f-stops versus h-stops?

[Will Wagner]

Howdy all, delurk post.

I recently got hold of a Rodenstock Imagon 300mm/5.8, and of course
the kit came with everything except the booklet. I've seen a few
posts in various fora which have forcefully stated that h-stops are
NOT the same as f-stops, and from some experimentation with polaroids,
I just can't tell; it seems close-ish, but I'm not sure if it's quite
right. And of course there are those other posts that basically say
"if you use the lens's aperture, you're doing it wrong." Well, that's
fine, because the aperture scale is blank anyway.

So do I just have to keep messing with the lens to find out just which
h-stop works for me at some exposure value? That's going to be a LOT
of polaroids, methinks. Or is there some sort of straightforward
relationship? I'd love to find a copy of the "Introducing the Imagon"
booklet, which probably tells the whole story, but can't find it
anywhere; I've found a couple links to PDF versions, but the links
were all dead.

Thanks,

Will

[Richard Knoppow]

(Will Wagner) wrote in message >...
> Howdy all, delurk post.
>
> I recently got hold of a Rodenstock Imagon 300mm/5.8, and of course
> the kit came with everything except the booklet. I've seen a few
> posts in various fora which have forcefully stated that h-stops are
> NOT the same as f-stops, and from some experimentation with polaroids,
> I just can't tell; it seems close-ish, but I'm not sure if it's quite
> right. And of course there are those other posts that basically say
> "if you use the lens's aperture, you're doing it wrong." Well, that's
> fine, because the aperture scale is blank anyway.
>
> So do I just have to keep messing with the lens to find out just which
> h-stop works for me at some exposure value? That's going to be a LOT
> of polaroids, methinks. Or is there some sort of straightforward
> relationship? I'd love to find a copy of the "Introducing the Imagon"
> booklet, which probably tells the whole story, but can't find it
> anywhere; I've found a couple links to PDF versions, but the links
> were all dead.
>
> Thanks,
>
> Will

The Imagon is a soft focus lens. The amount of softness is
controlled by varying the ratio of light coming through the margins of
the lens versus the center. Because of this it doesn't have definite
f/stops. Rather, the masks are calibrated in the equivalent amount of
light an f/stop would give. So the "stops" for an Imagon are used the
same way as those of a standard lens as far as calculating the amount
of exposure.
As is true of other soft focus lenses which depend on uncorrected
spherical aberration for the effect the f/stop can not be changed
independantly of the amount of softness. Spherical aberration varies
with the f/stop, becoming less as the lens is stopped down. The Imagon
adds to this some diffusion from the special obstructive diaphragm, so
it has an image character which is a little different from other soft
focus lenses.

Richard Knoppow
Los Angeles, CA, USA

[Will Wagner]

In article >,
Richard Knoppow > wrote:
(Will Wagner) wrote in message
>...
>> I recently got hold of a Rodenstock Imagon 300mm/5.8, and of course
>> the kit came with everything except the booklet. I've seen a few
>> posts in various fora which have forcefully stated that h-stops are
>> NOT the same as f-stops, and from some experimentation with polaroids,
>> I just can't tell; it seems close-ish, but I'm not sure if it's quite
>> right. [ snip ]
>
> The Imagon is a soft focus lens. The amount of softness is
>controlled by varying the ratio of light coming through the margins of
>the lens versus the center. Because of this it doesn't have definite
>f/stops. Rather, the masks are calibrated in the equivalent amount of
>light an f/stop would give. So the "stops" for an Imagon are used the
>same way as those of a standard lens as far as calculating the amount
>of exposure.

Thanks for the info, Richard. So for exposure purposes, an f-stop is
basically equal to an h-stop, which is what I had initially guessed.
Any ideas what the "h" stands for? At any rate, you've given me a
little more confidence with this lens. Some of my tests so far have
come out pretty cool.

