I'm very confused - please help

[tonyowen]

Attached (for the purposes of this post) are two very rough images generated through DSS and then PS3.

Both images were from from the same site, using the same equipment and the same settings, but two days apart.

Except that for the second the camera's tilt was greater.

Using DSS v3.3.2 I opened files, checked files and registered files and the auto (??) process began.

The results show (query011)  stars as 'dots' (query021) stars as 'trails'.

Query011 was generated using 10 images. Query021 using 29 images)

I also tried subsets ( first 12, last 17, middle 10 etc) of the 29 images but still got 'star trails.

Any ideas and revelations would be most welcome.

regards

Tony

[Stargazer33]

Hi Tony, do the single frames show star trailing or is it just in your stacked image?

If your single frames are okay then it is something in DSS that has gone wrong. If your single frames show trailing then it could be that your mount either lost power and so wasn't tracking, or your set-up may have hit the mount stopping the tracking, or your clutches weren't tightened fully and so you weren't getting any drive from the motors.

[ronin]

Although the earth rotates at a constant rate that is an angluar measure. The camera will show a linear movement and the stars that are further from the axis/centre of rortation will have to "move" at a grearter linear rate to maintain their position.

I simply suspect that this is what you re getting.

Extreme case consider the little Plough, Ursa Minor. Polaris will hardly move but the 2 stars at the end of the pan will move more.

[tonyowen]

Hi Tony, do the single frames show star trailing or is it just in your stacked image?

ronin, on 26 Oct 2013 - 11:49 said

Although the earth rotates at a constant rate that is an angulur measure

Thank you both for speedy replies.

Single frames DO NOT show stars trailing on the 29 image set - (the set that yield trails)

The camera was rigidly on a tripod

I terms of angular motion, the exposure time of 7s would yield just under 7arc minutes per frame. Also as I used exactly the same aperture and exposure time,

and given  two similar imaging targets, one results in trailing images the other does not - why the different results.

I wonders about corruption of DSS, so I removed DSS from my computer (Control Panel) and then reinstalling the program - but using the two sets of original images I get the same results - (one trailing stars the other discrete points).

Again, I'm open to any suggestions and help

regards

Tony

.

[tonyowen]

I terms of angular motion, the exposure time of 7s would yield just under 7arc minutes per frame

Oops that should be  1.75 arc min

regards

Tony

.

[tonyowen]

An update -

every one of the 29 frames shows stars as 'dots' without visible trailing, even at high magnification.

Using sets of 4,4,4,4,4,4 & 5 images I get no star trails.

HOWEVER using sets of 10,10 & 9 star trails appear.

I've tried changing the star detection limit from13% to 16% but this has no effect on whether or not the star trails are visible for the above sets of frames.

I thought that DSS aligned the 'stars' on each frame to prevent trails - surely relative between-star motion due to the 15 arcsec per sec rotation of the earth would be negligible even over centuries!!

How do I ensure that all of the DSS files, caches etc that might hold faulty data be removed. I've tried removal using Control Panel, checked that all obvious files are deleted, but still get the stair trails for some sets, ort all of these 29 images; when DS is re-installed..

Does anyone have any ideas at all

regards

Tony

[Stargazer33]

Hi Tony,

This is very confusing! If your single frames show pin point stars I don't know what DSS is doing wrong in order to trail the stars in the stack. When I watch DSS do its thing, I have noticed the programme not only shift the images in x and y but also rotate them - my tracking is really bad! So the rotation thing shouldn't be an issue.

It almost sounds like DSS is keeping its first offset and then applying that to all subsequent frames, rather than starting from scratch with each new frame.

I can't understand why it should work with your first set of images but not your second. Have you tried writing to the DSS programmers to see if they have any ideas?

[tonyowen]

Hi Tony,This is very confusing! If your single frames show pin point stars I don't know what DSS is doing wrong in order to trail the stars in the stack. When I watch DSS do its thing, I have noticed the programme not only shift the images in x and y but also rotate them - my tracking is really bad! So the rotation thing shouldn't be an issue.It almost sounds like DSS is keeping its first offset and then applying that to all subsequent frames, rather than starting from scratch with each new frame.

Hi Bryan

Your observations might indicate what could be happening.

After DSS has finished there are dx, dy and rotation values or NC listed..

You say 'when I watch DSS doing its thing' What setting do you use to watch the process?

Is there something I could have done that would cause your assumption of DSS keeping its first offset??

What I do is to open picture files, check them, then register them and then click ok, ok to run the apparently automatic process!!!

regards

Tony