Use of Filters on REAR Lens thread

Does anyone have experience using screw on filters on the REAR lens thread.
I am asking this because (yes, I'm a cheapskate) I would like to use some
smaller filters I own on lenses with headlight size objectives. I do know
enough to check that the filter cannot reach and damage the rear lens
element and intend to shoot some experiments, but that will have to wait a
few days. Thanks.

"Mark McGilvray" wrote in message
...
Does anyone have experience using screw on filters on the
REAR lens thread. I am asking this because (yes, I'm a
cheapskate) I would like to use some smaller filters I own
on lenses with headlight size objectives. I do know enough
to check that the filter cannot reach and damage the rear
lens element and intend to shoot some experiments, but
that will have to wait a few days. Thanks.
The filter can not damage the lens and this technique is
used pretty frequently. However, at least in principle, the
filter can degrade the image when used on the back of the
lens. This is because the light from the lens to the film is
convergent. When light which is convergent or divergent goes
through a flat block it is deviated adding chromatic and
spherical aberration. The effect depends on the angle of the
light, the thickness of the material, and its index of
refraction and dispersion. The best filters for this use are
gelatin filters. They are thin and gelatin is a relatively
low index of refraction.
When used on the front of a lens for pictorial work the
object is effectively at infinity. The light rays are
parallel when they enter the filter, so there is no
deviation. This is true down to perhaps 10X the focal length
of the lens and certainly down to about 20X.
In practice the filter may make no visible difference but
it should be tested. Since a parallel block can introduce
oblique aberrations check the corners of the image.


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

In article . net,
"Richard Knoppow" wrote:

"Mark McGilvray" wrote in message
...
Does anyone have experience using screw on filters on the
REAR lens thread. I am asking this because (yes, I'm a
cheapskate) I would like to use some smaller filters I own
on lenses with headlight size objectives. I do know enough
to check that the filter cannot reach and damage the rear
lens element and intend to shoot some experiments, but
that will have to wait a few days. Thanks.
The filter can not damage the lens and this technique is
used pretty frequently. However, at least in principle, the
filter can degrade the image when used on the back of the
lens. This is because the light from the lens to the film is
convergent. When light which is convergent or divergent goes
through a flat block it is deviated adding chromatic and
spherical aberration. The effect depends on the angle of the
light, the thickness of the material, and its index of
refraction and dispersion. The best filters for this use are
gelatin filters. They are thin and gelatin is a relatively
low index of refraction.
When used on the front of a lens for pictorial work the
object is effectively at infinity. The light rays are
parallel when they enter the filter, so there is no
deviation. This is true down to perhaps 10X the focal length
of the lens and certainly down to about 20X.
In practice the filter may make no visible difference but
it should be tested. Since a parallel block can introduce
oblique aberrations check the corners of the image.

You left out the more obvious focus shift = 1/3 the thickness of the
filter when it is behind the lens and the possibility that dust,
smudges, etc may start to come in focus on the back.

--
To reply no_ HPMarketing Corp.

In article ,
"Mark McGilvray" wrote:

using screw on filters on the REAR lens thread.
I am asking this because (yes, I'm a cheapskate)

You must be to spend money on film and take your time to shoot that film
not to mention load and process that film to take images with a filter
in the back and then intentionally put the filter on the back to degrade
the image you shoot to save a couple of bucks on the filter.

Unless the lens was made to accept interior or rear filters the filter
will degrade the image and create a focus shift. In addition filters
behind the lens offer no protection for the front element to protect it
from dust, snow, rain, fingerprints, overzealous lens cleaning, etc.

But you do save a penny or two - probably more as if you are this frugal
you probably are not buying good quality filters in the first place.

--
To reply no_ HPMarketing Corp.

Bob Salomon wrote:
In article . net,
"Richard Knoppow" wrote:


The filter can not damage the lens and this technique is
used pretty frequently. However, at least in principle, the
filter can degrade the image when used on the back of the
lens. This is because the light from the lens to the film is
convergent. When light which is convergent or divergent goes
through a flat block it is deviated adding chromatic and
spherical aberration. The effect depends on the angle of the
light, the thickness of the material, and its index of
refraction and dispersion. The best filters for this use are
gelatin filters. They are thin and gelatin is a relatively
low index of refraction.
When used on the front of a lens for pictorial work the
object is effectively at infinity. The light rays are
parallel when they enter the filter, so there is no
deviation. This is true down to perhaps 10X the focal length
of the lens and certainly down to about 20X.
In practice the filter may make no visible difference but
it should be tested. Since a parallel block can introduce
oblique aberrations check the corners of the image.


