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Re: DEC move problem during autoguide

ancient.sull
 

Unfortunately I don't see how to turn off Dec corrections in one
direction and still dither. Is it possible to do that?

If I turn off Dec corrections in _both_ directions the oscillations
do go away (and again I can't dither).

I _think_ that if I use another camera to guide the problem goes
away. I only tested that once for 10 minutes before the clouds came
in but didn't see any oscillations guiding with the other camera (the
Remote guide head rather than ST402. Changing to the Remote Guide
Head meant I was using a different socket to connect the Autoguide
Cable).

I went back and forth repeatedly East to West and had no
oscillations, and guided to within about 0.5 arc seconds (without
adaptive optics) in the Eastern sky but to the West repeatedly got
these swings in Dec (only).


--- In ap-gto@..., chris1011@... wrote:

In a message dated 2/10/2008 12:27:22 AM Central Standard Time,
ancient.sull@... writes:


I take it back. I now _do_ think the problem is electrical. Try
this:

I turned off corrections in Y. The zig zagging stopped. That
means it
isn't mechanical, right?

So it likely is a sticking relay somewhere or a problem with the
AG
cable.
NO! It is NOT a sticking relay. See my previous posts - and yes, do
turn off
one of the Dec directions if you cannot set up the guiding software
to avoid
this oscillation any other way.

Rolando


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Re: Need Tripod/Pier advice

Kent Kirkley
 

In a message dated 2/11/08 7:03:01 PM, lane_davis@... writes:


I have a Mach1 on that sits on top of an AP wood tripod AWT000). I
originally had an AP 130 f8 riding on it and the combination was very
solid. I choose the tripod because it was easy to level on uneven
ground. Recently, I bought an AP155 f7 and sold the 130. The
combination of the mount, tripod and 155 is a little less stable - a
little more vibration damping time from focusing and more vibration
from wind. I am considering moving to an AP pier or the Losmandy G11
tripod. Do you think this would be a more stable combination? Is one of
these likely to be more stable than the other? Do you have any other
advice?

Lane
Lane:

I'm guessing from the above that you are a visual observer and not an imager?
Not that it would make all that much difference, in this instance.

Either the AP portable piers or the G11 Mini-Pier would be fine.
The approximate cost of either is about the same (new).

I've had a 1200GTO on the AP10x48 inch portable pier for a long time.
Its a very solid platform.

My only complaint about the AP portable piers is that they don't have a
leveling feature.
At remote locations this can be a problem when polar aligning.
Some people use the tension rods to 'tilt' the pier a little but that's not a
good solution.
I think it wouldn't be a big cost to AP to add 6-8 inch leveling screws to
the legs.

The newer G-11 Mini-Pier tripod does have heigth and leveling capability.
(the early G-11's had long fixed length legs)

Kent Kirkley





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Re: DEC move problem during autoguide

Roland Christen
 

In a message dated 2/11/2008 7:02:17 PM Central Standard Time,
llp41astro@... writes:


I have been following this thread with interest. However, at the
risk of showing my extreme ignorance, this is the first time I have
read aboout "Guide Parameters" in the way you are referring.
The software must know how long to push the button at 1x in order to
compensate for a measured pixel error. The only way it knows how to do that is to move
the scope at the 1x rate for a period of time and then divide the resultant
pixel change by the time in seconds. If the scope moves at the rate of 15
pixels per second, and you calibrate for 10 seconds, then you will have a 150 pixel
change. The resultant parameter number which will be recorded for that
direction will be 15 (i.e. 150pix divided by 10 sec = 15 pix/sec). Since there are 4
directions, two + and two -, then you will have 4 numbers, +15, -15, -15 and
+15 and an angle of 90 degrees - that is if the camera is at right angles to
the RA and Dec direction.

How to determine your theoretical parameter number? Let's say that your
scope's focal length is such that it produces a 1 arc second per pixel plate scale.
If you calibrate at 0 Dec, the number which should theoretically appear in
the 4 parameter positions will be 15. Anything very much lower than that for Dec
will cause problems because loop gain increases inversely with this number,
i.e. smaller number = larger gain, gain becomes infinite when the number
approaches zero, and the mount will simply run away at that point.

For RA, it is a different story, because this number will get smaller the
farther you get away from 0 Dec. As you approach +- 90 degrees Dec, the RA will
not move anymore and the numbers for RA will be zero, theoretically.

