Back from the 2017 Nebraska Star Party

Ah, to be back in the land of 10,000 lakes and high dew points!

NSP 2017 is over, and it was a memorable one. Sunday (7/23) was clear and about as good a night as I've ever enjoyed at NSP--or anywhere, for that matter. The day had been in the low 90s, but the temperature dropped quickly as the sun set. There was a strong and gusty breeze that kept the mosquitoes away. (I realize big scope owners didn't like the wind, but I was imaging with a 200mm lens wildly overmounted on a CGEM.) The transparency was exceptional overhead; the Milky Way was nothing short of spectacular.  I don't think you could read by its light as one person predicted, but it was definitely casting a subtle, diffuse shadow.

I was able to collect some light frames of my current target, the Rho Ophiuchi Cloud Complex, then switch over to the Sadr area for the Butterfly:

The Rho frames have yet to be processed. The next night I decided to spend the entire night imaging the Veil:

What I like about this 200mm lens is how flat it is at f5.6, and free of vignetting.  There are two new things about these images:

1. Instead of stopping down the lens with its internal iris I used a step down ring. This gets rid of the diffraction spikes caused by  the blades of the iris.
2. I used PHD and BackyardEOS to dither the images.  It seemed to work very well!

The last night was cut short by clouds, so I only got five frames of the Rho area at 135mm:

As you can see, this lens has substantial vignetting.

By the way, 2017 NSP was on the hot side.  The Monday and Tuesday highs were 106 and 107 degrees, respectively. But it was the usual "dry heat" and both days had those great strong breezes.  I spent the afternoons sitting and reading semi-comfortably in the shade of the supper area canopy. Thank goodness NSP didn't happen the previous week when it had been both hot and humid.

Now it's on to eclipse planning and back to meteor counting!

Back To Imaging for a Bit; The Nebraska Star Party Nears

My wife got a new desktop computer after the 4th of July, and that translated into more than a week of transition from old computer to new. Because she didn't get a new monitor our ancient flat panel monitor was pressed into service so that she could run both computers at the same time. And because it was the monitor on my meteor-detecting computer, that activity was put on hold for the duration.

Luckily we just had a very nice run of third quarter moon clear nights. I was able to get out for two out of the three nights and tested the setup intended for the Nebraska Star Party. This year I'm not chasing any astronomical league program certificates so I'm keeping it simple: Big mount, DSLR, and short lenses.

From my second night out, here's an example:

It's the Lagoon and Trifid nebulae. This is a 200mm f/5.6 image based on only 10 4-minute light frames (ISO 800) and it gets reasonably deep.  This was taken at a light pollution yellow-green transition zone site; I'd like to try this again at NSP to see how much the difference in sky brightness affects the outcome.

Another target will be the Rho Ophiuci area and the dark lanes to its east. And, if there are enough clear hours, some of the dark nebulae that dot the area.  I may even try some super wide fields!

The weather at Valentine has been on the warm side, with some daily highs in the 100 to 105 degree range. The forecast for the first Sunday is much nicer at this point--A high of only 87, and a partly cloudy night with a pleasant low of 60. Monday's high is forecast to be only 88! It doesn't get much better than this.

The rest of this week is NSP preparation. No more imaging until then!

Meteor Detection Using Argo

I should have posted some of the screen caps to show what Argo is capable of showing when using TV stations for meteor detection. These are from a session monitoring CHBX Channel 2 Sault Ste. Marie, Ontario broadcasting at 55.24MHz.

Here's one showing a couple of typical events. At left is an epsilon reflection from a meteor, while the slanted line at right is probably an aircraft flying at flight level somewhere near the midpoint of a line between my location in Minnesota and CHBX.

The next image is of an overdense reflection from what I assume was a larger meteor.

Most meteor reflections are faint and very short in time span (less than a second). The overdense and epsilon reflections are less common, and can come in a variety of forms--here's one:

I would like to catch a nice head reflection eventually.

