Fuji GX 680 Bellows Factors

[winney]

I just did a portrait shoot with my gx 680. Its a new camera to me

and I've had great results so far. I just thought of something about

the shoot tho. I was focused pretty close and the bellows was fully

extended. I was metering my strobes on a hand held meter and didn't

factor for the bellows. Does any one have experience with bellows

factor for the 680? I was using the 210 and 300 and the regular

bellows, figure about 15cm of extention.

 

Thanks for your advice.

 

-michael

 

mdw@gomdw.com

[chris_waller]

I don't know the GX680 but on my Mamiya RB67 there is a scale on the focussing rack which gives the correct for bellows extension for all lenses. Failing that you could calculate the correction using the inverse square law.

[al_kaplan1]

The formula is focal length divided by f/stop = aperture. If you add 15cm extension to a 210mm lens you're at 360mm. So let's work this out:

 

we'll use f/4 for calculation

 

210 divided by 4 equals 52.5mm clear aparture

 

360 divided by 52.5 equals f/6.87

 

so you lose about one and one half stops with the 210mm lens.

 

300 plus 150 equals 450 divided by 75 equals f/6 so you lose a bit less, a tad over one stop.

[ken c oshkosh, wi]

Look <a href="http://www.dannyburk.com/fuji_bellows_extension.htm">here<a>

[jim_chow]

Easiest way to calculate is using the aperture scale. If it's a

210mm lens and you extend bellows by 15cm, that's 360cm.

Divide each by 10 to give 21 and 36. This is your equivalent

aperture. The difference between f21 and f36 is about the

difference between f22 and f36, about 1.5 stops. That should be

close enough. You need a simple method, 'cause after days

upon days of waking up early and sleeping late on extended

photo trips, one can easily blow something seemingly simple

like this from fatigue. :-)

[l_a_k_h_i_n_d_e_r]

This is an old thread. But calculating bellows extension needs a consideration of the nodal distance. The formulae and approaches suggested above are all fine, but the Fuji brochure tells us the magnification of a gx680 with 210mm lens extended fully is 0.22.

That is about 1/2 stop only of correction. I am not considering

the 40mm or 80mm extension rails here.

 

If you had great results so far, it could not be with severe underexposure suggested by the simple calculations.