need help for deep sky

[craigguk]

hi there i recently got a ZWO ASI120MC-S and wanted to use this for mainly planetary and deep sky objects the planetary seems to be fine i have no problems at all. the deepsky objects how ever seem to be struggling with, the stars dont seem to show up on the viewing software im using. im not entirely sure if its something im doing wrong or if its the telescope. im using the telescope that i am using is an celestron 114 lcm but do plan on upgrading with a budget of around £400 i would really appreciate your help

Edited December 23, 2020 by craigguk

[rickwayne]

Can you provide a little more detail on what you're doing? What software? How are you using it? Are you sure that your focusing is correct? If you can get planets, you ought to be able to get stars too, they're just dimmer.

You may have some trouble achieving what you want in deep-sky work with that gear, however. Your mount is designed for visual work, not for long exposures, and the 120MC-S's sensor is pretty small. Bright objects (M42, M31) will be way too large to fit in frame, and most smaller ones will likely be quite dim. The scope is also f/9, so that necessitates long exposures. If you can get it to focus, you might do better with your Nikon's larger sensor.

Not trying to discourage you, just trying to set your expectations. There is a reason the deep-sky big dogs have those really expensive mounts, and it isn't just bragging rights!

I would counsel one of two options:  Either do planetary stuff while you save up for a mount that's twice your budget, or pick up a camera tracker (e.g. SkyGuider or SkyTracker) and do your deep-sky work with a "prime" (non-zoom) telephoto lens on your DSLRs. You can pick up an old used manual-everything one, which will cut down on the expense -- autofocus and diaphragm do you no good in astro anyway!

 

[nephilim]

Unfortunately the kit you have isnt really suitable for imaging DSO's. The 120mc-s Is really just a planetary imaging camera (and quite a good one) or can be used as a guide camera, as mentioned above the sensor is very small & not really worth trying to image DSO's with.

Again as @rickwayne has said your scope & mount are also unsuitable for imaging, the scope is a bird Jones design & I'm afraid isn't rated very highly. If I was you I'd have a total rethink. Astrophotography isn't cheap & £400 will get you on your way but you would have to up your budget a little & go second hand.

firstly though I highly recommend you spend £20 on this as it'll give you a great deal of good advice on how to get started with AP & will save you a lot of money in the long run as it'll also let you know what not to buy. https://www.firstlightoptics.com/books/making-every-photon-count-steve-richards.html

Its doesn't seem all bad news though as the ZWO 120 is a very capable planetary camera ( I have the mono version but I use it as a guide scope) & as you sound like your getting good images with it for now I'd concentrate on getting better at that while you decide which way you want to with AP & reading the book I've linked will give you all the info you need on the best way to go about it.

Edited December 26, 2020 by nephilim

[michael8554]

Hi Craig.

Here's what the framing of M27 looks like with your scope and ZWO:

For larger DSO's try your DSLR.

The ZWO is probably more sensitive than a DSLR, so that's not the limiting factor.

When you were shooting Planetary you were probably using the ZWO in Video Mode, with very fast exposures.

For DSO's you use a Long Exposure mode, with exposures of several minutes rather than milliseconds.

Your mount is not really suitable for exposures that long, you will get star streaks rather than star points.

So experiment with exposures, staring at say 10 seconds, increasing until you start to see streaks, then back-off.

Use a DSO Stacking Software to stack lots of those exposures, enough to total at least 5 minutes, and see what you get 😆

If you're having trouble focusing on stars, start with the moon, then move to a bright star such as Capella.

Eventually, as others have said, you'll want to move over to a more suitable scope and mount.

Michael

Edited December 25, 2020 by michael8554

[craigguk]

thanks guys i think thats helped so much i didn't realise there was a difference in processes in planets vs dso so thats probably where i have been going wrong. the software im using is sharp cap along side with registax and dso (which i got to give deep sky objects a go). as said im getting really good results with the planets im pretty impressed with it. ill give my dlsr full frame a go and see how that plans out you have saved me from forking out for a new telescope ill put that on hold for now and check out that book. the image of m27 gives me hope as ive only been getting black images so it tells me i have definitely been doing something wrong so thank you.

[fifeskies]

I have an ZWO ASI 290 which is great for planets with Sharpcap  (similar to your 120)

 

For DSO capture I use the very capable free software APT  (Astrophotography Tools) and use the ZWO for guiding with (PHD2)

There are several excellent uTube guides on this.

 

I use exposure times of 90 sec to 360 seconds depending on target (per sub frame) and integrate up to 2 or 3 hours of exposure , without these long exposure times all you will see is an empty frame with a few stars ,  (if you are lucky with bright stars)

 

For DSO I use my D600 DSLR ,

(the ZWO are really very narrow field of view and only suitable for very tiny DSO)

 

Take a look at this

Orion Nebula (M42) with a DSLR, Start to Finish - Deep Sky Astrophotography - YouTube

 

and get that excellent book referenced above  Making Every Photon Count - Steve Richards | First Light Optics   before making any new purchases.

 

 

 

Edited December 26, 2020 by fifeskies

[fifeskies]

Most of the easy DSO are fairly big  (Not saying there are not good smaller targets , they just tend to be a bit more challenging)

Compare below the sensor size outputs for your scope and both cameras

And being faint some of the smaller ones will need guiding to get them , so the ZWO is best given guiding duties until you have used your DSLR as main camera to learn how it all works.

 

 

 

 

 

Edited December 26, 2020 by fifeskies