Jupiter 04-03-15 - Collimation really does help!

[PhotoGav]

The seeing was very wobbly tonight, but I spent ages out there in the cold fiddling with the Edge trying to collimate it properly. Having completely messed up the process by trying to use a camera to do it, I resorted to an eyepiece and managed to get it pretty much spot on in about ten minutes. I obviously had to give a bit of imaging a go with the new improved scope... Here's the result:

The processing is a bit quick and dodgy, but the headline is that the detail is very much improved. I now can't wait for a really good still night..... But I know that I will have to for ages, probably!

[MattJenko]

That is a magnificent result.

Was that with a barlow as well with the EdgeHD 8/ASI120 ?

[michael.h.f.wilkinson]

That is very nice. Collimation is very important in an SCT, but fortunately they generally hold collimation very well.

[PhotoGav]

Thanks Matt & Michael. Yes, it was with a 2x Powermate in there. As for collimation, I hadn't checked it for nearly a year... Lesson learned!

[DrRobin]

Collimation is about the most important thing with an SCT at high magnification. My C11 Edge was pretty close, but a tune up session a couple of weeks ago changed it from a very large jam jar to a correctly working telescope. The difference is resolution in mine was, I am guessing, the same as yours, quite a revelation.

It isn't easy to nail collimation, but providing you don't move the scope too much and is not subject to too much thermal shock it should keep it for a reasonable time.

As you say, just need some decent conditions now.

Robin

[PhotoGav]

Exactly Robin, a massive improvement in clarity. My problem is that I do have to move the scope outside for each session and then back into the warm at the end, so regular movement and thermal shock... Anyway, an eyepiece and diagonal are now in my imaging box and I will be more pro-active with them in future!

[DrRobin]

Exactly Robin, a massive improvement in clarity. My problem is that I do have to move the scope outside for each session and then back into the warm at the end, so regular movement and thermal shock... Anyway, an eyepiece and diagonal are now in my imaging box and I will be more pro-active with them in future!

Sadly that is the case for many Gav.  It won't drift that much, so next session have a look visually or with your camera and if you are getting good detail leave the collimation 'as is' since the seeing is so variable.  If the image is miles off pop your eyepiece in and make small adjustments to see if it comes better.  If it doesn't then it is more likely down to the seeing rather than a collimation error.

At least now you know what to look for and have the confidence to move the collimation to get it spot on.  Great images will follow.

Robin

PS I don't have any proof but I think that the extra corrector lens in the Edge makes them harder to get precise collimation.  I am sure there is more alignment required of the front corrector, position of the secondary and secondary collimation adjustment.

[PeterCPC]

Great shot Gav. I would be very interested to know what settings you used for the ASI as I have a similar set up.

Peter

[Leveye]

Beautiful,inspiring work. Thanks for sharing!

[PhotoGav]

Thank you Peter & Leveye.

Peter, here are the complete capture details:

FireCapture v2.4 beta Settings
------------------------------------
Camera=ZWO ASI120MC-S
Filter=UV
Profile=Jupiter
Diameter=44.19"
Magnitude=-2.49
CMI=268.3° CMII=83.3° CMIII=1.5°  (during mid of capture)
FocalLength=11000mm
Resolution=0.07"
Filename=Jup_231926.ser
Date=2015_03_04
Start=231926.130
Mid=232011.142
End=232056.155
Start(UT)=231926.130
Mid(UT)=232011.142
End(UT)=232056.155
Duration=90.025s
Date_format=yyyy_MM_dd
Time_format=HHmmss
LT=UT
Frames captured=3298
File type=SER
Binning=no
ROI=640x480
FPS (avg.)=36
Shutter=27.29ms
Gain=40
SoftwareGain=10 (off)
USBTraffic=100
Gamma=50
Brightness=0
WRed=59
Overclock=0
WBlue=83
AutoExposure=off
Histogramm(min)=2
Histogramm(max)=1980
Histogramm=48%
Noise(avg.deviation)=n/a
Limit=90 Seconds
Sensor temperature=6.5 °C
 

I went a bit low on the histogram and would aim for at least 60% I think next time. Previously I have aimed for 70%, but thought I would experiment a bit.

Processing wise, I ran the .ser file through PiPP, then the .avi went into AS!2 and I stacked 35% of 2473 frames. The resuting .tif was attacked with Wavelets in Registax6, and then tweaked quickly and badly in PhotoShop.

Hope that helps and I look forward to seeing your images of the bad boy of our Solar System very soon!

[PeterCPC]

Thanks Gav - very comprehensive. What capture software did you use?

I've been playing with Firecapture and Sharpcap and seem to get a higher frame rate with Sharpcap.

