Focus shift on new 35/1.4 FLE

[AlanG]

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I think as cameras and lenses increase in resolution and more focus precision is demanded then some kind of electronic communication transmitting the lens model and aperture to the rangefinder will be required to apply an offset to account for factors such as this.

 

Hasselblad does this via its AF system. It can compensate for focus shift caused by aperture change and also compensate for center spot focus and recompose errors by tracking the camera movement. (Ultra Focus, True Focus and Absolute Position Lock.) I don't know if any other manufacturer is working along similar lines.

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[ho_co]

MSUS, remember also that digital is more precise than film. You might yourself happy with the DoF scale of your 35 with floating element if shooting film.

 

For big prints with film, the rule was always stop down one stop more than your calculated DoF. That is, if your lens shows that you get adequate DoF for f/5.6, then shoot at f/8.

 

That's a minimum rule for digital, since we typically judge it at 100%.

 

To be conservative, on the M9, stop down another 1/2 to 1 stop from what the DoF scale shows, to f/8-11 or f/11 if the DoF scale shows that f/5.6 will do.

 

Focus shift is a factor of lens design, depth of field a factor of focal length, aperture, enlargement and visual acuity.

[okram]

Also cant see it. Safari.

[horosu]

OK.

 

Here's another try.

 

So, this was the actual scene (all photos handheld, center-crop at 100%)

 

[horosu]

Now the Double ASPH at f4

 

[horosu]

Now the FLE at f4;

 

[horosu]

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Then, the Double ASPH at f2.8:

 

[horosu]

Finally, the FLE at f2.8

 

[horosu]

I would be grateful if someone would confirm if it works or not (first batch were uploaded from my computer, these are linked from picassaweb).

 

Horea

 

P.S As I said, if there is interest I can provide the shots from the FLE from f1.4 to f4, so the focus-shift would be apparent

[okram]

They are here now.

It seems to me that your lens/camera is backfocusing with FLE, from the start.

 

 

 

 

ps. also, i would use a tripod, since 2cm of the body movement can produce this at 1.4

[horosu]

Yes, the lens is backfocusing as it is stopped down :-)

 

My camera works perfectly with the ASPHERICAL (as you can see from the shots above) and with the 50 Lux ASPH

[okram]

I mean- focus at 1.4 is not accurate- it is probable that its inaccurate to the rear end (further from the camera).

 

I use 35 Cron ASPH, and this would not be sharp enough for me wide open.

 

The stopped down ones are probably back focused since it is back focusing at 1.4.

 

Probably.

[horosu]

The shots were at f2.8 and f4, not at f1.4 or f2 (I have them, but I didn't post them as the shift is most apparent at f2.8 and f4).

 

I can agree that it may be my camera/lens combination, however, as I said I must be very lucky then, as my other lenses work spot-on.

 

 

Cheers, Horea

[mjh]

I have just checked the FLE shots at f2.8 and f8, but what minimal differences I can detect are inconclusive. If there is focus shift then these two images don’t show it.

[okram]

Well Horea, i apologize- it seemed to me logical to show some 1.4 to compare to 2.8 or 4, to see focus shift.

[mjh]

It would certainly help if the test setting was designed to show where the focus was. The shots shown so far do not since all the subjects are at the same distance.

[colorflow]

It's like saying, "shooting 100 frames a day is a good rule of thumb" ... no, it's not. It's just nonsense. See mjh's diagram above.

 

Poor analogy. "Shooting 100 frames..." is not useful. A rule of thumb must be useful but not necessarily precise. The 1/3-2/3 rule is useful (short of memorising mjh's charts) when selecting a focus point for a scene which in many instances is in the mid distance range. Precision is not called for in these cases especially, as stated by others, sharpness is relative and subjective.

[yanidel]

If we put the 1/3rd 2/3rd rule in the context of Leica's core applications, that is reportage and street photography, it is a good rule of thumb. Indeed, most subjects are in general in the 1 to 3 meters range.

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Hallo,

Look here: Leica M

[hoppyman]

Possibly of interest to some. In his New Leica Compendium, Erwin Puts has a comparison of focus shift between this lens and the previous model.

The text is not entirely clear (to me) but he describes a shift to the front of 3cm with the new lens and 5cm with the older one (from f/1.4 to f/2.8) at a nominal distance which must be 1m (3% error mentioned).

 

Personally I can only comment that I have made around 500 photos with my example and typically might shoot it around f/2.8 - f/4 and 2 - 2.5m for people. I have never personally observed any focus error that was not my own mistake. I have never used the older model not attempted any focus shift testing with the new one. It just works perfectly for me as I use it.

Three gals grins photo - Geoff Hopkinson photos at pbase.com

For her personal project on young women's self images photo - Geoff Hopkinson photos at pbase.com

[Pinocchio Wood]

Do slr autofocus lenses show focus shift as well? Or is this problem peculiar to manual focus lenses, or the rangefinder system itself.