Graflex.org

primus96 · Posted: Fri May 28, 2004 6:30 am Post subject:

I was thinking of adding a 165mm f6.8 Rodenstock Eurynar to my collection.
its 4 elements in w grps, uncoated in a dial-set Compur shutter.
Anybody got an idea of coverage?
This is another sort of double anastigmat, though a different design to the Dagor.
I beleive that Goerz did something similar and called it a Celor?
If flare is going to be a real problem I won't bother.

Les · Joined: 09 May 2001 Posts: 2682 Location: Detroit, MI

yep it's a dialyte type, just like the Celor, artar and 203 ektar and lots of process anastigmats.

Use the longest lens shade possible, and you should be fine. Shooting Christmas lights at night might be a bit interesting though.

primus96 · Posted: Fri May 28, 2004 2:53 pm Post subject:

This is the same sort of design that Kodak used in one of the Ektar range. Was it the 203mm WF Ektar or the 178mm Aero Ektar?
I have seen the field of the type quoted as 60 degrees. How do you work out image circle from that figure (if its right)?

Dan Fromm · Joined: 14 May 2001 Posts: 2144 Location: New Jersey

Dan Fromm · Joined: 14 May 2001 Posts: 2144 Location: New Jersey

primus96 · Posted: Sun May 30, 2004 10:04 pm Post subject:

Regarding this particular Eurynar:
It may not have been intended for process use as its in a shutter not a 'barrel' lens.
How will the lens compare to the likes of a Dagor for:
Flatness of field.
Maintenance of sharpness at the edge of the coverage.
I am aware that a dialyte may have quite a narrow angle of view (47 degrees). This ones 165mm so surely it should cover 4x5.
This is 6" and a bit more and a 6" Cooke Aviar would do 6x4 (www.cookeoptics.com).

If Les can clarify that formula for working out image circle we might find it useful

Les · Joined: 09 May 2001 Posts: 2682 Location: Detroit, MI

I had a nice illustration but can't for the life of me figure out how to get it posted.

So you'll have to bare with me.

Imagine the lens on the left and two rays coming out to the right describing the angle of view.

Now draw a center line bisecting the angle of view.

Now we have a right triangle and some 9th grade trig ahead.

The Tangent of the half angle of view (trig teachers call "B" multipied by the focal length will give us.... well it gives us half of the image circle. So we multiply it by two to get the diameter

So Dan's half right. Take his formula and muliply by two.

Example: 165mm lens, 47° AOV

47°/2=23.5°

B= 165 * TAN23.5
B= 165 * 0.4348

B= 71.74mm

AOV=2*B= 143.4880mm

AOV= 5.65"

[ This Message was edited by: Les on 2004-05-30 16:46 ]

t.r.sanford · Posted: Mon May 31, 2004 2:48 am Post subject:

This sort of calculation is very useful, and is often done by people contemplating lenses they cannot afford, or that do not exist! Computers are a great improvement over the "trig tables" in the textbooks of my youth, and even over engineering calculators, in performing it.

Before Microsoft uncoupled "Windows" from "MS-DOS," a BASIC interpreter came bundled with the operating system. Alas, that is no longer so, but one still can purchase a BASIC language, if one didn't think to retain it when upgrading from the last "MD-DOS" version.

BASIC expects angles to be expressed in "radians," for some reason that must have seemed good to Kemeny and Kurtz. This is the only annoyance in writing little BASIC programs to do all sorts of lens and format calculations. You convert degrees to radians by multiplying the angle in degrees by pi/180; you convert radians to degrees by dividing the angle in radians by pi/180.

That hurdle past, here is a small BASIC routine that tells you the maximum frame diagonal when you know the angular coverage of the lens. It orginally was written in "TI Extended BASIC," then modified for "GW-BASIC." "QuickBasic" can run it, and doesn't need the line numbers:

100 REM *** Finds image circle when given angle of coverage ***
110 CLS : DEFDBL D, P
120 PI = 22 / 7: DRC = PI / 180 '*** Degrees-Radians Conversion
130 INPUT "Angle of coverage="; AD '***the Angle in Degrees
140 INPUT "Focal Length (millimeters)"; F
150 AHD = AD / 2 '*** Angle, Halved, in Degrees
160 AHR = AHD * DRC '*** that same semi-angle in Radians
170 THA = TAN(AHR) '*** the Tangent of that Half Angle
180 DH = F * THA: D = DH * 2 '*** DH is Half the Diameter
190 PRINT "Image circle (frame diagonal)="; USING "###.# mm."; D
200 PRINT USING "(or ###.## ins.)"; D / 25.4
210 END

Dan Fromm · Joined: 14 May 2001 Posts: 2144 Location: New Jersey

t.r.sanford · Posted: Mon May 31, 2004 2:11 pm Post subject:

That is good to know. Does it come with a well-written manual? If it does, it's a first for Microsoft!

Les · Joined: 09 May 2001 Posts: 2682 Location: Detroit, MI

I'll stick to my K&E slide rule thanks. No batteries, no upgrades, no bugs.

t.r.sanford · Posted: Mon May 31, 2004 9:01 pm Post subject:

...I ever could figure out where to put the decimal points!

primus96 · Posted: Tue Jun 01, 2004 11:53 am Post subject:

Can anyone give us any help on writing the functions so this works on a Excel spreadsheet?
I can do it on a calculator, but the problem seems to be in getting the tangent of the half angle.
I tried the formula on a reuular calculator and got a image circle of 143mm for this lens - way too small for 4x5.
Thus I was releived to be outbid.

Nick · Joined: 16 Oct 2002 Posts: 494

RichS · Posted: Tue Jun 01, 2004 1:09 pm Post subject: