Invisible Pinwheel

[wsteel33]

Hi Guys

Any chance of some imaging/processing advice please.

I had a go at the Pinwheel (again) last night and thought I'd got some good data. 80 x 150sec at ISO 400, guiding was good, took darks, flats and Bias frames. I could see it there centre field when auto stretched in APT. I chose it as it was a 3/4 moon to the SE so I thought I'd go for something in the NW.

I was excited to process today thinking that this was going to be my best image yet. It seemed to stack fine in DSS, I had to drop the threshhold down to 5% to pick up 35 stars but I figured that that was because I went with a low(ish) ISO.

However... when I came to process and do my initial curves and levels in Photoshop.... nothing... its there, you can see it, but there seems to be no real data to process. I thought it might be my flats, they looked really bright and I'd read that some people found that washed out their image.

So I stacked again with just lights and darks.... same problem, no improvement.

I have shot this image before in April and It came out ok for a first stab (it was literally my first image).

The other image was using BYEOS, 61 x 60 sec at ISO 1600 (scope mount and camera were the same, Evostar 120, EQ6, Unmodded 600D), the sensor temp was 18degC for the first image (it was 32degC last night!)

I noticed that the histogram was very thin when processing today.. should that have set off alarm bells?

I have attached images with Histograms for reference. I have stretched last nights image so you can see it is actually there... I promise 😀.

Was ISO 400 just never gonna cut it? I went this low thinking that it would help noise reduction on a warm night.

What do you think happened here? All advice and constructive criticism enthusiastically welcomed.. I am eager to learn and further my skills.

What a hobby... frustration and amazement in almost equal measure.

Thanks in advance everyone.

Wayne

[Adam1234]

Hi, the Pinwheel galaxy is quite a faint target, being large it has a low surface brightness. You could try increasing your exposure time if your guiding allows for it

[wsteel33]

Just now, Adam1234 said:

Hi, the Pinwheel galaxy is quite a faint target, being large it has a low surface brightness. You could try increasing your exposure time if your guiding allows for it

Hi Adam

The first photo back in April was only 60 mins worth of data and, while not high quality, the galaxy came out fine. Last night I got 80 x 150 sec subs (3hrs 20mins in total!!) yet the image was none existant, I'm wondering if the fact that I went with ISO 400 last night as opposed to ISO 1600 back in April is the issue.... or am I missing something else.

Cheers

[Adam1234]

3 hours ago, wsteel33 said:

Hi Adam

The first photo back in April was only 60 mins worth of data and, while not high quality, the galaxy came out fine. Last night I got 80 x 150 sec subs (3hrs 20mins in total!!) yet the image was none existant, I'm wondering if the fact that I went with ISO 400 last night as opposed to ISO 1600 back in April is the issue.... or am I missing something else.

Cheers

I would say it's probably a mixture of the lower iso and, I think you mentioned there was 3/4 moon which would reduce contrast.

With a lower iso you would benefit from longer subs. 

 

 

[michael8554]

I shot The Pinwheel last night too.

240 seconds at ISO 1600 (Canon 6D handles that), as Adam said, it's a dim target:

 

Michael