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Forum: Photographic Technique
04-20-2015, 09:44 PM
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Thanks!! I had gone looking for something like this several times, but always came up empty. This is the first I had seen this information. I am somewhat amazed that at up through 100mm you are suppose to still be able to get the full 300 seconds of tracking. I was seeing 300 seconds up through 50mm (thinking in part that something was not right), and then I seem to remember doing something and getting something less. Apparently, I was pointing it in a different direction perhaps. I have essentially gone to a max of 4 minutes in order to not have any trailing in the corners. That seems to work pretty well.
At 0 declination, yes I can believe that the time could be shorter, since the object under observations' angular velocity across the sky would be at its greatest. Also at 90 declination, I can see that it would be pretty slow. It makes sense, I just was thinking of it is a much simpler sense.
I don't know that being level should have a lot to do with it.
In my younger day, I would pull out the math/celestial navigation books (from sailing the ocean blue) and figure it out. In my present geezer state, all I want to do is take pictures. Just call me intellectually lazy.
I am going to bed and perhaps think myself to sleep on this......
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Forum: Photographic Technique
04-20-2015, 05:53 PM
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I think that it is working - more than it isn't. Let me explain. To me it has appeared that Pentax has tried to make this fully automagic. Perhaps a bit too automagic. I wish that they would publish some numbers or at least a suggested table (focal lengths vs. suggested maximum exposure times). I have been able to go the full 5 minutes with the 10-17 @ 10 or the 8-16 @ pretty much the full range. Even at these wide focal lengths, at the full time frame, I started to see trailing in the corners, but not really in the center. As the focal length gets longer, the exposure time is suppose to be automatically recalculated to become shorter. At 300mm the computed exposure time is pretty short, something like 20-30 seconds. I have gone to some longer focal lengths and the system has let me dial in exposure times longer than what I thought was possible (or even practical). The second time or so, I tried with the focal length, the system came up with shorter exposure times.
At 21mm, normally you would see this type of trailing after about 30 seconds. So, at 5 minutes this is excellent. I just think that there is something of a bug in the unit in terms of how it calculates exposure times. I can't see, but I am also going to bet that the trailing is off into the corners, much more that what you will find in the center of the frame. I am also betting that if you set everything up once at 21mm take a shot at the units suggested maximum. Turn everything off, and then try again, it will probably come up with a shorter maximum time frame (second or third time around). That is why, I wish that they would publish an focal length / exposure table, to serve as an overall guide to folks. Automagic is great - until you have questions. I would give it a try at 3 minutes and 800 or 1600 ISO and see what you get. I am also remembering that the days are getting quite a bit longer up there, so it's probably going to be 10pm before it really starts to get dark.
Personally, it looks like you have some pretty dark skies there. You should be able to easily increase the ISO to say 800 and shorten the exposure to a couple of minutes. Essentially exposing to the right. Then through post processing you should be able to bring out a lot more stars.
20 feet from the house is plenty. 10 feet from the car I think is also good. The unit has an electronic compass that is coupled with the GPS unit. In order to track the stars, it needs to know the physical location (lat, long), time, direction and elevation angle. The lat and long position will provide the magnetic correction to the compass, so that it can calculate the true north vs magnetic north for your physical position. A big hunk of metal (car) close by, doesn't help with the compass' directions.
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Forum: Photographic Technique
04-18-2015, 03:26 PM
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I agree with Sagitta - same experience. On the K3, I want to say that the O-GPS1 was out before the K3 was announced, so the boxes and literature on the GPS does not reflect the K3. Also, somewhere I read that on the K3 you can disable the blue light. It can be a bit distracting when using the viewfinder.
Otherwise, it just performs as expected. I have used the map option on LightRoom 4 & 5. It is somewhat funny to see where it thought you took some of the images. I was taking a series of shots up against a large massive rock cliff in the Oak Creek Canyon area. With all of the reflections (multipathing) off the cliff, it thought I was in the creek a lot.
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Forum: Photographic Technique
04-14-2015, 05:36 PM
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I sort of looked at it a couple of times. It was really more than I wanted. For my needs and intentions, the O-GPS1 is perfect. small, light, calibrates easily, aim camera at what I want to shoot and it just tracks. Not a lot of muss or fuss. The 3 to 5 minutes (depending on the lens' focal length), is more than enough for me. Plus, I really want wide field images, rather than deep star images - however, that would also be fun to try.
Now, the dirty little skeleton in my closet is that I helped design and develop a star tracker for a little telescope down in Texas about 20 years ago. They have just recently upgraded it to hold another new instrument package and massive new cabling array to go dark matter/energy hunting next year. It's a 20 axis of freedom with a position accuracy of less than a human strand of hair. Here is a little video of them setting the new tracker (same design - beefier framing for the larger instruments feeding another 150 parallel instruments arrayed off to the sides). It took a 250 Ton crane to set it into position. (It's the February 24, 2014 update. You can skip the road trip and jump to about 1.20 minutes in. They apparently like to drive that crane up to the site a lot!!)