The RA numbers will almost always be correct and equal in the two directions
because the motors will never be asked to reverse direction. Reversing at 1x
is accomplished by stopping the motor and allowing the sky to move the star at
15 arc sec per second. The worm teeth are never unloaded and this "reversal"
takes place instantly. In Dec you must physically reverse motor direction,
therefore it becomes important for the worm to be fully meshed so that you do not
have huge time delay between forward and reverse motion.

Rolando


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Re: What Dec is best for calibrating was DEC move problem during au...

Roland Christen
 

In a message dated 2/11/2008 6:51:48 PM Central Standard Time,
ancient.sull@... writes:


One more question re calibration:

Calibrate near Dec 0? Or near the target? (Assume the target Dec isn't
too high. Say no more than +40).

I have "get dec from mount" ticked (and am running TheSky and Maxim)
Dec does not change, so you can calibrate anywhere, just not near the pole.
For best guiding I would uncheck the Dec value, because if it is checked, then
it modifies the RA gain depending on the Dec value. It is best to leave this
at 0 Dec. Again, this is for best guiding results.

Rolando


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Re: Mach 1

Roland Christen
 

In a message dated 2/11/2008 5:54:37 PM Central Standard Time,
ivanong@... writes:


The Mach1GTO takes a while to set up and take down. Many things to
screw and tighten- will take you about 40 min or so.
Really? Only takes me 5 minutes to set up my Mach 1. Plunk it into the pier,
tighten 3 hand knobs, attach scope to the dovetail plate, insert eyepiece,
look. What am I missing?

Rollie




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Re: DEC move problem during autoguide

Roland Christen
 

In a message dated 2/11/2008 3:50:44 PM Central Standard Time,
ancient.sull@... writes:


My problem is more like #2 - The mount tracks well for maybe a minute
or two, then starts going Y+, say. Rather than correct it just goes
further and further Y+ (total maybe 2-3 arc seconds). Finally the AG
algorithm brings it back to zero but soon (10seconds to 60 seconds)
it goes the other way (Y-).

This only happened to the west, but repeatedly to the West (two
nights in a row).

PoleAlignMax said my Polar Alignment error that night was less than
1/2 arc minute. It is certainly possible that PAM is wrong. With X
and Y corrections turned off I got less than an pixel drift in 5
minutes so the polar alignment has to be pretty good, right?

I will:

Recheck the alignment after PAM with a drift to be sure it is less
than my image scale (about 1.5"/pixel) per 5 minutes

Recalibrate to be sure that is right (the calibration was 30 seconds
in both axes and I was at 80% aggressiveness)

Post screen captures of the two AG settings pages and the tracking
error graph.

Is that what's needed?
If it goes +, then - then + etc, it sounds like your parameter numbers for
Dec are too low and you have loop gain that is too high, causing limit cycling.

30 sec calibration at 1x is fine, at .5x would be marginal and at .25x it
would be unacceptable.

Less than 1 pixel drift in 5 minutes is good enough to rule out sawtooth
oscillations and again point to high loop gain. Once you know your prameter
numbers by calculating them using your pixel scale and scope focal length, you can
determine if the numbers in your guider program are reasonable. If numbers are
too low, you can artificially raise them for that axis - let's say they
calculate, using your pixel scale and focal length, to be 12 and -12 for your Dec
axis. let's say that the numbers are 11.6 and -5. This is an instant red flag -
the numbers are not equal and one of them is way too low. This is a recipe for
instability. It is either caused by an improper cal run, or perhaps a very
large amount of reversal delay due to improper worm mesh. One quick way to fix
this temporarily is to raise the number from -5 to the theoretical value of
-12. You will find that the mount settles down instantly when the proper number
is placed into the box.

Rolando


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Re: DEC move problem during autoguide

Roland Christen
 

In a message dated 2/11/2008 3:31:43 PM Central Standard Time,
petrovic@... writes:


thank you for response! I have checked again my guiding parameters
and they are about as suggested in an earlier post on this forum
(Min=0.02/Max=0.3 backlash=0).
That is not a guide parameter number. Guide parameters are listed on the
Guider Settings page under X Speed and Y Speed. These numbers must match or be
close to what you calculate from your pixel scale/focal length.

As mentioned the polar alignment is not perfect, but maybe not the
cause for this problem. Mount tracks easy for hours most of time
within +/- 0.25 pixels.
I am not concerned about drift while autoguiding. What you need to do is
determine the drift when you are NOT guiding in Dec. What is the unguided Dec
drift?