Because Argo shows so many faint meteors, analyzing a series of screen caps will be interesting--and a lot of work.  I probably won't do much more with this until the Perseids, which fall conveniently between the Nebraska Star Party and the eclipse.

Meteor Detection using National Weather Service weather stations

This is more of an update on what I've been doing since I got things working using TV station video carrier frequencies. Last time I was able to get what looked like a decent diurnal cycle out of a day's observation of Channel 2 (CHBX, Sault Ste. Marie, Ontario); before that I'd tried using regional weather service stations and been stymied by what looked like aircraft-created reflections. I live about 6 miles from Minneapolis-St. Paul International Airport (A Delta airline hub) and it has a lot of traffic.

Argo did so well at getting the most out of the TV data that I thought it worth trying with the weather stations.  It did not fail me.

Here is an 8 minute plot of activity at 162.475MHz:

It's a real mess, isn't it? Most if not all of that is air traffic. To see what it's telling us, let's start with a quieter time and add a little annotation:

The curved lines are reflections from aircraft arriving or departing the airport; the horizontal lines are the carriers from several weather stations. Note that they're slightly out of tune. The audio shift between them is roughly equal to the difference in the carrier frequencies, so all four are within about 45Hz of each other, an error of one part in four million. The strongest two stations ("B" and "C") are probably Rochester MN and Spooner, WI.

Argo shows the reflections clearly. The first diagram contains not just curves like these but other lines that probably represent flyovers, diversions, and other course changes aircraft make near an airport. Unfortunately, none of them look like the things I was able to see with TV.

I'll let the system run overnight and hope that the signals don't saturate like they have in the past. Maybe I'll see some meteor signatures in the flight free early hours of morning?

If I don't, I'm going to have to question the usefulness of weather stations for meteor detection. Even with that negative result I'll probably take my setup to this year's Nebraska Star Party where the aviation activity is considerably less.

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The Virgo Cluster mosaic is now half done:

This is all I'm going to get this year, but it's not bad for such a terrible spring.

Meteor Detection: Some Initial Results

I've analyzed the results of a 24-hour run of the detection system from a few days ago and the results are promising.

The analysis was the visual inspection of 1,542 screen caps taken at 55 second intervals

The columns represent meteor counts in a given hour; for example, column 0 show that about 150 meteors were counted between midnight and 1 A.M. Because I tried to count only things that I felt were clearly meteor signals the above diagram represents an underestimate of meteor activity. Even with that, this is a fair replication of the diurnal meteor cycle. More days of data would be better, of course.

This was performed using my attic antenna monitoring Canadian station CITO, channel 3, at 61.26MHz.

When I went to repeat this it was evident that something had changed with the signal. Meteors were now producing a strange oscillating siren signal that appeared as interwoven sine waves on the waterfall chart.  I noticed that LiveMeteors.com was showing an anomalous signal as well, and shortly after that switched frequency to 55.24MHz, that of a channel 2 station (probably CHBX in Sault Ste. Marie, Ontario).

I've now switched to that same frequency and, using Argo, am collection another day's worth of data.  Argo presents what is essentially a highly zoomed version of the SDR# waterfall, but with a couple of advantages. Argo makes clear that when I use the channel 2 frequency that I'm monitoring several stations at once--there appear to be slight offsets in the carrier frequencies. It also makes it easy to see when a signal is due to a reflection of a local channel 2 from aircraft. (I'll post some diagrams showing this soon.) The Argo strip chart allows me to do a screen cap every eight minutes, which will make counting meteors much easier.

I'll post more as I start analyzing results and gain a better understanding of what Argo is showing me.

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And it's clear tonight! I should be able to get the first half of my mosaic done! Yay!!!

Meteor Detection Using Canadian TV Stations

Last time I wrote about the problems I was having with a meteor detection system that relies on National Weather Service weather radio stations. The problems were so substantial that I indicated I'd be looking into using Canadian TV station signals as the basis for meteor detection. I've now done that in at least a preliminary way, and the outlook is much more promising.

