Bibabutzemann

My latest Andromeda, had to throw away 1.5hours of integration due to windy conditions. My smol EQ3 doesnt like that at all

Now its only 2.6 hours, but im still happy with it.

Equipment: 130PDS + EQ3 Pro + EOS 1200D (full spectrum mod + L2 Filter)

Integration time: 63x150s @ISO 800

12 hours ago, Stuf1978 said:

Finally got round to giving the 130PDS a run out and have decided reflectors are a bit of a faff aren't they. I was intending to shoot the Wizard Nebula and thought I'd just set up as as normal and away I would go without issue, the scope had other ideas. I initially set up with an L-eXtreme filter but as I had no way of knowing where the focus point was I couldn't even find a star never mind focus. So I changed the filter for a UV/IR cut and changed tactics 😂

1. Balancing - this is a bit of a nightmare, I couldn't seem to get it nailed in declination. I thought I had it close at one point but the when slewing the mount (HEQ5 Pro) I'd hear the familiar sound of the gears grinding so the balance was obviously way off. I think I need to add more weight to the rear and get this sorted during the day before giving it another go. 

2. Star Shapes - These weren't great. I'm not sure if it's spacing or tilt.  I managed to grab 6x3 minute subs on M33 (ignore the lack of flats) to see what my stars looked like after I collimated the scope after it was delivered.  I suspect it's tilt (please correct me if I'm wrong) as the stars at the bottom of the frame were worse than at the top. I've included the image below with crops of each corner to show this. Would this compression ring help out in this case?:

https://www.firstlightoptics.com/adapters/astro-essentials-2-inch-compression-ring-adapter-for-sky-watcher-newtonians-and-72ed-refractor-m54.html

3. Diffraction/reflection pattern - This seems to be biased toward one side of the star (see centre crop). What's the cause of this? Although this doesn't look completely horrendous it will bother me so I would like to get it sorted if possible. I'm using the Baader CC for what it's worth. 

If I can get these issues sorted then I think it will be a great little scope as it seems to be a bit of a light bucket, so any help in getting these fixed would be appreciated.

Oh and I did manage to at least get an image of the moon out of the session so it wasn't completely wasted

200x0.001 second exposures stacked in Autostakkert and processed in Photoshop (ZWO ASI294C Pro)

Cheers,

Stu

Nice images! I also struggle with elongated stars with the MPCC. 

I think you should first rule out the source of the tilting. 

Go to a star rich area with a bright star in the centre. (For example Deneb)

Make sure to tighten the screws while pressing the cam against the focuser.

Now use the bright star and a Bahtinov mask to achieve perfect focus. Take an image .

Now rotate the camera by 180° and make sure to focus again. Take an image.

Now compare those images (with same orientation, to avoid confusion)

Case A : The same stars are stretched -> The tilting happens inside your telescope (Either focuser, secondary mirror or primary mirror).

This probably means you have to "just" collimate your scope. (I say probably because it could still be tilt due to a poor attachment between focuser and CC and its just coincidence, that you get this result. To be sure, just rotate again by 180° and see if still the same stars are misshapen.)

Assuming your 2nd mirror is descently collimated, you could first try to adjust the primary mirror while still having the bright star in the centre of your image in live view. Turn the screws so that the stars wanders in the direction, where you have more elongated stars. 

Then focus again and take a picture. Repeat those steps until the elongated stars are similar on all corners (or perfect in all corners  ). 

Now you can worry about perfect spacing. Try with different spacing rings on a similar target with a bright star in the middle many stars around.

I cant stress enough how important it is, to refocus everytime you touch your focuser. Otherwise it will mess up with your findings (Speaking from experience..)

Case B : The elongated stars are now in the opposite side -> This means the tilting happens at the CC or in the camera.

This could mean its due to poor attachment. 

If you still get the elongated stars on the opposite site, no matter how carefully you attach it, the tilting is inside of your CC, inside of your camera or at the attachment between camera and CC.

First thing i would do now is to lend a DSLR from someone and see how the CC works there.

Case C : Stars are now somewhere completely else elongated -> tilting is probably caused by poor attachment. (Those two screws are not very reliable as @alacant already pointed out.)

If you still have assymmetrical elongated stars after you ruled that out, you could now test if its Case A or B

I hope this helps. 

