D7000 Video Astrophotography Tests Last updated: 21 June 2011

Since my last observing session on 15 June, the days and nights have been windy, with some periods of cloudy and dusty skies. On Sunday, 19 June, there was some smokey haze from a new fire, this one south of Kitt Peak National Observatory (apparently no threat to Kitt Peak). These photos were taken with my iPhone 4 at sunset:

I mentioned in the previous report that I would have to investigate whether D7000 DSLR video recording could have the shutter speed changed. I didn't think it could, but the camera manual proved me wrong (page 60). In manual (M) mode, which is what I've been using since there was no camera lens attached, you can enable "Manual Movie Settings" and then set the shutter speed between 1/8000sec and 1/30sec, and the ISO from 100 to 25,600. Now I just need to determine what shutter speed (fast, to avoid blurring) and ISO combinations will work best at prime focus of the 8" LX200-ACF. To help with that determination I would use the bright star Vega (Mag 0) to substitute for the ISS, which varies in brightness from about 0 to -3. I wanted the fastest shutter speed at the lowest ISO setting that would still yield a usable image.

The skies were clear and the winds generally calm (for a change) on Monday, 20 June. I opened the observatory at 1820 MST, 104°F. The main goal for the night was to do some D7000 DSLR video astrophotography tests. At 1833 MST, viewed Saturn at 77X and 133X in the 8" LX200-ACF. At 1904 MST, used 206X, which provided a nice view of the planet and rings. At 1912 MST, used 364X. At 1936 MST, switched back to 133X to try for some Saturn moons; none currently visible though. But the view was excellent. Planet shadow on the rings, ring shadow on the planet, and Cassini Division were all visible.

At 1945 MST, I began setting up for my first D7000 DSLR video tests. I did some video recordings of Saturn at prime focus and prime focus + 3X TeleXtender. I used shutter speeds of 1/200sec to 1/500sec, and ISO settings of 500 to 6400. Saturn was just visible on the Live View screen, which gave me some hope that the video recordings would be useful. However, during post-processing on the computer, I discovered that the Live View was not an accurate indicator of the object's true brightness. All of the Saturn test videos were way underexposed.

I then slewed to Vega to video record it at prime focus + 3X TeleXtender. During the recording, I tapped on the telescope tube and rapidly slewed the star away from center, simulating slewing during ISS tracking. While seeing was not very good at this time, the tests seemed to work out. Here is a frame from a video at 1/1000sec, ISO 1600:

And a frame from a video at 1/2000sec, ISO 1600:

From these Vega tests, I believe that 1/2000sec at ISO 1600 will be a good starting point for my next ISS imaging attempt. Unfortunately, the next good ISS pass is not until next week, at the earliest.

I ended these video tests at 2037 MST and viewed M57, the Ring Nebula, at 77X. It was a nice view, although the twilight sky was still somewhat bright. At 2122 MST, returned to Saturn; four moons were visible at 77X. (Saw my first, and as it turned out, only Kissing Bug of the night. Maybe the spraying I did several days ago worked. It got away initially but was terminated a little later.) At 133X and 206X, the moons Titan, Dione, Tethys, and Rhea were easily seen. After checking SkySafari 3 Pro, I determined that Iapetus was also visible. What I had thought was a star was, in fact, Iapetus. Enceladus should have been visible as well, very close to Tethys. I began trying for Enceladus. I could not separate it from Tethys at 133X, 206X, nor 364X. However, at 619X, I could just see Enceladus. A six Saturn moon night.

I then began some DSO observing at 2133 MST at 77X. First was M20, the Trifid Nebula, low in the southeast. Then Centaurus A galaxy and Omega Centauri globular cluster. Unfortunately, both the Centaurus DSOs were low and in the sky glow from Oro Valley, and so the views were not as good as they were a few weeks ago. I then decided to check the AutoStar's "Tonight's Best" tour and see what it offered. I skipped some but did view M7 (open cluster), M22 (globular cluster), M4 (globular cluster), M6 (Butterfly Cluster, open cluster), M8 (Lagoon Nebula), M27 (Dumbbell Nebula), M17 (Swan Nebula), M11 (Wild Duck Cluster, open cluster), M5 (globular cluster), M52 (open cluster), M16 (Eagle Nebula), M104 (Sombrero Galaxy), and M68 (globular cluster).

