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[TomT]

Re: Happy Holidays
Mike Chibnik
Sat, Dec 29, 2018, 10:34 AM (3 days ago)
to bkm, me, Cezanne, TomT, Tim, Tim, Tom, Richard, Mike, Mark, Jerry, christopher, emilanes
COMET_46PWirtenan48.jpg
To all who asked how it took my images:
The first two were taken using my 80mm flourite Megrez using the CDS-600 camera.  The exposures for the Horse head nebula was 5 min exposures for a total of 15 min.  The comet pictures used 60 sec exposures as I haven't learned how to use the offset tracking with the Mesu-200 mount.  With a suggestion from Mark the Polemaster I've been able to get polar alignment that's nearly dead on so 5min exposures with the Megrez is no issue.   I used 48 - 60 sec exposures for that.  Attached to this new email is the comet using my C-8 fro a close in image.  It also used 60 sec exposures.  I have to admit that there didn't seem to be a difference in the pictures between the Megrez and C-8, maybe just a slightly larger nucleus.  As a matter of fact when I'm viewing the comet using binoculars I've been seeing something similar with just a hint of a smaller nucleus.  All images taken are with the new Opti-Pro light pollution filter which results in much darker backgrounds in spite of the new LED lights that have been installed.  The only issue is that when I try to use flats I get a rainbow effect with the filter not seen before. 
Mike


On Sat, Dec 29, 2018 at 12:44 AM bkm <spamcollector@cox.net> wrote:
    Tom and Mike,
    Seasons Greetings from the Isla Vista Shores.
    Tom, I like your early evening shot and the blue background.  Nice crisp star images.  The Pleiades have great detail.  Ally's Braid shows up nicely.
    Mike, your Horsehead Nebula picture did not survive going through Tom's reply.
    Here are my pictures of 46P/Wirtanen taken with my Nikon D500, C11 scope (2,800 mm focal length), and Orion Atlas Pro mount in sidereal tracking taken December 27th and 28th.
    The night was clear, low humidity (46%), and cold (41°F).  It was also windy, so the clear night sky wiggled.  I was up the entire night, and went to bed at 5AM.  Venus was brilliant then, low in the east, sort of like a first-quarter moon, and extremely wiggly.  I didn't take pictures.
    I found and photographed Comet Wirtanen.  It was high overhead between Auriga and Ursa Major.  All photographs that follow are single exposures.  This photograph was 30 seconds, ISO 6,400.  More photographs later.
>
I've done a fair amount of work on the mount electronics, and my alignment and tracking are now much better.
    1) Small 3-amp circuit breakers were added to the battery output connectors, as I had read on Cloudy Nights about a heater controller fire using just a battery power supply.
    2) Objective and eyepiece heaters were added to the Pentax 75mm SDHF APO finder scope.  When it was really humid (85%) at Bacara, both the unheated Pentax objective and eyepiece fogged up.  I already have an Astrozap eyepiece heater and dew shield on the C11.
    3) The Astrozap heater controller failed on both outputs simultaneously (no heat).  There was a gate-to-drain short in both big output FETs (field effect transistors) that drive the heating elements.
    In the controller, FET's are used as electronic switches to provide pulse-width modulated voltage to the heaters (either 12-volts, or 0 volts, variable duty cycle at a 400 Hz rate).  The failure was characteristic of electro static electricity damage (ESD).  The Astrozap controller has no protection from ESD.  I suspect the ESD damage occurred at Kings Canyon, where the relative humidity was only 19% - perfect for static electricity buildup.  Voltages in excess of 2,500 volts can easily be generated by clothing brushing against conductors, like dew heaters and scope mounts.  When the dew heaters with 2,500+ volts stored static charge are plugged into the Astrozap controller, the 55 volt breakdown rating of the FETs is exceeded, and they catastrophically fail.
    I added protection on both outputs and the 12-volt input using 27-volt TransZorbs.  Also, the output FET's were oscillating at very high frequency, a well known problem.  The solution was to add small resistors in series the the FET gates.  I also posted on Cloudy Nights about the problem.  Here is a picture collage of the components added to the pc board that is inside the Astrozap box.  It works well now.
>
The scope collimation was tweaked (it was slightly off).
I found that my mount was not well counterbalanced, which screwed up initial alignment.  I think the stepper motors lose steps with unbalance.  I also read on Cloudy Nights, that higher supply voltage helps eliminate the step skipping (like 15 or 18 V).
Heavens Above provides Comet Wirtanen ephemeris for the current date and  time: https://www.heavens-above.com/comet.aspx?cid=46P .  I got good initial mount alignment (about 4-minutes of arc from the CNP), and put in the RA and dec specified from Heavens Above.  Voila! there was Wirtanen.  Once I put my camera on the C11, I only had the Pentax 75mm SDHF APO finder scope with 20 mm 72° SWAN eyepiece for centering (25 power).  In the finder, Wirtanen was only visible as a smudge using averted vision.  Once I got it in view in the camera, centering was easy.  I ran the camera ISO to 102,400 and took 1-second exposures, and used the mount RA and dec buttons to center the comet in the camera display.
I wasn't aware of just how much turbulence fuzzies up images.  Here is a side-by-side comparison of Wirtanen taken at 1 second, ISO 102,400 and 30 seconds, ISO 6,400.  The 1 second exposure is noisier, but the stars are crisp.
>
Tonight, I was going to take pictures at ISO 204,800, or 409,600.  I can go to ISO 1.64 million, but these images are noisy. 
Tonight, even though the humidity is 54% and the temperature 46°F, the sky was not particularly clear.  I didn't set up.
During the astro photo session last night, I noticed that Wirtanen moved from picture-to-picture.  The D500 controller was then set to take a sequence of 30 second exposures at 1-minute, 15-second intervals.  The D500 was set for long exposure noise reduction.  It takes the picture, then immediately takes the same exposure with the shutter closed.  The second picture is subtracted from the first in the camera.  I also had the camera set for 2-second shutter delay mode, i.e., it raises the mirror, waits 2-seconds (for mount vibration to settle), then takes the exposure.  Thus, an exposure and noise reduction takes about 1-minute, 4-seconds.
Here is a collage of these pictures.  The comet can clearly be seen to move from frame-to-frame.  I didn't blacken the background or use star masks because I wanted to preserve the diffuseness of the comet.  The night sky was light polluted enough from Goleta's new bright LED streetlights, that neither the ion or dust tails were visible.
>
    Enjoy,    Bruce

