Pitch Black Skies

19 minutes ago, Fegato said:

The Light frame you posted is a different one to yours above?

Yes, the screenshot is from the LP test last night, just a blank patch of sky. I didn't save the subs, I just screenshot them for the ADU readings.

The fit file is M101 from a session a few weeks back.

I haven't ever adjusted the offset as I don't understand it.

I just want to add a screen shot of a bias and a 300sec sub of LP from my ASIair Pro too, to make sure I am reading it correctly.

On 19/04/2022 at 09:21, vlaiv said:

Just be careful that you need to properly calibrate your sub. Use one of the channels for measurement - green is probably the best as it carries the most of luminance information (humans are most sensitive to noise in luminance data).

I don't understand. Do I need to do some calibration as part of the experiment?

@vlaiv

Bias_1.0ms_Bin1_533MC_gain100_20220420-140701_-10.8C_0002.fit

Light_M101_300.0s_Bin1_533MC_gain100_20220402-231650_-10.0C_0002.fit

My results:

Mean ADUs

Bias 2797

30s 2822

60s 2847

120s 2896

180s 2948

300s 3047

The closest I can get to 56.25e was with the 300s sub.

√3047 = 55.19e

I didn't feel confident about exposing longer than 300s but I need to do that to reach 56.25e. Although is 300s+ not a bit excessive for an optimal exposure time with this camera?

1200 ADU above the bias mean ADU doesn't seem practical from the test results. For 300s I was only 250 ADU above it..

I think I've read that swamping the read noise X5 is a safe exposure length guideline.

How do I know I am swamping it X5?

Is it a case of measuring the ADU from a bias frame and then taking an exposure until it is 5x that ADU?

My camera is 533MC Pro. I use unity gain 100 under Bortle 4.

21 hours ago, 900SL said:

unity gain in Bortle 4 at f5 you may be overexposing at 300s exposures, if only a UV IR filter

But wouldn't the histogram be over on the RHS then?

I will try the bias method, sounds very straight forward.

15 minutes ago, 900SL said:

Are you using any filters?

UV/IR filter

M106 and neighbours

Just over 3 hours worth of guided data with a Skywatcher 130P-DS and a ZWO 533 MC-Pro.

Pre-processed with DSS and post-processed with Siril.

Just to give an update..

The mount is actually a bit quieter. It's not a huge difference but it does sound smoother.

Guiding numbers seem to have improved slightly too.

1 hour ago, david_taurus83 said:

Is that a new HEQ5? As already pointed out, may be quite than an older one to start with. My AZEQ6 sounds different to the one I had 3 years ago. I just figured they put different motors in the newer ones.

Yeah it's only couple of months old. Not sure what I was expecting really. It's my motors that are noisy. The belt mod can't help that.

28 minutes ago, alacant said:

Nice.

The main issue I have with Siril -and I admit to not having looked into this- is the detai. Almost certainly my lack of patience though!

  

It looks a lot cleaner when I put it through Topaz, however I only have the trial version. Another goodie for the wish list.

39 minutes ago, ONIKKINEN said:

The histogram does this weird dance that looks like a seismograph when you move the sliders, its normal. If you see posterization after moving the slider that still remains, you have stretched the image too far, or are processing a 16-bit file (save as 32bit always). I wouldn't bother with upping the gain, as you see there are diminishing returns from doing so. With your 5min subs i dont see how there could be any noticeable positives from doing so, but star cores would start to saturate earlier and so you would have fatter stars (the brightest ones).

This button stretches the image with the autostretch function, the same as the lower tool bar thing that only visualizes the data for you. But like the autostretch preview, it is very aggressive so i recommend you move the midpoint slider a bit back towards the middle after pressing the button. You will probably need to zoom in on the histogram to see where the slider even is after the autostretch by the way.

Ah I see, I was trying to move the midpoint before I had even pressed the auto-stretch button 

I see why the 32bit is so important now.

My thinking about the gain is if I increased to 200 I would have lower read noise and shorter exposure times leading to tighter stars possibly?

19 minutes ago, ONIKKINEN said:

This is normal, actually expected from skies as dark as yours and that camera.

Your camera has a huge dynamic range which makes saturating signal very difficult. The result is that all of the faint signal is usually in the black parts of the shot. I have had images that contain on average just 25 photons per pixel per sub and there is no issue.

But like you said stretching is no issue so there is no problem here with the histogram.

By the way the siril autostretch function is quite aggressive, especially for low noise images like yours so when actually applying the stretch to the histogram i recommend walking the midpoint slider a bit back from what the autostretch function wants.

