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Are IS lenses doomed ?



 
 
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  #11  
Old January 11th 07, 05:43 PM posted to rec.photo.digital.slr-systems
David Littlewood
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Posts: 250
Default Are IS lenses doomed ?

In article , David Kilpatrick
writes
Lionel wrote:

Also, I'm thinking IS in a 300+ mm lens is going to do a lot better
than on a chip.

On that, I agree with you. In-camera IS would need a huge amount of
travel to compensate for the amount of shake you get with big tele
lenses.

What actually happens with in-body IS is that the travel is the same in
extent, it's just the velocity (speed of travel) which increases with
longer focal lengths. Sony (Minolta) use angular momentum sensors,
since it is an angular shake which counts, so shake is not considered
in mms it's in degrees (or small fractions of a degree) plus velocity.
When a lens covers 8 degrees a quarter degree of shake is substantial,
when a lens covers 80 degrees it's not so much.


I think I must have missed some vital point here, David. How does an
angular movement of the camera, which moves the image in linear fashion
along the sensor, require a change in the angular orientation of the
sensor. ISTM that it must require a linear movement of the sensor to
correct it.

OTOH, it is quite feasible to change the location of an image on the
sensor by a small angular displacement of the image-forming beam
somewhere in the lens, and quite credible that this would require much
smaller movements.

If I have misunderstood this (and many others have too, including Canon,
who I see give a similar rationale for favouring lens-based IS), is
there a suitable web site which explains the position? I freely
acknowledge a lack of specific expertise here, and accept the situation
may be more complicated than my simple thoughts here.

However, you are 'safe' to shoot at 1/30th without IS on an 18mm lens,
but you have to use 1/500th to be safe on a 300mm lens (both APS-C
examples). The long lens magnifies the shake in effect, so that the
image moves as far in 1/500th with the 300mm, as it moves in 1/30th
with the 18mm.

The long lens only gets into 'huge amount of travel' if you try to
hand-hold 1/30th at 300mm. With anti-shake, you can do 1/8th and maybe
1/4 at 18mm. You can do 1/250 or 1/125 at 300mm. In each case, the
sensor is travelling about the same amount, but it is having travel
faster for the 300mm.

Shake does not just keep going in one direction, anway. It tends to be
tremor or vibration-like when it is not a brief, fixed jerk caused by
pressing the shutter. Sony's SSS will cope with tremors between 1Hz
(swaying gently back and forth once a second - heartbeat, breathing)
and 60Hz (someone just plugged you into a wall socket by mistake). Most
shake is apparently around 10Hz, a typical frequency of human body
tremor. So the system, whether in the lens or the body, has to respond
to acceleration, fixed velocity, vector (direction) including rapid
changes of all three.

Both in-lens and in-body IS appears to function equally well over a
wide range of conditions. It's not possible to state that in-lens IS is
definitely superior at long focal lengths, on in-body superior with
extreme wides and hand-held 1/4s. In practice I have found my KM and
Sony bodies very similar to Canon IS with 100-300mmm/70-300mm lenses
(the KM 100-300mm is much smaller and lighter than our early Canon IS
70-300mm, but I don't think this improves the efficiency - if anything
the large Canon lens is a bit easier to hand-hold steadily).

What I forget - and I suspect many others forget - is that you really
should not be able to use 1/30th with either system, if the lens is at
300mm. I do so regularly, and the result is nearly always perfectly
sharp. That's 4-5 stops of stabilisation, not the claimed 1-2 for the
older Canon lens, or 2-3 for the KM/Sony systems. Yet both, with a
little care, will give a high success rate.

I guess this is the ultimate test - if in-camera works as well as
in-lens, then it is as good. Would be good to see some rigorous tests
though.

David
--
David Littlewood
  #12  
Old January 11th 07, 06:52 PM posted to rec.photo.digital.slr-systems
l v
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Posts: 182
Default Are IS lenses doomed ?

VC wrote:
The release of Sony Alpha with the image stabilization in camera ( although
this is not new) highlighted the fundamental problem with Canon.
Canon have had IS lenses long ago as it would be very difficult to do
in-camera stabilization in film cameras. The digital cameras had to support
older lenses including the ones with IS. If Canon developed a camera with
in-body stabilization it would hurt Canon sales and reputation.
So I guess Canon will continue with its nonstabilized bodies and when Sony
or someone else will achieve the same image sensor quality Canon will find
itself in a very difficult situation.
There is a very small advantage in having IS in the lens but it is not
significant enough to grant double and triple cost of the same quality
lenses.
What do you guys think ?



