NEW Horsehead & Flame nebula - questions...

[Alveprinsen]

Light frames: 31 x 10 minutes.

Dark frames: 18 x 10 minutes.

Bias frames: 20

Flat frames : 19

Total exposure: 5h 10 min.

I took a picture of this nebula at 3/4th of a full moon last month, and it turned out about the same as this one I took yesterday at pretty good viewing conditions. I was not expecting this bad result with a clear sky, -2 degrees celsius and no moon.

My big question is this: What are these apparent brush-strokes that appear out of the picture as I stretch it?

Are these "brush strokes" simply noise? I guess I've reached the limits of my camera, or I am wrong here? They appear to "move" in the same direction and somewhat of a large circular motion....

Either way, this is unacceptable. And the ETA is still about 4 weeks for my new camera.

Sincerely, Alveprinsen.

[StuartJPP]

As far as I am aware it is camera noise. I get similar artefacts from my Canon 1100D when stretching heavily.

Is this a modified camera? What OTA are you using?

Forgot to add...what are you using to stack your subs?

[Alveprinsen]

As far as I am aware it is camera noise. I get similar artefacts from my Canon 1100D when stretching heavily.

Is this a modified camera? What OTA are you using?

Forgot to add...what are you using to stack your subs?

Its a Nikon D3100 unmodded.

The scope is a Evostar 80ED.

I am using DeepskyStacker.

My guess was noise too...

[lensman57]

I am interested in this topic too as I get these from time to time both and mainly with  the DSLR and once or twice with my cooled CCD. I often wonder if something is going on with DSS during the stacking.

A.G

[frugal]

I thought that the whole point of taking the bias, dark and flat frames was to remove the noise? Is it just the there are other sources of noise that can not be removed with these frames?

Sent from my GT-N7000 using Tapatalk

[RogerTheDodger]

I'm guessing that you didn't dither between the subs?

[StuartJPP]

The HH region is very rich in Ha and without a modified camera you will possibly need to expose for longer though I would have thought 10 minutes would have been enough..the flame should be a bit more defined I'd have thought.

I have seen this even stacking with other programs though, not just DSS. You could try a trial version if PixInsight to see how it copes and eliminate DSS as the culprit.

I thought that the whole point of taking the bias, dark and flat frames was to remove the noise? Is it just the there are other sources of noise that can not be removed with these frames? Sent from my GT-N7000 using Tapatalk

The purpose of stacking is to increase the signal to noise ratio. It will never be noise free but the more you stack the lower the noise will be.

[Alveprinsen]

I'm guessing that you didn't dither between the subs?

Care to elaborate on the term "dither"? I have yet to encounter the use of this term in conjunction with stacking subs.

[StuartJPP]

Dithering is where each sub (light) frame is moved by a couple of pixels so that the same region of the sensor is not used to capture the exact same region of sky for an entire imaging session.

This helps the stacking algorithm to eliminate fixed noise patterns of the sensor and not to stack it as signal.

An example is a stuck pixel, if it was present at the same position on each frame and so are all the stars it would be treated as a star.

If your guiding is too good it can be bad for your images without dithering.

[Alveprinsen]

Dithering is where each sub (light) frame is moved by a couple of pixels so that the same region of the sensor is not used to capture the exact same region of sky for an entire imaging session.

This helps the stacking algorithm to eliminate fixed noise patterns of the sensor and not to stack it as signal.

An example is a stuck pixel, if it was present at the same position on each frame and so are all the stars it would be treated as a star.

If your guiding is too good it can be bad for your images without dithering.

Thank you very much Sir for the clarification.

To answer your question - no, I have not been dithering between subs. I wouldn't even know how to do this other than driving the mount slightly at low speed.

And my guiding appears to be pretty spot on...

Perhaps I shall try another software for stacking my subs. But from what I understand, others in this thread have experienced identical problems with different software.

I will be receiving a deep cooled modded Canon 600D in approx. 4 weeks. The chip temperature will operate at between -30 and -25 degrees celsius regardless of exposure time... I wonder - will this eliminate such problems as these? I have looked at dark frames from such a camera, and it is the blackest black I've seen....

Sincerely, Alveprinsen.

[StuartJPP]

Although I don't guide myself I am sure that PHD or similar will support dithering. It is only done between subs, not during subs. So after the exposure has been taken, the mount is moved slightly before starting the next exposure.

There has to be a connection between the software that guides and the software that takes the exposures. A program such as MaximDL probably supports this in one.

I agree that it probably isn't the stacking software causing this issue but it is best to eliminate all possibilities.

Good luck with your new camera once it arrives...

[Alveprinsen]

Although I don't guide myself I am sure that PHD or similar will support dithering. It is only done between subs, not during subs. So after the exposure has been taken, the mount is moved slightly before starting the next exposure.

There has to be a connection between the software that guides and the software that takes the exposures. A program such as MaximDL probably supports this in one.

I agree that it probably isn't the stacking software causing this issue but it is best to eliminate all possibilities.

Good luck with your new camera once it arrives...

Thank you very much Sir.

I am now looking into dithering software. I've started a new thread on the topic of a certain piece of software I found by the name DitherMaster.

Sincerely, Alveprinsen.

[swag72]

Dithering will really help to combat noise. Regarding your artefacts in your image, I have had similar and it was caused by the bias frames. It may be worth you stacking again without the bias and seeing if that solves it.