I started immediately PulseGuide and took the first two test and both
showed very unusual images. The north move of cross test shows only a
small move, about 1/4th of the south cross side length.
That is not unusual. All that tells you is that the mount takes a significant
amount of time to reverse when going North and then South. The difference in
the length of these two arms is the dwell time or reveraso time. It says that
your worm gear is not fully engaged with the worm wheel. Normally it takes
about 1/2 second to fully reverse, so in a 5 second run north at 1x the line
will be short about 10%. If the line is short by 50% it says that your reversal
time in Dec is about 2.5 seconds. This is a bit high, so I would check the worm
mesh. This 2.5 second delay will impact your parameter numbrs in Dec for sure
and will result in the number being too low, which in turn means that your
loop gain is greater than 100%, which can easily cause oscillation.

You must understand the limitations of any system. If you do not understand
fully how a mount operates during guiding, you will constantly be chasing red
herrings up and down blind alleys. Nothing that you have posted indicates any
sort of electronic or software error in the system, either in the mount, the
guider software or in the camera.

To help you understand what may be happening, I will try to explain. I will
assume that you have some Dec drift, since you did not answer my previous
questions about the nature of the oscillations. During guiding, the guide software
will try to counteract a slow drift in Dec by sending small incremental
direction commands to the mount which are directly opposite to the slow drift. If
the parameter numbers are close to correct, these commands will always be equal
or slightly smaller than the observed pixel error - i.e. if the star drifts 1
pixel, the software, using your parameter numbers, will calculate the exact
time of the button push needed to bring the guide star back exactly one pixel.
If your parameter numbers are significantly too small, the guider software will
send a signal that is too large and the mount will respond with a move that
is larger than 1 pixel - this will cause an overshoot, which will generate an
opposite command, which generates an undershoot, which then generates and even
larger opposite command with larger overshoot etc etc etc - basically you have
an oscillating system. That is why you need to know these numbers, both from
a theoretical value and the actual value as calculated by your software -
check them, are they correct???

But let us suppose that the numbers are correct and the correct signal is
sent. Therefore, the guide star will always come back to the center of the guide
box. But what happens if for some reason the guide star goes above the line
opposite to the direction of drift? This can happen during moments of bad
seeing, or from a thermal situation where the guide star might be dancing about. If
the guide star goes above the line, your guide software will send a guide
signal to reverse the direction of the Dec axis by a small amount. As you have
discovered, the Dec axis will not reverse instantly, especially if your worm is
not in mesh and takes 2.5 seconds to reverse at 1x! 2.5 seconds at 15 arc sec
per second is 37.5 arc seconds of Dec motor movement, and to achieve this
level of motion, the guider software must send a number of guide corrections to
the mount before any motion is detected on the guide chip! All this time while
all these guide corrections are sent and acted on, the gear teeth are unloaded
and not engaged and the guide star is free to move around completely unguided.
If Dec drift is very low, then no problem and the Dec gearing will eventually
catch up with the guide star position and resume normal guiding. If the Dec
drift is significant, then the guide star will slowly drift off the center for
a period of time, and this could be 3 to 5 pixels or more before the guider
can send enough correction moves to the mount to reverse the motion again. The
result is a slow sawtooth when you look at the guide chart of that axis. So now
the question again: Do you have a slow sawtooth or do you have a fast
oscillation??? Please, (otherwise I can't help any more)..

Rolando





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Re: DEC move problem during autoguide

Roland Christen
 

In a message dated 2/11/2008 2:55:01 PM Central Standard Time,
ancient.sull@... writes:


Unfortunately I don't see how to turn off Dec corrections in one
direction and still dither. Is it possible to do that?
No, you cannot dither if one Dec direction is turned off.

What you must do is find the reason for oscillations. I will repeat again the
reasons for oscillation, and you must determine which oscillation you have.

1) Oscillations are fast and occur all the time. Reason - loop gain is higher
than 100%. Figure out what your parameter numbers need to be using pixel
scale/focal length of scope. Check this number against what the guide software has
calculated after you do a normal calibration run. Strong hint: Do NOT
calibrate at anything other than 1x, even if you feel strongly about guiding at .5x.
Hint #2: Do not calibrate for short time period - 5 second cal runs are way
too short and almost guarantee wrong parameter numbers in Dec.