Good introductions into this method are found here and here. In brief, there are a handful of Canadian TV stations that continue to broadcast powerful analog video carriers at frequencies that are near optimal for meteor detection.  Because these stations are located near the U.S.-Canada border, it's possible for most of the eastern and midwestern U.S. to use them for meteors.


There are only a couple of differences between this method and the one using NWS stations:

• The antenna. Not only must it be designed for the lower frequencies, but because you will be listening to a specific station you can use a directional antenna. One catch, though: With the switch to digital TV, lowband VHF antennas are becoming more difficult to find.
• Sidechannels. If you've watched MeteorsLive.com, you probably have noticed that it's tuned to 61.26MHz and not the nominal 61.25MHz. This is because transmitters have added side channels at +/1 0.01MHz in order to reduce interference between stations. Why 61.26 was chosen by MeteorsLive instead of 61.24, I don't know [Edit 6/21/17--now I do...see the next post.]

 Here are the stations that can be used:

Canadian TV stations useful for meteor detection (with channel number)

The nice thing about these is that they're all far enough away that aircraft arriving at and departing from the nearby airport can't cause enhanced reflections. At the same time all of them (except Channel 2 in Sault Ste. Marie) are far enough away that aircraft flying at flight level 410 also can't cause spurious reflections.

My antenna is an old FM/TV multi-element antenna hanging in the attic of a wood frame house. It's directed about 40 degrees east of north. I'm initially monitoring the same station in Timmins, Ontario, used by MeteorsLive.com , which is about 61 degrees east of north. The misalignment probably isn't significant given the antenna design.

I've surveyed the available channels, and only 4 and 6 did not show evidence of any meteor-like signals. Channel 4 in Sydney, Nova Scotia, is beyond the 1400 mile limit and can't provide single-reflection meteors. Channel 6 in Medicine Hat, Alberta lies at a right angle to the axis of my antenna.

Radio path between my position and Channel 3, CITO-TV, near Timmins, Ontario

I'm happy to say that Channel 3 at 61.26MHz is producing a substantial number of strong pulses that resemble those suggested to be reflections from meteors. It actually seems to be working, and working well.

The question now is: Are the meteor-like signal pulses really of meteoric origin, or is some other process at work?  The only way I know to answer this is statistically. Will meteor counts match the known diurnal variation? Will meteor counts become enhanced around the times of notable showers?

(In case you're asking why this couldn't be confirmed using an all-sky camera or some other visual means, you've got a point. A light-amplifying camera set up and pointing toward the transmitter might pick up a few meteors. In my case that camera would be pointing over the Twin Cities, and the light pollution would ruin any chance of picking up anything other than a bright fireball. Worth a try, yes, but not in my plans.)

At this moment I'm running the system, doing screen caps of SDR#'s waterfall display at regular intervals. I'm going to run it for 24 hours and analyze the data to compare frequency and time of day. I'll probably have the results later this week.

I'll do the same at the time of the Perseid shower in mid August.

Stay tuned!

Radio Meteor Detection

The June 2017 issue of the Astronomical League Reflector had an interesting article about someone's participation in the Radio Astronomy Observing Program. What caught my eye in Dr. Alex Vrenios' description of his efforts was his attempt at detecting meteors using forward scattering.

"Seeing" meteors using distant FM station signals scattered off ionized trails of meteors is nothing new.  I've never given it a serious try because the FM spectrum in the Twin Cities is almost saturated. It's difficult to find a frequency that isn't taken by a local station. Dr. Vernios solves this problem by using National Weather Service weather radio stations. NWS stations operate at seven different frequencies, and their coverage is designed to not interfere with other stations. It's usually the case where only one station comes in clearly. Tune to a station frequency that doesn't serve your location and you'll probably get only static, which is perfect.

