[IanCD]

Hi Serkan, Vieux Loup, all...

Thanks for the comments...

I appreciate there's no substitute for experience..!

Wim's links to tools were what I was looking for... not to use them to calculate for any given photo but because they've told me just how shallow depth of field is in a particular situation, and therefore how precise focus wiould have to be in that situation... or, if I want more latitude, how much I need to stop down to get that...



So pretty much as you suggest, VL - though could you clarify what you mean by "use spot measuring for your AF...?

Interesting, Serkan, that you drop down to f/3.5 with the 135mm... is that on FF..?



And, Wim / BC, if I can ask again without provoking an argument (please!!), if BC's calculation wasn't quite accurate, I'd still like to know how equivalent aperture (for DoF, not exposure) between FF and DX sensor is calculated, even if only in principle... one could get pretty much the same result as you did, BC, just by multiplying the aperture by the crop factor: 1.8 x 1.5 = 2.7...

Somehow, I doubt that's how this works - though happy to be told otherwise: it does seem pretty close to that on the [url="http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm"]CinC equivalents calculator[/url] (same link I posted earlier).

<img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='' />



Ian