The "No EQ" DSO Challenge!

[Stub Mandrel]

Someone suggested he looks at this thread...

[The Admiral]

Yes I did, and suggested he might get a more detailed response here than in the general imaging thread.

Ian

[The Admiral]

37 minutes ago, geopopescu2000 said:

Hello i have a question if someone can help me.

i Have an Skywatcher 120/600 with an ALt az Goto Mount. Also an Sony A7 and SOny A6500 and my question is if i can take picture with long exposure without star trails. I tried but my mount doesn`t track well and i thought i don`t know how to use it.

Thanks

What mount is it? As I said before, you won't be able to take long exposures. There are two aspects to this: general mount tracking, which to some degree is determined by how well you set it up, and field rotation, which you can't do anything about except keep exposures short. Depending on what part of the sky you are imaging, exposures will range between 15s and, say, 60s, if the general tracking of the mount is good enough. Have you looked through this thread? Does it raise any issues that you specifically want to ask about?

Ian

[Filroden]

1 hour ago, geopopescu2000 said:

Hello i have a question if someone can help me.

i Have an Skywatcher 120/600 with an ALt az Goto Mount. Also an Sony A7 and SOny A6500 and my question is if i can take picture with long exposure without star trails. I tried but my mount doesn`t track well and i thought i don`t know how to use it.

Thanks

Make sure you get a really good initial alignment, adding additional alignment points close to the area you want to image. This might help improve tracking.

You have a nice short focal length so as Ian says above, you should be able to get reasonable length shorts which can be integrated to improve their quality. 

[happy-kat]

i replied to the OP other thread I think there is a balance issue as the mount is tracking in azimuth but failing in altitude very much like my virtuoso did until i sorted out the balance the mount needed.

[Shaun_Astro]

Hola! I managed to get DSS to stack M33 from three night's imaging over August. It used 200x30s subs in total.

Even with 30 flat frames, the coma corrector introduces some very strange vignetting, that with the field rotation means I had to crop this pretty hard.

[Stub Mandrel]

14 minutes ago, Shaun_Astro said:

the coma corrector introduces some very strange vignetting

Unless you have your camera in exactly the same alignment to the scope every night, you need a new set of flats for each run.

I get around this by sighting across the flat bottom of the camera to the flat edge of the focuser to make sure they are almost exactly aligned. you should be able to get an alignment of better than 0.1 degree this way which is enough.

[The Admiral]

You've done well to get that Shaun. I didn't find it the easiest of objects, and I should think my Oxfordshire skies are rather darker than yours.

Interestingly, your spikes seem pretty sharp considering field rotation and it being a combination of 3 sessions.

Ian

[scitmon]

My first attempt with M31 which I am actually disappointed with.  I found it very hard to process due to image noise.  I am definitely going to attempt taking flats from now on! 

 

[Shaun_Astro]

3 hours ago, The Admiral said:

You've done well to get that Shaun. I didn't find it the easiest of objects, and I should think my Oxfordshire skies are rather darker than yours.

Interestingly, your spikes seem pretty sharp considering field rotation and it being a combination of 3 sessions.

Ian

Thanks,

I live on the outskirts of Woking and they are shutting all the streetlights off after 00:00 now, so it's gloriously dark and clear when conditions permit now.

There's about 11 degrees of rotation, but I think most of the shots were done with M33 around about the same place in the sky.

Edited August 29, 2017 by Shaun_Astro

[The Admiral]

11 hours ago, scitmon said:

My first attempt with M31 which I am actually disappointed with.  I found it very hard to process due to image noise.  I am definitely going to attempt taking flats from now on! 

Well I think you shouldn't be disappointed with it, the core is well defined and the lanes are visible. But a bit more information about the image would be helpful, such as scope and mount, camera, number of exposures, exposure length, any darks and bias frames, stacking and processing software.

If you take darks, make sure that you take plenty otherwise they can add noise. And yes, flats are probably more important.

Ian

Edit. OK, I see there is some info on the linked image, but it's quite helpful to have it on the post as well.

Edited August 30, 2017 by The Admiral

[happy-kat]

there is a separate post on processing help by scitmon I offered some suggestions there.

i find flats are not optional but darks are. bias are so quick it would be rude not to.

[scitmon]

On 30/08/2017 at 08:58, The Admiral said:

Well I think you shouldn't be disappointed with it, the core is well defined and the lanes are visible. But a bit more information about the image would be helpful, such as scope and mount, camera, number of exposures, exposure length, any darks and bias frames, stacking and processing software.

