[cuiv]

Hello!

I'm Cuiv, I have bought a Pentax K-1 last year. To be completely honest, I bought a Pentax camera solely for the Astrotracer functionality - overall the lenses just intimidate me though so I'm looking for good lenses for the activity! The number of available lenses is very intimidating, and it seems that telling them apart is super hard for the old ones. So I think I'll just go with a Samyang 135mm f2 lens, or one of the Askar lenses (or maybe a RedCat), but if you have suggestions please let me kno!

Also I am sad that the in-camera intervalometer feature only works with Astrotracer on the Pentax KP, but will likely be getting my sensor astro-modded and get down to it.

Yoroshikuonegaishimasu!

Cuiv

[MarkJerling]

Welcome to the forum!
Regards,
Mark

[Kerrowdown]

Welcome aboard, enjoy all the forum has to offer

[Unregistered User 8]

Hello Cuiv, welcome from Australia.

[interested_observer]

Welcome to the Forum!!!! What type of astrophotography are you interested in - wide-field (Milky Way landscapes) or deep space? The Pentax AstroTracer capability is better suited to wide-field, than deep space (the longer the focal length lens used, the shorter the exposure time with tracking). There is also an Astro group within the Forum - that is very active.

• Astrophotography - PentaxForums.com

[cuiv]

Thanks for all the replies!

To answer the question, I'm looking at deep sky astrophotography - I'm an experienced astrophotographer (with proper EQ mounts, cooled mono cameras, all sorts of narrowband filters, newts, cats, and other fracs, etc.), but the Astrotracer should be good for some widefield emission and reflection nebulae or larger galaxies (e.g. Andromeda) at fairly low focal length and exposure time (even 10-15s exposure time for subframes would so much better than 1 second for signal to read noise optimization).

I will look at the Astrophotography forum, thank you!

[Bob 256]

Thanks for all the replies!

To answer the question, I'm looking at deep sky astrophotography - I'm an experienced astrophotographer (with proper EQ mounts, cooled mono cameras, all sorts of narrowband filters, newts, cats, and other fracs, etc.), but the Astrotracer should be good for some widefield emission and reflection nebulae or larger galaxies (e.g. Andromeda) at fairly low focal length and exposure time (even 10-15s exposure time for subframes would so much better than 1 second for signal to read noise optimization).

I will look at the Astrophotography forum, thank you!

Welcome Cuiv!!

If you have EQ mounts, try the K-1 and a wide lens on them. One big advantage of the K-1 is its sensor and noise levels. The Astrotracer is good if you want an occasional shot without a mount and that shot will be limited time (due to the sensor only being able to accommodate so much image motion before it runs out of movement range). Also as you go to higher focal lengths with the Astrotracer, it has a harder time with tracking accuracy.

For wide fields, the Astrotracer can have issues with blurring edges of the field depending on where you have your camera pointed. Your EQ mount will be immune to such issues. Still, you can get some great shots using the AT.

I too purchased the K-1 with Astrotracer being one of its attractions, and it is a valuable feature, but I find myself using the K-1 with a small EQ mount more often than using the AT feature.

Anyway, good luck with your K-1. I'm sure you'll learn to love it and stay connected with the forum.

[damianc]

Welcome from the Scottish Highlands Cuiv

I've been following your YouTube channel for a while now and always look forward to new content. I'm fascinated with what you can do with the K1

[Sgrim]

Welcome to the forums. I too, am curious about the AstroTracer. I will also have to look into the group.

[interested_observer]

I've actually watched (and enjoyed) a number of your videos - particularly on the K1. Excellent work!!! Pentax really is in need of all the good exposure they can get.

I've been shooting with Pentax AstroTracer since it came out (I always seem to be experimenting with it) - initially with the o-gps1 using the K5 with the Sigma 18-35/f1.8 lens. Then about 5 years ago I bumped up to the K1 (mk I). I upgraded to the K1 to capture better star colors in the Milky Way. Let me add here that I ran into a gentleman out in the field one evening - he had just picked up a K70 and was trying to shoot the Milky Way. I pulled out my GPS unit and we put the Sigma 18-35/f1.8 on his body and he shot his first really great MW image right out of the gate. The K70 with the 18-35 is an absolutely perfect (and fairly inexpensive) combination for MW shooting. It equals the K1 (mk I) in terms of dynamic range (mainly due to the Acceleration Chip) especially in terms of star color. The K70 was announced about the time I picked up my K1 - I might have actually went for the K70 (I feel that it's that good - especially with the 18-35 which is the perfect MW lens).

In terms of astro, all I really shoot is wide field milky way - have not really gone into any deep sky. I did do some stacking with an old Tak 85mm/f1.8, at 3-second subs. Aligned and stacked several hundred of them.

I'm a software engineer/systems architect that had an opportunity to design the star tracking system for a little telescope down in Texas. As such, I've been somewhat frustrated to understand the source of the edge/corner distortion of astrotracing.

