IC1795 Fish Head Nebula Ha / Oiii / Sii first time dithering

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nexusjeep
Posts: 206
Joined: Thu Oct 18, 2018 3:01 pm
Location: Gloucestershire

IC1795 Fish Head Nebula Ha / Oiii / Sii first time dithering

Post by nexusjeep » Sat Sep 28, 2019 4:32 pm

Rather unexpectedly the weather cleared last night so rather than going to bed went out to the observatory to have a play with the new option for dithering as I gave never dithered before with SharpCap due to the loss of long exposures every 4 to 5 frames. The wind was a little higher than normal so tracking was a little worse than usual as it got up to 0.76 total error at the one point were normally it sits down between 0.3 to 0.4 arc seconds.

The target was the Fish Head which to me is the safer name as it looks way dodgier than that.

Equipment
Avalon M-UNO mount + EQDirect cable
APM LZOS 780/130 refractor + Riccardi 1.0x Flattener
Altair 60mm Guidescope + GPCAM290MM Guide Camera
Imaging Camera ASI1600MM-Pro at -20c
Filters 6nm Astronomik Ha / Oiii / Sii
Software Sharpcap Pro/ PHD2 / Stellarium / EQMOD / Astro Pixel Processor + Photoshop CC

Exposures Ha 18 x 180s / Oiii 17 x 180s / Sii 18 x 180s gain set to 200 offset at 50 dithered every five frames.

Bortle 4.5 - 5.0

Image_19_09_27 - IC1795 Fish Head Nebula Ha_x18_Oiii_x17_Sii_x18_180s_200g_Dithered by Nick Davis, on Flickr

Thanks for looking.

Cheers
Nick

umasscrew39
Posts: 316
Joined: Fri Apr 28, 2017 1:28 pm
Location: Central Florida
Contact:

Re: IC1795 Fish Head Nebula Ha / Oiii / Sii first time dithering

Post by umasscrew39 » Sat Sep 28, 2019 6:58 pm

Very nice, Nick. Congrats! I have yet to try dithering as the idea of losing some long exposures is too nauseating . Did you feel it made a big difference or was it hard to tell as you didn't do a direct comparison last night?

Bruce

nexusjeep
Posts: 206
Joined: Thu Oct 18, 2018 3:01 pm
Location: Gloucestershire

Re: IC1795 Fish Head Nebula Ha / Oiii / Sii first time dithering

Post by nexusjeep » Sat Sep 28, 2019 8:42 pm

Hi Bruce,
I think the image did look better with the dithering as the hot pixels and any pattern noise is broken up I have not used it in the past due to the loss of imaging time but since the last update were Robin makes the camera switch to 1s exposures and discard them while the dither is occurring and then automatically set the exposure back to the correct length after PHD reports the dither has been completed I thought I would give it a try.

It worked perfectly especially as this was my first time trying it I lost on average 12s to 15s whilst the dither sometime as as low a 10s depending how far it decided to move and then the exposure went to 180s as I had it set to that and then carried on as normal for another 5 frames then dithered again. The other plus side is with dithered frames to stack I can now also use Drizzle when I am running the integration and there was a definite improvement in the final integrated frame for Ha, Oiii and Sii with this added as well.

Cheers
Nick

BlackWikkett
Posts: 372
Joined: Sat Jun 23, 2018 8:48 pm
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Re: IC1795 Fish Head Nebula Ha / Oiii / Sii first time dithering

Post by BlackWikkett » Sun Sep 29, 2019 4:32 am

Well done Nick really captured a lot of detail. I've been using dither with SC since Robin introduced it server versions ago. I've just lived with loosing a light frame which wasn't really that bad since I'm usually doing 30 sec or 1 min exposure. Now that the dithering lose is only a few seconds during the settle it's great. Keep up the great images!

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