The downside of using NWS frequencies is that they are not particularly good at scattering from meteors. Compared to an optimal frequencies like TV channel 2 (55.25MHz, more about that in another post) they reflect only about 1/25th as well. That's a whopping 14dB drop in potential received signal. NWS stations also tend to be very low power and run only 1.0 or 0.3 kW. (That's compared to a typical 50 or 100 kW for TV stations.)

That said, the approach seemed innovative and worth a try.  Also in its favor is the extremely low cost of the needed components.  Here's what is needed:

• A crossed dipole antenna that's built to receive NWS frequencies. 
• An RTL-SDR USB dongle. This is a simple device that turns your computer into a digital tuner. It has excellent frequency resolution and sensitivity.
• SDRSharp software for contolling the dongle and presenting the results. It's free!
• Chronolapse freeware for performing timed screen captures of the SDRsharp display.

The antenna is easy to make if you don't plan on requiring it to be weatherproof. The dongle is available from Amazon, and the needed software is downloadable. The entire project can be assembled in one or two days, but finding the optimal settings for SDRSharp may take longer. I'll have more on that later, but for the moment let me show you what the results look like.

To start, here is a map of the surrounding NWS stations of interest with their frequencies. My location is indicated by the red circle.

Next, here is a typical FFT power spectrum and display of power levels shown in a "waterfall" diagram.

You will want to click this to see it full scale. The top portion of the diagram shows instantaneous power as a function of frequency; the seven NWS frequencies are marked.  During daytime three stations can be heard: The one serving my area, loud and clear; A 300W station in Norwood/Young America, poor; a 1000W station at Clearwater, very poor. A signal is evident at 162.4MHz, but no voice is discernible. That leaves three frequencies (162.4, 162.45, and 162.525MHz), none of which has any signal evident. However, as you can see, there has been a short burst of signal at 162.525MHz.

Another example:

This shows an approximately seven second burst at an otherwise silent frequency.

Note that in both cases only one frequency showed a burst, suggesting that the cause was something local to the transmitting station or the path between it and the receiver.

Bursts like these appear to happen frequently during the daytime. However, there are also longer and weaker bursts that show more complex structure. Are those cause by meteors or some other phenomenon?

Sadly, it appears most of the bursts are being caused by reflections from local aircraft. After using the system for a while it became obvious that the bursts were coinciding with air traffic departing from the nearby airport. Recording the waterfall chart all night showed that there were no bursts overnight until a little after 5 A.M., when departures starting taking place.

That's circumstantial evidence. But there is more: I zoomed the frequency scale to see what was happening in the way of Doppler shifts:

Most of the bursts looked just like this, with a significant Doppler shift that diminishes over time as  an aircraft passes. The magnitude of the shift indicates a speed of about 200 mph, which is consistent with a departing, climbing commercial jet.  A meteor would not show this kind of signature.

So the NWS-based system won't work for me unless I can reject the aircraft signals. This is a problematic task.  There's a chance a system like this would work if it wasn't operating a few miles from an airport, but I'll have to leave that to others to discover.

For now I'm moving on to trying out the method utilizing Canadian TV stations that broadcast video carriers at more optimal frequencies. More on that next time.

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One more piece of the mosaic imaged (but not yet processed). There's an outside chance I'll get it half finished this year. 7 down, 9 to go:

Virgo Cluster Mosaic Progress

Last year I talked about creating a Virgo Cluster mosaic that would be suitable for poster-sized printing. Progress has been slow thanks to the abysmal weather we've "enjoyed" this spring, but it's hardly hopeless to think this won't be finished by the time of ALCON 2018. (The convention is being held here in the Twin Cities, and the notion was that a mosaic poster might be sold as a fund-raiser.)

Here's a graphic of my current progress in terms of the 4x4 grid:

Green = completed sub-image

That's six of the required sixteen sub-images done.

Here's a look at the top row stitched together using Microsoft ICE:

Not much to see in this row other than M98 at far right and M100 at middle right.