[Zakalwe]

I've seen that streaky noise in DSLR shots before. I also struggled to control it when I was using a 50D for astro use. In fact, it was one of the main reasons why I went to CCD imading.

[Alveprinsen]

I just combined my old 3/4 full moon data with the 5h 10 minutes of data from last night.

The result is still horrible... just horrible in a more esthetically pleasing way... I have to look into that dithering stuff....

Sincerely, Alveprinsen.

[ollypenrice]

Dithering is not normally by several pixels but by less than one. If it's by several it will work for noise reduction but it is also intended to work in conjunction with a stacking routine called Drizzle, which, in conjunction with Dither, can resolve sub pixel detail. Whatever, moving between subs by a small amount is a good idea. I've tried to dither in Nebulosity while guiding in the compatible PHD but the system frequently failed to relocate itself and kept on trying, wasting vast amounts of imaging time.

As Zakalwe says, this is very much a DSLR noise pattern. You can't beat CCD but not all DSLR images suffer from this. I don't know the cause.

Olly

[Alveprinsen]

Dithering will really help to combat noise. Regarding your artefacts in your image, I have had similar and it was caused by the bias frames. It may be worth you stacking again without the bias and seeing if that solves it.

Gonna try that! Thanks.

[glowingturnip]

 just horrible in a more esthetically pleasing way

I'll second that, there's definitely a cracking picture trying to come out there.

Weird streaks, they're not all in the same direction, and the stars don't seem to exhibit them.  Couldn't be light leaking into the camera, maybe through the eyepiece could it ?  Either onto the light frames or the calibration frames ?  I've had a light leak onto dark frames before that took me ages to figure out.

[lensman57]

I just combined my old 3/4 full moon data with the 5h 10 minutes of data from last night.

The result is still horrible... just horrible in a more esthetically pleasing way... I have to look into that dithering stuff....

Sincerely, Alveprinsen.

Hi Alve,

I have been searching the web and the reason for these streaks are unclear, there is possibility that they are caused by master bias file, the remedy is apparently taking, combining about 200 bias files and probably half as much dark frames to combat the noise pattern but it is not a sure thing ( Pixinsight Forum). There is also a possibilty that the dark frames are mismatched in terms of the temperature to the sensor but then again your noise pattern  is slightly different. The only way to be sure is to stack the subs with no calibration frames applied and see if there is significant difference. From my reading also appears that these noise patterns are usually but not exclusively associated with DSLRs. As for your dithering, your capture program must support the dither in conjunction with guide software. PHD does support dither but I have Nebulasity3 and these two communicate. I am not quite sure if APT supports this but my gut feeling is that it does as it is always looking for PHD on start up. If you manage to dither then you need to drizzle to recover the resolution during combining and stacking. One word of caution regarding a cooled DSLR, please make sure that the set up has the ability to remove moisture and condensation from the innards of the camera, cooling will cause condensation and if this is not dealt with there may be problems as condensation builds up.

PS: All this makes me think that the money I spent on my second hand  used 314L+,  was money well spent, just a shame about the size of the sensor but life is about compromising where appropriate.

Regards,

A.G

[Alveprinsen]

Hi Alve,

One word of caution regarding a cooled DSLR, please make sure that the set up has the ability to remove moisture and condensation from the innards of the camera, cooling will cause condensation and if this is not dealt with there may be problems as condensation builds up.

Thank you for extensive information. I will look into all of those.

As for cooled DSLR and ability to remove moisture and condensation... that sounds tricky. I know that QHY8L CCD camera has a silicone attachment thingy for just that. My future camera however does not. I will have to ask the manufacturer about this.

Sincerely, Alveprinsen.

[Alveprinsen]

Oh, I re-processed the data without bias files, and I avoided over-stretching it. This is the result. I will run another test now with no calibration files whatsoever...

Alveprinsen

[Zakalwe]

Thats a massive improvement!

[Alveprinsen]

Thats a massive improvement!

Yeah...

Perhaps I've simply over-stretched and need more data in order to pull more details... Noise is still there though, although less visible - obviously.

I just did a re-stacking of the data without any calibration files. Results is the same, just more hot-pixels and some insane vignette... The "brush strokes" are still there if I stretch the image enough. Perhaps it is as previously suggested - a mismatch between the dark frames and the light frames. When I do lights, I let the camera capture them for 5 - 6 hours straight. Then I do the flat fields, bias frames, and sets the camera to do dark frames for 2-3 hours. The temperature varies with.. perhaps +/- 5 degrees in that period.

I do 10 minute exposures, with 30sec waiting time between each exposure.

I think I just need absolutely insane amounts of data to make anything useful with the Nikon D3100. The total exposure is 9h 40 minutes at this time when combining my 3/4 full moon data with the data from two days ago.

Orion comes up over the horizon earlier and earlier as we progress into winter. By the time I get my new camera, it will rise early enough for me to be able to let the camera continuously collect data for perhaps 9 hours at a time, given that the skies stay clear for the entire evening.

Interesting times are ahead.

[lensman57]

Oh, I re-processed the data without bias files, and I avoided over-stretching it. This is the result. I will run another test now with no calibration files whatsoever...

Alveprinsen

Much better, well done.

Regards,

A.G

[Twisted Lip]

Wow, I cannot believe the difference, its practically a different image. looks great!