DOF where is it?

[Ororaro]

I think here are some misunderstandings though you all are not wrong.

If you want to get same dof at the same FOV so one has to always to compensate about a stop on smaller sensor. M8 with 35mm lens gets about 50 mm fov of film but you have to use dof marks from 35mm, not 50mm as you do with film. So dof are not same if you use both 35 and 50mm lenses on different bodies to get same 50mm fov.

This is true only if you MOVE in order to recompose. But even if you MOVE, the dof markings on the lens are still valid.

Anyway, I'm out. This is ridiculous.

 

[Ororaro]

I think I see what is happening and think it might shorten the thread if you all state your assumptions. A couple of things seem right:

1) markings on the lens are correct, regardless of the medium of capture. If this were not true, then you could change the optical nature of the lens by inserting a cardboard mask over a portion of the film/sensor. This seems an obvious counterfactual. Note that this says nothing about comparisons of lenses of different focal lengths, which of course have different optical qualities.

2) perception of DOF will change somewhat with print size. If you don't think this is right, come on over and see some of my contact sheets. Circle of confusion is otherwise a red herring in this debate.

3) FOV changes when you sneaker-zoom (that is, move your position relative to the subject to compensate for a crop factor). Of course then you have to re-focus, and that _will_ change your depth of focus.

I like to think of a lens casting light on a sensor as the same as a flashlight shining on a wall. Your "format" is just the size of the rectangle you are carving out of the circle of light on the wall. If you don't move the wall or the flashlight, nothing else about the image (except the crop) will change.

Simple.

 

[Ororaro]

NB23, no, it's not the same thing. Part of the formula for calculating CoC takes into consideration the ultimate enlargement of the image. The acceptable (to the viewer) CoC changes with the degree of enlargement of the image.

You are treating DOF as a constant, which it is not.

Please cut it off with the COC and enlargement of the image. I don't care fo the "ultimate enlargement of an image". You're somewhat steering the whole debate with this concept.

The dof marks of a 50mm lens stay accurate on a M6 as well as on a M8, do they? Forget the coc and enlagrgement of an image. Can you simply answer this?

 

[gdi]

Note: the very first words of the explanation in that article are: "For an equivalent field of view." So: if you were to test the assumptions in this article with four different cameras each with a 50mm lens (assume an APS digicam, a 35mm camera, a 6x6 MF camera and an 4x5 field camera), you would have to have each camera in a different position to hold the field of view constant. This will mean, in turn, that the lens-to-focal-plane distance will be different for each set up. So of course the depth of focus will be different in each of these situations. But this is not a function of the sensor/film size, it's a function of moving your rig around and changing the relationship between the lens and the sensor/film plane.

Ben Marks

I know attention spans are short in the Internet Age, but is fair to pick a single sentence out out of a multipage article upon which to summarize it? Mr. Atkins explains the various confusing situations related to DOF - COC differences, Format differences, etc., if you read it all.

The information regarding use of the DOF scale on the lens lie further down - in the Addendum in context of a 1.6 crop camera:

"So with the lens set to f16, we need to look at the DOF scale markings about 1/2 way between f8 and f11 as shown below."

 

[gdi]

The dof marks of a 50mm lens stay accurate on a M6 as well as on a M8, do they?

Ned - look at the Bob Atkins article - he clearly explains why they would be accurate on the M6 but not M8.

Is it enough of a difference in practical use to cause a problem with photos? Maybe not, maybe so - would around a stop less DOF matter for the situation?

 

[Ororaro]

Ned - look at the Bob Atkins article - he clearly explains why they would be accurate on the M6 but not M8.

Is it enough of a difference in practical use to cause a problem with photos? Maybe not, maybe so - would around a stop less DOF matter for the situation?

I read it and I know about it. I think we're confusing concepts. If one shoots with a ff camera and a 1.3 crop, both with the same lens and on a tripod, and shooting the same subject (which doesn't move), the dof will stay the same on both formats.
I try to keep my posts short because english is not my first language (more something like third) so I don't start to be incoherent.

As usual, this dof thread have gone way out of hand with everyone pulling in the direction they want it to go. Not everyone is necessarily wrong but it's gone all over the place.

 

[Ororaro]

Let's take this example:

I have 2 cameras on a tripod (a M8 on one and a M6 on the other). They both have a 50mm lens set at f4 and they both focus on the same subject that is exactly 10 feet away from the film/sensor plane.

A: Will both images have the same dof?
or
B: Will both images have a different dof?

 

[tomasis]

This is true only if you MOVE in order to recompose. But even if you MOVE, the dof markings on the lens are still valid.

Anyway, I'm out. This is ridiculous.

Right you said what I stated in my comment but when you move to recompose, then dof becomes deeper on cropped sensor. It is not same anymore.

