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!

Revisiting the Tamron 135 mm Lens.

Perfection is a terrible thing, being both difficult to define and impossible to achieve. It can stand in the way of getting something done, and lead a person to reject things that fail to meet your estimation of perfection. It has led me to consider getting rid of my old Tamron 135 mm lens. (Yes, I'm talking about that lens again. I could subject you to more battery talk, but no one really wants that, right?)

The Tamron was dropped from my integrated flux nebula imaging project for two primary reasons: the mounting ring I had made it all but impossible to consistently orient the camera, and it was showing too much aberration. 

I've now purchased a much better ring from Agena Astro. This ring and the dovetail it's on will also help with the limited rotation the old one allowed. The extended ring release knob release knob also eliminates the difficulty in turning the old knob, which was tight against the ring itself. I doubt the new ring will be "perfect," but it may be much more adequate that what it replaces. 

As for the aberration, I blamed that problem mostly on incorrect backfocus. I had assumed 45 mm was needed (44 for the camera plus 1 for the filter). My setup had backfocus of 12.5 (camera) + 20 (filter wheel) + 10 (canon to M42 adapter) plus 1 mm (spacer ring) for a total of 43.5 mm. This was 1.5 mm short, and the way people talk in forums that was seriously incorrect. 

But what if it wasn't? Watch this video. The imager is attaching an ASI 2600MM (my camera) with the same ZWO EFW as mine, a 135 mm lens (not the same as mine, sadly. She had the Rokinon 135 mm lens that I continue to lust after), used the same Canon-to-M42 adapter as mine, and a 1 mm spacer ring for a total backfocus of 43.5 mm (the same as mine). That gets her nice flat fields, so it's probably the case that my backfocus isn't the issue, it's the lens quality. 

A late-1970s Tamron at f/4 is no match for a modern lens like a Rokinon even if their inflation-adjusted prices aren't all that different. The obvious fix is to stop the Tamron down, perhaps to f/5.6. To do this without spiked stars requires a 58-24 mm step down filter adapter. (I found a 58-25 mm adapter on eBay ($2 + $15 for shipping), so I'll be shooting at f/5.4, which is close enough. Delivery date is projected to be August 18, two days before the Northern Nights Star Fest. 

These two issues settled (perhaps) the Tamron will continue to live.

If it arrives in time, I'll take it north and skies permitting put it to work on this:

Heart and Soul Nebulae with the Double Cluster

This is a very rich field ...

Above image with annotation

... with so much nebulosity and open clusters, too!

First priority will be collecting the green and red channel light frames to complete the IFN image. That should take only one night with time left over for more luminance frames. The Tamron will come out on the second clear night, assuming there is one. If the Tamron's aberration is still significant, I may switch to my 200 mm Olympus lens which has already proven itself to be flat-field at f/4. The Olympus will narrow the field to just the two nebulae.

Just in case NNSF produces four nights (!) of clear sky I'll bring along the 200 mm lens for some fun! And maybe even my 50 mm Olympus lens, why not.

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In terms of comfort sky clarity this summer has been one of the worst on record, with days and nights alternating between excessive heat and humidity, rain and severe weather, overhead smoke, and very poor air quality. In fact, half the days since mid-May have featured one of these unpleasantries (per the State Climate Office). My hope that the smoke will diminish before NNSF is only that, a hope. I'm fairly sure the fires will be much reduced by the time of the Iowa Star Party in October, but it would be nice if the new moon in September is also smoke-free!

We're currently in the midst of a multi-day air quality alert covering the entire northern Midwest. Yesterday morning the air smelled of sulphur and the sky has been a perpetual brown.

Air Quality Map @ 2 PM CDT 08/01/2025 (graphic from fire.airnow.gov)

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August 1 brings more tariffs, and it's time to check on that Rokinon lens. The "new" tariff on on South Korea is about the same as the existing one, so it's no surprise that the Rokinon is holding steady at $449.

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That's all for this time, next post is in late August with results from the NNSF (I hope!)

