The 1.3 factor problems

[Symeon]

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

[teo]

As the M8 places its "film plane" further back giving a x1.35 factor

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]

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?).

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, 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]

Hi Simon,

As the M8 places its "film plane" further back giving a x1.35 factor

As mentioned by the other posters above, the M8 registration distance is the same as with film Leicas. But:

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.

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.

[nikonhswebmaster]

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.

Any discussion of all this has become a mess on here, simply because some folks refuse to discuss it politely. BUT

The lens is always a 50 mm, f/2 no matter what you use it on. If you put it on an enlarger or a 4x5, it would still be a 50 mm f/2 (it would however produce a circle on 4x5).

It is however, when mounted on an M8, equivalent to a longer 35 mm lens in coverage and foreshortening (telephoto effect). "Equivalent" is the relevant term here. However the focal length of the lens is not changed, and has nothing to do with the camera it is mounted on.

But bottom line is a lens is a lens, the f-stop is a ratio between the physical optical length of the lens and the opening of the aperture.

[dcsang]

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 :D

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]

Deja Vú....

:)

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.

[edrodgers731]

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!

[ferider]

You are right, Ed, of course, except for the term DOF (including the lens scale) being defined for a fixed enlargement and viewing distance.

[edrodgers731]

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? :)

[dcsang]

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!

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" :D

Cheers
Dave

[edrodgers731]

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.

:D

[angeloks]

Deja Vú....

Déjà vu...

[antiquark]

worth repeating...
http://www.dofmaster.com/dofjs.html

Select "Leica M8" in the list to find the DOF.

[RF-Addict]

worth repeating...
http://www.dofmaster.com/dofjs.html

Select "Leica M8" in the list to find the DOF.


and compare it to a FF sensor, like the 5D with the same focal length and f-stop...

[dcsang]

and compare it to a FF sensor, like the 5D with the same focal length and f-stop...


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 :D

Dave

[edrodgers731]

"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.

[RF-Addict]

:angel::):eek:

[ferider]

"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.

Who cares about paper, it's all about 800x600 web images ... :D

[charjohncarter]

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.

[nikonhswebmaster]

Whátevér :D



Im waiting for Ned...:)

Ditto...

I have used the same Nikkor telephotos on both 2 1/4 Bronica, and 35 mm, so this is an old story I figured out 40 years ago. Such a fuss over nothing.

Oh Ned??? Ned???

[sonwolf]

Symeon,

The Bob Atkins website has a detailed explanation of depth of field and its relation to digital cameras. His excellent DOF calculator will give all the relevant information for an M8.

http://www.bobatkins.com/photography/technical/digitaldof.html
http://www.bobatkins.com/photography/technical/depth_of_field_calc.html

[charjohncarter]

sonwolf, thanks even I can understand that site.

[Gabriel M.A.]

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.

Leica has special pricing for those "ignorant of the basic laws of optics". It comes with a specially designed Sharparatamat f/64

[edrodgers731]

Bob Atkins.. "...to give the same view..."

Derp.

[dcsang]

Bob Atkins.. "...to give the same view..."

Derp.

Ya.. let's give that whole quote now shall we? I mean, may as well "give credit where credit's due" and all that... :D
For an equivalent field of view, the EOS 10D has at least 1.6x MORE depth of field that a 35mm film camera would have - when the focus distance is significantly less then the hyperfocal distance (but the 35mm format needs a lens with 1.6x the focal length to give the same view).

But ya.... the DOF is the same no matter what.. or different....

I remember this argument like it was a beer commercial.. "Tastes GREAT !!! / LESS FILLING !!!"

Dave

[jaapv]

Any discussion of all this has become a mess on here, simply because some folks refuse to discuss it politely. BUT

The lens is always a 50 mm, f/2 no matter what you use it on. If you put it on an enlarger or a 4x5, it would still be a 50 mm f/2 (it would however produce a circle on 4x5).

