[Peter Manning]

Hi tempelorg,
I am very impressed by your shots! My infinity focussing is still dodgy, though I have worked out how to get better results with tracking - simply dont allow any mobile electronic equipment withion about 3 metres of camera... If I leave my mobile phone away from the camera i get close to the indicated times: following is a stack of 2 x 3 minutes @ f2.8 iso3200 PK30 with Tamron 90.
Regards, Peter.

Attached Images

 

[tempelorg]

Peter, what you say makes sense. I had tried the AstroTracer at other times where I had much more electronic equipment with me, e.g. iPhone and iPad, and I had start trails all over. My latest shots where pretty "naked" device-wise. This supports your findings, i.e. to keep everything electronic far away.

For focussing, there's two thoughts:
1. Get yourself a Bahtinov filter made (see astrojargon - Bahtinov Focusing Mask Generator: Overview).
2. I usually just take several shots near infinity and move the focus ring a tiny bit with each image, then I check the results on my iPad (to which I transfer the imgs wirelessly with an Eye-Fi card, but you could also get Apple's Camera Connection Kit, which requires that you remove the memory card from the camera, however).

Still, I believe the biggest problem is atmospheric turbulences. Hence the higher you get the better, I suppose.

[Peter Manning]

Hi again tempelorg,
lol - if I try focusing with electronic aids - iPad etcetera - astrotracer won't track! It is a matter of taking care what you wish for: with K30 (at least), interval shooting is disabled by the astrotracer/gps... IF I connect a third party intervalometer? It interferes with the astrotracer/gps lmao.. I used to be vocal about the lack of computer tethering since the K20D.. GUESS WHAT? A computer interferes with astrotracer/gps. :-D I guess I don't really want tethering after all! Peter.

[MJSfoto1956]

Odd behavior last night. I shot a series of 60 second Astrotracer images @ 250mm f/4 ISO 1000 of Ursa Major (The Big Dipper). Most of the images reliably gave distinct point-like stars, but as I continued to angle the lens upward beyond 45 degrees in order to follow my guide star, I started seeing unmistakable star trails recorded in the exposures. Shortening the exposure to 50sec, then 40sec, and finally 30sec, it returned to point-like stars at 40sec but then got worse at 30sec.

So my advise is for those using the DA* 60-250mm (or perhaps the 300mm) feel free to use the 250mm at 60 seconds as long as the angle of the lens is below 45 degrees (i.e. halfway between the horizon and directly overhead). Once you go much above 45 degrees, some randomness may introduce itself into your image taking and you might have to reduce your time by half in order to have reliable non-trail, point-like stars.

YMMV

Michael

[Stone G.]

Once you go much above 45 degrees, some randomness may introduce itself into your image taking and you might have to reduce your time by half in order to have reliable non-trail, point-like stars.

I have come to the belief that this may be systematic rather than random. Here's the reason why:

If you look at your exif data (you will need ExifTool or similar to get the full information) then you can see that the camera faithfully records roll (horizontal) and pitch(altitude) up to 45 degrees. After 45 degrees altitude all readings are:

Roll = -45 (!)
Pitch = 45

That is, the inclinometers seem to stop working at altitudes beyond 45 degrees.

Something tells me, that there must be accelerometers involved when you go to +45 degrees of altitude and if you go in small incremental steps there may/might/could be a source of error to be found there? It is only recently that I found this, but as soon as my @#!&% cloudy skies clear, I do intend do to a bit of systematic"research" here.

[MJSfoto1956]

hmmm. not seeing it in the EXIF data for my image. Here's what I have:

