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Fun with MF images - ARCHIVED - FOR VIEWING ONLY

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Bob

Administrator
Staff member
Could be a out of alignment sensor, or perhaps a slightly cocked internal lens element.
It is really tough to be sure with this image, but the plane of best focus seems to curve a bit to my eye, almost sort of an elliptical region, which strikes me as possibly lens related.
thanks
-bob
 

Jack

Sr. Administrator
Staff member
That's a good call Bob, the "plane" of focus does appear to be oddly curved, which would indicate an cocked lens element and not an out of parallel sensor...
 

stephengilbert

Active member
Jack,

Isn't it possible that the rail car is sufficiently close to the camera to account for the apparent anomaly? It might be that the bollard is just within the range of sharpness, while the near end of the car is too close to be.

Steve
 

Bob

Administrator
Staff member
I would take that rig and find me a nice brick wall to shoot dead square.
Shoot as wide as it goes then stop down shot by shot to see what happens.
-bob
 

Jack

Sr. Administrator
Staff member
Jack,

Isn't it possible that the rail car is sufficiently close to the camera to account for the apparent anomaly? It might be that the bollard is just within the range of sharpness, while the near end of the car is too close to be.

Steve
There are a whole bunch of things that could be going on. First is, very few lenses that are highly corrected for distortion render a "plane" of sharp focus. Instead it often follows the path of a gentle second-order curve that bends toward the camera as we approach the edges of the frame. And with aspheric elements, I've even seen this curve appear as third order ("W" or mustache shaped), which is really screwy to look at!

The Leica 70mm is an asphere and the plane of focus seems to flow AWAY from the camera toward the edges which would lead me to conclude it is a gentile 3rd order progression. Thus I would suspect that we are dealing with a mustache plane of focus in this 70mm lens design coupled with a sensor that is slightly out of parallel with the lensmount.

Of course, none of this would have been visible with film, but now we're down to 100% view on 6 micron pixels, which is the same thing as saying we expect about 6x more stringent CoC's with these MF sensors than we ever did for MF film...
 

docmoore

Subscriber and Workshop Member
Exactly --- or more precisely swings AND tilts! That image looks like the lens plane is not parallel to the sensor, with lens angled slightly up and right relatively. Or it could possibly be partially what Thomas was referring to, soft corner performance exacerbating the effect. According to the EXIF the shot was taken at f8, so I am surprised by this behavior. Methinks some gear testing may be in order for xpixel...

PS: Actually, the non-planar OOF rendering may be what gives the illusion of depth that Victor is seeing...

Here is the relative POF as I see it, axis in yellow:
Looking at the rail ties there appears to be 10+ degrees of swing....camera not pointed paralled to the line?

Bob
 

gogopix

Subscriber
The answer is; 42!

Remember the question?

Trying to dope out POF etc from reduced jpgs is quite a challenge. I think it's time to just step back (figuatively :D ) and see if the images are pleasing and have good qualities. From the non analytical comments seems they are impressing people, including me.

FWIW, fucus is 1/3 freom 2/3 back from POF and I think both Guy and Jack are focused (sic!) too close in. The yellow circles of Guy seem to be way up at the front of the focus range, and the reds are not in focus at all (except the tank top.

With 7-8 elements in 5-6 groups sherical lenses will have a somewhat curved plane of focus, and all lenses are a 'little off' Without an ASPH component you get color separation too.

What I'm going to do is just collect a bunch of S2 and compare to my images and some Phase and some hasseys. It's really the only way to see whether one system is pleasing TO ME. Others may want to try.

Actually Guy's larger images may be more valuable, and some of Tim's that he posted. I will look at on my 2560x1600 at 30" Not the best, but this kind of pixel peeping can drive you mad :ROTFL:

Victor
 

tjv

Active member
I tend to think the things people are seeing are because of the type of sharpening applied, in terms of masking and pixel width and what type of structures are emphasized by it, and the effects of downsampling then compressing for the web. Simple as that I reckon.
 
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