[Mapleleaf-Mick]

I have a K3 and was looking at purchasing a Pentax Astrotracer for my camera. After reading up info on the unit I have a couple of questions:

Is the unit all inclusive. I. E. does it contain the GPS unit as well as the tracer?

I read that there is a maximum time of 5 minutes. Is that enough time to get decent shots?

Is it better to use a wide angle lens say 12mm on my crop sensor K3 or use my Bigma with a 1.4 teleconverter?

Any suggestions would be appreciated.

Thanks for reading my post.

Michael

[DougieD]

This site has some decent examples of what can be done with the O-GPS1 with regard to deep sky astrophotography:
Accueil / Albums / Astrophoto / Ciel Profond | PhotosSteph

My understanding is that the longer the focal length, the less tracking time the O-GPS1 gives you. So, you really need a fast lens if you are going to get great results with long focal lengths.

[CarlJF]

I have a K3 and was looking at purchasing a Pentax Astrotracer for my camera. After reading up info on the unit I have a couple of questions:

Is the unit all inclusive. I. E. does it contain the GPS unit as well as the tracer?

Yes.

I read that there is a maximum time of 5 minutes. Is that enough time to get decent shots?

It depends on what you mean by "decent shots". It certainly gives you much more options and capabilities than without astrotracer. But it's not a replacement for a telescope on an equatorial mount.

Is it better to use a wide angle lens say 12mm on my crop sensor K3 or use my Bigma with a 1.4 teleconverter?

Wide angle works fine, but you can get some star trails on the border or the corners. I'm not sure the Bigma with a teleconverter would be a good option, or work at all. Even if it works, you will have a hard time to find and point a specific object in the sky... I would say the longest practical FL to use is about 300mm.

[gifthorse]

1. The Astrotracer and the GPS are one single unit. The GPS tags your images with latitude and longitude whenever it is on, even when using the Astrotracer function.
2. Five minute maximum depends on several factors. Primarily, the shorter the focal length the longer the possible exposure time. You will not get five minutes of exposure with the Bigma.
3. Much depends on what you want to photograph at night. For some types of night photography the astrotracer isn't needed or won't help. You need to decide what you want to photograph at night and then figure out whether the Astrotracer will help you.

[SeaRefractor]

Some fast clarification in case I didn't read your message correctly.

1. You have a K3 and want to know if it's all inclusive, meaning a GPS and Astrotrace are built into the camera body right?

Answer: No, I believe this is being confused with the newer K3 II, the main difference is the K3 has the built-in flash but no GPS unit (optional O-GPS1 must be used for Astrotrace) and the K3 II has the built-in GPS but no Flash (hotshoe with external flashes must be used).

2. I use the Astrotrace function and it works very well.

3. Don't worry about the length of exposure. It's not the length of time that provides you the amazing astrophotography but the clarity of the sky and how well the lens collects light.

* Tripod is a must, any motion will result in poor results. Be sure not to scrimp as a flimsy mount will be next to useless as small vibrations occur from wind, etc...
* Really fast lenses (f1.4 or 1.8) will result in a need for less exposure time, longer exposures are necessary for slower lenses (where the aperture has a larger number).
* The longer the exposure, the more "noise" is introduced. This is where a shorter exposure may result in less stars, but will be better looking. Many of the eye popping photo's use multiple exposures and then an external application like Star Stack to stack them all into a single photo that has low noise and amazing detail. I use an old 50mm f1.4 lens that is manual focus (doesn't matter as AF cannot focus on the stars, you'll have to manually move it to infinite focus) along with 45 second exposures (so the Astrotracer helps those to be pinpoint) and then stack them. When I use a 100mm telephoto at f5.6, I have about 1.2 minute exposures and stack those as well. I need to run longer because it's a slower lens.
* The best lenses for milky way and other "large" stellar expanses is to go as wide as you can without going into fish-eye. The reason is that the fish-eye lenses don't work well for Astrotrace, the way the lens collects the light isn't uniform across the lens and you'll have long commas on the edges while the center is pin point.

[Mapleleaf-Mick]

Thank you SeaRefractor for that excellent info. That is exactly what I was looking for. I have a Tokina 400 F5.6 I wanted to try as well as the Bigma but it sounds like they are to slow. I ďo have slower F1.8 lenses that I could try. Primes are the way to go I would expect. Nothing under 20mm for wide angle?

[SeaRefractor]

It'll be trial and error under 20mm, for starting out and due to cost of lenses I wouldn't recommend going wider. If you find ultra-wide lenses at a great price and wish to use them for landscape and other terrestrial photo's, you can then try them with the Astrotracer feature. Typically you'll find what I was referring to in terms of pin point centers and comas to the sides.

A faster F1.8 is going to mean that you can have a lower ISO for a shorter duration for great results. The 400mm F5.6 is possible, but you'll likely need ISO 800 along with a 2 minute exposure. The interesting thing is that there is a rule called the "500 Rule", this is for cameras that do not have the Astrotracer feature and need a large number of photos stacked to approximate the same results. Essentially the rule is:

500/focal length = longest exposure in seconds before stars trail in camera without astrotracer or "barn door mount".

