Astrophotography – Page 16

Autoguiding the iOptron ZEQ25 with an SBIG STi

A small, light telescope mount, a small refractor, and a modern autoguider. Seems like a perfect setup! There are a few issues…

The setup is pretty straightforward. A TeleVue 76mm riding atop the iOptron ZEQ25 mount. Atop the TV-76 is a red dot finder and an SBIG STi autoguider. The guider is attached with a bit of custom machining and uses the SBIG accessory kit, including a 100mm lens giving a 2.7 x 2.0 degree field of view. With such a wide field of view the guider also functions as a finder to aid in aligning and framing the photographic telescope.

iOptron ZEQ25 & TeleVue-76 — The iOptron ZEQ25 set up for astrophotography with a TeleVue-76 and Canon 60D

The arrangement is controlled by a laptop, either an older 17″ laptop, finding a second life in the astrophoto rig. Or for a more portable, and less power hungry setup, a small netbook can be used. It may be desirable to set up the iPad for telescope control, removing this function from the laptop. If it were not for guiding the computer could be dispensed with completely. The SBIG STi requires a computer to operate.

Without guiding the performance is not satisfactory. Even with a modest focal length of 380mm there are objectionable guiding errors. The frame at right shows the errors seen during a four minute exposure. Based on my first impressions I would expect to need guiding on any exposure using more than 100mm and a few minutes exposure.

C/2011 L4 PanStarrs No Guiding — Comet C/2011 L4 PanStarrs, TV-76mm and ZEQ25 mount with no guiding during a 4 minute exposure

Everything connects fairly easily, a few more cables than I would like, but it is still marginally portable and not a huge chore to assemble. The challenge now is to verify the setup, configure all of the software, and to take a few photos to prove to myself that it all works properly.

A few steps here have not gone smoothly..

Configuration? There are a lot of setups to check. All of the correct software and drivers… Planetarium software, autoguiding software, camera control, ASCOM, all of the hardware drivers, etc., etc. After everything talks it is a matter of checking settings and tuning the setup with several parameters in the software and on the mount that need to be checked.

I am using PHD to do the guiding, a bit of kit I have used for a while. It works quite well with straightforward controls. It does have quite a few parameters that require checking to tune the control algorithms.

The iOptron controller has a setting for guiding speed in the menus. This is purported to be a fraction of sidereal speed by the manual, up to 100%, but the menu reads as if it is 100x on the controller. I suspect the manual is correct here, will need to test.

The first issue cropped up fairly quickly. I could get no motion from the mount while sending corrections with the STi. PHD was unable to calibrate, no motion. I attempted to use the manual controls in PHD with similar lack of motion. (See update below)

To troubleshoot I needed to make sure that the guide port on the ‘scope worked. I grabbed a Losmandy hand controller and connected it to the ZEQ25 guide port. This worked, the port was working properly and I could see what the guide speed setting on the controller really meant. It looks like 100x is 100% of siderial speed, or close enough.

USB to ST-4 Guiding Port — A copy of Gene Nolan’s USB to ST-4 guiding adapter

I have another device I could try, a USB to ST4 adapter designed by Gene Nolan. This is also supported by PHD Guide and ASCOM driver framework is always installed on my imaging computer. After some issues with finding the correct cable setup the USB to ST4 adapter worked just fine.

Parameter	Value
RA Aggressiveness	100
RA Hysteresis	10
Max RA Duration	750ms
Search Region	15pix
Min Motion	0.1pix
Calibration Step	2000ms
Time Lapse	0ms
Dec Guide Mode	Auto
Dec Algorithm	Resist
Dec Slope Weight	5
Max Dec Duration	750ms
Star Mass Tolerance	0.5
Noise Reduction	None

PHD Guiding Paramters for STi w/100mm lens and iOptron ZEQ25

At this point I can calibrate and guide with good results. I am out of USB ports on the laptop, and had to unplug the mouse, but at least it is working.

Some tuning of the parameters in PHD has started to result in very nice guiding graphs and some excellent test images. These could probably be refined a bit more, but they are working for now. The PHD help menu has a fairly good description of each of the parameters, there is also a great guide to PHD on the Rose City Astronomers website.

Guiding Test Image — Guiding Test: 240sec with a TV-76 and 60D on a ZEQ25 mount

A 100% crop of an image is included at the left, nothing exciting, just a section of starfield near Vega. What is nice about the images is the perfectly round stars. The image was taken at 384mm effective focal length. Will need to do this again with the AT6RC at 1096mm for a more stringent test.

It is really necessary to set the autoguide rate to 100% when using shorter focal lengths. Otherwise the mount does not move very far during each calibration step, as a result calibrations take a very long time and will sometimes fail.

