The "No EQ" DSO Challenge!

[Stub Mandrel]

Well done Yamez, a great first result with nice detail in the core. I think you will be able to reduce the noise significantly by going to ISO800 and stretching the image rather than using ISO3200.

[Yamez]

ok i will do that for next time, the moon was a pain so the next time i'm out early in the morning there won't be a moon  

[Nigel G]

Hi Yamez, Welcome to the No eq DSO challenge .

This is a great image first stack or not. Well done.

I see you used 3200 iso, this could be the main noise contribution, I normally use 1600 iso as most others do I think, occasionally 800 iso. Mind you the moon doesn't help either.

Flats are well worth the effort, making processing quite a bit easier,

Maybe try 20 to 30 seconds at 1600, the more subs you get the less noise there will be also.

Cheers

Nige.

 

[Yamez]

at 20 seconds on my mount trailing starts to be introduced, is there anyway or any settings i can use on my goto mount to track the object better. FYI i have to use my x2 barlow with this setup otherwise i can't get into focus. The only way to fix this is to move the primary mirror closer to the secondary but i really don't want to be messing around with my scope as it is my first and haven't even had it a year yet. And i will for sure use a lower ISO.

[Nigel G]

1 minute ago, Yamez said:

at 20 seconds on my mount trailing starts to be introduced, is there anyway or any settings i can use on my goto mount to track the object better. FYI i have to use my x2 barlow with this setup otherwise i can't get into focus. The only way to fix this is to move the primary mirror closer to the secondary but i really don't want to be messing around with my scope as it is my first and haven't even had it a year yet. And i will for sure use a lower ISO.

Ok, with a barlow you will struggle with tracking and loss of light.

I had the same trouble and had to modify my focuser to allow prime focus. I have the 150p.

Leveling your tripod and a good 2 star alignment should get the required tracking.

Good luck

Nige.

[The Admiral]

Welcome to this particular, rather niche, thread Yamez . You'll have seen my comments after your original post, but keep up the good work.

Cheers, Ian

[Yamez]

Thanks everyone, I shall definitely spend more time leveling my mount, its always one thing that I never do only if I'm changing from grass to patio. On my 2 star align I always make sure the 2 stars i chose are spread out far apart. For example Vega and Capella.

[Nigel G]

Ideally the 2 chosen stars would be within 100 degrees of each other and a similar altitude but its not that critical

As your image was taken through a x2 barlow star trails would happen much sooner so your alignment might not be that bad at all.

Nige

[The Admiral]

+1 to what Nige said. Vega and Capella are almost on opposite sides of the sky, so it's not giving the mount much of a chance to calibrate itself. If you think about it, the mount has a stored picture of the starry heavens, but it needs to work out whether there is any 'tilt', in any direction, to the hemisphere. If the alignment stars are opposite each other in the sky, it can really only do this in one plane. By including alignment stars which are roughly at right angles to each other, then the mount can work out any tilt in two orthogonal planes, which is necessary for accurate alignment.

The mount does this by knowing the exact time and location, from which it can work out where stars should be, and compares them with what is actually the case. So, if you use alignment stars which are due north and south, it seems to me that because their change in altitude with time is relatively small, the errors in determining that tilt will be larger. So I tend to choose alignment stars not in those directions, if I remember . It's also why you shouldn't use Polaris as an alignment star because its position doesn't significantly change with time, so the mount can't get any useful alignment information from it.

Ian

[jimbo747]

I also make sure to take up any slack when aligning, I center on a star, press enter, then adjust the controls to make sure the gears just start ticking before pressing 'align' - if in the east the mount tracks right so I use a bit of left last. Doing that means I get objects like Jupiter bang on center even with a 2x barlow on my 127 mak.

 

I also only ever use 3 star alignment, partly because the 3rd star is used to calculate angles of the previous 2, and also because I have no idea what stars I'm looking at unless I have my phone and skymap in front of me.

Edited October 23, 2016 by jimbo747

[Victor Boesen]

2 hours ago, Yamez said:

Hi

I was linked to this thread after posting my First M42 image taken with a Nikon D3300 attached to my Skywatcher 130P on an Alt-Az mount. I got 20x10seconds of subs and some darks and bias' before the clouds came rolling in. Stacked in DSS and processed in Photoshop.

ISO 3200 + a 50% moon... Anyway here it is.

It is noisy and am hoping to get some more subs to add to it. This is my first ever image of any nebula.