Poor Weather & Caregiving: Renewing my Science Fiction Reading; The Tariffs at Work: Rokinon 135mm f/2 Lens Price Update:

Note that this post has little to do with astronomy or astrophotography, so if that's your only interest save yourself some time and move along 😉 

I've been astro-inactive for a while. There haven't been many opportunities for imaging; spring of 2025 in Minnesota has been cold and cloudy at night and sporting occasional snowfalls that recoat the ground. More important is that my wife had knee replacement surgery near the end of March; I've been home acting as her caregiver until she regains her mobility so even if the weather had been cooperative I really couldn't have be going out all night for imaging sessions.

What I've been doing instead is taking advantage of waiting room time by reading recent science-fiction novels. Given my age it's hardly a surprise that most of my sci-fi reading in the past has been of Golden Age authors (Asimov, Heinlein, and Clarke) with some of the 1960s and 70s anthologies of other authors mixed in. Larry Niven features large in these because I like hard sci-fi. I'm not entirely stuck in the past, though. I've read most of Ursula Le Guin's novels, much of Connie Willis's work, and several books by David Brin. And yes, even all three Three-Body Problem novels (more or less).

For My wife's post-op month I decided it was time to see what current sci-fi writers are creating. I decided the Hugo Awards would serve as a good guide and started reading my way through the last decade of winning novels. I hesitated at first given that the Hugos include fantasy but decided blending in some "soft" fiction would be good way to grow out of the hard sci-fi rut I was in.

Here are the first two weeks of intensive page turning summarized in capsule reviews, with a few notes for people who don't want to read certain types of content. The year shown is that of the associated Hugo award.

2024 Some Desperate Glory, by Emily Tesh.

This is the story of a woman born and raised on an asteroid fitted out as a militarized stronghold. It's the last, best hope of humanity to resist the conquest of the Majo, a collection of alien species slowly expanding its influence through the galaxy. 

Tesh writes in a way that challenges you to keep up with the story; her style reminded me of Le Guin's in The Lathe of Heaven. While some reviewers semi-dismissively lump the story into the "space opera" category, I think it has some significant things to say about both technology and humanity. The plot leaned a little too much on the deus ex machina trope, but the pacing kept me from being overly bothered.

Content Notes: AS, SC and a whole lot of violence.

2023 Nettle & Bone, by Ursula Vernon

Characterized as a dark fairy tale, this is pure fantasy with kingdoms, princesses, and spell-casting godmothers. It reads as an adult, grittier take on childhood fantasies. I had a little trouble with what seemed like a sluggish start, but once the author started adding supporting characters the pacing improved greatly, becoming a mix of humor and drama.

And then there's the scene in the Goblin Market, which alone is worth the price of the book.

2020 A Memory Called Empire and 2022 A Desolation Called Peace, both by Arkady Martine.

At one level these explore the ramifications of a technology that permits the transfer of knowledge, experience, and to some extent personality from one person to another. (The method here is strictly technological and not biological as with the symbionts of Star Trek.) The focus is on a woman thrown into the role of ambassador to a galactic empire. She's only somewhat prepared for what happens, and part of the fun and terror is her having to cope with an alien (albeit human) culture. The author's world-building is based on real past human empires and is fascinating to see unfold.  

Fans of Babylon 5 may wonder if the author intentionally borrowed from that TV series. The protagonist comes from a large, rotating space station (some of the descriptions could fit the Babylon 5 station). There are jump gates that permit movement through the empire and the empire itself resembles what the Centauri might have become if not checked by other spacefaring races and their own lapse into decadence. There's even an aged, ailing Emperor with intrigue between those maneuvering to be his successor. Oh, and let's not forget the mysterious attacks by large, shimmering black, and cloaked vessels from far jumpgates. They sometimes scream as they depart.

I don't mean any of that as complaint. If you want an extensive empire with far-flung possessions spanning tens of parsecs, you need to explain some way of getting around that old wet blanket Einstein. Jumpgates, wormholes, warp drives, hyperspace, folded space, infinite improbability drives, or whatever, numerous authors have already explored the territory. As long as you don't steal technology by its proper name (Sheewash Drive, for example) you're fine. The story is more important than the mundane tech bits.

