Galaxy NGC55

[Striker]

Worked on this galaxy tonight.

Taken with Cooled modded Canon 350D on 10" Meade LX200R

30 x 5 minutes ISO400 at F8 autoguided

Canon chip temp -1°c
Ambient 15°c
Humidity 55%

Calibrated in Imagesplus and processed in PS CS2

Started imaging this low on the horizon but generaly happy with the result.
Still have to deal with field curveture and that ugly donut I cant work out where it's coming from.

Higher Rez...warning 1.7mb
http://www.users.on.net/~striker/NGC55_full.jpg

Hope you like.

[[1ponders]]

Nice Tony :thumbsup: Have you uploaded an uncompressed version anywhere yet?

[ballaratdragons]

WOW Toenails, what an absolute Stunner !!!!!!!!! :eyepop:

I LOVE it!!! :)

[Striker]

Thanks guys......happy with the image just some minor details I need to fix that is really annoying me at the moment.

Higher rez uploaded...I have adjusted the start of the thread.

[h0ughy]

tony, couldn't you have taken a practice shot and rotated said cooled camera diagonally to take in said monstrous galaxy? Having said that, what great detail and wow factor again!

[[1ponders]]

Great detail and clarity Tony, take a bow. :clap:

[EzyStyles]

thats a stunner tony.NGC55 is very faint and hard to capture.

[Starkler]

Warning - Silly noob question:

Are you finding that having a cooled camera is making a big difference?
Have you tested both cooled and uncooled?

[RB]

Houghy, you took the words right out of my mouth, just wondering why you didn't frame it better Tony?
Apart from that it's a stunner mate, amazing detail and great processing work.

[RB]

I see what you mean about the donut Tony.
Curious to see what's causing it.
Has it occured before in other images?

:shrug:

[iceman]

Very nice Tony, what FL is that at?

[Striker]

Very true Houghy...it would have been easy for me to rotate the camera so it was framed better...my fault...no excuse Tony....wont happen again.



It sure has...all my images with the focal reducer does but it wasn't on my first images using the FR...?????....cant see the donut without the FR imaging at F10.



Approx 2000mm focal length



Geoff there is definitely a small increase in performance with less noise but is less noticeable doing 3-5 minute exposures, where I think it will improve results is in summer time when it's hot up here and also doing extremely long exposures at a dark site...something like 20+min exposure's.

Basically anytime when heat noise becomes a problem there will be a beneficial increase to signal noise ratio.

Thanks guys and I am sorry I did not frame the image properly...somehow my mind was more on this stupid donut and how to fix it.

Also it can not be dust on the reducer because I just got it replaced this week with brand spanking new one...same results.

[h0ughy]

not being funny I think it might be where the cooler meets the CCD chip and that it is temperature gradients:shrug:

[Lee]

Thats a great pic - glad I didn't post my NGC55 effort now hehe.....

[Striker]

But it's not there imaging at F10...????

Surely if it was a sensor or filter related I would see some signs of it no matter what focal length I am imaging..as below...no reducer imaging at F10 with cooled camera.

I happy for some suggestions...getting very frustrated with this.

Also something that make no sence to me is that whatever the reason it should atleast flat field out..well it's not..?????

I think I should go back to online gaming and kill people in clan wars....less frustrating....lol

[[1ponders]]

Tony, the donut may well be there at f10 but it is not obvious. By the size of that donut it looks a long way down the imaging train. Also it doesn't look like a dust donut, it looks more like a very out of focus star. I wonder if it could be an internal point reflection of light? Is it in the same place everytime you image; ie on the long side of the image? or does it move to the short side if you rotate the camera?

I'd even go so far as to take a stab at an internal light source (light leaking in around a loose fitting, back through the view finder, etc ) from the camera reflecting back on the inner surface of the FR. That's just a guess thought

[Striker]

My option are open....its very much possible Paul.

Here is a flat frame with the same set up done yesterday with reducer.....I cant see the donut on the flat but saying that I am sure I saw some flats with it....i'm going crazy.

Will do some tests tonight on different areas of the sky see if it moves.

Thanks for your help

[JohnG]

Hi Tony

My thoughts are similar to Paul, it seems way too big for a dust donut. Do you shoot with the cover on the viewfinder, could be a slight light leak from when they re-asembled the camera after the mod. Might be worthwhile trying a shot or two with the cover on, I have always made a habit of shooting with the cover on anyway.

I know I am getting an internal reflection from my Tak focal reducer and it shows as a round, greenish tinged donut but only when there is a bright star in the FOV.

