IC1318 Butterfly Nebula Cygnus

[Fay]

Well, Mike, when I zoom in, the stars on the new one are cross shaped, different to the original.

[MarkS]

Fay,

Open both images in your favourite image processing application then flick between the images.  You'll see that all the tiny stars have been effectively filtered out in the 2nd image.  The median filtering will do that.

I prefer the first image because, even though it is more noisy, it shows all the detail.

But we haven't yet got to the bottom of those "distorted" stars in the top right.  I think DSS is needlessly applying a fancy transformation during alignment with the unintended result that the stars in the top right fail to align. 

This can be manually prevented as follows:
1) Select "Register checked pictures ..." in the usual way
2) When the dialog appears, hit the "Stacking Parameters ..." button
3) Click on the "Alignment tab"
4) Choose "Bilinear" instead of "Automatic" and hit O.K.

I'll be interested to see if that does a better job.

[Fay]

I will do that today Mark, thanks.
I am getting to the point of not using the FR. That image & the dreaded Pelican, were the first two that I have used the FR with the Canon. All the previous images seemed ok, when it was not used. Although those images were of only M31 & Pleiades, stars more spread out.

The Fr has always been ok using the SX.

It is so difficult to get to the bottom of because of our constant cloud cover.

[Mike]

I think the wide field of view on the Canon plus making it wider with the FR might be distorting the image too much.

[Fay]

Mike, I agree with you.
Yesterday I went thru all my images & the only two that are bad are the last two I have taken, the only one's using the FR. When I come back from Bromley I will have a close look at M27, no FR used, but taken with the modified camera.
I have just restacked in DSS using all combinations, median, kappa sigma, average & even mosaic.................. no difference.

I have looked so much on the net for images taken with ED80's/350D & focal reducers. There were only a couple, & they looked ok, 99% seem to be taken without. I found a couple of discussions on the subject & think that it is a problem pending. One person will say WO 0.8 is better, another, the Celestron, but there is a tradeoff.

Next time I get out, I will not use it. I have to make sure the camera chip is in straight as I only have a guarantee for 3 months. Can never get outside to sort it out!

[Fay]

PS.

at least I get the full 2" without the FR. Also the WO 0.8 fr/flattener was only designed for scopes with focal length of the ZS66, around 300-400. The ED80 is 600mm. I thing a Televue goes past 600mm, not sure, but don't want to spend any more in case is doesn't work. 

[Mike]

.....have to make sure the camera chip is in straight as I only have a guarantee for 3 months. Can never get outside to sort it out! ..

You don't need stars to do that.

Simply print off a grid like this - http://www.artlex.com/ArtLex/g/images/grid.gif onto paper and put it at the end of your garden. use a scope or a zoom lens to take a picture of it making sure it is completely flat to the plane of your CCD (a piece of string between the two and a right angle will check that. make sure you do both planes). Then check the resultant image for distortion - http://www.photodesk.iconbar.com/tut/pix/brl/grid1.jpg - The lines should be perfectly parallel, if they are warped it will show up clearly on the image of the grid and you can print out the resultant image and hold a ruler next to the lines to see how straight they are, etc.

[Daniel]

My feelings exactly, Im going to give the focal reducer another go when we have good conditions (saturday night's looking good) to see if it was setup aswell as the crappy conditions we had last time to make the stars look faded compared to the image I did before without the reducer. otherwise I might just crop the coma around the edges off

[Fay]

That's great Mike, I will do that asap. What a good idea!!!!!!!!!!!!

[Mike]

When initially composing the image line up the etched lines in your viewfinder with the lines on the grid to make sure your orientation is correct.

[Fay]

Well, Mike, I did the best I could today. I was about 25' away from the graph & tested it with no focal reducer & with focal reducer. I got the graph in the most offending corners & changed the angle of the camera, and used the ED80.

I could see no problems, the graph looked straight & even.

Don't know if this test counted, if I was far away enough.

DSLR went down, so had to delete & reinstate it. I did try to stack in DSS but it would not do it. it would have been good to have been able to do that.

I have spent hours doing this, so hope test conditions were adequate, if not, then plan B. Wait for a bit of clear sky.

[Mike]

....I got the graph in the most offending corners & changed the angle of the camera, and used the ED80..

Not sure what you mean by that Fay. You are meant to have filled the entire Field of View with the graph paper. Is that what  you did?