[Selenium_27]

Was there the hen or the egg first ?
I don't know but I've got another metaphysical question..

Why is there a red 8 on the pentax wide angle lenses (K,M,A,F) ranging from 16 to 35 ?

Example below with the 28/3.5 :

There is also a red number in the distance scale which the hyperfocale at f8.
But why f8, why not f11 ?
Is there a reason behind ?
(best sharpness at 8 for all the range ?)

[Adam]

I'm not 100% sure, but I think it might have something to do with the IR markings (notice the orange line on the distance scale). Also, I believe that F8 was used for standard exposure calculations back in the old days, but I could be wrong. In any case, it was definitely a popular setting!

[littledrawe]

Isn't there an entire subculture devoted to "f8 and be there" perhaps Pentax was a booster for the club or something?? The Masons could be involved as well since looking at the 8 sideways it is an infinity symbol. . . . . . .

[johnyates]

F8 is generally the sharpest aperture on WA lenses.
When you line up the red aperture and distance you have set the hyperfocal distance. IOW everything from half the (focus scale) indicated distance to infinity will appear to be in focus.
On the pictured lens, with all the reds lined up, everything from 5ft to infinity will appear to be in focus due to depth of field. Note--this is for FF cameras, on a crop camera YMMV.

[goubejp]

Not at all, the red marks where to help (in the past there was no autofocus) adjusting lens on the hyperfocal distance; you have to align the red figure (f8 here) with the red mark on the barrel and the red mark on the distance scale (3 meters here); when all these marks are aligned, the depth of field of the lens goes from infinity to some distance varying with the focal lens; this works only with wide angles (so the reason that these marks do not appear beyond 35 mm). That allowed to shoot without adujsting the focus.
Regards

[monochrome]

I asked my daughter the question. She says (she recalls she was taught in college) Pentax believed at f/8 most outdoor daylight shots would meter above 1/30, therefore were hand-holdable. The objective for amateur photographers upgrading from a fixed-focus rangefinder during the Spotmatic era was to handhold without attending to focusing. Pentax marketed to enthusiast amateurs - so they made some simple guides. The markings carried over to the WA K-mounts.

Canon lenses had a more complex color-coding to indicate hyperfocal distance at various apertures.

Here's a good article on Hyperfocal distance - and a ton of other stuff linked as well.

[civiletti]

Also, I believe that F8 was used for standard exposure calculations back in the old days, but I could be wrong. In any case, it was definitely a popular setting!

It still is.

[John Poirier]

Coincidentally, I was looking at a Spotmatic II manual just a couple of days ago. Pentax used the term "Fixed Focus Setting", with the followining explanation:

"Because of the considerable depth of field of wide-angle lenses, you can use them as fixed focus lens if the diaphragm and distance scanes are set properly."

My guess is that this was aimed, as others have said, at newbies.

I do use the DOF scales on wide angles a lot for pre-focusing purposes, but tend to use f/11 while being a bit more conservative about acceptable DOF than the scales are.

John

[pete-tarmigan]

The manual that came with my SMC-M 28mm f2.8 said specifically that the 8 was red to indicate that f8 was the hyperfocal distance. I don't know if I still have the manual.

[joe.penn]

I'm an F8'errrrrrrrrrr

[Kerrowdown]

Not at all, the red marks where to help (in the past there was no autofocus) adjusting lens on the hyperfocal distance; you have to align the red figure (f8 here) with the red mark on the barrel and the red mark on the distance scale (3 meters here); when all these marks are aligned, the depth of field of the lens goes from infinity to some distance varying with the focal lens; this works only with wide angles (so the reason that these marks do not appear beyond 35 mm). That allowed to shoot without adujsting the focus.
Regards

It's what he said, I remembered this from the old days.

[Selenium_27]

Thanks a lot for your answers..

[Odinz]

Here is a copy of the page from the manual that came with the K series lenses explaining the 'Fixed Focus Marks'

[stevebrot]

F8 is generally the sharpest aperture on WA lenses.
When you line up the red aperture and distance you have set the hyperfocal distance. IOW everything from half the (focus scale) indicated distance to infinity will appear to be in focus.
On the pictured lens, with all the reds lined up, everything from 5ft to infinity will appear to be in focus due to depth of field. Note--this is for FF cameras, on a crop camera YMMV.

This is a common feature on 35mm and wider lenses, including the lens on my Olympus XA.


Steve

[OutOfFocus]

I was taught to just line up the infinity distance mark with the line corresponding to the selected aperture. The other line would tell you the closest distance that would be in focus.

Seems very simple to me and works for any aperture.