Can someone give me a 101 please

[jannie]

I had a discussion with a videographer friend about depth of field, shutter speeds, ISO and was explaining the relationship. I thought the frame rate would change if you wanted to keep the ISO constant and change the depth of field - he had no clue.

How does this work with DSLR video - what changes when you change the aperture (without changing the ISO or available light)?

[DjfLoYd]

From my understanding of your question, when you change the aperture on the DSLR, in full manual mode, you will either over or under expose. The DSLR does not automatically adjust ISO or shutter speed to compensate for the more or less light you are now letting through due to the aperture change.

If shooting 25p on a 5d mk II with a prime lens for example, and you want less dept of field you would open the aperture (as this would make the largest difference in DOF). If you found that subsequently the image is over exposed you would either have to drop the ISO lower if possible, increase your shutter speed (not recommended as it has other effects on motion blur that could be undesireable), decrease the amount of light on your scene or use a ND filter of appropriate strength.

Hope this answers your question.

[Nicholas de Kock]

Pretty much what Loyd said, when filming you try to keep you shutter speed constant at twice the rate of your frames per second for example when you film at 25P your shutter should be constant at 1/50 this gives a pleasing motion blur. When you shoot at a higher shutter speed you get a staccato effect which has it's place like the battle scene in Gladiator or Saving private Ryan. Unlike photography you do not change your exposure with your shutter but you will decrease the amount of light entering your camera with a ND filter, close your iris or use the ISO.

[jannie]

Unlike photography you do not change your exposure with your shutter but you will decrease the amount of light entering your camera with a ND filter, close your iris or use the ISO.

thanks, this makes sense (as well as Loyds comments), but can you use different ISO settings or is this set for you?

[Nicholas de Kock]

Yes you can change the ISO as you need, the lower your ISO the cleaner your image. I personally never shoot above ISO 1600 on the Canon DSLR's when filming video but even at ISO 1600 it's pretty noisy however this is based on technology & as newer better sensors are developed we will be able film at higher ISO ratings with pleasing results - the Sony FS-100 is an examples of this you can shoot at ISO 6400 with very good results.

[Forgiss - Sean Nel]

...Unlike photography you do not change your exposure with your shutter but you will decrease the amount of light entering your camera with a ND filter, close your iris or use the ISO.

and on this point... it seems we will be getting some variable ND filters soon... friggin finally!