The quality of the writing is what matters, and in these two novels it more than compensates. 

Content Notes: AS, SC

2021 Network Effect, by Martha Wells

This is the fifth entry (and first novel) in a series call the Murderbot Diaries. I've only read the  introductory novella (2017's All Sytems Red) , and it was a fast, breezy, and intriguing read. Network Effect is a full-length novel and it's recommended that one read everything leading up to it before taking the plunge. So I'm making the collection a birthday gift suggestion and it might be my reading material for this summer's Northern Nights Star Fest (if I'm not stuck at home when her other knee is replaced!)

Content Notes: Lots of violence, as you might expect when the protagonist is named Murderbot. 

2019 The Calculating Stars, by Mary Robinette Kowal

It's no spoiler to say this is an alternative history novel. If you don't mind reading about the many injustices inflicted on 1950s women and minorities (both religious and racial) this is an enjoyable throwback novel that in many ways is very remindful of the 2016 book and movie Hidden Figures.

The story combines both hard science and social commentary. The writing is adequate, occasionally rising to excellent -- particularly at the conclusion. This is the first book in a series of three.

My suspension of disbelief was mildly tested by what I felt like was an overstatement of what the described technology was capable of doing.

2016 The Fifth Season, 2017 The Obelisk Gate, and 2018 The Stone Sky, all by N. K. Jemisin

Yes, an unprecedented three consecutive Hugo awards!

These are world-building carried to an amazing extreme. At this time I'm in the third book and would love to explain what's happening, but my understanding of it is a work in progress. Riding along with the characters as they try to understand what's happening to their world is a big part of the fun. 

The story unfolds in a rather unconventional manner, but that's in keeping with the plot. I'd say more, but it's almost impossible to do so without resorting to spoilers.

Content Notes: Quite a bit of violence, much of it like something from a very dark version of Frozen. 

2015 The Three-Body Problem, by Cixin Liu (translated by Ken Liu) 

This wasn't read during this month's blitz, but I'm including it to round out the decade. This introduces a very alien culture and instantiates the Dark Forest answer to the Fermi Paradox. I enjoyed this book, but found the subsequent two novels (The Dark Forest and Death's End) so unreadable that I hopped rapidly through them to reduce the pain.

Content Notes: Mind-numbing content (mainly in book three and the second half of book two.) 

Content Notes for those to whom these things are important:

AS: Alternative sexualities. I found these were important to the plots, but you may feel differently.

SC: Non-gratuitous Sexual Content. Interestingly, it was The Calculating Stars that had the most explicit sex, suggesting that the author was making the story compatible with readers of romance novels. The only sex scene that felt a little out of place was in A Desolation Called Peace. (And no, I'm not going to tell you what chapter it was in so you can just skip right to it.)

All the stories involve spoken vulgarities, and most feature violence of varying degree.

If you're someone who resents anything that seems the least bit "woke," I'd suggest you stick to the Hugo winners from several decades past. Better yet, focus on the Retro Hugo Awards that recognize works from 1939 to 1954. Two of my favorite stories are there, Asimov's 1951 winner Pebble in the Sky (the first sci-fi I read) and Clarke's 1954 nominee Childhood's End. The latter is an amazing story, and it only lost the award because it was up against the equally amazing and iconic Fahrenheit 451 by Bradbury.

Just so you know, my wife's recovery is coming along wonderfully, and I truly hope that my next post will include some astrophotography news. 

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Tariff Watch:

[UPDATED : On April 5 the B&H Rokinon 135mm lens Canon EF version price rose to $479, $30 up from what it was on April 4. It's now up $110 from it's pre-tariff price in early February of $368. That's an increase of 30%. 

But hold on! The price dropped back down to $449 on April 6!  Was yesterday's price hike an error, or a preview of what happens when they need to restock? Wait and see!