WOW. A few thousandths ! ! !Originally Posted by Drew Wiley
I'm a Master Tool and Die Maker with over 50 years experience.
I normally work with tolerances of 1/10th of a thousandth, sometimes tighter.
My gage blocks are accurate to a few millionths of an inch.
I'm also moderator of the Metrology section of the Practical Machinist forum.
That's the largest forum for machinists in the world.
I don't do woodwork.
- Leigh
If you believe you can, or you believe you can't... you're right.
$2.50 Front surface Kodak mirror
https://www.surplusshed.com/pages/item/L3750.html
Stop being cute, Leigh. If you happen to use a 30x40 inch vac easel I seriously doubt it's within a 1/16" of true flatness. Mine was cannibalized from a $200,000 process camera made in Japan and weighs around 300 lbs (easel alone). I can stand on it without deflecting it out of focus. Now if you want to make a big vac easel out of pink granite like a machinists surface, more power to you. That would cost a pretty penny from Starrett, and be lots of fun drilling the vac holes and channels too! Or try twelve square feet of precision flat stock, which has to be routinely oiled or it rusts - that oil should be real good for photo paper! I was selling Starrett to hundreds of machinists fifty years ago; and some of them worked at Lawrence Berkeley Lab to subatomic standards! Go argue with them about who's got the most expensive tape rule! They've got Starrett rigs that can draws contour maps in millionths of a measured surface, and that's just the tip of the iceberg. Starrett actually began by making cabinet tools. Just look at any hundred year-old catalog. The parts are even interchangeable, as you very well know; just the metal finishes have improved. But I am glad to hear there is a community of tool and die makers still around. Plenty of start-up companies in this country go bust because they can't find any. Our educational system did a terrible disservice by poo-pooing manual trades, just like your own mistaken impression of woodworkers, who often have to factor all kinds of squirrely variables a machinist doesn't. I'm certainly glad my Ebony wooden camera was made by someone with a machinists background, even if it is only pitiful pattern grade mahogany suitable for a pitiful old guy who no longer carries his Sinar on two-week backpacks. It would be a lot more precise if it too was made of pink granite; but alas, they only offered the
choice of ebony wood or mahogany.
Since one main objective of leveling enlarger components is to make all four corners of the image on the easel come into sharp focus at one position of the focusing adjustment, I adjust or shim the appropriate components until this happens. It's that simple, folks: no lasers, no front surface mirrors, and no precision tools beyond a good focusing magnifier and an appropriate test negative. For a test negative in a condenser enlarger, lightly sand a piece of film with coarse and fine sandpaper. This hillbilly approach may well offend engineers, but it works better than trying to emulate the sophisticated techniques that are essential in some other applications.
Do you have to re-shim when you significantly change easel to carrier distance? Sounds like a lot more work than doing it right the first time. I have no disregard for hillbilly shortcuts. I'm from real hillbilly roots; and if anyone on the planet deserves a honorary phD in Jerryrigging, it's me! But I've also long
had access to good tools, so why not use them? But one thing I never do is cross the line into duct tape land - nope, I don't go there. I don't drink Mountain
Dew either, even though the cans might make good shim material.
Drew, I've never noticed a need to re-shim when changing easel to carrier distance. My ancient DeJur enlarger with its round 2 inch column seems to eliminate that problem, although correcting for a too thin replacement baseboard and the enlarger's perspective control demands occasional checking.
Some of the electrical contacts on the power supply to my beloved old Omega eventually gave up the ghost. I had actually clipped off tabs from feeler gages
from way back when I fixed my own cars to use as shims to the rotating base and the neg stage, which I jerryrigged with improved adjustability. By that time
I already had a couple Durst units set up that have all the relevant adjustments factory built-in. And having begun this game on a very tight budget myself in earlier days, I can certainly admire anyone who finds simple solutions to otherwise pricey problems. The fanciest control on my huge home-built enlarger came free as a
lucky find military surplus item. But precision is all relative. I once had someone up at LBL bring and demonstrate to me an electronic measuring device along with a two-inch thick block of Starrett pink granite - allegedly the most dimensionally stable machinist's surface available at that time, then asked me to breathe on it. Merely the temperature change due to my breath caused enough dimensional expansion to alter the dimensional reading! That was decades ago. I can't even mentally correlate to what can be done now, though from time to time experiments get explained to me, minus the math. But since photo paper is only so flat even on a vac easel, if the corners looks crisp under my Peak grain magnifier, good enough.
Drew, my view is that a vac easel is a very Pro gear that ensures flatness without thinking about it and it's fast, for the production efficiency sake, but anyway there are other ways to ensure perfect paper flatness.
First, if sides are slight curled, going up, then perfect flatness is obtained with the easel. Another way is placing a flat glass (those from a mirror are really flat) on the easel, and spraying 3M Re Mount glue on it, this has the same effect than a vac easel.
Paper flatness under an enlarger should satisfy most printers if it is held to within 0.5mm. Of course better flatness can mask other errors. Other photographic processes demand much tighter tolerances. For example, when contact duplicating graphic arts halftone negatives onto diazo film with a quite large light source, the drawdown time for 30x40 negatives was several minutes. If our vacuum easels hadn't started the drawdown from the center of the film, it might have been hopeless.
The biggest problem with any laser gizmo is that it only gives you one on axis point without giving you the other more important points such as the corners and edges... The flatness of the baseboard and easel are critical, as there can be a trend of a slow rolling warp where most of the image plane can be ok, but areas can be off...
First, one should get a good straight edge and lay it across the baseboard and corner to corner and look for bumps and depressions, especially where the easel corners/edges sit, then check the easel to see how it sits there...
Lasers don't tell you where the issue is (like baseboard, easel, column, negative stage, etc, so can be very confusing...
I service enlarges with a straight edge, and a tall machinist height gauge with a long precision arm that can reach deep into the carrier seating area, and with the carrier in place...
Alignment affects not just corner to corner sharpness, but affects light falloff, subtle contrast shifts (from lens slight defocus shifts with slight OOF contrast loss) etc...
Granted, LF enl's can get away with more, but smaller formats suffer more... If one ever had to align a small format enlarger quite out of alignment, and saw the before prints, you know what I mean...
Steve K
Posting Permissions
Reply With Quote
Bookmarks