The middle two sub-frames need to be reprocessed to minimize the substantial moonlight in them. They were imaged during a first quarter moon which was nearby in the sky. This first row suggests that the finished mosaic will be the equivalent of a single 150 megapixel image taken at a focal length of about 135mm. The sub-images are taken using a Canon T2i (18 megapixels).

I wonder how long it will be before consumer-grade DSLRs are sold with 150 megapixel resolution. The new full-frame Canon 5DS has a 50.6 megapixel sensor!

There's a chance I may be able to get a couple more images done this week to put me at the halfway mark, but the Cluster's availability for imaging is fading fast as time goes on.  The next new moon will be the last opportunity to image it this year.

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Next time: First attempts at meteor detection using National Weather Service weather radio stations, a home-built antenna, and an SDR dongle. And possibly more venting about the President and my pseudo-conservative, pseudo-intellectual, Congressional Representative.

PoleMaster--A Quantative Estimate of Accuracy

It's one thing to say how nice a PoleMaster works based on a practice run indoors, but the real measure of its usefulness is the accuracy of its polar alignment (PA). A practical measure of PA accuracy can be found by examining images of either long exposure time or a sequence of short exposures taken a considerable time apart. The other night I was able to do the latter by taking 4 minute exposures during the course of about 1.7 hours.

To get an estimate of PA error one needs to know the declination drift rate and the declination of the target.  A good reference for how this is done is an article by Frank Barrett, "Determining Polar Alignment Accuracy."
 
I shot 15 light frames using autoguiding and then aligned the first and last in the sequence using ImagesPlus. A nice feature of IP is that it tells you the field rotation it had to apply during frame alignment; when aligning two frames, it tells you the rotation it performed to bring the second frame into alignment with the first.  In my test case the rotation was 0.02 degrees (72 arcseconds); the elapsed time between the start of the two frames was 65.3 minutes.

Given the above data (and the declination of my field of view) Barrett's Equation 1 yields a polar alignment error of 4.4 arcminutes, which is almost 9 times the maximum accuracy suggested by QHY, the maker of Polemaster. Some caveats are in order:

• This was the first time I used PoleMaster. As with most things, I expect the quality of my alignments will improve. I did use the rough and fine polar alignment methods.
• The coarse reporting of rotation angle by IP means the estimate could be between 3.3 and 5.5 arcminutes.
• The rotation reported by IP is sensitive to the choice of alignment points, and will vary substantially when close to zero like it is here.

Should I be disappointed that the accuracy was not what QHY suggested it might be? Not at all--it's actually quite good if you're autoguiding!

Consider what happens when you guide. The guide star is held motionless in or near the field of view. An error in the polar alignment will cause the FOV to rotate around the guide star. The distance the stars rotate will be proportional to the alignment error and the distance from the guide star. A guide star at the center of the FOV will cause the greatest distortion of star shapes at the four corners of the field.

Since this will get highly mathematical quickly, I'll try to make a worst-case example and see how bad it can be. I'm going to assume that the guide star is within the FOV (as it was for my test case) and located at one of the corners.That star will remain fixed thanks to guiding, but the image will rotate slowly around it because of PA error. In a long exposure this motion will result in oblong or streaked stars, with the worst effect at the greatest distance from the guide star. This will be at the corner opposite the guide star.

Let's set an arbitrary limit of a star being oblong by one pixel. Any more than that and we won't be happy.

The distance between opposite corners is calculated from sensor dimensions in pixels; for my DSLR it's 6,230 pixels. The rotation rate calculated above (0.02 degrees in 65.3m) corresponds to 0.0000053 radians per minute.  The tangential star movement is therefore R * 0.0000053 pixels per minute, which equals 0.033 pixels per minute. Take the inverse of this to find the time it would take for the star to move one pixel: 30 minutes. Therefore one can expect to be able to use 30 minute exposures and have only a one pixel of star elongation at worst when the PA error is around 4 or 5 arcminutes.

