questions about the brian peterson book

hi all
following the advice of many board members I bought and (even) started reading "understanding exposure" (ed2) by Brian Peterson.

now a lot of the stuff is very intuitive and I like some of his descriptions, but i noticed something...which is "new" to me....

I have two questions:

1.) He uses really small apertures sometimes. and he gets amazing bokeh at f5.6 - in such that I can't usually get even at 1.8 on my nifty fifty. He claims that out of the various factors that influence Bokeh (though he never uses that word per se) that the aperture is the most important. (If he mentions later in the book about the distance from the subject to the background, I am not aware since I am not very far in the book.)

It was my understanding that after the area of f11-16, diffraction plays such a role in the pictures that it is usually problematic to get into these values - especially if you are interested in sharp pictures. (i know that the concept of sharp pictures is a bit probelmatic, but flow with me on this one)

2.) equivalent aperture: He mentioned while comparing P&S to DSLR/SLR cameras that the a P&S f2.8 is not the same aperture as a f2.8 on a DSLR (pg 46 for those of you following at home) - but rather P&S f2.8 = DSLR f11! This is the frist time I heard of that (though it certainly jives with my experiences as I am in the passage between P&S to DSLR right now) and would be interested in understanding why and how that can be. I mean, the aperture is a physical measurement of the hole in our picture box and is proportional to the focal length of the lens....
can someon explain this one to me, please.

anyway, thanks for any direction

2) I think it is because the sensor is even smaller than the ones on crop cameras slr, though I don't know enough of what he is trying to say in that book

1) His 35mm film frame is going to have a narrower DOF than your 7D, all else being equal. Aperture is a big factor in DOF, but of course so is the relative distance of the camera, subject, and background.

2) Yes, I believe diffraction has to do with how small/close your pixels are packed. So a 10MP 1.6x crop sensor is going to suffer from diffraction at a larger aperture than a 10MP full frame sensor. But you have to weigh that against getting the DOF you need. I see diffraction increase rapidly beyond f/16 on my 5D.

3) His experience mirrors mine. I just happened to be doing some tests between my 5D and my wife's Powershot tonight and at the same exact settings, the 5D had a much narrower DOF than the P&S. Everything is scaled down in a P&S. Small sensor, short lens, tiny aperture. It think the absolute size of the aperture and the very short focal length (wide angles tend to have large DOF) is what causes the large DOF you see in a P&S.

The reason a P&S has a much greater DoF at the same aperture as a DSLR is because it is using a much smaller focal length lens.

Try taking the same picture at f/2.8 with your DSLR using a 10mm lens and with a 200mm lens. The DoF on the wide angle will be much greater.

It's one of the reasons why P&S cameras can be used by complete photographic no hopers and still produce a sharp image. What it strugggles to do is give a nice foreground/background separation using shallow a DoF because it's construction does not lend itself to that type of photography.

equivalent aperture:
in regards to the answers above - I understand how the crop factor would make a certain lens have a "different" focal length in comparison to the 35mm film camera, but why does a smaller sensor affect the proportion between size of aperture and the focal length (which as far as I understand is the formula for the figuring out the aperture values). When we figure out these values, do we use absolute values or equivalent values?

in regards to the diffraction comment from Mike_d: so the diffraction is not solely an optical effect, but is also dependent on the sensor itself? So a canon 10d (fewer Mpxls) will be affected less by diffraction than my 7d (two crop DSLRs) and the 5d classic will suffer less than the 5dII? I will exmaine that issue. When does 35mm film suffer from diffraction? Are there differences in 35mm vs medium and large format films cameras in regards to diffraction?

Sorry for the confusion....

The typical P&S has a sensor the measures 5.25x7 mm. That is 37 mm^ in area, compared to the 864 mm^ of a full frame. Even the image circle from a 6 or 7 mm. lens will fill that tiny area. The crop factor is around 5. F-number is focal length divided by aperture diameter, so at f2 the 6 mm. lens has a physical aperture 3 mm. across. On a full frame with a lens with the same field of view, a 30 mm. lens, that aperture would have a f-number of f10 and would produce roughly the same DoF (using a CoC of 0.006 for the P&S and 0.03 for the full frame in order to adjust for the different amounts of enlargement to obtain the same print.)

Only indirectly. Diffraction is a product of the size of the aperture. It is light bending as it passes close to the edge of the opening. The smaller the opening, the greater the proportion of bent light to light that has passed straight through. As the diffraction increases (as the f-number goes up) a theoretical point is reached where the blurring caused by diffraction is greater than the sensor can resolve. For my 5D2 that point is f10. For a 10 MP P&S it is f3 (!). For a 7D it is around f7, for my 40D it is f9 and for my Xt it is f10. That means that the three croppers shot at f11 would produce much the same resolution. However, at f5.6 the resolution of the 7D is far greater than the other two.

tzalman - thanks for the description. I have started reading on the web about diffraction and in general it seems intuitive UNTIL i get to the CoC (circle of confusion). It seems that I have a bit more reading and understanding to do.

but essentially, if this is true that my 7d theoretically starts having resolution problems from "earlier" aperture sizes (in part because of the photosite density), it would seem logical to me that for photography which needs the smallest apertures (many examples in brian peterson's book are at f22-32) and even macro photography (thereby allowing for usable smaller apertures), it would be better to go "backwards" and get for instance a 10d...but in practice is that what happens?