Pentax has done a good job in describing the system at a high level, especially their use case. However in terms of differences - in particular with respect to EQ mounts, really nothing has been addressed. You may/probably already realize this - but just in case, let me bore you to death for a minute.

There are a couple of fundamental differences between an EQ mount's approach when compared to Pentax AstroTracer's approach

• EQ Tracking - A EQ tracking mount, takes the traditional approach treating the camera (sensor) and lens as a single monolithic unit and rotates it around the earth's polar axis to stabilize the stars. If you take successive shots, the stars will/should stay stationary within the frame (given error-free tracking).

• AstroTracer (AT) Tracking - The AstroTracer tracks by moving the internal sensor in opposition to the earth's rotation, within the clamped and immobile camera body with the attached lens. Essentially, Pentax uses X-axis, Y-axis, and combined XY-axis twisting movement to simulate the EQ Trackers polar axis rotation. This works very well for periods of time of about 1.5 to 2.5 minutes (even though the mirror box within the camera body has space for the sensor to move for about 5 minutes of tracking time) and depending on the amount of star trailing you are willing to tolerate. This approach does introduce some error into the image (the star trailing within the corners and along the edges). This induced error has a couple of sources; 1) rotational distortion - when the sensor moves in the XY plane in a twisting motion - think of an airplane's propeller. The tips of the propeller move (angular distance) at a much faster rate than does the center of the propeller - hence the bulk of the star trailing in the corners/edges. 2) Lens distortion - lenses are designed to have the light come through a single point on the lens face to strike the sensor. With AT, both the sensor and the stars are in motion, so during the long exposure, the light hitting the sensor will be moving across and through the stationary lens. The corners/edges of a wide-angle lens will slightly amplify this distortion a bit with its movement across the lens. Also, since the camera/lens are immobile, when taking a series of frames, the stars will move out of the frame, forcing the photographer to reframe the overall image in time.

With the difference in tracking approaches - why use the Pentax AstroTracer? For me, I'm looking for good natural star colors across the Milky Way over landscape frame. Out in the field, the MW is not really all that colorful and blown out as it appears in many images. Using a 15mm lens, with a 90 second tracked exposure, which works out to be 6x longer than a non-tracked shot (~15 seconds) [Note, I like to use the online calculator at Night Sky Photography Shutter Speed Calculator – tl-photography ]. I have an easier setup, no alignment problems, an easy 1-minute calibration and I'm ready to shoot. Even though I'm in the Arizona Territories, I usually have an unobstructed horizon, but up north there are forests, where the trees obscure Polaris, which leaves you guesstimating your polar alignment.

My friend (with the K70) picked up a star tracker (which works very well) for 4-minute exposures and they look absolutely stunning. He uses AT about 70% of the time and the tracker about 20%. We bring an extra tripod for the star tracker, so that he shoots using AT while he's futzing with the polar alignment on his EQ tracker. I just like the ease and simplicity of the Pentax astrotracer approach. I get more star light, better star color, while maintaining a very natural overall pleasing image.

A couple of months ago, my friend decided to upgrade to the K1 mk II, which with the Acceleration Chip has an improved dynamic range of about 1.5 stops. The choice of the body was easy, The difficult decision was the lens. The K mount does have a limited selection of fast wide-angle lenses, especially faster than f2.8. He picked up 2, the Sigma 35/f1.4 and the Rokinon 14/f2.8. The problem is, with the fast wide lenses, comes vignetting and coma, where stopping down to f2.8 or so removes a lot of the problems. You wind up having to stop down your fast wide lens, for improved image quality - thereby somewhat removing the advantages of the lens. You can also stitch (50%) to cover the corners/edges with the center of adjacent frames. This is where Sony, Nikon, Fuji, and Canon have some lens advantages - but you give up the astrotracer. So, it all comes down to balancing and selecting your tradeoffs in terms of how you shoot along with the results that you want to capture. As touched on earlier, the combination of the K70 and Sigma 18-35/f1.8 is the best of both worlds. The K70 has an excellent, matches the K1 with dynamic range - especially at ISO 640 and above. The 18-35 lens has no coma, no vignetting (on the crop sensor), well-controlled distortion and for the MW is really the perfect lens. There really is no full-frame lens to match its performance (unfortunately).

I've been shooting with the Pentax DFA 15-30/f2.8 along with the Zeiss 25mm/f2.8 ZK. The prime is sharper than the zoom. I would like something faster, but then you inherent additional problems. The FA 31/f1.8 Ltd is excellent, but has coma. Other wide-angle lenses are available, but slower in aperture.

We go out with 3 bodies, 6 lenses, 3 tripods, a tracker, 2 chairs - and lots of water. Here is a link to his IG page - Login ? Instagram

[cuiv]

Oh wow, I didn't realize some here would be aware of my Youtube channel, much less actually watch my videos!


interested_observer, those results are amazing!!

