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View Full Version : ASTRO: Comparision of C14/IMG1024S with AP155/ST10XME


Richard Crisp
February 16th 04, 01:06 PM
I used the same 3nm FWHM Cust Sci filter for both images.

The C14/Dream Machine (IMG10124S) camera was exposed for 20 minutes x 3
exposures.

the AP155/ST10XME was exposed for 15 minutes x 6 exposures.

Unfortunately I blew it: I should have exposed the AP155/ST10XME at 1x1
binning, but used 2x2 binning instead.

If I had done the 1x1 binning, then the plate scales would have been pretty
close: C14/DM: 1.12 arc-sec/pixel versus AP155/ST10: 1.29 arc-sec/pixel.

But using the 2x2 binning on the AP155/ST10XME gave me 2.59 arc-sec/pixel
instead :-(

The AP155 system was operating at f/7 while the C14 was operating at f/12.46

From an exposure perspective, the 2x2 binning used for the ST10 gave me a 4x
speedup, so equivalent exposures at 1x1 binning would have been one hour
sub-exposures for the same exposure depth.

Here's the comparison, flawed as it is:

http://www.rdcrisp.darkhorizons.org/comparison_of_ap155edf_page.htm

I will check, I may have some other data better for comparing. Still I think
the comparison is interesting. One thing that surprised me is that the stars
are a bit tighter with the C14. Although the larger aperture favors tighter
stars, I think the figuring of the optics for the C14 is not up to the same
level as the AP155. Still both did credible jobs.

Richard

Szaki
February 16th 04, 02:58 PM
There is some price difference , between the two scopes, also.

Julius


"Richard Crisp" > wrote in message
om...
> I used the same 3nm FWHM Cust Sci filter for both images.
>
> The C14/Dream Machine (IMG10124S) camera was exposed for 20 minutes x 3
> exposures.
>
> the AP155/ST10XME was exposed for 15 minutes x 6 exposures.
>
> Unfortunately I blew it: I should have exposed the AP155/ST10XME at 1x1
> binning, but used 2x2 binning instead.
>
> If I had done the 1x1 binning, then the plate scales would have been
pretty
> close: C14/DM: 1.12 arc-sec/pixel versus AP155/ST10: 1.29 arc-sec/pixel.
>
> But using the 2x2 binning on the AP155/ST10XME gave me 2.59 arc-sec/pixel
> instead :-(
>
> The AP155 system was operating at f/7 while the C14 was operating at
f/12.46
>
> From an exposure perspective, the 2x2 binning used for the ST10 gave me a
4x
> speedup, so equivalent exposures at 1x1 binning would have been one hour
> sub-exposures for the same exposure depth.
>
> Here's the comparison, flawed as it is:
>
> http://www.rdcrisp.darkhorizons.org/comparison_of_ap155edf_page.htm
>
> I will check, I may have some other data better for comparing. Still I
think
> the comparison is interesting. One thing that surprised me is that the
stars
> are a bit tighter with the C14. Although the larger aperture favors
tighter
> stars, I think the figuring of the optics for the C14 is not up to the
same
> level as the AP155. Still both did credible jobs.
>
> Richard
>
>
>

Richard Crisp
February 16th 04, 03:00 PM
"Szaki" > wrote in message
news:[email protected]_s04...
> There is some price difference , between the two scopes, also.
>
> Julius
>

Not to mention availability considerations.