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You need to do it away from large metal objects (cars, trucks, metal buildings). It is good to 45 degrees up in elevation. The calibration is easy, and the camera is held by both hands, so its well controlled. You might need the do the cal process a couple of times at first, since it will still think that its in Japan, until it syncs up. It is really easy. I had the same concerns - but they disappear quickly. You just need to be careful and be aware of your surroundings. Here is a video. The cal process is about at the 6 minute mark...
You Tube
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Forum: Photographic Technique
04-13-2015, 06:49 PM
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Evening - Yes, I remember this one, especially. I was getting tired, its around midnight, it was the last shot of the evening and it was throw up your hands and toss everything up and see what sticks to the ceiling. Plus, I had not seen any of the images from earlier in the evening. I did not know what I did not know. I had also done a lot of research on line on this. Reading is one thing, doing is slightly different. Sitting in your office making rational decisions is one thing, out in the field is yet another.
It's looking east. The little glow on the horizon is Globe, AZ about another hour away. I knew that the Milky Was was going to be along the eastern horizon. I was not smart enough to realize to crank up the ISO. At this time, shooting at ISO 200 was really high for me as I always shoot landscapes at ISO 80.
So, based on this one shot, I would do the following - using the f stops (doubling or having)... I'll use a chartISO 1600 @ 300 sec @ f3.5 (wide open for the 10-17)
ISO 3200 @ 150 sec @ f3.5
ISO 6400 @ 75 sec @ f3.5 (the ISO is getting a bit too high here, so then I would go to a faster lens)
ISO 6400 @ 37 sec @ f2.5
ISO 3200 @ 37 sec @ f1.8 (So, I could make the same shot with the 31Ltd with the same light in about 30 seconds w/o GPS) Lost Dutchman is near Apache Junction, AZ and is in the Yellow band as defined by the DarkSkies Finder. Similar lighting to the Lake Tahoe area. Mono Lake is much darker, 3 areas darker, which will bring out the available light substantially better - less background light to contend with (all the light you want to capture is what you want - not light pollution). So, I am going to guess that is going to be worth a stop's worth. So, that would make ISO 3200 @ 30 sec @ f2.8 doable. You have to remember that this is not a digital science. It's not black and white, works or does not work. It's analog, works pretty well, works better. You will always get something that will turn out with post processing.
Let me go through my shots and see what I can find at ISO3200 @ f2.8 as an example....
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Forum: Photographic Technique
04-13-2015, 05:12 PM
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I started doing some astro last year - both, with and with out the GPS unit. Your initial assumptions are pretty spot on. The conclusion I came to was, if you are including landscape in the foreground don't use the GPS and use the fastest lens you have available - wide open. If you are just going for the stars, use the GPS and you can use slower glass for the desired field of view. If you are going to stack, in order to stabilize (align) the stars positions, the landscape is going to blur.
Here is a thread I started about my adventure. It's more of just a running narrative (log) on both shooting and post processing. You can see that I was somewhat wandering around, trying things out, seeing what works - and doesn't. Both with and with out the GPS. It stretches across a few months. Also, the astro folks here on the Forum are absolutely wonderful. They provided a lot of post processing advice, suggestions, examples and encouragement. They had the knowledge and skill - I happened to have some relatively clear dark skies and a camera.Here are a few quick take aways, that I found during my quest....- High ISO is your friend. Depending on how dark it is, ISO 1600 @ 30 sec is going to be a good starting point. f2.8 if you have it - and adjust from there. I really appreciate the 31Ltd at f1.8 - to the point of thinking about acquiring the Sigma 18-35/f1.8.
- Bring a folding chair, and a red head lamp (REI @ ~$15-$20) and a wired shutter release, tripod and head.
- Focusing and framing in the dark is more difficult than it appears. Crank up the ISO all the way to 51200 @ ~5 sec for test shots, so that you can see on the camera's rear monitor what your framing is against the landscape. You can also check your focus this way. I used an ballhead, but have since picked up an old used gearhead (Manfrotto 410), so that I can make more precise changes one axis at a time.
- I like the old wide manual focus lenses, because at the end of the focus range its infinity (well for most lenses) - which makes focusing in the dark a bit easier.
- Bring a laptop to down load the images to for a real quick check to see if you did something stupid, or if you see something that you might lead you to try something different before you leave.
- You are going to burn through batteries.
- I just started locking the mirror up, since I was not using the viewfinder, SR should be disabled.
- Keep some notes of what worked and didn't, and what you want to try next time out.
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