I can't find the article but I remember reading about the comparison
between in-camera IS and in-lens IS. It stated that the in-camera IS
would prevent a full sized sensor from working with the in-camera IS.
It stated that the camera would be very large to allow for full sensor
movement and the light from the lens could fall off the edges of the
sensor, therefore even a larger then full sensor was needed, thus making
the camera even larger.

Am I blowing smoke or does anyone else remember this?

--

Len
  #13  
Old January 11th 07, 07:01 PM posted to rec.photo.digital.slr-systems
RichA
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Posts: 2,544
Default Are IS lenses doomed ?


VC wrote:
The release of Sony Alpha with the image stabilization in camera ( although
this is not new) highlighted the fundamental problem with Canon.
Canon have had IS lenses long ago as it would be very difficult to do
in-camera stabilization in film cameras. The digital cameras had to support
older lenses including the ones with IS. If Canon developed a camera with
in-body stabilization it would hurt Canon sales and reputation.
So I guess Canon will continue with its nonstabilized bodies and when Sony
or someone else will achieve the same image sensor quality Canon will find
itself in a very difficult situation.
There is a very small advantage in having IS in the lens but it is not
significant enough to grant double and triple cost of the same quality
lenses.
What do you guys think ?


The bad of lens-based IS: COST!
The good. If one lens goes down, it doesn't take the whole camera with
it, compared to if IS in the camera goes down.

  #14  
Old January 11th 07, 08:02 PM posted to rec.photo.digital.slr-systems
Ståle Sannerud
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Posts: 92
Default Are IS lenses doomed ?


I can't find the article but I remember reading about the comparison
between in-camera IS and in-lens IS. It stated that the in-camera IS
would prevent a full sized sensor from working with the in-camera IS. It
stated that the camera would be very large to allow for full sensor
movement and the light from the lens could fall off the edges of the
sensor, therefore even a larger then full sensor was needed, thus making
the camera even larger.

Am I blowing smoke or does anyone else remember this?


It's quite obvious if you think about it. The lens throws a circular,
fixed-size image into the camera. The size of this image circle is designed
to cover the film frame (or sensor, obviously) and not a smidgeon more than
necessary- or, if the image circle size IS significantly bigger than the
film frame you will have to carry around a lens that is correspondingly
larger, heavier and more expensive than would otherwise be the case.

Now, with in-camera IS the sensor has to move around to "chase" the image as
it wobbles around the sensor plane as your hands shake. The image circle is
of course constant and stays in place, so the sensor has a hard limit on how
far it can move in any direction before parts of it actually pokes out into
the darkness outside the image circle.

So, in-body IS is a good idea only as long as the image circle is
sufficiently larger than the sensor. A full-frame sensor on a full-frame
lens is a particularly bad candidate for in-body IS, an APS-sized sensor on
a "digital" APS-sized lens with reduced image circle size ain't too hot a
proposition either. Full-frame lens and APS-sized sensor gives you the most
leeway.

Compare this to an IS lens, which de facto lets the image circle chase the
wobbling image so that it stays in the same place relative to the sensor.


  #15  
Old January 11th 07, 08:44 PM posted to rec.photo.digital.slr-systems
John Francis
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Posts: 80
Default Are IS lenses doomed ?

In article ,
Ståle Sannerud wrote:

I can't find the article but I remember reading about the comparison
between in-camera IS and in-lens IS. It stated that the in-camera IS
would prevent a full sized sensor from working with the in-camera IS. It
stated that the camera would be very large to allow for full sensor
movement and the light from the lens could fall off the edges of the
sensor, therefore even a larger then full sensor was needed, thus making
the camera even larger.

Am I blowing smoke or does anyone else remember this?


It's quite obvious if you think about it. The lens throws a circular,
fixed-size image into the camera. The size of this image circle is designed
to cover the film frame (or sensor, obviously) and not a smidgeon more than
necessary- or, if the image circle size IS significantly bigger than the
film frame you will have to carry around a lens that is correspondingly
larger, heavier and more expensive than would otherwise be the case.


It's not at all obvious. It very much depends on focal length, of course.
But for medium telephoto and onwards (say 200mm focal length and upwards)
the size of the image circle has very little effect on lens size and weight.
A 300mm/f4 for a 6x7 camera is just about identical in all dimensions to a
300mm/f4 for a 35mm body, and costs just about the same. The determining
factor for size (and weight, and cost) is the fromt element.

Mind you, a 50mm lens for a 6x7 system *will* be larger/heavier/costlier
than a 50mm lens for a 35mm camera.

  #16  
Old January 11th 07, 11:34 PM posted to rec.photo.digital.slr-systems
David Kilpatrick
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Posts: 693
Default Are IS lenses doomed ?

David Littlewood wrote:
In article , David Kilpatrick
writes

Lionel wrote:

Also, I'm thinking IS in a 300+ mm lens is going to do a lot better
than on a chip.