Another observation. When guiding near the pole, shooting comet PanSTARRS at near +80° declination, I encountered very regular declination errors using PHD. Every couple minutes the dec error would deviate by about a pixel, alternating in each direction. Shutting off the declination correction worked pretty well, the mount was polar aligned accurately enough that there was very little declination drift.

I still have yet to understand just why the STi will not directly interface with the ZEQ25, something in the ratings of the photo-isolators used in the STi? The manual simply states these are good to 25mA and 25V, which seems generous for the task. It may be in the voltage levels, I did discover that the iOptron uses 3.3V on the guide port. Perhaps the STi will not pull down low enough for a valid low logic level? I built the USB to ST-4 adapter with MOSFET optocouplers, these can switch harder than standard photo transistors.

UPDATE– The interface issue was just a cabling problem. The same cable I use with my Losmandy G11 does not work, it is flipped from the pinout needed for the ZEQ25. With a corrected cable I now connect the STi directly to the guide port on the ZEQ… It works.

TeleVue-76 to STi Autoguider Mount

A rigid mount to adapt the TeleVue-76 to the SBIG STi autoguider? I need such a solution, I have both of these bits of kit that need to be wed together for the minimal astrophoto setup. As I am unlikely to find such a part commercially, I would have to make it myself.

Another couple hours in the machine shop were in order, another small pile of aluminum chips. This actually went pretty quickly, these are easy cuts to make. No tapping is required, the four holes are simply drilled through. The two hours included design and cleanup for a quick project.

STi to TV-76 Mount — The SBIG STi to TelevVue TV-76 mount

TeleVue Autoguider Mount — Mechanical drawing for a mount to attach an SBIG STi autoguider to a TeleVue refractor

I came up with the design on the fly. A piece of aluminum from the scrap bin and a couple quick measurements of the ‘scope and guider. I simply cut aluminum until it seemed about right. It was only after the fact that I produced a drawing of the finished item.

The TV-76 has a rather non-standard mounting point on top for accessories like this. A pair of #10-32 threaded holes, 0.75″ apart and located in a slot 0.625″ wide milled into the mounting ring. This seems simple enough. An adapter made for the TV-76 should work with any of the TeleVue refractors that use this mounting. Another concern is that the solution must also be very rigid, any flexure between the autoguider and the telescope will result in smeared stars.

The design assumes that you have the additional guiding kit sold by SBIG for the STi autoguider. This provides the mounting rings that clamp the camera body.

The hardware required will be two ¼-20 x 1½” socket head cap screws, and two #10-32 x 1″ socket head cap screws. A pair of plastic press on caps convert the #10 screws to knobs. All parts you can find in a neighborhood hardware store.

The mount is 1.5″ high to set the autoguider away from the main OTA, as to not encounter any vignetting. This also allows space to get fingers onto the mounting knobs. The dimensions are chosen so that standard screws protrude by just the right amount. I messed this up on the one I made, machining the center to far. As a result a few washers are needed for the screws that mate with the refractor. This is fixed in the mechanical drawing.

To co-boresight the TV-76 with the autoguider it was necessary to slip a 1/4″ washer between the mount and the rear ring as a shim. With that in place the same object is centered in both fields of view. The STi has a 2.7° x 2.2° field when used with the 100mm lens supplied in the SBIG accessory kit. With this wide field of view it also serves as a finder to locate and frame the photographic target.

It assembles nicely, a good start. The true test will be the quality of the images produced by the rig.

Comet C/2011 L4 PanSTARRS

Well past perihelion comet C/2011 L4 continues to put on an impressive show. Amateur sky-watchers have been enjoying the impressive anti-tail reaching out a few degrees from the coma. True, you may need a telescope or at least good binoculars to see the comet. It may be dimming, but still worth the effort to observe.

The iOptron ZEQ25

I had been looking to acquire another astrophoto toy. The desire is for a small, portable astrophoto setup. Yes, I am aware that the words “portable” and “astrophoto” do not really belong in the same sentence, all things are relative.

Thus I have decided on the new iOptron ZEQ25. It is a new design, with some radical differences from the more traditional German equatorial mounts.

The mount is pretty small, a mere 10 pounds of steel and aluminum. Compact enough to be packed into a suitcase for air travel. Performance sufficient to do wide field astrophotography with focal lengths up to 1000mm and a DLSR camera. Perfect for use with either my TV-76 or AT6RC. Unlike my old Losmady G-11 it features a modern GOTO system and can be run from the computer.