Keep in mind that this is only a very rough estimate, and it ignores how the effect varies with the parto of the sky being imaged.  To minimize field rotation effects, follow a couple of rules:

• Keep your autoguiding scope reasonably well aligned with the axis of your imaging optics; if possible choose a guide star near the center of your image
• Always align light frames with both translation and rotation

The idea that a 4 to 5 arcminute PA accuracy is good matches my impression from the images I collected. My polar alignment is usually obtained using an impatient application of the drift method assisted by PHD2 guiding. It's rarely ever the case that stack of subs doesn't need some minor cropping to get rid of field rotation effects at the edges of the FOV.

My first time imaging with PoleMaster produced no edge effects. That's a huge improvement over my usual polar alignment. Combine that with the ease of using PoleMaster and it's clear to me that it represents a great innovation for astrophotography.

Polemaster--Better than advertised!

It's been a week of disruptions and minor mayhem here, with clear nights that have been out of sync with my ability to take advantage of them. Until last night, that is.

My new Polemaster polar alignment tool worked quickly to give me a good polar alignment (as yet unconfirmed photographically). This was my first time trying it and I doubt if it took more than ten minutes to go through the basic and precise alignments. Some comments:

• You initially need Polaris in the field of view. All I did is level the mount, set the altitude for my latitude, and get it eye-aligned with north. No bending down or stooping to sight through the polar axis. This brought Polaris into the field, although near the bottom.  I adjusted altitude and azimuth further to roughly center Polaris before beginning the alignment process.
• Don't be put off by the coma you see around stars that are away from the center of the field of view. This isn't an imaging device for making pretty pictures; think of it more as a star detector. The coma shouldn't enter into the centroid calculations in a way that matters to the result, anyway.
• Under the glow of my inner red-zone sky the device had no trouble finding the needed stars; The field looked best with the gain set to maximum. 
• Several times you are asked to use the software to rotate the field of view. The rotation steps are a little coarse, making it difficult to exactly center stars in the target display circles. I don't think this matters much at all; all you need to do is get it reasonably close to the center.
• At one point you use your hand control to rotate the field of view and see that a star stays on a displayed circle. If it goes off the circle you have to start over, but with modest care when specifying stars (using double clicks) the star will stay right on the circle.
• Unless the manual has been rewritten, ignore it for the actual process of aligning. Instead follow the on-screen guidance--it's clear and perfect.
• The USB cable is kind of short, but not so short as to cause a problem. Next time I use it I'll try adding a short USB extension cable.
• When I was done the precise alignment indicator (showing a tiny box and circle whose centers will coincide when alignment is perfect) suggested that I was within atmospheric limits of perfect. Simply touching my mount would lead to a shift away from perfect.  This makes me wonder if the process is best performed when the mount is already loaded for imaging.

In summary, the Polemaster alignment procedure was smoother and simpler than I expected. Although I don't yet have tracking data or an image to confirm the quality of the polar alignment, I'm confident it was at least as good as most of my manual efforts using PHD or visual drift. And it was much faster and easier!

Micro Update

It may be clear tonight! That means I can test my new PoleMaster. I probably won't do any imaging because I'll be in my light-polluted back yard. I could travel to Cherry Grove observatory, but the recent heavy snowfall (about 15 inches at the observatory) has probably made the site unusable.

Tomorrow I hope to add a glowing review of the PoleMaster to the many that have been written.
 

A New PoleMaster Waits for Clear Sky; Step-down Rings

Another inch or so of fresh snow here as March begins, along with continuing clouds at night.

PoleMaster update: My PoleMaster (PM) arrived and all is well so far as I can tell without some stars to try it on. I'm not going to give you an "unboxing" description other than to say it arrived quickly from OPT and in perfect condition. Withing the cardboard shipping box QHY encloses the PM in a tin box. I'm not sure if this is supposed to be for storage or marketing effect.

