Hi all: I've tried to search the net for this answer, but haven't come up with it. I'm looking to buy a 4x5 soon, to replace my Crown Graphic for studio use. My objective is portraiture, so I'm looking for lenses in the 3-400 range. I can't seem to find a formula to determine how much bellows draw my camera would need to accomodate such a lens in CLOSE UP, NOT infinity. I know, for example, that I'd need a twelve inch bellows-draw to bring a 300mm lens into focus at infinity, but I don't care about infinity, I want to focus at 5-6 feet. Can anyone tell me how to determine that so I can make a wise choice in cameras?

Thank you

-- Joshua Slocum (jayslc@yahoo.com), June 27, 2001

Answers

Joshua,

I have run into nearly the same issue a few years back. I wanted to know how close I could focus a 300mm lens at my maximum bellows draw. The formula is:

1/f = 1/So + 1/Si

f = the lens focal length (mm) So = the object distance (mm) Si = the image distance (mm)

This is the Gaussian Thin Lens equation, and maybe not exactly the right one to use, but I have verified the results on numerous occations. I have this on a spreadsheet, so I ran your setup:

Lens = 300mm Object distance = 1500mm (a little under 5 ft) Image distance = 375mm (the bellows draw)

Godd luck,

~Ted

-- Ted Brownlee (OMFBH@AOL.COM), June 27, 2001.

Hey Todd, thanks so much for your help! That really makes this easier.

-- Josh Slocum (jayslc@yahoo.com), June 27, 2001.

In addition to extending the bellows, you can also make or buy "extension tube" lensboards. There are also telephoto design lenses which require less extension than the standard formula indicates. I use a 360mm telephoto lens on an extension tube board for portraits with a field camera which has only 12" of bellows.

-- Chris Ellinger (chris@ellingerphoto.com), June 28, 2001.

Joshua:

You can figure this out by formula but it also helps to think about what type of specific studio shots you will take. If you plan on doing portraits, I would think in terms of full-body portraits, head/torso portraits, and head shots. A 300mm lens would be nice for head shots but shorter lenses (180,210,240) work fine as you move towards full-body portraiture. And unless you plan on doing very close facial details, anything over 300mm might be overkill. Indeed, a 300mm lens focused at 1:1 will produce an image covering roughly the lower lip to the top of the eyebrow.

Shorter lenses, combined with full or half body shots, should not pose many significant bellows extension problems. On the other hand, a 300mm lens at 1:1 will require about 24 inches of bellows extenstion. You should also think about whether your studio work will eventually include other areas such as still life, closeup, or tabletop images. These areas may involve image to object ratios that are greater than you might find in portraiture. A 300mm lens would be reasonable but you may find that closeup work results in much longer bellows extensions. Here, a 36 inch bellows might be called for. I hope this perspective helps.

......................................

-- Dave Willison (dwillisart@aol.com), June 28, 2001.