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Old 20-07-2019, 03:14 PM
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Slawomir (Suavi)
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Radioactive Trifid

Hi all,

I was able to take advantage of a run of cooler and drier nights and continued with my experiment with the Trifid.

I tried something new, at least to me, and aimed at putting together a pure narrowband SII-HA-NII Trifid. As expected, NII and HA turned out to be quite similar, if not identical, while SII is relatively weak, so getting any colour in the image was like squeezing water out of a rock.

Luminance is a composition of Ha+SII+NII. Total 40 hours of exposure.

Astrobin image in here, and, if you are truly brave, please check the high resolution version here.

If we get a good night or two in the near future, I may try a more traditional HA+SII+NII_RGB hybrid, or may chuck OIII into the mix as well

Thank you for looking
Suavi

EDIT: Version 2: https://www.astrobin.com/full/416173/B/?nc=user
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Last edited by Slawomir; 20-07-2019 at 05:29 PM.
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Old 20-07-2019, 03:20 PM
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ChrisV (Chris)
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Beautiful plumage. That 30 hours really brings out the structure. A nice companion to your recent lagoon
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Old 20-07-2019, 03:40 PM
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Quote:
Originally Posted by Slawomir View Post
I tried something new, at least to me, and aimed at putting together a pure narrowband SII-HA-NII Trifid. As expected, NII and HA turned out to be quite similar, if not identical, while SII is relatively weak, so getting any colour in the image was like squeezing water out of a rock.

Looks good Suavi. If that colour is squeezing water from a rock you obviously squeezed hard!


Kevin
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Old 20-07-2019, 04:06 PM
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Andy01 (Andy)
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Phwoar, that's bold - even for my exotic tastes!
Ghostly goodness though - might be even better once you get some RGB stars in there to compliment the NB hues.
well done
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Old 20-07-2019, 05:28 PM
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Slawomir (Suavi)
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Quote:
Originally Posted by ChrisV View Post
Beautiful plumage. That 30 hours really brings out the structure. A nice companion to your recent lagoon
Thank you Chris. I nearly gave up on putting the colour image together.

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Originally Posted by kosborn View Post
Looks good Suavi. If that colour is squeezing water from a rock you obviously squeezed hard!


Kevin
Yes, she is very colourful for sure

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Originally Posted by Andy01 View Post
Phwoar, that's bold - even for my exotic tastes!
Ghostly goodness though - might be even better once you get some RGB stars in there to compliment the NB hues.
well done
Thank you Andy. A tough object to do nicely in narrowband, now after going through a bit of processing struggle myself, I appreciate your narrowband masterpiece even more



A new tweaked version: https://www.astrobin.com/full/416173/B/?nc=user

Thank you for looking
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Old 20-07-2019, 08:39 PM
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Pretty wild looking image and you got some interesting structure in the outer parts of the nebula.

Your polar alignment seems to be off though causing some egginess to your stars which is costing you some image sharpness as well. I noticed this on some of your other images.

I find TPoint a great way to get a perfect polar alignment in around an hour or less time and well worth the time investment. I use accurate polar alignment routine in the Sky X and TPoint.

Greg.
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Old 21-07-2019, 06:27 AM
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Slawomir (Suavi)
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Thank you Greg for your advice. My observations lead me to believe it is my FTF flexing though.

If anyone likes challenges, I recommend having a go at Trifid in HA+SII+NII
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Old 21-07-2019, 06:49 AM
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codemonkey (Lee)
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Great work, Suavi! Technically excellent (as usual), though I have to admit I'm not totally sold on the palette; my wife loves the colour though and she's a tough sell... I rarely get anything more than an eye roll out of her.
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Old 21-07-2019, 06:55 AM
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Quote:
Originally Posted by Slawomir View Post
Thank you Greg for your advice. My observations lead me to believe it is my FTF flexing though.

If anyone likes challenges, I recommend having a go at Trifid in HA+SII+NII
Try running your focuser upside down. They flex more when in normal orientation than when upside down. Yuri from TEC tested that on TEC180 focusers.

Greg.
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Old 21-07-2019, 07:35 AM
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Great work, Suavi! Technically excellent (as usual), though I have to admit I'm not totally sold on the palette; my wife loves the colour though and she's a tough sell... I rarely get anything more than an eye roll out of her.
Thank you Lee. I was disappointed with my inability to create a more interesting tri-colour image out of this data. Collecting traditional OIII instead of NII would have opened more palette possibilities. Happy your wife likes the colours though


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Originally Posted by gregbradley View Post
Try running your focuser upside down. They flex more when in normal orientation than when upside down. Yuri from TEC tested that on TEC180 focusers.

