further help needed with Rebel/ M95 possible setup

Thanks, Chris, for the tip you provided in my last thread. I have also been
following a couple of the other threads here and *magically* I can now see
what M95 will look like with a Canon Rebel T3 and my ETX-90, according to
the program CCD Calculator. Note that I choose the "Canon 400D" option in
the program camera list since the T3 wasn't an option. I hope this has the
same CCD area as the T3. Assuming it does, I still have a problem.
Coupling the camera directly to the ETX, the field of view appears to be
huge and a lot bigger than I thought (unless I am in error). I'm concerned
that the field will be too large to sufficiently show a good sized M95 and
SN. Is there anything I can do about this or will the image still look fine
after cropping? Another possible problem: the only clock drive I have is
the one built into the ETX-90RA. Of course, I'm going to mount the base on
a heavy duty tripod I have here that was originally made for broadcast TV
cameras, but I'm concerned about the weight of the camera affecting the
drive. Is it still possible to get 30 second error free exposures assuming
I can get the mount into a good polar alignment?

Thanks again,
Ron

On Mon, 2 Apr 2012 11:39:45 -0400, "L Ron Hubble"
wrote:

Thanks, Chris, for the tip you provided in my last thread. I have also been
following a couple of the other threads here and *magically* I can now see
what M95 will look like with a Canon Rebel T3 and my ETX-90, according to
the program CCD Calculator. Note that I choose the "Canon 400D" option in
the program camera list since the T3 wasn't an option. I hope this has the
same CCD area as the T3. Assuming it does, I still have a problem.
Coupling the camera directly to the ETX, the field of view appears to be
huge and a lot bigger than I thought (unless I am in error). I'm concerned
that the field will be too large to sufficiently show a good sized M95 and
SN. Is there anything I can do about this or will the image still look fine
after cropping?

Don't worry about the field of view. What you are interested in is the
scale of the object. In this case, your camera has 5.2 um pixels and
your scope has a focal length of 1250 mm. That means your image scale
is 0.86 arcsec/pixel. Since that's probably oversampled considering
your seeing conditions and tracking capability, there's no point in
trying to get finer resolution. At that scale, M95 (which is ~3 arcmin
in diameter) will produce an image 209 pixels wide. That's very good
for this object- larger than I got on a semi-professional research
scope a couple of weeks ago.

http://cloudbait.com/csas/sn2012aw.jpg

Another possible problem: the only clock drive I have is
the one built into the ETX-90RA. Of course, I'm going to mount the base on
a heavy duty tripod I have here that was originally made for broadcast TV
cameras, but I'm concerned about the weight of the camera affecting the
drive. Is it still possible to get 30 second error free exposures assuming
I can get the mount into a good polar alignment?

I would think you should be able to manage 30-second exposures if you
are very careful with aligning and balancing the scope/camera. But the
only way you'll know for sure is to try it. You can only take analysis
so far... at some point you need to do some experiments.

On Apr 2, 10:39*am, "L Ron Hubble" wrote:
*Is it still possible to get 30 second error free exposures assuming
I can get the mount into a good polar alignment?

Thanks again,
Ron

It is highly doubtful that you will get 30 seconds of error-free
tracking at your pixel scale and focal length using the simple spur
gear drive in the ETX, even with perfect polar alignment. Precision
mounts running exact sidereal drive rates with zero periodic error can
only accomplish this near the zenith, and must change drive rates in a
complex fashion in order to accurately follow the stars across the
sky. You will undoubtedly get some sort of image in 30 seconds, and if
you know advanced processing techniques, you can actually use data
that has trailed stars. You will need many many 30 second images and
combine them and process them to bring out detail, but since the core
of M95 is so bright, and the SN is also bright right now, the task is
somewhat easier.

Uncarollo

Thanks again, Chris. I took a look at your image and it is indeed very
good, IMO. May I ask what size scope, exposure times, camera, etc?

When I look at others taking the M95/SN images, I do see pretty long
exposure times as uncarollo pointed out. Some of these longer times were
with the larger scopes.