<exif:GPSVersionID>2.3.0.0</exif:GPSVersionID>
<exif:GPSLatitude>42,8.707N</exif:GPSLatitude>
<exif:GPSLongitude>70,44.2923W</exif:GPSLongitude>
<exif:GPSAltitudeRef>0</exif:GPSAltitudeRef>
<exif:GPSAltitude>4650/100</exif:GPSAltitude>
<exif:GPSTimeStamp>2014-03-07T03:25:49Z</exif:GPSTimeStamp>
<exif:GPSSatellites>11</exif:GPSSatellites>
<exif:GPSStatus>A</exif:GPSStatus>
<exif:GPSMeasureMode>3</exif:GPSMeasureMode>
<exif:GPSSpeedRef>K</exif:GPSSpeedRef>
<exif:GPSSpeed>5/100</exif:GPSSpeed>
<exif:GPSTrackRef>T</exif:GPSTrackRef>
<exif:GPSTrack>22658/100</exif:GPSTrack>
<exif:GPSImgDirectionRef>T</exif:GPSImgDirectionRef>
<exif:GPSImgDirection>4071/100</exif:GPSImgDirection>
<exif:GPSMapDatum>WGS-84</exif:GPSMapDatum>
<exif:GPSProcessingMethods>GPS</exif:GPSProcessingMethods>

Is it know by some other name other than "roll" or "pitch"?

Michael

[asgr]

Having got my astro-tracer in August last year, I finally took a trip to a proper dark site. I had a bit of mixed luck with calibration and star trails, but a few shots (even quite long ones) came out really well. These are probably the best of the bunch:





Overall, pretty happy. Looking forward to my next observing trip- I'll be going to Siding Springs for some 'real' observing in July, so I'll take it with me then.

[MJSfoto1956]

I have come to the belief that this may be systematic rather than random. Here's the reason why:

If you look at your exif data (you will need ExifTool or similar to get the full information) then you can see that the camera faithfully records roll (horizontal) and pitch(altitude) up to 45 degrees. After 45 degrees altitude all readings are:

Roll = -45 (!)
Pitch = 45

That is, the inclinometers seem to stop working at altitudes beyond 45 degrees.

Something tells me, that there must be accelerometers involved when you go to +45 degrees of altitude and if you go in small incremental steps there may/might/could be a source of error to be found there? It is only recently that I found this, but as soon as my @#!&% cloudy skies clear, I do intend do to a bit of systematic"research" here.

hmmm.. I'm not 100% convinced of your theory (at least from what my exif data is showing) -- I do think the system is somewhat "random" though. Here is a spreadsheet I compiled of a few tests of a new 60-250mm lens and Astrotracer pointing towards the Big Dipper. Note that each successive image I slightly increased the angle of the camera to point further away from the horizon (i.e. each image was closer than the previous to directly overhead). I *ASSUME* that the GPS Altitude as listed in the EXIF is the angle of my camera? If so, then zero must be directly overhead?? Note that *ALL* of my shots taken with the 250mm were at greater than 45 degree angle!!

Michael

[Stone G.]

hmmm. not seeing it in the EXIF data for my image. Here's what I have:

It isn't in the GPS part. Here's the portion (line 3+4 below) and what follows down to, where GPS-data begins:

Level Orientation : Upwards
Composition Adjust : Off

Roll Angle : -45
Pitch Angle : 45
Composition Adjust X : 0
Composition Adjust Y : 0
Composition Adjust Rotation : 0
WB RGGB Levels Daylight : 17750 8192 8192 13142
WB RGGB Levels Shade : 21208 8192 8192 9809
WB RGGB Levels Cloudy : 19125 8192 8192 11237
WB RGGB Levels Tungsten : 10667 8192 8192 24380
WB RGGB Levels Fluorescent D : 21917 8192 8192 12666
WB RGGB Levels Fluorescent N : 18792 8192 8192 14094
WB RGGB Levels Fluorescent W : 17083 8192 8192 17427
WB RGGB Levels Flash : 20125 8192 8192 12094
WB RGGB Levels Fluorescent L : 14292 8192 8192 21808
WB RGGB Levels User Selected : 17750 8192 8192 13142
Contrast Detect AF Area : 0 0 0 0
Camera Temperature 2 : 18.2 C
Camera Temperature 3 : 18.1 C
Camera Temperature 4 : 18 C
Camera Temperature 5 : 18 C
Flashpix Version : 0100
Color Space : sRGB
Exif Image Width : 4928
Exif Image Height : 3264
Interoperability Index : R98 - DCF basic file (sRGB)
Interoperability Version : 0100
Sensing Method : One-chip color area
File Source : Digital Camera
Scene Type : Directly photographed
Custom Rendered : Normal
Exposure Mode : Manual
Focal Length In 35mm Format : 75 mm
Scene Capture Type : Standard
Contrast : Normal
Saturation : Normal
Sharpness : Hard
Subject Distance Range : Distant