Nice image, especially with an alt/az mount! You caught the trapezium in the core as well!!

Edited October 23, 2016 by Bossen

[SteveNickolls]

Hi Yamez,

One 'technique' I use with my Synscan Alt-Az mount is to place a house brick in the eyepiece tray, it's 3kg mass helps to steady the mount, it might work for you. Another is to centre the alignment stars with an eyepiece with a cross hair. As others have said I think your limitation is having to use the barlow lens. You could try some wide view shots having your camera piggyback on the telescope as the mount tracks. You will need to align your finder/eyepiece/camera. I bet you will get longer and accurate tracking that way and some targets are better framed in wider fields.

Cheers,
Steve

[Yamez]

3 hours ago, SteveNickolls said:

Hi Yamez,

One 'technique' I use with my Synscan Alt-Az mount is to place a house brick in the eyepiece tray, it's 3kg mass helps to steady the mount, it might work for you. Another is to centre the alignment stars with an eyepiece with a cross hair. As others have said I think your limitation is having to use the barlow lens. You could try some wide view shots having your camera piggyback on the telescope as the mount tracks. You will need to align your finder/eyepiece/camera. I bet you will get longer and accurate tracking that way and some targets are better framed in wider fields.

Cheers,
Steve

I shall try putting a brick on the tray, how would i piggy back the camera on the telescope? Will i need special equipment?

[Nigel G]

8 hours ago, Yamez said:

I shall try putting a brick on the tray, how would i piggy back the camera on the telescope? Will i need special equipment?

You need tube rings and a dovetail bar, which will add a couple of pounds to the weight. 

Another alternative  is to get a dovetail bar and connect the camera direct to the mount, shown in the photo. 

The bar will cost around £15 and I think you get the correct screw to attach the camera with it..The 210mm lens in this photo was £30 on ebay, 

Nige.

Nige

[SteveNickolls]

9 hours ago, Yamez said:

I shall try putting a brick on the tray, how would i piggy back the camera on the telescope? Will i need special equipment?

Hi,

+1 to what Nigel G has said. My own approach was this but for a refractor-

I bought an extra tube ring so I can mount the camera on the side or top of the telescope and a ball head to allow for collimation of the camera with the eyepiece/finder. The arrangement has performed fine with no unexpected movement of the ball head or camera. The Synscan mount has proven a good workhorse even with all the extra parts that must affect balance. 

Good luck.

Steve

[The Admiral]

An alternative may be something like this : https://www.firstlightoptics.com/alt-azimuth/skywatcher-l-bracket-dovetail.html

The only issue might be aligning on a star without a finder if the camera lens doesn't offer a very wide view. I guess if you are using a zoom, then finding your way around might be eased. I've not personally tried this though, so others may correct me.

Ian

[Nigel G]

Correction,  as Steve has said, you need  1 tube ring and no dove tail bar,  the camera screw comes with the ring not the bar, alternatively a dovetail bar.

FLO  sell the Skywatcher 130 tube rings and dovetail separate.

This is a 200mm ring with the camera  screw and a dovetail bar with slight addition to be able to turn the camera  90 degrees. 

Nige.

[SteveNickolls]

1 hour ago, The Admiral said:

An alternative may be something like this : https://www.firstlightoptics.com/alt-azimuth/skywatcher-l-bracket-dovetail.html

The only issue might be aligning on a star without a finder if the camera lens doesn't offer a very wide view. I guess if you are using a zoom, then finding your way around might be eased. I've not personally tried this though, so others may correct me.

Ian

Ian hits the nail right on the head regarding alignment. For very wide shots accurate direction is not so critical but as you increase the FL of your lens it becomes important to be pointing right. Even more so if you need to slightly adjust the framing. You will also find that even very bright stars only come into view (if you use Live view or similar) when very close to focus and it's easy to get frustrated. That's why I have gone to the lengths I have to ensure camera/eyepiece and finder point exactly together as it saves time and bother later. It's also important to take your time getting the best focus and I've found moving the focus in and out a few times helps you best judge things. Some cameras have a magnification capability in Live View to help with focusing. There are pieces of software (APT and BYEOS/BYNikon) that can help for some makes of camera but TBH you're far better left doing things manually for now. I usually take some trial shots to check framing of the object and adjust as required. For very wide view shots again it's not an issue. Some camera lenses creep in use and move out of focus due to gravity. Not had that problem on my Canon 75-300mm lens but worth keeping an eye out when you first use your lenses.

