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Esteemed Contributor
Posts: 3,816
Registered: ‎06-11-2013

Re: DSLR 101 3.0


@ebiggs1 wrote:

"... depending on depth of field, a range of distances will be in acceptable focus."

 

This called the hyperfocal distance. It is the closest distance at which a lens can be focused while keeping objects at infinity acceptably sharp. When the lens is focused at this distance, all objects at distances from half of the hyperfocal distance out to infinity will be acceptably sharp.


A "range of distance" for accpetable focus is just "depth of field".  "Hyperfocal distance" is a slightly different concept.  

 

For any given lens focal length and aperture value, there is a focus distance which will maximize the depth of field.  That magic value which maximizes depth of field (just for that specific focal length and aperture value) is the "hyperfocal distance".  Any other value may achieve a very broad depth of field, though not necessarily the most broad depth of field possible.

 

Every lens focal length, focused distance, and aperture value combination has a "depth of field" -- but it's not necessarily the "hyperfocal distance".

 

A new photographer might think that to maximize depth of field they could just focus the lens to infinity and use a high aperture value, like this:

 

Infinity.jpg

 

The above camera lens is set to f/22 (which should generate a broad depth of field) and it is focused to "infinity".  If you look at the blue boxed area that I've annotated, this shows the range of distances at which your subjects should be in acceptable focus.  It looks like everything from about 12' to "infinity" will be in focus.  

 

The problem with this is that it wastes some depth of field.  Because the lens is "also" focusing a range of distances which are "beyond infinity" and since nothing can be "beyond infinity" we really just lose the benefit of that range.

 

So to achieve a true "hyperfocal" distance, we can change our focus distance like this:

 

Hyper-Focal.jpg

 

In this example, since I'm using f/22, I move the "infinity" mark on the focus ring to the "f/22" mark on the back-side of the depth of field.  Everything between the two f/22 marks on the depth of field scale should be in acceptable focus.  Notice my blue box is much bigger and now everything from about 6' to infinity is in acceptable focus. This change has gained about 6' in the near-foreground area which will now also be in acceptable focus.

 

This concept (the second shot) is the magic "hyperfocal distance" for this 50mm lens at f/22.  There is no other focus distance which can achieve a broader depth of field than this one.

 

DoF marks are still found on many prime lenses, but not so much on zoom lenses... because the DoF depends on the focal length.  Once upon a time, most zoom lenses used a "push/pull" to slide the lens longer or shorter.  Today most lenses have a zoom ring that rotates (no longer a push/pull -- though there are still some push/pull lenses around.)    Push/pull lenses had a sweeping set of arcs to draw the DoF marks -- but it's not possible to do this with zooms that have a rotating ring (which is most modern zooms.)

 

With zoom lenses today, best to look up the depth of field on a table.  If you have a smartphone there are a number of apps you can use.  You can also make printed tables.  

 

To learn about DoF in the beginning, it might require that you consult the tables (or apps) often, but I find that with enough photography you eventually get a feel for how much depth of field you get in a situation.  As you compose favorites types of subjects using favorite lenses and similar compositions and distances, you find the settings that work -- and arrive at the point where you can take a shot, dialing in the correct settings without even really thinking too much about it (because you've done so much shooting.)

 

Tim Campbell
5D III, 5D IV, 60Da
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Posts: 11,664
Registered: ‎12-07-2012

Re: DSLR 101 3.0

Exactly. I knew you could say it better than me.

However, the COC does depend on the sensor and its MP.  Even how the print or what ever is displayed or viewed.  And, yes, Bob from Boston, all these are related.  You do not have one without the other.  COC usually menas, what the human eye can resolve and what is called the 'blur' factor.  No lens is perrfect at aiming all the light spectrum to a single  point.

EOS 1DX and 1D Mk IV and several lenses!
Esteemed Contributor
Posts: 3,816
Registered: ‎06-11-2013

Re: DSLR 101 3.0


@ebiggs1 wrote:

Exactly. I knew you could say it better than me.

However, the COC does depend on the sensor and its MP.  Even how the print or what ever is displayed or viewed.  And, yes, Bob from Boston, all these are related.  You do not have one without the other.  COC usually menas, what the human eye can resolve and what is called the 'blur' factor.  No lens is perrfect at aiming all the light spectrum to a single  point.