It is however, when mounted on an M8, equivalent to a longer 35 mm lens in coverage and foreshortening (telephoto effect). "Equivalent" is the relevant term here. However the focal length of the lens is not changed, and has nothing to do with the camera it is mounted on.

But bottom line is a lens is a lens, the f-stop is a ratio between the physical optical length of the lens and the opening of the aperture.

You are so right; and the DOF is determined by relative enlargement, NOT by focal length. Now if you stay at the same place, your image gets cropped by a smaller format, so a 50 mm lens will give a smaller image, so to get the same effect the paper you have to print it on will be smaller. The DOF is the same.
If you print it on the same size of paper, your enlargement gets more, so your DOF gets more shallow. Mind you, still with the same lens.
If you take a different lens, a 35 mm one for the same FOV and don't change your point of view, you change the enlargement of the scene, and again change the DOF.
The immemorial rule for different formats, which is second nature for all of us who shot both 135 and medium format: With the same field of view, at the same distance, a smaller format will yield a deeper DOF.
It is as simple as that, my friends. With a format difference of 1.4, the difference in DOF is one stop. Add to that that the DOF is more steeply defined on a sensor than on film because of the thickness of film, the effect is enhanced. So on the M8, with a format smaller by 1.3, you cannot go wrong if you mentally visualize the DOF you would have had in your film days with the same image, and close down one stop on your DOF scale
Nothing less, nothing more, forget all calculations and convoluted theories.

[edrodgers731]

Less filling! :)

Nobody is trying to compare apples to apples. How about this: Take a 47mm lens on the M8 and take a picture. Then take the same shot with a 69mm lens on an M7 from the same spot.

Damn.. Somehow it's still different. WHAT ARE WE GOING TO DO?

:D :) :D :)

Now I'm just having some real fun!

[BillBlackwell]

This issue is only complicated because we make it so.

Take a picture with a 35mm camera (any lens will do). Make a full-frame print (any size will do). Then trim the edges reducing its size by a ratio of 1:33:1. That's it.

This is precisely why they call it a "crop-factor."

[dcsang]

ya.. Jaap's right - the M8's DOF with the same lens vs the M7 yields a greater DOF.. he said it himself :D
With a format difference of 1.4, the difference in DOF is one stop. Add to that that the DOF is more steeply defined on a sensor than on film because of the thickness of film, the effect is enhanced. So on the M8, with a format smaller by 1.3, you cannot go wrong if you mentally visualize the DOF you would have with the same lens closed down one stop more than you actually do, compared to your film days.

:D :D :D

Dave
(I told you I "loved" these threads....)

[edrodgers731]

This issue is only complicated because we make it so.

Take a picture with a 35mm camera (any lens will do). Make a full-frame print (any size will do). Then trim the edges reducing its size by a ratio of 1:33:1. That's it.

This is precisely why they call it a "crop-factor."

Yeah! We star-bellied Sneetches are better than you non-star-bellied Sneetches!

Bill, that's how I like to think about it, but the other argument is just as valid. It's like that old story about the blind men feeling up an elephant. To the one holding the tail, the one holding the tusk doesn't know squat about elephants!

[Ben Z]

Some people like to debate the science, and that's fine. But in terms of practical use when actually taking pictures, it's like this:

To get approximately the same composition from the same distance that I would get with my 50mm lens on my M6, I have to use a 35mm lens on my M8. A 35mm lens gives more DOF from the same distance as a 50mm lens, regardless of what the format is, so in this example, I have the DOF of a 35mm lens in the FOV of a 50. In practice, this is easily observed.

If subject isolation is a consideration, one can shoot at one f-stop wider, which reduces the DOF. Unless of course one is already shooting wide open, which is where the trouble comes. That is why I am a bit ticked that I sold my 35 Summilux-ASPH back a while, and can't see myself paying what they're going for these days.

[jaapv]

ya.. Jaap's right - the M8's DOF with the same lens vs the M7 yields a greater DOF.. he said it himself :D


:D :D :D

Dave
(I told you I "loved" these threads....)

It appears you actually understood it...;).And picked up on a sloppy way of formulating :(.