IC1805 and IC1848

[RobertM]

Taken with new setup : 34 x 600s Baader 7nm Ha filter, unguided, FLI ML8300 Camera at -30C and Canon 200mm f/2.8 lens stopped down to f/3.2
This is the second and last image from an all night session on Sat 24th October from my back garden in Orpington.

Stacked in MaximDL, Gradient Exterminated and all further processing (levels/curves etc) in PS.



Link to full size:http://gallery.orpington-astronomy.org.uk/albums/userpics/10031/Group2-GE-SSLC.jpg

Robert

[MarkS]

A stunning image with so much depth!

I think the stars look slightly oversharpened in this one though - they have "shadows", giving them a slightly 3D appearance.

Mark

[RobertM]

Thanks Mark, I see what you mean about the stars, they are a bit yucky.  My intention was to sharpen the nebula not the stars so I'll have a reprocess tonight and see what I can do.  I really do need a processing workflow, it's all a bit random at the moment!

[Daniel]

That is just spectacular Robert, as Mark said, so much depth the 24th was that windy night wasn't it? This seems like the ideal solution for nights like this.

You have more detail in those objects than i've ever been able to get, makes me think seriously about the FLI now, im weighing up all the pros and cons of all the camera's then going to buy one at astrofest in february.

Looks like whatever it is, the 8300 is the sensor to go for!

Daniel
:O)

[Mac]

 
that is fantastic.
Cant wait to start to image again

[Tony G]

Great images, and lovely widefields Robert,

Cant wait to start to image again

Can't wait to start imaging! 

Tony G

[JohnP]

Robert - unbelievable FOV with the setup you have. Fantastic image & must be great to be able to do 10mins unguided... I look forward to the reprocess & I am sure you plan to add some RGB at some stage...

Can't wait to start imaging! 

Tony you have got all the kit so no excuse.... !!! You can even power your laptop from 12V now without having to convert to 240VAC first so come on let's see some images..

John

[Fay]

Really great, Robert, unguided, nice round stars........sigh

[Tony G]

Can't wait to start imaging! 

Tony you have got all the kit so no excuse.... !!! You can even power your laptop from 12V now without having to convert to 240VAC first so come on let's see some images..

Yeah John, but sometimes drink gets in the way and stops me, plus its always night-time when I look at starting to image. 

Tony G

[Fay]

 

[MarkS]

Robert,

As a matter of interest, what background level were you achieving (either in electrons or ADUs).

BTW, I'm scheduled to give a fascinating talk on (image) noise at the forthcoming members evening - it will be of interest to imagers and (hopefully) non-imagers as well.

Mark

[RobertM]

Mark,

The minimum background ADU was 1350 (median approx 1500)  on frame 19 which was half way through at 2:38am.  At that time the center of the frame was at 69 degrees altitude (airmass 1.06).  All the frames were 600 seconds (10 minutes).

Should be an interesting talk.  It's a big subject so I hope you have enough time ?

Robert

[MarkS]

Robert,

Is that bias adjusted?  i.e. what ADU do you get for a very short exposure in the dark? Zero?

The gain is apparently 0.4e/ADU:
http://www.narrowbandimaging.com/images/ml8300_ptc_dtc_crisp.pdf

Mark

[RobertM]

Mark,

The frame is as it came out of the camera, I just picked the darkest part of the image.  The bias frames have a median of approx 1080 ADU so bias adjusted the background would be 1350 - 1080 = 270 ADU.   The gain is the same as the SXV-H9 and Atik314L ... 0.4e as the well depth is about 25,000e too.

Robert

[MarkS]

Some quick maths:
270 ADU is 110 electrons (at 0.4e/ADU).  

Also, you were using a very fast focal ratio.  If you used F6.4 instead of F3.2 it would only be 28 electrons in 10 minutes.

Such a low background definitely shows the efficacy of your extreme narrowband H-alpha filter.

Mark

[RobertM]

Yes but if I used f/6.4 a lot of the dynamic range would have been wasted due to the low signal and of course read noise might have been an issue.  Also 200mm f/6.4 = a 31mm objective = 40mm of wasted aperture and expensive glass.

7nm filters aren't extreme, I would have preferred 3nm but the costs were astronomic !

Robert

[MarkS]

No, I wasn't suggesting that you use F6.4 - I was just converting the background signal to units I'm more familiar with!

As you say, you should always use the fastest focal ratio possible to capture all the photons you can ...

[Rocket Pooch]

Hi Robert,

Not bad, if I had to be critical about the image I'd make the following observations.  The brighter stars look too which and there is a lot of noise in the image, so I'm assuming the DDP was a bit extreeme and thats why the white is very white, also a median filter could be a good move.

I do like the FOV and also the framing thats fab and the lens obviously performs.

Chris