GPS Version ID : 2.3.0.0

[MJSfoto1956]

so here is summary my EXIFtool analysis of the images shot two nights ago at 250mm: all images have the exact same pitch and roll!! (trust me, I was definitely adjusting the angle of the camera between each shot). While you "may" be right about the recorded values for pitch and roll being false after 45 degrees, I think the GPS Altitude value is in fact providing the correct values (with the assumption that zero is directly overhead, not on the horizon). And given that I was still able to get star "points" even at extreme (i.e. 45+ degrees) angles, I think my takeaway from my limited tests is this: One should shoot at least THREE Astrotracer images, with the expectation that at least 50% of the images will exhibit some sort of star trail. In other words, this is not a device that you can depend on shot after shot to "nail" the image. Even with that knowledge, I think Astrotraer is still quite useful -- just that I need to set my expectations correctly, especially with long lenses.

YMMV

Michael

P.S. the EXIFtool recorded pitch angle for all my 250mm images is 64 and the roll angle is 4

[MJSfoto1956]

e.g.

Level Orientation : 1
Composition Adjust : 0
Roll Angle : 4
Pitch Angle : 64
Composition Adjust X : 0
Composition Adjust Y : 0
Composition Adjust Rotation : 0

[SunValley]

Greetings

Thought I'd put my two cents as I've been strugling with these issues myself. What I found was that the higher you point the less precise the azimuth becomes. I input the exact time and location in a planetarium program (namely Cartes du ciel), find the centre of the picture and locate it in the planetarium map. Here are some results



The unit never quite gets the altitude right but for some reason it doesn't seem to affect the results. It seems that if the unit can get the azimuth right the picture is going to be good. I'll keep comparing gps vs planetarium data to see if that holds true. Of course not much you can do about it in the field...

Here's a picture I took last weekend. GPS and planetarium data were very close for the 5 X 40s images I took to make the picture (the galaxy was 30 degres high). I used a K-30 with an smc -M 200 mm f/4.0 lens wide open. Stacked with DSS, sky gradient removed with iris, then treated in pse11.

[Stone G.]

so here is summary my EXIFtool analysis of the images shot two nights ago at 250mm: all images have the exact same pitch and roll!! (trust me, I was definitely adjusting the angle of the camera between each shot). While you "may" be right about the recorded values for pitch and roll being false after 45 degrees, I think the GPS Altitude value is in fact providing the correct values (with the assumption that zero is directly overhead, not on the horizon). And given that I was still able to get star "points" even at extreme (i.e. 45+ degrees) angles, I think my takeaway from my limited tests is this: One should shoot at least THREE Astrotracer images, with the expectation that at least 50% of the images will exhibit some sort of star trail. In other words, this is not a device that you can depend on shot after shot to "nail" the image. Even with that knowledge, I think Astrotraer is still quite useful -- just that I need to set my expectations correctly, especially with long lenses.

YMMV

Michael

P.S. the EXIFtool recorded pitch angle for all my 250mm images is 64 and the roll angle is 4

That's a bit strange. I just cannot get a pitch-angle higher than 45 degrees (tried it again on Jupiter this very evening: Roll = -31 and Pitch = 45). Well, K-3 and K-5 may differ here.

Anyway, I shot a few more images and went back into my library of older pictures. Just a few examples:

Orion shot on 30 december 2012 in a ruaral area. Here are selected EXIF-data as Phil Harvey's ExifTool reads them::

Camera Model Name : PENTAX K-5
Date/Time Original : 2012:12:30 22:24:57
Camera Orientation : Horizontal (normal)
Level Orientation : Horizontal (normal)
Roll Angle : 0.5
Pitch Angle : 27.5
GPS Version ID : 2.3.0.0
GPS Latitude Ref : North
GPS Longitude Ref : East
GPS Altitude Ref : Above Sea Level
GPS Time Stamp : 21:24:55
GPS Satellites : 09
GPS Status : Measurement Active
GPS Measure Mode : 3-Dimensional Measurement
GPS Speed Ref : km/h
GPS Speed : 0.66
GPS Track Ref : True North
GPS Track : 204.16
GPS Img Direction Ref : True North
GPS Img Direction : 163.76
GPS Map Datum : WGS-84
GPS Processing Method : GPS
GPS Date Stamp : 2012:12:30
GPS Altitude : 17.9 m Above Sea Level
GPS Date/Time : 2012:12:30 21:24:55Z
GPS Latitude : 56 deg 4' 29.54" N
GPS Longitude : 12 deg 26' 9.16" E
GPS Position : 56 deg 4' 29.54" N, 12 deg 26' 9.16" E

(Note that GPS "Altitude" is height above sea level - not very reliably measured by the way).