As the Astrotracer function prevents the trail issues, I use this as a loose guide to figure out what is the shortest time I want to expose with Astrotracer function for a given lens and then push it up from there. I then continue to increase the time and take multiple shots. After I've done this it gives me the "feel" of what my lenses are capable of doing and for how long I can expose before the image is over exposed. Remember SD cards allow you to take as many pictures as you'd like, so don't scrimp.

Please note that your 400mm lense will be a very small area of the sky, it would be better suited for "planetary" photography of Mars, Saturn, Jupiter, etc. The length of exposures will need to be less than for stars as the planetary motions are slightly different than for stars that are light years distant. Not enough that it moves out of the viewfinder, but just enough to impact image clarity/detail. With the F5.6 I would plan on over 30 or more 20 second exposures at ISO800 stacked as the planetary movement will result in loss of detail if you do an exposure too long.

Note, viewing the images on the preview feature on the camera will be "underwhelming", you have to bring them into Lightroom so that you can adjust the image appropriately and you'll find that the stars the sensor was able to detect will then "POP" into an amazing image. Again, stacking as I'd described above with multiple images and using Star Stacker applications will result in the best images with the least amount of noise and incredible detail (DeepSkyStacker, StarStax are both "freeware" that I've used. A new one for me is RegiStax, this was recommended by many and seems to do a better job of registering each star for better alignment, this one is also free). The slightly tedious portion is you need to apply the image adjustments with LR for each image before saving it out as JPG for the stacker software to "stack".

[Mapleleaf-Mick]

Very very interesting and informative. Thank you very much for taking the time and effort to respond. I have lightroom but to be honest I am a bit afraid of "stacking". Don't know a damn thing about it. As I mentioned previously, I have a number of good Pentax primes 35's and 50's @ f1.8 or so which may do the trick. I really want nebula or planetary pics versus just star points in the sky. Maybe I am being overly optimistic with the gear I have and the experience I possess.

Michael

[Stone G.]

Thank you SeaRefractor for that excellent info. That is exactly what I was looking for. I have a Tokina 400 F5.6 I wanted to try as well as the Bigma but it sounds like they are to slow. I ďo have slower F1.8 lenses that I could try. Primes are the way to go I would expect. Nothing under 20mm for wide angle?

400mm and f/5.6 isn't entirely 'senseless'. I regularly use my catadioptric 350mm f/5.6 lens together with my K-5 and K-3 plus the O-GPS1/Astrotracer. You just have to realize that accurate calibration becomes ever more important with increasing focal length and you must expect your success rate to drop accordingly. You can see some of my results with various lenses here:


DSLR Astophotography: Astrotracer Images with Pentax GPS Unit O-GPS1

(And note that I have gone up to even 700mm f/11 with some success on rare occasions).


If you are a pixel-peeper and if you go below some 20mm in FL, you will notice that stars become stretched as you move away from the center of your images. This is because Astrotracer can only move in up-down and left-right steps and rotate along the optical camera axis. Thus, unlike a camera mounted on an equatorial platform, Astrotracer cannot ensure that the sensor 'tilts' in order to retain its posistion relative to the position on the celestial sphere where the optical axix was pointing at the beginning of the exposure.


Overall, I should say that Astrotracer works best with lenses in the 24 - 200mm FL range - but do experiment with what you have to gain your own experiences.

Very very interesting and informative. Thank you very much for taking the time and effort to respond. I have lightroom but to be honest I am a bit afraid of "stacking". Don't know a damn thing about it. As I mentioned previously, I have a number of good Pentax primes 35's and 50's @ f1.8 or so which may do the trick. I really want nebula or planetary pics versus just star points in the sky. Maybe I am being overly optimistic with the gear I have and the experience I possess.

Michael

If you want nebulae more than Milky Way panoramas (which can be very rewarding in itself) then you do have to consider longer focal lenghts (from, say 135mm and up). Again, please refer to the sample images I have linked to. If you want planetary detail more than Jupiter with its 4 moons as tiny 'dots', then you are in Telescope Land. In all immodesty I can point to my own homepage again:


Camera Settings for Astrophotography


- and whether you are afraid or not, you WILL eventually have to venture into stacking. And it really isn't that 'terrible' after all: Just load your pictures into a program like Deep Sky Stacker; ask the software to do the stacking and then use some sliders to darken/lighten your resulting image until you see your target. After that, you may undoubtedly want to look into the refinements. A starting point could be this tutorial:


Deep Sky Stacker


Have fun with your venture into the many-sided aspects of Pentax DSLR Astrophotography!

[Mapleleaf-Mick]

Thank you very much Stone G. for your great suggestions and information. I will indeed view your pictures and visit the website pages you recommended.

Michael

[SeaRefractor]

Stone G, thanks! You did a great job explaining that better than I for the reason with ultra wide and lenses larger than 200mm.

I didn't think to post the star stacking tutorial either.

This is a good example of the benefit of a community like this forum.