Cheers,
Steve

Edited October 24, 2016 by SteveNickolls

[Nigel G]

With the last few nights being cloudy, I have been thinking and reprocessing and thinking, A dangerous past time is thinking!

My thoughts. With exposure lengths in mind, Quoting back to NGC 7000, around 1.5 hours of 45 second exposures and the added 4 or 5 90 second exposures.

The 90's made a big difference to the final image, more colour, detail and easier processing. collecting the normal data, in this case the 45s was easy with around 90 % keep rate, but the 90s were not so easy, approx 1 hour to collect the 4 or 5 frames. One question is, is it worth the wasted time gathering the few long subs.

My experience with adding just a handful of longer subs to the same stack has been positive every time, adding just a few long as possible subs makes a big difference, more than if you stacked the same amount of exposure time with the shorter subs. 5 x 90s is better than 10 x 45 but takes much longer to get the good frames. But is possible.

The down side is, with the British weather. The few nights we get the chance normally cloud will spoil the session so time wasted trying to get the extended subs is data lost.

It takes 1 hour to get 5x90s, so in the same time 60x45s could have been collected. Is 60x45s better than 5x90s ?

If you persist with getting a handful of longer subs they do eventually come. Maybe only 1 in 8 or 10 though.

I don't think its so important on a target like M42 and M31 though where a huge amount of data can be gathered with just the shorter exp's.

Any thoughts ?

Nige.

 

[The Admiral]

That's a thorny and often implied question, and I don't really understand the underpinning science. I always refer back to this thread: https://stargazerslounge.com/topic/245183-to-stack-or-not-to-stack-30-x-1s-1-x-30s/#comment-2664662

So far as I can tell, all things are equal, except for the read noise, which of course is higher the more subs you have, and the influence of sky-glow. Thus with a low noise camera, the more you can get away with. We actually need a bit of background light to get the sensor into the linear part of its response, so the question is, if you are just moving the response further up a linear response curve, what do you gain? Statistics presumably, but then you're taking more subs to counteract that. At the same time though, there seem to be a lot of folk who are definite that a longer exposure is better! I think that the longer your subs are, the deeper you'll see, but I may have that wrong. I may not be helping here!!

I would just add that I'm in favour of doing dual duration imaging where the dynamic range is large, such as with M42, short to capture the bright bits, and long to capture the fainter bits.

Ian

Edited October 26, 2016 by The Admiral

[The Admiral]

1 hour ago, Nigel G said:

With the last few nights being cloudy, I have been thinking and reprocessing and thinking, A dangerous past time is thinking!

It takes 1 hour to get 5x90s, so in the same time 60x45s could have been collected. Is 60x45s better than 5x90s 

Hang on! In an hour you'd get 40 x 90s or 80 x 45s subs.

Ian

[Filroden]

5 minutes ago, The Admiral said:

Hang on! In an hour you'd get 40 x 90s or 80 x 45s subs.

Ian

But wind/tracking reduces success rates. Longer exposures mean lower chances of success. That's why I've been sticking to 30 seconds as I'm at almost 100% for tracking. 

[Filroden]

I think Ian's summarised it. Once your exposure time gives enough signal then the main difference between many short vs few long exposures comes down to a trade off between two factors: accumulating read noise exceeding other noise (many short) vs worse SNR for fewer long. Of course, we all know many long exposures is the best option but we've got mounts to fight

I don't know why the 5 x 90s improved your image so much other than to think that the shorter exposures were not giving you enough signal to get into that sweet spot.

[Filroden]

Finally I think I might have a clear evening! So, after my mount's wifi threw another wobbly (too many networks nearby interfere with it) and three alignments later, I'm imaging NGC1333. I think I may have lost my first 25 lum subs as my final alignment was slightly less accurate and my centre of fov has moved

And just lost the next 3 because I forgot to set cooling again!

Edited October 26, 2016 by Filroden

[The Admiral]

Good luck Ken, often a case of "more haste, less speed". I've been out in an all too rare clear sky trying to optimise the sensor-flattener spacing, but even by 20.30 the gear was covered in dew, so I don't know how long imaging would have been practicable. Given that they are forecasting a foggy morning, perhaps it's none too surprising. I managed to nudge a tripod leg trying to align on my second star, so had to repeat the first one again!

Ian

Edited October 26, 2016 by The Admiral