Exposure Compensation for 210mm

[Slade Zumhofe]

At 1:1, the extension is 2x focal length, and the exposure compensation is 2 stops.

With 31 cm extension and a 210mm lens, you need one stop compensation. Think of the aperture scale: 22, 32, 45... The 210mm focal length is 21cm, think of "a tough below 22". Rack it out to a bit below 32cm, and that's one stop. A bit short of 45cm is two stops.

I "think" what I am about to say is what Ole said--only in American terms. A 210mm lens is 8.25 inches--call it 8 inches. Think of this as f/8. If you extend your bellows to 11 inches--call it f/11, 16 inches = f/16 and so on. The difference between f/8 and f/....whatever your extension equals in stop is the amount of exposure increase you will need. Just convert all your lenses to inches--and take the closest f/stop. Remember 25mm is about 1 inch.

Sounds very elementary but it really works. I have tested it on every lens just short of 1:1---can't say for sure if it works for that or not.

Hope this helps.

[Eric Woodbury]

Slade

This is the rule I use and have for 20 years. It always works, 1:1 or otherwise. Maybe not close enough for chromes, but I'm not a chrome.

[Ken Grooms]

I just got my camera about an hour ago and I already love it!

The accessories will arrive Thursday (from Calumet), but I'm already practising. I placed a subject close-up - about 4 feet away. I measured the length of the camera with bellows closed - about 8 inches. Then I measured after focussing with the bellows racked out - about 12 inches. So, according to what everyone is saying, I'll either open up one stop or double the exposure time. Am I right?

(As a side issue - what is the optimal aperture for the Rodenstock 210mm f/5.6 Sironar-N MC - f/22? Thanks.)

P.S. I can't believed the condition my camera and lens is in - they look practically new!

[Andrew O'Neill]

Isn't the formula: Bellows Extension Squared divided by Lens Focal Length Squared?? I've always used this to determine exposure compensation...

[Slade Zumhofe]

You are correct Andrew--some say (bellows extension/focal lenght)squared--all the same actually.

The method described above has some math behind it but it does work and is used to get rid of the math.

This is a great article I found regarding this principle--has a connection to this forum as well.

http://www.largeformatphotography.in...ws-factor.html

[Alan Davenport]

I measured the length of the camera with bellows closed - about 8 inches. Then I measured after focussing with the bellows racked out - about 12 inches. So, according to what everyone is saying, I'll either open up one stop or double the exposure time. Am I right?

Perhaps not. The baseline for bellows calculations is with the lens focused at infinity, and it's not at all clear that you started there. At infinity focus, by definition, the bellows extension is equal to the focal length of the lens. You then calculate exposure compensation based on how much MORE the bellows are extended from the infinity position.

[Slade Zumhofe]

Since he was originally talking about a 210mm lens I assume he meant focused at infinity when he said "closed is 8in.". "Closed" probably wasn't the best choice of words but I think I knew what he meant.

To answer your question--yes. If you use the f/stop--f/8 to f/11(ish)--method that would be 1 stop. If you want to do the calculations: (12/8)squared....or 2.25. This gives you an exposure factor of 2.25 rounded to 2x or 1 stop.

Hope this helps.

[Mtang]

These tips on using the fstop scale as a guide is great, thanks.
One thing that's unclear to me is - are you suppose to be adding the fstop adjustment (say it's 1 stop, adding from f/8 to f/11 keeping the same exposure time)? If so, it seems counter-intuitive to me, since you need more light to compensate for the bellows extension, wouldn't you open the aperture wider or subtract the fstop
(say to f/5.6)?
Thanks,
Mylinh Tang

[Slade Zumhofe]

That is correct. I can see how you could misread this into thinking that is what you need to do with exposure--go from f/8 to f/11. The method only helps you determine how much extra exposure is needed to compensate for the bellows extension. You may be at f/32 or f/22--doesn't matter. f/8 represents an 8 inch (210mm) lens and f/11 represents the length of the bellows when focused at a close object or 11inches of bellows extension. If your settings were at f/32 you could open up one stop or...increase your length of time (shutter speed) by one stop. Either way--with this example you are correct--you need 1 stop MORE exposure.

[Mtang]

Got it. Thanks.