Focusing issue

[rpcrowe]

I always use a lens hood, whether shooting indoors or outside. A correct hood, not only blocks stray light from impacting the contrast of a shot but, it also acts as an insurance policy against physical damage to the lens.

I generally purchase third party lens hoods for lenses which are not equipped with hoods by their manufacturer. The third party hoods serve the dual purpose (shade and physical protection) as OEM hoods but, cost a fraction of what you might pay for a hood supplied by Canon...

Here is an example of a generic hood for the 18-135mm Canon lens...

http://www.ebay.com/itm/EW-73B-Lens-...EAAOxyY3ZRzQff

This hood is shipped from China; you should be able to get it for the same price shipped to India...

[William W]

I agree this is NOT an issue with incorrect or inadequate Auto Focus

*

After forensic examination I conclude that there is not just one issue.

1. Depth of Field:

I agree with George and others that this is an issue, further I’ll add:

Technical evidence -

> If that is the Full Frame Crop and the man is about 1.7m tall, then the Camera is situated about 1.5m from him.

> at F/5.6 and 18mm for an APS-C Format the DoF is about 1.4m

> considering the angle of the GROUP of Subject relative to the lens’s axis, the DEPTH of the Group of Subjects easily exceeds 1.4m

> DoF issues are visually evidenced by the man’s shirt being less sharp than the RH (red) sleeve on the woman’s dress at camera left.

Conclusion (as others have stated) it matters not which point attained Auto Focus on any Subject within that group, there is simply not enough DoF to render the whole group as “tack sharp”

*

2. Flare:

I agree with Richard’s analysis and rationale and also Ted’s comments.

No need to expand on those two comprehensive replies - but to add two points to Ted's comment about Veiling Flare (which is abundant in the image):

a) Veiling Flare will be exacerbated if there was a FILTER on the lens. Mentioned because there appears to be a GHOST IMAGE on the man which is another indication of a Filter on the lens

b) Veiling Flare is typically worse in Zoom Lens and when used at the Wide Angle. Mentioned because a zoom lens was used

c) Note Richard's comment above regarding using a LENS HOOD - doing so will lessen the likelihood of Veiling Flare

*

3. Under-exposure – (attempted to be corrected in Post Production):

Per the same rationale as localized flare, underexposure can render the appearance of “un sharp” because underexposure can result in the lack of shadow detail; lack of mid tone contrast; and lack of acutance.

It appears the shot was made indoor at night time under ambient room light - ceiling mounted light with a yellow/green cast.

As an example: A room 4m x 3m and average ceiling height, with two 40 watt fluorescent tubes mounted on the ceiling, will render a scene that requires an exposure (approximately): F/5.6 @ 1/13s @ ISO1000.

The shot was pulled at F/5.6 @ 1/200s @ ISO1000 – so on any account of what the room lighting actually was - we can reasonably assume that the shot is somewhere between 1Stop and 4 Stops underexposed. (Maybe more).

One sample of the visual evidence of underexposure is in the area of (what should be shadow) in the eaves outside the window: that area presents with excessive noise and such is indicative of overenthusiastic “exposure gain” made in post production.

*

4. Subject Movement:

The FACE is usually the first area and the dominate area of the Subject which attracts the Viewer’s Eye. If the face exhibits Subject Movement then the Viewer’s Eye (often) interprets the (whole) image as “soft”.

There Head of the Woman (Camera Left) appears to be moving backwards, from the camera.

The Head (and shoulders) of the Man appears to be moving forwards, toward the camera.

Both movements are evidenced by edge blur seen on areas of the face which are not congruent to blur seen at other areas of the person which appear in the same Plane.

*

5. Lack of / or inappropriate Sharpening in Post Production:

Just a guess – the emphasis in Post Production was on getting a suitable exposure and not sharpening.

WW

[rpcrowe]

This just brought back a memory of my early digital days when I switched from a 28-135mm f/3.5-5.6 IS lens to a 24-70mm f/2.8L as my go-to mid range zoom.