Does the 10d outperform the 7d or 5dmark ii in small aperture performance?

Have a look at this site, the bottom of the page:
http://www.tawbaware.c​om/maxlyons/calc.htm
For a crop sensor the point at which adding more pixels than the 10D's 6 MP will not bring greater resolution is f12. Above that (f16, f22) the 7D will do no better than the 10D. But it will do no worse either. And for every bigger aperture than f12, the 7D will outperform the 10D and at every aperture greater than f7 it will outresolve every cropper in the market. So if you shoot mainly macro theoretically the 7D has less to offer you, but most people shoot even landscapes at f8 or wider, where the 7D rules (among croppers).

His book was written around likely a manual focus film SLR from 1991. This was before the dawn of 100-200% pixel peeping on computer screens looking for effects of diffraction. He's been a professional photographer for quite some time and he uses the aperture he desires and has obviously been happy with the results.

We would all be better off if we chose shot settings for the end result we wanted; yet it seems so many people just let the camera get shot settings for them or use settings from forums they read online without taking control over your camera and having a result in mind.

Understanding Exposure by Bryan (not Brian) Peterson is more a view into his style of photography and use of apertures than anything else. He seems to have used either f5.6 or f22. He has a 3rd edition coming out later this year.

ceriltheblade wrote in post #10269874
1.) He uses really small apertures sometimes. and he gets amazing bokeh at f5.6 - in such that I can't usually get even at 1.8 on my nifty fifty. He claims that out of the various factors that influence Bokeh (though he never uses that word per se) that the aperture is the most important. (If he mentions later in the book about the distance from the subject to the background, I am not aware since I am not very far in the book.)

Just to back up to this first matter, you are right that the distance to the subject matters, as does the distance between the subject and the background, and the focal lenght used. When you are looking for subject focus isolation and background blur (the "better" terms you might use rather than "bokeh") you take each of these things into consideration, and the mix isn't always what you would expect. In fact, a lot of times I'm shooting things in nature that are fairly distant, but with a long focal length I can get good subject isolation even when using a narrower-than-expected aperture. I have shots taken at f/11 that actually show a fairly narrow depth of field because I'm shooting with a 560mm focal length (400mm + a 1.4x TC).

So, yeah, I do a lot of general shooting at f/4 and f/5.6 to both get some subject isolation with enough of the subject in focus, and then if at those apertures I get quite cose to a subject, say to a flower, and take a shot the depth of field can be quite narrow and the background quite blurred even at only inches away. It's a somewhat fluid subject but once you learn a few things and get some practice you can develop your own "rule of thumb". And, there are places like dofmaster.com that can give you a more technical set of guidelines as well.

thanks all for the discussion. It is very informative. I am more of an academician and I wonder how much of this information would be included in MFA degree courses....because it is really interesting. I mean, the difference between the three "small" factors of aperture, time and ISO completely does not cover the intricacies which are involved in every artistic choice in how to use the camera....

anyway,
tzalman - thanks very much for the link and the description. I think that your signature quote is so apt for discussions like this. I am trying to intigrate both the theory and the practice....thanks for your ideas
Happysnapper90 - sorry about the misspelling bryan's name and thanks for the correction
I am starting to notice the differences (I never shot film ever, so I apologize for the ignorance in regards to the differences) between each system....
Anyway, I agree with you that the craftsman needs to know how to use his tool - and hence I am reading and I ask questions on this forum and read the answers of other people's questions as well.
I did not know that he has a third edition coming out...I wonder how different it will be.

tonylong - you mention the other aspects of background blur and I think, intuitively, that they go hand in hand with the aperture as important factors....I was just quoting the book...and trying to understand the specific statement that he made. Thanks for your clarification. I wonder if there is any information out there about the distances needed from camera to subject and subject to background distances in regards to background blur (or maybe proportion thereto).
Your statement about this being a fluid subject seems exactly my (and others?) problem when trying to understand the whole issue. I suppose (I know) that I lack the experience of most of the people on this board, so I am trying to understand as much as possible as I experiment....
kind of what Bryan said - so I can consistently get results that I am imaggining for the same exposure...

Thanks all

Ceril I mentioned but you may have missed a reference to dofmaster.com. This actually has on online calculator that shows how your depth of field changes as you change your parameters. Because there are variables in all this that include viewing size and magnification due to sensor size, bear in mind that when you see things spelled out in inches, that is under specific conditions and it might be better to use it to get a "ballpark" for the given scene. It does, though, give specific measurements.

tonylong - thanks a lot. I had indeed missed your mention. I will check that out. He has plenty of options (iphone, windows, plamOS), so I can print out some of the charts for work alongside my experimentation.

Thanks again