Depth of field with close up photos

[Ole Tjugen]

Now thats thinking outside of the box!

Depends on the box - some of my boxes can be seen at www.casket-set.com and I can assure you that image field curvature is inside most of them!

[Drew Bedo]

Hey, I like that approach. Instead of seardching out and buying a lense,would it be easier to modify a holder so that it that curves the film? The film would have do dome outward from the center. Maybe by fooling atround with disks of card stock (stepped and stacked like a wedding cake) in themiddle of the holder and masking-tape to hold the edges of the film, you could get the curved shape that would work.

[Dan Fromm]

Drew, its easy to wrap a sheet of film around a cylinder. Or inside a cylinder. But how to wrap it around a sphere? Melons, as mentioned by the original poster, are usually closer to spheres than to cylinders. Yes, I know, some squash are closer to cylinders, but he asked about melons.

[ic-racer]

Hey, I like that approach. Instead of seardching out and buying a lense,would it be easier to modify a holder so that it that curves the film? The film would have do dome outward from the center. Maybe by fooling atround with disks of card stock (stepped and stacked like a wedding cake) in themiddle of the holder and masking-tape to hold the edges of the film, you could get the curved shape that would work.

I actually did this with enlarging paper once, in order to compensate for film curvature and some lens field curvature (both in opposite directions, as it would be.) Since my project involved the 'other side' of the lens, I found that I needed to raise the center of the paper six centimeters higher than the edges. That was just not possible. (So, I got a glass carrier...)

Since you are on the film-side of the lens, your only going to need a few millimeters. You can figure out how much you need with the lens equation.

SIDE NOTE: I do recall Fuji making a curved field 35mm lens in the 70s. As you turned a ring the field became more and more spherical.

[Drew Bedo]

Dan;

It won't be perfictly spherical, but its worth trying out. The curvature will only be a few millimeters.

[Dan Fromm]

Um, Drew, if the melon is approximately spherical how can it be imaged sharply on a cylinder? Getting all of the front half of the melon (that's as much of it as the lens can see) in focus requires wrapping the film on, as it were, the rear half of a melon-shaped object to keep the film-to-rear node distance the same for all points on the film. A cylinder won't do.

ic-racer, please reconsider. With a near deep subject I think that more than a few mm of movement at the film plane are needed to maintain focus across the subject. Otherwise we'd be able to change magnification from, say, 1:2 to 1:1 with only a small change in extension.

Cheers,

Dan

[Drew Bedo]

Ok, well maybe the cardboard disks won't work that well...it would be cheap enough and easy enough to try out.

Other options seem not to be effective or available. Moving the subject through a slice of light actually WOULD work.

A description of this Technique may be found on page 122-124 of;

PHOTOMACROGRAPHY: An Introduction
William White, PhD
Focal Press, 1987

If the mellon project is important, than this is a proven technique that will get the job done.

[Wilbur Wong]

My memory banks recall that years ago certain catadioptric telescopes had curved fields of focus. I think some amateurs stretched their film over a domed form. . . Also some very large telescopes I am remembering utilized ground non flat glass plates . . . But alas, this recall is from several decades ago.

[Wilbur Wong]

Ok, well maybe the cardboard disks won't work that well...it would be cheap enough and easy enough to try out.

Other options seem not to be effective or available. Moving the subject through a slice of light actually WOULD work.

A description of this Technique may be found on page 122-124 of;

PHOTOMACROGRAPHY: An Introduction
William White, PhD
Focal Press, 1987

If the mellon project is important, than this is a proven technique that will get the job done.

I'm curious about this, of course this makes perfect sense, but would the resulting image appear to be a flat disk without a sense of curvature?

[Drew Bedo]

Hello Wilbur,

This technique has been used for macro imaging small objects, I see no reason why it would not work for macro imaging larger subjects. I did a short web-search using "Dynaphot" and got a couple of hits. I can't seem to cut-and-paist to this message field though. The information is out there.

Regards,