Flat Field

[hooman_aryan]

<p>Which lenses are considered flat field lens? What is a typical designation on any of the major lens makers such as Schneider, Rodnestock, Nikon and so on?</p>

[leicaglow]

<p>I don't know all of them, but generally lenses for copy work or macro are flat field. I use Schneider Claron-G lenses that are flat field, and I think some old lenses like the Cooke's were as well. Is there a particular use you have in mind for one?</p>

[frank_menesdorfer]

<p>As Michael stated above, probobly there is no manufacturers of lens who haven't made flat lens for industrial copy work both Rodenstock and Nikon have it. macro lenses are less common.</p>

[kelly_flanigan1]

<p>Even Flat field process camera lenses like the Apo-Ronars are NOT flat field lenses. One has to stop them down to say F22 to get the corners in focus. An enlarging lens at F9 is more flatfield than a process lens at F9; *BUT* the enlarging lens has the defect of distortion of say 0.5 to 1 percent. This distortion is not an issue with pictorial work; but a total mess with a process work; where map panels will not align. Thus with a process lens; the distortion is about 1/10th or better less than an enlarging lens; but they may be as sharp.</p>

[kelly_flanigan1]

<p>****At closer distances; try a good 6 element enlarging lens for flat field work.</p>

<p>Here we have a 17 foot long process camera that shoots a 24x36" negative; the originals can be about 60" by 102" big. The lenses are a 360mm F9; 60mm F9 and a 890mm F14 Apo Ronars; typically used at F22; the 890mm at F32 too .</p>

<p>The very common injection on photo.net is that process lenses are flat field lenses. This broad brush statement in lay hands is dangerous. Process camera lenses are ( mostly were today) usually used in flat field applications. ****BUT the lenses are only really flat field when stopped down.****</p>

<p>There is a graph on page 67 of the 1951 Kinglake book "Lenses in Photography" that shows resolving power versus "focus steps" (lens position) for a 19" at process lens wide open at F11. The curves show that the field CURVES INWARD at 5, 10, 15 and 20 degrees; and OUTWARDS at 25 degrees. That is why we process camera users stopped the lens down; to quash field curavature with more DOF.</p>

<p>Process camera lenses do not *have* to be some military super sharp lenses either; they work at 1:1 to about 1:4 there in their normal application. A typical job would only be a 2 to 2.5 x enlargement; thus 20 line pairs per mm is plenty.</p>

<p>****A good enlarging lens here is what we use here with our two 4x5 " digital scan backs for flatfield work; a 135mm F5.6 Schneider Componon-S works well.</p>

<p>Componons in shutter were the Durst copy camera shooting and enlarging lenses for many decades. They came from the factory in Compur shutter. Often the leaf shutters were *ONLY* used for grey scale work with fast Kodak Pro copy films. With slow asa 6 lith films we use timed lights; the leaf shutter often stayed at T or B for months.</p>

<p>Thus an Ebay surplus say 210mm F5.6 Componon in Compur leaf shutter of our 1968 Durst 138S 5x7 copy settup is a *RISKY EBAY BUY*; the shutters often lived a life in darkroom fumes of Kodalith; stopbath; Kodak rapid fixer with acid; farmers reducer.</p>

<p>On several times we had these shutters fail at the worst times; they were often a corroded mess. Thus we finally have TWO of them of them; one for lith work; and the good shuttered one kept in the office away froms the corroding fumes. It gets old to getting a CLA every year or two.</p>

<p>In some old threads folks "pictorial" folks asked about if it was *possible* to place a Componon in shutter; when it was already done when cars had tail fins and Acorn UHF tubes were the rage in Project Mercury. The odd thing is when these old threads were active; there were three different Componons in shutter on Ebay as active auctions!. The graphics arts/repro industry is a different branch of Photography; thus the knowledge base seems to be way different. A Componon in shutter on a Durst copy camera in the 1970's were as common as iPhones or laptops at a Starbucks today. It is life if on a Ford Mustang board if folks pondered if would be possible for Ford to build a farm tractor; when it was done already before any of us were born.</p>

<p><img src="http://d6d2h4gfvy8t8.cloudfront.net/1238354-lg.jpg" alt="" />irs</p>

