Slide rules?

Does anybody know where I can go to get slide rules to print out (preferably free)?

I'm trying to do a nice slide rule so that I can gauge my depth of field on my 17-35 and 28-75 zooms. Ideally, I'd like to do it for up to 300mm.

I've seen them as a linear slide rule but al I can find for home printing is circular or tables. Slide rules are easier to use in the field than tables.

Anybody any ideas?

http://dofmaster.com/

Yes. Seen that - that's tables and circular calculators. I'm looking to have a linear slide rule. Oh well, I guess I'll have to get busy with a ruler, pen and scissors and design my own.

DOF is as much concept as calculation. You could try my Excel-based DOF calculator (click the link in my signature) and print out some table at various focal lengths.

What you need in the field is a guide that gets you in the ballpark.

Yes. It's a crying shame they don't put DOF guides on lenses any more. I'd say this is the biggest flaw of the Canon system - because you can't turn the aperture manually, they stopped putting DOF lines on the lens barrels.

I dunno. DOF, or how you define it, varies by camera format (size of film/sensor) and nowadays the same lenses are used on different camera formats. And since it varies by focal length, it's pretty tough to put such a guide on a zoom lens, unless it's a push-pull type.

Canon do put DoF markings on the distance scales of some prime lenses - the EF 85mm f/1.2L II is the example that comes to mind, though there's many others. Sometimes the scale is quite fulsome, sometimes it isn't. The EF 50mm f/1.4 only has f/22, and it's not along amongst the longer primes - I guess there just isn't room for markings for more usable apertures (which would come inside f/22).

It doesn't matter that the aperture is under electronic control from the body. What does make these scales less practical is the short travel of the focussing ring on an autofocus lens. It's almost impossible to put usable DoF markings on a zoom lens.

I believe most EF mount have a distance scale that the body can read (E-TTL uses it). If so, a DoF guide that appears on the LCD would be useful, as would embedding distance in the EXIF.


David

DOF scales in zooms are impractical as it varies for each focal length. I do think that high-end primes have such a scale.

Slide rules and circular calculator have the same problem: it has to be different for each focal length. A mess if several primes and unusable for zooms.

I have yet to do this but I recommend tables in set of two laminated back to back. Easier to read and can be linked together with a key ring.

Now what would be nice if some group of programmers at Canon got together and put the calculations in the camera then displayed that data in the viewfinder.....never mind I was just dreaming, better now.

I think Minolta did that or was it Canon?