The "No EQ" DSO Challenge!

[The Admiral]

On 02/05/2017 at 22:57, jimbo747 said:

Apologies to anyone in Derbyshire. Since my starsense arrived 2 weeks ago there hasn't been a single clear night, it's still on the box in fact.

I'm off out Friday, so of course it's forecast to be crystal 

I got my StarSense 3rd week in March and used it (grappled with it!) for the first time on 25th. Since then I've had no opportunity to use it again, mainly because it has been cloudy or the forecasts were predicting poor conditions and I didn't feel like hauling everything from upstairs into the garden. And now the nights are getting rather short (and I'm not by nature a night-owl ).

I suddenly got interested in the latest challenge, until I realised that it was time limited and there would likely be no chance of imaging this side of summer. Pity, it's made for us Alt-Az imagers!

Ian

Edited May 4, 2017 by The Admiral

[rotatux]

1 hour ago, The Admiral said:

I suddenly got interested in the latest challenge, until I realised that it was time limited and there would likely be no chance of imaging this side of summer. Pity, it's made for us Alt-Az imagers!

Are you talking of this one ?

 Yes it's made for us :-D or at least we are about equal with EQ mounts... Just have to get out all night for good DSO views.

Still somewhat manageable, it's currently dark here by 22:00 to 22h30 (on holidays in my deep country site).

Weather says 2 or 3 hours clear of clouds tonight, I hope it's right...

[Stub Mandrel]

My reading is (and I may be reading far too much into this) that they have chosen this especially to encourage Alt-Az and EQ3 imagers  -  or maybe to get us to Put Up or Shut Up!

Of course, I have only gone and ordered a guide camera off FLO ...

Edited May 4, 2017 by Stub Mandrel

[The Admiral]

1 hour ago, Stub Mandrel said:

My reading is (and I may be reading far too much into this) that they have chosen this especially to encourage Alt-Az and EQ3 imagers  -  or maybe to get us to Put Up or Shut Up!

Of course, I have only gone and ordered a guide camera off FLO ...

Don't get too paranoid Neil . But it strikes me that it is a tall order anyway, given the lousy weather and shortening nights, irespective of the equipment used. Not to mention the Moon 

Ian

[Stub Mandrel]

There will be lots of photos of M13 entered!

[Filroden]

NAN and Pelican, Elephant Trunk, Heart & Soul, Iris, etc are all pivoting around for the 12:00 to 2:00 slot when it is darkest. All within range of 30s shots over a couple of hours.

[The Admiral]

Sadly, in the wrong part of the sky for me, and in any event, I'm afraid you won't catch me out of bed at that sort of time Ken! 

A half-hearted astronomer 

[Filroden]

Just now, The Admiral said:

A half-hearted astronomer 

So Soul only?

[dph1nm]

Holiday outing in South Wales at the end of March with a south facing site. Venerable Nexstar 102SLT + Canon 1000D + Skywatcher LP filter.  Subs are all 30secs - total exposures between 10-30 minutes. ISO1600, processed with DSS and Gimp; flats and bias used. Have to throw away the 25-30% of the subs with very bad tracking, but the rest I keep and stack, and the result is round (if rather fuzzy) stars.

NigelM

[The Admiral]

6 minutes ago, Filroden said:

So Soul only?

Boom-....

Ian

Edited May 5, 2017 by The Admiral

[Stub Mandrel]

1 hour ago, Filroden said:

NAN and Pelican, Elephant Trunk, Heart & Soul, Iris, etc are all pivoting around for the 12:00 to 2:00 slot when it is darkest. All within range of 30s shots over a couple of hours.

Not in my landscape, I can just about see ESE over the top of the house but that's on the edge of the local LP hot spot. My main 'window' is SSE to SW. W to NW is my darkest sky but also tall trees :-((

[happy-kat]

That's a good selection NigelM. I particularly like M104.

[Nigel G]

2 hours ago, Filroden said:

NAN and Pelican, Elephant Trunk, Heart & Soul, Iris, etc are all pivoting around for the 12:00 to 2:00 slot when it is darkest. All within range of 30s shots over a couple of hours.

It looks bleak here in the Southeast cloud, cloud and more cloud sadly. The Elephant trunk is on my want list since my first attempt some months ago with my unmodded camera and 150p on the Star discovery mount.

I think this is one I haven't shown, I can't remember how long or how many exposures. but its something to look at  

I checked the date, early November.

I haven't had a chance to do any in weeks, whats going on with the weather - is it El nino fallout form last year ?

Nige.

[rotatux]

After several months without getting outside because of bad weather, can't resist to post some results trying new gear (camera body and lens).

Markarian's Chain and neighbours: Exposure's not right and result is missing depth, but as this is my first at this subject. Stunned by the number of catchable galaxies sitting there.

Pleased with the result and the new lens, but not yet good enough to post to the 30sDSO challenge.

See here for details.

[The Admiral]

Nice wide-field shot Fabien, with lots of 'spinners' visible; it's a rich area of sky. And that's with only 7 minutes of exposure, with a lot more frames you might even get some colour into the galaxies. It would be interesting to plate-solve and get idents for them all!

Ian

[rotatux]

2 hours ago, The Admiral said:

It would be interesting to plate-solve and get idents for them all!

nova.astrometry.net is down with 503 just now, but @Uranium235 already posted a even wider FoV of this region in a giant annotated image, in the "imaging with 130PDS" topic.
 Next try I shoot at this (and post a better version), I shall remember to add a plate solve version.

2 hours ago, The Admiral said:

And that's with only 7 minutes of exposure, with a lot more frames

In fact the result could have been even better if I pushed the ISO (which my new cam would easily allow) but the odds -- fov rotation, dust and nearby 68% moon -- were against me. Next try in a few days (weather and moon permitting).