<p><img src="http://d6d2h4gfvy8t8.cloudfront.net/1238404-lg.jpg" alt="" /></p>

[frank_menesdorfer]

<p>"The very common injection on photo.net is that process lenses are flat field lenses. This broad brush statement in lay hands is dangerous. Process camera lenses are ( mostly were today) usually used in flat field applications. ****BUT the lenses are only really flat field when stopped down.****"</p>

<p>What do you know? You always learn something, Thanks kelly</p>

[kelly_flanigan1]

<p>Enlarging lenses; the more modern latest ones often have less diaphram blades. Older ones of the same design; the NON cost reduced ones often have more blades; and give a better look for out of focus stuff in tabletop 3D stuff.</p>

<p>Enlarging lenses are designed not for infinity; but of course closer ratios.</p>

<p>In a recent shoot of a 1942 giant 42x72 inch blueprint of a P38 Lightning; the 135mm F5.6 Componon-S worked well at between F11 to F16. The 72" dimension determined the copy ratio . 72/42=1.7 our 50 megapixel scan back is 10x7cm; a 10/7=1.4 ratio. With some super tight framing; the actual scan was about 75" morphed to the 10 cm scan back. Thus the ratio was (75*2.54)/10= 19. The Componon-S was not really optimized at 1:19; that is really more like a mural ratio. But here it recorded all the dimensions; dates; the tiny 1/8" names in the title block with ease and signed names that are about 1/2mm thick in line width . The 42" blueprint is larger than our 36" wide color or B&W scanners; I really did not want to farm it out.</p>

<p>I lucked out because the crusty Lockheed checker had decent text sizes; ie old school like they did for microfilm backup.<br /> RANT ON<br /> Today with CAD many newbies really seem not to care; there can be 1/32 or 1/64" or 1/100 type on a 30x42 inch drawing. This happens where there is no old fart to force standards. Alot of this foolish microtype just drives up printing costs. Scanning a 30x42 inch drawing with greyscale; faint blue; faint yellowcolor and then microtype makes scanning a real SOB; thus costs are radically higher to make copies. The sad thing is there are OCEANS of space to make the text 10 times larger; and all the color key could have been with different line types. Some of this is government stuff too; you tax dollars wasted.</p>

<p>RANT OFF :)</p>

[kelly_flanigan1]

<p>Frank; my basis for knowing is just a few things:)</p>

<p>(1) The Rodenstock data sheets from Germany for our 1970's three process camera lenses.<br /> (2) Acti cameras engineer who spent 3 days setting up our 30K buck process camera<br /> (3) The sales guys at Acti<br /> (4) the statement on the label of the camera<br /> (5) our *own tests* that showed that if one stops down to F22; one gets better corners.<br /> (6) 1/3 century worth of usage on one camera; built into one of my buildings.</p>

<p>The serial number for each of the three Apo Ronars is actually engraved on the scales on the 17 foot camera bed; since focus is not by ground glass; but by computer. This at first was by table; then HP65; then HP97; then Basic on a TI99/4a; then on an PC once the IBM PC came out. The lens board and copy board have precision detents every inch along the 17 foot one ton + rail. Then a 1/1000 micrometer sets it to 1/1000 inch. One chooses a copy ratio; then a lens; then one sets the lens and copy board to the 1 inch detents; then one move the slow mo to dial in the micrometers. It is all set up for those serial number lenses; all focal lengths and lens constants are in the tables and computer programs. Process cameras went obsolete due to digital; in the 1988 to about 1995 time frame.</p>

<p>htsThe MTF data on process lenses often has a lower cycle per mm than other lenses; since in usage a process camera really is not doing much as far as enlargements. Process lenes will work at infinity; they are just not the sharpest tack. For ULF they often overkill; since one usually is jsut contact printing. If one uses a short process lens on a 4x5" for landscapes (with enlarging); Symmar would work better; or even my 1930's Angulon. If in doubt do your own tests; that is what matters.</p>

[frank_menesdorfer]

<p>No doupt, nice info about the "flat lens" as I said one can always learn something new. <br /> Thanks again! :-)</p>