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From: DanP on 1 Jun 2010 11:08
On 1 June, 13:50, James Nagler <jnag...(a)spamproofed.net> wrote:

> There's no free lunch with the mechanical contrivances in a dSLR. The only
> way to take a vibration-free image is by opening the shutter (securely
> mounted on a sturdy and dampened tripod) in a totally dark room and using
> an off-camera flash to expose your subject 30-60 seconds after you have
> opened the shutter. Off-camera flash is required because the firing of the
> flash itself imparts an impulse of motion.- Hide quoted text -

So explain me why my shot of the moon taken with a Canon SX100 at
360mm equiv is worse than the one taken with the Canon 500D at 250mm?


DanP
From: James Nagler on 1 Jun 2010 11:20
On Tue, 01 Jun 2010 15:43:52 +0100, bugbear
<bugbear(a)trim_papermule.co.uk_trim> wrote:

>James Nagler wrote:
>>
>> My 16" diameter (20" dia. OTA) reflector telescope weighs a total of 255
>> lbs. when completely set up. The cast-iron mount and counter-weights alone
>> weighing in at about 150 lbs. of that. Yet I can lightly tap the telescope
>> tube and it take about 20-40 seconds for the vibrations to completely
>> dampen down. (The "tap test" is well known to amateur astronomers, anything
>> under 60 seconds for vibrations to dampen down is considered "good".) It is
>> a well balanced telescope, just a standard 9v battery is enough to power
>> the tracking and go-to system (it is that well balanced). But at high
>> magnifications (600x-1000x) even the slightest disturbance will set up
>> visually obvious oscillations.
>
>Indeed. Fortunately most photographers are working
>at the equivalent of MUCH smaller
>magnifications.
>
> BugBear

This is true, but for the pixel-peeper, the above is valid information. You
will not get pixel-level resolution on any DSLR unless you lock up the
mirror and allow vibrations to damp-down before the exposure is made.

From: RichA on 1 Jun 2010 21:50
On May 31, 1:34 pm, Val Hallah <michaelnewp...(a)yahoo.com> wrote:
> On May 31, 7:17 pm, Rich <rander3...(a)gmail.com> wrote:
>
>
>
> > On May 31, 2:45 am, Val Hallah <michaelnewp...(a)yahoo.com> wrote:
>
> > > On May 31, 12:42 am, RichA <rander3...(a)gmail.com> wrote:
>
> > > > On May 30, 1:59 pm, Val Hallah <michaelnewp...(a)yahoo.com> wrote:
>
> > > > > On May 30, 5:58 pm, RichA <rander3...(a)gmail.com> wrote:
>
> > > > > > Perfect example.  Guy shoots a Panasonic GH1 hand-held at 1/3 sec and
> > > > > > f16 and wonders why his shots aren't sharp.  P&S's are weaned on
> > > > > > cameras that have infinite DOF and limited apertures (often don't
> > > > > > close down to lower than f6.3) so to them, the discipline needed to
> > > > > > shoot a DSLR or EVIL camera is alien.
>
> > > > > >http://forums.dpreview.com/forums/read.asp?forum=1041&message=35451698
>
> > > > > he needed one of these
>
> > > > >http://www.flickr.com/photos/40732837(a)N07/4628023291/
>
> > > > Here's one with the camera (well, the G1, GH1 with lesser sensor) he
> > > > couldn't get a sharp shot with and a long lens.
>
> > > >http://www.pbase.com/andersonrm/image/116038333/original
>
> > > how much did that lens cost ;?)
>
> > $300.00 I built it myself.  All it is is a 120mm wide, f8 1000mm
> > achromat.
>
> sounds cheap, do you have a picture of it ?

