[K-M - Sony] Damn! Now let's move on...

Paul Rubin wrote:

> David Dyer-Bennet <dd-b.RemoveThis@dd-b.net> writes:
>
>>I seem to remember the Nikon 2100 doing so, also.
>
>
> That would surprise me since the 3100 doesn't (unless I haven't
> spotted it).

Certainly surprised me. I went and dug my Canon A60 out & it does have
manual exposure.
 >> Stay informed about: [K-M - Sony] Damn! Now let's move on... 

On Fri, 27 Jan 2006 01:17:09 GMT, no_name <no_name.TakeThisOut@no.where.invalid> wrote:
> David Dyer-Bennet wrote:
>> Nonsense. Cheap digital P&S cameras are much more likely to support
>> manual exposure than cheap film P&S cameras are.
>
> Which cheap digital P&S supports manual exposure?

Define 'cheap'. Off-hand, the Canon A510, street price ~$180-190, has
full manual controls, including manual focus.

-dms
 >> Stay informed about: [K-M - Sony] Damn! Now let's move on... 

In article <NNidndVQK42L6UTenZ2dnUVZ_tGdnZ2d RemoveThis @comcast.com>, William
Graham <weg9 RemoveThis @comcast.net> writes
>
>Yes. I would have thought that mirror "slap" wouldn't affect the exposure
>for more than a second or so.

Generally that is probably true - you get away with it because the scene
contrast is quite low. It is much more demanding when scene contrast is
very high - and stars in a clear deep black sky are about as bad as it
gets.

>I would think that wind and earth vibration
>(like from the passing of trucks and the like) would be a much bigger issue
>with star photos.

Not if you site the tripod properly it isn't.

>My uncle built his own observatory when I was a kid, and
>he built the motor drives that tracked the stars in his telescope himself.
>But I wasn't interested in those days, so I didn't learn anything from him.
>(the story of my life) By the time I was old enough to be interested, all
>the people I could learn anything from were dead....:^)
>
I was going to post this in my previous reply but decided it was more
info than you needed, but since you have mentioned it, I'll add it now.
Some years ago a friend of mine designed and built his own 12"
Newtonian, complete with mount and observatory. I built the electronic
drive for it, so that he could dial up sidereal rate, lunar rate and,
with the aid of some tables, the exact rate to compensate for planetary
motion too. After a couple of weeks of using this he reported that he
was getting a 20arcsec cyclic error. I suspected my drive, he suspected
his mechanical design. Reviewing the mechanical design he came to the
conclusion that the worm drive was creating stress on two stub axles
that were 1/2" diameter but only 2" long. He revised the design and
replaced these with 3" diameter steel, still the same length. Problem
disappeared. Vibration of the drive never was a problem, flexure of the
mount was.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)
 >> Stay informed about: [K-M - Sony] Damn! Now let's move on... 

"Kennedy McEwen" <rkm RemoveThis @nospam.demon.co.uk> wrote in message
news:V2GviIEQCj2DFw3X@kennedym.demon.co.uk...
> In article <NNidndVQK42L6UTenZ2dnUVZ_tGdnZ2d RemoveThis @comcast.com>, William Graham
> <weg9 RemoveThis @comcast.net> writes
>>
>>Yes. I would have thought that mirror "slap" wouldn't affect the exposure
>>for more than a second or so.
>
> Generally that is probably true - you get away with it because the scene
> contrast is quite low. It is much more demanding when scene contrast is
> very high - and stars in a clear deep black sky are about as bad as it
> gets.
>
>>I would think that wind and earth vibration
>>(like from the passing of trucks and the like) would be a much bigger
>>issue
>>with star photos.
>
> Not if you site the tripod properly it isn't.
>
>>My uncle built his own observatory when I was a kid, and
>>he built the motor drives that tracked the stars in his telescope himself.
>>But I wasn't interested in those days, so I didn't learn anything from
>>him.
>>(the story of my life) By the time I was old enough to be interested, all
>>the people I could learn anything from were dead....:^)
>>
> I was going to post this in my previous reply but decided it was more info
> than you needed, but since you have mentioned it, I'll add it now. Some
> years ago a friend of mine designed and built his own 12" Newtonian,
> complete with mount and observatory. I built the electronic drive for it,
> so that he could dial up sidereal rate, lunar rate and, with the aid of
> some tables, the exact rate to compensate for planetary motion too. After
> a couple of weeks of using this he reported that he was getting a 20arcsec
> cyclic error. I suspected my drive, he suspected his mechanical design.
> Reviewing the mechanical design he came to the conclusion that the worm
> drive was creating stress on two stub axles that were 1/2" diameter but
> only 2" long. He revised the design and replaced these with 3" diameter
> steel, still the same length. Problem disappeared. Vibration of the
> drive never was a problem, flexure of the mount was.
> --
> Kennedy

I was also going to mention this:
I have often thought that the best way to do this was with two stepper
motors, a horizontal drive motor, and a vertical drive motor, and a
computer. First you put the crosshairs on a star, and then click the mouse.
Then after a few minutes, you put the crosshairs back on the same star, and
click the mouse again. The computer calculates the amount of horizontal and
vertical drift that took place between the two clicks, and adjusts the
velocity of the two motors to track that drift, and it doesn't either know
or care what caused the drift. - All reasons for the drift are automatically
compensated for, as long as the drift is linear during the next time period,
during which you are going to take the picture.
 >> Stay informed about: [K-M - Sony] Damn! Now let's move on... 

