Stupid Question: Aperture

I have mounted a lens into a shutter that has a mismatched aperture scale.
When the shutter's aperture reads F8, the blades are wide open for my
lens: the diaphram blades are a tiny fraction of a millimeter larger than
the diameter of the middle lenses of my lens. Close enough for the moment.

Now, I know that my lens is F4.5 wide open when the shutter aperture reads
F8, but are the other physically smaller aperture values for the shutter
_relative_ to mine - in other words, the shutter's F8 is F4.5 for me;
that's a given, but is F11 on the shutter F5.6 for me, and so on to F32
which would be

My lens The shutter's indicated aperture
4.5 8
5.6 11
8 16
11 32

No?

one_of_many wrote:

: I have mounted a lens into a shutter that has a mismatched aperture scale.
: When the shutter's aperture reads F8, the blades are wide open for my
: lens: the diaphram blades are a tiny fraction of a millimeter larger than
: the diameter of the middle lenses of my lens. Close enough for the moment.

: Now, I know that my lens is F4.5 wide open when the shutter aperture reads
: F8, but are the other physically smaller aperture values for the shutter
: _relative_ to mine - in other words, the shutter's F8 is F4.5 for me;
: that's a given, but is F11 on the shutter F5.6 for me, and so on to F32
: which would be

: My lens The shutter's indicated aperture
: 4.5 8
: 5.6 11
: 8 16
: 11 32

: No?

You may want to consider sending the lens to S.K.Grimes and have a new scale made.
--




Keep working millions on welfare depend on you
-------------------

In article , Frank Pittel
wrote:

one_of_many wrote:

: I have mounted a lens into a shutter that has a mismatched aperture scale.
: When the shutter's aperture reads F8, the blades are wide open for my
: lens: the diaphram blades are a tiny fraction of a millimeter larger than
: the diameter of the middle lenses of my lens. Close enough for the moment.

: Now, I know that my lens is F4.5 wide open when the shutter aperture reads
: F8, but are the other physically smaller aperture values for the shutter
: _relative_ to mine - in other words, the shutter's F8 is F4.5 for me;
: that's a given, but is F11 on the shutter F5.6 for me, and so on to F32
: which would be

: My lens The shutter's indicated aperture
: 4.5 8
: 5.6 11
: 8 16
: 11 32

: No?

You may want to consider sending the lens to S.K.Grimes and have a new
scale made.

Not neccessary if I can determine whether the F-stops are relative as
shown above.

(one_of_many) wrote in message ...
In article , Frank Pittel
wrote:

one_of_many wrote:

: I have mounted a lens into a shutter that has a mismatched aperture scale.
: When the shutter's aperture reads F8, the blades are wide open for my
: lens: the diaphram blades are a tiny fraction of a millimeter larger than
: the diameter of the middle lenses of my lens. Close enough for the moment.

: Now, I know that my lens is F4.5 wide open when the shutter aperture reads
: F8, but are the other physically smaller aperture values for the shutter
: _relative_ to mine - in other words, the shutter's F8 is F4.5 for me;
: that's a given, but is F11 on the shutter F5.6 for me, and so on to F32
: which would be

: My lens The shutter's indicated aperture
: 4.5 8
: 5.6 11
: 8 16
: 11 32

: No?

You may want to consider sending the lens to S.K.Grimes and have a new
scale made.

Not neccessary if I can determine whether the F-stops are relative as
shown above.

That would be true, except for one thing. (And it bit me once.)
Differing lens designs will manage with the light between the cells
in a different manner. That means one thing -- "4.5" may be in slightly
from the current "8" position. You could easily be off by 1/3 stop
but probably not any more than that.
I say that it bit me once when I put an old Xenar 150/4.5 cell set into a
shutter with a different scale. After shooting once I saw the difference
and was able to compensate. Shooting a series of chromes with a known
system (like your 35mm or medium format) and a series with the 4x5 will
provide a suitable comparison that won't cost you time without your equipment.

Enjoy,

Collin
KC8TKA

In article ,
(Collin Brendemuehl) wrote:

(one_of_many) wrote:
[...]

That would be true, except for one thing. (And it bit me once.)
Differing lens designs will manage with the light between the cells
in a different manner. That means one thing -- "4.5" may be in slightly
from the current "8" position. You could easily be off by 1/3 stop
but probably not any more than that. [...]