The 28-135mm was an adequate lens but required a lot more PP work in sharpening and contrast correction than the 24-70L. I would venture a guess that the 18-135mm would also need additional PP along those lines.

[Shanghai Steve]

Hi there
You've been given lots of correct technical advice (of varying relevance) but one vital piece of advice I don't think you have been given is....people can be asked to move. The shot you posted is admittedly less than perfect. This is due to several factors, almost all of which are human. In future, place your subjects correctly, in one focal plane, in the best light possible. Feel free to move them around, change the environment, get some children to hold up white T-shirts as reflectors or whatever...make a game out of it. Also, using the wide end of a zoom might give you greater depth of field but is often optically inferior. There is a classic quote "If your pictures aren't any good, get closer." In this situation, perhaps a torso shot might have been better, with the plate of food held up.
Above all, keep experimenting and have fun.

[William W]

. . . Also, using the wide end of a zoom might give you greater depth of field but is often optically inferior. . .

For clarity about the relationship between Depth of Field and Focal Length:

If the FRAMING of the shot is the same, using a Wide Angle Lens does NOT provide a greater Depth of Field.

If the FRAMING of the shot is the same, then the DoF is the same no matter what Focal Length Lens is used - provided that the Aperture and the Camera Format also remains the same.

WW

[george013]

For clarity about the relationship between Depth of Field and Focal Length:

If the FRAMING of the shot is the same, using a Wide Angle Lens does NOT provide a greater Depth of Field.

If the FRAMING of the shot is the same, then the DoF is the same no matter what Focal Length Lens is used - provided that the Aperture and the Camera Format also remains the same.

WW

I've a bit trouble to understand that.
1.
What is the framing. Let's say I've a doorpost with a ratio of 2:3. I can cover my sensor with an image of that door and call it my frame. Now I double the distance to the door. Than I need a focal length of 1/2 the first (I think). In this example a subject on 10m and an focal length of 50mm. That will become 20m and 100mm ( I still assume, not being sure).

2.
The dof stays the same. What's meant with that? The beginning of the dof, the end of the dof or the traject of the dof. In the calculator called near limit, far limit and total.

3.
Using the dof-calculator.
Distance 10m, focal length 50mm, f8: dof near 6.23 far 25.3 total 19.01 in front 20% behind 80%
Distance 20m, focal length 100mm, f8: dof near 15.4 far 28.7 total 13.3 in front 35% behind 65%

Where is the fault?

George

[xpatUSA]

I've a bit trouble to understand that.
1.
What is the framing?

It is the same as magnification I think. That is to say, if something fills the frame with a 50mm lens then you put 100mm and walk back until the something again fills the frame the magnification is the same and can be called "equal framing" (for normal distances).

The dof stays the same. What's meant with that? The beginning of the dof, the end of the dof or the traject of the dof. In the calculator called near limit, far limit and total.

Yep, go here https://www.cambridgeincolour.com/tu...h-of-field.htm and read under the heading "CLARIFICATION: FOCAL LENGTH AND DEPTH OF FIELD".

DOF is normally expressed as the total (far - near).

3. Using the dof-calculator.
Distance 10m, focal length 50mm, f8: dof near 6.23 far 25.3 total 19.01 in front 20% behind 80%
Distance 20m, focal length 100mm, f8: dof near 15.4 far 28.7 total 13.3 in front 35% behind 65%

Where is the fault?

George

My spreadsheet gives different values too, but I'm sure Bill will explain.

[george013]

I've a bit trouble to understand that.
1.
What is the framing. Let's say I've a doorpost with a ratio of 2:3. I can cover my sensor with an image of that door and call it my frame. Now I double the distance to the door. Than I need a focal length of 1/2 the first (I think). In this example a subject on 10m and an focal length of 50mm. That will become 20m and 100mm ( I still assume, not being sure).



George

That's wrong off course. The angle of view is getting smaller, so the focal length bigger. As in the example.

Ted,
The camera I used in the calculator was a Canon 7D. It was there so I left it there.

George

[Mike Buckley]

I don't understand the causes, but based on experience I would expect the longer focal length at twice the distance as in the above example to produce a narrower depth of field than the shorter focal length. So, the data in that example is no surprise to me.