2) Oscillations occur on a semi-regular basis, on the order of once every 3 -
5 minutes. This is almost always caused by a mount that is not properly polar
aligned and has significant Dec drift on the order of 3 - 4 pixels in a 5
minute period. If yopu don't fix this, then you will have Dec oscillations, and
the only way to eliminate them is to turn off one direction.

Does any of this make more sense to you now? Which oscillations do you have?
If you want help figuring out what is going on and how to fix it, we need the
above information. A picture of your tracking Error Graph will also help,
along with a picture of your two Guider Setting pages (Settings and Advanced).
Post them in the files section temporarily until we can figure out what is going
on (please no tables of numbers at this point).

Rolando




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Re: Mach 1

observe_m13
 

--- In ap-gto@..., "doctp12" <doctp12@...> wrote:

Hi,

I am new to this forum, just received a AP 130 f/6 [1995] and Eagle 6.
Awaiting my Mach 1 in late May.
What do you think of this combo.? Good for visual and/or
Astrophotography?
YES!

CCD Photography?

YES!

Please post all good as well as bad
points about all of the above.
You will need the field flattener for any large CCD ST11K or FLI16803
cips otherwise should be ok as -is.

Any shortcuts to the learning curve?

No. You are going to have to learn how to set it up and to polar
align. There is a lot of information out there on how to do it. RTFM.
It is well written and has a lot of info. Read parts of it multiple
times if you are not familiar with the concepts. Most everyone learns
teh same way you are going to - by reading about it and doing it. One
thing to help out with the polar aligning is getting the PAS. One of
the most beneficial methods of learning is by joining your local astro
club and going out with them to learn how someone sets up similar
equipment and ask questions or aks tehm to explain what they are doing
as they do it. I don't know the level of your knowledge but learn the
sky fairly well especially the brighter stars. They are going to be
your friends for polar aligning and calibrating the keypad to the sky.
People can help out on specific questions but take things one step at
a time. Don't unwrap it and expect to be taking CCD pictures that
night unless you are taking pictures of it, not through it. I would
start out by leaving all the CCD stuff for later. Learn how to set it
up, learn how to polar align. An excellent polar alignment isn't
necessary for visual use but it certainly is for long deep exposures
with CCD's. Spend the time to learn how to get very close without the
CCD. The more you do it, the easier it becomes and it is going to be
the startng point for critical CCD polar alignment at some point. You
will have to learn all about guiding and working with the software to
control the camera, etc. Above all, look through the scope. If you get
frustrated trying to get that last tweak of polar alignment to work,
take a break, release the clutches a bit and manually point the
telescope at a known star. Tighten the clutches up a bit so that they
no longer slip easily, pick that star out of the list on the keypad
and 'RCAL' on it. Go on a sky tour with the keypad. Lots of things to
do. Have fun!


Any chance that this could double as a "grab and go" setup for a 1/2
hour after work viewing session or should a completely different setup
be aquired for that purpose [e.g. A.Z. mount?]
Oof, it's pretty heavy for a 'grab and go'. Maybe leaving it set up,
ready to go on some JMI wheels to roll it around? If you can do that,
then mark the spot it goes so that you can return it to where it was
relatively accurately, and be ready to go quite quickly.

Sorry for the very elementary questions, I am really new to this level
of sophisticated equip.!

Thank you.
Tom.


Power Issues

Dean Salman <cluster@...>
 

I was in the desert this weekend and had 125 amp new battery which I
had my ST-10 camera and the AP 1200 on. I thought for sure I could run
both of these on the same battery, I was wrong. the slewing sounded
weak and it finally gave out. The battery was still at 12.5 volts but
I guess with the extra pull from the camera it was not going to fly.

So I guess I have to put a deep cycle battery for just the mount and
nothing else on it. That is a bit of a pain since I have to carry
extra batteries. So if that is the case, at what point does the AP
mount die with the battery, even by morning the battery it was on was
down to 12.3 volts. A fully charged battery is 12.9 volts (somewhere
around there), I guess I need to run the system at home for a couple of
days and see if I can be in the field more than one night since there
is a 2 day star party in Arizona in April.


