Latest image a step backwards - please help - lots of pics

[Fordos Moon 306]

I had a successful session the night before last - my first with guiding using the ASi120MM on my ST80, atop my ED80 through which I imaged with my unmodified Canon 1100D and focal reducer. I was pleased with this image using 13 x 300 second lights with darks and flat frames:

Then last night I thought I would try M51 and things have not gone so well. However I only took 6 x 400 second lights, 3 darks and used the previous flats as still ISO800.

This was my first image out of DSS with a star detection of 50 stars:

There appears to be a distinct lack of colour, I did moved the right hand RGB/K pointers for blue and green to the left a bit as I am sure someone once said make the peaks a bit fatter but I think that now a BAD idea.

So I tried again without flats and the colour came back(?):

But very noisy - but there is the colour!

And I tried a third time this time including flats but set at "average" not "median", star detection 47 stars and got another dull image:

This is my image from last year which was an unguided attempt using 30 x 70 second lights:

Now I guess my questions are as follows:

1. Please confirm I should take a LOT more lights?

2. Should I reduce exposure down a lot from 400 seconds to reduce noise on a fairly moonlit night?

3. Where did the colour go?

4. Why did the image look better when I DIDNT use flats?

5. Any other advice please!

ps - already saving up for a weeks training at Olly's place hopefully next year!

[wxsatuser 5,480]

I think you need a lot more lights.

Make sure your flats are taken with the exact setup as for lights.

If you move anything the flats will be next to useless.

[Fordos Moon 306]

I think you need a lot more lights.

Make sure your flats are taken with the exact setup as for lights.

If you move anything the flats will be next to useless.

Thanks Mike - I should have taken flats after the session rather than using the previous nights and yep roger that - more lights!

[wxsatuser 5,480]

Thanks Mike - I should have taken flats after the session rather than using the previous nights and yep roger that - more lights!

I forgot to mention exposure time.

For exposure aim for somewhere  between 25 to 40% of the in camera histogram.

Exposure length depends on sky conditions, light polution etc.

Some nights I can do 900secs and others are around 180secs, yours may be higher or lower.

[Fordos Moon 306]

I forgot to mention exposure time.

For exposure aim for somewhere  between 25 to 40% of the in camera histogram.

Exposure length depends on sky conditions, light polution etc.

Some nights I can do 900secs and others are around 180secs, yours may be higher or lower.

http://stargazerslounge.com/topic/216990-backyardeos-and-histograms/

This is my post on just that topic! The BYE histogram was about 30% without the Astronimik CLS filter but the red channel appeared clipped with it in place.

[IanL 985]

One question is how did you make the flats? i.e what was your light source?  Do they have a colour cast on them (you'd need to check using something that displays the RAW without applying any kind of white balance)?

OSC flats are easiest to take in daylight with a diffuser of some sort over the scope; artificial light sources may not give out a true white light (even if it looks white by eye).  This can lead to a significant colour cast and usually a lot more noise in the under-exposed channel(s).  Depending on how the software applies the flats, this may make it harder to get a decent colour balance in the image plus it will almost certainly be noisier in that channel in the final result.

You can usually sort out the former issue with a bit of processing, but not the latter.  If you're relying on your software to automatically balance the colour, bad flats might well throw it off course.

Of course it might be any number of other issues, but that is one to explore.

Edited May 19, 2014 by IanL

[dph1nm 352]

DSS images do come out without much colour. This is a feature not a bug. Just up the saturation slider (I always use a setting of 20) and you will recover the colour information.  Also, don't worry too much about what it looks like on the DSS screen anyway - it can always be adjusted afterwards in a photo-editing package.

NigelM

Edited May 19, 2014 by dph1nm

[Fordos Moon 306]

One question is how did you make the flats? i.e what was your light source? Do they have a colour cast on them (you'd need to check using something that displays the RAW without applying any kind of white balance)?

OSC flats are easiest to take in daylight with a diffuser of some sort over the scope; artificial light sources may not give out a true white light (even if it looks white by eye). This can lead to a significant colour cast and usually a lot more noise in the under-exposed channel(s). Depending on how the software applies the flats, this may make it harder to get a decent colour balance in the image plus it will almost certainly be noisier in that channel in the final result.

You can usually sort out the former issue with a bit of processing, but not the latter. If you're relying on your software to automatically balance the colour, bad flats might well throw it off course.

Of course it might be any number of other issues, but that is one to explore.

Ian thanks for your response. I take flats with an aurora Flatfield I got from Germany. If anything it puts a slight blue colour across the image.