Understanding Exposures not Understood

[RxForB3]

I do have an android smart phone. Do you have a specific dof calculator you recommend?

 

[Rephargotohp]

Here's my opinion, Having been a Photographer for over 40 years I do understand the triangle But everyone raved about the book so I bought it. I thought it was a pamphlet and a vehicle for him to show pictures of his hit wife and brag about it. But everyone loves the book so what do I know.

Here's the thing with your DIF question, When framed equally, ( Equal magnification) Distance to subject and focal length cancel each other out and you will have the same DOF no matter the Focal Length/Distance to subject. So the only thing that will affect DOF is Aperture.

As far as him recommending f/22. Yes it will yield the greatest DOF but it will also introduce Diffraction within the lens and cause the image to be soft, especially on a cropped sensor camera.

As far as Hyperfocal distance goes, it's not the cure all to everything. It provides for the maximum DOF for a given Aperture. However it doesn't provide for the sharpest image, especially if you have a singular subject close to the camera. The sharpest point will be the point of focus and everything else is just wintin the field of acceptable focus.

The best of all worlds were to place your subject at the point of focus and that point being the hyperfocal distance also. So your subject would be the sharpest and then you would have a filed of focus from 1/2 the distance to your subject to infinity.

The reason that a wide angle lens will appear to have a deeeper DOF, has to do with perspective compression of bringing the background into closer view with a telephoto lens. You can then see that the backgrund is OOF even though the DOF is exactly the same it just to the eye doesn't appear that way.

You also have to take FOV into account with your Gecko shot. The shot's BG will look entirely different shot with a 18mm at 1' DTS than with a 180mm 10' DTS

The reason he suggests metering the blue sky is that in essence you are turning your Camare's Reflective meter into a Incident meter and metering the light that lights the scene (skylight) instead of what is reflected off your subject

 

[Rephargotohp]

And if you do focus at something 2' away without a distance scale on the lens, remember that it is from the Sensor plane not the front of the lens

 

[RxForB3]

Thanks for the great info! I think at this point I know just enough to confuse myself. Sometimes a little knowledge is a dangerous thing

 

[FitzTML]

I've read the book and learned from it.

When people talk about the exposure triangle, it does seem like most of the information is copied directly from the film days when ISO was not adjustable. One thing to consider is that (most) cameras operate most efficiently at ISO 100 so the adjustment of the ISO should reflect this (i.e. change shutter speed or aperture before increasing the ISO).

The triangle boils down to using the shutter speed to freeze or show motion, aperture to narrow or widen the focus plane. ISO and/or additional light is thrown in there.

One takeaway is that film and sensors don't have the same capabilities as the human eye and are quite limited.

 

[gsgary]

Not recommended by me

 

[pgriz]

I'll probably be repeating things people already said, but here goes...

Prime lenses (those that don’t zoom, but have a single focal length, like 50mm or 135mm, or 200 mm) generally have both the distance scale on them, and a bunch of brackets that mark the effective DOF for that lens at different f/stops. Zoom lenses don’t.

If you go to the DOF calculator link posted by EchoingWhisper, you will see a nice diagram that shows DOF and hyperfocal distance. Playing around with the calculator, you find some of the following:

• For a given lens and focal length, DOF increases with aperture (f/22 has more DOF than does f/5.6)

So, 50mm lens on a Canon 7D, set to an aperture of f/5.6, focused at 20 ft., will have a DOF of about 11 ft. (15’11” on the near end, 27’0” at the far end). At f/22, the near point is at 9’9”, and the far point is at infinity.

• At the same distance, wider focal lengths give more DOF than do longer focal lengths, EEBE (everything else being equal).

So a 200mm lens on a Canon 7d, set to an aperture of f/5.6, focused at 20 ft., will had a DOF of about 8” (compared to 11 ft with with 50mm lens set to the same aperture and distance).

• At the same distance, with the same lens, and with the same aperture, larger sensors give more DOF than do smaller sensors EEBE.

So if we switched the Canon 7D (which has a sensor with a crop factor of 1.6x) and replace it with a Canon 5D MkII, which has a full-size sensor, the DOF is now almost 19 ft (near side at 14’2”, far side at 33’11&#8221 at 50mm, f/5.6 and 20ft. focusing distance.

In principle, the plane of focus is exceedingly thin if you have a sensor with infinite resolving power. But in the real world, film media and sensors have limitations, beyond which you just can’t get more detail. That limitation can be expressed as a “circle of confusion” Sensors with large sensing elements have relatively “large” circles of confusion, whereas sensors with very densely packed sensing elements have very small circles of confusion. And this means that something ahead or behind the point of exact focus, will still look in focus if the corresponding out-of-focus circle is less than what the sensor can resolve.

Now how to use this information?