Re: Power Issues

Kent Kirkley
 

In a message dated 2/11/08 1:18:54 PM, cluster@... writes:


I was in the desert this weekend and had 125 amp new battery which I
had my ST-10 camera and the AP 1200 on.  I thought for sure I could run
both of these on the same battery, I was wrong.   the slewing sounded
weak and it finally gave out.  The battery was still at 12.5 volts but
I guess with the extra pull from the camera it was not going to fly.

So I guess I have to put a deep cycle battery for just the mount and
nothing else on it.  That is a bit of a pain since I have to carry
extra batteries.  So if that is the case, at what point does the AP
mount die with the battery, even by morning the battery it was on was
down to 12.3 volts.  A fully charged battery is 12.9 volts (somewhere
around there), I guess I need to run the system at home for a couple of
days and see if I can be in the field more than one night since there
is a 2 day star party in Arizona in April. 
Dean:
Although I usually get power 'from the grid' I have run my 1200GTO and
STL-11000 w/Remote Guide Head and Robo-Focus with a series 27 Deep Cycle battery,
all night, with no problems.
To help keep the battery warm, I have it in a small 'Igloo' type cooler which
insulates it from the cold and serves as a seat if necessary.

As Roland says, set the slew speed to 600 as it consumes less 'juice'.

Kent Kirkley


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Re: Power Issues

Roland Christen
 

In a message dated 2/11/2008 1:19:06 PM Central Standard Time,
cluster@... writes:


I was in the desert this weekend and had 125 amp new battery which I
had my ST-10 camera and the AP 1200 on. I thought for sure I could run
both of these on the same battery, I was wrong. the slewing sounded
weak and it finally gave out.
Cold weather will drop battery voltage quite fast. When the air temperature
drops below 40 degrees and you have a heavy load plus you are powering other
equipment, the actual terminal voltage can drop below 12 volts. Run the slewing
at the lowest setting, 600x. The mount does not require much power while
tracking - on the order of 400 - 600 milliamps, so that is not the source of power
drain. A 125 amp hour battery woudl have enough juice to power the mount for a
week solid. When slewing at 600x, the mount will draw between 1 - 2 amps,
depending on how cold it is. The main problem is increasing battery internal
resistance in cold weather, so when current is being drawn, there is an internal
voltage drop that reduces the available battery terminal voltage. If it were
just the mount tracking, the battery would not really notice much load, but when
you add peripherals, the current drawn by these items will drop the terminal
voltage below the safe working level.

You can also add a 6 volt battery in series with the 12 volt to make 18
volts. The mount will actually draw less current and be able to slew at full slew
speeds.

Rolando


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Re: Whacky moon last night

Woodwind
 

Bib,

Thanks for the comments.

Some replies from guys on the CCD-newastro site suggested it was refraction caused by an inversion layer of some sort. My friend re-checked his times and reckons he was out by 30 minutes and it was at 8-45pm (2045hr) local - which might help account for the setting times. I suppose that a moon low on the horizon would also be more susceptible to an inversion layer.

Apart from that explanation - or a cloud (which seems a bit lame) we are still in the dark.

Murray

astronomertoo <bobc22@...> wrote: Hi Murray,
Yes, interesting. Sounds like the Tampa Moon Monster is on the
prowl. Actually it really was incredibly transparent, and
absolutely steady air last night from my vantage point about 1-1/2
hours drive north of Tampa. I was taking advantage of the skinny
phase and looking at details in/around Mare Crisium, and other large
craters NE of it that are normally hard to see into. The moon
started off pretty steady at sunset but within an hour went into my
western trees and I gave it up. I do not know what time the moon
set last night, but by 2115 hr it would have been pretty low. I do
not know if Tampa was still having clouds last night or not.
I spent the next several cool hours in the 50s, with water pouring
off my scope, yet with some of the best steady air I have seen in
recent times. Mars was very good, Saturn was etched. I looked at
many things, but kept going back to the Trapezium, throwing all
kinds of fun combinations at it from 200-330X, from short Pentax
orthos, Binos, Nagler 3-6Z, even all the heavy combos of the TV Big
2X and Powermate 4x with the Jumbo Naglers 20/26, and Pan 35mm. It
is totally amazing how the latter big glass works so well with the
old 130mm f/8 Starfire EDT. They all gave nice air around E and F,
as well as airy discs around the others. It was a fun night, but I
missed the moon eater.
Please let us know what the answer was.
BTW, tonight was clear, and drier-but was visually very watery air.
Last night was the good one.
Bob Cuberly
Citrus Springs, FL

