Image size etc query

[Fay]

IN my IC1318 there is an amassed area of stars, top right.


When I look at individual images, it does not seem so apparent.

When I stacked in DSS, there was a small message that said the images were not the same size, this has also come up as I am trying to re process in AstroArt. I have looked at all the images info & they are all 600s @ISO 800, one of the images is 599scs, not sure if this would make a difference. The flats & dark flats are all 0.8 secs @ ISO 100, does this make a difference.
If not, what can be a different size.
Hope someone has an idea.

Thanks

[Ian]

that sounds weird.

Can't help. It looks a bit like sums.

I'm not so good at the "putting the numbers together and getting them to come out right" thing today.

I doubt exposure length would make the difference, the resolution is the resolution. Perhaps one is corrupt?

[Mike]

That can't be right. Maybe a glitch in AstroArt? Why not process in Maxim it's a lot easier?

[Fay]

Ian, you look more than good at putting numbers together, especially today!!!!

I think anyone would have to go a very long way to beat Mac or Mark.

DSS also told me that the images were not the same size.  I have been trying to find out where anything differs, but have failed. When I stacked just light & dark, the message did not come up. Astroart would not even start.

I will try Maxim, if I know what I am doing.
 

[Mike]

Fay - I can show you at the imaging session on Friday.

[RobertM]

Be careful with Maxim, I found the 450d images crashed it so I had no option but to use DSS.  It's not as configurable or fast but processed the large RAW files without any problem.  I would always use maxim where possible but combining 20 images and darks was one step too far.

[Fay]

I have just had that experience, Robert, 5 minutes ago. I had to close it down. I then tried just the Darks & lights, it took ages, but did not align them properly.

[Fay]

Mike I will bring laptop on Friday, thanks

[Fay]

I am wondering if a large chip, like a  DSLR or larger ccd camera, needs a different focal reducer to a 0.8.

[Mac]

I am wondering if a large chip, like a  DSLR or larger ccd camera, needs a different focal reducer to a 0.8.

The only thing you have to watch with a different focal reducer on larger CCD's is vignetting. http://en.wikipedia.org/wiki/Vignetting

if you use a 0.6 then you will notice a slight vignetting, although you will probably get away with this in astropotography.

however using a 0.3 on a DSLR or very large chip will produce a greater amount of vignetting.

for the wider field of view.

Mac.

ps i was just wondering howmant times i could mention the word vignetting in a passage
vignetting, vignetting, vignetting, vignetting, vignetting, vignetting,vignetting

looks like 12

[Ian]

the other thing is that any aberrations introduced by the FR get worse towards the edge of the frame, the DSLR's large sensor would be more likely to pick that sort of thing up than an astro ccd.

[MarkS]

You need a reducer because it also flattens the field (unless you have an expensive Ritchey Chretien telescope!).  A flat field is extremely important for the large CCD of a DSLR.

I use a 0.63 reducer.  Yes, I have a lot of vignetting, but shooting flat frames does the business!  I'll demonstrate this on Friday at Mike's imaging session (unless it's clear and we're all outside actually imaging!).  I also tried a 0.3 reducer but that caused intolerable vignetting.

[MarkS]

Fay,

Download Iris onto your laptop (http://astrosurf.com/buil/us/iris/iris.htm) along with your raw files then on Friday at Mike's we can use it to see what is going on.  There is, no doubt, a simple explanation.

Mark

[Fay]

Will do, Mark

[Mike]

Looking at the original image I think that one or more of your images are rotated somehow around the bottom left corner and the alignment hasn't compensated for that so that you have double images of stars top right.

A simple two star alignment on two stars at either corner will sort that out.