M51 from last night with issues

[steviemac500]

Somewhat inspired by RMS's efforts the other day.... Nearly 3 hours of data, 65 x 3 minute subs at ISO 800 but lost a lot due to the wind. 15 darks and 40 bias. Did flats this morning (I'm in Cyprus so the sky is very good) but I cant get rid of the problems on the camera sensor? Have been following the recommended tutorials = Doug German but always seem to have a lot of noise in the centre, I don't tend to have a delay inbetween shots -could this cause it? Also, I'm thinking of a new DSLR to replace the 1000D, any recommendations?

[andyboy1970]

NIce image.

Getting flats to work consistently seems to be an issue. I have stacked images with all the same subs, darks & flats and found I get different results.

Try playing with the stacking options.

[wimvb]

Did you use dithering? It seems that the noise in the center of the image has a pattern to it that can be avoided by dithering, i.e. move the sensor 15 pixels between exposures.

See this youtube clip:

https://www.youtube.com/watch?v=PZoCJBLAYEs

You can also minimize (but not eliminate) this pattern by cosmetic correction in PixInsight, or cleaning up the raw images in e.g. RawTherapee.

 

Hope this helps

[RSM]

Hi. I use dithering as suggested by wimbv for my recent image of M51. I find it cuts down on the background noise and allows me to stretch the image much more in the histogram phase of processing.  I also don't use flats (never saw any noticeable improvement with them in the past) but find I am heavily reliant on the dynamic background elimination (DBE) function in pixinsight to get rid of strong vignetting. For info, I do all my stacking and processing in pixinsight. Finally I used a function called multiscale linear transformation which allowed me to sharpen the image up greatly. Good luck with your attempts in future. In my relatively limited experience, it's partly trial and error to find what works best for you. 

Richard

[Ken82]

Try adding 20seconds between exposures  it cools the sensor slightly and will be beneficial 

[steviemac500]

Thanks guys, appreciate all the info. I'll have a look at dithering but I can't afford Pixinsight!!!! I'll also try adding a delay to my shots too. Onwards and upwards!!!

[steviemac500]

6 hours ago, RSM said:

Hi. I use dithering as suggested by wimbv for my recent image of M51. I find it cuts down on the background noise and allows me to stretch the image much more in the histogram phase of processing.  I also don't use flats (never saw any noticeable improvement with them in the past) but find I am heavily reliant on the dynamic background elimination (DBE) function in pixinsight to get rid of strong vignetting. For info, I do all my stacking and processing in pixinsight. Finally I used a function called multiscale linear transformation which allowed me to sharpen the image up greatly. Good luck with your attempts in future. In my relatively limited experience, it's partly trial and error to find what works best for you. 

Richard

What's the best way to dither? I use PHD2 for my guiding.

Thanks.

[wxsatuser]

Can't help with PHD dither but I dither with my Lacerta MGEN and use about 12pixels in a spiral pattern.

Dithering brings out so much more in an image.
I had never seen the brown dust around NGC 1499 until I started dithering.

[Astrosurf]

Excellent image, steviemac. and the advice on here is great! I'll have a go at dithering myself.

If you can get yourself a Canon EOS 600D, and get it modded, then you'll have a great, lowish-noise camera. Plus it has a flip screen which is very useful in those awkward positions! This is one of my images taken with mine. It's a bit noisy because I didn't take enough subs. Plus conversion to JPEG doesn't help! (Needs dithering! )

This guy does modding. He's ecellent. http://cheapastrophotography.vpweb.co.uk/

What processing software did you use? If Photoshop, try the healing brush tool for the dust bunnies.

Alexxx

[steviemac500]

That site has some good deals on second hand 600Ds. What's the difference between one that is astro modified and the more expensive Baader modified?

[Ken82]

The Baader modification just means the filter has been replaced and not completely removed , for astronomy purposes it has no advantage . But for terrestrial photography it would be better as you can still use auto focus etc etc. 

 

Read this - 

http://www.astronomiser.co.uk/eosmod.htm

 

[steviemac500]

So basically if I don't intend using it for anything else, I don't need the Baader mod?

[Ken82]

Yep

[RSM]

18 hours ago, steviemac500 said:

What's the best way to dither? I use PHD2 for my guiding.

Thanks.

I don't use PHD2 I'm afraid. I have the Lacerta guiding system and use a 14 pixel dither. I've seen lots of posts which refer to PHD guiding on SGL so if you post that as a separate thread I'm sure someone will help you out. Like other have said, it makes a huge difference to the image quality.