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Fun with MF images 2024

W

wattsy

Well-known member
Still getting the hang of the XCD 28P. I like the focal length a lot but I'm not sure if there is some strong focus shift going on when I'm stopped down to F8 or more. I focus manually and feel that the plane of focus (which, incidentally, seems quite curved) becomes shifted back in the actual photograph. Has anyone else with this lens (e.g. @MGrayson) noticed anything like this?

907x CFV 50C II and 28P


 
MGrayson

MGrayson

Subscriber and Workshop Member
wattsy said:
Still getting the hang of the XCD 28P. I like the focal length a lot but I'm not sure if there is some strong focus shift going on when I'm stopped down to F8 or more. I focus manually and feel that the plane of focus (which, incidentally, seems quite curved) becomes shifted back in the actual photograph. Has anyone else with this lens (e.g. @MGrayson) noticed anything like this?

907x CFV 50C II and 28P


Click to expand...
I *have* noticed focus shift at f/8, but have had a hard time giving a convincing demonstration of it. Stopped down focusing works pretty well, even when magnified. Focus peaking is often clearer at f/8, so it's a good thing to try. I reset on of my buttons to DoF preview (now I just have to remember which button...😆).

I just did the experiment again twice. The first time, definite focus shift. The second time, no focus shift. I'm not touching the focus ring on the lens. How can there be variation? Too much coffee early in the morning. I'll have breakfast and try again.

I just want to add that focus shift is not an innocuous problem. Every f/8 light ray is still there at the f/4 aperture, and if part of the entering light is focusing on a different plane, then that limits the possible sharpness wide open.
 
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W

wattsy

Well-known member
MGrayson said:
I *have* noticed focus shift at f/8, but have had a hard time giving a convincing demonstration of it. Stopped down focusing works pretty well, even when magnified. Focus peaking is often clearer at f/8, so it's a good thing to try. I reset on of my buttons to DoF preview (now I just have to remember which button...😆).

I just did the experiment again twice. The first time, definite focus shift. The second time, no focus shift. I'm not touching the focus ring on the lens. How can there be variation? Too much coffee early in the morning. I'll have breakfast and try again.
Click to expand...
Thanks for doing this. It's interesting you notice some variation. That is my early experience too. What I am now doing is focussing on part of the scene that is at the front of the range of what I want in focus and assuming that the depth of field will largely go backwards from there. Mostly that seems to be a good method so far but after reviewing some photos taken last night, I notice a few where the depth of field seems to be behind and beyond the point on which I'm sure I was focussing. (I was doing it all handheld so I can't be certain that I hadn't been sloppy). I don't expect the 28P to be perfect – it's not marketed as a lens for landscape and, given its size and price compared to the non-P lenses, I assume there are compromises in its optical design. In truth, my 45P, which I like very much, also has some DOF weirdness but in the opposite direction (I find that I need to focus back into a scene to ensure a good DOF balance as the DOF tends to come forwards from the point of focus).

Unfortunately (for reasons I cannot understand) the 907x doesn't have a DOF preview option unless you have the grip (whereby you can customise one of the buttons) so I can't do stopped down focussing. Within reason, I can learn to live with any idiosyncrasies of the 28P, I just wanted to check that I haven't got a duff lens that would necessitate the tedious process of getting it replaced or serviced.
 
FloatingLens

FloatingLens

Well-known member
wattsy said:
Still getting the hang of the XCD 28P. I like the focal length a lot but I'm not sure if there is some strong focus shift going on when I'm stopped down to F8 or more. I focus manually and feel that the plane of focus (which, incidentally, seems quite curved) becomes shifted back in the actual photograph. Has anyone else with this lens (e.g. @MGrayson) noticed anything like this?

907x CFV 50C II and 28P


Click to expand...
I no longer have the 28P, but I also did notice some unexpected focus behavior (talking about achieving the best DOF over the entire frame).
In my experience focussing in DOF preview helps with accuracy and focus peaking, like Matt said. Also, like with many wide angle lenses I believe it helps not to focus the center spot, but 1/3 towards the edges. Especially at f8 where DOF ist still limited.
 
V

vjbelle

Well-known member
If I had to pick between the two poisons (Focus Shift and Curvature) I would much rather deal with focus shift as it is something I can control and get excellent results. Curvature has no control other than stopping way down to equalize the image and by that point diffraction has stolen a lot of pixels. I guess there is always that once scene where curvature just happens to work out but those are pretty rare.

Victor B.
 
MGrayson

MGrayson

Subscriber and Workshop Member
vjbelle said:
If I had to pick between the two poisons (Focus Shift and Curvature) I would much rather deal with focus shift as it is something I can control and get excellent results. Curvature has no control other than stopping way down to equalize the image and by that point diffraction has stolen a lot of pixels. I guess there is always that once scene where curvature just happens to work out but those are pretty rare.

Victor B.
Click to expand...
I've never successfully managed the Roger Cicala grassy slope field curvature test. It looks really good when he does it...
 
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