Also, thanks for the primer on Astrotracer vs EQ mount. I think one of the issues with Astrotracer is also that the sensor will tilt, which is also a cause of oblong stars in the corners. For me though, I want something I can take hiking to dark skies and not have to worry about polar alignment or anything like that. A simple, plop the tripod down system is what I want, and Astrotracer delivers. Then I can launch the imaging, but recenter frequently (which also asks as dithering).

I was hesitating on the K-70 (smaller size, more portable, fully articulated screen - which every camera should have), but what really stopped me was:
- need to get the separate GPS unit (more complexity, I'm already annoyed enough at needing an intervalometer - Pentax, you may persevere with what I consider to be a misguided approach wrt mirrorless, but how about making your firmware open-source?)
- The acceleration chip. From what I read on the K-1m2 it does weird stuff to the raw output. I hate anything that does weird stuff to the raw output - makes calibration much more of a question mark. On the charts it just looks like high gain conversion (sudden dip in read noise => sudden rise in dynamic range), but from what I read, the raws have some level of processing due to the acceleration chip. I don't need the increased dynamic range if it's going to unraw my raws! If I'm careful with individual frame exposures, I can recover dynamic range via stacking (and I'm used to a camera with just a 12bit ADC, low dynamic range is kind of my specialty!)
- Pixel pitch. 3.9 microns vs 4.9 microns - smaller is better for resolution, but I prefer larger for photon collection and more resistant to star trails. Plus despite the heavy undersampling, I can recover some resolution via dithering+drizzling
- The solenoid of death

In terms of lenses, I'm looking at slightly tighter fields (Pleiades, Orion, etc.) I would love it if there were more lenses available for full frame Pentax, and of better quality. But right now, my two main choices:
- Askar 200mm F4 astrograph: perfectly flat field across full frame, very well corrected, accepts 2 inch filters directly in the lens (Optolong L-Pro, L-eNhance, L-eXtreme, etc.), excellent lens collar. HEAVY.
- Samyang 135mm f2: decent flat field across full frame, very fast. But no filter, sensitive to tilt (and thus to astrotracer), etc.

I'm almost thinking about getting a used K-70 astromodded (there is one on Yahoo auctions for 550 USD right now) for less weight and more flexibility. But I wonder...

[interested_observer]

Oh wow, I didn't realize some here would be aware of my Youtube channel, much less actually watch my videos!

There are so few folks doing anything with Pentax, those that do - stand out.

I think one of the issues with Astrotracer is also that the sensor will tilt, which is also a cause of oblong stars in the corners.

No, the sensor does not tilt. If it were to tilt, and break the sensor plane, you would lose focus. That is the main reason all the movement is within the X / Y plane. The trailing of the stars in the corners and along the edges is purely due to "propeller" effect (where the stars appear to move faster along the edges than in the center of the frame. If it were due to anything being out of the sensor plane, then you would see the problem immediately, rather than resolving the problem with shorter exposure times.

For me though, I want something I can take hiking to dark skies and not have to worry about polar alignment or anything like that. A simple, plop the tripod down system is what I want, and Astrotracer delivers. Then I can launch the imaging, but recenter frequently (which also asks as dithering).

The Pentax approach is perfect for this use case.

- The acceleration chip. From what I read on the K-1m2 it does weird stuff to the raw output. I hate anything that does weird stuff to the raw output - makes calibration much more of a question mark. On the charts it just looks like high gain conversion (sudden dip in read noise => sudden rise in dynamic range), but from what I read, the raws have some level of processing due to the acceleration chip. I don't need the increased dynamic range if it's going to unraw my raws! If I'm careful with individual frame exposures, I can recover dynamic range via stacking (and I'm used to a camera with just a 12bit ADC, low dynamic range is kind of my specialty!)

There was a lot of discussion when it originally came out. It's somewhat similar to Sony's attempt with their "stareater". However, whatever they actually do - they have avoided Sony's "stareating" results. It apparently does some signal processing in terms of noise reduction, but exactly how it accomplishes it - we don't know.

Pentax offered to update the original K1 to the K1 mkII. At the time from what I read, it was thought that it would start processing at around 1600 ISO. I passed and kept my original body - unmodified. In looking at the charts, it actually starts at ISO 640. There is another gentleman back east on Cape Cod who only shoots with the original K1 - Cape Nights Gallery - Cape Night Photography. He has a couple of YouTube videos on astro and somehow managed to damage his original K1 and went looking for a used K1 (unmodified) for a replacement.

The folks down in the astrophotography area which is pretty much devoted to deep space should be able to provide a lot of knowledge on the lenses.

[tokyoscape]

Oh wow, I didn't realize some here would be aware of my Youtube channel, much less actually watch my videos!

Come on, you are famous. I think a lot of people here watching your channel including me. But I have never done Astro Photography. I am doing more of night cityscape and night street photo on Instagram. Welcome to the forums.