[jephi]

I just returned from a (camel) trekking holiday in Namibia and would like to share my pictures and experiences using my Pentax K5 and the O-GPS1 for astrophotography in the field.

NOTE: This contains a number of hints for improvement, so Pentax employees should read on :-)

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PREAMBLE
I recently sold my telescope because of two reasons:
I live in the middle of a big, light polluted city (Berlin) :-(
I do a lot of outdoor activities, e.g trekking, so I want minimum weight for my camera equipment.
So I was looking forward to using my K5 with the O-GPS1 device under the dark skies of southern Africa.

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DATE & LOCATION:
End of November 2011 in Namibia, around the tropic of capricorn, i.e. 23.5deg south of the equator.

THE SKY:
- Early summer
- Night temperature 8-15deg Celsius
- Milky way appears late, around midnight :-(
- Dusk starts around 04:30h :-(
- Most pics taken around new moon :-)


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THE GEAR
Total weight of all my photo gear was below 3.3kg including my tripod, filter, spare batteries, charger and the cases.
So it was ok to carry it :-)

- Pentax K5
- Pentax FA 50mm f1.4
- Sigma 10-20mm
- Pentax DA 55-300mm
- Pentax O-GPS1
- My mini tripod (1960s, modified, height 30cm) used when a wall or big stone was a available to place it on
- A Novoflex high-class tripod (borrowed from our tour guide), up to 1.7m used when no wall was available
- 3rd party wireless remote shutter

I use the remote for shutter release in the mirror up mode to reduce shake.


This is the gear I used for the following pictures :-)
So per picture the weight of the set-up was typically around 1.5kg. Beat that!

POST-PROCESSING
Some basic adjustments were done in Apple Aperture.
NO stacking of pictures! As I was in the middle of nowhere I had to keep an eye on battery life, so I decided not to do multiple picture for later stacking
NO denoising!
Pictures are cropped and probably reduced in size to comply with the upload restrictions in this forum.

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USING O-GPS1

- Easy to attach in the camera in the dark.
- The blue light is FAR too bright, especially as it shines right into your eye when looking through the viewfinder :-(
I put duct tape onto the blue LED to reduce its shine :-)
(The same is true for the red blinkenlight on the camera when in the remote shutter mode. Again, tape it dim :-)
- Power consumption is low. I used my O-GPS for some 9h in all and it still runs on the same rechargable AAA battery :-)

CALIBRATION
This somewhat remains a mystery to me.
It seems that the rotational movements during calibration must be above a certain angular speed for getting a successful calibration, but how fast and wild to I have to turn the camera? Is faster better?
There are two menu items concerning the calibration, one in the GPS menu and the precision calibration in the astro tracer menu.
Are they related to each other? If so, is there a sequence to obey?

TRACKING TIME
As a rule of thumb I used no more than 50% of the indicated maximum tracking time.


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RESULTS

Results depend on the orientation of the camera! Looking east or west seems to produce much better results compared to north or south, which produce star trails when using more than 100mm focal length!
This is what I shall refer to as the "calibration mystery".

Focal length Result
10mm middle of picture is ok. Towards the outer edge star trailing occurs (due to wide angle distortion?!)
20mm ok
50mm ok
300mm ok for easterly and westerly directions and elevations below 45deg.
NOT ok for northern and southern directions star trails appear. (The calibration mystery)



STELLAR OBJECTS


Milky Way and Great Magellan Cloud
Southerly, 04:45h
Then it was located north-south passing straight overhead.
10mm f4 ISO3200 160s



Southern cross, coalsack and lambda centauri nebula (IC2948)
Southerly, approx. 30 deg elevation
50mm f2.8 ISO3200 100s



Eta Carina Nebula NCG3372
Above the southern cross
50mm f2.8 ISO1600 100s



Great Magellan Cloud and a meteor
Southerly, approx. 30deg elevation at 22:00h
50mm f2.2 ISO1600 120s

Not pictured: On 300mm star trails appear :-( (The calibration mystery)


Orion Nebula M42
Easterly, approx 30deg elevation at 22:00h
300mm f5.8 ISO6400 60s





Andromeda Galaxy
Northerly, approx. 45deg elevation around 22:30h
300mm f4 ISO6400 40s
NOT ok. Star trails appear :-( (The calibration mystery)






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Recommendations to Pentax:

Must have:

- A tiltable screen would be really useful for shots exceeding 30deg of elevation
- Provide a way to dim all lights on the backside of the camera
- More detailled instructions for a "high quality" calibration
- Debug the north-south calibration mystery (or tell me how I can do it)

Nice to have:
Integrate the piggy bag box into the next camera.


