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02-29-2016, 06:47 AM   #1
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Two simple questions about O-GPS1 with the K-3

Hi,

I've been playing a bit with the O-GPS. It's working of for the most part, but two things make me wonder:

1-I'm supposed to be able to use it to mark GPS locations and do simple navigation:

Pentax O-GPS1 GPS Unit Review - Features In-Depth (I) | PentaxForums.com Reviews

How do I use this on the K-3? Manuals don't help, and I haven't found out how to access that menu.

2-when using astrotracer, I'm supposed to automatically have my exposure time limited by the focal length. It appears that it is not so (using a DA21 and a HD 16-85). The camera always allows me to use 5 minutes (haven't tried more) which can result in some star trails. I would expect the exposure time to automatically decrease if I change the focal length.

02-29-2016, 07:04 AM   #2
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1. Simply put the unit on and turn it on. When it has the GPS location, a quick GPS calibration to get the direction fixed, and shoot normally. The data should be embedded in the EXIF. Simple Navigation is different though, as far as I know it is not available on the K-3, only K-5II/K-50 and lower. That's a bummer.

2. Usually it is best to half the suggested exposure time to avoid trails. However when you get wider than 50mm equivalent the corners will show some trailing due to lens distortion. The Astrotracer is mostly good for longer than 50mm equivalent lenses.

At least this is what I came up with researching on the unit before I got mine.
02-29-2016, 08:33 AM   #3
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QuoteOriginally posted by bdery Quote
1-I'm supposed to be able to use it to mark GPS locations and do simple navigation.
Yes and no: As said above, your position (and heading) is embedded in EXIF and you can use software such as GeoSetter to display those.





But you cannot have Simple Navigation with a K-3. On the RICOH product page you can see which features are availble with which camera models:


GPS UNIT O-GPS1 | RICOH IMAGING


QuoteOriginally posted by bdery Quote
2-when using astrotracer, I'm supposed to automatically have my exposure time limited by the focal length. It appears that it is not so (using a DA21 and a HD 16-85). The camera always allows me to use 5 minutes (haven't tried more) which can result in some star trails. I would expect the exposure time to automatically decrease if I change the focal length.

It depends not only upon focal length but also on where on the sky you are aiming. The closer you are to the celestial equator, the faster the angular movement of the stars will be. You can see the approximate maximum allowable exposure times on the same product page:


Specifications | GPS UNIT O-GPS1 | RICOH IMAGING


As you can see, tolerances are quite high for your focal lengths - PROVIDED THAT you do not crop and that you do not pixel-peep! I agree that halving these maximum exposure times are closer to reality and if you crop very tightly, you may have to reduce those times even more.

Last edited by Stone G.; 02-29-2016 at 08:46 AM.
03-03-2016, 06:13 AM   #4
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QuoteOriginally posted by Sterby Quote
as far as I know it is not available on the K-3, only K-5II/K-50 and lower. That's a bummer.
QuoteOriginally posted by Stone G. Quote
But you cannot have Simple Navigation with a K-3.
That's a bummer indeed.

QuoteOriginally posted by Stone G. Quote
It depends not only upon focal length but also on where on the sky you are aiming. The closer you are to the celestial equator, the faster the angular movement of the stars will be.
I can understand that. However, using a 16-85, the max exposure time remained at 5 minutes even when playing with the zoom. I would expect it to change a lot between 16mm and 85mm.

03-03-2016, 01:15 PM   #5
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QuoteOriginally posted by bdery Quote
That's a bummer indeed.
Well, my guess is that this feature was left out because of limited user acknowledgements. If you read user reviews of the O-GPS1, everybody speaks about geotagging and Astrotracer, but hardly anyone abot Simple Navigation, (my own review is an exeption). I'd say that it is a fun feature to have but not really that useful or 'needed'.

QuoteOriginally posted by bdery Quote
I can understand that. However, using a 16-85, the max exposure time remained at 5 minutes even when playing with the zoom. I would expect it to change a lot between 16mm and 85mm.
I see your point. If 5 minutes at 85 mm approaches the limit for how much the sensor can be moved, then one would expect that that amount of movement would allow for 25 minutes of tracking with a 16mm lens. However, there is yet another restriction in the way Astrotracer works: The sensor can only be moved in the fixed sensor plane, left-right, up-down, rotate. It cannot be tilted away from that plane. And during long exposures, the projected images of stars on the celestial sphere onto the flat, two-dimensional sensor will follow curved trajectories moving in very different directions.

This is illustrated here with a 2-hour exposure of the trails of stars below and above the celestial equator, approximately marked by the planet Jupiter:


Pentax K-3 + Samyang 14mm f/2.8 lens. Star trails recorded over approx. 2 hours.

Astrotracer simply cannot compansate for that and the result of a, say, 25 minutes exposure with a 16mm lens using Astrotracer would be that stars become more and more stretched out in different directions the futher out from the center they are.

So, I assume that the O-GPS1/Astrotracer designers decided that 5 minutes would be about the maximum to produce acceptable 'point-like' star images across the entire frame. (If you crop tight or pixel-peep, this "stretching-effect" will be quite obvious even after about one minute with such wide-angle lenses).

Last edited by Stone G.; 03-03-2016 at 01:27 PM.
03-03-2016, 01:51 PM   #6
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I understand what you write, no problem. It still doesn't explain why I get 5 minutes at 85mm. I strongly doubt that I would be able to avoid star trails at that focal length (haven't tried it). Or maybe I could indeed?

Maybe I should try to use the 69-250 at 250mm and see if the device does indeed limit the exposure time?
03-04-2016, 11:40 PM   #7
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QuoteOriginally posted by bdery Quote
I understand what you write, no problem. It still doesn't explain why I get 5 minutes at 85mm. I strongly doubt that I would be able to avoid star trails at that focal length (haven't tried it). Or maybe I could indeed?