All true!  Cropping in is not much different than having shot with a longer focal length lens when the shot was taken and it actually effects DoF in the same way.  When you crop and in and enlarge an area, you make everything bigger -- including the blur -- and that reduces the DoF.

 

And "no lens" includes the human eye.  I watched an episode of "Brain Games" (on Netflix).  It's shocking how bad our eyes actually are.... and how much our brain compensates by assembling an image that our eyes don't actually see.

 

Tim Campbell
5D III, 5D IV, 60Da
Super Contributor
Posts: 487
Registered: ‎03-17-2015

Re: DSLR 101 3.0

 

This is a article, I think, is refuting DOF as I understand you guys are explaining it.  I'm not saying it is, I don't know...I'm learning.   Is he, "Ken", saying the same thing you guys are, or is his take a different spin on DOF???     Your feedback of what Ken says here would be very helpful..

 

 

 

 

 

http://www.kenrockwell.com/tech/focus.htm

VIP
Posts: 11,664
Registered: ‎12-07-2012

Re: DSLR 101 3.0

Rockwell is OK but he is loose with details and accuracy soemtimes.

EOS 1DX and 1D Mk IV and several lenses!
Super Contributor
Posts: 487
Registered: ‎03-17-2015

Re: DSLR 101 3.0

Thanks Obiwan, that's good info for me.  I did'nt know much about him and was reluctant to accept with he said on face value.  I do know ehough to not run with just anything I read online.

Esteemed Contributor
Posts: 3,816
Registered: ‎06-11-2013

Re: DSLR 101 3.0


@jazzman1 wrote:

 

This is a article, I think, is refuting DOF as I understand you guys are explaining it.  I'm not saying it is, I don't know...I'm learning.   Is he, "Ken", saying the same thing you guys are, or is his take a different spin on DOF???     Your feedback of what Ken says here would be very helpful..

 

 

 

 

 

http://www.kenrockwell.com/tech/focus.htm


Well... I made it all the way to the 2nd paragraph... and Ken is already wrong.  <sigh>

 

Ken is a bit of a hack.  He blogs to suppliment income and sometimes he says controversial or just out-right wrong stuff.  I suspect part of the time he does it because he doesn't know... and part of the time he does it because controversy drives traffic to his website.

 

My feedback on Ken is.... don't read Ken.

 

Tim Campbell
5D III, 5D IV, 60Da
Super Contributor
Posts: 487
Registered: ‎03-17-2015

Re: DSLR 101 3.0

[ Edited ]

@TCampbell wrote:

@jazzman1 wrote:

 

This is a article, I think, is refuting DOF as I understand you guys are explaining it.  I'm not saying it is, I don't know...I'm learning.   Is he, "Ken", saying the same thing you guys are, or is his take a different spin on DOF???     Your feedback of what Ken says here would be very helpful..

 

 

 

 

 

http://www.kenrockwell.com/tech/focus.htm


Well... I made it all the way to the 2nd paragraph... and Ken is already wrong.  <sigh>

 

Ken is a bit of a hack.  He blogs to suppliment income and sometimes he says controversial or just out-right wrong stuff.  I suspect part of the time he does it because he doesn't know... and part of the time he does it because controversy drives traffic to his website.

 

My feedback on Ken is.... don't read Ken.

 


LOL LOL LOL...coming from you and Biggs says alot.  I know all I need to know about his opinion.....Thanks much.

 

BTW...Since this topic is DSLR 103 3.0,      Everything you guys say here may be valuable, to not just me, but also other newbies who may look in.  Some of you peeps are amazing with the knowledge you have.  Won't mention any names, to protect the innocent, but a few of you guys are Human Photography Dictionaries.

Super Contributor
Posts: 487
Registered: ‎03-17-2015

Re: DSLR 101 3.0

Anyone know anything about a Photographer named "David Peterson".  I've been geting literature about photography courses he teaches online.  Any info would help.  

Super Contributor
Posts: 487
Registered: ‎03-17-2015

Re: DSLR 101 3.0

 I'm not sure which way the Canon 70-300mmL lens "Ring Mount" attaches to the lens the correct way.  I tried both ways with the foot  pointing backward toward the camera, and the opposite way, pointing out away from the camera.  Weight distrubution seemed best with the ring foot pointing forward away from the camera, but I want to make sure that's best way.  Which way is right, or is there a right and wrong way?   Their was no instructions in the box, and this is my 1st heavy L lens.

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