Edited May 11, 2017 by rotatux

[The Admiral]

57 minutes ago, rotatux said:

In fact the result could have been even better if I pushed the ISO (which my new cam would easily allow) but the odds -- fov rotation, dust and nearby 68% moon -- were against me. Next try in a few days (weather and moon permitting).

Yes, the Moon isn't helping and it's a fight to get anything! I'm not sure that you would achieve much by increasing the ISO would you? The image would require less stretching but you will be starting with a noisier image. At the end of the day, it's photons, photons, and yet more photons .

Ian

[Uranium235]

1 hour ago, rotatux said:

nova.astrometry.net is down with 503 just now, but @Uranium235 already posted a even wider FoV of this region in a giant annotated image, in the "imaging with 130PDS" topic.
 Next try I shoot at this (and post a better version), I shall remember to add a plate solve version.

 

You mean this one? (give it a few moments to load, its very big!) But, it wasnt with the 130pds, it was from the Star 71. If I'd chosen the 130 to do it, I'd still be on it now!

Its the full size image, so to read it just click on the image - then hit the full size button.

First it has to be solved, then annotated by AstroimageJ (it will perform both tasks for you) - but its not automatic, you have to search the image for something fuzzy then click to send the co-ordinates to the SIMBAD/LEDA database for a match.... which took a long time on an image this size.

[The Admiral]

Gosh! Well done that man 

Ian

[SteveNickolls]

6 hours ago, rotatux said:

Pleased with the result and the new lens,

Yes well done. Interesting to know what objects will look like at various FL's.

Cheers,
Steve

[rotatux]

2 hours ago, The Admiral said:

I'm not sure that you would achieve much by increasing the ISO would you? The image would require less stretching but you will be starting with a noisier image.

I should explain more precisely: The background was limiting exposure because of the nearby moon and dust. I wanted to use 30s because that was the (theoretical) max in that zone to avoid FoV rotation, then had to severely limit ISO to get an acceptable bg level. But at such iso level I have quite high saturation capacity (I would say too much!), and the sensor could be used IMO more efficiently at higher ISO. Thinking back, higher ISO and shorter subs would have lead to more frames (and less noise) within given time.

[rotatux]

2 hours ago, Uranium235 said:

You mean this one? (give it a few moments to load, its very big!) But, it wasnt with the 130pds, it was from the Star 71.

Yes exactly thanks for pointing to it

Didn't exactly remember where I saw it, so cited from memory -- wrong of course.

[Uranium235]

4 minutes ago, rotatux said:

I should explain more precisely: The background was limiting exposure because of the nearby moon and dust. I wanted to use 30s because that was the (theoretical) max in that zone to avoid FoV rotation, then had to severely limit ISO to get an acceptable bg level. But at such iso level I have quite high saturation capacity (I would say too much!), and the sensor could be used IMO more efficiently at higher ISO. Thinking back, higher ISO and shorter subs would have lead to more frames (and less noise) within given time.

You might want to read this very interesting article from Christian Van den Berge :

http://dslr-astrophotography.com/iso-dslr-astrophotography/

I found it rather illuminating (pardon the pun) when it came to choosing the best ISO for a fast lens on a DSLR. Its about finding what point your camera becomes "ISOless", which turned out to be ISO200 for my Canon 1000d... yes, very low but it helped an awful lot when it came to preserving star colour. As long as the data is properly calibrated, read noise should not be much of an issue - unless you are chasing a very weak signal, in which case bump up the ISO a bit (maybe to 400) to reduce the effect read noise has on very weak signals, extend the exposure, then merge the ISO 200&400 sets as an HDR image (so you have colour in every part of the image, including stars).

 

[SteveNickolls]

As regards which ISO to use if you experiment using different ISO settings when imaging you will come to some workable conclusion to best fit your own equipment and imaging location. The link Uranium235 gives is most interesting. I've also found www.sensorgen.info useful too. During my short stint astro-imaging so far under bad suburban skies I have gone from using ISO 1600 to 800 and to now 400 with my Canon 600D, the last drop albeit when using EQ tracking as I can get longer exposures than when using my Alt-Az mount and in combination with fast lenses (can be down to f/2) really hoover up those photons and when having more dynamic range left available is important. With my Canon 600D Sensorgen indicates that by coming down from ISO 1600 to 400 the pixel well saturation point increases from 2001e- to 7578e- while dynamic range increases from 9.4 to 10.7   Using a higher ISO setting you are really just making the image brighter, there's no more detail and will sacrifice the dynamic range when later processing the image. Good luck experimenting, it's very much part of the fun.

Cheers,
Steve

[The Admiral]

11 hours ago, rotatux said:

I should explain more precisely: The background was limiting exposure because of the nearby moon and dust. I wanted to use 30s because that was the (theoretical) max in that zone to avoid FoV rotation, then had to severely limit ISO to get an acceptable bg level. But at such iso level I have quite high saturation capacity (I would say too much!), and the sensor could be used IMO more efficiently at higher ISO. Thinking back, higher ISO and shorter subs would have lead to more frames (and less noise) within given time.

My first thought is just use more subs. But, if you are limited for time, then I'm not sure it would work like that. Straight off the top of my head, I would have thought that the noise levels would have risen in proportion to gain, i.e. ISO, but the noise would only have reduced as the root of the number of subs.

I've come to the view, rightly or wrongly, that provided your 'sky' exposure is getting a way up the histogram, then ISO won't make any difference, for the same exposure. (I've never been clear on whether read noise increases with gain or not!). Except, and as Steve points out, you do gain from the improved dynamic range at lower ISOs. The base ISO that Uranium235 refers to is essentially the ISO at which the sensor output is not amplified before the ADC, and so offers the maximum dynamic range.

When I've more time I'll take a look at that link.

Ian