[zx-m]

I noticed that the "8" on my S-M-C 35/3.5's aperture ring is orange (the other numbers are the usual white). I know that every lens has its optimum aperture, which is usually somewhere between f/5.6 and f/11. Thus, does the orange "8" indicate that the manufacturer considered f/8 to be the peak of performance for this lens?

Thanks,
Glen

---

Last edited by zx-m; 06-02-2008 at 08:37 AM.

[Zewrak]

I noticed that the "8" on my S-M-C 35/3.5's aperture ring is orange (the other numbers are the usual white). I know that every lens has its optimun aperture, which is usually somewhere between f/5.6 and f/11. Thus, does the orange "8" indicate that the manufacturer considered f/8 to be the peak of performance for this lens?

Thanks,
Glen

You can read more about it Hyperfocal Distance under the topic "Focusing on the Hyperfocal Distance".

[ChrisPlatt]

It's for setting hyperfocal distance. For complete instructions
go to pentaximaging.com and download the "SMC Lenses" .pdf file:

http://www.pentaximaging.com/files/manual/SMCLenses.pdf

See figure 11, on page number 17 (16 according to my Acrobat reader).

Chris

[PFH]

I have the same markings on my 28/3,5. On my lens it means that if you line up the 8 with the orange marking on the distance scale and the arrow, the lens is sharp from 5 ft to infinity. It was very usefull for snapshots.

[zx-m]

Thanks...in my case, is the hyperfocal good for only f/8, or would it be f/8 and beyond?

Glen

[ChrisPlatt]

Yes, smaller apertures will be fine. Or just use the DOF scale on the lens.

Chris

[jslifoaw]

For DSLRs, you may want to stop down more since the enlargement is typically greater. So for the snapshot mode, I would suggest F/11.

[zx-m]

I do not have a DSLR, but thanks, Jeremy.

Glen

[mk07138]

Just to chime in, but I believe that the orange markings also have something to do with shooting IR. Since the IR filter blocks most of the visible light its hard to focus and I believe that the orange markings make that easier, but I could very well be wrong. Seem to recall that from somewhere though.

[ChrisPlatt]

the orange markings also have something to do with shooting IR.

The red line in the DOF scale is the infra-red focusing mark.
The red aperture number on Pentax WA lenses is for hyperfocal distance.

Chris

[deudeu]

Thanks guys, I think that I am starting to understand this hyperfocal business.

Just one important question: Does the fact that we are using a small sensor have any impact on the hyperfocal distance?
I don't understand everything about optics but I am guessing that it shouldn't have any consequence, since the DOF depends on the lens and aperture. For instance, my 28mm has a greater DOF on my small sensor than a 42mm would have on a FF (at a given aperture of course), right? If I am wrong and someone can explain to me why, I would be very grateful.

And one not as important question:
Is Hyperfocal mode what is used for disposable cameras and all of those old film P&S? I think i remember some of them said autofocus on them, but i don't remember ever hearing any noise or anything that hinted that something was going on with the lens.

[Canada_Rockies]

Thanks guys, I think that I am starting to understand this hyperfocal business.

Just one important question: Does the fact that we are using a small sensor have any impact on the hyperfocal distance?

I don't understand everything about optics but I am guessing that it shouldn't have any consequence, since the DOF depends on the lens and aperture. For instance, my 28mm has a greater DOF on my small sensor than a 42mm would have on a FF (at a given aperture of course), right? If I am wrong and someone can explain to me why, I would be very grateful.

Yes, there is a difference caused by the sensor size. Hyperfocal distance assumes a certain circle of confusion ( the size of the blur from a single point object ), and that depends on the enlargement ratio. For the M lenses, the circle of confusion was based on an 8x10 inch print viewed from a normal viewing distance (10 inches??), as were all the hyperfocal calculations in those days. With the smaller sensor size, for the same subject size, you need to enlarge your image 1.5x as much: 12x15 inches. So the circle of confusion on the sensor is exactly the same, but when you enlarge the image for viewing and/or printing, the circle of confusion will be half again as large.

And one not as important question:
Is Hyperfocal mode what is used for disposable cameras and all of those old film P&S? I think i remember some of them said autofocus on them, but i don't remember ever hearing any noise or anything that hinted that something was going on with the lens.

The disposables depend on the hyperfocal distance, as the lens is fixed focus. It should be noted that disposable cameras are designed for the casual user, and enlargements beyond 4x6 inches are not often requested by the usual users of these cameras.

[deudeu]

Yes, there is a difference caused by the sensor size. Hyperfocal distance assumes a certain circle of confusion ( the size of the blur from a single point object ), and that depends on the enlargement ratio. For the M lenses, the circle of confusion was based on an 8x10 inch print viewed from a normal viewing distance (10 inches??), as were all the hyperfocal calculations in those days. With the smaller sensor size, for the same subject size, you need to enlarge your image 1.5x as much: 12x15 inches. So the circle of confusion on the sensor is exactly the same, but when you enlarge the image for viewing and/or printing, the circle of confusion will be half again as large.

So that means that to be on hyperfocal with my small sensor i need to actually focus a little bit further that what's written on the hyperfocal chart on my lens?
For exemple, the chart on the lens says that to get hyperfocal at f.8 you need to focus at 10 feet. On a small sensor i would actually need to focus at 15 feet?

[Canada_Rockies]

So that means that to be on hyperfocal with my small sensor i need to actually focus a little bit further that what's written on the hyperfocal chart on my lens?
For exemple, the chart on the lens says that to get hyperfocal at f.8 you need to focus at 10 feet. On a small sensor i would actually need to focus at 15 feet?

My personal choice would be to leave the lens at the hyperfocal markings, but to stop down one additional stop, to f/11. This will increase the depth of field, and then you should be able to enlarge the image more before the circle of confusion "destroys" your print.

I caution that stopping down further runs the risk of degrading the image with diffraction as the aperture gets so small that the diffraction of the light on the aperture edge becomes more and more prominent compared to the correctly focused image.

[deudeu]

Thank You very much Canada_Rockie!

I will go experiment with this as soon as possible. Hopefully f11 won't be too slow for my intended purpose: people.