f/22 & f/32?

[Nokton48]

I have many process large format lenses that will stop down to f/240 or f/360. Essentially a pinhole at those apertures.

For 4x5" photography f/22 or f/32 in a pinch is the practical point (if you do the math and decide upon your "circle of confusion") at which diffraction is not an issue.

With smaller format I am seldom so concerned with sharpness........ It is about mobility and responding to more "fleeting moments".

Reminds me of what W. Eugene Smith once said - "There is nothing worse than a sharp picture of a fuzzy concept".

 

[ka7197]

Be f the focal length, d the diameter of the entry pupil (not the physical iris!), and k the f-stop number. Then k = f/d and d = f/k.

For a given image format, diffraction depends on d (absolute aperture) but diffraction blur depends on k (relative aperture). So the loss of sharpness through diffraction will be always the same for a given relative aperture—be it f/16 on an 18 mm lens or f/16 on a 135 mm lens.

However, diffraction blur also depends on the image format—less effective blur for larger formats. That's why large-format shooters can get away with smaller apertures without worrying about diffraction blur. So lenses for 35-mm format usually can be stopped down no further than f/16 or f/22 usually (and f/32 rarely) while lenses for large-format view cameras typically go down to f/45, f/64, or f/90.

 

[JoeV]

Can anyone answer how the f/stop scale progresses when the aperture is a polygon shape (because of a fixed number of aperture blades) rather than a circle?

~Joe

 

[sojournerphoto]

Can anyone answer how the f/stop scale progresses when the aperture is a polygon shape (because of a fixed number of aperture blades) rather than a circle?

~Joe

The f stop scale is used in the same manner. The area progression should be the same and any inaccuracy due to the shape changing (area always scales by a square law) as you stop down is likely to be immaterial.

Mike

 

[sojournerphoto]

I have seen a lens with f/64.

I have a lens that stops down to f64, but it's a 210mm apo-symmar and covers 5 x 7

I've also got an old 135 elmar (pre tele-elmar) that stops down to f32

 

[rluka]

Optical diffraction aside:

• Is there any special reason for these f-stops? A special purpose like landscapes, etc. for expanding the depth-of-field?
• Are these super small stops to balance the relatively slow 2.8? As in, I might be using faster film to compensate, but in daylight I need to stop down.

How practical, or significant is the use of these smallest aperture when taking pictures ?
🙂

 

[M Currie]

Optical diffraction aside:How practical, or significant is the use of these smallest aperture when taking pictures ?
🙂

It probably depends on the lens and the subject, but I have used the smallest aperture on a "gauss" type Nikkor 105/2.5 lens, which also goes to F32, either in order to maximize depth of field or to allow fill flash with the slow sync speed of a Nikon F shutter. Not very often, but there's certainly no harm having it there. I did an informal test of the diffraction on this lens (Nikon F on a tripod, Velvia, sunny day, burdocks on snow), and found that although it's present, it's really not much of a problem at normal magnification, and I can certainly imagine the occasional time where added DOF is worth the tradeoff.

 

[Mcary]

Optical diffraction aside:How practical, or significant is the use of these smallest aperture when taking pictures ?
🙂

Very significant when working within 6-18 inches of your subject with a 90mm, 100mm, 150mm or 180mm lens. Which is why the smallest aperture of most macro lens is either F22 F32.