Newbie Question on Fuji MF lenses.

[raytoei@gmail.com]

I like my Fuji GW690II camera. It has a 90/f3.5 lens and it produces a whopping 6x9 negatives. A couple of things has been bugging me and I hope to use this forum to ask intelligent questions on this lens (or at least, hope that someone can point me to the right direction):

a. Why is there a f32 aperture on this camera ? Assuming I use a 100iso film in 120 format. And assuming a bright Sunny 16 or as recent members have pointed out that Sunny 11 is more relevant in certain geographies, isn't f22 - f32 redundant ?

I read that such small apertures isn't unique to mf, even large format cameras have f64 apertures like that used by A.Adams.

Is the answer due to optimum sharpness ? ie. the lens is sharpest at f32 ? The only reference I could find was on dof and the apertures for the lens to achieve optimum sharpness.
( http://www.kenrockwell.com/tech/focus.htm )

As a corollary, does it mean that if I focus at f3.5 at infinity, it may not be as sharp ?

b. Does the DOF change at f4 between 35mm and 120mm format ? In 35mm lens, a 50mm lens at f4 is pretty deep, a portrait picture, assuming a well aligned RF, would capture most of the facial features. On my Fuji 90mm lens at f3.5, i find that i have to be very precise in my focusing, and I do get misses. Is this normal ?

Here is a picture captured yesterday morning. The film used is Kodak T-Max 400, captured at f22 and 1/250. I adjusted the contrast digitally which in retrospect I should have used orange or red filter instead.

thanks

raytoei

 

[sper]

As the film gets bigger your lenses get longer in order to cover the format and maintain a normal field of view. Also as your leses get longer you have less depth of field, so you often need smaller apertures to get everything in focus. It doesn't really have anything to do with sharpness, just depth of field.

Also larger formats are often used on tripods, so it doesn't matter how much you stop down.

 

[x-ray]

A 90mm lens on 35 mm has the same dof as a 90 mm on 4x5 for a given image size. If you fill a 35 frame with a person standing and use the same focal length on a 4x5 and fill the frame with the same subject your dof is more shallow at the same aperture.

As you stop your lens down from f3.5 the dof increases. Sharpness increases until you are two or thee stops down and then sharpness decreases due to diffraction. Best sharpness is 2-3stops from wide open on most lenses.

These are professional cameras and were designed to shoot with studio strobes. Some strobes are so bright and can not be reduced enough in power fOr exposures in the 8-16 range so smaller alertness are marked. Also you may want to stop down for increased dof in some cases. Also by using slow film and small apertures it's possible to get longer exposures for motion blur. I've had lenses for my view cameras that stop down to f256.

As the speed of a lens increases and the format increases you will find focusing much more critical and you may miss focus. It requires much more care focusing than with a 35mm camera.

 

[ottluuk]

Actually, quite a few 35mm lenses can be stopped down to f/32 or even f/45 for extra depth of field - this is quite common on macro and long telephoto lenses.

At these very small apertures, diffraction degrades images quality significantly. But the larger the format, the less you need to enlarge your negative to arrive at a given print size so the negative effect of diffraction is less visible in MF and LF images compared to similarly sized prints from 35mm.

I used to use f/22 a lot to get maximum DOF for landscapes (35mm) but the images were not as crisp as those shot at medium apertures. These days I generally use f/2.8 - f/11, pay more attention to where I place the focus point and worry less about getting everything sharp from 50cm to infinity 🙂.

 

[raytoei@gmail.com]

thanks for all your reply.

Fuji GW690 is sharpest at f11 according to
http://www.hevanet.com/cperez/MF_testing.html

To create a dramatic sky, assuming 100iso film:

f8.5 + 1/60+ Orange G (hoya) + tripod for stability.

raytoei

thanks

 

[pagpow]

Hi, raytoei,

Thanks for reminding me of that resource. Unless I am misreading, it shows the GW690III to be sharper at f5.6 than f11 (equal middle and edge and sharper central) and f8 shows better resolution center and edge than f11, so the sweet spot is f 5.6 to f8/11, depending. That should extend your hand holding options, if interested.

G