[xpatUSA]

I've a bit trouble to understand that.

<>

3.
Using the dof-calculator.
Distance 10m, focal length 50mm, f8: dof near 6.23 far 25.3 total 19.01 in front 20% behind 80%
Distance 20m, focal length 100mm, f8: dof near 15.4 far 28.7 total 13.3 in front 35% behind 65%

My own spreadsheet allows me to enter magnification, so I entered 1:200 at f/8 and did the DOF calc (based on my monitor dot pitch & viewing distance, not the standard print):

f-length, distance and total DOF came to:

50mm, 10.05m, 57m
100mm, 20.1m, 114m

Something seems to be amiss somewhere . . .

[William W]

My post #25 was brief; simplistic; and specific to both the remark I quoted and also the sample image of the three people.

The CiC Tutorial, to which Ted linked in Post #27 also is correct in substance, but also is not fully detailed.

Note in that CiC Tutorial the qualifier "virtually" is used viz:

"If the subject occupies the same fraction of the image (constant magnification) for both a telephoto and a wide angle lens, the total depth of field is virtually* constant with focal length" (op cit)

***

What this is all about is the Axiom of Depth of Field and it is a useful Axiom to apply for Portraiture and General Photography when we are using "typical" or "common" Shooting Distances.

Without the mathematics, the basic principles of the Axiom are:

If the FRAMING, APERTURE and CAMERA FORMAT remain the same the DoF will be constant irrespective of Focal Length used.

The Axiom begins to fail as the SUBJECT DISTANCE approaches the HYPERFOCAL DISTANCE

The Axiom begins to fail as the FOCAL LENGTH approaches ULTRA WIDE ANGLE

The Axiom begins to fail as the SUBJECT DISTANCE becomes VERY SHORT, (esp. for WA lenses which have short Min. Focus. Distance)

The axiom begins to fail for some "Close-Up" Photography

##The Axiom is predicated on a particular derivations of DoF formulae and those formulae do not deal with MACRO PHOTOGRAPHY (life-size and greater) and for this reason the Axiom does not concern Macro Photography. (However please see post #36 which explains that DoF does remain constant if the MAGNIFICATION is constant during Macro Photography, irrespective of Focal Length.

***

There are quite a few previous conversations here at CiC about this topic, Grahame (Stagecoach) started one based my DoF Cheat Cards for use with a 135 Format Camera:





(Note the recurring number patterns - very easy to learn by rote)

***

DoF is not "exact", although we use mathematics to find the DoF it is still only a guide and the Axiom (and my mention of it here) is not about starting a conversation concerning which precise CoC to use or the History of a 10" x 8" print viewed at arm's distance or the resolving power of the average human eye.

In the DoF sheets above, the DoF figures are rounded to the conservative - they are for practical use "in the field".

The point is, mostly all Photography can be put into three broad categories:

1. Macro and Close-Up (at really small Subject Distances)
2. Landscapes (at really big Subject Distances)
3. All the other stuff - e.g. Portraiture and all pictures of other living things and inanimate objects (at "typical" or "common" Subject Distances)

Box 3 is very big and the Axiom can be very useful when making all those pictures.


***

BTW there is also a Rule of Thumb for the RATIO of "In Front of" and "Behind" the Plane of Sharp Focus.

I note this topic has been mentioned in this thread and also in a recent other thread where a Kodak Handbook was mentioned.

Not sure what Kodak book it was, I have many.

It is a good idea to ONLY apply the "one third in front and two thirds behind" for FULL LENGTH PORTRAITS and similar, at "common" Subject Distances.

For example it is a good rule for a Full Length Group Portrait of twenty people set in three rows with the front row sitting on the ground, second row on seats third row standing - focus on the heads of the front row and it is reasonable to expect that the feet of the front row will be OK in focus and the heads of the back row will be OK in focus too: assuming a suitable Aperture is used.

Similarly, Full Length Shot of two people standing close to each other and one behind the other - focus on the ear/eye of the front person, etc: again assuming a suitable Aperture is used.

