Symeon
Established
A few months ago I posted a question on the DOF of Leica lenses which has been altered by the M8's x1.3 factor. I got little response and so I forgot about it. But the problem is recurring and U had to do some tests myself using an M6 and M8 and a whole set of test targets, etc. My results were exactly what I feared.
To believe that the old Leica lenses fitted on the M8 are subject only to a so-called "crop" effect due to the smaller sensor is a serious mistake. The focal length of a lens is calculated from the distance of its first focal point (inside the lens) to where the film plane is located inside the camera - in this case, to where the M8's sensor is. As the M8 places its "film plane" further back giving a x1.35 factor, all Leica lenses are changed, not only in focal length but also in actual f-aperture and the resulting depth of field. Thus, a Summicron 50/2 becomes a 67.5/F2.7 which makes it a kind of a portrait lens. To believe that maximum aperture (the speed of a lens) remains unchanged when the focal distance has changed is a fallacy, an ignorance of the basic laws of optics.
Now the Leica people obviously wouldn't have liked to reveal all these truths when they launced their pricey object. That all old classic optics will work fine, is the truth, but that photographers will have to treat them as "new optics" and learn how to use them from the start, would not make very good publicity for the M8. One reason why Leitz has to produce totally new optical designs,6-bit coded and slower in speed. It is not really to open up the market to more people who cannot afford the Summiluxes, but because these new "Summarits" or what have you, are engineered for the M8's special digital geometry.
By the way, I do use an M8 with all the old Summicrons, a tele-Elmar and a Super-Angulon and I am quite pleased. But focusing through the RF of the M8 means very little to my lens' barrel markings, and especially as far as DOF is concerned.
Please correct me if I wrong.
Regards,
Simon
To believe that the old Leica lenses fitted on the M8 are subject only to a so-called "crop" effect due to the smaller sensor is a serious mistake. The focal length of a lens is calculated from the distance of its first focal point (inside the lens) to where the film plane is located inside the camera - in this case, to where the M8's sensor is. As the M8 places its "film plane" further back giving a x1.35 factor, all Leica lenses are changed, not only in focal length but also in actual f-aperture and the resulting depth of field. Thus, a Summicron 50/2 becomes a 67.5/F2.7 which makes it a kind of a portrait lens. To believe that maximum aperture (the speed of a lens) remains unchanged when the focal distance has changed is a fallacy, an ignorance of the basic laws of optics.
Now the Leica people obviously wouldn't have liked to reveal all these truths when they launced their pricey object. That all old classic optics will work fine, is the truth, but that photographers will have to treat them as "new optics" and learn how to use them from the start, would not make very good publicity for the M8. One reason why Leitz has to produce totally new optical designs,6-bit coded and slower in speed. It is not really to open up the market to more people who cannot afford the Summiluxes, but because these new "Summarits" or what have you, are engineered for the M8's special digital geometry.
By the way, I do use an M8 with all the old Summicrons, a tele-Elmar and a Super-Angulon and I am quite pleased. But focusing through the RF of the M8 means very little to my lens' barrel markings, and especially as far as DOF is concerned.
Please correct me if I wrong.
Regards,
Simon
teo
Well-known
Mmm... sorry, but the crop factor is simply because the sensor is smaller than 35mm film (due to cost and technical difficulties), the "sensor plane" is at the same distance as film cameras, otherwise it couldn't be in focus (right?).
edrodgers731
Member
Yeah, I think you are right on that. Anyway, how could they move the sensor back? The old film plane was in the absolute rear of the body. Now they did make the M8 slightly thicker, but that's just for the fact that the sensor is thicker than film. If anything it's a bit closer. Just a hair, if that.
I think the main imaging difference between film and digital is the medium. Film has much more thickness than the sensor, and therefore focus is less forgiving on the M8. When I say film is thicker in this case, I mean the optical recording plane.
So really, the crop factor does not have anything to do with DOF. The medium might, but not the crop.
angeloks
Well-known
Well, the sensor is simply smaller. Take a film picture and cut the edges to get an image 1.33x smaller, that's exactly what it is. It gives the impression of having a bigger DOF since you often crop the out of focus areas.
ferider
Veteran
Hi Simon,
As mentioned by the other posters above, the M8 registration distance is the same as with film Leicas. But:
Here you are completely right, simply due to the geometric crop factor (COC get enlarged, etc). But for some reason this has been debated a lot in the past - it seems hard to understand that the DOF scale on a Leica lens is not valid anymore ...
There is another caveat that users seem to have difficulty with: due to reduced camera Effective Baselength + more shallow DOF, the same lens is harder to focus on an M8 than, say, on an M6. Also, the thin sensor is less forgiving and lens tests are easier ...
On the upside, this has kept used prices of 90/2 Summicrons and 135/4 Elmars down
Best,
Roland.
As mentioned by the other posters above, the M8 registration distance is the same as with film Leicas. But:
Here you are completely right, simply due to the geometric crop factor (COC get enlarged, etc). But for some reason this has been debated a lot in the past - it seems hard to understand that the DOF scale on a Leica lens is not valid anymore ...
There is another caveat that users seem to have difficulty with: due to reduced camera Effective Baselength + more shallow DOF, the same lens is harder to focus on an M8 than, say, on an M6. Also, the thin sensor is less forgiving and lens tests are easier ...