In article <krydndstMfIKOUfeRVn-iw.TakeThisOut@comcast.com>, William Graham
<weg9.TakeThisOut@comcast.net> writes
>
>I was also going to mention this:
>I have often thought that the best way to do this was with two stepper
>motors, a horizontal drive motor, and a vertical drive motor, and a
>computer. First you put the crosshairs on a star, and then click the mouse.
>Then after a few minutes, you put the crosshairs back on the same star, and
>click the mouse again. The computer calculates the amount of horizontal and
>vertical drift that took place between the two clicks, and adjusts the
>velocity of the two motors to track that drift, and it doesn't either know
>or care what caused the drift. - All reasons for the drift are automatically
>compensated for, as long as the drift is linear during the next time period,
>during which you are going to take the picture.
>
Do the maths - too many errors build up because you are extrapolating
from your initial estimate of motion. Also, the stars move in an arc
through the sky, not a straight line, so you need some reference of
where the pole is (ie. radius of the arc for that particular star) for
such technique to even remain within the errors of the extrapolation.

It is pretty well established that the simplest solution is a single
compensation drive on a polar aligned equatorial mount - ie. the axis of
rotation is aligned with the earth's, and thus rotation compensates for
it in a single motion. There are lots of variations.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)
 >> Stay informed about: [K-M - Sony] Damn! Now let's move on... 

"Kennedy McEwen" <rkm.DeleteThis@nospam.demon.co.uk> wrote in message
news:QvS+khCBtr2DFwWb@kennedym.demon.co.uk...
> In article <krydndstMfIKOUfeRVn-iw.DeleteThis@comcast.com>, William Graham
> <weg9.DeleteThis@comcast.net> writes
>>
>>I was also going to mention this:
>>I have often thought that the best way to do this was with two stepper
>>motors, a horizontal drive motor, and a vertical drive motor, and a
>>computer. First you put the crosshairs on a star, and then click the
>>mouse.
>>Then after a few minutes, you put the crosshairs back on the same star,
>>and
>>click the mouse again. The computer calculates the amount of horizontal
>>and
>>vertical drift that took place between the two clicks, and adjusts the
>>velocity of the two motors to track that drift, and it doesn't either know
>>or care what caused the drift. - All reasons for the drift are
>>automatically
>>compensated for, as long as the drift is linear during the next time
>>period,
>>during which you are going to take the picture.
>>
> Do the maths - too many errors build up because you are extrapolating from
> your initial estimate of motion. Also, the stars move in an arc through
> the sky, not a straight line, so you need some reference of where the pole
> is (ie. radius of the arc for that particular star) for such technique to
> even remain within the errors of the extrapolation.
>
> It is pretty well established that the simplest solution is a single
> compensation drive on a polar aligned equatorial mount - ie. the axis of
> rotation is aligned with the earth's, and thus rotation compensates for it
> in a single motion. There are lots of variations.
> --
> Kennedy

Of course....You are right.....I was assuming (stupidly, I might add) that
the drift was in a straight line, even though I have seen dozens of time
lapse star photos with their circular orbits around the North Star......
 >> Stay informed about: [K-M - Sony] Damn! Now let's move on... 

Daniel Silevitch wrote:

> On Fri, 27 Jan 2006 01:17:09 GMT, no_name <no_name DeleteThis @no.where.invalid> wrote:
>
>>David Dyer-Bennet wrote:
>>
>>>Nonsense. Cheap digital P&S cameras are much more likely to support
>>>manual exposure than cheap film P&S cameras are.
>>
>>Which cheap digital P&S supports manual exposure?
>
>
> Define 'cheap'. Off-hand, the Canon A510, street price ~$180-190, has
> full manual controls, including manual focus.
>
> -dms

Guess I should have said inexpensive, although given the way the value
of the dollar has declined, $200 isn't an awful lot. Cheap has other
connotations besides low price.

FWIW, the P&S digital I have does have manual controls, I just never
looked at them, using an SLR or DSLR whenever I wanted manual control.

I've kept the P&S digital for when I needed it quick & dirty without
having to think about exposure control; for those times when the scene
to be captured is more important than the image itself.
 >> Stay informed about: [K-M - Sony] Damn! Now let's move on...