Photo Techniques Magazine and Bellows-Extension

[James Bleifus]

I don't know about other LFers but I've struggled a bit factoring bellows-extension into my exposures. The Jan/Feb issue of Photo Techniques Magazine has a chart that makes calculating exposure with extension easy. Might be worth a look if you've had problems like me.

Cheers, James

 

[eumenius]

Oh, I always use a disc tool to compensate for bellows factor - it can be found for free at http://www.southbristolviews.com in PDF format. It's so easy and convenient - print it out, clue to cardboard, cut and use. Two scales there, by the way. If it's broken or dirty - throw it away and make a new one

 

[matt miller]

I have a "QuickDisc" (http://www.salzgeber.at/disc/down.html) in my bag, but very rarely do I use it. I usually just guess. Crude, but effective.

 

[roteague]

I have a Minolta meter with a ground glass attachment. I take my readings directly off the ground glass, and don't worry about bellows extension factors.

 

[Daniel Grenier]

I too use the QuickDisc. It works perfectly well and is very quick and simple to use. This is a must have in any kit IMO and it is free for anyone to use.

 

[jimgalli]

James, here's the quick and dirty way that works just fine. I have an 8" lens but the bellows is 11 inches. The difference is the same as f8 to f11. 1 stop. And so on. I have a 14" lens that's at 20" f14 / f20, roughly same as f16 to f22 = 1 stop. 14" lens at 16" f14 / f16 = 1/3 stop. KISS.

 

[David A. Goldfarb]

I have a Minolta Booster II, but I don't use it that often. Outdoors it's too much trouble to keep out stray light. Maybe if I get a Black Jacket I'll use it more.

Instead I have a chart on the back of each of my LF cameras and one in my notebook for converting magnification ration to exposure factor. I either estimate or measure the magnification by comparing the field of view to the dimensions of the format, or for amenable subjects like still lifes, I'll actually put a ruler in the scene and measure it on the groundglass, like with the QuikDisk, except rulers are more ubiquitous than 4" disks.

 

[steve simmons]

Here is my easy rule and it works regardless of the focal length.

For every 25% you extend the bellows beyond the infinity position add 1/2 stop. For every 50% add one stop, for a 100% exension (for a 1:1 reproduction) add two stops.

for example

a 6"lens extended to 9" add one stop
a 6" lens extended to 7.5 " add one half stop

an 8" lens extended to 10" add one half stop, etc., etc.

steve simmons

 

[Dave Wooten]

Jim I wish I had thought of that....I used to tell my students to just compute the f stop needed for the new focal length (actual size of the f stop opening in mm) which is what you have done in a much simpler manner...

 

[smieglitz]

...I have a 14" lens that's at 20" f14 / f20, roughly same as f16 to f22 = 1 stop...

and is the same as f/1.4 to f/2.0 = 1 stop

The same trick will work when figuring flash exposures and distance since we are dealing with a squared measurement (radius squared for lens area and distanced squared ala the inverse-square law for flash and other point source lights). If one knows the f/stop at 10 units distance, all other combinations work just like the f/stop progression. For example, if f/11.0 works at 10 feet, f/8 will work at 14 feet, f/5.6 at 20 feet, f/4 at 28 feet, f/2.8 at 40 feet and so on. (Think 1.0 to 1.4 to 2.0 to 2.8 to 4.0, etc., for the full stop distance figures.)

Joe

 

[Nacio Jan Brown]

Disc for close-ups

I use the disc type calculator for close-ups as well but instead of printing out the a disc I use a CD. To get the measuring scale to correspond takes only a couple of minutes on a photocopy machine tweaking the reproduction size. There had to be some use for an AOL CD. njb

 

[djkloss]

I cancelled my subscription to PHoto Techniques because of all the digital stuff. I guess I'll have to get a copy of this article. By no means am I an expert, but I enjoy trying new things and trying to figure things out on my own. Anyway.......I put together a spreadsheet that caluclates this stuff for me. I used the formulas I found in books.

Here it is...it's an Excel spreadsheet and all you have to do is plug in the numbers. I only tried it once or twice so am not sure it's that accurate. -Would appreciate feed back

Oh...I guess I can't attach an Excel file, so I'll have to upload it to my website - gasp! That means you may have to see my other images - please be kind! Give me a few moments so I can upload it. If that doesn't work, I can send the file if you email me direct.

thanks.........

Dorothy
http://eriephoto.com

 

[vet173]

James, here's the quick and dirty way that works just fine. I have an 8" lens but the bellows is 11 inches. The difference is the same as f8 to f11. 1 stop. And so on. I have a 14" lens that's at 20" f14 / f20, roughly same as f16 to f22 = 1 stop. 14" lens at 16" f14 / f16 = 1/3 stop. KISS.

I read this and thought " I like this ". I tried it out and it worked great. Thanks, Jim.

 

[mikepry]

Or..............with Expo Dev one click of a button figures it out in about 1/5000 of a second on my Palm.