On the upside, this has kept used prices of 90/2 Summicrons and 135/4 Elmars down
Best,
Roland.
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dcsang
Canadian & Not A Dentist
I love these types of discussions.
Mainly because they inevitably end up as a case of semantics.
I would concur with a very basic understanding of what you've stated Simon.
I've tried, in my own unscientific "dumbed down" way, to state the same thing here in other threads but the illuminati have stated that I'm a heathen for believing such things
All I know is, on any camera that has a crop, there is a difference in "how an image appears" at maximum aperture when compared to the same full frame image when given that the framing of the subject of both images are the same. Some say DOF never changes regardless of what camera you put your lens onto (crop body or not) and others would say it's the bokeh that's altered. To me, I am just going to say, the image looks "different".
Cheers,
Dave
Mainly because they inevitably end up as a case of semantics.
I would concur with a very basic understanding of what you've stated Simon.
I've tried, in my own unscientific "dumbed down" way, to state the same thing here in other threads but the illuminati have stated that I'm a heathen for believing such things
All I know is, on any camera that has a crop, there is a difference in "how an image appears" at maximum aperture when compared to the same full frame image when given that the framing of the subject of both images are the same. Some say DOF never changes regardless of what camera you put your lens onto (crop body or not) and others would say it's the bokeh that's altered. To me, I am just going to say, the image looks "different".
Cheers,
Dave
ferider
Veteran
IMHO, the biggest source of confusion is mixing up the terms "physical focal length" and "equivalent focal length". And since fstop is relative to focal length, one also can talk about physical f-stop and equivalent f-stop. Semantics, like Dave said.
Roland.
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edrodgers731
Member
This is always blown up beyond what it needs to be. As simple as I can make it:
Take a shot with an M7, print a 4x6. Trim the edges evenly to make a 3x4.5 image.
That's what you get with the M8 when you use the same lens.
The middle section of the exact same image, same DOF, same aperture. The focal length is identical no matter how big your negative is.
Imagine if you had to recalculate your exposure and focus every time you put a different sized piece of photo paper under your enlarger!
Take a shot with an M7, print a 4x6. Trim the edges evenly to make a 3x4.5 image.
That's what you get with the M8 when you use the same lens.
The middle section of the exact same image, same DOF, same aperture. The focal length is identical no matter how big your negative is.
Imagine if you had to recalculate your exposure and focus every time you put a different sized piece of photo paper under your enlarger!
ferider
Veteran
You are right, Ed, of course, except for the term DOF (including the lens scale) being defined for a fixed enlargement and viewing distance.
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edrodgers731
Member
See.. Now I've gone and made it all muddy!
Let me rephrase:
Set up your enlarger to expose a 4x6 print. Go ahead and make one.
Then with the same lens, aperture, focus, head position, and exposure time, Place a 3x4.5 piece of paper down and expose it.
You get the same DOF in both, in fact if you trim down the 4x6, you can't tell them apart.
How's that? Better?
Let me rephrase:
Set up your enlarger to expose a 4x6 print. Go ahead and make one.
Then with the same lens, aperture, focus, head position, and exposure time, Place a 3x4.5 piece of paper down and expose it.
You get the same DOF in both, in fact if you trim down the 4x6, you can't tell them apart.
How's that? Better?
dcsang
Canadian & Not A Dentist
Conversely,
Take a shot with an M7, print a 4x6.
Take the same shot with the M8 - you'll have to "move back" so that the framing is the same as the M7 - keep your aperture the same as the M7 shot.
Print the 4x6.
Now look at the images and see if it's still "the same"
Cheers
Dave
edrodgers731
Member
Yeah, yeah.. Of course. It all depends on how you want to think about it.
I choose to think of it as a crop. It's easier than trying to work out how many steps I must take and how I must adjust my aperture to get the "equivalent" standard of some other camera system.
It's easier to clap my hands on my ears and say "NANANANANANANANANANANA" while others are working out exactly how the shot looks different from certain points of view.
I've been a bad boy.
I choose to think of it as a crop. It's easier than trying to work out how many steps I must take and how I must adjust my aperture to get the "equivalent" standard of some other camera system.
It's easier to clap my hands on my ears and say "NANANANANANANANANANANA" while others are working out exactly how the shot looks different from certain points of view.
I've been a bad boy.
angeloks
Well-known
Déjà vu...
antiquark
Derek Ross
worth repeating...
http://www.dofmaster.com/dofjs.html
Select "Leica M8" in the list to find the DOF.
http://www.dofmaster.com/dofjs.html
Select "Leica M8" in the list to find the DOF.
RF-Addict
Well-known
dcsang
Canadian & Not A Dentist
Now now.. that sort of talk is blasphemous around these parts and could get you either excommunicated or strung up by your big toes... or both
Dave
edrodgers731
Member
"NANANANANANANANANANANANANA!"
COC is different.. Not just the size of the sensor. This is all so silly.
edit:
So I guess smaller papers have different focus properties as well.
COC is different.. Not just the size of the sensor. This is all so silly.
edit:
So I guess smaller papers have different focus properties as well.
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RF-Addict
Well-known
:angel:
ferider
Veteran
charjohncarter
Veteran
I have two 1.5 factor DLSRs. I don't know enough about optics to really wade in here, but there is something more going on than simple sensor/image crop. I have noticed DOF and F Stop inconsistencies. Whether DOF/FSTOP is chicken and the egg, I again don't know.