wide apertures/ whole figures in focus

[davidhampshire]

how can a lens,   such as the 77lmtd,   at f1.9 produce a whole figure ( model )  in focus,   ( some recent shots i saw viewing ppg )  and not just a model's nose or ear of something?      there are photos i've seen too with the 85mm 1.whatever it is that does the same thing,   at wide apertures,     i don't understand,  based on the depth of field scales and all of that.    when i shoot at wide apertures,  things are just in focus for a small band ( if i get the focus )    ?  dave

[spyglass]

Distance from camera plays a big part. Look at the following 4 situations. All 4 situations based on a 76mm focal length lens, an aperture setting of f1.8. In each situation the depth of field available for a possible subject increases. The difference between the 4 situations is camera to subject distance. As the subject is positioned farther away from the camera the possible depth of field (or band as you have called it) increases.

Situation 1) when the subject was 2ft away from the camera the available depth of field was 0.01 ft  (focus started at 1.99 ft and ended at 2.01 ft)

Situation 2) when the subject was 10ft away from the camera the available depth of field was 0.37 ft  (focus started at 9.82 ft and ended at 10.2 ft)

Situation 3) when the subject was 20ft away from the camera the available depth of field was 1.49 ft  (focus started at 19.3 ft and ended at 20.8 ft)

Situation 4 when the subject was 30ft away from the camera the available depth of field was 3.37 ft  (focus started at 28.4 ft and ended at 31.8 ft)


I have the Pentax 77mm ltd lens and use it for full length portrait work. Unless your subject is a midget, you have to have in excess of 15ft between your subject and the lens. So Situation 3 shows that it is physically possible to achieve a full length portrait shot and have the subject in focus from front to back (unless the subject is thicker than 1.49 ft)

Play around with the Online DOF Calculator l It is a good learning tool to explore and understand DOF, aperture, lens to subject relationships, etc.

I would like to point out that the goal in portraiture is not to use the largest aperture possible. Aperture is a control means that determine DOF and exposure. You can have a soft out of focus background  with a small aperture (this is generally preferred as it guarantees greater success of having the subject in focus). You simply position your subject farther away (in front of ) the background, and employ front focusing. (Front focusing is where you allow the majority of the available DOF to fall in front of the subject as opposed to equally balanced in front of and behind the subject. The only time you are stuck with having to select a large aperture is when physical conditions demand (like limited space, or low lighting conditions).


Spyglass

[davidhampshire]

oh wow,   thank you spy,   this is the most articulate explanation i could ever hope for;   very clear to understand,    it's perfect.     even to help me understand why i need to refer to the chart more,  as well,    thanks.
dave

[Ron Kruger]

That was pretty good, Spy. As far as apature for portraits are concerned, I think anything under 2.8 is problematic and much prefer to vary the distance and pattern of the background, plus lighting, to achieve good bokeh. It was the last thing I had in mind when I bought it, but my DFA 100mm Macro f-2.8 is the best portrait lens I have: good bokeh and great flesh tones.

[Frogfish]

Very nice explanation Spyglass.

Two possible nitpicks though, one is just a minor maths error, it's 0.2 ft for sample one. Also as a rough guide don't we as a general rule of thumb have 1/3 in front, and 2/3 behind, in focus and not 50/50 ?

[Mike Pearson]

Excellent explanation Spy 

Mike

[spyglass]

Two possible nitpicks though, one is just a minor maths error, it's 0.2 ft for sample one. Also as a rough guide don't we as a general rule of thumb have 1/3 in front, and 2/3 behind, in focus and not 50/50 ?

Thanks Frogfish for spotting and pointing out the error in example 1. This is an issue with the Online DOF Calculator and is probably related to a rounding error within the program.

In regards to a focusing "general rule of thumb" I would have to disagree (although everyone is entitles to have and adopt whatever general rules they feel work). I believe focusing is dependent on the photographic situation at hand. Front & Back focusing is an important technique. For instructional purposes it is best to show that there is a region before and after the point of focus, that this region (depth) can be increased and decreased based on aperture selection, and that distance is relevant. Armed with this understanding the user can slide the region in either direction (to the front or to the back) to include or exclude elements within a composition in terms of focus.

Unfortunately today the trend with images seems to be fixated on everything being razor sharp and maximum depth of field.  I blame an over reliance on automatic features. Autofocus and Automatic Exposure creates general average photos that play to common denominators. Selective focus is as powerful as a spotlight when wishing to bring attention to a subject within a composition.


Spyglass

[davidhampshire]

i go too with the idea that too much is autofocused,   and autoexposed,    i think it's why i like the manual lenses ( though i know i can manual focus with modern ones too )     but anyway,   it's enlightening to learn about the distance/  aperature/  in-focus area ,   thanks spy.   and the rest of you,   also,  thanks.
dave

[Pacerr]

. . . the user can slide the region in either direction (to the front or to the back) to include or exclude elements within a composition in terms of focus.

An often overlooked focusing tool is use of the 'stop-down/DoF feature' to assess the effect of aperture on DoF. I haven't totally lost this habit, and still use it frequently when manually focusing, but the combination of smaller view finders and AF lenses seems to make it less attractive or disciplined today.

To really appreciate the usefulness of this feature one almost has to experience the view through an LX or MX body with a bright  F1.4 or 1.7 lens attached.

I'm not convinced I actually see all that much through the DSLR view finders compared to the better FF film bodies, but the habit at least makes me aware of the need to consider the effect of aperture on DoF as I shoot.

I also have a habit of occasionally running 'DoF drills' using the on-line programs or charts I've built for my various lenses. This often happens when someone poses one of those "not sharp, DoF" question on-line and I cross-check the tables to see just how realistic their expectations are. I also sort of force myself to 'pre-flight' most close-up/macro setups.

H2

[davidhampshire]

i've tried that depth of field preview on the k-5,   pacerr,   by pushing the lever around the shutter button all the way over,  but never really could tell much from it;     it would be nice if the viewfinders were bigger and easier for manual focusing as on the film cameras,    are the medium format digital camera viewfinders better?     wonder if the prices of those will ever come down to something even almost, as a dslr price.     thanks