On that, I agree with you. In-camera IS would need a huge amount of
travel to compensate for the amount of shake you get with big tele
lenses.

What actually happens with in-body IS is that the travel is the same
in extent, it's just the velocity (speed of travel) which increases
with longer focal lengths. Sony (Minolta) use angular momentum
sensors, since it is an angular shake which counts, so shake is not
considered in mms it's in degrees (or small fractions of a degree)
plus velocity. When a lens covers 8 degrees a quarter degree of shake
is substantial, when a lens covers 80 degrees it's not so much.



I think I must have missed some vital point here, David. How does an
angular movement of the camera, which moves the image in linear fashion
along the sensor, require a change in the angular orientation of the
sensor. ISTM that it must require a linear movement of the sensor to
correct it.


I didn't mean the sensor changes angle in any way - it correct while
remaining strictly plane-parallel in its film plane. The calculation as
to how much linear movement to give is based on research into camera
shake, which shows that linear movement of the entire camera is rare and
causes very little visible shake; angular (so-called rotational) shake
is universally the main cause of unsharpness, but it has to be corrected
by a linear movement of the sensor corresponding to the image movement.

This subject has been discussed to death on the Sony forum on dPreview
as a result of a misinformed ideas by a physics graduate (it's very easy
to get it wrong if you think camera shake is a displacement of the lens
axis, rather than a dip/swing/tilt of the lens axis).

My conclusion, after some very useful posts from others including one
which emphasised that long lenses don't need greater sensor movemen if
you stick to the rules about shutter speeds (with the IS factor
included), was that the programming is pretty complex and relies on
'typical' shake detection. There is no way the sensors in the Sony can
really tell whether displacement, rotation, etc is causing them to
detect motion. Somewhere in the system (same goes for IS in lens) the
designers have said 'if the signal from the sensors is THIS, the
required correction will be amost certainy be THIS'. It is not actually
a direct link.

David
  #17  
Old January 11th 07, 11:41 PM posted to rec.photo.digital.slr-systems
David Kilpatrick
external usenet poster
 
Posts: 693
Default Are IS lenses doomed ?

Ståle Sannerud wrote:


Compare this to an IS lens, which de facto lets the image circle chase the
wobbling image so that it stays in the same place relative to the sensor.

In fact the displacement in IS lenses does cause loss of illumination
(asymmetrical vignetting) as well as localised aberrations. One of the
main arguments against using IS lenses is that at the best (IS turned
off) they may not entirely match the performance of similar non-IS
designs, and at the worst (moving element or group at maximum
displacement) optical performance will be visibly compromised.

One slightly ironic point is that so far all the sensor-stabilised
cameras have been 1.5X APS factor. In practice, even lenses like the
11-18mm and 10-20mm wide angles provide 2mm or more coverage beyond this
at their shortest setting - the Tamron 11-18mm will cover full frame at
13-14mm. Yet Canon uses 1.6X sensors, which would be even better (more
room to move round!) with sensor-based IS than the 1.5X format.

The only lens I know which causes problems with sensor-based IS on the
KM/Sony 1.5X bodies is the Sigma 30mm f1.4 - it was, I think, really
designed to work on Canon 1.6X or Sigma 1.7X sensors, and it's already
pushing its coverage on 1.5X when wide open.

David
  #18  
Old January 11th 07, 11:46 PM posted to rec.photo.digital.slr-systems
King Sardon
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Posts: 242
Default Are IS lenses doomed ?

On Thu, 11 Jan 2007 20:02:55 +0100, "Ståle Sannerud"
wrote:


I can't find the article but I remember reading about the comparison
between in-camera IS and in-lens IS. It stated that the in-camera IS
would prevent a full sized sensor from working with the in-camera IS. It
stated that the camera would be very large to allow for full sensor
movement and the light from the lens could fall off the edges of the
sensor, therefore even a larger then full sensor was needed, thus making
the camera even larger.

Am I blowing smoke or does anyone else remember this?


It's quite obvious if you think about it. The lens throws a circular,
fixed-size image into the camera. The size of this image circle is designed
to cover the film frame (or sensor, obviously) and not a smidgeon more than
necessary- or, if the image circle size IS significantly bigger than the
film frame you will have to carry around a lens that is correspondingly
larger, heavier and more expensive than would otherwise be the case.

Now, with in-camera IS the sensor has to move around to "chase" the image as
it wobbles around the sensor plane as your hands shake. The image circle is
of course constant and stays in place, so the sensor has a hard limit on how
far it can move in any direction before parts of it actually pokes out into
the darkness outside the image circle.

