M101 Part 4

[Rocket Pooch]

Ok this one is with 10 5 minute subs, it looks better to me.

[JohnP]

Hi Chris,

They both look good to me - I'm suprised the 10min Ha hasn't bought out more detail..? I guess you are going to combine the two - it'll be interesting to see the composite? The images look quite noisy - Is that because the subs were so long?

John

[Rocket Pooch]

Hi,

Its because of the background noise, for the highlights in the image at 10 minute subs I get an adu of 65000 for the ight star this is actually too much, the backgound is about 6400 i.e. 10% of the foreground in Ha, this is really noisy 9/1.

For the older versions last time the peak was 65000, but the backround noise is 22000 about 30% 6.3/3.3.  So although the Ha is less noisy, M101 is not a good Ha target hance the dimness.

I'm going to play with the image I have to see what I can get out of it.

Just for reference the M33 I took at headcord was approx 40000 and 4000 for 2 minute subs using the neodium filter with no saturation at all.  Simply put the shorter exposure at headcorn gave a mush better signal to noise ration 9/1 with the exact same kit.

I can do a couple of things to improve the image which I will try.

[JohnP]

That definitely looks better & a lot less noisy - was this the 5min & 10min subs combined..? I'm just a bit suprised because when I imaged it a month or so ago I could only do 30secs subs because of alignment & Ampglow & level of detail is not a lot worse than your 10min images. I would have just expected a much deeper image with your setup & length of exposure - like you say I think 101 is one of those hard galaxies to image...

Cheers,  John

[Rocket Pooch]

I know I keep harping on about it, but it is the light polution at my house, its just that bad.

On that night I could just see the plough (orange) the sky very orange with a big gradient.  

Therefore the sky affected the SN of the image even in Ha, I'd give the transparancy about a 3/10.

Have a look at this 10 minute Ha RAW



This is a two minute raw at headcord



Sorry non broadband users.

[JohnP]

The raws explain all.....! It'd be great if you could try m101 at the end of the month at Headcorn. To compare I've attached one of my 30 sec raws with my sc3 from Bromley - you can barely see the galaxy.... you can just about make out the central core



Cheers, John