M20

[Gem (Grant)]

Hi all,

Here is last weekends effort at M20. I tried 5 min images for the first time. This image is around 30 x 5 min plus darks and bias.

Scope: 9.25" SCT at f 6.3
Camera: ATIK 320E
Guiding: 80mm refractor with QHY5 and using PHD
Processing: Astroart and Pixinsight trial version

Comments or help appreciated!

[blink138 (Pat)]

hello grant that looks nice, that isnt the actual image size is it mate?
if it isnt how do you "magnify" the bit you want?
the file size was big when i clicked on the thumbnail so couldnt see it very clearly that way
i have been checking out the differences with guidescope versus OAG of late for trying longer exposures
the discussions for and against are very interesting
pat

[Gem (Grant)]

I compressed it into the jpeg, but it isn't cropped or anything. Since Iceinspace only allows 200kb, I compress the images I post. I think I compressed this a bit too much though since it is 105kb... I am ssuming too that you are clicking the fit to window option up the top right of your screen on iceinspace when viewing the image.

[Rex]

Nice Grant. Beautiful picture.

[blink138 (Pat)]

"I compressed it into the jpeg, but it isn't cropped or anything. Since Iceinspace only allows 200kb, I compress the images I post. I think I compressed this a bit too much though since it is 105kb... I am ssuming too that you are clicking the fit to window option up the top right of your screen on iceinspace when viewing the image."

er.......no, i didnt know that that was there
thanks grant
i just thought that the image would have been smaller with thje f6.3 reducer thats all
pat

[Gem (Grant)]

No probs!
Scope has 2350mm focal length without the reducer and 1480mm with it. Hard to get a widefield shot!! It also makes tracking that little bit harder...

[bazaud (Barry)]

Nice!

Barry

[Shiraz (Ray)]

Hi Grant

Apart from the scale, your image looks very nice overall, with quite round stars and well focused detail.

However, as Pat was hinting at, you have a major mismatch between the camera and the optics. The 320 camera has small pixels and has been designed for use with short focal length systems - and your scope has a long focal length, even with the reducer. As a general rule,you should aim for between 1 and 2 arc sec per pixel for good to average seeing - you have much less than 1/2 arc sec at full fl and less than 2/3 arc sec with the reducer. This oversampling greatly reduces your field of view and sensitivity to no real advantage. You need a camera with much bigger pixels.

To demonstrate the effects of oversampling, the following is a summary of your system compared with the same scope and a QHY8 camera (which has more and much larger pixels):
field of view - QHY8 will have more than 10x the field of view of the 320 (the bigger chip covers much more of the focal plane)
sensitivity - QHY8 will be roughly 3x as sensitive as the 320 (each large pixel intercepts more light than a smaller pixel)
star size - QHY8 will yield stars about 1/3 the size(area) of those from the 320 (each star covers fewer of the large pixels)

this is not to endorse the QHY8 particularly (although it might be a good choice) - there are other cameras with relatively large pixels that would match fairly well to your scope. You could even consider a DSLR and use binning to increase the effective pixel size to match the optics.

This is also not to knock the 320 - it looks like a nice camera, but it does not match at all well with your scope. Sorry to be so negative.

regards ray

EDIT: just scaled your image to 33%, balanced colour to boost red a bit and sharpened a little with unsharp mask - the result is much better than the majority of m20 images found by Google. The underlying image quality is very good.

[Gem (Grant)]

I hear your point regarding the QHY8, however:

1. the QHY8 is a few hundred dollars more expensive;
2. the readout noise is much lower for the 320;
3. I plan on getting a short tube refractor soon;
4. (and most importantly) the 320 was a surprise present from my wife - so who am I to complain???

Anyway - thanks for the feedback. Good to know anything that helps to improve my imaging. As for the roundness of the stars - I think my wife's processing definitely helps.