Maybe I should try to use the 69-250 at 250mm and see if the device does indeed limit the exposure time?
Hi, I use a lot the O-GPS. But my English is trespauvre to explain the details and tips.

What you should know is that the O-GPS is capricious ...

Avoid places where there are large metal masses.
Make a good "fine calibration" of astrotracer.
If you want to obtain "star point" in the center, difficult to exceed:
90 "with 16mm,
30 "with 50mm
20 "250mm

If the mode is used "MUP", the sensor starts to move when the mirror rises. This is a bug, and I think there is a loss of time of possible exposure.

For starters, the Milky Way is a good subject with 16mm.
.

To focus (manual of course), use the 100% LineWiev with the "PEAK" activate.

I hope it's a few tips can help you ..[COLOR="Silver"]

---------- Post added 05-03-16 at 10:43 ----------

Last edited by bruno.cirou; 03-05-2016 at 12:00 AM.
03-04-2016, 11:58 PM   #8
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QuoteOriginally posted by bdery Quote
I understand what you write, no problem. It still doesn't explain why I get 5 minutes at 85mm. I strongly doubt that I would be able to avoid star trails at that focal length (haven't tried it). Or maybe I could indeed?

Maybe I should try to use the 69-250 at 250mm and see if the device does indeed limit the exposure time?
somes exemples

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03-07-2016, 06:21 AM   #9
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QuoteOriginally posted by bruno.cirou Quote
somes exemples
Could you share more details about your technique? That's exactly the kind of results I'm trying to achieve. If you prefer to do it in French, since you say you're not comfortable in English, French is my main language.

Thanks!
03-07-2016, 01:44 PM   #10
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QuoteOriginally posted by bdery Quote
Could you share more details about your technique? That's exactly the kind of results I'm trying to achieve. If you prefer to do it in French, since you say you're not comfortable in English, French is my main language.

Thanks!
Please translate for us, I am also interested.
Also I have a DA 35/2.4 and a DA 16-45/4, are these lenses usable for similar starscape/landscape shots?
03-08-2016, 06:20 AM   #11
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QuoteOriginally posted by Sterby Quote
Also I have a DA 35/2.4 and a DA 16-45/4, are these lenses usable for similar starscape/landscape shots?
Both are usable for sure. It depends on the field of view you're looking for.
03-20-2016, 06:15 AM - 3 Likes   #12
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Désolé d'avoir mis beaucoup de temps pour répondre, j'avais pas mal de chose à faire ces temps ci.
Le O GPS est vraiment un outil sympathique pour faire du "grand champs" en astro. Mais il est très limité pour le "ciel profond". L’intérêt en plus d'évité le filé des étoiles est qu'il va permettre de concentrer les photons sur des zones plus petites du capteur et donc d'obtenir une exposition plus importante pour un même temps d'exposition.
Comme un autre l'a déjà dit, le temps de pose maximum peut varier en fonction de l'orientation. Les temps annoncés par l'astrotracer doivent au moins être divisé par 3.
Pour ma part j'habite l’Île de la Réunion et il y a de grosses perturbation magnétique. Il faut donc re- étalonner la boussole à chaques déplacements.
Pour les longues sessions, penser à prendre plusieurs batteries pour le O-GPS, il est tres gourment en énergie. En ce qui concerne le mien, j'ai quelques fois des problemes des "faux contacts avec le sabot du flash peut etre du l'oxydation car l'air est bien salé à la Réunion.
J'utilise aussi très souvent le 10mm Samyang pour photographier la Voie Lactée mais il faut accepter que les étoiles soient un peu filées dans les angles car le O-GPS ne peut compenser les aberrations géométriques.
Comme je l'ai dit "in english" il faut soigneusement faire "l’étalonnage fin". Il ne faut pas hésiter à le refaire plusieurs fois si il se fait difficilement, en chageant d'orientation.
En générale, je fais 2 clichés, 1 avec le O-GPS "ON" et un "OFF" pour le paysage (exposition identique) que j'assemble sous Photoshop. Il m'arrive aussi de multiplier les clichés pour les empiler en utilisant les techniques "astro" pour éliminer du bruit et augmenter le rapport signal/bruit et pouvoir augmenter la luminosité/exposition.
Je conseille à tous d'aller sur des sites web "astro" pour s'imprégner des techniques de traitement d'image qui sont très importantes pour obtenir des images de meilleur qualité.

Pour le "ciel profond" j'ai réussi quelques images avec le 60 250 mm mais dont je ne suis pas pleinement satisfait. Obligé de travailler a 25600iso car mon temps de pose était limité à 10". "La Carenne" dans le ciel de l'hémisphère sud:

500px.com/photo/72015103/astro-by-bruno-cirou?ctx_page=3&from=user&user_id=8152939

Cette image est le résultat de l'empilement de 5 prise de vue en mode "satistique/médiane" sous PS5 exended pour réduire le bruit. L'avantage du 60-250 à 250 est qu'il n'a pas trop de déformation et qu'il est plus facile d'aligner les clichés pour l'empilement.

Dans l’hémisphère nord on peut faire Orion, Andromède... Pour repérer les objets du ciel j'utilise "Stellarium" gratuit sur mon Nokia Lumia 930 mais il y a d'autres logiciels...
"Voila" ce sont mes grandes lignes de l'utilisation et je cherche encore... le mieux est de se plonger dedans et travailler...
A si, pour la navigation GPS, j'utilise mon téléphone avec HERE map (offline)

Good Shoot

Bruno
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