Re: Newbie looking for advice/uber oops
- --- In email@example.com, "Geoffrey Ogden"
> --- In firstname.lastname@example.org, "ubergroovin" <ubernator@h...>Ok, I was thinking like Geoff also, most people think of the olympus
> > Since you mention that you are a pro 35mm film guy,
> But I'm a professional photographer and want to
> > dabble with my
> > > Olympus E-1 on well founded optics.
> Uber oops, Keith. The Olympus E-1 is a 4.9 MP camera.
as a film camera, as OM-1's are very popular among
astrophotographers. I am happy with nikon manual bodies myself, even
without a mirror lock.
I still think the c9.25 is a winner for imageing, and the chip of a
DSLR is almost as big as 35mm, and bigger than many CCD cameras, so
you still get the benifits of the improvements of the c9.25.
The construction of the c9.25 is much more rugged than the OTA of the
RCX400, and there is alot less than can go wrong (the RCX has all
kinds of electronics inside the OTA even).
The RCX is not yet proven, and the c9.25 is... and I also think you
would be happier with a gem than you would be with a big huge wedge
A C11 is another consideration, but it does not have the same optical
design of the c9.25, the unique overacheiver of the SCT type.
Correction to my earlier post, the c9.25 does not have a smaller
obstruction than other SCTS, but from the looks of things, it is
smaller than the obstruction of the RCX.
A C925 is about $2000 with XLT coatings, and $6000 could buy one hell
of a mount, or a $3000 CGE mount (or save and get the CGE925 package)
and alot of needed accessories, such as focal reducers, LP filters,
IR filters, UV filters, premium eyepieces for visual use, a CCD/DSI
for autoguiding etc... It is the accessories that add up... a $4000
CGE925 setup could come to $8000 when all is said and done =)
- --- In email@example.com, Bruce MacDonald <brumac@g...>
> I'd be interested in knowing how a numeric value in a file canWell there are a couple of different ways to go about it - you are
> reveal how it has been changed to some other numeric value.
> Do you have any references?
> Perhaps it is done statistically, but however it is done,
> I'm fascinated.
correct for one way.
The first scenario is pretty straight forward. If you know before
hand that the digital file (doesn't matter if it is a picture, a
movie, or a M$ Word document) requires authentication, there are
plenty of well understood and defined methods for watermarking,
digitally signing, etc a file. At a later date, the file can easily
be assessed to determine if the watermark or digital signature has
been altered - pretty straight forward and common practice. It does
require you to know before hand that you want to authenticate the
file at a later date and have the schema set up in advance.
But I don't think that is where you were heading. I think you are
more concerned about when Bubba submits a picture of green aliens
landing in his back yard and claiming "See, ET visits me every
thursday to watch Friends and drink beer" is that a valid picture.
For that, you are on the correct track - statistical testing can be
done to detect modifications to digital pictures.
I'll preface some of this first: I don't believe that if a single
pixel had its shading changed in a 6MP file that these methods would
detect it. Having said that, neither would your eyes. When we are
talking about manipulating files, it is of the magnitude that the
human eye can actually perceive the change (otherwise, why would you
make the change, right?) Doing something like RBT stated - removing
a person in front of a white wall or making someone appear to be
doing something in a picture that wasn't actually done at the time it
was taken. Fair enough?
Here is a link to a LARGE (long and big file size) that talks about
several different statistical methods that can be used to detect
modifications to pictures. Different tools work better for different
types of edits, but the gist is the same.
There are plenty of other references as well - I just picked one that
gave a couple of different spins on it.
Also - this is just the stuff that is in public domain. I'd bet a
years salary that the folks at Ft Meade, Langely, etc have even more
sofisticated tools/methods that they've been using for years.
PS - I suppose we should probably continue this thread offline -
other than the Alien in the backyard, we've probably strayed far
enough from astonomy that it is no longer germain to this group...