Now I can also check what Cartes du Ciel (CdC) has to say about the position of the Orion nebula at the time of shooting:

Star
HR 1895 HD 37022
Flamsteed Number: 41
Bayer Letter: THE1
Constellation: Orion
Visual Magnitude: 5.13
Color Index: 0.02
Spectral Class: O6p
Annual Proper Motion: 0.004 0.002

J2000 RA: 5h35m16.50s DE:-05°23'23.0"
Date RA: 5h35m54.84s DE:-05°22'55.3"

LyngbyHovedgade 2012-12-30 22h25m ( TU + 1h00m )
Sideral Time : 4h54m
Hour Angle : 23h18m
Azimuth :+168°06'
Altitude :+28°16'

Rise : 17h38m Azimuth:+98°45'
Culmination : 23h11m
Set : 4h43m Azimuth:+261°15'

Both Camera Pitch and CdC altitude correspond nicely with each other and GPS image direction is well within the 10 degrees acurracy, specified by Pentax, as checked against CdC Azimuth.

I did a few testshots at various altitudes and directions this evening. Here, I show just one example, Sirius shot from my 4th floor balcony in the city:

First some ExifTool-data:

Camera Model Name : PENTAX K-5
Date/Time Original : 2014:03:09 20:21:20
Camera Orientation : Horizontal (normal)
Level Orientation : Horizontal (normal)
Roll Angle : 0
Pitch Angle : 16.5
GPS Version ID : 2.3.0.0
GPS Latitude Ref : North
GPS Longitude Ref : East
GPS Altitude Ref : Above Sea Level
GPS Time Stamp : 19:21:04
GPS Satellites : 05
GPS Status : Measurement Active
GPS Measure Mode : 3-Dimensional Measurement
GPS Speed Ref : km/h
GPS Speed : 0.67
GPS Track Ref : True North
GPS Track : 256.19
GPS Img Direction Ref : True North
GPS Img Direction : 169.33
GPS Map Datum : WGS-84
GPS Processing Method : GPS
GPS Date Stamp : 2014:03:09
GPS Altitude : 44.5 m Above Sea Level
GPS Date/Time : 2014:03:09 19:21:04Z
GPS Latitude : 55 deg 46' 6.44" N
GPS Longitude : 12 deg 30' 24.18" E
GPS Position : 55 deg 46' 6.44" N, 12 deg 30' 24.18" E

And then data from CdC:Star

HR 2491 HD 48915
Flamsteed Number: 9
Bayer Letter: Alpha
Constellation: Canis Major
Visual Magnitude: -1.46
Color Index: 0.00
Spectral Class: A1Vm
Annual Proper Motion: -0.553 -1.205
SIRIUS; Canicula; Dog Star; Aschere

J2000 RA: 6h45m08.90s DE:-16°42'58.0"
Date RA: 6h45m46.94s DE:-16°43'54.0"

LyngbyHovedgade 2014-3-9 20h21m ( TU + 1h00m )
Sideral Time : 7h21m
Hour Angle : 0h35m
Azimuth :+188°44'
Altitude :+17°11'

Rise : 15h30m Azimuth:+119°49'
Culmination : 19h49m
Set : 0h09m Azimuth:+240°11'

While camera Pitch and CdC Altitude continue to correspond nicely, camera direction of image is off by 19 degrees from the Azimuth found with CdC. This is a demonstration of the fact that the last image was shot from my balcony with lots of concrete reinforcement and other local magnetic disturbances.

[gs2c]

Last December I went to Yunnan Gaomeigu.Use K5 shot a group of sky photos, and share with everyone.

[gs2c]