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08-10-2015, 01:01 PM   #1
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Stupid question ahead concerning Astrotracing & GPS on K3 II

Tomorrow night is my first excursion into astrophotography using my K3 II. I've read the manual and it seems absurdly simple. So I'm feeling stupid here but want to ask a question just to make sure.

Does GPS have to be precisely calibrated before using astrotracing?

Now that I think about it, I have a limited lens selection. I have the 50 1.8, 35 2.4, 18-135, & 55-300 (all Pentax). Which would be the better choice.

Any advice on settings? Thanks.

08-10-2015, 01:26 PM - 1 Like   #2
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I generally recommend using fast, wide primes for astrophotography so that you can use the lowest iso possible. If you're happy with the angle of view of the 35mm, give it a spin, but I think you might need to go wider.

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08-10-2015, 03:50 PM - 1 Like   #3
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QuoteOriginally posted by MyTZuS Quote
precisely calibrated before using astrotracing
would recommend doin so when in the astrotracer function.....not necessary to both calibrations though


as far as lens selection goes depends on your goals..........milkyway or static star field with landscape go wide, if you get over 30 seconds exposure time (which you should get) try 200 iso+/- and even stop the lens down a stop or so (experiment)...be sure to get an image of the foreground without using the astrotracing function to blend them together....as the sensor moves so does the things that do not..........if you are goin for nebula or deep sky objects try a longer focal length (will have much shorter exposure time).....go wide open and bump iso up 800-1600 area.........btw focus to infinity manual is usually best bet........I have the o-gps and its an adventure every time using it....the time and experience are helpful and frustration levels have dropped as I have different expectations when using it anymores
good luck and dark clear skies!!!
08-10-2015, 03:52 PM - 1 Like   #4
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QuoteOriginally posted by MyTZuS Quote
Does GPS have to be precisely calibrated before using astrotracing?
Yes, you will want to for any exposures over 15 seconds.
Also, it helps if you are not near any large metal objects both when you do the calibration as well as when you shoot the photos as these can reduce the accuracy of the tracing. So it's a good idea not to stand directly near a car, nor over a concrete slab which typically has lots of metal rebar inside.
Be sure and see the Video here: Calibration | GPS UNIT O-GPS1 | RICOH IMAGING

QuoteOriginally posted by MyTZuS Quote
50 1.8, 35 2.4,
As a starting point, try the 50/1.8 around 2.4-2.8 and the 35/2.4 around 2.8 -3.5

08-13-2015, 08:27 AM   #5
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Thanks guys for the help... my results are posted here: https://www.facebook.com/jamesshinnphotography

I'm going to setup tonight using a different strategy. Going to use the interval shooting & the WR 18-135 set at 18mm & f4. Infinity focus will be another challenge as it was with my posted pics. And, I'm going to figure out how to use LiveView to focus with since that might help me with the infinity settings. Never ever have a I used the LiveView, in fact, I have it turned off.

Thanks again!
08-13-2015, 11:08 AM - 1 Like   #6
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Yes, critical focus is a big challenge and a key component of good astrophotos, especially with high resolution bodies like the K3II. It's generally more difficult with wide angle because it's harder to see the defocus spread. Have you tried putting a bright star or planet in the middle of the frame and then using live view at maximum magnification? Some lenses suffer stop-down focus shift, so sometimes it will seem that you've nailed focus during composition, but then it ends up out of focus during the exposure. Until you figure out which of your lenses (if any) have focus shift on stop-down, you can test by making short exposures at high ISO to verify if critical focus has been achieved, and then switch to lower ISO longer exposures for the actual photos.
08-13-2015, 02:38 PM - 1 Like   #7
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pics look good and focus seems fine!

---------- Post added 08-13-15 at 05:28 PM ----------

a link to 1 of the 2 meteors I got lucky enough to get in frame
https://www.flickr.com/photos/123743029@N04/19928402034/in/dateposted-public/
08-14-2015, 07:19 AM   #8
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Nothing but clouds last night. :-(

08-14-2015, 02:27 PM   #9
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bummer.....started out with clouds but they thinned out decently but alas not a single meteor!
08-16-2015, 12:26 AM - 1 Like   #10
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QuoteOriginally posted by MyTZuS Quote
Tomorrow night is my first excursion into astrophotography using my K3 II. I've read the manual and it seems absurdly simple. So I'm feeling stupid here but want to ask a question just to make sure.

Does GPS have to be precisely calibrated before using astrotracing?

Now that I think about it, I have a limited lens selection. I have the 50 1.8, 35 2.4, 18-135, & 55-300 (all Pentax). Which would be the better choice.

Any advice on settings? Thanks.
The question is more: what do you want to see ?

Milky way, or deep sky ?
Milky Way : <50mm
Deep Sky >100mm

Use high Iso (>800), and f/2.0 or f/2.8 and you can see a lot of object.
I use the GPS calibrated (sometimes precisely, sometimes not)

Some examples of what i shoot with the K3 & OGPS-1 :

With the Sigma 18-35mm f/1.8 Art @18mm f/2.0 60s


With the Tamron 70-300mm @300mm 40s Iso800


My advice : use the LV and with focus peaking for your MAP !
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