At 2227 MST, began setting up to image M11, the Wild Duck Cluster, with the D7000 DSLR at prime focus. Did a focus test image using the star Altair and the Bahtinov Mask. Here is the Wild Duck Cluster, 30 seconds, ISO 2000:

At 2308 MST, the eastern sky was beginning to brighten from the rising waning gibbous moon. The moon finally appeared over the hill to the east at 0006 MST. I then began waiting for it to rise above a tree. Finally, it cleared the tree and beginning at 0054 MST, I did some lunar imaging with the D7000 DSLR. This image was taken at prime focus of the 8" LX200-ACF, 1/200sec, ISO 400:

I next did some video tests on the moon. Here are some selected frames from the video recordings. First, 1/1000sec, ISO 1000:

Next, prime focus + 3X TeleXtender, 1/250sec, ISO 1000:

Next, prime focus + 3X TeleXtender, 1/5000sec, ISO 3200, cropped to show some shadows:

And this still image, prime focus + 3X TeleXtender, 1/250sec, ISO 1600:

A note about video astrophotography with the D7000 DSLR: I had to increase the image brightness and contrast in QuickTime Pro in order to bring out the details in the video. This will be necessary for ISS passes as well. But this technique does provide for very short exposures that can eliminate image blurring, whether due to atmospheric seeing or telescope motion. I plan to do more video astrophotography with the D7000 DSLR.

At 0108 MST, I ended imaging and did some lunar viewing at 133X, 206X, and 364X. Shadows along the terminator and the south polar region were especially nice.

Closed the observatory at 0130 MST, 73°F.

Some More Notes on Tracking the ISS

On my previous report, I discussed some tips on tracking the ISS (or any satellite). Dick Seymour posted the following information on ISS tracking with an AutoStar II (probably also applies to the other model AutoStars) on the LX200GPS Yahoo Group.

Subject:	[LX200GPS] Space station tracking
Sent:	Friday, June 17, 2011 10:03:49
From:	autostaretx (rseymour@wolfenet.com)
How it works (very short edition):
During the "calculating pass" portion, the scope determines and
remembers about 100 or so *incremental* steps for the path.
(think "up two, over four at speed ZZZ", not "GoTo xx yy")
During the pass itself, it "plays back" that list of steps, about one
per second (for an ISS pass).
When you adjust the path to recenter the satellite, the next "up two,
over four" happens from *there*, and the subsequent steps likewise are
based upon that new spot.
----
The scope *does* change tracking speed during a pass... you can hear it
"rev up" as it nears the zenith.
If, however, you ever use ASCOM to drive your scope from a PC, that
(unless you tell it not to in the ASCOM driver setup dialog) may have
silently set your scope's Maximum Slew Speed to only 3 or 5 degrees per
second (instead of its usual 8 or faster)...  and that setting is
remembered across power off/on cycles.
You can check and change that from the Autostar's Setup/Telescope/Max
Slew Speed  menu setting.
-----
Alt/Az -mounted scopes have problems keeping up with passes that go
within 10 degrees of zenith (straight overhead), and polar-mounted scope
have problems near the pole.  There is a limit to the speed a scope can
slew.  For that reason i may choose to mount my scope differently on an
evening i'm planning to follow a "high elevation" pass.
----
Recently (within the last week) other satellite chasers have been saying
that the TLEs (and Heavens-Above's predictions) have been a little "off"
for the ISS... sometimes as much as two minutes in error.
--------
If you can't capture a satellite as low as the Autostar's "AOS"
prediction thinks, you should either change the Autostar's setup menu
AOS altitude to one that works for you, *or* start at the predicted AOS
position a few seconds *early*, let the scope rise to where you do
expect to see the ISS, and then tap Enter to pause.
(instead of slewing up and *then* starting the pass)
That will move you "down the list" of "steps", so that the Autostar will
be tracking at the speed of that higher elevation instead of at the
speed of the "beginning" of a pass.
The scope does not recalculate anything during a pass, since it would
always be behind.  It only "plays back" the original list if incremental
steps.

have fun
--dick

Dick also mentioned Brent Boshart's SatelliteTracker, available for download from the Files area of the satellitetracker Yahoo group:
http://groups.yahoo.com/group/satellitetracker/

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