I think you focussed too much on the fact that everything through lens is the same It depends on which question we want to answer.

 

[kuzano]

I don't understand any of this thread... I just>>>

I don't understand any of this thread... I just>>>

I just use the DOF, FOV, and COC (called the DOVFOVCOC) plugin in Photoshop. And like a good little photoshopper, my last Work Flow function is the sharpen tool.:angel:

 

[Ororaro]

Right you said what I stated in my comment but when you move to recompose, then dof becomes deeper on cropped sensor. It is not same anymore.

I think you focussed too much on the fact that everything through lens is the same It depends on which question we want to answer.

I know everything there is to know about dof, just as everyone else who know about dof.

Yeah I know, the dof discussions can go all over the place, depending where one wants them to go. I wass only answering the OP's question.

DOF is an extremely simple concept.

 

[tomasis]

Let's take this example:

I have 2 cameras on a tripod (a M8 on one and a M6 on the other). They both have a 50mm lens set at f4 and they both focus on the same subject that is exactly 10 feet away from the film/sensor plane.

A: Will both images have the same dof?
or
B: Will both images have a different dof?

It is same dof but you get different images. One is 66mm and another is 50mm. We are talking about real world photographing, right. If you like 50mm fov and you buy m8/rd-1, which lens are you gonna to buy to get fov 50mm? Then in the case if you like short dof of 50mm lens at f2 on film, how are you gonna to do to get same dof on m8/rd1?

 

[gdi]

Let's take this example:

I have 2 cameras on a tripod (a M8 on one and a M6 on the other). They both have a 50mm lens set at f4 and they both focus on the same subject that is exactly 10 feet away from the film/sensor plane.

A: Will both images have the same dof?
or
B: Will both images have a different dof?

That answer is in the Bob Atkins article - the M8 will have less DOF and it makes sense to use the DOF markings for a larger aperture than the aperture you are using.


From the article referenced by Sitemistic:
"Using the same lens on a small-sensor camera and a full-frame camera, the small-sensor image has 1.6x LESS depth of field than the full-frame image would have (but they would be different images since the field of view would be different)"

Replace the 1.6 with 1.3 above for an M8...

 

[tomasis]

I know everything there is to know about dof, just as everyone else who know about dof.

Yeah I know, the dof discussions can go all over the place, depending where one wants them to go. I wass only answering the OP's question.

DOF is an extremely simple concept.

I agree completely and I'm not much too smart to understand all mathematic formulas and physics but I had to try out real options instead and looked at images. It is what I draw my conclusions based on my experiences. I think that to judge by all mathematics and numbers only add more confusion not only to my poor brains but others also.

 

[rxmd]

Well, you're wrong. What you're saying is the same as seeing depth of field increase in a 4x6 print by just cutting 1 inch off each side.

You don't sound like you've tried this. Just do it one day. It's very instructive.

Make a big print from one of your Noctilux pictures with its supershallow DOF. Then make another and cut away half of it the way you suggest. You now have two prints of different sizes. That's why we have to look at them from different distances, because that's what we normally do when prints are differently sized. That's why every single DOF formula on the planet, including the one used by Leica for printing the DOF scales on their lenses, is based at some point on assumptions about the ratio of print size to viewing distance. You will find that DOF in the two prints is indeed different.

Alternatively, make an 8x10 and a 4x6 from the same negative from one of your Noctilux pictures. Cut away 2 inches on each side from the 8x10. Look at the two resulting 4x6 prints and tell me if they have the same DOF. They won't. If you want to, put a diagonal ruler in there so that you can quantify what you see. This is exactly the M8 situation with a cropped sensor, except that the M8 crops before printing and here we crop after printing. The M8 crops slightly less of course, but you can repeat the same experiment with the appropriate sizes. Try it one day.

Fred is right on this. There's no use being right on principle if in order to be right you have to pick your comparison in such a way that it becomes useless.

Philipp

 

[rxmd]

But regardless of the sensor, the markings on the lens are correct. Always correct.

No.

Just to back this up with some numbers, I have here a medium format wideangle, a Zeiss Jena Flektogon MC 50/f4. Quite a decent lens if I may add this. Here's a couple of hyperfocal distances from the DOF scale engraved on the lens:

f/22: ca 1.8m
f/11: ca 3.5m
f/5.6: ca 6.5m

This is from a 50mm lens. Now Ned, take a Leica 50 of your choice, look at its DOF scale and compare. Then tell me if the DOF markings on my Flektogon are going to be of any use if I use it on a 35mm body. We notice that the 35mm body is a crop camera relative to the sensor format that the DOF scale on the Flektogon was designed for. Then tell me if the DOF scale on your Leica lens is any use on a crop camera.

