[Gimbal]

So, if using a zoom lens, the camera doesn't calculate compensation for focal length changes?

It will compensate for the zoom, unless it's an old lens that doesn't report the focal length camera, in which case you will have to manually enter the focal length.

[photoptimist]

So, if using a zoom lens, the camera doesn't calculate compensation for focal length changes?

The point of the calibration is to measure the strength and direction of the magnetic field as affected by all the stuff in or near the camera. If the zoom lens contains steel parts (e.g., retaining rings, springs, cams, clips, aperture blades, motors, etc.) those will affect the magnetic field and if those steel parts are on the zooming parts of the lens, then zooming may change the magnetic field environment. Whether it's enough to really affect the shot is a complex function of many variables but the best thing to do is to calibrate with everything configured as close to the intended shooting conditions as possible.

Astrotracer does use the reported focal length of lenses that send that info to the camera so the optical effects of zooming are accounted for. But if zooming affects the magnetic field, and you zoom after the calibration, then the camera may think it's pointed a few degrees different than it is and not properly correct for the motion of the stars.

[Gimbal]

It seems impossible to get a better accuracy then +-15 degrees, so I made an experiment.

I turned the camera in the direction where the error was the largest, I then taped a piece of a metal paperclip on top of the prism house in such a way that the error was minimized. Then I turned the camera to the new largest error which where about 90 degrees from the original one and again I taped another piece of the paperclip on top of the prism house in such way so that the error was minimized.

And now the error was down to +-5 degrees in any direction. Success, and I figured that maybe I should do something more portable that could be attached and removed sitting in the flash shoe.

But then I tried a new calibration with the compensation clips still attached, and unfortunately the original error was back. My compensation clips where compensated for.

Back to the drawing board. Hm, maybe an adjustable metal bar on top of the prism house that I can rotate until the compass shows exactly the heading I want... Not pretty but maybe it can improve the astro tracker performance?

[MJKoski]

Thanks for these thoughts. Didn't think about all moving metallic parts at all...

[PhilRich]

Does the K-1 display the compass heading? If so, where, I've been looking for it. Thanks.

[Gimbal]

Yes it can, press info button twice to get to the display options, then step to the rightmost option for electronic compass and hit ok.
Note that this will also turn on the GPS.

[PhilRich]

Yes it can, press info button twice to get to the display options, then step to the rightmost option for electronic compass and hit ok.
Note that this will also turn on the GPS.

Thanks for the quick reply!!

[monochrome]

Does the K-1 display the compass heading? If so, where, I've been looking for it. Thanks.

Easiest way is press Info, press Info again, select Compass Display (rightmost choice).

[siegbert]

In order to use the astro tracer it's necessary to have the electronic compass calibrated. And even though the calibration process says that the calibration procedure is "OK" the result can differ quite a lot from time to time.

With the ogps-1 on my K-5 i could after a couple of trials get a pretty good accuracy. Usually less then 3 degrees error for most of the directions but often there were one direction that could be up to 5 degrees in error. But all in all quite good.

With the K-1 I have yet to get under 15 degrees in error in the "bad" directions. Usually about 20 degrees in error in some directions and less then 3 in others. Very inconsistent.

But during my tests I also found out that the movable LCD affects the compass with up to 10-15 degrees in some directions depending on the position of the LCD. So moving the LCD in or out turns the compass. This does not happen in all directions though.

So I figured that since I will have the LCD out and tilted when doing astro work I will also have to have the LCD out when calibrating. But while that does give a different result compared to having the LCD tucked in the accuracy didn't improve much.


The procedure I use to check the compass is to first align the tripod head (which have a 360 degrees scale) so that 0 degrees on the scale has the camera pointing to the north. Then I attach the camera and watch the compass heading on the LCD and compares with the scale on the tripod. Turn into different directions and compare. Do not have the camera mounted on the tripod when aligning to the north since the camera body is full of magnets and will affect any compass used to align the tripod.


So the question is, has anyone else checked the accuracy of the built in compass, and did you get at better result?

It‘s my experience also. Just by turning the backside screen, with the camera on a tripod, the shown direction can changes up to 10 – 15°.



So you must not turn the screen after calibration.



Thanks for your hint, it was helpful finding my problem.

[gaweidert]

When I was out photographing comer Neowise last year I found that the GPS my camera K1 would not calibrate with my D FA 150-450 lens attached. So I mounted a 50mm and it worked fine. Then, without turning the camera off, I swapped lenses and added the correct focal length. Maybe it was all the metal in the long lens screwing things up.

[Bob 256]

When I was out photographing comer Neowise last year I found that the GPS my camera K1 would not calibrate with my D FA 150-450 lens attached. So I mounted a 50mm and it worked fine. Then, without turning the camera off, I swapped lenses and added the correct focal length. Maybe it was all the metal in the long lens screwing things up.

Could well be but did the calibration issue continue when you returned to the DA FA 150-450? Any magnetized metal near the camera can foul up the calibration and the compass. Usually, aluminum and stainless steel are employed in lenses and they are non-magnetic but there are bound to be some iron based parts which can be magnetized and may give issues. You don't want to place any strong magnets near your gear.