Back From NNSF: Tamron 135mm Verdict

NNSF 2025 was better than average; I had two solid nights of imaging. I might have had three if I had stayed over on Sunday night--but I'm not really sure if it was clear that night.

The first night (Wednesday) was a dusk-to-dawn session and I used my FSQ-106 to collect the green and red channel data I needed to complete my integrated flux nebula image. Plus a few more luminance and blue frames, just because I could. I'll be processing that data in the next couple of weeks.

Thursday night was lost to clouds, but Friday night was fine and I went until about 3 A.M. using the Tamron for wide-field views. The Tamron was stopped down to about f/5.4, basically reducing it to a one-inch f/5.4 telescope that no one in their right mind would use for imaging. It wasn't surprising that the results were less than adequate. Here's the Veil:

Final result, significantly cropped to hide flat frame errors

This is based on about 60 frames in the LRGB ratio of 2:1:1:1, with each frame a 120 s exposure. Bias, Dark, and Flat frames were applied; processing was in PixInsight.

That's not completely terrible if you only look at the much scaled-down size. But the faults are still there.

There's an overall blue cast to stars, due to problems with the red focal point and probably chromatic aberration. 

The stars are quite bloated, probably because of the tiny aperture used. I tried to reduce them as best I could, but you can see how the Veil is almost lost in all the stars.

There was good news, the new mounting ring made rotating the camera easy and reliable. And stopping down the lens and processing with BlurXterminator made the stars nice and round even in the corners:

PixInsight Aberration Inspector Panel

The red focal point was substantially different from what NINA expected based on filter setoff training. The Astrodon LRGB filters I use are essentially parfocal, so I have to assume this is some sort of lens fault.

Final judgement: I don't want to do wide field at a sluggish f/5.4, I don't like bloated stars, and autofocus is something I can no longer live without. This image just isn't what I consider acceptable, and I also like to guide and dither. Although the above image used neither and turned out fine -- the G-11 tracks well enough at 135 mm -- I think some dithering might be helpful. So: the Tamron will be relegated to daytime use and I'll need to find a replacement. How about that Rokinon? Or maybe the identical Samyang? Why pay an extra $50 for the brand name?

Here's the kit to go with a 135mm f/2 Samyang: A cradle from Astrodymium that will let me attach a guide camera and a ZWO EAF, giving me my precious autofocusing!

Now let's address the backfocus issue, something that has plagued my use of Canon lenses with the ASI 2600. The desired backfocus is something like 45 mm (44 mm + 1 mm to compensate for the filters I use). Conventional wisdom says you must be within +/- 2 mm, and that being within +/- 1 mm is preferred.

Solution 1 is to use a Canon to M42 adapter with maybe a 1mm spacer ring: ASI2600 (12.5 mm) + ZWO EFW (20 mm) + Canon adapter (10 mm) + spacer ring (1 mm) = 43.5 mm backfocus. That's off by 1.5 mm, which might be enough to show up visually. It would be nice to slip in another space ring, but there just isn't enough thread depth for it.

Here's a video by someone with exactly the same gear I would be using, and she's happy with it.

I don't know if that will hold true for me, though. Maybe variations between lenses might be enough to require a closer backfocus match. Maybe imaging at f/2 changes the amount of filter backfocus compensation? It would be nice to have some options.

Which brings us to Solution 2: ASI2600 (12.5 mm) + ZWO EFW (20 mm) + spacer ring (1 mm) + (extension spacer) 5 mm + spacer ring (0.9 mm) + M42 adapter (5.5 mm) = 44.9 mm. (I don't have two 1 mm spacers.)

There's even a Solution 3, since I have a 7.5 mm extension ring: ASI2600 (12.5 mm) + ZWO EFW (20 mm) + (extension spacer) 7.5 mm + M42 adapter (5.5 mm) = 45.5. I actually prefer this as it it eliminates the spacer rings and allows all the threads to engage more fully.

All the orders have been placed, and things start arriving in only two days! Plenty of time to get this assembled and running before the Iowa Star Party in October.

Next time, the IFN image and a look at the new Samyang!

Northern Nights Star Fest Featured a Wonderful Aurora; Trying to Image the Soap Bubble

I've returned from the Northern Nights Star Fest, where I had two solid nights of imaging. The first was cut a little short by a spectacular display of aurora, not that I minded at all. 

Most of the night the northern horizon had been aglow. Not terribly bright, but obviously there with occasional pulses within it. 

