Focus test results with my GSN

[ampguy]

I did a bunch of tests with my GSN with Reala 100 (ISO at 50 for most tests), and have concluded that my GSN rear focuses at f1.7, but is spot on by about f2 and f2.8. Is this by design, or are others getting perfect focus at 1.7 and throughout?

The photos are here:

and most were taken on a tripod with cable release. For the series of Tabasco bottles, focus was on the center one, but not the lettering, of the green label on the neck of the center bottle.

First was 1.7, 2nd 2.0, 3rd 2.8, 4th 4.0, 5th was scale focus. distance was 1 meter.

On the DSLR test pages, first was VF focus at f1.7, 2nd was scale focus (both of these were 0.8m distance)

For the latter 2 DSLR test pages, distance was changed to 1m, first was f1.7, 2nd f2.0.

Outdoor tests were a mix of 1.7/2.0, with sky photos at f8, and f11.

Some don't quite match up but the gist of the test shows that for f1.7, I should focus about 7 cm back at 1m distance.

 

[Nickon51]

GSN focus

GSN focus

The focus doesn't change with aperture but the depth of field does.
If you look at the first photo, the focus is best on the rear bottle. That is where the camera is actually focussed. As you shut the aperture down, the depth of field increases and the closer bottles are more legible, but the focus is still on the rear bottle which is still sharper.
It may help to adjust the close end of the range finder to get the lens focus and the double image to coincide, but you need to take care that it doesn't put the infinity focus out.
The focus set by the scale is more accurate than the range finder at that distance. You don't say what aperture you used but it has the same amount of vignetteing as the first photo so I assume is f1.7. The point of focus has shifted further foward. The power point and the tile edge are less clear but the middle and front bottle are much clearer.
Good luck in sorting it out.
Cheers
Greg Nixon

 

[ampguy]

Thanks Greg

Thanks Greg

Yes, the 5th bottle photo, scale focused, was also f1.7.

For now, I'm just going to front focus close up and wide open by a few inches, or stop down to f2 or f2.8. I'm wondering if other GSN users are getting spot on focusing accuracy at f1.7?

I haven't really tested infinity other than a couple of daytime sky photos, but have verified the shutter is staying open to 30 seconds, so may try some full moon shots tonight on the tripod.

The focus doesn't change with aperture but the depth of field does.
If you look at the first photo, the focus is best on the rear bottle. That is where the camera is actually focussed. As you shut the aperture down, the depth of field increases and the closer bottles are more legible, but the focus is still on the rear bottle which is still sharper.
It may help to adjust the close end of the range finder to get the lens focus and the double image to coincide, but you need to take care that it doesn't put the infinity focus out.
The focus set by the scale is more accurate than the range finder at that distance. You don't say what aperture you used but it has the same amount of vignetteing as the first photo so I assume is f1.7. The point of focus has shifted further foward. The power point and the tile edge are less clear but the middle and front bottle are much clearer.
Good luck in sorting it out.
Cheers
Greg Nixon

 

[bronney]

wide open, spot on around 1 meter:

http://www.flickr.com/photos/bronney/2071328196/in/set-72157602876664969/

http://www.flickr.com/photos/bronney/2071327736/in/set-72157602876664969/

 

[ampguy]

wow!

wow!

very nice!!

wide open, spot on around 1 meter:

http://www.flickr.com/photos/bronney/2071328196/in/set-72157602876664969/

http://www.flickr.com/photos/bronney/2071327736/in/set-72157602876664969/