God! DOF Scale in my Lens DOES NOT Agreen with the Hyperfocal Formula!

I have a Zeiss Planar 1.4/50. When I focus on the infinity, the DOF
scale indicates the hyperfocal distance for F16 is about 3.3m. But
work from the formula, it follows that

h = f^2/(N*c) = 50^2/(16*0.025)

the above should be 6.25m.

It's a big difference with what on the sale. What's wrong? What about
your 50mm lens?

Thanks in advance.

-
narke

 

Hyperfocal distance is the point where the *farthest* reach of DOF is
infinity. In other words, HF falls somewhere (roughly one-third) of the
distance between the closest "acceptable focus" point, and infinity.

So, don't focus at infinity. Instead, focus where the outside of the
DOF scale touches infinity. Your focus (center) pointer at that time should
indicate HF distance, and of course the other side of the DOF scale
indicates a much closer distance.

There are other factors that may rear their ugly heads, as well. Not
all 50mm lenses are true 50mm focal lengths, and "acceptable focus" can be
a bit arbitrary.

All that said, the Zuiko 1.4 sitting on my desk seems to fall just
shy of 5 meters.


- Al.

 

This is pretty serious - your lens is defective and will have to be
returned.

Or possibly the manufacturer used an optimistic CoC of 0.047mm instead
of your rather tight 0.025mm.

My 50mm lens? Most 35mm format lenses use a CoC of about 0.25-0.35mm,
and 2 1/4" tend to use 0.05-0.06mm.

Feel free to use whatever CoC you want... it will not affect the
performance of the lens.

King Sardon

 

This is pretty serious - your lens is defective and will have to be

But ... how this happened, it sounds imposible! the lens can shoot, it
just works, I did not find any problem until a seriously check the
sclale!

 

Your lens is NOT defective!

As someone else posted, it is all about what circle of confusion the
manufacturer uses to calculate and the depth of field scales.
The results depend on how much you enlarge the image and your quality
requirements. The depth of field scales are suggestions/hints: Objects
near the ends of the scale will not be perfectly in focus; but the
degree to which that is visible depends again on how much the image is
enlarged.

In practice I tend to use the scales conservatively. That means that I
stay well within the suggested zone of "sharpness", for example by using
the f/5.6 scales when shooting at f/8.0.

FYI: The scales on my Zeiss Planar 50mm f/1.4 (old Rolleiflex mount)
show a minimum hyperfocal distance of slightly over 3 meters at f/8.0:
Sound familiar?
My Soviet 50mms are slightly over 4 meters and old Pentax SMC Takumar
50mm f/1.4 gives just under 5 meters.
That doesn't mean that the Zeiss is better (or worse) than the Pentax,
just that they used different circles of confusion to place the scales.
It does mean that I'll "trust" the Pentax scales more and use the Zeiss
scales more conservatively.

Chris

 

Your lens is NOT defective!

As someone else posted, it is all about which circle of confusion the
manufacturer uses to calculate the depth of field scales.
The results depend on how much you enlarge the image and your quality
requirements. The depth of field scales are suggestions/hints: Objects
near the ends of the scale will not be perfectly in focus; but the
degree to which that is visible depends again on how much the image is
enlarged.

In practice I tend to use the scales conservatively. That means that I
stay well within the suggested zone of "sharpness", for example by using
the f/5.6 scales when shooting at f/8.0.

FYI: The scales on my Zeiss Planar 50mm f/1.4 (old Rolleiflex mount)
show a minimum hyperfocal distance of slightly over 3 meters at f/8.0:
Sound familiar?
My Soviet 50mms are slightly over 4 meters and my old Pentax SMC Takumar
50mm f/1.4 gives just under 5 meters.
That doesn't mean that the Zeiss is better (or worse) than the Pentax,
just that they used different circles of confusion to place the scales.
It does mean that I'll "trust" the Pentax scales more and use the Zeiss
scales more conservatively.

Chris

 

Gee, maybe you could just take a picture or two and figure out what
works for you? Should anyone really care what someone else has decided
works for them?

 

This might help. Online HF calculator:
http://www.johnhendry.com/gadget/hf.php
Film best,
me

 

Run it again with a CoC of 0.033 and you'll be closer at about 4.7 m.
CoC 0.045 at about 3.5 meteres..
etc.

You choose the CoC based on the print size.
The larger the print size, the smaller the CoC required to have good
detail in the "field".

The lens markings really know nothing about the DOF of the image at
taking time or printing time. Surprising, eh? They're just a
guideline, usually for an 8x10 print.

It would appear that Zeiss believe the CoC for the lens should be 0.045
which is not very ambitious of them. Actually sounds more like a medium
format CoC / DOF markings. (6x6 is about 0.06 CoC).

