M1 The Crab Nebula (180 sec f/7 unguided)

A place to share images that you have taken with SharpCap.
Forum rules
Please upload large images to photo sharing sites (flickr, etc) rather than trying to upload them as forum attachments.

Please share the equipment used and if possible camera settings to help others.
Post Reply
User avatar
Menno555
Posts: 307
Joined: Mon Apr 20, 2020 2:19 pm
Location: The Netherlands
Contact:

M1 The Crab Nebula (180 sec f/7 unguided)

Post by Menno555 »

M1 The Crab Nebula

Getting to know the scope and mount better and better: I'm now able to do unguided, 180 second exposures with the small FOV of the Zwo ASI385MC uncooled planetary camera :) The ASI294MC Pro is sadly still not back.
Also getting to know SiriL better and better. The Photometric Color Calibration especially is cool and useful: besides the color calibration, it provides also info like the actual focal length (used the reducer) of 1471 mm (makes it theoretical f/7), resolution of 0.526 arcsec/px and a FOV of 16' 57.90" x 09' 36.25".
It is visible that the ASI385MC is not really made for DSO: I know it is well focused but because of the "fatter" stars, it looks out of focus for me. But all in all I am very happy with the result.

The Crab Nebula is one of the bigger objects I really wanted to capture and really I love it. Will be back at it once the cooled camera is back so I can capture it in more detail.

The Netherlands, Bortle 7/8
Meade LX200 8" f/10 ACF OTA
Ioptron CEM25EC mount (no guiding)
Optolong L-Pro filter
Optec Lepus Standard 0.62x reducer
Zwo ASI385MC planetary camera

Captured with SharpCap Pro
40 x 180 sec / Gain 100 / Offset 15 / White balance R50/B50

Stacked in DeepSkyStacker
40 lights / 20 darks / 100 flats / 100 darkflats

Processed in SiriL 0.99.6 (1.0.0 beta2) and Photoshop
SiriL: background extraction, photometric color calibration
Photoshop: levels, curves, RGB alignment, reduce noise, contrast enhancement.

Image
timh
Posts: 114
Joined: Mon Aug 26, 2019 5:50 pm

Re: M1 The Crab Nebula (180 sec f/7 unguided)

Post by timh »

Hi Menno,

Also one of my favourite objects and perfect for long focus. The elements represented by the different colours (always a somewhat subjective representation - despite using photometric colour correction never quite the same on different occasions) are fascinating and interesting to compare with the Veil. Nice image at 3 min unguided is amazing. Do you use the hand controller PEC correction function to correct for the RA periodic error ? I have also just bought an Ioptron mount (CEM 70) and noticed that it is an option for unguided use (although on its first few nights out it has been guiding using PHD2 at 0.7 to 1.1 arcsec which is seeing limited for me).

best wishes
Tim
User avatar
Menno555
Posts: 307
Joined: Mon Apr 20, 2020 2:19 pm
Location: The Netherlands
Contact:

Re: M1 The Crab Nebula (180 sec f/7 unguided)

Post by Menno555 »

Hi Tim

Yes, the colors were a challenge. I did do an image search and colors are all over the place :) But I got these colors maybe cause of the broad narrowband Optolong L-Pro filter. I took some fiddling in Photoshop though to get them all showing.

About the mount: I have the CEM25EC and that has Real Time PEC, so I don't have to do that manually, there is even no option to do that manually. Before this one, I had the CEM25P and that has manual PEC and tried that ... and it did work a bit but not really that good IMHO.
What I have to do manually with the CEM25EC though is the tracking rate and I also did this with the CEM25P: I use the User Defined Sidereal Rate and tweak that. When capturing, I have 1 star zoomed in at 500% in the SharpCap bullseye overlay and when I see it moving, I adjust that. It depend on how high or low you are: over here for zenith it's around 0.9994 and for around 70 degrees it's around 0.9986.
And just with like the CEM25P, I alter polar alignment on the fly if needed: when I see the star moving in DEC, I adjust the Azimuth Adjustment Knob until that movement is gone and then adjust the User Defined Sidereal Rate until there is (almost) no star movement.
But most of the CEM25EC power comes from the optical encoders: Ioptron claims <0.3 arc second RMS and that claim really delivers :)

Menno
VPR
Posts: 16
Joined: Sat May 09, 2020 3:40 pm

Re: M1 The Crab Nebula (180 sec f/7 unguided)

Post by VPR »

Hi Menno,

Very nice image for unguided subs. I also like the way you have gone about getting to this point – with the adjustment process detailed. It is ‘food for thought’ :idea: . Thanks for sharing and keep up the good work.

Best regards,
V.P
umasscrew39
Posts: 377
Joined: Fri Apr 28, 2017 1:28 pm
Location: Central Florida
Contact:

Re: M1 The Crab Nebula (180 sec f/7 unguided)

Post by umasscrew39 »

Excellent, Menno! The Crab is always a crowd pleaser.

Bruce
timh
Posts: 114
Joined: Mon Aug 26, 2019 5:50 pm

Re: M1 The Crab Nebula (180 sec f/7 unguided)

Post by timh »

Thanks Menno,

Yes you explained that before about your manual guiding technique I remember. I also get now that the Ioptron 'EC' mounts are a bit different (mine isn't an EC) and allow the encoders to correct for RA tracking error to high accuracy. The way you describe sitting on a star and keeping it still - I wouldn't be at all surprised if your manual guiding isn't actually better than what is normally achieved with PHD2 - it seems more like a manual version of OAG? Anyway your pictures are testament to how well it works --well done.

Tim
User avatar
Menno555
Posts: 307
Joined: Mon Apr 20, 2020 2:19 pm
Location: The Netherlands
Contact:

Re: M1 The Crab Nebula (180 sec f/7 unguided)

Post by Menno555 »

Thanks V.P and Bruce!

And Tim, I think you just hit the nail on it's head: I am indeed a human OAG! :lol:
It's a good description of what I do but instead of moving the mount, I alter the tracking rate. With only a big difference: once I am dialed into the right settings, almost no check is needed anymore because of the accuracy of the tracking. That dialing in is getting good captures after around 5 to 10 minutes and then up to 20 minutes of fine tuning while capturing. If it is better then PHD2, I don't know: never used that.
One major disadvantage though: no automatic dithering, so I also do that manually. I tried to use the Sequencer of the Beta for that but so far no succes.

Menno
Post Reply