Some of the Kodak Handbooks that I have, use those two example pictures for the "one third / two third" rule of thumb.

***

A practical general twofold rule of thumb for the ratio of "in front of" and "behind" is:

As the FRAMING becomes a TIGHTER - then the ratio becomes closer to half / half.

As the FOCAL LENGTH gets LONGER the ratio becomes closer to half / half.


WW

Footnote: Para ## has been edited - please see reasons for editing below

[William W]

What is the framing.

FRAMING is the IMAGE as it is “framed” in the VIEWFINDER or on the GROUND GLASS SCREEN

For the purpose of this discussion if we want to keep the same FRAMING, then when you use your DoF Calculator this would mean you need to maintain the same FIELD OF VIEW dimensions.

*

The dof stays the same. What's meant with that? The beginning of the dof, the end of the dof or the traject of the dof. In the calculator called near limit, far limit and total.

The Depth of Field is a linear measurement from the near point to the far point, in your words “the total”

*

Using the dof-calculator.
Distance 10m, focal length 50mm, f8: dof near 6.23 far 25.3 total 19.01 in front 20% behind 80%
Distance 20m, focal length 100mm, f8: dof near 15.4 far 28.7 total 13.3 in front 35% behind 65%

For those calculations you have used approximate 0.019mm for the Circle of Confusion. I assume that is your preference (or the default of the calculator that you use) for an APS-C Format Camera.

BTW I would generally use, and recommend to use, 0.016mm for an APS-C Format Camera: as I mentioned earlier, I tend to be ere on the conservative side, when calculating DoF.

*

Where is the fault?

Your calculation used a 50mm lens on an APS-C applied a Circle of Confusion at 0.019mm and then set SUBJECT DISTANCE = 10m

At F/8, using a CoC at 0.019mm, for a 50mm, the HYPERFOCAL DISTANCE is 16.4m

The “fault” is simply the Axiom is beginning to fail because the Subject Distance is approaching the Hyperfocal Distance.

WW

[William W]

Working example – consider this image made at a “typical” or “common” Subject Distance:



Let’s assume it was made with a 135 Format Camera using a 135mm lens (it was)
Let’s assume F/2 Aperture (it was)
Let’s assume Subject Distance is 6.8m (it was about that - I did not crop much)
Let’s set Circle of Confusion equal to 0.025mm (that’s what I typically use)
The calculator concludes DoF = 0.249m

*

Change lenses to 100mm
For same FRAMING the Subject Distance is now 5.04m
The calculator concludes DoF = 0.249m

*

Let’s change lenses to 50mm
For same FRAMING the Subject Distance is now 2.52m
The calculator concludes DoF = 0.25m

*

Let’s change lenses to 200mm
For same FRAMING the Subject Distance is now 10.07
The calculator concludes DoF = 0.249m

***

Assessing how the Axiom begins to fail from another point of view -

If we stop down to F/5.6 but keep all other parameters the same, there is a minor variance in the DoF between FL = 50mm and FL =200mm.

There is a little bit more variance if we stop down to F/8 . . . etc

Because as we decease the aperture - the SUBJECT DISTANCE will begin to approach to the HYPERFOCAL DISTANCE.

WW

[Shanghai Steve]

This is all very interesting but perhaps not particularly relevant? People use different focal lengths differently.

[dem]

Thank you Bill for the detailed explanation. One thing that I am slightly puzzled about is your comment about DOF axiom not holding for macro.

The focus distance in macro is always much shorter than the hyperfocal distance, so the DOF axiom should work. Right?

If I calculate DOF for a full frame camera at f/16, I got the same value of 5 mm for any of these combinations of a focal length and a focus distance:

35 mm - 10 cm
70 mm - 20 cm
140 mm - 40 cm
280 mm - 80 cm

They all give the same framing and 5 mm for DOF.

Can we count macro in?

[William W]

. . . One thing that I am slightly puzzled about is your comment about DOF axiom not holding for macro.. . .
Can we count macro in?

Hi Dem,

You are correct.

