Dpreview does away with formal resolution tests in theirreviews

On Wed, 02 May 2012 06:54:35 -0700, RichA wrote:

On May 2, 5:52Â*am, Eric Stevens wrote:
On Wed, 02 May 2012 01:02:35 -0400, John A.
wrote:









On Wed, 02 May 2012 13:29:03 +1200, Eric Stevens
wrote:

On Tue, 01 May 2012 15:51:17 -0400, Alan Browne
wrote:

On 2012-04-30 22:55 , Eric Stevens wrote:
On Mon, 30 Apr 2012 19:13:56 -0400, Alan Browne
wrote:

On 2012-04-30 11:58 , RichA wrote:
http://www.dpreview.com/reviews/olympusem5/

Very nice stabilization system (pitch, roll, yaw, y, z).

I suspect only the X and Y rotational axiis matter Â*much.

Translation (y,z) are a lot of it (same as the Sony system).

The weakness of that is pitch and roll is also present. Â*Yaw is a
lesser concern. Â*When you depress the shutter you can easily roll
the camera a little. Â*Along the lens axis, if not well balanced, is
the other concern (pitch).

Pitch movement of the lens axis is the same as roll around the X
axis.

My point is that roll only matters if it deflects (as distinct from
rotates) the lens axis. The lever effect of a long lens axis (to the
subject) makes such movements critical.

So if the camera is spinning about the lens axis so as to turn, say,
ten degrees during the exposure, that will make no difference to the
shot so long as said axis itself doesn't move?

I was considering only the movements likely to be encountered in normal
use. I'm not quite sure how you could obtain 10 degrees rotation during
any exposure sufficiently short for any stabilisation system to have
any effect. In fact, I don't think any stabilisation system could cope
with 10 degrees of rotation.

Regards,

Eric Stevens

It can't. You'd have to have something like they use in the fire
control system of tanks to deal with that. I don't think it would fit
in the camera.

The gun (main armament) in a tank is a little larger and has to cope with
much greater movement than that which occurs in a camera.



--
Neil
Reverse ‘a’ and ‘r’
Remove ‘l’ to get address.

On Thu, 03 May 2012 05:49:02 -0500, "C. Neil Ellwood"
wrote:

On Wed, 02 May 2012 06:54:35 -0700, RichA wrote:

On May 2, 5:52*am, Eric Stevens wrote:
On Wed, 02 May 2012 01:02:35 -0400, John A.
wrote:









On Wed, 02 May 2012 13:29:03 +1200, Eric Stevens
wrote:

On Tue, 01 May 2012 15:51:17 -0400, Alan Browne
wrote:

On 2012-04-30 22:55 , Eric Stevens wrote:
On Mon, 30 Apr 2012 19:13:56 -0400, Alan Browne
wrote:

On 2012-04-30 11:58 , RichA wrote:
http://www.dpreview.com/reviews/olympusem5/

Very nice stabilization system (pitch, roll, yaw, y, z).

I suspect only the X and Y rotational axiis matter *much.

Translation (y,z) are a lot of it (same as the Sony system).

The weakness of that is pitch and roll is also present. *Yaw is a
lesser concern. *When you depress the shutter you can easily roll
the camera a little. *Along the lens axis, if not well balanced, is
the other concern (pitch).

Pitch movement of the lens axis is the same as roll around the X
axis.

My point is that roll only matters if it deflects (as distinct from
rotates) the lens axis. The lever effect of a long lens axis (to the
subject) makes such movements critical.

So if the camera is spinning about the lens axis so as to turn, say,
ten degrees during the exposure, that will make no difference to the
shot so long as said axis itself doesn't move?

I was considering only the movements likely to be encountered in normal
use. I'm not quite sure how you could obtain 10 degrees rotation during
any exposure sufficiently short for any stabilisation system to have
any effect. In fact, I don't think any stabilisation system could cope
with 10 degrees of rotation.

Regards,

Eric Stevens

It can't. You'd have to have something like they use in the fire
control system of tanks to deal with that. I don't think it would fit
in the camera.

The gun (main armament) in a tank is a little larger and has to cope with
much greater movement than that which occurs in a camera.

And they don't worry about rotation about the axis of the barrel.

Regards,

Eric Stevens

On 2012-05-03 16:58:13 -0700, John A. said:

On Fri, 04 May 2012 08:49:23 +1200, Eric Stevens
wrote:

On Thu, 03 May 2012 05:49:02 -0500, "C. Neil Ellwood"
wrote:

On Wed, 02 May 2012 06:54:35 -0700, RichA wrote:

Le Snip

It can't. You'd have to have something like they use in the fire
control system of tanks to deal with that. I don't think it would fit
in the camera.

The gun (main armament) in a tank is a little larger and has to cope with
much greater movement than that which occurs in a camera.

And they don't worry about rotation about the axis of the barrel.

IIRC they actively (or passively?) encourage it in the projectile.

To answer the question regarding encouraging rotation of the
projectile, there have been some changes in the manner tank guns gain
accuracy. Up until 1986 the M1 Abrams used the Royal Ordnance L52/M68
105mm rifled canon which proved inadequate.

In 1986, the upgraded M1A1 received the Rheinmetall L44/M256 120mm
smoothbore cannon. That is the gun currently found on all of the
upgraded Abrams tanks and the fine German Leopard 2.

The standard ammo most used is the kinetic energy penetrator type
M829/A2/A3 or Armor-Piercing, Fin-Stabilized, Discarding Sabot (APFSDS)
round. Rotation is not required, shear acceleration is all that is
needed to get that dart down range to punch through most anything.

It also fires the M830A1 High Explosive Anti-Tank, (HEAT) round which
also employs a sabot surrounding the primary submunition, no rifling
required.

Then it gets very nasty when it comes to engaging personnel with the
M1028 anti-personnel canister (APC) cartridge which delivers 1098
tungsten balls in a shotgun effect which is lethal out at 600 meters.

The latest projectile the M1/A1 Abrams and Leopard 2 are firing is the
XM1111 Mid-Range Munition Chemical Energy round or MRM-CE. This is a
guided munition using a dual mode seeker combining imaging IR and
semi-active laser guidance.
Guess what, no rifling is needed for the APC or MRM-CE.

Having said all of that the British Challenger 2 uses the L30A1 120mm
rifled gun, which still spins those English versions of the APFSDS
rounds, with their specialized "high explosive squash head" HESH rounds
down range.


--
Regards,

Savageduck

On 2012-05-03 16:49 , Eric Stevens wrote:
On Thu, 03 May 2012 05:49:02 -0500, "C. Neil Ellwood"

The gun (main armament) in a tank is a little larger and has to cope with
much greater movement than that which occurs in a camera.

And they don't worry about rotation about the axis of the barrel.

There are limits to any comparison across systems.

--
"A person with a new idea is a crank until the idea succeeds."
-Samuel Clemens.