DOF 1:6 using 300mm Symar S on 4x5 Velvia

[parkerm@freenet.co.uk]

Hi Folks;
I'm trying to photograph some of my wife's work. She is a fine artist so we are talking about paintings. However the surface has variations of up to a 15mm in depth due to impasto technique.

I'm stopping the lens at about f11 + one third but i seem to be getting loss of sharp focus at the edges. Also I don't think the definition is what it should be.

My question is: if I get more flash power on the subject and stop down to f22 should that solve the problems or do I just need to accept that I should get a lens better adjusted for closer focus (I have a fujinon A series 180mm in mind).

If so what would be the best use of the 300mm lens which I bought for both portraits and to photograph paintings.

A mistake maybe?

Comments will be much appreciated.

Regards

Mike

[Ernest Purdum]

What size are the paintings? And what film format? If the paintings are less than about four times the size of the film, a lens intended for close-up work would be better, but I wouldn't give up on the Symmar until you tried it at a smaller aperture. Unless you have other use for an 180mm Fujinon A, One of the shutterless process lenses now so readily available would be a ;ess expensive alternative that should give fine results.

You may not need to get more flash power (if you mean buying something) to stop down to f22. Multiple flashes should work if everything is locked down solid.

Have you checked that the painting and camera back are totally square with each other? This is a common source of poor performance in this kind of work.

[Dan Fromm]

Hmm. First thought was that coverage wasn't adequate, but that's just plain dumb. You have more coverage than you can possibly use. Poorer lens performance off-axis than on- shouldn't hurt you.

Second thought was that you're focusing in the wrong place. At 1:6 DoF is very nearly symmetrical about the plane of best focus. If you're not focusing midway between the painting's high and low points, you're wasting DoF.

Third thought is that perhaps you're being too exacting. At f/13 with a CoC of .014 mm you should get just 15 mm of DoF. Your lens should deliver around 120 lp/mm at low contrast to the film in the plane of best focus, around 70 lp/mm at the edges of DoF. I don't know how much of that Velveeta can capture, since I don't use it. You ought to be able to get a good print at 7x, i.e., the size of the original. But if you examine the trannies at 12x the edges will by god be fuzzy. Everything on film is fuzzy at 12x.

If you stop down to f/22 the lens will deliver around 70 lp/mm to the film, i.e., maximum resolution will equal the acceptable CoC of .014 mm. And you'll have a whopping 26 mm of DoF, more than you need.

If the Symmar won't do it, look for a process lens that's very good near wide open. If I had to grab one without having tried all of 'em, I'd go for a dialyte type Apo Nikkor. I have three of 'em (2x305, 420, 480) and they're all better wide open than the handful of other process lenses I've tried out seriously. Open flash with a 305/10 at f/11 and very carefully focused just might do for you.

You might also consider doing a long-distance apprenticeship with Henri Gaud (see http://photothequegaud.free.fr/trichromie/ ) and shoot on black/white film. TMX and Acros should both outresolve 4x5 Velveeta. If, that is, you're a really crazy perfectionist.

But before you do much more, why don't you ask your 300 Symmar and Velveeta what they can do for you at f/16 and f/22? I mean, its just two shots.

Good luck, have fun,

Dan

[Ed Richards]

Do not worry about getting more flash power, just use multiple pops.

[parkerm@freenet.co.uk]

Thanks guys. I appreciate this. Multiple flashes! yep. Obvious when someone points it out. Thanks also for the very learned advice on DOF. I'll persevere with the Symmar and see what we get.

Mike

[tpersin]

you could also use a longer exposure? the painting isn't going anywhere