# Are a LF shutter markings more accurate wide open or stopped down?

Printable View

Show 40 post(s) from this thread on one page
Page 2 of 2 First 12
• 05-05-2010, 11:47 AM
fschifano
I think you need to measure everything, the focal length and the aperture. See Jay Bruner's video on the subject:

http://www.youtube.com/watch?v=CIFNdfjem18&feature=user
• 05-05-2010, 12:07 PM
jnanian
frank is spot on ...

btw its a 210/370 ...

( have fun )
john
• 05-05-2010, 12:43 PM
epatsellis
You need to measure the entrance pupil, the apparent size of the aperture through the front element, I hold the lens at arms length and measure with plastic calipers.

The f.l. is easy to measure, focus at infinity, mark the bed/rail. Focus at 1:1 (use a ruler and measure the image on the g.g.), mark the rail/bed. Subtract the second number from the first and you have your f.l.

Aperture is simply f.l. divided by entrance pupil diameter (expressed in the same units, of course)
• 05-05-2010, 01:20 PM
fschifano
Quote:

Originally Posted by BetterSense
...I get 29mm fully open--that's 210mm/29mmm =7.25! That's quite a bit smaller than f/5.6 eh?

Not that much really. The difference is approximately 2/3 stop. Don't use a dial caliper. A steel ruler marked of in millimeters is good enough and easier to get right. Measure the apparent diameter of the aperture through the entrance pupil. If the hole isn't circular measure from corner to corner and side to side and average the two. It's close enough.
• 05-06-2010, 11:06 AM
John Koehrer
So measure apparent rather than actual diameter?
• 05-06-2010, 11:19 AM
fschifano
That's what you do.
• 05-06-2010, 11:51 AM
Q.G.
Quote:

Originally Posted by fschifano
[...] Measure the apparent diameter of the aperture through the entrance pupil. If the hole isn't circular measure from corner to corner and side to side and average the two. It's close enough.

means that you shouldn't

Quote:

Originally Posted by fschifano
Oh yeah, measure the aperture from the front, not the back. If you can remove the front cells to measure it, even better. [...]

Show 40 post(s) from this thread on one page
Page 2 of 2 First 12