If you take darks, make sure that you take plenty otherwise they can add noise. And yes, flats are probably more important.

Ian

Edit. OK, I see there is some info on the linked image, but it's quite helpful to have it on the post as well.

My apologies yes I should have included that.  I used a Skywatcher 80ED Ds-Pro (without Focal Reducer) on a Skywatcher AZ goto mount with a Canon Eos 1000D.  I took around 200 x 15 second exposures for lights, but many of the later exposures where badly effected by dew on the scope lens.  A dew heater strip is definitely in my next order to FLO.  I also took 20 darks and 20 biases at the end of the session too.  Stacked with Deep Sky Stacker and processed with Star Tools.

Edited August 31, 2017 by scitmon

[Chinapig]

Here's a wee snap from a recent trip to the southern hemisphere.

The fuzzy blob is the Omega Centauri globular cluster, NGC 5139.  A single 10-second exposure, at ISO6400, taken on an Olympus EM5 ii mounted on a static tripod, using a 14-150 zoom at close to max - so approx 300mm at full-frame equivalent.

Far more of a holiday souvenir than a great pic, but it's not often that you find a globular cluster that's big enough and bright enough for a quick snap!

[rotatux]

Here's some planetary for a change: 2 sample shots of Saturn taken on 2017-06-11.

Details: ~120s FullHD @ 30p movie crop mode, Olympus E-PL6 with Celestron 127MAK/1500mm and x3/x2 APO Barlows on NexStar SLT, processed with cvastroalign.

(indulgence requested, I'm still learning how to process planetary footage and use cvastroalign)

Edit much later: realized this is not in the thread's subject (not DSO), I should not have posted here. Oops :-/

Edited September 15, 2017 by rotatux
typo

[Shaun_Astro]

Superbly clear last night, I could see the bands in the milky way over head and Andromeda and the Double Cluster just by looking up with averted vision.

Took some frames of M45, I'm still struggling to rid of the vignetting by using flats, I probably need to take more than 10, and I think my mirror was misting up while taking them.

Here's 132x19" subs. 

I realise taking 15-20 second subs allows me to keep most of them. 30" was too much for my mount with this 600mm scope on it, and I was chucking out 70% of frames.

I managed to keep about 70-80% now with 20", which means 45 mins of subs out of every hour of taking them, instead of only 20 mins!

Planning to add to this in the near future so less stretching and exaggerating of the vignetting is required.

 

 

 

Edited September 15, 2017 by Shaun_Astro

[happy-kat]

That is rather lovely lots of nebula and stuff. Be keen to see how it evolves with more data. I take quite a lot of flats more like 25-30.

[rotatux]

3 hours ago, Shaun_Astro said:

Here's 132x19" subs. 

I realise taking 15-20 second subs allows me to keep most of them. 30" was too much for my mount with this 600mm scope on it, and I was chucking out 70% of frames.

Don't be discouraged, I too face a mount that doesn't want to be stable enough more then 20-30s (more often 20). My keep rates vary from 22 to 80%, so you're pretty up the score I think if you would read back this thread it would be somewhat the same for others. You're on your way.

Nice image, you caught much nebula. However I find it's strangely too noisy given the high number of frames you stacked. Maybe you had to stretch very aggressively ? What ISO were your subs ? Did you shoot low on horizon ?

[Stub Mandrel]

5 hours ago, Shaun_Astro said:

Superbly clear last night, I could see the bands in the milky way over head and Andromeda and the Double Cluster just by looking up with averted vision.

Took some frames of M45, I'm still struggling to rid of the vignetting by using flats, I probably need to take more than 10, and I think my mirror was misting up while taking them.

Here's 132x19" subs. 

I realise taking 15-20 second subs allows me to keep most of them. 30" was too much for my mount with this 600mm scope on it, and I was chucking out 70% of frames.

I managed to keep about 70-80% now with 20", which means 45 mins of subs out of every hour of taking them, instead of only 20 mins!

Planning to add to this in the near future so less stretching and exaggerating of the vignetting is required.

 

 

 

Lots of nice nebulosity.

That is very fine grained noise, a quick experiment here suggest you can make a big improvement even with the most basic of noise reduction.

[Shaun_Astro]

I used 10 x dark and 10 x bias frames, but not enough it was very late. And I stretched it way too much.

 

I'll add to this and calibrate it better with more darks, flats and biases. This is kind of a WIP!

 

[The Admiral]

7 hours ago, Shaun_Astro said:

I used 10 x dark and 10 x bias frames, but not enough it was very late. And I stretched it way too much.