You left out the more obvious focus shift = 1/3 the thickness of the
filter when it is behind the lens and the possibility that dust,
smudges, etc may start to come in focus on the back.

If the camera is focused with the filter on, that type of focus shift should
be eliminated.

--
.~. Jean-David Beyer Registered Linux User 85642.
/V\ PGP-Key: 9A2FC99A Registered Machine 241939.
/( )\ Shrewsbury, New Jersey http://counter.li.org
^^-^^ 08:00:00 up 6 days, 6:21, 4 users, load average: 4.36, 4.30, 4.25

In article ,
Jean-David Beyer wrote:


If the camera is focused with the filter on, that type of focus shift should
be eliminated.

But not image degradation. And it does nothing to protect the front
element. And if the lens shifts focus as the aperture changes and you
don't refocus you may still have a shift.

--
To reply no_ HPMarketing Corp.

Bob Salomon wrote:
In article ,
Jean-David Beyer wrote:



If the camera is focused with the filter on, that type of focus shift should
be eliminated.


But not image degradation. And it does nothing to protect the front
element. And if the lens shifts focus as the aperture changes and you
don't refocus you may still have a shift.

True enough. But if the lens is stopped down, you may have less trouble with
flare caused by the filter if the filter is behind the lens installed behind
the lens. But I am splitting hairs, obviously.

--
.~. Jean-David Beyer Registered Linux User 85642.
/V\ PGP-Key: 9A2FC99A Registered Machine 241939.
/( )\ Shrewsbury, New Jersey http://counter.li.org
^^-^^ 09:00:00 up 6 days, 7:21, 3 users, load average: 4.08, 4.17, 4.21

In article ,
Jean-David Beyer wrote:

But if the lens is stopped down, you may have less trouble with
flare caused by the filter

So you would possibly stop down enough to further degrad the image from
diffraction.

And good filters don't flare. The SH-PMC coatings that Heliopan uses on
their SH-PMC filters pass 99.9% of the light striking it to the lens.
That is less flare then the typical camera lens coating and equals or
betters most MC on modern lenses. Plus this coating repels moisture,
dust and water to further improve the image.

--
To reply no_ HPMarketing Corp.

In article ,
says...
Does anyone have experience using screw on filters on the REAR lens thread.
I am asking this because (yes, I'm a cheapskate) I would like to use some
smaller filters I own on lenses with headlight size objectives. I do know
enough to check that the filter cannot reach and damage the rear lens
element and intend to shoot some experiments, but that will have to wait a
few days. Thanks.



In spite of all the nay sayers, I've done it for years with no problem.
Several lenses had threads on the inside that could be used and on one
lens I used a pushon adaptor that fit.
I've never had any problem with focus shift either, although (except
for deep red) I usually focus with the filter in place.

--
Robert D Feinman
Landscapes, Cityscapes and Panoramic Photographs
http://robertdfeinman.com
mail:

"Richard Knoppow" wrote in message
ink.net...

"Mark McGilvray" wrote in message
...
Does anyone have experience using screw on filters on the REAR lens
thread. I am asking this because (yes, I'm a cheapskate) I would like to
use some smaller filters I own on lenses with headlight size objectives.
I do know enough to check that the filter cannot reach and damage the
rear lens element and intend to shoot some experiments, but that will
have to wait a few days. Thanks.
The filter can not damage the lens and this technique is used pretty
frequently. However, at least in principle, the filter can degrade the
image when used on the back of the lens. This is because the light from
the lens to the film is convergent. When light which is convergent or
divergent goes through a flat block it is deviated adding chromatic and
spherical aberration. The effect depends on the angle of the light, the
thickness of the material, and its index of refraction and dispersion. The
best filters for this use are gelatin filters. They are thin and gelatin
is a relatively low index of refraction.
When used on the front of a lens for pictorial work the object is
effectively at infinity. The light rays are parallel when they enter the
filter, so there is no deviation. This is true down to perhaps 10X the
focal length of the lens and certainly down to about 20X.
In practice the filter may make no visible difference but it should be
tested. Since a parallel block can introduce oblique aberrations check the
corners of the image.


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


Thank you , Richard, this is exactly the information I wanted.