Thank you, Collin. By your comments is seems that in princlple I was
correct. I will begin testing exposure/developments in an hour. It's a
beautiful bright sunny morning here in Minnesota, perfect for some work.

Best,
John

"one_of_many" wrote in message
news

I have mounted a lens into a shutter that has a mismatched
aperture scale.
When the shutter's aperture reads F8, the blades are wide
open for my
lens: the diaphram blades are a tiny fraction of a
millimeter larger than
the diameter of the middle lenses of my lens. Close enough
for the moment.

Now, I know that my lens is F4.5 wide open when the
shutter aperture reads
F8, but are the other physically smaller aperture values
for the shutter
_relative_ to mine - in other words, the shutter's F8 is
F4.5 for me;
that's a given, but is F11 on the shutter F5.6 for me, and
so on to F32
which would be

My lens The shutter's indicated aperture
4.5 8
5.6 11
8 16
11 32

No?

You can calibrate the aperture scale for the new lens. I
would make a new scale, perhaps the simplest method is to
put some white tape over the old scale.
The _effective_ aperture of a lens is not the size of
the hole in the iris diaphragm. Rather it is the diameter of
the entrance pupil. It turns out that this is easier to
measure than the physical diaphragm size.
You will need a card with a small hole in it. A
flashlight or other small light source. A flat mirror large
enough to cover the front of the lens. Some thin paper.
The lens and card must be mounted parallel. If you are
working with a view camera you can use the camera as a
makeshift optical bench.
Mount the mirror over the lens. Put the flashlight in
back of the hole in the card. Adjust the lens until the
reflected image of the light is focused back onto the card
near the hole. Now, remove the mirror and place a
translucent screen over the lens. Thin writing paper works
fine. There will be a circle of light projected onto the
paper. The diameter of this circle is the _effective_ size
of the stop. It may be larger or smaller than the physical
stop, depending on the magnification of the lenses in front
of it.
The diameter of this circle of light is devided into the
focal length of the lens to get the stops. Simply adjust the
iris to the sizes you want to have marked and mark them.
This is a very accurate method of calibration.
I am presuming you know the focal length of the lens. The
marked focal length will be close enough although you can
use the same rig to measure the actual focal length. I've
posted the method to this group several times. Probably a
Google search for my name and the keyword autocollimation or
autocollimate will find them.


--
---
Richard Knoppow
Los Angeles, CA, USA

In article .net,
"Richard Knoppow" wrote:

[... see the good article ..]

I am presuming you know the focal length of the lens. [...]

Yes, thanks to government specs I do.
http://course1.winona.edu/jstafford/newlens1/

"one_of_many" wrote in message
news
In article
.net,
"Richard Knoppow" wrote:

[... see the good article ..]

I am presuming you know the focal length of the lens.
[...]

Yes, thanks to government specs I do.
http://course1.winona.edu/jstafford/newlens1/

That's some chunk of glass! By "true Biogon" I wonder
_which_ biogon this means? There are two Zeiss designs named
Biogon. The first was designed by Bertele and was based on
his orignal Sonnar for the Contax camera. The second Biogon
was a Roosinov type lens. This is a type which is used for a
great many modern wide angle lenses such as the Schneider
Super-Angulon. From its appearance this is what you have.


--
---
Richard Knoppow
Los Angeles, CA, USA

In article .net,
"Richard Knoppow" wrote:

Yes, thanks to government specs I do.
http://course1.winona.edu/jstafford/newlens1/

That's some chunk of glass!

I have four of them in various states of machining and also one pristine,
as-issued which I will save for the very final version if this all works
out.

Our saint of lens testing out there has a stock version that maybe he will
have time to test. His lens has scratching and an abraded coating on the
rear element which was unacceptable to me. I suspect it's also been bumped
arount too much. Dunno how that one will work out.

By "true Biogon" I wonder
_which_ biogon this means? There are two Zeiss designs named
Biogon. The first was designed by Bertele and was based on
his orignal Sonnar for the Contax camera. The second Biogon
was a Roosinov type lens. This is a type which is used for a
great many modern wide angle lenses such as the Schneider
Super-Angulon. From its appearance this is what you have.

It is of the later design. The lens is of relatively recently manufacture.
Coverage across the format is so even that I cannot detect darkened
corners. IN addition, distortion seems to replicate the Zeiss 38mm Biogon
- which is to say almost none. Very interesting - a giant Biogon which
allows up to 12 degrees of rear tilt. But it's a _monster_ to schlep.