--- In ap-gto@..., "mphammick" <mphammick@...> wrote:
>
> I know this is a tad off track on this board, but it might be of
interest.
>
> An acquaintance of mine emailed me last night with a curious
report of
> a sighting he and a friend made last night of the moon. He
described
> is as follows:
>
> The crescent of the moon was clearly visible and as we drove along
a
> circular shadow appeared across the lower part of the moon
obscuring
> the lower, central part of the crescent so that the two ends
appeared
> to be disconnected. As the circular "shadow" rose the two ends of
the
> crescent looked like two horns which grew shorter and shorter.
>
> He added that this was seen near Tampa at 2115hr local time and
that
> there was no local geographical feature that could have caused
this.
> Cloud cover was less than 30% and no clouds were seen across the
moon.
> The shape of the shadow seemed similar to an eclipse.
>
> He is a very low-brow astronomer and has assured me in several
emails
> that this is not a spoof.
>
> Did anyone else see this ? Is there a logical explanation for what
he
> saw ?
>
> Murray
>


Re: DEC move problem during autoguide

Roland Christen
 

In a message dated 2/10/2008 12:27:22 AM Central Standard Time,
ancient.sull@... writes:


I take it back. I now _do_ think the problem is electrical. Try this:

I turned off corrections in Y. The zig zagging stopped. That means it
isn't mechanical, right?

So it likely is a sticking relay somewhere or a problem with the AG
cable.
NO! It is NOT a sticking relay. See my previous posts - and yes, do turn off
one of the Dec directions if you cannot set up the guiding software to avoid
this oscillation any other way.

Rolando


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Re: DEC move problem during autoguide

Roland Christen
 

In a message dated 2/9/2008 10:23:03 PM Central Standard Time,
ancient.sull@... writes:


Backlash? (Backlash might delay correction but shouldn't cause these
sudden jumps, right?) Something else mechanical in the mount?
something about vertical plumes of heat rising from the roof?
Turn off one of your Dec directions. If this settles down the guiding, it is
an indication that you have too much Dec drift.

Sudden jumps are caused by the guide star going across the zero point
momentarily and the guiding software then tries to reverse the direction of motion.
Basically this starts a vicious cycle of "chasing the seeing". Most people do
not set their Min/Max move settings properly, so the guiding software can
sometimes shoot the the guide star many pixels in the opposite direction if there
is a very momentary position change of the guide star. There are many ways to
avoid this problem, but the simplest is to turn off one of the Dec directions.

Rolando


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Re: AP-1200 in High Humidity/High Heat

Roland Christen
 

In a message dated 2/9/2008 9:02:02 AM Central Standard Time,
uwpf23@... writes:


I will be using (and leaving) my AP-1200 in a high-humidity/high
heat observatory this summer here in Arkansas. Temps inside the
obsv. during the day will approach around 120 degrees F for a few
hours during the daytime in peak of summer. Humidity will be pretty
high too with dewpoints in the 70's.

Are there any extra precautions I need to take to prevent the AP-1200
from getting corrosion or other damage in this kind of environment?
It gets hot here too, sometimes around 100F/100% humidity. I've had my mounts
out for many years in all kinds of weather and they never needed anything.

Rolando


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Re: DEC move problem during autoguide

Roland Christen
 

In a message dated 2/9/2008 4:41:45 AM Central Standard Time,
petrovic@... writes:


I have strange phenomena since few days autoguiding my AP900 with
STL11k. First positive DEC move (+Y) produces erratic movement and
mount start to oscillate with full +/- moves.
Whenever you have oscillations it usually points to loop gain greater tha
100%. Firsts thing to ALWAYS check are the parameter numbers for the RA/Dec
directions in your autoguider program. First, you must calculate them based on your
pixel scale/focal length, then you must verify that they are close to this
number in the Dec direction. If the Dec numbers are considerably smaller, then
you will most likely get Dec oscillations (smaller than ideal numbers always
means that the loop gain is larger than 100%). One of the ways that you may
obtain these small numbers is if you try to calibrate at .5x instead of 1x and if
you calibrate for a very short time period (say 5 seconds cal time versus 10
or 15 seconds).

The second likely cause of Dec oscillations is that your polar alignment is
off to the point that you are getting substantial Dec drift in a 5 minute
period (check it to see if it is more than about 3-4 pixels in 5 minutes) If there
is substantial Dec drift, you will probably get a long period oscillation, a
sort of sawtooth fast rise, slow decline in Dec. If this happens, turn off one
of the Dec difrections.

