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SL's DOF limit display question


jmahto
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I don't own SL (not yet..) but I am curious about it's DOF limit display. Isn't DOF limit dependent on acceptable circle of confusion? Which is dependent on final enlargement size?

 

For M lens one can simply read the DOF limit for one or two stops higher than shooting aperture if the enlargement is more that 5x7. I am curious how SL DOF limit are adjusted based on final enlargement?

 

Reference:

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The article in following link states:

"As I explained above, the circle of confusion determines what detail in our pictures appears in focus and which not. Unfortunately, the size of the circle of confusion must also be based on a certain picture size.  In most cases that is an approximate enlargement of seven times or a 5 x 7 inch enlargement from a 35mm negative or full frame digital sensor.  With other words, up to a 5 x 7 inch size enlargement our pictures will display maximum sharpness and maximum depth of field.

 
But what about enlargement greater then a 5 x 7 or if considerable cropping is necessary?  Does that mean the depth of field scale on our lenses is useless?  Not at all.  All we need to do is use the depth of field settings on the lens with an aperture one or two stops larger than the aperture in actual use.  With enlargements of 8 x 10 or 11 x 14, the next larger aperture will usually be sufficient.  If the enlargement size is greater than that, use a two stop larger aperture.

"

http://gmpphoto.blogspot.com/2012/03/depth-of-field.html

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A 7x enlargement of a 35mm frame is 7x10.5 inches, not 5x7 inches, or close enough to the standard 8x10 reference print that 99% of all DoF scales have been based upon since the 1930s or before. I'm sure the SL is calibrated to the same reference DoF print standard, and that there is no current user setting to adjust its DoF readout. 

 

For any camera, if you want more DoF, you stop down a bit more without altering your focus setting. If you want less, you open up a bit without altering the focus setting. The SL's DoF readout is a suggested reference, that's all, just like the scales on any lens. 

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I guess the SL calculation does not reflect the focus shift issue from the 24-90mm?

 

 

There is no "focus shift issue from the 24-90". That has been proven again and again. If anything, with fw1.2, there was an AF aberration that caused the lens to set focus nearer the close focus limit of the DoF than at the orthodox "best focus" critical plane. My understanding is that this was corrected with fw2.0.

 

That has nothing to do focus shift at all. 

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Thank you Ramarren.

Good to read that if this was an issue it has been resolved! (I do have the SL now but not the 24-90 yet)

 

For reference, my 2 sources are:

 

http://diglloyd.com/index-leica.html - he has somewhat of an update that indicates that 2.0 may improved things, but his lens has not been re-rested with 2.0 as far as I know

https://blog.mingthein.com/2015/10/21/premiere-review-2015-leica-sl-601/

 

Look also at this review:

http://scenictraverse.com/blog/2016/3/8/50v50

It is strange to see the background bokeh of the 24-90 being more pronounced than the one from the Noctilux at the same aperture.

For me, as long as the focus point is not lost by this possible focus shift when stopping down, I can make good use of this.

Edited by kikouyou
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"Focus shift" is the wrong term for the problem these folks were reporting, which is an AF system issue. Focus shift is an optical aberration of a lens such that the focus plane shifts when the lens' iris is shifted from one setting to another, typically from wide open to closed down two or three stops. This is proven, over and over again, not to happen with the SL24-90 lens when you use manual focus (the only way to test it sensibly, taking the activity of the AF system out of the game).

 

The issue that Lloyd and others have reported is that the critical focus setting at certain focal lengths and focus distances is set by the AF system to a different spot in the focus zone from where they expected it ought to be set based on typical AF system behavior in other cameras. This is not to say that it's ever been out of focus ... Just placed at a different point in the focus zone. Who knows but that Leica may have programmed it this way intentionally...

 

So "focus shift" has never happened with the SL24-90, and the issue being referred to is a quirk of the AF system with this lens, at least with firmware 1.2. As far as I'm aware, fw2.0 re-tuned the AF system.

 

Personally, I have never seen a problem with how the AF system worked in the SL with SL24-90, and I've had both body and lens since the camera was released on Nov 16, 2015. That said, I generally don't use AF very much, even when I'm using the SL24-90 lens, because I prefer to focus manually most of the time anyway.

 

I have no need of looking at reviews and reports. I've seen them all already, long long ago. The whole "problem" has been a non-issue from the start raised by a couple of rather overly hypercritical people who have to find something to complain about no matter how insigificant a behavioral quirk might be. I've made over 17,000 exposures with the SL to date and of the probably 3000 or so of those made with AF, I've yet to find a single mis-focused image traceable to this particular quirk of the AF system.

Edited by ramarren
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Thank you Ramarren, very useful clarification.

How do you explain the bokhey differences between the Noct and the 24-90mm in the Kristen Meister blog (3rd link)?

Edited by kikouyou
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Thank you Ramarren, very useful clarification.

How do you explain the bokhey differences between the Noct and the 24-90mm in the Kristen Meister blog (3rd link)?

 

 

 

Well, blur and depth of field are different things. You can easily have more/less pronounced blur while maintaining the same depth of field (which in itself is an aberration). There's differences in lens design, focal length, fall off characteristics, focus point accuracy and others that will cause a different look to images that one might assume would look the same. It's common for people to look at the blur in an image and assume it's a part of depth of field when that's hardly ever the case.

 

Gordon

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I like when there is a fast fall off between in focus and out of focus or at least when there is a sharp decrease of contrast between the area in focus and out of focus. From this stand point the 24-90 seems attractive!

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I like when there is a fast fall off between in focus and out of focus or at least when there is a sharp decrease of contrast between the area in focus and out of focus. From this stand point the 24-90 seems attractive!

 

 

For a zoom, I think the 24-90 renders very nicely. I'm more pleased with it's rendering than I am with it's resolving power, which is high. Leica have done a very nice job with the 24-90 (and 90-280 for that matter).

 

I also have the Noctilux that I use with my SL. I think it's superb on the SL.

 

Gordon

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I only have M lenses right now. And I have 3 50mm (which one get to love with the M). The noct, the APO and the Mate.

I see myself going between the noct and the APO a lot, they have their respective virtues...

The noct on SL is much easier to use... And 1/16000 allows me not to take my ND filters to much.

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