Yes, it is a telescope. Basic refractor telescopes are uncompressed
optics (for the most part), no heavy negative elements to make them
small. The lens and cell came from Sky Instruments, about $220 it and
the focuser. The tube was surplus aluminum tube. The rest I did
myself.

http://www.pbase.com/andersonrm/image/125151707

From: DanP on 2 Jun 2010 13:33
On Jun 2, 2:50 am, RichA <rander3...(a)gmail.com> wrote:
> On May 31, 1:34 pm, Val Hallah <michaelnewp...(a)yahoo.com> wrote:
>
>
>
>
>
> > On May 31, 7:17 pm, Rich <rander3...(a)gmail.com> wrote:
>
> > > On May 31, 2:45 am, Val Hallah <michaelnewp...(a)yahoo.com> wrote:
>
> > > > On May 31, 12:42 am, RichA <rander3...(a)gmail.com> wrote:
>
> > > > > On May 30, 1:59 pm, Val Hallah <michaelnewp...(a)yahoo.com> wrote:
>
> > > > > > On May 30, 5:58 pm, RichA <rander3...(a)gmail.com> wrote:
>
> > > > > > > Perfect example.  Guy shoots a Panasonic GH1 hand-held at 1/3 sec and
> > > > > > > f16 and wonders why his shots aren't sharp.  P&S's are weaned on
> > > > > > > cameras that have infinite DOF and limited apertures (often don't
> > > > > > > close down to lower than f6.3) so to them, the discipline needed to
> > > > > > > shoot a DSLR or EVIL camera is alien.
>
> > > > > > >http://forums.dpreview.com/forums/read.asp?forum=1041&message=35451698
>
> > > > > > he needed one of these
>
> > > > > >http://www.flickr.com/photos/40732837(a)N07/4628023291/
>
> > > > > Here's one with the camera (well, the G1, GH1 with lesser sensor) he
> > > > > couldn't get a sharp shot with and a long lens.
>
> > > > >http://www.pbase.com/andersonrm/image/116038333/original
>
> > > > how much did that lens cost ;?)
>
> > > $300.00 I built it myself.  All it is is a 120mm wide, f8 1000mm
> > > achromat.
>
> > sounds cheap, do you have a picture of it ?
>
> Yes, it is a telescope.  Basic refractor telescopes are uncompressed
> optics (for the most part), no heavy negative elements to make them
> small.  The lens and cell came from Sky Instruments, about $220 it and
> the focuser.  The tube was surplus aluminum tube.  The rest I did
> myself.
>
> http://www.pbase.com/andersonrm/image/125151707

So, for the moon shot, what was the focal lengths for the eyepiece and
camera?
Magnification is huge.

DanP
From: Chris Malcolm on 9 Jun 2010 19:38
In rec.photo.digital James Nagler <jnagler(a)spamproofed.net> wrote:
> On Tue, 01 Jun 2010 15:43:52 +0100, bugbear
> <bugbear(a)trim_papermule.co.uk_trim> wrote:

>>James Nagler wrote:
>>>
>>> My 16" diameter (20" dia. OTA) reflector telescope weighs a total of 255
>>> lbs. when completely set up. The cast-iron mount and counter-weights alone
>>> weighing in at about 150 lbs. of that. Yet I can lightly tap the telescope
>>> tube and it take about 20-40 seconds for the vibrations to completely
>>> dampen down. (The "tap test" is well known to amateur astronomers, anything
>>> under 60 seconds for vibrations to dampen down is considered "good".) It is
>>> a well balanced telescope, just a standard 9v battery is enough to power
>>> the tracking and go-to system (it is that well balanced). But at high
>>> magnifications (600x-1000x) even the slightest disturbance will set up
>>> visually obvious oscillations.
>>
>>Indeed. Fortunately most photographers are working
>>at the equivalent of MUCH smaller
>>magnifications.
>>
>> BugBear

> This is true, but for the pixel-peeper, the above is valid information. You
> will not get pixel-level resolution on any DSLR unless you lock up the
> mirror and allow vibrations to damp-down before the exposure is made.

Unless the shutter speed is fast enough.

--
Chris Malcolm
Warning: none of the above is indisputable fact.
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