I know what you mean about overemphasizing. I do it all the time, but in
this case the driving force is that I am borrowing the camera so I don't
have much time to experiment much.

BTW, would you or anyone else here happen to know how long a SN like this
will remain so before fading into oblivion?

Ron


"Chris L Peterson" wrote in message
...
On Mon, 2 Apr 2012 11:39:45 -0400, "L Ron Hubble"
wrote:

Thanks, Chris, for the tip you provided in my last thread. I have also
been
following a couple of the other threads here and *magically* I can now see
what M95 will look like with a Canon Rebel T3 and my ETX-90, according to
the program CCD Calculator. Note that I choose the "Canon 400D" option in
the program camera list since the T3 wasn't an option. I hope this has
the
same CCD area as the T3. Assuming it does, I still have a problem.
Coupling the camera directly to the ETX, the field of view appears to be
huge and a lot bigger than I thought (unless I am in error). I'm
concerned
that the field will be too large to sufficiently show a good sized M95 and
SN. Is there anything I can do about this or will the image still look
fine
after cropping?

Don't worry about the field of view. What you are interested in is the
scale of the object. In this case, your camera has 5.2 um pixels and
your scope has a focal length of 1250 mm. That means your image scale
is 0.86 arcsec/pixel. Since that's probably oversampled considering
your seeing conditions and tracking capability, there's no point in
trying to get finer resolution. At that scale, M95 (which is ~3 arcmin
in diameter) will produce an image 209 pixels wide. That's very good
for this object- larger than I got on a semi-professional research
scope a couple of weeks ago.

http://cloudbait.com/csas/sn2012aw.jpg

Another possible problem: the only clock drive I have is
the one built into the ETX-90RA. Of course, I'm going to mount the base
on
a heavy duty tripod I have here that was originally made for broadcast TV
cameras, but I'm concerned about the weight of the camera affecting the
drive. Is it still possible to get 30 second error free exposures
assuming
I can get the mount into a good polar alignment?

I would think you should be able to manage 30-second exposures if you
are very careful with aligning and balancing the scope/camera. But the
only way you'll know for sure is to try it. You can only take analysis
so far... at some point you need to do some experiments.

On Mon, 2 Apr 2012 18:06:14 -0400, "L Ron Hubble"
wrote:

Thanks again, Chris. I took a look at your image and it is indeed very
good, IMO. May I ask what size scope, exposure times, camera, etc?

The image was made with a 16" DFM RC, using an Apogee Alta U47 1Kx1K
back illuminated camera. The image is a stack of ten 90-second frames.

BTW, would you or anyone else here happen to know how long a SN like this
will remain so before fading into oblivion?

This is a Type IIP supernova which peaked about a week ago, at ~Mv
12.7. It's currently around Mv 13, and this type of supernova will
typically show a very slow decay of 0.0075 magnitudes/day for quite
some time- probably another three months or longer.

"Chris L Peterson" wrote in message
...
On Mon, 2 Apr 2012 18:06:14 -0400, "L Ron Hubble"
wrote:

Thanks again, Chris. I took a look at your image and it is indeed very
good, IMO. May I ask what size scope, exposure times, camera, etc?

The image was made with a 16" DFM RC, using an Apogee Alta U47 1Kx1K
back illuminated camera. The image is a stack of ten 90-second frames.

If yours are that, I can only imagine what it will be for the puny ETX. I
suppose I could stack luminances over many nights as long as the SN
brightness remains, but this would take too much time. Also, not having
gone the DSO astrophotography route before, I'm new to dark frames, flats,
etc so that's only going to cut into my timing.

So, this time at least, it looks like I'll just admire the work of others.

Thanks again for your time and response.

Ron


BTW, would you or anyone else here happen to know how long a SN like this
will remain so before fading into oblivion?

This is a Type IIP supernova which peaked about a week ago, at ~Mv
12.7. It's currently around Mv 13, and this type of supernova will
typically show a very slow decay of 0.0075 magnitudes/day for quite
some time- probably another three months or longer.