M8 Depth of Field

[sps]

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I remember reading something about the crop factor affecting depth of field negatively. The recommendation was to refer to the d-o-f markings for the next smaller aperature.

 

I just received a new 28/2 'cron with the 6-bit coding. The manual is new and makes reference to the M8, the crop factor, etc., and says that the d-o-f remains unchanged despite the crop factor.

 

Thought you guys would like to know.

 

Savvas

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[Jamie Roberts]

Savvas,

 

IIRC it's not the crop factor that affects the DOF for hyperfocus. It's the fact that the f stops were computed many years ago for making a print of no more than 8 * 10" (and even less). If anything, at a given fstop, the crop factor /sensor size adds a little DOF, which one reason why some folks still prefer a 1.33 crop.

 

So when you're going to make a 30 * 40" print from an M8 file, you might want to stop down a bit more to make sure critical focus is maintained when using hyperfocussing.

[tashley]

I remember reading something about the crop factor affecting depth of field negatively. The recommendation was to refer to the d-o-f markings for the next smaller aperature.

 

I just received a new 28/2 'cron with the 6-bit coding. The manual is new and makes reference to the M8, the crop factor, etc., and says that the d-o-f remains unchanged despite the crop factor.

 

Thought you guys would like to know.

 

Savvas

 

Think of it this way: a 28mm on an M8 is actually a 36mm. Plus, whatever the instruction book says, the commonly agreed way of marking DOF scales was based around the days of film, where enlargements tended to be smaller and people couldn't chimp at 100% within seconds, nor view files at 100% on screen within minutes.

 

DOF doesn't switch on and off at exact points. It fades in and out. What looks in focus at 6x4 will be blurry at 24X16 and so on. It's called (aptly!) 'circles of confusion'.

 

For me, the safest way to get satisfactory (NOT perfect) focus at any point other than the exact plane of focus is to use two stops inside the rings on the lens at any focal length above 35mm effective. But I'm fussy about focus!

 

Best

 

Tim

 

ps don't forget that DOF extends further backwards than forwards and this is not correctly reflected on all DOF scales on lens barrels. The ratio is usually about 2/3rds back to 1/3rd forward but it varies per lens. I am slowly learning that understanding all this requires direct physical experience of a given lens on a given camera, at a range of apertures. There's no substitute for it!

[luigi bertolotti]

DOF is not an exact science... it is "historically" based on film AND film behavior... and, being in a certain sense "eye-dependent" is related also to enlarging... I have old 6x9 cm CONTACT PRINTS from my father : looking at them, you see perfectly focused small prints with excellent DOF... try to enlarge, and you see that a 105mm lens at 4,5 or 6,3, not rangefinder coupled (old Ikonta, not Super...) gives a terrible DOF. I have not experience with DigiCameras, but think that the mix of CCD behavior, enlargment, post processing can change totally the concept of DOF as we know it in film.

[sps]

So I guess if one wants multiple things in focus, the closest object should be the primary focal spot. Thanks for the explanations.

[tashley]

So I guess if one wants multiple things in focus, the closest object should be the primary focal spot. Thanks for the explanations.

 

 

That's about right. On a 50 'lux you DOF is about the depth of a cigarette paper wide open but at f4 you can focus on the tip of the nose and have some hope of getting the eyes and lips in focus but you can kiss goodbye to the ears til F5.6!

 

;-)

 

Tim

[wparsonsgisnet]

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... ps don't forget that DOF extends further backwards than forwards and this is not correctly reflected on all DOF scales on lens barrels. The ratio is usually about 2/3rds back to 1/3rd forward but it varies per lens....QUOTE]

 

If you think in logarithmic terms, it is half-way. If you mark ponts on a log scale, say 1,2,3,4,5,...10, the 2 will be 1/3 for the way from 1 to 3; the 5 will be 1/3 of the way from 1 to 10.

 

We are fortunate enough to be allowed to use logarithmic scales for many things analogue. Sound volumes, as we hear them, work similarly, I believe. The Richter (not Sviatov) scale, by which earthquakes are measured is also logarithmic.

[eudemian]

Tim, could you please expand on this statement I am not sure exactly what you mean (more a matter of my limited knowledge)

 

"For me, the safest way to get satisfactory (NOT perfect) focus at any point other than the exact plane of focus is to use two stops inside the rings on the lens at any focal length above 35mm effective. But I'm fussy about focus!"

 

I have started to play around with hyperfocal focusing and it is very interesting, so any help you can give I would appreciate.

 

Tom

[tashley]

Tim, could you please expand on this statement I am not sure exactly what you mean (more a matter of my limited knowledge)

 

"For me, the safest way to get satisfactory (NOT perfect) focus at any point other than the exact plane of focus is to use two stops inside the rings on the lens at any focal length above 35mm effective. But I'm fussy about focus!"

 

I have started to play around with hyperfocal focusing and it is very interesting, so any help you can give I would appreciate.

 

Tom

 

 

Of course Tom. And this is how my brain gets it - a real optical expert would disagree but probably not by much.