About 1:30AM the glow became much brighter and began to expand upward from the horizon. Soon it was bright enough to cast shadows and was casting pillars upward, starting with an intensely blue streak that was initially mistaken for the onset of a Steve event. By 1:45 intense upward pulsing had begun contained within a bright-edge envelope. Pulses were rapid bright and chaotic, and their areal extent grew to encompass the entire northern half of the sky. My impression of them was driving at high speed through very patchy fog, brightly lit by the car's high-beam headlights. The dominant color was the usual pale green, with some reds in more persistent bright patches closer to the horizon.

The impact of the aurora was quite evident in the stream of two-minute luminance exposures I was taking:

Mean pixel brightness during the imaging session.

Notice that in my impatience I started imaging at 9:18, well before the end of astronomical twilight (9:42) and you can see the sky continuing to darken through my 15th frame at 9:43.  At about frame 97 (1:02AM) the sky begins a slow brightening probably due to the aurora. At frame 101 (1:08) the brightening rate begins accelerating. 

I was imaging a 2.5 x 1.7 degree field centered on a point between the Crescent Nebula and the Soap Bubble in Cygnus. At 2 AM this was at about 53 degrees altitude directly west. The bright boundary (a curtain?) began moving through the field at about 1:53AM and took perhaps ten to twelve minutes to fully exit. Once clear of my FOV the field was full of pulsations which gradually weakened.

The period of intense auroral activity in the FOV is better seen in this expanded view:

Expanded view of auroral interaction with FOV; not the frame numbers have been offset by 120 for better legibility

By the end of my session at about 3AM the aurora was gradually dimming but still a strong source of natural light pollution. Because the aurora created nasty gradients as it crossed the FOV I'll have to discard those frames, along with others nearby in time.

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Oh, the image I was collecting data for is being processed (see first results later in this post). I don't have much hope for the target (the Soap Bubble Nebula next to the Crescent), so I'm processing the luminance first to see if I can see any sign of it. I have 118 good frames (not quite four hours) after tossing a handful of poor tracking frames and those around the time the aurora was bright.

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Other NNSF personal news:

This was the first time that I performed on-site collection of flat frames (and dark flats). I used NINA's built-in Flat Master to vary my light panel's brightness. This made it possible for all the frames to be one second exposures. Flat Master collects flat darks for all four LRGB channels. Since these are all at the same exposure time, three of the channels' flat darks are redundant. This means a little time wasted, but since this can be done during twilight no harm is done, and the extra files can simply be deleted.

Power consumption was about what was expected. With the laptop-specific battery powering that, the main battery handled the first night's 5.5 hours of mount, dew, and camera cooling with 163Wh. The second night's 4.5 hours consumed 136Wh.  This averages to about 30Wh per hour of imaging or a continuous power requirement of 30W, which is the number I wanted to determine for planning my energy use. 

Let's apply that to the upcoming Iowa Star Party in the first week of October to see what will be needed. That night there are about 9 hours 23 minutes available for imaging. Let's assume three nights of clear sky, so that's at most about 28 hours of imaging. Sounds great!  28 hours x 30W =  840Wh, which is about 240Wh more than my battery can provide. Therefore, I need either AC or solar for charging. Day length is about 11.5 hours, and let's assume the first and last two hours of daylight is unproductive. That gives 7.5 hours to get that 240Wh. That's 32Wh per hour of daylight if it's to be restored in day, or 16Wh / hour if in two days. I think a 50W solar panel should be up to this charge rate, so I've put my 100W panel up for sale. Now I just need to find a replacement in time for October!

UPDATE: I looked at what was for sale on Amazon and saw that the 50Ah battery I previously purchased was on special with an added dealer discount. By far the simplest solution is to bring a second battery and swap it in after the second night's imaging, or patch it into to my power box through the charging port so the two batteries can operate in parallel, providing almost 1.2KWh. Not only an amazon special, but a 10% off dealer discount, too. I went for it.

As for the laptop-aux battery, it was still at 13.3V rest voltage after the two nights, so it's unlikely to need recharging.

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Just registered for the Iowa Star Party, one of my favorites--when it's not crazy hot and humid as it almost always is when it's in late July or August. I've suggested to them that they might be better off holding it in September, and this year they finally moved it -- to October! The average highs then are around 70 and at night it drops to the upper 40s. That's my kind of weather!

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So how did that soap bubble image turn out?  I think "barely there" is the best I can say. Here's the full field at 1/5 scale:

1/5 field LRGB

Okay, Let's get rid of those stars and look at the central portion of the image:

This is a teeny bit better; the Bubble is at lower left, click to enlarge

It's clearly there and has a hint of the correct color shift toward blue, but it's still nothing close to adequate. 