Get fcalc as a handy tool. www.tangentsoft.com and also see

http://www.nikonlinks.com/unklbil/dof.htm for recipes and so on.

Cheers,
Alan.

 

0.047 would be pessimistic. Hell, it's almost as bad as a MF lens.

 

You're flirting with a "troll" label.

 

Good point. Most people don't really know how to choose a DOF/hyper-f
based on the lens markings. (And on my lenses that have the markings,
they are so tight on the barell as to be useless for the purpose). With
the CZ's I rented in the fall, it was a beaut.

Cheers,
Alan.

 

In message <> - "narke"
:>
:>I have a Zeiss Planar 1.4/50. When I focus on the infinity, the DOF
:>scale indicates the hyperfocal distance for F16 is about 3.3m. But
:>work from the formula, it follows that
:>
:>h = f^2/(N*c) = 50^2/(16*0.025)
:>
:>the above should be 6.25m.
:>
:>It's a big difference with what on the sale. What's wrong? What about
:>your 50mm lens?
:>
:>Thanks in advance.
:>
:>-
:>narke
:>

Hi

The .025 value is normally used for 35mm film. I'm not familiar with Zeiss
equipment, is it Medium Format?
The CoC value is related to the amount of magnification required to produce at
certain size print. For example, to produce an 8"x10" print, a 35mm neg
requires more magnification than film used in a MF camera. Therefore the 35mm
film needs a smaller CoC value.
Just as an FYI, CoC for more DSLR's is .010.

Hope this helps
Rob
www.rcp.ca

 

[SNIP]

This discussion prompted me to re-read the instructions that come with a
Rodenstock DoF calculator, as I half remembered them saying something about
a standard for the CoC. Sure enough, they begin by saying that the
calculator is based on the "internationally standard" CoC for 35mm of
0.03mm, and uses proportionally larger Cs of C for larger formats. It
doesn't say whose standard that is, and I doubt that it is an ISO one since
clearly the main manufacturers of 35mm lenses use so many different values
where I would expect that if there was a standard some at least would use it
and boast that they did (if only to distinguish themselves from Sigma, who
wouldn't use it...)

It is true that I've noticed just from looking at lens markings that Pentax
is rather conservative about DoF, using a small CoC that places them at one
end of the scale, while Zeiss seems more optimistic - which in this context
is not a good thing - out at the other. No problem once you are used to
it, and know what the markings mean, of course, but a pain for anyone who
has lenses from multiple sources all using different assumed CoC figures.



Peter

 

just as an FYI, CoC for more DSLR's is .010.

just interesting that, why DSLR's use a such small CoC value? Does it
mean the focus capacility of a digital camera bad than a film one?

 

Your lens is NOT defective!

Glad to hear that. I beleived it after I visited a camera store today
and checked another CZ' lens, a 1.7/50mm, the Hyferfocal of it is even
small than mine -- a little short than 3 meter. Amazing! Even the same
manufacture use differenct CoC values for their similar products.

Istay well within the suggested zone of "sharpness", for example by
using the f/5.6 scales when shooting at f/8.0.

It's a good ideal. But now, I decide to print a big sheet for DoFs of
every posible situations (a few distances I often used for every
f-stop) and just forget the scale.

 

It would appear that Zeiss believe the CoC for the lens should be
0.045 which is not very ambitious of them.

Did you mean that contax made a sharper lens than others and so they
decide to use a bigger CoC?

 

So, don't focus at infinity. Instead, focus where the outside of the

Oh ... I dont understant your method, could please you explain it
again? What means " forcus where the outside of the DOF scale touches
infinity"?

 

In message <> - "narke"
:>
:>> just as an FYI, CoC for more DSLR's is .010.
:>
:>just interesting that, why DSLR's use a such small CoC value? Does it
:>mean the focus capacility of a digital camera bad than a film one?
:>

It's to do with the physical size of the sensor. DSLR's with a full frame
sensor (like Canon 1Ds) have a CoC of .025 to .030.

Rob
www.rcp.ca

 

Align the infinity symbol with your chosen aperture (based on your exposure)
on the DOF scale.

Or said another way:

For HF the infinity symbol should be aligned (i.e. across from) with the
f-stop value on the DOF scale you have chosen for your exposure. After you
have done this the closest distance of acceptable focus will then be aligned
with the same value f-stop on the opposite end of the DOF scale.

Below is a diagram of a distance scale and DOF scale for a 50mm lens set for
Hyper Focal:

6ft........12ft.......inf.
|
f22........O........f22

As per the diagram above the aperture is f22, 6ft is the minimum focusing
distance and infinity is the maximum focusing distance.
Sign,
me