rdc


>
> "Richard Crisp" > wrote in message
> om...
> > I used the same 3nm FWHM Cust Sci filter for both images.
> >
> > The C14/Dream Machine (IMG10124S) camera was exposed for 20 minutes x 3
> > exposures.
> >
> > the AP155/ST10XME was exposed for 15 minutes x 6 exposures.
> >
> > Unfortunately I blew it: I should have exposed the AP155/ST10XME at 1x1
> > binning, but used 2x2 binning instead.
> >
> > If I had done the 1x1 binning, then the plate scales would have been
> pretty
> > close: C14/DM: 1.12 arc-sec/pixel versus AP155/ST10: 1.29 arc-sec/pixel.
> >
> > But using the 2x2 binning on the AP155/ST10XME gave me 2.59
arc-sec/pixel
> > instead :-(
> >
> > The AP155 system was operating at f/7 while the C14 was operating at
> f/12.46
> >
> > From an exposure perspective, the 2x2 binning used for the ST10 gave me
a
> 4x
> > speedup, so equivalent exposures at 1x1 binning would have been one hour
> > sub-exposures for the same exposure depth.
> >
> > Here's the comparison, flawed as it is:
> >
> > http://www.rdcrisp.darkhorizons.org/comparison_of_ap155edf_page.htm
> >
> > I will check, I may have some other data better for comparing. Still I
> think
> > the comparison is interesting. One thing that surprised me is that the
> stars
> > are a bit tighter with the C14. Although the larger aperture favors
> tighter
> > stars, I think the figuring of the optics for the C14 is not up to the
> same
> > level as the AP155. Still both did credible jobs.
> >
> > Richard
> >
> >
> >
>
>

JJK
February 16th 04, 04:04 PM
I'd expect a thermally equilibrated C-14 to go deeper than an AP155,
everything else being equal.

I think a more interesting comparison would be between an AP 10" f/14.6
Mak-Cass and the C-14.

Were the images taken on the same day and time (i.e., was the seeing the
same)?

Are the two cameras matched in quantum efficiency at the wavelength in
question?

Were the images processed the same way (there are halo artifacts in the C14
image)?


"Richard Crisp" wrote:
> I used the same 3nm FWHM Cust Sci filter for both images.
>
> The C14/Dream Machine (IMG10124S) camera was exposed for 20 minutes x 3
> exposures.
>
> the AP155/ST10XME was exposed for 15 minutes x 6 exposures.
>
> Unfortunately I blew it: I should have exposed the AP155/ST10XME at 1x1
> binning, but used 2x2 binning instead.
>
> If I had done the 1x1 binning, then the plate scales would have been
pretty
> close: C14/DM: 1.12 arc-sec/pixel versus AP155/ST10: 1.29 arc-sec/pixel.
>
> But using the 2x2 binning on the AP155/ST10XME gave me 2.59 arc-sec/pixel
> instead :-(
>
> The AP155 system was operating at f/7 while the C14 was operating at
f/12.46
>
> From an exposure perspective, the 2x2 binning used for the ST10 gave me a
4x
> speedup, so equivalent exposures at 1x1 binning would have been one hour
> sub-exposures for the same exposure depth.
>
> Here's the comparison, flawed as it is:
>
> http://www.rdcrisp.darkhorizons.org/comparison_of_ap155edf_page.htm
>
> I will check, I may have some other data better for comparing. Still I
think
> the comparison is interesting. One thing that surprised me is that the
stars
> are a bit tighter with the C14. Although the larger aperture favors
tighter
> stars, I think the figuring of the optics for the C14 is not up to the
same
> level as the AP155. Still both did credible jobs.
>
> Richard

Richard Crisp
February 16th 04, 05:51 PM
"JJK" > wrote in message
...
> I'd expect a thermally equilibrated C-14 to go deeper than an AP155,
> everything else being equal.
>
> I think a more interesting comparison would be between an AP 10" f/14.6
> Mak-Cass and the C-14.


I'd love to have the 10" AP to use for the comparison!


>
> Were the images taken on the same day and time (i.e., was the seeing the
> same)?

Unfortunately no

>
> Are the two cameras matched in quantum efficiency at the wavelength in
> question?


They aren't matched very well anywhere. The KAF3200ME in the ST10XME has
lower QE pretty much across the board.
It also has 6.8 x 6.8 micron pixels versus 24x24 micron pixels.

About the only thing that is matched is the plate scale is similar in the
Thor's image. The plate scale of the c14/img1024s is 1.12 arc-sec/pixel
while for the AP155/st10xme, it is 1.29 arc-sec/pixel.


>
> Were the images processed the same way (there are halo artifacts in the
C14
> image)?

processed very similarly. The image saturated in the C14 (the brighter
stars). Saturated images that have been deconvolved usually show rings
around the stars.

