«

"Owamanga" <owamanga-not-this-> a écrit dans le message de
news: ...
> On Tue, 02 Aug 2005 05:38:09 -0400, Ed Ruf <>
> wrote:

>
> I was under the impression that the viewfinder cover's purpose is to
> allow for accurate metering without viewfinder light effecting the
> outcome. Once the shutter is tripped the mirror blocks the light from
> the viewfinder doesn't it?

It should, but how to be absolutely sure? Some mirrors are smaller than they
used to be... (more recessed in more compact models?)
According to Canon (EOS D. Rebel for example) the use of the viewfinder
cover should be seriously considered.

Anyway, as said here after, if the flares show up in every night long
exposure regardless of the orientation of close sources of artificial light,
the viewfinder cover should not be the solution.


>
> Anyway, as others have suggested, this is caused by on-camera chip's
> thermal radiation affecting the sensor. Dark frame subtraction can
> help, but it, added to the hot-pixel filter stuff the D70 does
> automatically doesn't lend itself to scientific-quality astronomy
> images.
>
> I remember reading somewhere that there is a trick of turning the
> camera off during it's RAW write that will prevent it from running the
> hot pixel filter (which kills most of the fainter stars). I don't
> recall the details though.
>
> --
> Owamanga!
> http://www.pbase.com/owamanga

On Tue, 02 Aug 2005 12:38:55 GMT, in rec.photo.digital Owamanga
<owamanga-not-this-> wrote:

>On Tue, 02 Aug 2005 05:38:09 -0400, Ed Ruf <>
>wrote:
>
>>Try the les cap photo as Sheldon suggested. Also, don't forget to use the
>>viewfinder cover as any stray light captured by this will be recorded as
>>well. The purple cast you mention is in normal exposure shots as well?
>
>I was under the impression that the viewfinder cover's purpose is to
>allow for accurate metering without viewfinder light effecting the
>outcome. Once the shutter is tripped the mirror blocks the light from
>the viewfinder doesn't it?

I stand corrected. Should have checked the manual before putting foot in
mouth.
----------
Ed Ruf Lifetime AMA# 344007 ()
See images taken with my CP-990/5700 & D70 at
http://edwardgruf.com/Digital_Photog...ral/index.html

Okay, this thread was driving me nuts, so I took a few 2 minute exposures
with my D70 and the lens cover on. Completely black image from side to side
and corner to corner. Some were taken with the viewfinder convered, some
not.

Sheldon

Sheldon <> wrote:
> Okay, this thread was driving me nuts, so I took a few 2 minute exposures
> with my D70 and the lens cover on. Completely black image from side to side
> and corner to corner. Some were taken with the viewfinder convered, some
> not.

Sheldon,

Glad to hear that.

If there are any other D70 users out there who would be willing, I would
appreciate additional data points. Please let me know if you have any
noise problems with long exposures.

Thanks guys, you've been most helpful.

Kevin wrote:
> Sheldon <> wrote:
>
>>Okay, this thread was driving me nuts, so I took a few 2 minute exposures
>>with my D70 and the lens cover on. Completely black image from side to side
>>and corner to corner. Some were taken with the viewfinder convered, some
>>not.
>
>
> Sheldon,
>
> Glad to hear that.
>
> If there are any other D70 users out there who would be willing, I would
> appreciate additional data points. Please let me know if you have any
> noise problems with long exposures.
>
> Thanks guys, you've been most helpful.
>
>
Ok, I had a bash as well. At 2 minutes with NR Off & lens cap on I got a
purple flare at the top left corner while viewing it on the camera's LCD.

With NR On there was no purple flare.

BUT .... looking at both pictures ( RAW ) in Nikon Capture there was no
purple flare in either of the shots ... now I'm lost ??
Bernard

Sheldon --

Important detail: was NR on or off??

-=-Joe


In article <YZednWrSMamllG3fRVn->, Sheldon
<> wrote:

> Okay, this thread was driving me nuts, so I took a few 2 minute exposures
> with my D70 and the lens cover on. Completely black image from side to side
> and corner to corner. Some were taken with the viewfinder convered, some
> not.

Kevin <> wrote:
> We notice that on many of these long exposure shots, there are purple
> blobs in the upper left corner. Seems like the longer the exposure, the more
> pronounced the blobs are.

As others have pointed out, the simplest solution is to turn
on noise reduction.
See also
http://www.ooblick.com/text/noise-reduction/
for some pictures of this phenomenon.

--
Andrew Arensburger, Systems guy University of Maryland
arensb.no-bloody- Office of Information Technology
A problem can be found for almost every solution.