Secondly, is it possible to upload a version of the instructions where the "bottom" is noted as one rotates the camera? I can't seem to grasp the star and circle concept.
Thank you!
Can you point me to the direct post? I may still have the image. Not sure why it's missing.
p.9 #4 · FM Lens test for Centering (Mount tilt / swing)
Fred Miranda wrote:
Thank you. It's been restored. It was definitely an important image to help readers understand the post.
Thanks Fred!
This bit still confused me with the red circle:
Fred Miranda wrote:
3) Flip the camera upside down, and take two more pictures by positioning the same target at the same location above. The subject will be at the same location on the frame (Star symbol) but you will be actually taking a picture of the BOTTOM RIGHT and TOP RIGHT areas (Red Circle) since the camera is now upside down.
Can I ignore the red circle and just frame the image as the instructions suggest?
I've modified your instructional image to show a viewfinder with an EV bias to further illustrate when the camera should be upside-down below:
p.9 #5 · FM Lens test for Centering (Mount tilt / swing)
weatherproof wrote:
Thanks Fred!
This bit still confused me with the red circle:
Can I ignore the red circle and just frame the image as the instructions suggest?
I've modified your instructional image to show a viewfinder with an EV bias to further illustrate when the camera should be upside-down below:
Yes, you can ignore the circle while shooting. It simply marks the area you'll compare later in your editing software. The whole process is much easier than it sounds. It usually takes about 30 seconds to take the four shots and another minute to check the results in Lightroom. That way, I can quickly tell if I have a good copy of the lens without any second-guessing.
p.9 #6 · FM Lens test for Centering (Mount tilt / swing)
I've always noticing some strange phenomenon of my lens performance (have it for more than a year now), particularly the field of focus appeared to be slightly tilted. I decided to kill a cat with my curiosity and do the four corner test. Here's the image (pardon my lack of creativity of arranging the test images):
(You may open it in separate tab for full size)
I noticed when I shoot an object at mid distance, and if there are symmetrical objects on both side, the right corner often looked more mushy than the left, admittedly it only show up when pixel peeping, and never distract the subject matter.
Looking at the result (lower set), to my eyes the right corners appeared to be slightly smeared than the left corners, however when shooting landscape (upper set, filled up with windows of a residential building), all 4 corners looked about the same.
So the question is - will you dismiss this lens, or people should be more encouraged to make decision based on real world shooting?
I admit that I was a bit distracted by the result, but I had bad experiences in the past where a well centered copy having worse rendering and color than the supposedly inferior copy, so I decided to not play the game...
p.9 #7 · FM Lens test for Centering (Mount tilt / swing)
jeffersoncasey wrote:
...I had bad experiences in the past where a well centered copy having worse rendering and color than the supposedly inferior copy, so I decided to not play the game...
Test shots are not necessarily real world meaningful. There's the aperture/point-of-focus variable and front and back object placement (near and far). A lens might have left/right/top/bottom/corner/edge issues, compounded or negated by field curvature and an inexact infinity hard stop. If you shoot enough asymmetrical lenses you can know what you have with one or two typical real-world shots, and whether the issue is important or not. Practical over perfection...
Second of five copies (I have four) of a Skopar 25mm ltm. Perfect on the right, less so on the left (wide open):
p.9 #8 · FM Lens test for Centering (Mount tilt / swing)
After seeing your example I just realized how nitpicking I am, yours is visible even on web viewing size. I own only 2 lenses for the past few years (excluding Q2) so I kinda need to fact check myself. Your respond is much appreciated! mapgraphs wrote:
Test shots are not necessarily real world meaningful. There's the aperture/point-of-focus variable and front and back object placement (near and far). A lens might have left/right/top/bottom/corner/edge issues, compounded or negated by field curvature and an inexact infinity hard stop. If you shoot enough asymmetrical lenses you can know what you have with one or two typical real-world shots, and whether the issue is important or not. Practical over perfection...
Second of five copies (I have four) of a Skopar 25mm ltm. Perfect on the right, less so on the left (wide open):
p.9 #11 · FM Lens test for Centering (Mount tilt / swing)
Just a quick note on lens centering. Over the years I've seen real improvement from pretty much everyone, Leica, Cosina, Fuji, Sony, you name it. The newest releases I have tested have been consistently well centered with very few bad apples. It feels like tight tolerances are now baked into the design process so the lenses can handle mass production and still deliver for modern high MP sensors. Definitely a different story than it was 10 years ago.