Suppose you have a Canon 7D with a 18-55mm zoom lens. You have a scene where you want to capture the flowers at your feet at 6 feet, and you want the horizon to also be in focus. Let’s also say that you decide that the 55mm focal length give you the most pleasing framing. Running the little DOF calculator, you find out that the hyperfocal distance at f/32 is 16’6” and the near point is 8’7”. Not enough. But if you zoom out to 40mm, the hyperfocal distance at f/32 is 8’9”, and the near point is at 4’5”. Perfect! So you find something at 8’9” away from you, set your focus on that, lock the focus, then reframe your picture with the flowers in the foreground and the horizon in the back, and Voila! You got everything in focus that you wanted.

Now wasn’t that simple?

 

[RxForB3]

Gotcha. I was already understanding most of that, but hadn't looked into the circle-of-confusion. Mainly, though, I wasn't understanding how exactly to implement the hyperfocal distance. It's kind of like exposing to something other than your subject (sky for instance). Focus away from the subject, lock it, then recompose. Thanks!

 

[CMfromIL]

Here's my opinion, Having been a Photographer for over 40 years I do understand the triangle But everyone raved about the book so I bought it. I thought it was a pamphlet and a vehicle for him to show pictures of his hit wife and brag about it. But everyone loves the book so what do I know.

I had zero experience shooting with the exception to my fully automatic P-N-S camera, and I thought the book was pretty good. Gave me a much better understanding of the basics, and how the 3 pieces play together.

I wouldn't expect that someone with 40 years experience could really gain much insight from the book. No more than I could from reading a basic drivers ed book on how to drive a car, something that I've been doing now for 25 years.

It certainly didn't make me an 'expert', but it did make me think a lot more about the camera settings when I go out to take pictures. I think that's where the value is.

 

[Rephargotohp]

1st 3 words "Here's my opinion" doesn't have to be yours. Value is Value and it is different for everyone. I'm just jealous he has a Hot wife to shoot. I just took a Picture of a tree ...but it was perfectly exposed

 

[RxForB3]

He apparently does videos for adoramatv and I watched some of them. They were better than the book, I thought, but one thing was kind of funny. One video was of him taking pictures of his daughter on a pogo stick. A few videos later he was in London taking macros of garbage with his daughter just hanging out in the background watching him make the video. There were more comments about the "cute girl" in the background than about the video itself! One guy asked for her number. No one seemed to realize it was his daughter...or that she's probably 14 or 15...or maybe they did...

 

[Helen B]

I had a look through Understanding Exposure. I wasn't all that impressed with it, even as a beginner's book, and it does have some bad information in it.

The reason he suggests metering the blue sky is that in essence you are turning your Camare's Reflective meter into a Incident meter and metering the light that lights the scene (skylight) instead of what is reflected off your subject

I suggest that you think of it more as using a reference midtone, just as you would use your hand, or grass, or the pavement (sidewalk). The sky you should be using to measure isn't really the source.

And if you do focus at something 2' away without a distance scale on the lens, remember that it is from the Sensor plane not the front of the lens

Be careful with that one. If you are using a DoF calculator you may find that they use the distance from the lens (strictly speaking the distance from the front or first nodal point of the lens) because that is what is calculated by the usual DoF formulae. This will only matter close up, of course. To give an accurate distance to the image plane you would need to know the lens' "nodal space", and that varies from one lens to another.

 

[EIngerson]

I see a bunch of people saying the guys methods might be in question. Is there comments on his results? I like the images he takes. If he's getting results like that, how can his methods be wrong?

 

[Helen B]

I think that most of the methods he uses are sound - he doesn't propose anything unusual or new or radical - it's all commonly used technique that has been taught for a very long time. What I found lacking were his explanations, some of which were quite misleading. That may not matter to someone who doesn't need to understand what they are doing. I know plenty of excellent photographers who don't understand why they do what they do, just as I know a guy who is an excellent mechanic that knows every nut, bolt, shim and gear in the overdrive of his Triumph TR2, but he has absolutely no idea how an overdrive works.

 

[EIngerson]

I think that most of the methods he uses are sound - he doesn't propose anything unusual or new or radical - it's all commonly used technique that has been taught for a very long time. What I found lacking were his explanations, some of which were quite misleading. That may not matter to someone who doesn't need to understand what they are doing. I know plenty of excellent photographers who don't understand why they do what they do, just as I know a guy who is an excellent mechanic that knows every nut, bolt, shim and gear in the overdrive of his Triumph TR2, but he has absolutely no idea how an overdrive works.

Fair enough. I'm one of the "don't know why" guys. As a self taught photographer (I use that loosely with all the internet help I get) It helped me put some things together. It also gave me a ton of ideas of things I need to look into. It holds true, the more you know, the more you don't know.