One question if I may - why capture in SER rather than AVI?

I have never tried a UV filter - I usually use a IR blocking filter. I also usually keep the gain much lower so I think some experimenting is called for.

Peter

[swag72]

Nicely done Gav

[PhotoGav]

Peter - I use Firecapture. I find it brilliant as it offers easy control over all the variables. I capture a raw 16 bit file, which has to be a .ser rather than .avi - the theory being that the 16 bit gives a higher quality capture. As for the UV Filter, that is just what the settings say - I haven't put any extra filters in front of the camera, just it's own standard filter in the camera. Yes, in theory I think the lower the gain the less noise, but it is a trade off between frame rate and gain to get the best result. I await your findings on that subject and the chance to carry on experimenting myself.

Thank you Sara - at least it's something to do on those moon-drenched clear nights!

[PeterCPC]

Gav, thanks again.

I might give Firecapture another go but, when I was last out, it was only giving about 16fps but when I used Sharpcap it went up to 60fps. I don't know why that is. When I used Firecapture I tried using a Debayered capture using GB and smoothhue - I tried nearest neighbour but the colour did not seem quite right. When I tried another and turned off Debayer the Debayer tool would not accept the vid saying that it was not Y800.

Peter

[Pete Presland]

Cracking image always worth doing a quick star test prior to an imaging run, especially when you can be imaging for several hours and the test only takes a few minutes. Trouble is i am always so eager to see what the seeing conditions are going to be like.

[Stargazer33]

Some nice detail in the belts in that image Gav. Well done!

[Blazar]

Excellent Gav....I was out as well, and either my seeing was a lot worse, focus was off, or I need to check collimation...something I have never done. SO if you could point me to a good tutorial (or just send me some pics of what you did then it might help me as well.....any advice much appreciated...

this is what I ended up with (which was ok, but was hoping for better)...:

[PhotoGav]

Steve, that's looking good. Are you using a barlow of any sort?

As for collimation... Slightly a dark art, but one definitely worth learning! You need to centre on a bright star, then de focus slightly - I found that twisting the focus one way was better than the other, but I cant remember which way... You need to have a fairly high power eyepiece in to view (in fact I use two eyepieces, a wider angle one for centring the star and a higher power one for checking collimation). You will see the central obstruction and a couple of dark rings outside of that. You are aiming to have everything perfectly centred. Here's a pic robbed from the net that shows what you are aiming for:

You move the central obstruction around by adjusting the screws on the secondary mirror. Definitely worth investing in a set of Bob's Knobs to make the adjustments easier. I keep all three screws tight and loosen one and tighten the other two to make small adjustments. It is a matter of trial and error to see what adjustment moves the central disc in which direction. It all takes a bit of time and patience, but it isn't difficult, just fiddly. Remember, make small adjustments and recentre the star after each adjustment.

Good luck!

[PhotoGav]

Here's another pic that could make the adjustments a bit less trial and error!

[Space Cowboy]

Nice capture Gav!

[teleskopjo]

But how would you know that it's perfectly centred.. just eyeballing it?

Steve, that's looking good. Are you using a barlow of any sort?

As for collimation... Slightly a dark art, but one definitely worth learning! You need to centre on a bright star, then de focus slightly - I found that twisting the focus one way was better than the other, but I cant remember which way... You need to have a fairly high power eyepiece in to view (in fact I use two eyepieces, a wider angle one for centring the star and a higher power one for checking collimation). You will see the central obstruction and a couple of dark rings outside of that. You are aiming to have everything perfectly centred. Here's a pic robbed from the net that shows what you are aiming for:

image.jpg

You move the central obstruction around by adjusting the screws on the secondary mirror. Definitely worth investing in a set of Bob's Knobs to make the adjustments easier. I keep all three screws tight and loosen one and tighten the other two to make small adjustments. It is a matter of trial and error to see what adjustment moves the central disc in which direction. It all takes a bit of time and patience, but it isn't difficult, just fiddly. Remember, make small adjustments and recentre the star after each adjustment.

Good luck!

[Grotemobile]

This might help..Worked on mine, using a star.

Steve

[opticalpath]

I don't use Firecapture but I read somewhere that it has an option to display a reticule that would assist with centring.

Other tools are available that provide a reticule overlay such as  Al's Reticle  and Mire de Collimation. 

Adrian

[mikeskor]

An excellent result and I like how you have captured color on a moon.

[PhotoGav]

But how would you know that it's perfectly centred.. just eyeballing it?

Indeed, I tried to use a camera and reticles and stuff, but failed miserably. I found it much easier, and perfectly effective, just to use the Mk1 Eyeball!