Allow film to flatten between exposures

This is not a question but more of a "commercial" for two of the

articles on Robert Monaghan's Medium format articles page

(http://www.smu.edu/~rmonagha/mf/index.html).

 

The two articles are found on:

 

http://www.smu.edu/~rmonagha/mf/flat.html

 

http://www.smu.edu/~rmonagha/mf/focus.html

 

The articles deal with the importance of film flatness. In summary

I interpret the articles as follows: For all apertures larger than

f16 we need to be aware of variations in film flatness. In other words

for most of our photography (at least for me). Very small variatons

from a perfectly flat film will reduce the sharpness and contrast

from a lens quite significantly (a contrast reduction of appr. "45%"

is mentioned for relatively minor variations). In other words, your

favorite lens is not giving you all that it can and neither can it

deliver consistent results since the film flatness will not be

consistent.

 

Film flatness will be affected by film-pressure plate softness/

hardness. It will be affected by the swing of the rear shutter in

SLR's with leaf shutter lenses (since they are the ones who have

rear shutters in the camera body) which creates a vacuum during

exposure. It will be affected by the time that the film has been

allowed to rest between exposures (the film is most buckled

immediately

after winding). It will be affected by the film holder mechanism

etc. etc.

 

The solution seems to be to either accept that the image sharpness

is good enough as it is or to let the film rest for a while between

exposures (to flatten after winding), to use mirror lock up (which

also opens the rear curtain in the SLR - reducing possible vaccuum

during exposure), to check that the pressure plate hasn't got to

sloppy.

 

I post this because I feel that even though film flatness is an issue

that gets debated frequently the two articles provide a deeper

understanding of the problem and also state that it takes pretty

small apertures to get rid of this problem. Since many lenses are

at their optimum on f5,6 - f11, when film flatness still is a problem,

all precautions need to be taken to minimize this problem.

 

It also explains why Contax use their RTS III when they shoot the

pictures that they blow up for their exhibition-posters (RTS III =

vaccuum film plate).

Interesting point. With the MF cameras that really run the film back and forth, like the hassey, I understarnd this is an issue. With the cameras that keep the film straight as possible, this is less of an issue. This in some part may explain why, very experiened printers report that the fuji and p67 tend to give the sharpest results of all MF cameras. The p67 is used for astronomical photography for this very characteristic. I am constantly impressed with the wonderful sharpness of my large B&W prints from my p67.

I think that if what we're shooting in medium format allows us to wait for the film to flatten we really should be using large-format sheet film anyway.

One of the old Rollei TLR promoters (Fritz Heinle?) recommended winding just before you shoot because the film would then be at its maximum tension. Waiting would allow the tension to relax and the curl to return.