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CONCLUSION
I guess this will / can never replace a tracking telescope, but at 80 grams extra for astro tracking in the field this is an nice device that could become great after some debugging :-)

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Last edited by jephi; 02-16-2012 at 11:52 PM. Reason: Minor corrections in text

[pentaman]

Wow, beautiful pictures - and my interest in astronomy is coming back just reading what is possible!

[interested_observer]

Wonderful images!!!!! Also, your suggestions amplify on observations on the GPS unit from others, in particular calibration difficulties. The north/south orientation was also noted. I do really wish that Pentax would get the GPS unit / calibration / K5 sensor tracking correct as it does have some great potential - and its a unique capability un to Pentax. With the great sensor and the ability for DFS to be disabled, the K5 does have some great astro potential. This is something that I am really interested in using also. I did a star tracking system almost 20 years ago, that used a similar concept, so I know that it is doable, Pentax just needs to get it right.

The other aspect is the rear screen, if the K5 had tethering built in, then this problem would not be as significant.

I think that you need to write this up and send it to Pentax, and not depend on them finding it. Also, this bring up another suggestion, that possibly the Forum needs an area for the GPS unit, so that Pentax can find postings such as this....

[krp]

Good job on the pictures and review. Maybe you can contact Pentax about the calibration issues? It seems like I haven't seen a whole lot of pictures showing what this accessory is capable of.

[Gimbal]

I would like to have a "calibration exposure"-option.
You set up the camera as you intend to shoot and take a calibration shot, where the camera expose for 30s (or so, depending on focal length) without tracking. Then the camera analyze the star trails and calculate the correct speed and motion to counteract it in the following shoots.

[KansasHorizons.com]

Seems you found what I did. You cant track with this thing except in a few directions and variably. Funny thing is that my sigma Bigma at 500 MM tracks better than my 90mm etc. I think the items is bugged and useless. I sent 2 of them back. And batteries? I couldnt get them to last more than 2-3 hours.

- Power consumption is low. I used my O-GPS for some 9h in all and it still runs on the same rechargable AAA battery :-)

CALIBRATION
This somewhat remains a mystery to me.
It seems that the rotational movements during calibration must be above a certain angular speed for getting a successful calibration, but how fast and wild to I have to turn the camera? Is faster better?
There are two menu items concerning the calibration, one in the GPS menu and the precision calibration in the astro tracer menu.
Are they related to each other? If so, is there a sequence to obey?

TRACKING TIME
As a rule of thumb I used no more than 50% of the indicated maximum tracking time.

--------------------------------------------------------------------------------------------------------------------
RESULTS

Results depend on the orientation of the camera! Looking east or west seems to produce much better results compared to north or south, which produce star trails when using more than 100mm focal length!
This is what I shall refer to as the "calibration mystery".

[jbinpg]

I recently bought an O-GPS1. Haven't had many clear night opportunities to try the astrotrack function. Got a couple of frames of Jupiter off tonight while the high clouds were moving in. It seems to behave as advertised. Relevant EXIF data follows:


GPS Version ID : 2.3.0.0
GPS Latitude Ref : North
GPS Longitude Ref : West
GPS Altitude Ref : Above Sea Level
GPS Time Stamp : 01:15:51
GPS Satellites : 10
GPS Status : Measurement Active
GPS Measure Mode : 3-Dimensional Measurement
GPS Speed Ref : km/h
GPS Speed : 0.98
GPS Track Ref : True North
GPS Track : 79.24
GPS Img Direction Ref : True North
GPS Img Direction : 118.9
GPS Map Datum : WGS-84
GPS Processing Method : GPS
GPS Date Stamp : 2011:12:19

And the resultant image. Note that the actual disk image of Jupiter is much smaller than shown here using my old SMC Super Tak 135/2.8 wide open at ISO80. The high clouds caused unavoidable blooming. Two minutes was too long for exposing the bright planet but I wanted it to be long enough to induce star trails if the tracking function was not working. There is a jiggle evident with zooming in but that was from me fumbling with the camera during exposure. I did find that if I did the "coarse" calibration first, then the precise calibration went better. And it always failed if I tried the calibration when the camera was mounted on the tripod. I had to do it before I mounted it.

