Skynet exposed

by Ted Frimet

dare you seize the galaxy?

Hello Everyone,

I am new to Skynet and am trying to get started.  I have watched the videos but am confused on a couple things and would appreciate any advice.

For my first photo, I am trying to photograph M101.  Since these dimmer objects have a longer exposure time and use up credits quickly, I’d like to get this first shot right.  

Here are my questions:
1) Filters.  In the video, the lady drags in a separate screen from out of nowhere that gives more details about which filter is recommended for her demo shot on Saturn.  I can’t find this “recommendation” screen anywhere, so my questions are:  where is the screen located?  Do you have a recommendation on your own experience for a filter for galaxies (M101 magnitude 7.86) ?  

2) Exposure Time.  I see in the video that there is a recommended maximum exposure time. For M101 it is 120 with HiLum filter.  When you take your images, do you just choose the max time or will it be overexposed?

I see M101 can be photographed by a couple telescopes, but at a later time.  How do I select what time I want to request the telescope to take the image?  And when you set the time, is it our DST time or GMT or local time at the telescope?

Many thanks,

Rich

To answer your question on “which filter is recommended for her demo shot on Saturn”, click on the below link,
http://skynet.unc.edu/astr101l/Labs/lab1.pdf

and search for “PROCEDURE: A. OBSERVE WITH SKYNET

3. Observe Planets.

You will find the below table, which will list Saturn, its recommended filter, and exposure duration, as found in the above PDF.

Here is a copy of that table:

It isn’t too intuitive to find the “V” filter on Skynet. You are probably selecting telescopes, then filters which are supported by those telescopes.

I might suggest you reverse your selection process. That is, choose the filter first, and select from the list of telescopes then presented that offer those filter options.

Look for this graphic on Skynet:

As you can see, I have selected “Filters” after assigning my target. On the filters page, you will find the recommended “V” filter for Saturn. The selection looks just like this:

Where GenG (generic G’reen” is listed as “V”, greenish filter.
 Or you might try the Astrophotography Green filter.

Moving onto the second part, of your first question… Do you have a recommendation on your own experience for a filter for galaxies (M101 magnitude 7.86) ?

In the same referenced Skynet Lab, there is a table for recommended exposures and filters. The “open filter” setting is recommended for Spiral Galaxies.

Here is a shot of the Whirlpool galaxy at 30 seconds exposure, with Open filter setting:


We arrive at your second question.  I see in the video that there is a recommended maximum exposure time…When you have taken your images, do you just choose the max time or will it be overexposed?

The maximum time is presumed to keep the camera from overexposing. Having said that, go ahead and experiment. I haven’t tried past the maximum exposure time. You might find Skynet software presenting you with a warning, and a limitation on scope selection. See below:

I really enjoy your third and final question. It’s the best! How do I select what time I want to request the telescope to take the image?  And when you set the time, is it our DST time or GMT or local time at the telescope?

In the Skynet user interface, where you select your filters, and telescopes, you will find an advanced options. It will appear just below your AAAP time account information.

Select the check box titled “Delay the start of this observation until …UTC.” And fill in a time.

At first blush, and for a few entries, you may enter incorrect information. It happened to me.

If you are permitting Skynet to automatically choose the next available telescope, then it will, of course, make any adjustments to ephemeris data and time parameters for you.

Here is a referenced link on the web for EST to UTC conversion. https://www.worldtimebuddy.com/est-to-utc-converter

Rich, the 800 lb gorilla in the room is that when you are selecting a target, and it is in the “horizon” window then all is well.

A horizon graph, like the one below, may provide you with a good chance of getting an image:

However, if there is no target visibility (nothing above the 30 deg elevation marker – or a complete lack of “colored” lines – then cancel your request, and choose another target. This will most likely happen with planets. Alternatively, you could change the minimum visible hours from “1.0” to, say, 0.5 and try to squeak in an observation.

I hope that this has been of some help for you, and our readers, and enriches the experience with the Skynet Robotic Telescope Network.

Rex had a really good solid reply. It appears below:

Thanks Ted, those comments are really helpful in answer to Rich’s questions.  I’ll add a couple of other thoughts here.   

The CCD cameras in Skynet have anti-blooming sensors (e.g., KAF-16803), beneficial for imaging dim objects such as galaxies.  If a pixel registering a brighter area (e.g., galaxy core) becomes saturated (exceeds well depth capacity) it will not bloom vertical streaks the way non-anti-blooming CCD sensors do.  At longer exposures pixels corresponding to fainter regions of the object continue to increase in value as brighter pixels max-out (at the well depth value for the sensor), improving the overall image character by showing fainter regions with greater intensity.   

120 sec is a good starting point for galaxies.  Try “bracketing” a few exposures to see how this affects the image.  My SSRO group using PROMPT2 at Cerro Tololo uses 30 minute sub-frames for all deep sky work, and here at home in NJ I use 15 minute sub-frames.  However, as mentioned at the meeting, exposures of this length need active autoguiding to correct small tracking errors (otherwise even very small errors lead to trailing, out-of-round stars).  Skynet generally does not make auto-guiding available to the user due to complicating features, although it’s possible that at deeper levels in the user priority chain guiding may be possible.  

Luminance (L) filters are really IR cutoffs and are used mainly to attain parfocality with the other R,G, B filters.  Any filter in the light path causes a small but significant change in focal length, so not having a filter would cause problems.  Having to adjust focus for filter changes is inefficient.  Color imaging of deep sky objects is done by taking a series of L, R, G, and B filter frames and combining in software to make the color composite.  The luminance (L) filter has the greatest sensitivity (highest quantum efficiency) since the others filter out broader wavelengths.  It’s interesting to compare pixel brightness data for the same object at constant exposure times with L compared to R, G, and B filters.   

— Rex

Epilogue:

I had inquired to Rich if we could use his follow-up, and publish results. Below, is our Amateur Astronomer’s first image taken from Skynet. It is M51 with its histogram adjusted in Afterglow software, ranging: min 40 max 99.2. The histogram feature, is a constraint on how much “white” and how much “black” will show thru in the final image.

Way to go, Rich! Awesome!!

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This entry was posted in December 2017, Sidereal Times and tagged , . Bookmark the permalink.

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