Philipp

 

[jaapv]

I know everything there is to know about dof, just as everyone else who know about dof.


DOF is an extremely simple concept.

The first statement is sadly negated by the second.....

 

[gdi]

It looks like the OP has disappeared (wonder why?)

But I think we can all now agree that the answer to his original question is that the DOF markings on the lens are more accurate for film/Full Frame than they are for an M8 (or an RD-1). The question each photographer has to answer for themselves is - Isit worth worrying about? In most cases, I would think not - but when I use hyperfocal focusing, I use the markings for a larger aperture to be more accurate .

(Note the original question didn't have the complications of comparing the use of different formats like "keeping the same FOV", same viewing distance, etc. Simply do the DOF marking mean the same thing (i.e., do they "work" the same))

Has anyone using an M8 ever gone to the trouble to calculate a proper Depth of Field table for any Leica lens, like we used to do in the old days? I mean, do the numbers on our lenses (giving you an idea of the Dof at a given aperture) mean the same thing on the M8? Or has the x1.3 digital factor changed everything?
Regards.

 

[greypilgrim]

I must be crazy....

I must be crazy....

for sticking my nose in here but nothing I'll duck fast

A great site for this is:

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

The one thing that is a "truth" is that DOF is an illusion. By definition, there is only a single plane that is in focus. DOF is purely about the appearance of objects being in focus. There are many quotes at the site above that state this (and it is true based on the "laws" of optics, basic physics).

http://www.dofmaster.com/dof_defined.html

The next thing that you can see on this site is that

1) If the distance to the object is constant
2) If the focal length is constant
3) If the aperture is constant
4) if the film size or sensor size is different

5) Then the DOF will be different

try it on the calculator.

HOWEVER, if sneaker zooming is used to make the image the same size on each of the different film/sensor sizes (ie the distance changes), the DOF will appear to be the same UP TO A CERTAIN point:

http://www.dofmaster.com/dof_imagesize.html

Finally, this is something I believe to be true, but I have nothing firm to back it up:

Print size affects the appearance of focus only if you stand or view from the same distance when looking at different size prints. This is almost the reverse of the distance to the subject effects mentioned above. If you view different size prints from the distances necessary to make each of the images appear the same size, their circle of confusion will be the same and hence their DOF will appear the same.

Ducking and running now

Doug

 

[ferider]

Ever since the M8 was released this subject comes up again and again. Not that hard really, play with dofmaster and you will see. For fixed COC size on the medium (film or sensor), the DOF of a lens is the same independent of the format. For fixed COC size in the final print, assuming a fixed print size and viewing distance the DOF is format dependent. For example, an 80/2.8 6x6 lens has about the same DOF as a 50/1.4 35mm lens.

But in use who cares ? Anybody "buffers" the hyperfocal distance like I do ? I.e., the lens scale shows me f8 is OK from here to infinity, but I will use f11, anyways ? In use it's very qualitative.

What is more important for RFs is that due to less DOF (and on the M8 less magnification), fast lenses are harder to focus on smaller format. Forget about 75/1.4 on the M8, for instance . Or 90/2 on RD1s.

Ducking, too ...

Roland.

 

[Benjamin Marks]

These threads could be an interesting example of how easy it is to misunderstand one another, given the limitations of the forum. I suggest everyone pick up a camera and post images proving their points. The laws of physics will not change based on the vehemence of our disagreement.

A bit of subjective description of how I use my lenses may help.

From a purely subjective point of view, I have never paid much attention to "crop factors" in my photography. I do a lot of portraiture at the near limit of my lenses' ability to focus. This tends to be my limiting factor and not either i) the size of the image on the film or sensor or ii) hyperfocal distance (where I rarely use any of my lenses). As an example, a 50mm lens is my favorite focal length, regardless of whether my "sensor" is APS, a 1.3 crop for the M8 or the whole frame of 35mm film. My M8 currently has a 50/1.5 Sonnar, my M5 has a 50 Summicron and XP2 film, and my 5D has a Canon 50/1.4 on it right now, sitting on the side-board across from me. It is my favorite focal length because of the relationship of in focus and out-of-focus areas, its rendering of perspective and so forth. Given my biases, it should be no surprise that I have eschewed digicams with a 12mm "normal" lens and the like -- I may be able to get the same field of view with the little sensor, but for the photography I do things just don't look right to me when rendered with a lens of that focal length.

It also should be no surprise that I completely agree with Fred's comment above, that "you use the camera that is in your hands." However, when I switch lenses between the M5 and the M8, to the extent I need a general guide, I use the DOF markings on the lens in front of me, without reference to the sensor size. This is because I am not generally reproducing the field of view between the two cameras -- at least it's not my goal.

Peace.

Ben Marks