I hope to make a more scientific comparison of the cameras in the future by
swapping cameras into the same scope on the same night etc. Just need clear
skies to do so.

Someone had told me that for extended objects like nebulae, that the f/ratio
was the determining factor in exposure time. That apparently is not all of
it.

Richard

>
>
> "Richard Crisp" wrote:
> > I used the same 3nm FWHM Cust Sci filter for both images.
> >
> > The C14/Dream Machine (IMG10124S) camera was exposed for 20 minutes x 3
> > exposures.
> >
> > the AP155/ST10XME was exposed for 15 minutes x 6 exposures.
> >
> > Unfortunately I blew it: I should have exposed the AP155/ST10XME at 1x1
> > binning, but used 2x2 binning instead.
> >
> > If I had done the 1x1 binning, then the plate scales would have been
> pretty
> > close: C14/DM: 1.12 arc-sec/pixel versus AP155/ST10: 1.29 arc-sec/pixel.
> >
> > But using the 2x2 binning on the AP155/ST10XME gave me 2.59
arc-sec/pixel
> > instead :-(
> >
> > The AP155 system was operating at f/7 while the C14 was operating at
> f/12.46
> >
> > From an exposure perspective, the 2x2 binning used for the ST10 gave me
a
> 4x
> > speedup, so equivalent exposures at 1x1 binning would have been one hour
> > sub-exposures for the same exposure depth.
> >
> > Here's the comparison, flawed as it is:
> >
> > http://www.rdcrisp.darkhorizons.org/comparison_of_ap155edf_page.htm
> >
> > I will check, I may have some other data better for comparing. Still I
> think
> > the comparison is interesting. One thing that surprised me is that the
> stars
> > are a bit tighter with the C14. Although the larger aperture favors
> tighter
> > stars, I think the figuring of the optics for the C14 is not up to the
> same
> > level as the AP155. Still both did credible jobs.
> >
> > Richard
>
>

Richard
February 16th 04, 08:52 PM
"Richard Crisp" > wrote in message >...
> I used the same 3nm FWHM Cust Sci filter for both images.
>
> The C14/Dream Machine (IMG10124S) camera was exposed for 20 minutes x 3
> exposures.
>
> the AP155/ST10XME was exposed for 15 minutes x 6 exposures.
>
> Unfortunately I blew it: I should have exposed the AP155/ST10XME at 1x1
> binning, but used 2x2 binning instead.
>
> If I had done the 1x1 binning, then the plate scales would have been pretty
> close: C14/DM: 1.12 arc-sec/pixel versus AP155/ST10: 1.29 arc-sec/pixel.
>
> But using the 2x2 binning on the AP155/ST10XME gave me 2.59 arc-sec/pixel
> instead :-(
>
> The AP155 system was operating at f/7 while the C14 was operating at f/12.46
>
> From an exposure perspective, the 2x2 binning used for the ST10 gave me a 4x
> speedup, so equivalent exposures at 1x1 binning would have been one hour
> sub-exposures for the same exposure depth.
>
> Here's the comparison, flawed as it is:
>
> http://www.rdcrisp.darkhorizons.org/comparison_of_ap155edf_page.htm
>
> I will check, I may have some other data better for comparing. Still I think
> the comparison is interesting. One thing that surprised me is that the stars
> are a bit tighter with the C14. Although the larger aperture favors tighter
> stars, I think the figuring of the optics for the C14 is not up to the same
> level as the AP155. Still both did credible jobs.
>
> Richard

The C14 shows better resolution, more detail in most areas. The contrast
of the AP155 shot seems "pushed." I noticed less tonal details in the
cloud and the "grain" is more noticeable in the AP155 shot. But
display good detail.
-Rich

Richard Crisp
February 17th 04, 12:30 AM
"Richard" > wrote in message
om...
>
> The C14 shows better resolution, more detail in most areas. The contrast
> of the AP155 shot seems "pushed." I noticed less tonal details in the
> cloud and the "grain" is more noticeable in the AP155 shot. But
> display good detail.
> -Rich


the ap shot is more grainy because the exposure depth was not as good as the
c14 shot. When you push it hard, it gets grainy.