Greg.
Thank you Greg - didn't know that. There is also a bit of side-to-side flex, which I tried minimising with tightening bolts (one is hidden and to access it the drawtube needs to be taken out), but I found out very soon that too much tightening makes autofocusing with HSM unreliable. After taking recent images and being unable to rectify this, I'm pretty much set on replacing the focuser at some point, but for now I have accepted this limitation and just trying to enjoy imaging. In the past I didn't see this flex because I used to have a narrow window on the sky and used to get max 2-3 hours per night with the same telescope orientation. Now, when following the same target for from east to west, flex became apparent, and by elimination (PA, guiding etc) I now believe that elongated stars are becasue of the focuser. It was difficult to pinpoint the issue, particularly given the reputation that FTFs have.

Last edited by Slawomir; 21-07-2019 at 07:46 AM.
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Old 21-07-2019, 09:08 AM
Placidus (Mike and Trish)
Narrowing the band

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To fix flexure in the focuser, we attached a very rigid bar, 25x25 mm square hollow, and half a metre long, and bolted very securely to the dovetail, to run from the dovetail backward to a point level with the camera, and about 250 mm out from the side of the camera body. That acts as a rigid reference point. We then ran a stainless steel strut (250 mm long, obviously), hinged at both ends, to run between the camera body and this rigid anchor point. Since we only ever need to move the focuser a couple millimeters at the very most, this system provides great lateral stability to the focuser (in the direction it most naturally wants to fall) without putting any appreciable strain on it.

In principle, one would need two such struts, one to take flop in one direction, and another to take flop at 90 degrees, but in practice only one direction was important.

The hinge pins on the strut, and the attachments and all the other components have to be extremely rigid, or it won't work. There is an adjustment screw to set the length of the strut very precisely, so there is no strain on the focuser in the neutral position.

Also, the strut needs to be very long compared with the amount of focuser travel, or moving the focuser in and out a long way will put strain on the focuser. The lateral stress on the focuser is given approximately by square(h)/2R where h is the focuser movement and R is the length of the strut, so for us, a 2 mm focuser movement and a 250 mm strut, the lateral stress on the focuser is only 8 microns. (It gets very rapidly worse after that.)

The strut not only helps prevent elongation of the star during an exposure; it also helps prevent change in focal length by preventing the tilt and flop.

Hope that helps a tiny bit.

Mike
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Old 21-07-2019, 10:39 AM
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I am surprised a high end Feather Touch focuser is flexing. I ran quite a heavy load on mine with none. Proline 16803, filter wheel, MMOAG, guide camera, cables. All perfect.

The focuser probably has adjustment screws on the underside that may need tightening. There must be threads about how to do that.

How do you know its the focuser?

I might add that I used to get similar looking stars with a Starlight Express 694 camera. After chasing the guiding to no avail it came to light later it was the camera firmware that was making a bump on one end of the stars. A firmware fix from Starlight fixed it. Perhaps these Sony sensors are prone to that?

Greg.
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Old 21-07-2019, 01:30 PM
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Slawomir (Suavi)
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Thank you Mike and Trish for sharing your solution - it sounds interesting and surely is a good and cheaper alternative to changing the focuser.

Greg - I'm generally happy with the focuser's performance, but as I recently looked into it more carefully, I noticed that while everything is threaded in, star shapes slightly vary depending on the telescope's orientation, that's why I suspect it is the focuser.

And then I look at images taken by professionals, and I really stop worrying about slight imperfections and just enjoy imaging
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Old 21-07-2019, 03:14 PM
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Anth10 (Anthony M)
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Suavi,
You’ve hit the nail on the head, ultimately enjoying the craft should always be at the forefront. I run a very rough and ready setup which certainly cannot be compared to the rigs in this forum however I can agree with the comments you make regarding camera tilt due to focuser issues. I have found this to be the case as imaging continues past the meridian and although I don’t run autoguiding my polar alignment is more than acceptable and holds its own in the east and drifts more as the scope moves west. There is a tendency for the rack and pinion I’m using to loose it’s grip during a session as the scope rolls with the ecliptic. As long as you can try and remedy the imperfections and taken on advice given that’s all you can do.
The knowledge shared within this forum is most enlightening.
Keep up your good work!
Anth
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Old 21-07-2019, 07:28 PM
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Atmos (Colin)
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I can't say I'm exactly sold on the colour palette either but the details and depth are excellent!
It looks even better on my new 27" monitor than it ever would have on my 15" laptop screen
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