Hobart Helix

graham.hobart (Graham stevens) · #1 16-11-2011, 03:10 AM

Hello old beans, got some more time between rampant squalls to exercise my small refractor. This is a product of 20 x 4 min lights and calibration frames, lost the rest due to strange goings on with the neighbours and then the Moon . Cursed cheese.
happy happy joy joy as Ren & Stimpy would say
Graz

rcheshire (Rowland) · #2 16-11-2011, 08:19 AM

Graham.

Viewing your last 3 posts, your system tracks very nicely and focus looks good, and more signal would make a difference

The Helix image is quite streaky. This is usually the result of not dithering between shots and is very difficult to get rid of. Calibration frames will not fix it - Did you take any calibration frames?

Rowland

graham.hobart (Graham stevens) · #3 16-11-2011, 01:23 PM

Yep- took some calibration frames on same system but didn't dither- I will next time though as you can dither via APT/PHD interface.

Visionoz (Bill) · #4 16-11-2011, 02:37 PM

At least your tried Graham and got some returns on your effort!

I tried and got dots, spots & specks!!!

Great!

Cheers
Bill

graham.hobart (Graham stevens) · #5 17-11-2011, 01:18 PM

Have to say though that the advice I got here from a few of the regular posters has been very helpful to get rid of my gradients caused by probably the LCD screen/ view finder and also cut down loading times by turning off in camera noise reduction.

adman (Adam) · #6 17-11-2011, 09:27 PM

Hi Graham - good to see you getting out there and amongst it.

Looking at your shots they tend to strike me as too noisy for the number of subs you have....how hard are you pushing the data when you process the stacked image? What ISO is the camera set to? Can you get any indication of the sensor temperature from the EXIF data - if you use APT this has the facility to add it to the filename.

Cheers,
Adam

graham.hobart (Graham stevens) · #7 18-11-2011, 08:28 AM

I agree about the noise. Most of the pics recently were ISO 400 and last night I took some more I noticed EXIF as 17'c.
I also wonder how much more time you need to add to dither?
I did 34 exposures x 4 mins last night with dithering and it took the best part of 3.5 hours.
Any help?
Graham

adman (Adam) · #8 18-11-2011, 08:48 AM

34 X 4 mins = 136 minutes add in 10-20 secs or so per sub for downloading etc is only another 5-10 minutes - say being generous 2.5 hours total. The extra hour spread over 34 subs is about another 1.5-2 minutes per sub for dithering....

it doesn't sound outrageous, but at the same time it does seem too much. Are you using APT for capture - there are some settings in there about how far to dither and how long to wait afterwards for the scope to settle - can you check those?

Adam

graham.hobart (Graham stevens) · #9 18-11-2011, 08:53 AM

I can check PHD tonight -I know I had interval between dither? as 10 secs
The noise in the images- the only thing I can think of (apart from pushing the data too much after stacking), is that I am using a set of master calibration frames which I took the other night , a series of different exposure length darks, some flats from a light box and dark flats. All taken with same camera and same scope- the only difference I can think of is that my calibration frames had camera internal noise reduction on, the lights didn't.
Would using 'on the night' darks really make that much difference or is it me just pushing the data too much?
The helix was 80 mins of iso 400 so I was surprised how noisy it was.

adman (Adam) · #10 18-11-2011, 09:09 AM

as long as your darks are a similar sensor temperature and same iso and exposure length they should be fine - but if any of those are significantly different, then do some more and see what happens - you can always do another more appropriate set of darks and then re-process...?

Adam

graham.hobart (Graham stevens) · #11 18-11-2011, 09:27 AM

I will try that later as looks like clouds are here for the night.
Cheers
Graz

midnight (Darrin) · #12 19-11-2011, 02:51 AM

Tracking seems spot on (I've spent the last 6 months battling this!!)

All you have to do now is get rid of the noise. Impressive!

Darrin...

adman (Adam) · #13 19-11-2011, 09:16 AM

Quote:

Originally Posted by graham.hobart

...Most of the pics recently were ISO 400 and last night I took some more I noticed EXIF as 17'c....

I find with my 550D that any temps around 20 degrees give an 'acceptable' level of noise - so winter time imaging in Brisbane is the go - but during the summer when its still 25 degrees in the evening - the sensor reaches 38 degrees - then its a little festival of noise, and you tend to get more of the streaky pattern coming through.

Adam