For Macro Photography, it doesn't matter (for example) if a 50mm macro lens or a 200mm macro lens is used for (example) a 1:1 shot - in both cases the Depth of Field is exactly the same, provided that the MAGNIFICATION; APERTURE and CAMERA FORMAT remain constant.

Also, for the SAME MAGNIFICATION the DoF extends equally in front of and behind the Plane of Sharp Focus.

As the magnification reduces, for example to 1:10, the Depth of Field using either Lens stays constant but the DoF is not equally distributed in front of and behind the plane of focus.

***

The reason for my error (which I have now corrected) -

There are several formulae which can be used to calculate DoF.

One of those Formula easily/simply shows how the Focal Length of the Lens is irrelevant to the DoF for "Typical Subject Distances".

In part of my responses above, I cut and pasted sections from my teaching notes, which are more detailed and have many various formulae for DoF.

What got lost in that translation and confused my haste was that the FORMULA for DoF for 'Normal Photography' - the Formula that I use to show how the Focal Length doesn't matter - is not suitable to use for Macro Photography.

The other message in my teaching notes is to: be aware that some of the general DoF calculators available "on line" are NOT suitable for Macro DoF Calculations.

Thanks for picking the error up and alerting me to it, sorry for any inconvenience caused.

WW

[William W]

This is all very interesting but perhaps not particularly relevant? People use different focal lengths differently.

People use information differently, too.

The way different people use information can be one way of measuring "relevance" of that information to those different people.

One great attributes of CiC, which is extolled by many CiC Members, is the breadth and diversity of the conversations in which we all partake as: readers; contributors; or both.

Another (of the many) virtues here at CiC is the relative lack of negative and barbed comments: most commentary here tends to forward the conversation - not simply criticize it.

WW

[george013]

Hi Dem,

You are correct.

For Macro Photography, it doesn't matter (for example) if a 50mm macro lens or a 200mm macro lens is used for (example) a 1:1 shot - in both cases the Depth of Field is exactly the same, provided that the MAGNIFICATION; APERTURE and CAMERA FORMAT remain constant.

Also, for the SAME MAGNIFICATION the DoF extends equally in front of and behind the Plane of Sharp Focus.

As the magnification reduces, for example to 1:10, the Depth of Field using either Lens stays constant but the DoF is not equally distributed in front of and behind the plane of focus.

***

The reason for my error (which I have now corrected) -

There are several formulae which can be used to calculate DoF.

One of those Formula easily/simply shows how the Focal Length of the Lens is irrelevant to the DoF for "Typical Subject Distances".

In part of my responses above, I cut and pasted sections from my teaching notes, which are more detailed and have many various formulae for DoF.

What got lost in that translation and confused my haste was that the FORMULA for DoF for 'Normal Photography' - the Formula that I use to show how the Focal Length doesn't matter - is not suitable to use for Macro Photography.

The other message in my teaching notes is to: be aware that some of the general DoF calculators available "on line" are NOT suitable for Macro DoF Calculations.

Thanks for picking the error up and alerting me to it, sorry for any inconvenience caused.

WW

The dof calculator doesn't work for macro. The dof calculator works with the assumption that the focal length and the image distance, distance between sensor and optical middle lens, is the same or nearly the same. When doing macro the difference is getting bigger. When doing a 1 to 1 macro the difference is 100%.

George

[Shanghai Steve]

Another (of the many) virtues here at CiC is the relative lack of negative and barbed comments: most commentary here tends to forward the conversation - not simply criticize it.

WW

It seems you've got your nose put out of joint, which is...sigh-inducing. I am also surprised that you are surprised that at some point in your impromptu tutorial, someone pointed out that your plethora of facts don't in fact, make much difference.
Or have I stumbled into the internet equivalent of a closed shop?

[xpatUSA]

It seems you've got your nose put out of joint, which is...sigh-inducing. I am also surprised that you are surprised that at some point in your impromptu tutorial, someone pointed out that your plethora of facts don't in fact, make much difference.
Or have I stumbled into the internet equivalent of a closed shop?

Bill has a certain literary style but does know his stuff, IMHO.