So, in-body IS is a good idea only as long as the image circle is
sufficiently larger than the sensor. A full-frame sensor on a full-frame
lens is a particularly bad candidate for in-body IS, an APS-sized sensor on
a "digital" APS-sized lens with reduced image circle size ain't too hot a
proposition either. Full-frame lens and APS-sized sensor gives you the most
leeway.

Compare this to an IS lens, which de facto lets the image circle chase the
wobbling image so that it stays in the same place relative to the sensor.


Camera shake shakes the image, not the image circle, which is fixed by
the optical axis (with IS is turned off). With IS now on, the
corrective element moves the image circle around so that the image is
placed correctly.

So yes, IS lets the image circle chase the wobbling image so that it
(the IMAGE) stays in the same place relative to the sensor. The
relationship between sensor and image circle is the same as for
in-camera IS. The difference is that with lens-based IS, the image
circle moves, whereas with in-camera, the sensor moves.

The image circle demands are the same for the two situations. However,
not having to have an IS group in the lens allows for a simpler
optical design (read: cheaper and maybe better performance).

KS

  #19  
Old January 12th 07, 12:09 AM posted to rec.photo.digital.slr-systems
David Littlewood
external usenet poster
 
Posts: 250
Default Are IS lenses doomed ?

In article , David Kilpatrick
writes
David Littlewood wrote:
I think I must have missed some vital point here, David. How does
an angular movement of the camera, which moves the image in linear
fashion along the sensor, require a change in the angular orientation
of the sensor. ISTM that it must require a linear movement of the
sensor to correct it.


I didn't mean the sensor changes angle in any way - it correct while
remaining strictly plane-parallel in its film plane. The calculation as
to how much linear movement to give is based on research into camera
shake, which shows that linear movement of the entire camera is rare
and causes very little visible shake; angular (so-called rotational)
shake is universally the main cause of unsharpness, but it has to be
corrected by a linear movement of the sensor corresponding to the image
movement.


Thanks; I think misunderstood your previous post. The above matches my
understanding; clearly you are right that linear displacement will cause
a very small effect compared with angular changes.

This subject has been discussed to death on the Sony forum on dPreview
as a result of a misinformed ideas by a physics graduate (it's very
easy to get it wrong if you think camera shake is a displacement of the
lens axis, rather than a dip/swing/tilt of the lens axis).


Not a forum I follow, but thanks.

My conclusion, after some very useful posts from others including one
which emphasised that long lenses don't need greater sensor movemen if
you stick to the rules about shutter speeds (with the IS factor
included), was that the programming is pretty complex and relies on
'typical' shake detection. There is no way the sensors in the Sony can
really tell whether displacement, rotation, etc is causing them to
detect motion. Somewhere in the system (same goes for IS in lens) the
designers have said 'if the signal from the sensors is THIS, the
required correction will be amost certainy be THIS'. It is not actually
a direct link.

I can imagine this would be a reasonable approximation, except for
lenses where there is significant shape distortion at the edges (i.e.
very wide lenses) - but these are the IS is least needed in normal use.

David
--
David Littlewood
  #20  
Old January 12th 07, 02:23 AM posted to rec.photo.digital.slr-systems
Mark²
external usenet poster
 
Posts: 3,185
Default Are IS lenses doomed ?

Skip wrote:
"VC" wrote in message
...
snip a bunch of words
There is a very small advantage in having IS in the lens but it is
not significant enough to grant double and triple cost of the same
quality lenses.
What do you guys think ?

I keep seeing this bandied about as the premium for IS/VR, but
nowhere do I see it in actual practice. It is about a $400-500
increase in price over the non IS version, if such does exist in the
lineup. The only times this has occurred is with the old 75-300, a
cheap lens with a gimmick, as far as I am concerned


I think it was more than a gimmick. I used that lens in Alaska in 1997, and
it allowed decent shots that would have been total garbage without it. Was
it a great optic, in strict optical terms? No. Did it render FAAAAR better
captures than its non-IS sibling would have? Absolutely. --I was hanging
out the window of engine-running shuttle-buses in Denali. -No tripod or
monopod was possible. In situations like these, the lens was definitely
worth having. I gave it to my dad, and he's happily shooting with it on
his 10D...

, the 70-200 f2.8L
($1100 vs $1600) and the current 70-200 f4L ($600+ vs. $1100). Not
exactly triple the price. When you get into the long teles, the
price premium becomes such an insignificant part of the whole as to
drop out of consideration, like with the 600mm f4L at more than $7000.
So far, newer Canon IS lenses maintain their lead over sensor based
IS, the 24-105 f4L and 70-200 f4L IS lenses give a minimum of 4 stops
of correction.


--
Images (Plus Snaps & Grabs) by Mark² at:
www.pbase.com/markuson


 




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