Rule of thumb for Canon IS lenses - and ISO settings?

[jepsie]

Hi all,

I have the otherwise great Canon 5Dm2 and I really enjoy the auto ISO.

However, the camera does not take the IS on IS lenses into consideration, and I was wondering if there was a rule of thumb to calculate how many ISO stops (is it called that?) you can manually compensate with after having applied ISO automatically with an IS enabled lens.

Anyone??

To give you an example:

With auto-ISO, I take a shot of my Cornflakes box at ISO 1250. I manually adjust that down to ISO 250 and still get the ingredient list equaly sharp.

24 - 105 @ 105mm.

Iso 1250 vs. ISO 250 - quite the difference!

/jepsie

[sybren]

Funny that you think in terms of iso-compensation. I always think of IS as giving me more headroom in shutter speed. Anyway, it really depends on the body, the lens, the focal distance you use it at, etc. What's more important: it also depends on you. When you can hold your hands really still, you can get more "stops" difference out of your IS. When you're a shaky bastard, the IS won't help nearly as much.

[jepsie]

Yup - I guess this goes both ways ;-)

But no need to spoil a handheld picture with ISO 1250 when 250 is more than enough to keep it sharp.

[sybren]

And that's why I have my camera set up at full manual exposure - no surprises, and I get exactly what I want to get (or at least what I asked for )

[jepsie]

Well - I think Id be missing out on some good shots, if I only used full manual. Sure, for landscape or some portraits - no problem, but for some situations like street photography or news photography, auto ISO is king - especially if...

But if you introduce auto ISO, wtf dont you take IS into consideration... I mean, the camera actually takes focal lenght into consideration, so I guess applying the information to some algorythm that takes both iso, is, focal lenght etc into consideration should be manageable. Oh well, maybe next firmware upgrade.

In the meantime... Anyone dare to estimate the relationship between ISO and IS?

If not I guess I'll run some tests and eventually figure it out myself ;-)

[OsmosisStudios]

The cameras auto-iso system assumes you want to freeze action: IS helps you take pictures of objects that are standing still, but its useless with a moving subject: the AUTO-ISO is trying to give you a fast enough shutterspeed to freeze the subject's motion, not only your own.

[jepsie]

Ach, wouldve been handy to manually adjust whether you want to stop motion OR shoot with a low ISO. Anywho - I'll try to figure something out and will post results back as there for sure must be some rule of thumb applying to this. . I think this is one of those things Canon slowly gets right - I remember my beloved 40D also had an auto ISO function, meaning it automatically chose ISO 400 for all shots. Very usefull, Canon ;-)

[OsmosisStudios]

How about setting the ISO yourself? AutoISO really isnt the best option: it's the last thing you should be playing with to get your exposure right.

[inkista]

Originally Posted by jepsie

With auto-ISO, I take a shot of my Cornflakes box at ISO 1250. I manually adjust that down to ISO 250 and still get the ingredient list equaly sharp....

A stop is a doubling of the light, or a doubling of the iso.

So, 1250 -> 625 -> 312, so you're getting just a little bit over 2 stops from the IS. That's typically what I find with the 24-105's IS: you can always count on two stops, but not necessarily more than that, despite marketing claims. So, whatever number the autoexposure gives you for iso, quarter it, and that's about where you want to be. With shutter speed, you can quadruple it (i.e., 1/100s -> 1/25) and you'll be ok. And with aperture, you can stop down two full stops and still be ok.

This is why we use a stop/EV as a measurement for exposure: you can swap it among the three main settings however you please.

So, in shutter speed terms, with the 1/focal_length rule, if you're shooting at 105mm, you want your shutter speed to be at 1/105s or faster. But with the IS turned on, that means you could go down to 105 -> 52 -> 26, so 1/25s or so is probably your handholding limit, shutter speed wise.

Sybren--for a lot of newbies, thinking in terms of ISO actually makes sense, because it's the single control you can easily grasp the effect of with P&S cameras, and it's the one control nearly everyone with a P&S uses.