on me rather than laugh!

 

Say I want to take a picture of a nudibranch at 15m in UK waters (so it's not veyr light down there) and I want the background to be black. I set the F stop to around F22 yes? But then I may have to open the shutter speed so much so that the shot becomes blurred (ok I know they don't move fast but you get my gist)

 

Do I just set myself a minimum shutter speed that links to my strobe and rely on manual strobe settings to give enough light, adjusting as I go along, or is there a better / right way to get the effect I want?

 

Once again apologies, I really am very much learning!

Well it depends a little on what camera and strobe you are using so that information would be helpful. But you are basically correct. You are wanting to underepose the background and properly expose the foreground. So you use a high aperture value. You should then set the shutter speed to be somthing that is fast enough to not cause blur. Usually 1/90 is sufficient, but sometimes 1/60 will work and to be conservative you might pick something like 1/125. Your camera light meter should now be telling you that the picture will be very underexposed. That's OK because the strobe will fill in the foreground. Depending on how your system works, you then either pick a manual strobe power that will give you what you want, or rely on TTL and adjust the flash exposure compensation if necessary.

Mike

Thanks very much Mike, much appreciated.

Currently I'm using a Canon 400D and a S&S YS 90Duo strobe but struggling with the lack of power control hence the question really I guess.

Am trying to decide between the Ikelite DS125 and the Inon Z240, I like the fact the Inon has multi power settings which prompted the question

Thanks again

Thanks very much Mike, much appreciated.

 

Currently I'm using a Canon 400D and a S&S YS 90Duo strobe but struggling with the lack of power control hence the question really I guess.

 

Am trying to decide between the Ikelite DS125 and the Inon Z240, I like the fact the Inon has multi power settings which prompted the question

 

Thanks again

I find that the four power settings on the DS-125 are plenty for me. Anything other adjustment is more easily made by moving the strobe slightly or adjusting aperture (which for me is easier because I don't have to reach over to the strobe) gets the "in between" steps just fine.

Mike

Great, thanks for your help (again!)

Please note that the shutter speed will make very little difference to subject if it is being lit by the strobe - as long as you don't set it faster than the sync speed. What I mean here is that if you are lighting the nudibranch by strobe and you set the aperture at f/22, you won't get any more or less light from the strobe by varying the shutter speed.

If you want a black background, set the shutter speed to the fastest speed that is still in sync with the stobe. For the 400D that is 1/200". If you are not getting enough exposure from the strobe, either move the strobe to a higher setting or go for a larger aperture.

Also note that the "power" settings on a strobe generally don't change the brightness of the strobe but rather the duration. On full power, the duration is probably something like 1/1000" and as you reduce the "power", you are actually reducing the time the strobe is lit. On low power, the duration may be as little as /10,000". Even on full power, it is generally quick enough to freeze most motion.

That's fantastic help, many thanks ATJ, most appreciated.