 

On any lens, at any aperture, the only thing that is in exact focus is that two dimensional point which is at the exact plane of focus. Everything else is out of focus. It's just that with wider lenses and smaller apertures, all those other out of focus things are not very out of focus at all. So much so that they may appear in perfect focus, and the amount by which they are OOF may be beyond what the sensor can resolve.

 

So the amount by which their out of focus-ness is revealed will be exaggerated by viewing at 100% crop, by big enlargements, and by very discerning sensors. But the amount by which they are actually OOF will vary according to focal length, aperture, distance from plane of capture and whether they are behind or in front of the point of exact focus.

 

Hyperfocal technique is based on an 'I can live with that degree of OOF' decision. You say, 'my/my expected viewer's tolerance for exact sharpness is such-and-such at my anticipated viewing resolution/print size. That equates, on this lens at this aperture, to a hyperfocal 'zone' between let's say 5 feet away and 8 feet away within which I can safely assume everything will be within acceptable focus.'

 

BUT increase the size of the enlargement, or perhaps the resolving power of the sensor, or even the critical faculty of the viewer, and that might all change.

 

A real world example: I like to print large or sometimes crop close. This, plus the M8's uncanny resolving power, means that I don't feel safe with hyperfocal focussing. I do it, it often works, but it is no guarantee. Even on my CV15mm (not RF coupled) which most people say is so wide that at f5.6 you just set it to a hyperfocal distance of 4 feet, which is where the DOF scale tells you that you'll have focus from about 2 feet to infinity. And I know that this doesn't work FOR ME because I've done it and when I want focus, I want it right, not 'good enough.'

 

For me the rational focus strategy with that lens is to set it at infinity at F5.6 because then infinity will most certainly be in focus, and everything from about 8 feet to infinity will look as if it is. But if the main subject is closer than that I will always, unless in a real hurry, guess the distance and dial it onto the lens.

 

IMHO the shots that really get the WOW factor are either just aesthetically fantastic and sod the question of focus - perfectly valid - or those that have some relevant part of the subject in fantastically accurate focus. And I'll get flamed for this but I can often tell, from a roughly 1000 pixel wide preview on screen, whether such a point exists.

 

Phew. Sorry for banging on!

 

Best

 

Tim

[eudemian]

Bang away Tim, that is very useful.

So many techniques to master, still I think the M8 deserves the best you can offer, it certainly reciprocates.

 

Tom

[footnoteblog]

So to sum up, generally:

 

-Everything at the focal point of the lens is in focus.

-The hyperfocal area (slightly in front, and more behind the focal plane) looks in focus, but is definitely not in focus.

 

If you went to most photography schools you'll learn this by year one.

[dhoelscher]

Here's a good web page on depth of field .... including an alternative method of hyperfocusing in which you simply focus at infinity, and then your aperture (within diffraction limits) can be used to calculate what is the smallest detail that will be in focus .. I'm still looking for the web page that shows this concept clearly visually ...

 

Depth of field

 

This is the guy that came up with the "focus at infinity" concept: DOF Revisited

[rosuna]

This article provides an explanation:

 

http://www.luminous-landscape.com/essays/Leica-M8-Perspective.shtml

 

R.

[tashley]

So to sum up, generally:

 

-Everything at the focal point of the lens is in focus.

-The hyperfocal area (slightly in front, and more behind the focal plane) looks in focus, but is definitely not in focus.

 

If you went to most photography schools you'll learn this by year one.

 

 

Yes you would. But most of us didn't/won't go to photography school and so we learn our lessons in a different way. I have learned a lot from this forum and if I can pay back I should. Anything wrong with that?

 

Tim

[sps]

Thank you all very much. I've never been satisfied with hyperfocal distance shooting results. Now I understand why.

 

While you guys take the shot, I'll be the one missing it fiddling with my focus wheel.

[tashley]

Thank you all very much. I've never been satisfied with hyperfocal distance shooting results. Now I understand why.

 

While you guys take the shot, I'll be the one missing it fiddling with my focus wheel.

 

As do we all my friend!

 

Tim

[footnoteblog]

Of course not. After I read my post, I realized how condescending it sounded; didn't mean to.

 

Anyway, my point it, it's not hard to learn, if you took basic photography (highly recommended), then it would be a simple lesson and more hands-on, with a decent instructor. You also learn a lot more in classes than poking around forums and guessing bits of information you may require, and having some structure. That's all.

 

 

Yes you would. But most of us didn't/won't go to photography school and so we learn our lessons in a different way. I have learned a lot from this forum and if I can pay back I should. Anything wrong with that?

 

Tim

[AlanG]

I went to two photo schools but all most of us really need to know about depth of field we can figure out for ourselves by testing:

 

Set up a "typical" subject and shoot it at various f stops. Then look at each image and decide how much depth of field you require for your application. Compare that result with the reference marking on the lens barrel and make a note of the difference to use in the future. For 8x10 and smaller prints, you may be happy with the settings on the lens. For larger prints, you may decide you need more DOF.

 

It is pretty easy to do this test with a digital camera.

 

Also, keep in mind that when judging prints, you should have a standard viewing distance. Usually this is at least the length of the diagonal of the print.

 

If you plan to view at 100% with your face right up against the monitor, you may be pushing things.

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