    On 12/28/2018 10:50 PM, Tom Cez wrote:
>     Mike,
>     Very nice shots.  What is the camera that you are using?  Did you track the comet (46P/Wirtanen?) & for how long?
>     Attached is a 8 second wide shot with the faint comet between the Hyades and Pleiades, Dec 15 early evening east, iso12800, Olympus OM-D EM5II, adjusted with Windows 10 Photo program.
>     Tom Totton
>
>     On Fri, Dec 28, 2018 at 3:31 PM Mike Chibnik <chibnikm@gmail.com> wrote:
>         If I don’t have a chance to give you a call I want to wish you all a Happy New Year.
>         After all the fires, smoke, rain and winds I managed to get some imaging in.  The one thing that I’m learning about the one-shot CMOS camera I have is you need enough exposure to get into the area for decent detection while trying not to saturate the pixels which will cause you to loose color rendition.  The Horse Head Nebula image shown is a stack of three five minute exposures.  This gave much better results than stacking 30-60 min of 60-120 second exposures.  The main reason for my reluctance to try 5 min and longer exposures was due to the fact that all exposures were unguided.
>         With respect to scope making I’m coming up with a new Foucault light source using a fiber optic jumper and a high power green led source.  I’m looking into figuring how to couple more light into the fiber without having to resorting to an expensive GRIN lens.  I hope the point source will give better Mirror readings .
>         Again Happy holidays from the Sacramento Delta
>         Mike