Back Focus Revisited, more weird questions.

Markus Klatt · May 6th, 2010, 04:08 AM

@Ivan & Goerge

Thank you so much for your help and detailed explanations! After not touching my EX1R for a while I now had the chance to test carefully, two evenings for several hours.

I put a Siemens Star printed with laser on high quality carton on a white wall, the camera stood 2,9m directly in front of it, connected via HDMI to 50'' Kuro FullHD plasma TV. I put light left and right 1,5m away from the star, just enough to open iris at -3db fully, WB at 3200°, PP + steady shot + wide conversion off, 1080/25p. I tested with shutter on and off.

The result was not that obvious as I hoped ;)

So, my backfocus is definetly not bad. I really tried hard to see any differences at the Siemens star between "focussed while zoomed totally in Z99" and "zoomed out Z0". There is no sharpness improvement in the outer parts of the star and almost nothing to see on the structure of the wall or when I try at some images around. Almost means there is mini-tiny-nuance one could imagine, but nothing obvious. So, at any projection smaller than a very good 50'' display one will not see a difference.

What one could recognize when trying to change the zoomed out focus was, that the very inner parts of the star (maybe 1/4 inner diameter) was not becoming noticebly sharper, but on the display some kind of "cross" formed in the star, where the inner parts were bending together. Since this bending is nothing what is there in reality I do not know if this was better or worse than the zoomed in focus. At around Z50 this nuance/bending was not visible at all.

So, my question is: even if this is a tiny backfocus offset, can a flangeback adjust be that precise to improve it?
I tested so often with MF/AF and FullMF. The PushAF may find the perfect focus - but only after pumping a dozend times several seconds long and the result is not always 100% accurate. If the flangeback adjust is just a little unprecise like PushAF I won't touch by backfocus like it is at the moment.

Thank you again,
Markus

May 6th, 2010, 04:08 AM	#16
Markus Klatt Regular Crew Join Date: Jul 2004 Location: Berlin, Germany Posts: 169	@Ivan & Goerge Thank you so much for your help and detailed explanations! After not touching my EX1R for a while I now had the chance to test carefully, two evenings for several hours. I put a Siemens Star printed with laser on high quality carton on a white wall, the camera stood 2,9m directly in front of it, connected via HDMI to 50'' Kuro FullHD plasma TV. I put light left and right 1,5m away from the star, just enough to open iris at -3db fully, WB at 3200°, PP + steady shot + wide conversion off, 1080/25p. I tested with shutter on and off. The result was not that obvious as I hoped ;) So, my backfocus is definetly not bad. I really tried hard to see any differences at the Siemens star between "focussed while zoomed totally in Z99" and "zoomed out Z0". There is no sharpness improvement in the outer parts of the star and almost nothing to see on the structure of the wall or when I try at some images around. Almost means there is mini-tiny-nuance one could imagine, but nothing obvious. So, at any projection smaller than a very good 50'' display one will not see a difference. What one could recognize when trying to change the zoomed out focus was, that the very inner parts of the star (maybe 1/4 inner diameter) was not becoming noticebly sharper, but on the display some kind of "cross" formed in the star, where the inner parts were bending together. Since this bending is nothing what is there in reality I do not know if this was better or worse than the zoomed in focus. At around Z50 this nuance/bending was not visible at all. So, my question is: even if this is a tiny backfocus offset, can a flangeback adjust be that precise to improve it? I tested so often with MF/AF and FullMF. The PushAF may find the perfect focus - but only after pumping a dozend times several seconds long and the result is not always 100% accurate. If the flangeback adjust is just a little unprecise like PushAF I won't touch by backfocus like it is at the moment. Thank you again, Markus