Jack

Attached Images

 

[jephi]

Thanks for all the feedback.
I have added a photo of the gear that was used to take the photos.

Cheers, jephi

[jbinpg]

Here is another one taken a couple of nights ago using the O-GPS1, this time of M44, the Beehive Cluster, in Cancer. Seeing was good. Used my old M100/4 at f5.6 for 90 seconds at ISO200. Limiting visual magnitude here is about 10. Results could have been improved with stacking but a single frame using the O-GPS1 confirms the low dark noise of the K-5 sensor.

Jack

[Gimbal]

Here is my attempt at the m42 nebula, using an old K125mm 3.5 and the O-GPS1.
13 pictures, 30 sec exposure stacked with GRIP and then some curve action in PS.

[d00d]

Wow impressive shots!

I just got mine today and am frustrated by the lack of understanding on my part and the dismal failure of the manual to inform me better. I'm not even sure if this is functioning properly, the battery indication light has yet to illuminate and the Sat light blinks at me regardless. The calibration method only gives me an OK after I've done 2 of the 3 axial rotations! I had the GPS indicator showing on the top LCD at one point but now it's gone.

I think I just need to return it and get another... Bah!

Any thoughts/suggestions/postage greatly appreciated.
-----------------------------------

OK never mind... I guess the unit can't receive anything inside the house. I took it outside and after a short span it locked on.

[danny_falin]

There is something very basic that I do not understand, why do you stack multiple exposures witch are the same? what good is to stack 10 or 2000 exposures each one by 30 sec, shouldn't they all look the same?

unless you're making nightsky panorama I see no point of using hundreds of photos equally exposed, please someone enlighten me, I like very much this kind of photography

[Stone G.]

There is something very basic that I do not understand, why do you stack multiple exposures witch are the same? what good is to stack 10 or 2000 exposures each one by 30 sec, shouldn't they all look the same?

unless you're making nightsky panorama I see no point of using hundreds of photos equally exposed, please someone enlighten me, I like very much this kind of photography

Well, the point that you are missing is that those 10 or 2000 exposures are NOT the same.

Why? There are several reasons, the most prominent being:

1. Air turbulence (we talk about 'seeing') make the image flicker and will smear out fine detail in photographic exposures. Stacking many images will enhance detail and clarity.

2. Noise is a statistical phenomenon (we are not talking hot or dead pixels here) and no two images will have exactly the same noise. Stacking many images will help smoothing out that noise.

As a very simple example, here we have a single exposure and just 5 identical exposures stacked. No other processing has been made at this stage:



You will note how some of the faintest stars stand out more clearly and how the noisy background is levelled out. That was just 5 images. Now take 2000........

[Gimbal]

As Stone G wrote, it's a pretty efficient way of improving signal to noise ratio. Any single exposure of the m42 nebula (I posted above) pretty much look like crap compared to the combined/stacked picture.

[danny_falin]

Thanks guys,
more and more questions follow up..

1. The stacking of the pictures is done by special, "for this purpose only" software? I imagine that standard panorama stitching software would not be appropriate. What software do you use for this task?

2. How is the noise reduction applied? Frame by frame during the raw conversion, or the stacked image is filtered by the stacking software?

3. is the 50mm m 1.7 lens appropriate for this task, I have only the 50mm, the 18-55kit and Pentax k 35mm f3.5 lens at this point, so I'm guessing the 50 being the longest and the fastest(1.7) is better choice

4. is the pentax gps module reliable for few minutes (lets say 3-4) tracking with wide lens like the 18-55 kit lens at 18mm? It's costy for me and I'm still considering it. My goal is to catch the milky way, not to identify the sand grains on mars. Is this goal realistic with the lens I got?

Any general information about this kind of photography is welcome. Any good source of information about when and where to look in the sky.