Interesting, I wonder if you could be getting that dark river effect that 20Da owners complain about.

Thinking out loud.

Cheers

JohnG

BTW, nice shot, heaps of detail. :thumbsup:

[h0ughy]

just had a play, you can see the main circle in the frame, so with internal reflection you have the rest of the puzzle. how you fix that I have no idea?:sadeyes:

[RB]

Sorry to go off topic but I haven't heard about this, can you give some detail John about what this effect is with the 20Da?

[Striker]

Thanks guys,

I will do some more test tonight.

I have tried to stretch the flat image to see any signs of this donut....I cant see it in the flat image above please let me know...the outer ring is no problem..thats just vignetting from the reducer

[RB]

Tony it's not there in the flat, I can't find it either.

[Striker]

Thanks Andrew....I needed to make sure.

Thanks again.

[JohnG]

Hi Andrew

On the ImagesPlus Group, a lot of owner's of the 20Da have been complaining of getting a light and dark striped effect on some of their shot's, has been dubbed the "Dark River Effect". I am not sure of the details as it apparently only effects that particular model.

I will go back through the archives and have a look if you like and see if any work-arounds have been found and post them if you want.

I havn't taken that much notice of the problem because I have a 350D and for some reason it is not affected.

Cheers

JohnG

[h0ughy]

sorry tony, must have been an optical illusion, you look at it for long enough you see circles

[RB]

Thanks heaps John, I'd appriciate it. I havn't noticed it with my 20Da or maybe I didn't know what to look for so I'm very interested.

:thumbsup:

[Striker]

Just spoke to Brad Moore.....

His theory is that its the combination of the reducer and filter that is reflecting light back up into the secondry...this is a theory not an ouright confirmatiom of the problem...just something else to try.

To test...take of the filter and shoot just through the reducer then second test alter position of reducer closer to the chip.
3rd test position filter differently in image train.

Will keep you posted.

[JohnG]

Hi Andrew

Here's an explaination of the "Dark River Effect" an email from ImagesPlus Group.

Quote

'Several members of this forum have commented in the past on the dark
river effect, and asked Mike Unsold to look into addressing it with
IP. I have run into the effect in many of my photos. It's not easy
to correct for it. I thought I would share what I have learned, at
least what I think I have learned. Maybe you have some other
thoughts, test results, ideas, processing techniques, etc. Please
share what you know, so maybe we can get a good fix for it. Mike is
working on it now, so our collective input can help.

Here's what I know about the dark river effect on Canon 20Da's:

1. It is a darkened area that shows up in the sky background area on
longer (and deeper) astrophotos. It looks like a broad band across
the horizontal frame, running across the middle third of the frame.

2. The dark river shows up in both lights and darks. However the
effect in darks is NOT eliminated by subtracting the darks from the
lights. Dark calibration of the lights actually exaggerate the dark
river (you subtract a darkened area from a dark area, making it
darker).

2A. What is it? Or what causes it? It seems to be an area of the
chip that has less sensitivity to low level signals and noise. The
pixel levels are lower in the river by about 80 to 150 counts of a 16
bit full well. (That translates to less than a count on an 8 bit full
well). Treating it like a bias correction might work, but see note
10 below.

3. The river is stronger in longer exposures and higher ISO
settings. If you shoot 5 minutes or less, you probably won't see
it. On dim object astrophotos, the more you stretch the histogram to
see the dim nebula, the more the river shows up.

4. There is a temperature sensitivity, but I don't have enough
samples to fully characterize it. So far I believe the effect is
strongest at mid temps around 40 to 50°F. I see less at 30° and at
75°.

5. I have not heard anyone say they have the effect in any cameras
other than the Canon 20Da. Does it show up in modified or stock
20D's and Canon 350's? Or Nikon's?

6. You can see it if it's there using Images Plus>Color>Brightness
Levels and Curves>Digital Development and setting the Break Point to
500 or less.

7. The pattern of the dark river changes with exposure duration. On
my camera at 70°F, darks up to 20 minutes are generally a horizontal
band, or series of dark bands across the frame. At 30 minutes and
longer, the river turns into "Lakes" or blotchy areas across the
middle of the frame.

8. The areas of the river are not the same in darks and lights. I
had hoped that they were the same, so that darks could be used to
identify the river, without running into the subject of the image,
and be used to correct for the river. Unfortunately, this idea won't
work.