If the oscillation is fast +- and on-going, you probably have too high a loop
gain caused by: see above.

Rolando


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OT: measuring critical camera parameters using PTC/DTC methods

Richard Crisp
 

I performed some tests recently on my ancient Dream Machine camera
using the Photon Transfer method pioneered at JPL by Janesick and
Elliott beginning in the 70s..

In effect it consists of taking pairs of identical darks and or flats
(for some of the tests) and plotting noise sources versus signal

many things can be learned including

1) quantifying DSNU, PRNU (dark signal non-uniformity, photo response
non-uniformity), camera gain

2) read noise, full well, dark current rate and a pile of other
interesting parameters. For example you can tell if your clock
voltages are causing a reductio in well capacity, see anomalous kinks
in the linearity, look at linearity, charge skimming and many many
other critical parameters

3) effectiveness of flat fielding is another critical parameter that
can be learned as welll

the first two curves I showed are the simplest ones; Photon Transfer
Curve and Dark Transfer Curve.

We normally discuss things like this in the ccd-imaging-technology
group on Yahoo in clse there's interest in more things along this
line. I plan to make several more examples using different cameras
and show other types of plots in the near future

http://www.narrowbandimaging.com/dark_transfer_curves_page.htm


Re: Whacky moon last night

astronomertoo
 

Hi Murray,
Yes, interesting. Sounds like the Tampa Moon Monster is on the
prowl. Actually it really was incredibly transparent, and
absolutely steady air last night from my vantage point about 1-1/2
hours drive north of Tampa. I was taking advantage of the skinny
phase and looking at details in/around Mare Crisium, and other large
craters NE of it that are normally hard to see into. The moon
started off pretty steady at sunset but within an hour went into my
western trees and I gave it up. I do not know what time the moon
set last night, but by 2115 hr it would have been pretty low. I do
not know if Tampa was still having clouds last night or not.
I spent the next several cool hours in the 50s, with water pouring
off my scope, yet with some of the best steady air I have seen in
recent times. Mars was very good, Saturn was etched. I looked at
many things, but kept going back to the Trapezium, throwing all
kinds of fun combinations at it from 200-330X, from short Pentax
orthos, Binos, Nagler 3-6Z, even all the heavy combos of the TV Big
2X and Powermate 4x with the Jumbo Naglers 20/26, and Pan 35mm. It
is totally amazing how the latter big glass works so well with the
old 130mm f/8 Starfire EDT. They all gave nice air around E and F,
as well as airy discs around the others. It was a fun night, but I
missed the moon eater.
Please let us know what the answer was.
BTW, tonight was clear, and drier-but was visually very watery air.
Last night was the good one.
Bob Cuberly
Citrus Springs, FL



--- In ap-gto@..., "mphammick" <mphammick@...> wrote:

I know this is a tad off track on this board, but it might be of
interest.

An acquaintance of mine emailed me last night with a curious
report of
a sighting he and a friend made last night of the moon. He
described
is as follows:

The crescent of the moon was clearly visible and as we drove along
a
circular shadow appeared across the lower part of the moon
obscuring
the lower, central part of the crescent so that the two ends
appeared
to be disconnected. As the circular "shadow" rose the two ends of
the
crescent looked like two horns which grew shorter and shorter.

He added that this was seen near Tampa at 2115hr local time and
that
there was no local geographical feature that could have caused
this.
Cloud cover was less than 30% and no clouds were seen across the
moon.
The shape of the shadow seemed similar to an eclipse.

He is a very low-brow astronomer and has assured me in several
emails
that this is not a spoof.

Did anyone else see this ? Is there a logical explanation for what
he
saw ?

Murray


Mach 1

doctp12 <doctp12@...>
 

Hi,

I am new to this forum, just received a AP 130 f/6 [1995] and Eagle 6.
Awaiting my Mach 1 in late May.
What do you think of this combo.? Good for visual and/or
Astrophotography? CCD Photography? Please post all good as well as bad
points about all of the above. Any shortcuts to the learning curve?

Any chance that this could double as a "grab and go" setup for a 1/2
hour after work viewing session or should a completely different setup
be aquired for that purpose [e.g. A.Z. mount?]

Sorry for the very elementary questions, I am really new to this level
of sophisticated equip.!

Thank you.
Tom.