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View Full Version : Coverage question Fujinon-W 300 - I am puzzled!

Robert McClure
22-Jan-2007, 07:15
Hello!

I have two quick questions related to the following lens currently up for bid on E-bay:

http://cgi.ebay.com/FUJINON-W-300mm-f-5-6-in-COPAL-SHUTTER-327483_W0QQitemZ270081786059QQihZ017QQcategoryZ15248QQrdZ1QQcmdZViewItem

First, considering this lens will stop down to f90, and if image circle is 420mm at f22, can I actually calculate what circle would be at f32, f45, f64, and f90. Will it cover 7x17 at stops smaller than f22, say at f64? Short of actually testing, can I draw any conclusions?

Second, I notice that more often than not, image circles are generally cited at f22. Is this because at smaller stops it often becomes doubtful that a lens will continue to perform acceptably? I mean, in the case of the above lens, should I expect that usable image circle beyond f22 will continue to increase and that for contacts even f90will be adequate?

Must I test or is there info out there (Sandy King, etc.)?

Robert McClure

steve simmons
22-Jan-2007, 08:38
IMHO you are over thinking this situation, Most mfg'ers give the image circle at f22 becasue there is little gain past that point. By gain I mean significant increase in size of the image circle beyond that point. If a lens did not have enough coverage at f22 I would not buy it hoping that closing down to 32 or more would make any practical difference.

Refraction, what happens to the image at very small f-stops, is really more of a problem in theory than in reality. People will write pages and pages of math formulae about this problem but in the real world if you have a choice between a little refraction and getting enough dof take the refraction and live with it.

View Camera has done articles on Fuji lenses and we did a two part series last Summer on making your photos sharp which included all of the necessary math for those so inclined.

steve simmons

John O'Connell
22-Jan-2007, 09:21
Refraction occurs at all lens stops, because the lens always bends the light.

Image softening from diffraction increases with f-stop number. Only you can tell if it will be too much of a problem, but I'm with Steve in generally choosing to ignore diffraction effects and stop down for depth of field.

sanking
22-Jan-2007, 12:09
The circle of acceptable performance for contact printing will improve some on stopping down from f22 to f64, but exactly how much varies by lens and there is no formula. However, you should not expect in increase in the useful circle of illumination of more than about 10&#37; - 20%.

The coverage data provided by lens manufacturers is not very useful for ULF work if contact printing is anticipated, which is the norm rather than the exception. With contact printing the print will have acceptable sharpness, even at close viewing distance of about 10 inches, if resolution is at least 5-10 lppm. As you stop down a lens, diffraction reduces resolution. For contact printing sharpness will suffer at about f90 and above so I personally never stop down to more than f90. With 4X5 and 5X7 where magnification of 2X or more is anticipated I would avoid stopping down to more than f32 or f45.

There is a formula you can use to determine the maximum possible resolution in lppm of a lens, but it varies according to wavelength. I personally use the formula 1500/A, where A is the aperture of the lens. For example, if you stop down the lens to f100 the maximum resolution possible is 15 lppm.

The two part series in View Camera magazine mentioned by Steve Simmons treats this subjet very well.

Sandy King

Robert McClure
23-Jan-2007, 13:11
Many thanks, gentlemen!

Robert McClure