using Rodenstock or Schneider lenses wide open?

[christian_balslev_van_rand]

Hi,

I just realized that large format lenses are optimized for use at smaller apertures, from f/11 onwards. However, I

would like to know if either Rodenstock or Schneider-Kreutznach make any lenses that are usable at wider aperture?

I'm looking to buy the upcoming Fotoman 6x9 camera, and I would use it hand held a lot, with a wide angle lens.

Either a 47mm, 55mm, 58mm, 65mm or 75mm. Do you know of a lens within theses focal lenghts that is usable at,

say f/8, or even f/5.6?

[bob_salomon]

No. Not wide open. Rodenstock Apo-Grandagon lenses are optimized for f11 and are made in 35, 45 and 55mm. The Apo

Sironar Digital lenses are optimized at f8 and will work for you on 6x9cm.

[michael_darnton1]

There's a site on the web somewhere where someone explores the very question you asked and discovered that aside from coverage, which expands at smaller openings, most lenses do just fine wide open. If you do some google searches, you'll find a lot of pages about people dismantling the old wive's tale that large format lenses don't work well at their maximum openings.

[michael_darnton1]

Ah----here it is:

http://www.hevanet.com/cperez/test/BigMash210.html

[kelly_flanigan1]

Lens designers do not optimize designs so they are best when stopped down a few stops; nor does a car designer optimize a cars best gas mileage to be at 35mph to 40 mph either. Its just the way most designs are; due to real world engineering. With a lens one has diffraction when stopped down; and abberations when opened up alot. A better lens will peak at a faster fastop; since the abberations are contolled better. With cars one has rolling resistance at slow speeds; and air drag at high speeds; with a peak in mpg in the region sort of where rolling and wind drag are equal. Neither lens or car designer "optimizes" the design to peak in the mid range; its just the way gods laws work out. Making a car with less air drag makes the peak mpg occur at a higher speed; making a lens have less abberations makes the design peak at a faster fstop. Most all cars and lenses are not fine at the fastest speed; the mpg and resolution is almost always way worse. With LF and a typical user there is this 0.007 inch possible tolerance error that often further ruins wide open performance. With LF many folks dont enlarge much; thus the textbook poorer performance is often not such an issue. A sharp 16x20 print is typically only a 4.5 x enlargement with a slightly cropepd 4x5 negative; that means 20 line pairs on the negative makes a great 16x20 print.

[kelly_flanigan1]

Its better to say a Acme 150mm F5.6 has its optimum Fstop on axis af F11; and F16 in the corners; than to declare the lens was "optimized" at these stopped down fstops; were the lens is best. The lens designer considers all the practical f stops in the design of a lens; and strives to "optimize" EACH FSTOP to be as good as he/she can design.

[kelly_flanigan1]

With a lens manufacture defect like tilt; or an older lens with element separation one has a degraded lens. Note how some of Chris Perez's nice test results of the regular 90mm Angulon are great; other serial numbers are just average. With a degraded lens the wide open performace is often poorer; and the stopped down fstops are not degraded as much.

[kelly_flanigan1]

The cataracts in the human/dog etc eye the opaqued region often starts in the center of the lens. Thus one/fido:) has a big contrast drop when ones eyes are stopped down; and a less drop in contast when ones iris is open alot. In this case the "best fstop" moves to the faster fstops; because one has less blockage to see thru. Thus a ND filter; ie sunglasses can boost the contrast of a scene; because the eye's iris is opened more. The opaque region is often yellowish; thus things that are blue look different.