Some commenters have mentioned that the included USB cable is a little short. I don't think this will be a problem because the PM mounted on my CGEM's polar axis port is basically stationary.

A really nice touch concerning the cable is that it attaches solidly to the PM using two small thumbscrews. I hope this helps correct one of the banes of using the Orion StarShoot Autoguider camera, which seems almost eager to drop its connection during polar alignment.

The adapter for my CGEM mount fits perfectly; The PM camera locks with ease onto the adapter. The Camera sits on the mount without any play and can be removed easily when alignment is done.

The PM manual is every bit as difficult to understand as people have said. I would guess a better translation is in the works--it's needed!

I'll say more after I actually use the PM.


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It's common practice to stop down a lens when imaging with in order to give sharper stars and less chromatic aberration. This is usually accomplished using an iris made of metal vanes that form an adjustable diaphragm. Because the inside edge of the diaphragm resembles an equal sided polygon, it causes a spike-like diffraction pattern that can be very evident around bright stars. here's one from the image I posted last time:

A Most Imperfect Star

The purple blob just left of the star is an internal reflection from somewhere in the lens. Multi-coating can only do so much, apparently. And you can see the dimmer stars suffer from shape and aberration problems. It's a $40 lens, so I'm not expecting anything close to perfection.

The spikes in the image are from stopping the lens down to f/5.6 from its wide-open f/4. Perhaps you don't mind spikes like these in your images or think that they add esthetic appeal.  If you don't like them, or simple like round stars better consider using a step-down ring (SDR).  An SDR attaches to a lens just like a filter and act as a bladeless diaphragm. Here's what one looks like:

55mm to 37mm Step Down Ring

To figure out which one is right for you there are two numbers you'll need to know: The filter size for your lens and the iris diameter for the focal ratio you plan to use. Let's take my Tamron 135mm lens as an example.

We begin by finding a little circle with a vertical line through it on the lens. It looks like a Greek letter phi and will have a number next to it.  Usually this is found on the specs ring at the front of the lens, but on my Tamron it's on the side of the lens. As it turns out, my Tamron takes a 58mm filter.

I find that the Tamron works well at f/4 rather than its wide-open f/2.5. The f/4 objective diameter of a 135mm lens is just 135mm divided by 4, or 33.75mm.

Therefore I would use a 58mm to 34mm SDR. Easy! Or maybe not.  SDRs don't come in every possible size, so you may need to take an inner ring size that's not quite what you want or get creative by using multiple SDRs.

Because SDRs have threads on the inner circle it's possible to fit one into another. It happens that the SDR my Tamron wants is not one I could find. There is a 58mm to 55mm SDR, a 55mm to 37mm SDR and a 37mm to 34mm SDR; used together they give me the 58mm to 34mm I want!

As it turns out, my Zuiko 200mm lens needs a 55mm to 37mm SDR, so I have two reasons to buy it. And if I want, I can use the two smaller SDRs on my Zuiko to give it a focal ratio of f/5.9.


How will this all work out? I'll let you know when the SDRs arrive from Ebay and the sky clears!

The delight of BackyardEOS, A rare night in February

Last Friday night was an exceptional evening in Minnesota.

• The Moon was out of the sky from dusk to almost 1 A.M.
• It was clear
• The dark site observing field was essentially snowless
• It was an incredibly warm evening--by 1 A.M. it had fallen only to around 40F.
• The wind was for the most part very light to calm, so there was no real wind chill factor.

 Best of all my evening was free!

It's difficult to emphasize how rare that evening was. The February 17 average high and low for nearby Cannon Falls is 29 and 10, so it was a good 20 degrees warmer than average. Usually the warmer weather correlates positively with clouds, too.

I originally intended to image the Witch Head nebula because my previous image of it is rather poor; noisy and crossed by an amazing number of geosynchronous satellites. A slow start to the evening made me go with something a little easier--the far brighter M42 area. It turned out better than i expected for 2.1 hours of 5 minute exposures at f/5.6:

I was able to faintly capture some of the dimmer clouds in the outlying areas just to the left of M42. The red patch at the upper right of center edge is an extension of the Horsehead nebula area.

