ISO control / Shutter Speed question

[james_tigerwoods]

I've been shooting in low light a lot recently in "P" mode and I've noticed that my D40 is pretty quick to switch down to ISO1600.

I'm happy to shoot in "P" mode, but not altogether thrilled about ISO1600 due to the graining you get.

So I've got two questions really:

On a D40, can I stop it from doing this without using Manual mode.

But in general - what's the difference between using a lower shutter speed and (say) 400ISO and using 1600ISO and a higher shutter speed?

Not sure if I'm making sense, but what I'm driving at is a better understanding of how use and to mix & match ISO and shutter speed.

Thanks

JTW

[Ed_P]

What type of low-light stuff are you shooting James?

[james_tigerwoods]

Ed_P said:

What type of low-light stuff are you shooting James?

Nothing special - I just happen to have been to some indoor functions recently (christening, wedding reception) - nothing I'd bother trying really hard at, but when I'm trying to photograph my daughter and it drops to 1600ISO, the grain on it can be a bit poor.

It's not so bad if I'm using the flash (always the speedlight), but it still sometimes flips to 1600.

[andy-xr]

The flipside being of course, if it stuck to ISO400 and you had exposures at say 1/10th, there'd be loads of blur

Seems to be a characteristic of the D40 to do this on matrix metering, mine does it too. You can set max ISO in the Auto ISO settings from memory, faster glass/wider apertures would also help but then you've got depth of field to consider as well on your focus points

[james_tigerwoods]

There is a "fear" there as I've still not learnt to use manual mode properly yet - I've done aperture and speed priority, but not manual - I should, I know that, but just haven't mastered that yet.

[Ed_P]

I suspect that others will advise this too, but to really take control when using Speedlight flash indoors is to use Manual mode on the camera. This way, the camera's gizmology is not making the decisions for you.

I realise that you specifically didn't want to use Manual mode, but it really can be liberating once you've gained the confidence (through practice/trial and error). A good "default" setup is:

Camera on Manual, ISO 400 (or 800 if image quality acceptable), Aperture F2.8 or F4, Shutter on maximum sync speed. Speedlight on ETTL (or Nikon equivalent), High-Speed Sync - Enabled.

The camera's settings are controlling the "ambient" lighting in the room. Take a test shot and adjust using shutter speed. The Speedlight is contolling the "subject" lighting. Control using Flash Exposure Compensation (FEC). These are the only two controls that you need.

My favourite blogs on flash photography are by Ed Verosky and Neil van Niekerk. Definitely worth following.

[Ed_P]

james_tigerwoods said:

I've done aperture and speed priority, but not manual - I should, I know that, but just haven't mastered that yet.

You won't master it until you start using it James! Once you have, you'll never go back.

The thing is; it's so easy these days with digital. Practice is cheap (once you've invested in Speedlights, off-camera cords, IR/Wireless control, lightstands, softboxes/umbrellas!). Seriously though, with a decent speedlight with tilt/swivel, you can get great, natural effects and we've all got an easily-accessible "test" environment; at home with the lights off.

I remember my first attempts. I put the camera in Manual and adjusted ISO, aperture and shutter speed so that the camera's metering was showing around -1.0. The flash was on ETTL and swivelled round to bounce off the wall behind me. I took the shot. It was perfect! It can be that easy; I'm definitely a Manual man now ..

[RobDickinson]

It sounds like the D40 is using auto ISO on P mode.

On nikons you can set a range I beleive BUT this doesnt take into account the focal length of the lens.

So its assuming the longest end of the lens or something.

Assuming your using the kit lens..

So it'll give you a good shutter speed for 55mm even if your at 18mm.

And this will be at f5.6 too.

ISO 400 vs ISO 1600 is 2 stops (400-800-1600), so your looking at 4 * the shutter speed if you want to shoot at ISO 400 ( say 1/50th to 1/10th) much harder to hand hold BUT I assume nikons Auto ISo isnt taking into account VR.


This is where fast lenses come in. An f2.8 lens would be able to shoot at the same shutter speed as the kit lens but at ISO 400!

[RobDickinson]

Oh and as for manual mode, the camera still meeters in manual mode, so you know if your close to what it thinks is the correct exposure, you just need to controll how thats achieved.

In low light this typicaly means setting aperture to the largest available then shifting the shutter speed, and incrementaly bumping the ISO untill shutter is quick enough to avoid blur.

For flash shoot in manual mode too.