I'm still trying to wrap my head around the spherical-aberration-
caused focus shift that I've seen discussed; I think the light has
come on for me as far as the physics behind it goes, but I haven't
really *seen* any evidence of it. Refining focus after opening the
diffusion grille doesn't seem to make any change in the positions of
the standards.

Will
--
Will Wagner / / http://www.ymb.net/
"Keep it simple: as simple as possible, but no simpler." -- A. Einstein

[Bob Salomon]

In article >,
(Will Wagner) wrote:

> In article >,
> Richard Knoppow > wrote:
> (Will Wagner) wrote in message
> >...
> >> I recently got hold of a Rodenstock Imagon 300mm/5.8, and of course
> >> the kit came with everything except the booklet. I've seen a few
> >> posts in various fora which have forcefully stated that h-stops are
> >> NOT the same as f-stops, and from some experimentation with polaroids,
> >> I just can't tell; it seems close-ish, but I'm not sure if it's quite
> >> right. [ snip ]
> >
> > The Imagon is a soft focus lens. The amount of softness is
> >controlled by varying the ratio of light coming through the margins of
> >the lens versus the center. Because of this it doesn't have definite
> >f/stops. Rather, the masks are calibrated in the equivalent amount of
> >light an f/stop would give. So the "stops" for an Imagon are used the
> >same way as those of a standard lens as far as calculating the amount
> >of exposure.
>
> Thanks for the info, Richard. So for exposure purposes, an f-stop is
> basically equal to an h-stop, which is what I had initially guessed.
> Any ideas what the "h" stands for? At any rate, you've given me a
> little more confidence with this lens. Some of my tests so far have
> come out pretty cool.
>
> I'm still trying to wrap my head around the spherical-aberration-
> caused focus shift that I've seen discussed; I think the light has
> come on for me as far as the physics behind it goes, but I haven't
> really *seen* any evidence of it. Refining focus after opening the
> diffusion grille doesn't seem to make any change in the positions of
> the standards.
>
> Will

The H stops used by the Imagon = the fstop in the shadow area with
negative material.

--
To reply no_ HPMarketing Corp.

[Bob Salomon]

In article >,
(Will Wagner) wrote:

> In article >,
> Richard Knoppow > wrote:
> (Will Wagner) wrote in message
> >...
> >> I recently got hold of a Rodenstock Imagon 300mm/5.8, and of course
> >> the kit came with everything except the booklet. I've seen a few
> >> posts in various fora which have forcefully stated that h-stops are
> >> NOT the same as f-stops, and from some experimentation with polaroids,
> >> I just can't tell; it seems close-ish, but I'm not sure if it's quite
> >> right. [ snip ]
> >
> > The Imagon is a soft focus lens. The amount of softness is
> >controlled by varying the ratio of light coming through the margins of
> >the lens versus the center. Because of this it doesn't have definite
> >f/stops. Rather, the masks are calibrated in the equivalent amount of
> >light an f/stop would give. So the "stops" for an Imagon are used the
> >same way as those of a standard lens as far as calculating the amount
> >of exposure.
>
> Thanks for the info, Richard. So for exposure purposes, an f-stop is
> basically equal to an h-stop, which is what I had initially guessed.
> Any ideas what the "h" stands for? At any rate, you've given me a
> little more confidence with this lens. Some of my tests so far have
> come out pretty cool.
>
> I'm still trying to wrap my head around the spherical-aberration-
> caused focus shift that I've seen discussed; I think the light has
> come on for me as far as the physics behind it goes, but I haven't
> really *seen* any evidence of it. Refining focus after opening the
> diffusion grille doesn't seem to make any change in the positions of
> the standards.
>
> Will

The Imagon expects a very strong lighting ratio like 5:1 rather the 3:1
in order for the halation to work properly. That means no umbrellas, no
open shade. You need a strong key light with parabolic type reflectors
to get the Imagon effect.

--
To reply no_ HPMarketing Corp.