[d00d]

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

And here's some informational pages for further reading on the subject:

How Image Stacking Works

grelf.net - Camera following the stars

[Stone G.]

@danny_falin.

1. I believe most people start out with free-ware and most of us with Registax. Personally, I have never gone any further. (And yes, it is dedicated software for astro-stacking).

2. The stacking process, as pointed out in the two foregoing replies, is a signal-to-noise improvement process in itself. You would normally make some further processing either in registax or in a general digital image editing software (Gimp, PhotoShop, PaintshopPro,....). I prefer the latter. Here additional enhancements and noise reduction may be applied.

3. You can use all three lenses. Obviously the faster and larger (in terms of actual physical aperture) lenses will record more in less time. Primes are usually better than zooms because they have less light loss and less internal reflexions, but before you buy anything, try what you have - but mind you that not all lenses produce clean stellar images when used wide open.

4. Others will have to answer to that. I am not the lucky owner (yet!).

Perhaps you can find some additional inspiration here:

Camera Settings for Astrophotography

[jephi]

@danny_falin:

Hi Danny,
1. & 2. I cannot answer. I am not a stacker, yet.

3. The 50mm m f1.7 should work great.
Focal length: 50mm will get you "big pieces" of the Milky Way .
A fast lens is good :-)
You will have to use manual focus, which can be a bit tricky.
18-55 should be fine.
Increasing ISO can give you some advantage.

4. 3-4 min could be OK for the 18-55mm. But I am not sure. O-GPS1 users experience very different things in terms of tracking accuracy.

Anything wider than 18mm might not make sense anyway:
The wider the lens, then less absolute movement the sky will make across your cameras sensor, which will follow. 18mm should still be fine. BUT due to distortion at the outer edges of the lens, the wider, the more "smearing" you will get at the edges, because the stars projected to the edges of the sensor will move faster / different than the stars projected to the middle. The sensor, of course, is not flexible in itself to adjust to that. Have a look at this picture taken at 10mm: The stars at the edges seem to "flee" from the center:



Cheers from Berlin,

jephi

[jephi]

BTW:
Does anybody know if the recent K5 firmware update to 1.12 fixed the strange "calibration mystery" where "east/west" was more accurate than "north/south"?

Thanks for any information.

Cheers from Berlin,

jephi!

[LaurenOE]

In this thread I heard some folks call the O-GPS-1 "worthless", send me a PM if you *really* don't want it anymore!

[danny_falin]

jephi, very beautiful pictures btw. I really want to experiment now, even without tracking..


Thanks guys, for providing even more than enough info, for shooting the stars
regars

[d00d]

BTW:
Does anybody know if the recent K5 firmware update to 1.12 fixed the strange "calibration mystery" where "east/west" was more accurate than "north/south"?

Thanks for any information.

Cheers from Berlin,

jephi!

I'm going to say no. The calibration mystery still exists here in N. America at the 33rd parallel. My rig won't even calibrate when positioned N/S, only when I turn 90° will it calibrate in any mode. The compass and GPS modes are not why I bought this item and being frustrated in the operation of the device makes my enjoyment less than 'stellar'. I may just get a decent scope w/GEM and try the traditional approaches.

The other issue is with stacking software. I've been using Keith's Image Stacking and it's got a pretty large learning curve and doesn't seem to tolerate inexperience with the UI. I cannot get a grip on running GRIP on a Mac, so I haven't tried that yet.

Stone G.- The 'Camera Settings' link is brilliant and a must read for all who endeavor into astrophotography

Overall I think my experience is muddled by a middling lens (50-200 4-5.6 kit zoom) and not enough experimentation/experience with astrophotography, but I think the device has promise in the hands of a more experienced person.

[jephi]

O-GPS1 Users,

concerning the calibration:

I just came across the "official Pentax calibration website" Calibration | GPS UNIT O-GPS1 | PENTAX

It features a video of the camera turning during calibration.

While I do not expect this to solve the North-South calibration mystery, least it reduces one potential source of error.

At the moment it is just too cold in Berlin for me to go out and do some tests ;-)

Cheers from Berlin, jephi

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?

[Gimbal]

That video is a mystery in itself. The text talks about turning 180 degrees in each direction but the guy in the video doesn't manage to turn 180 degrees in any direction as far as I can tell.

Personally I start with holding the camera still and turn myself a little more then 360 degrees at a steady pace, and then continue with the rest of the movements.

[jbinpg]

I understood the calibration to be performed as in the video with the person standing still and only rotating the camera. I do the "rough" and then the precise calibration in that order and it seems to work fine.

Jack

[d00d]

That video is a mystery in itself. The text talks about turning 180 degrees in each direction but the guy in the video doesn't manage to turn 180 degrees in any direction as far as I can tell.

Personally I start with holding the camera still and turn myself a little more then 360 degrees at a steady pace, and then continue with the rest of the movements.

Exactly! I rotate the camera a full 360 on all 3 axis by hand. And why does it claim calibration for me after only 2 axial twists are given during the basic calibration sequence?

Also note the 'Notes' section, so I should leave the camera back in Kamuela instead bringing it up to the summit on Mauna Kea (WM Keck)? lol! And I wonder how much influence underground electrical wires would have?

[Gimbal]

And why does it claim calibration for me after only 2 axial twists are given during the basic calibration sequence?

I've noticed that too, it sometimes signals OK before the turning around the vertical axis is even begun (the compass calibration). But then the compass is usually messed up.
Since I noticed that I always do the "compass turn" first in the sequence and then it works pretty good.

[d00d]

I've noticed that too, it sometimes signals OK before the turning around the vertical axis is even begun (the compass calibration). But then the compass is usually messed up.
Since I noticed that I always do the "compass turn" first in the sequence and then it works pretty good.

Gotcha, I had considered something along those lines (changing up the order of rotation). I'll give that a shot here in the next day or two. Thanks!

[d00d]

Here's the last attempt at usage:



Stack of 7 images, 200mm kit zoom - 30 seconds @ 3200iso.

I'm probably out of my league attempting to capture this object in the first place, but what the heck. I need to keep shooting and improve my technique. I'm going to give it another go after I calibrate the unit properly and the sky is yielding to my efforts. I do want to add that the program I used to stack the images is not very forgiving in terms of user interface, so I think the hint of trails present may be due in part to the rotational aspects of the app than the O-GPS1 (though some is present in the originals, I 'm suspecting my lack of usage with the app helped create more... I think).

[falconeye]

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".

Sounds like a lack of precision in the compass. An accurate compass is certainly challenging to achieve ...

I wonder if there then shouldn't be an option to manually enter the precise heading (which could be derived from pointing to a known star, or to polar star first).