Ad Astra Observatory

On Jun 9, 2008, at 9:13 AM, Jimbo S. Harris wrote:

> Art Morton wrote:
>>>> How much of the Veil were you able to cram into one shot? I would

>>>> assume that you could get either 6960 or 6992 but not both at
>>>> once…
>>>> I can only get one of these on the ST-8, I was going for 6992. I
>>>> had imaged it early with the AT-EDT 80 and wanted to compare
>>>> images and color. I can not get both of them in the FOV.
>>> The 80 would do a better job — more room around the object, and

>>> probably some of the wispy “middle” stuff, too.
>>
>> You are correct. I did get just one or two good frames for NGC
>> 6960(I think that is the one to the west) I have attached it. The
>> object is just too big. The 80 will do a far better job on that
>> one. I also have to find out how to handle that darn bright star.

> I hate to suggest this, but maybe adding some diffraction spikes
> would throw enough light out of the star and into the spikes that it
> would help your blooming problem? Just a thought. Diffraction spikes
> affect “point” sources more than extended sources, so I’d expect the
> nebula would still show up well.

/*

Very funny.

*/
>
>> I have attached one of the green frames. I did not get the others,
>> because the sun came up. I will have to try again later. This is
>> a 600 second exposure and it seem like it is not enough or there is

>> just little green in the object.
> There’s not a lot of green in the object. There’s a little OIII, but
> that’s it. It’s mostly pink.

/*

I need to calibrate the filters I am using. They are a little

different to the SBig ones, and I never correctly configured the color
combine. I just started shooting.

*/
>
>>> I am still fighting some kind of RA drift demon.
>>>> GFG! Are you guiding with Max or is this unguided drift?
>>> Max or ST-4 native. Both exhibit the problem.

>>>> Did you use the polar alignment tool in the Gemini? Can you tell
>>>> me a little more of what is going on?
>>> It seems like I did this, but I’m still a little confused about
>>> the polar alignment tools and the A: E: display — when I pick the
>>> first few stars as I’m aligning, it says “off by 30+ arcmin”, then

>>> as I get more stars, it starts saying smaller and smaller errors
>>> until it says “off by 1 arcmin” at which point I stop. Does this
>>> mean that it’s correcting for a bad polar alignment, or does it
>>> mean that it thinks I have a good polar alignment? I’m confused.

>> */
>>
>> Ah Ha! This is not the polar alignment tool. What you are talking
>> about is building a Pointing Model.
> There are 2 polar alignment tools in the Gemini menu. Polar Align
> Assist requires *no pointing model*. Polar Axis Correct requires
> *pointing model to be set up with at least 5 stars*.

>
> So, I was going to do Polar Axis Correction, so I set up my pointing
> model. When I set up the pointing model, this is what happens:
> 1) cold start
> 2) goto bright star -> synchronize
> 3) goto another bright star -> additional align (this is the

> important part) A: is usually like 34′ and E: is similar, maybe 20′
> 4) goto a third star -> additional align now A: is something like
> 14′ and E is 1′ or so

> 5) goto a 4th, 5th, etc. star, meridian flipping as necessary At
> some point, I get A: 0′ and E: 1′ and then I stop building the
> pointing model.
>
> So the question is, am I building in a correction for a misaligned

> polar axis into the pointing model? I’m unsure why the errors seem
> to get smaller and smaller as I put in more stars.
>
> What I’m saying is that I think that I’m misreading those numbers.
> They are not telling me that my *polar alignment* is great, just
> that the *pointing model* is good enough to overcome my crappy polar

> alignment.

>
>>
>> You would have remembered all this. PinPoint tells me more often
>> than not that I am within 1 Degree of north. Most of the time, I
>> auto guide, but if there are not a lot of stars in the field, I
>> have NOT guided and gotten good results up to 600 sec with a good

>> alignment. There is not drift and you have seen the 0.00
>> corrections. I am impressed with the thought and the math that
>> went into this too.
>>
> I need to get this part figured out. I think my polar alignment is
> off.

/*

I think so too, but just a little. The pointing model does not
correct anything with the polar alignment. It will however allow you
to find things and put them in the center of the eye piece when the
polar alignment is not real good.

*/
>
>>
>> I have also used the method you have posted on your page. That

>> works perfect too, so I am wonder if the settings for the mount are
>> correct, and that may be worth another visit.
> I need to do my “CCD alignment” routine again. One problem that I’m
> having is that I have no earthly idea how to get the Gemini to go at
> 2x sidereal. I’ve sent James Bielaga an email asking him how to get

> that done. Without getting the drive to turn off in one direction,
> the alignment routine will not be as accurate.

/*

Yea, I have not been able to do that. Unplugging the cable makes the
Gemini cranky.

*/

>
>
> I did the polar axis correction routine over the weekend. It
> suggested I move the polar axis some in azimuth, which I expected.
> BTW, my polar alignment scope still says that Polaris is in the
> wrong spot. I’m not sure what to make of that. I didn’t try any long
> exposures. I’m so tired right now that I kept bumping into the mount

> and screwing up my pointing model.

/*

I do not use my polar scope for perfect alignment, just to get some
where close. Once I am close I use the software tools to get the
alignment I need to image unguided. My polar scope does not have a
very precise fit. There is plenty of slop, so I know that I can only
get close with it, but not right on.

The only other thing I can think of is to make sure that the Gemini
Base is level.

*/
>
>
> More later.
>
> J