When M42 began to sink I went to comet 45P and got almost an hour and a half of that:

This wasn't deep enough to get even a hint of the fainter, bluer tail. Oh, well...I'll take it!

One of the best things of the night was using BackyardEOS for the first time. It's a joy to use, and despite its power it keeps things easy to use. Next time I'm going to use it to tackle the mystery dithering!

I also got a demonstration of PoleMaster, a hardware/software tandem that makes getting an excellent polar alignment easy, fast, and actually fun (well, compared to drift aligning, anyway). It's definitely on my to-buy list ($300 from OPT). I would really like to take some very long light frames this year in Nebraska, and this would help. Even though PHD2's polar alignment utility is slick and gives good results, I can see how much easier (and probably better) PoleMaster would make getting a good PA.

Workshop presentations

The topic at the recent workshop was guiding for astrophotography, and a club member sent me a link for a really good explanation of how to guide.

Here it is (It's for PHD 1.13, but although some things have changed with PHD 2, this remains a great read!

The folks working on PHD 2 have also prepared a guide for using it. It's not as comprehensive a treatment as the above source gives, but it's a fine explanation of PHD 2 usage.

Want to download PHD? Here's where you go:

PHD 1

PHD 2

I recommend PHD 2 because of its new features--I particularly like the drift polar alignment tool. If you have multiple guide scopes, guide cameras, or imaging mounts, you may like the ability to create profiles for different combinations of those. I've found version 2 to be more stable than version 1, but that may only be on the OS I use (Windows Vista) I hope to upgrade my imaging laptop this year to a Windows 10 model and will have more to say when that happens.

Brief update

Last night was our club's second imaging workshop. The topics were guiding and focusing, and I can't say I did a good job as the sole presenter. The audience was amazingly diverse in interest and skill levels, and I had been given all of 24 hours to prepare. Regardless, it seemed as if most had a good time and there was a sense that we should meet more often.

After my presentation we went to the observatory and tried to do some guiding. The club scopes use ST-80/Starshoot Autoguider combos for guiding, and the software is good old PHD. At first we couldn't get the guiding working; the scope was wildly out of focus. Once past the focus issue, the mount simply refused to respond to movement commands from PHD during calibration.  As it turned out the SSAG to mount cable had gone missing; it may have been removed when the scope pier was replaced and never returned. A hunt failed to turn up the cable, but luckily I had one with me and we were finally able to get the mount guided. By this time most of the attendees had dispersed (it was 15F) so not much more happened.

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Next weekend is a candlelight skiing event at a central Minnesota state park, and I'll be shooting some demonstration images to complement views through a friend's refractor. I really hope it won't be as cold as it was last night!

ALCON 2018 Graphics

The big Virgo Cluster mosaic is still on track.  Imaging can't really start until late February or March, which will give me some time to learn about MSICE, the software I will used for merging the mosaic's panes. I've got to create this spring so it's ready as a promotional item for ALCON 2018, which is being held in the Twin Cities. I designed the logo for the event, seen below in two versions:

Our club is organizing some imaging workshops for the late winter and spring. I've been temporarily been put in charge of the processing workshop and it will be a challenge. Approach it by general methodologies or concentrate on specific software packages? That's something to be worked out with attendees--what they want is what we'll do.

I completed my AL Globular Cluster imaging and will be getting the certificate at the next club meeting. How I went about it (getting most of the list globs in one image of M31) may trigger a change in the imaging rules--Bob Kerr administers the list and is a member of the club, and I've talked with him about it.

It's almost time to put together the third annual list of regional star parties for the club forum. I think the August total solar eclipse is making scheduling a little difficult for clubs.

More about the eclipse and my plans for it--perhaps next time.