AT6RC & ZEQ25 — AT6RC atop an iOptron ZEQ25 mount, note the additional counterweight necessary

The chatter over at Cloudy Nights was promising. A few early production mounts were in the hands of some stateside amateurs, and they have been posting their impressions and images. I was particularly impressed by the measurements of periodic error with results around two arc seconds. This was a small mount that could very easily be a good astrophoto option.

I ordered the mount from the good folks at OPT. It was not yet listed in the website catalog, but a phone call confirmed they were expecting delivery of three mounts shortly. I put down my deposit. A week later I had confirmation that the mount had been received and was ready for shipment to Hawaiʻi as promised.

Continue reading “The iOptron ZEQ25”

Downpour

It looks like it may clear. There should be a few dark hours before moonrise. Maybe I can get the new astrophoto rig out and get everything working properly.

Nothing like two tenths of an inch of rain in half an hour to put a damper on astronomical plans.

Maybe it will clear later.

Scope and Rain — A tropical downpour ends plans to use the ‘scope.

Staying on the Summit After Dark

Beaches? Tropical gardens? The volcano? Yeah, BTDT, not what I came to Hawaiʻi for. Visiting Mauna Kea is at the top of the list for some folks who visit our island, a priority I can fully understand. Even better? Bring a camera to this spectacular mountain. After six years of working on Mauna Kea I still carry a camera and find new shots. Some of the most fascinating photographic opportunities occur after the Sun has set. For those who pursue shots in the dark, long exposure photography, the summit provides a setting that is worth the effort to shoot.

The Keck 1 Laser undergoing engineering tests, Subaru telescope in background

The summit is open after dark, but not unconditionally, I need to stress some explanations concerning that. Officially the Mauna Kea Comprehensive Management Plan limits public recreational use to ½hour before dawn and ½hour after dark. This has not been strictly enforced any time in my experience on the mountain. There is no gate in use, you will see people drive up the summit road in the middle of the night.

So what are the real rules for summit access after dark?

Continue reading “Staying on the Summit After Dark”

Comet C/2011 L4 Pan-STARRS

The weather finally broke, leaving a clear western sky and a chance to photograph the comet. I set up and managed just a few shots before the comet set into the top of a tree across the street.

At least I was able to get on-sky. Much more than can be said about our ‘scopes on the mountain. Observing was cancelled earlier this afternoon, there is too much ice on the domes to operate safely. At least the ice was pretty, and photogenic.

Shift a Little Weight

The trade-winds have returned for the evening. And while they are welcome for the comfortable temperatures they bring, the winds are unwelcome for the problems they create at the telescope. I am trying to get in one last exposure sequence for the evening, but the guider graph shows trouble. There are constant errors, not small errors either. The Right Ascension axis seems to be the issue, with errors of +/-3 pixels on the guider. This is just not going to work.

I watch the graph for a while, trying to figure out what I can do. I have had an issue where the guide star was the source of the problem, two stars to close together, a double star I did not notice when selecting my guide star. I stop the guider and select another star… The problem continues.

As I feared, my problem is most likely the wind this evening, a continual issue on this rock I live on. A speck in the middle of a very large ocean, the winds are a fact of life here. I only shoot with small telescopes, less sail area to catch the wind with a short tube. A TeleVue 76mm, an AT6RC, or simply a wide angle camera lens. The smaller scopes provide less loading for the old Losmandy G11 I mount them on.

I decide to try something else, shifting the balance to load the RA gear down. I gently slide the counterweight down the shaft about an inch. There is barely a blip on the guider as I make the adjustment. Better yet the guide error graph settles down! Looks like I will be able to get in a few more exposures before putting the ‘scope away.

Guider Error Graph — The guide error graph showing the effect of shifting a counterweight.

Postcard from the Universe – Comet C/2012 K5 (LINEAR)

Another product of imaging earlier this week. Comet C/2012 K5 (LINEAR) is fading, but still bright enough to image. Right beside Orion it was well placed to target from my driveway. Just refreshing my comet hunting skills, getting ready for the show over the next few months as C/2011 L4 (PanSTARRS) comes into view.

Postcard from the Universe – NGC1365 and Supernova 2012fr

A photo taken from my driveway of NGC1365 and supernova 2012fr. It is a bright supernova in a classic barred spiral galaxy. I had observed NGC1365 in mid-October with the 18″, noting the beautiful spiral structure. The supernova appeared about two weeks later. I have since observed it in a couple telescopes, including Cliff’s 24″.

The nova seems to be fading now, it peaked around 12th magnitude in November. Currently about 14.5 magnitude, but still easy with the AT6RC and Canon 20Da camera.

The barred spiral galaxy NGC1365 and SN2012fr