comparing 2.1 and 7.8 hours exp.time...

[Dietmar]

hi folks,
cloudy nights - no new data - so I was playing around with old data.
here is a comparsion between an image of 7331 I have taken last year and this year.
the data is on the image.
last year procedure:
image acquisition in SX original software. I applied a slight streching filter adn colorconverted the images at once. these were stored as 16 bit TIFF...I didn`t know better. exp time of subs was 2,4 and 6 min. in PS I reduced the bloated stars in size...
this year: image acqu. exp time of subs was 9 and 12 minutes. in astroart4 - unprocessed FITS were stored and preprocessed in astroart, CCD sharp and registax...the rest was done on PS...

to me it is quite astonishing, that there are only a little more stars in the background,...perhaps there are simply not more in this region...
on the other hand those almost 4times more data brought up star colors very nicely. (and also the galaxy)
difference in detail is mostly due to better seeing and transparency - and of yourse more single frames to reduce issues from the CCD.
well, one could expect that after 4times more exp.time there would also be more luminosity in the galaxy's periphery...but I think I would have to add much more time for this purpose...
here is the image with all data:
http://www.stargazer-observatory.com/7331-comp.htm

thanks for looking,
Dietmar
www.stargazer-observatory.com

[iceman (Mike)]

Lovely comparison and a beautiful image, Dietz.

I think the 7.8 hours is definitely a cleaner, smoother image with better colours.

[Lee]

Great shots, both of them..... but the longer exposure has better (slightly) contrast and colours I think.
Wow - your 9" folded apo is an interesting scope.... I've never seen one before.

[jase (Jason)]

Nice comparison Dietz. This hammers home the truth of the importance of longer subs when using linear chips.

[Dennis]

Several of the fainter stars in the “short” exposure are much more visible in the “long” exposure. The texture, detail and depth in the “long” exposure are quite breathtaking compared to the “short” exposure.

If I had only seen the “short” exposure, I would have considered it to be a superb image in its own right. The “long” exposure is literally out of this world.

Congratulations on both images and thanks for posting the comparison.

Cheers

Dennis

[skeltz (Rob)]

the longer exposures are far better,it slowly i suppose gets to the diminishing point of returns.a bit like say buying a 4 inch refractor for $4000.00 and a 6 inch for $140000.00..
but the extra time which costs nothing is well worth it ...as i am finding out!!
Have fun with your equipment dietz
cheers rob

[felix]

the photos are amazing! the 7.8hrs is definitely a lot more exciting than the 2.1hrs, the colour from the spiral galaxy is a lot more crisp and colourful and the surrounding galaxies are also generally noticeably brighter too! as rpsastronomy said, the extra time costs nothing! and i think we all agree the 7.8hr exposure looks better

great photos!

[Ric]

Hi Dietz, they are both lovely images but as you say the extra time really brings out the fine detail especially in the fainter galaxies.

Great work

[janoskiss (Steve H)]

Awesome. Love seeing galaxies in the background of galaxy shots. The scale of things in the universe is mindblowing.

[Dr Nick (Nick)]

Very nice work!

[Dietmar]

...thanks for your feedback, Mike, Lee, Jase, Dennis, Rob, Felix, Ric
n' Nick.

to add all information I want to continue...
last year I acquired the frames in SX original software, applying some slight streching filters to them and color converting them before sorting them as 16 bit tiffs. these were aligned in images plus not using a dark frame or a defect map.
single frames were 2, 4 and 6 min subs...much too short - but I did not know that better...
the displaying mode in SX original software is somewhat different to astroart...in astroart you can read the "counts" telling you, what is perfectly exposed and what not - so this way you can find out the perfect exposure time for each object - or for star colors:

I did not have astroart4 at this time...
my processing knowlege and skill has "changed" over the time now...

this year I acquired the images in astroart (automatic routione while I am spleeping in the obs...(- and storing all files as 16 bit FITS.
preprocessing is sone in astroart including a defect map - but no dark...
reamining hotties werre eradicated by a global /r,g,b median filter)

this comparsion is not thought to be a highly sophisticated scientific study - it is more like comparing apples with strawberries,...but I wanted to demonstrate the "over all" difference...

anyway:
conclusions for me:
~10 min subs are very good for starcolors in my slow system
~a defect map is a handy feature to work the small amount of hotties you will get with this nice sony-color chip...the remaining hotties can be erased with a median filter (loss of stars possible...?)
~exposure time like 2-5 minutes is too little to gather data in faint objects
~preprocessing in AstroArt4 is much more powerful than in SX original software
~background improves a lot with increasing number of exposures that have a reasonable single exp time
~exp time less than (let`s say) 5-6 minutes in galaxy-like objects even lots of frames can not bring up faint structures.

good luck to all!