It's just that when moving the midpoint slider, the histogram is moving very erratically. Do you think it would be better in future if I increased the gain to say 200 instead of unity 100?

First attempt with Siril

I've noticed that my histogram is way over to the left. Does that mean I'm clipping my frames? The image is 24 hrs of 300s @ unity gain under Bortle 4. I'm using 130P-DS and 533MC-PRO.

There is a ton of detail in the auto- stretched image.

I have a primary baffle fitted to my 130P-DS and I'm wondering if it would actually be better to remove it.

The baffle is designed to cover the 3 primary mirror clips and it does an excellent job at that.

However, there is another method to remove the interference from the primary mirror clips and that is to fix the primary mirror to the backplate with silicone adhesive, and ditch the clips completely (credit to Alacant for this idea).

This method has the added benefit of also preventing lateral movement from the mirror cell.

The main reason I am wondering about whether to remove the baffle is because it is increasing the telescope's focal ratio, consequently slowing the telescope down.

With the baffle fitted, I have calculated the focal ratio to be 5.45.

Focal length ÷ aperture = focal ratio

649mm ÷ 119mm = 5.45

Without the baffle, I have calculated the focal ratio to be 4.99.

Focal length ÷ aperture = focal ratio

649mm ÷ 130mm = 4.99

This means that without the baffle, the telescope is 84% faster for the same SNR?

Focal ratio^ ÷ focal ratio^ 

5.45 × 5.45 = 29.7      4.99 × 4.99 = 24.9

24.9 ÷ 29.7 = .84

For 10hrs of data with the f5.45

I would only need 8.4hrs with the f4.99

Apologies in advance if this has baffled anyone

15 minutes ago, powerlord said:

startnet2++

How can I download this? I'm on Windows. Had a search for it last night but no joy.

5 hours ago, Bibabutzemann said:

I have no idea how startools works but those big black halos around the stars make the image look unnatural. In PS/Darktable this happens when i sharpen too much or when the sharpen radius is too big.

Also i would really avoid clipping the background. You will loose so much of the precious data you collected. All the small galaxies in the background get lost. This also adds to an unnatural look. 

Third thing that stands out to me, that there are barely any colours left. But i guess this is preference.

Again, i dont know Star Tools and which steps causes these issues.

I only tried Star Tools in a trial period and realized i got faster the results i wanted with other software.

Just for fun i would try processing with Siril+ Darktable, which are both free and easy to use. 

 

 

Thanks for the feedback, I'll have another attempt.

22 minutes ago, The Lazy Astronomer said:

Startools can output as tiff, jpeg and png.

Okay I've just figured out how to do it.

It doesn't show a drop-down menu in the file type for me when saving. It just says 'All files' and I have a manually type either .jpeg, .PNG, etc after the file name to get it to save it in that format.

Pity about the patent, however you're obviously very mechanically and inventively minded so maybe you can come up with another clever concept some time?

Thanks for sharing your interesting story.

@Dave S @The Lazy Astronomer

I use Startools. It seems to only output as .tiff.

What about loading it into GIMP and exporting from there?

I suspect the tiff viewer app on my phone is the culprit.

After I process my images on the laptop, I usually transfer the .tiff to my phone via bluetooth. When I open the picture with tiff viewer app the image looks poor.

I'll then open the .tiff with Adobe Lightroom and export it as .jpg for uploading to this forum.

The end result always looks degraded. Is there a better way to go about this?

7 minutes ago, malc-c said:

I started all this belt modding of the HEQ5 over a decade ago, and the first thing I found was that the sound had changed.  No matter how much I adjusted the gearing to reduce the backlash between the central gear and both the worm and motor gears, or how much lithium grease I used, there would still be that graunching sound as the motors spooled up and down at the start and end of a slew.  As soon as the belt was fitted the sound changed and all I could hear was the spooling of the motors.

Here is a video I made in 2012 demonstrating the testing and experiments using off the shelf parts.  This was before Dave form Rowan engineering developed the kit idea and used CNC components that suited the stock gear ratios so the handset could be used

The mount isn't a great deal quieter, but it sounds a lot sweeter just hearing the steppers spooling rather than the gears meshing / graunching!

That's really cool, didn't realise you were behind it, excellent work!

It's probably because my mount is practically new. Had I of waited another few months, the graunching sound would more than likely have crept in.

Like you said anyway, it's the numbers that matter.

I'll be able to test it tonight and give an update.

7 minutes ago, AstroAdam said:

Sounds like you tuned out some of the row previously anyway then.  Also, mine was an older HEQ5, even when I got it, so was probably louder due to wear by the time I modded it...

What kind of numbers are you achieving on guiding now?