I think it's come out rather well Shaun, but like Fabien, I too find it strangely noisy. As Neil says though, a bit of noise reduction on the image could work wonders. But, where is the noise coming from? I would guess that apart from benefiting from an increase in the number of subs, you should think about increasing the number of darks significantly too. It is oft said that you should take as many as you can, at least the same number as lights. The reason is that you are subtracting one noisy image from another, and the net result is that the noise will be combined and therefore increase. By taking as many darks as you can the noise introduced from that component will be minimised. Likewise bias frames I think, but to do that takes no time at all given the short exposure necessary. It is a chore I know, and that is why some of us are not bothering with darks and just using the bias frames as a substitute. If you are using a DSLR the value of dark frames is questionable in view of the lack of temperature control and stability throughout the session, and the fact that dark noise is very sensitive to temperature. However, on the other side of the coin its use does allow correction of the gross artefacts such as amp glow.

Incidentally, this particular subject benefits from short exposures in my view because of the star brightness could be overwhelming.

Ian

Edited September 16, 2017 by The Admiral

[SteveNickolls]

18 hours ago, Shaun_Astro said:

I realise taking 15-20 second subs allows me to keep most of them. 30" was too much for my mount with this 600mm scope on it, and I was chucking out 70% of frames.

I managed to keep about 70-80% now with 20", which means 45 mins of subs out of every hour of taking them, instead of only 20 mins!

Thanks for posting, your image shows the nebulosity well and you have good round stars. You mention being able to see the Milky Way though that will have been higher than where M45 was but you must have reasonable dark sky to help with signal v noise. Is there anything you can do to improve the exposure time beyond 19 seconds? I'm thinking of making sure the tripod is as rigid as it can be, maybe trying a weight in the eyepiece tray. Haven't used the Star Discovery mount but the older Alt-Az Synscan can yield 60-70 seconds of tracking with coaxing and at 60 seconds 100% can be 'keepers' so I'd think some extension of imaging time could be wrought out of it. Perhaps your mount is showing signs of struggling with the weight of the telescope and camera (must be headed for the maximun payload of 5kg)? These light weight mounts have a lot of flexure potential in their design being really made for observing not imaging. As for dark frames my view has come full circle over using them. Unless you take say x50 to complement your short light exposures you could be making things worse as Ian says. The time involved with taking x50 19 second dark frames amounts to just under 16 minutes so quite do-able in the field. I'd also advise taking x50 Bias and Flat frames to for stacking and see what improvement they also bring to the mix.

Have you also tried switching off 'Live View' when ready to take images, it is said to help prevent the build up of glow in the lower left corner of Canon DSLR's as the sensor detects the stray heat as infra-red signal? Additionally the optical viewfinder can be taped over so no stray light seeps in that way and any red led on the body of the camera also taped over.

Do keep posting your images.

Cheers,
Steve

[happy-kat]

@Nigel G has I think tried his ed80 on the star discovery mount but off to of head I can't recall the exposure length he managed. 

When you say you can't use the subs when longer in what way are they no good is it trailing? Are the trails vertical?

I use my bias files to create a master dark and don't take any darks at all. 

[Shaun_Astro]

8 hours ago, SteveNickolls said:

Perhaps your mount is showing signs of struggling with the weight of the telescope and camera (must be headed for the maximun payload of 5kg)?

Yeah it's at the 5kg capacity, and 600mm is quite a long FL with this kind of setup I think. I'm happy with 20" over 30" if it allows me to keep this many subs.

8 hours ago, SteveNickolls said:

The time involved with taking x50 19 second dark frames amounts to just under 16 minutes so quite do-able in the field. I'd also advise taking x50 Bias and Flat frames to for stacking and see what improvement they also bring to the mix.

Have you also tried switching off 'Live View' when ready to take images, it is said to help prevent the build up of glow in the lower left corner of Canon DSLR's as the sensor detects the stray heat as infra-red signal? Additionally the optical viewfinder can be taped over so no stray light seeps in that way and any red led on the body of the camera also taped over.

Yeah I didn't use live view for a while before.

 

I kind of knew I needed a lot more darks and bias & flats, just wanted to see how it would fare without them. TBH I stretched this more than I normally do. Thanks for the feedback and advice, next time I shall use at least 40 darks, bias and flats!

[happy-kat]

An unorthodox approach but works for me as darks don't.

Try this stack approach. new process in dss: lights with your bias files (no darks)  register those files. then look where registered files went and copy and rename the master bias. add this new file as a master dark file. now process the stack.

Edit: Don'tDon't forget to add flats too.

Edited September 18, 2017 by happy-kat