This is based on 3.93 hours of luminance, and each of the RGB channels averaged close to 1.27 hours. What's this in terms of total exposure time? Adding together all the light frames (there were 233) that's about 7 3/4 hours of photons collected. To my way of thinking it's more like 5.2 (3.93 + 1.27) hours.  Whatever way you slice it, it wasn't enough, and double (or even triple) the time is going to be desired to make this look halfway decent. It might also be useful to take the luminance a little deeper. So maybe this will be the target for the Iowa Star Party?

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One last thing, it seems to me that Donald Trump has only one purpose in life: The feeding of his own Ego.  This is not unusual for politicians (see: Lyndon Johnson) but Trump pushes it to pathological limits. You saw in the "debate" how easily his vanity can be used to manipulate him. This is not a tactic invented by Harris; it's a lesson the world has learned from his interactions with authoritarians such as Putin. Trump envies his abuse of power and would seek to imitate it here, replacing the rule of law with the rule of the iron fist. Because I don't think the Grand Experiment of Democracy has yet to run its full course, I will not cast my vote for someone who seeks to sacrifice it to his need for self-gratification.

Oh, and Trump's policies, particularly toward women, stink.

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That's enough for this post. Have fun everyone! See you in October in Iowa!

Plans for Summer '24

Because last year's plans went so well (which I write with heavy sarcasm) I'm going to make new, possibly better plans for this year.

Star Parties! From none last year to three this year?

The Iowa Star Party finally moved their party date from the usual late August to October. Now although I just love camping in sweltering heat and dew point temperatures of 70+ degrees F, this is a welcome change. It's bound to be cooler in October, I hope, and by then the expected layers of smoke will be gone or at least diminished. As soon as registration opens I'm signing up, and that's meant with sincerity. 

Iowa Star Party

The IaSP has always been one of my favorites. It doesn't have the darkest sky, but the facilities are nice and the observing field is big and open. Civilization (small-town Iowa style) is only minutes away in Coon Rapids (population 1279). My imaging target will be a revisit of IC 348. Here's my image of it from Stacy, MN in 2014:

The bright star is Atik (Omicron Persei) and the dark clouds beneath are Bernard 3 and 4. This was imaged with my TV-102 and ST8300 Camera.  I thought at the time it was an interesting subject, and now I'll go after it with better gear, better sky, and (I hope) more time on target. There is a large emission nebula in the right half of the image that is barely hinted at here. Definitely needs better data!

Northern Nights Star Fest

With the Iowa Star Party vacating the labor day weekend there's no longer the usual schedule conflict with the NNSF, a north-woods party sponsored by the Minnesota Astronomical Society. The dark sky is spectacular for this party; aside from clouds the only thing that might cause problems is a nice Aurora. I've already made my reservations for this and have selected a target: the Soap Bubble. This is a pretty little planetary nebula sitting near the Crescent nebula in Cygnus. Here is my 2013 image of the crescent:

This Ha+OIII narrowband image from my light-polluted back yard is far too brief to capture the Soap Bubble; if you know just where to look in this image you can see it's not there. Sometimes the data simply aren't adequate. Repeated attempts at overprocessing failed to pull it out of the noise. The hope is that with the dark sky of the NNSF and a few nights on this one one target using LRGB--it will be there!

Nebraska Star Party

NSP is always a challenge. Heat. Thunderstorms. Mosquitoes, little prickly pear cacti, and in recent years, unusually high humidity.  Add to that layers of forest fire smoke and even unhealthy air quality as Canada burns. (It's possible the smoke may be part of a long term trend.)  I hope to go, but it will probably be a wait and see game to see if it's worth the travel time.

If I do make it, I think I'll update yet another old image of mine, M8 (the Lagoon). Two solid nights on the Lagoon should produce something spectacular! And if there are three or four good nights I'll tack on an overlapping frame to make a mosaic of M8 and M20 (the Trifid Nebula)

From the 2013 Iowa Star Party:

Nothing special, but I was pleased with it at that stage of my deep sky imaging. The scope was a 72mm f/6 refractor. Eleven years later I'll use a 106mm f/5 scope; I should be able to do much better.

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Next post --- I'm still looking for a reasonably close-in camping location that is convenient to use on a same-day basis and has at least green-zone darkness as defined by this scale. I visit two new campgrounds two hours from a southern suburb of Minneapolis, and revisit three others that I previously found unsatisfactory to see if anything has changed. See what I learned this time around.