9. What works to correct for it? I have two methods, but neither is
perfect.
9A On astro images with a small subject and lots of uniform dark
sky, Use Jerry Lodriguss' method for flat fielding. See
http://www.astropix.com/HTML/J_DIGIT/VIGNET.HTM (http://www.astropix.com/HTML/J_DIGIT/VIGNET.HTM)

9B Manually create an adjustment layer to see the river and create a
fill/mask layer (heavily blurred) with the inverse of the sky in the
river area. Play with the Fill and Opacity % controls to neutralize
the river, then turn off the adjustment layer and flatten the image.
This may require several iterations because the river is actually
several thinner bands, with different intensities. This method is
tedious and non exact, but allows trial and error if the subject of
the image is extensive.

10. What doesn't work? As mentioned above, you can't get rid of the
river by subtracting the darks, it isn't noise in the classical
sense. Correcting the darkened areas in freshly calibrated/un-
stretched images (or combined images) risks a sky background color
shift in the river if done before the color balance is adjusted for a
neutral sky.

11. What may work? I want to try this, but have to wait until the
next dark of the Moon. Take my light images of my selected target
for 10 minutes or more, than take one or several additional lights,
same setting, but move the scope off the target and into an area of
the sky that has few bright stars (these "river images" don't have to
be guided). Then use it ( de-starred and blurred) as a mask to
correct the river.

12. Mike Unsold has been asked to create an automated process in
ImagesPlus, and Mike has agreed to try. He may have an idea of how
to automate a corrective process, I hope so. I'm documenting what I
have learned to help him or others understand the problem and
contribute to a good solution.'

Hope that helps explain it a bit better.

Cheers

JohnG

[tornado33]

Howdy
First, great NGC55 pic, lost of inner detail and wow. 2.5 hours, that beats my best of 2 hours lol. AS for the optical effects, it is unusual it doesnt flatfield out, as in theory it is caused by light, which flatfielding should eliminate, though as we see it doesnt appear strongly in your flatfield. Could it also be stray light from the sides, do you use a dewshield? I get flatter images if I use a dewshield, as it seems that sometimes light can come in from the side and find its way into the focusser, as this light hasnt came off the mirrors, it isnt elimated by flatfielding, the foot long dewshield I use all but elimnates it.
With my 6 inch Schmidt Newtonian, I get an odd ring effect similar to yours, Im assuming its a product of the corrector plate which is not antireflection coated, and plays havoc with secondary reflections from bright stars. Flatfielding eliminates it however.
Scott

[Striker]

Anything is possible Scott...it could be stray light but I do have a long dew shield permamantly attached.

The dew shield is also a high quality one with matt black flocking the entire internal length.

I have plenty to try tonight.

[RB]

Just out of curiosity Tony, are you running the cooler when you take flats?

[tornado33]

Yes I see the shield in the pic, that should be more then enough to stop stray light. Sure is a curiosity what the cause of the optical effects is that flatfielding cant get rid of.
One final thing, I used to do flatfielding using a floodlight lighting up the white wall of the house, however with the modded camera excess IR light seemed to be causing effects in the flatfield that led to a faint ring like area in the middle of the finished images. I now use a fluro light, and , holding it by hand, illuminate the white wall of the garage with the scope pointing at it. I aim for flats with the histogram roughly in the middle. The fluro light is low in IR light, so only visible light goes into making the flat. Perhaps your focal reducer is passing IR light differently. Might be worth trying that, illuminate somethign white, such as a square of cardboard held in front of the scope with a fluro light and see if that helps. I also tried sky flats with my system but always seemed to get uneven results.
Scott

[tornado33]

I should point out that looking at Star Atlas pro, youve caught background galaxies in your ngc55 shot down to mag 18 :)
Scott

[richardo]

Hi Tony,
I like the detail you picked up, the colour and also the stars look tight and natural.
I sort of agree that the framing could be a little better to rotate the Galaxy in to the diagnal of the chip.

Looking at the,... 'donut' in the image, I'd say with out too much doubt that it is the reflection of your primary and secondary mirrors coming off a filter, a corrector, a reducer or the piece of glass that covers the camera chip.
I use to get this when I had a focal reducer in with my VC200L and tried over stretching.

Hope this might help solve the mysterious 'Donut"

Cheers
Rich

[Striker]

Thanks Rich,

My first test with no filter worked well...could not see and donut.
second test was to apply the filter between the chip and fr instead of the end after the FR.....early testing seems to be no reflection.

I am not prepared to say that is the problem but early tests suggest the light is being reflected by the filters back up onto the secondry as per Brad Moore and Richardo's theory.