### 4x5 with 210 lens.when i take a picture of head and shoulders it is underexposed by how much should i open up by ?

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using a 4x5 with a 210 lens i keep underexposing when taking head and shoulder shots.Is there a formula to work out how many stops i should open up by.

-- eric belgrave (ericb@sunbeach.net), July 20, 2000

There is a test you can do and it is usually shooting a white wall at 4 stops under and 5 stops over the meter reading. When the film is just barely dense you've got it. I'm not going to explain it, but it is in at least 3 books. Then you figure it out with your development. For instance, my 240 Schnider has such a slow shutter it is 2 stops over, and my little Ektar is fast. Then you fudge. If you run the test you always know. Lots of people hate calibrating, and I'm not Zone calibrated, but it sounds like you need at least a fudge calibration. Dean

-- Dean Lastoria (dvlastor@sfu.ca), July 20, 2000.

Bellows extension requires a 1/2 stop exposure increase for every 25% increase in bellows draw. In other words, a 10 inch lens at infinity requires no increase, at 20 inches extension a 4 x increase or 2 stops, at 15 inches extension, 1 stop and at at 12.5 inches a half stop increase.

-- Sean yates (yatescats@yahoo.com), July 20, 2000.

Hi Eric... There is a bellows factor to figure in... as if it all was easy to start with!!!

When the camera to subject distance is less than 10 times the focal length of the lens, more time is needed.

Bellows length squared(you have to measure with a ruler) divided by the lens size squared gives you the "magic" number that you must multiply the metered exposure with.

For example, using a 10 inch lens at less than 100 inches...

A 20 inch bellows draw at focus, squared =400

Using a 10 inch lens, squared = 100

Bellows squared divided by lens size squared is 400 divided by 100 for a factor of 4...

I hope this helps, Eric... it is easier to do than explain. It is better described in the Steve Simmons book... Best wishes - Dave

-- Dave Richhart (pritprat@erinet.com), July 20, 2000.

I agree with Sean and Dave in their assessment of your problem, and I believe they are correct in their calculations... however, you may find this simple (and free I might add) tool useful for compensating light falloff due to bellows extension. It's call Quick Disk, and it can be found at this web site... http://www.salzgeber.at/disc/index.html I think it will be useful enough to get you in the ballpark in your exposures. Good luck!

-- Gary Jones (jonesgp@dteenergy.com), July 21, 2000.

I have been using the Quick Disc when taking head and shoulder or full face shots with a 210mm lens on a 4X5 camera. The exposures are band on, every single one. The Quick Disc is easy to use and very accurate. I guess there is such a thing as a free lunch!

-- Mark Nowaczynski (archivalprints@home.com), July 21, 2000.