How much can I close the aperture with Canon 600 f4 and Mark IV ?

Hi all,
I need to get a shot using the Canon 600 f4 IS and the Mark IV in which DOF would be as wide as possible.
How much can I close the aperture before I encounter optical problems like diffraction etc.

Thanks guys,
Ofer

I was happy with shots I took at f11 with the 600mm

Thanks Michael, I also have quite a few images I took at f11 and even f14 but I wonder whether I can push it to f16 or even f18....<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p>
Here is an interesting calculator I came across and by using it looks like I can push it up to f18 if I intend to print 90 cm and view it from a meter away.<o:p></o:p>
Anyone with some better technical knowledge than myself - please let me know whether that sounds reasonable...:e3
<o:p>http://www.cambridgeincolour.com/tut...hotography.htm</o:p>

Ofer,

The main factor of diffraction is reduction in contrast in the fine details. For a 1DIV, with 5.7 micron pixels, the f/ratio where diffraction reduces contrast to zero at the pixel to pixel level is a little slower than f/8. The blur filter hides some of these effects, so f/11 to f/16 is the pixel-to-pixel sharpness limit. But if depth of field issues make you lose more sharpness, then by all means go slower, e.g. to f/32 (or whatever the limit for the lens is).

Figure 8 on this page shows the reduction in contrast.
http://www.clarkvision.com/articles/telephoto_reach/

Roger

Thanks Roger,
Just to make sure I got it right - you think IQ won't suffer even if I go f16? I would be happy with this as it will allow me enough DOF for this particular shot.
Thanks,
Ofer

Ofer (and Roger)- I would expect the diffraction to be more or less lens-independent (?). Here is a thread I started in macro that shows the effects of diffraction using the EF 100/2.8 Macro lens and the 1DIV.

http://www.birdphotographers.net/for...read.php/82776

In panel 5 you can clearly see the effect starting at f11- as predicted- and which for be becomes unacceptably large at F22 and F32. BTW I had a chance to repeat the test with the newer EF 100/2.8L version of the lens and obtained the same results.

Hi Ofer,

Image quality due to increasing diffraction is impacting at f/1 and slower (yes, I said f/1)! But most of the time we accept the degradation. In the case of depth of field, closing down the aperture and the loss due to diffraction is often less than the loss in DOF if the aperture was kept open. In general, I don't worry about diffraction. If I need a certain aperture to get the needed depth of field, I use the aperture needed. Better to have a little diffraction than to to have a major component in the image out of focus.

If the image is static, you can take multiple images, say at f/8 and stack them, moving the focal point between frames. There is software for such stacking. For example, see helicon focus.

If the subject is moving, often the problem becomes one of maintaining a fast enougn shutter speed to stop the motion.

Every situation is so different and digital makes it easy to test in the field: just try it and examine the image to see if the settings are best.

Roger

Thank you for the excellent input guys!
Much appreciated,
Ofer :w3