Good luck and CS, Patrick

PS: i know in my pictures above its not perfect, but its good enough for me to dont care. 

Altough, right after if went through this procedure (Mix of Case A and C) i got the following result

On 06/10/2021 at 13:17, vlaiv said:

Maybe using Ha as luminance would solve that?

RGB can be binned x2 or x3 if it is only supplying chrominance data as we are far less sensitive to loss of detail in chrominance than in luminance.

Here is quick and dirty example of using Lum from Ha version on RGB only version in gimp:

Hi,

How did you manage to use the Ha Image as luminosity without altering star size?

Edit: oh i think i found a way myself in PS. I made the RGB image black and white and merged it in "Lighten" mode with the Ha image.

Then i used that as luminosity to get the HaRGB. Really nice and a game changer for me. Why didnt i find it sooner....

1 hour ago, Tan Zhi Qi said:

Awesome picture! What software did you use to process this image? Is it Photoshop or PixInsight? 

Thank you! I use DSS+Siril+Photoshop

DSS for stacking

Siril for Background extraction, color calibration and some stretching

Photoshop for the rest

Pleiades, 4 hours integration 

Equipment:

130PDS + EQ3 Pro + EOS 1200D (full spectrum mod + L2 Filter)

It is really challenging to process.

Normally i use Starnet++ to remove Stars, process the nebula and add stars later. This was literally impossible for me with this target

@alacant

Really beautiful pictures you got there. How do you get those stars so shiny and punchy 😮

Here is a result from last weekend: 

130PDS + EQ3 Pro + EOS 1200D (full spectrum mod + L2 Filter)

91x150s= 3h47.5min @ISO800

Thanks for all your helpful replies!

I finally really took time to sort out the source of the problem (on a bright moon night), so im prepared for the big summer targets 

There were two main steps that solved the issue:

Step 1: Better collimation:

After doing laser collimation, i continued to do some finer adjustments with star collimation and the dslr:

1a)  I used a bright star in the middle for faster focusing with the Bathinov mask. Then i made short exposures to see in which corner the stars were stretched the most

1b)  Then in liveview i collimated the primary mirror in way, so that the bright star moved towards the worst corner a little bit

I repeated 1a and 1b three times and i got fairly symmetrical coma.

Step 2: Distancing of the Coma corrector

After Step 1 i noticed the stars where stretched towards the centre of the image on all corners.

This means, i had to increase the distance between chip and corrector.

With a distancing ring, i increased by about 1.5mm

Now im finally happy with the star shape :=)

Further notes:

- I had to make sure to press the camera against the focuser when tightening the clamping screws. Otherwise i had asymmetric elongated stars on different corners. 

- I also tested possible flex problems. But i didnt notice any movement of the collimation laserpoint when i pointed my telescope in diffierent directions.

- I think filters change the required distancing between chip and corrector, since i noticed stronger coma with the cls-ccd Clip Filter. 

Now i  hope it will stay like this 😅

Unfortunately it was very rainy for the last few days here in Germany...

Today i had only 15 minutes for testing and it wasnt very accurate, so i will try properly before posting any results.

But one thing i immediatly noticed is that you have to be careful with refocusing when you change the distances.

Because when youre slightly out of focus, you also get strong distortions in the corners.

So be sure to use a Bahtinov mask and take your time.

Thank you so much for your replies!

If the graph from the link is correct, the mpcc is too close to the sensor.(if it would be too far, i would have to buy a thinner T2 Adapter)

I think i will try different distances by unscrewing the corrector a tiny bit.

If i get better results i may buy an old camera filter to fix it, thanks edarter.

Will post any results here.

CS Patrick

Hello, i just recently got my 130 PDS and a Baader MPCC3.

I use a EOS1200Da for imaging.

My problem is, that i get stretched stars on the edges. Here an example, the heart nebula (unfinished, only 2 hours exposure time)

Looks pretty bad to me.

I read a few other threads on this topic and as far as i understand, the spacing between corrector and chip should be 55mm, which is achieved by using a common T2 adapter for EOS. 

So spacing shouldnt be the cause of the problem, right? Any ideas? Collimination should be about right, i used the barlow method with a laser.

Also i get D shaped stars when out of focus, but thats because of the focuser...But i dont think it affects the focused image that much.

CS Patrick