Hi Bob, >You can't necessarily have both because if you shoot 35mm your CoC's too small.
Exactly, hence the original query! It's always useful to have other experience to draw from. I think we may have gone off a a bit of a tangent with DOF.. I mean, I know it's related knowledge, but I think I missed a stop somewhere back there and I'm now somewhere else. :-)? :-(? Rgds, Ryan ----- Original Message ----- From: "Bob W" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Monday, December 29, 2003 9:15 AM Subject: Re: Just curious ... > Hi, > > well, now you've put me on the spot! These numbers are useful for > predicting how big you can go before you start to lose apparent > sharpness, but they depend on what you as the photographer are trying > to achieve. That's why they can't be treated as rules. In the end you > decide how big you want your prints to be and that's that. Whether > they are sharp or not is for the viewers (who include you) to decide > for themselves. You probably want the critical parts to look sharp > from about 15cm away because people peer closely at exhibition prints, > instead of being good and looking from the regulation distance. People > also typically want to look at quite large prints, but don't adjust > their viewing distance, so you have to consider these human factors, > rather than just relying on the numbers - you want it to look sharp > from about 15cm away, but you want it blown up to about 60x40cm > (24x16"). You can't necessarily have both because if you shoot 35mm > your CoC's too small. 0.009mm. Sorry. > > I suppose in theory you could measure some important points and scale > them up to see if they would look sharp in a bigger print. More > practically you could look at the depth-of-field in an existing proof > print, say 15x10cm (6x4") and work out approximately how big you can > reasonably go before it starts to look unsharp, or keep zooming in > with the enlarger until the critical parts start to look unsharp. > > There's a nice simple explanation and diagram of CoC here: > http://www.tpub.com/content/photography/14209/css/14209_37.htm. You > need to grasp this to understand depth-of-field, which depends on it. > In your example below, you will have reduced depth-of-field in the > prints compared to smaller versions, or the same size seen from a > different viewing distance. This may or may not be important - only > you can decide. At some magnification and distance nothing will look > sharp; at others, everything will. > > 0.036mm is not a number you have to try and conform to, it's just a > pragmatically useful reference point used as a constant in optical > calcualtions. You probably could conform to it by shooting for a > specific size of print, being very careful about your depth-of-field > calculation, and controlling the viewing distance, but really this > is only likely to be practical (if at all) if you're shooting for > billboards or something. > > -- > Cheers, > Bob > > > Sunday, December 28, 2003, 2:04:33 PM, you wrote: > > > Thanks Bob. That more or less forced me to relook through old bookmarks > > which at the time, I looked at, cringed, then consciously decided to revisit > > sometime in the future :-) I can't say I more than vaguely grasp the concept > > of CoC. So say I've made an A1 sized print (594x820?) from 35mm- viewing > > from 1.5m to 2m would (I think) look like: > > > c = (36 * 1500) / (1000 * 594) = 0.091mm. > > c = (36 * 2000) / (1000 * 594) = 0.121mm > > > Now for the more ignorance-revealing bit: How then would I make use of those > > figures? Does it mean I need to readjust one of the variables to conform to > > 0.036mm? Like for 4x5 it'd be closer to 0.1 wouldn't it? > > > Rgds, > > Ryan > >
