The "No EQ" DSO Challenge!

[Herzy]

7 hours ago, Nigel G said:

A possible target for the test could be M17 Omega nebula, around the same altitude as Saturn in the southern sky atm.

I took this during the full moon last night and it was close to the target, because of the moon I could only get 15s exposure at 400 iso and only 30 minutes worth before the faint clouds started to arrive. 

Nige.

I haven't been out either because the moon is wrecking my view of the Eagle Nebula which I have an ongoing project on. You mentioned earlier how you feel you've reached the limit of your mount/scope so I'll chip in on that. Longer exposures and more of them will help... ALWAYS. Due to diminishing returns 4 hours will produce 2x less noise then 1 hour. 4 hours is a long time but it is worth it. If you put in that kind-of time you will get amazing images fast. Another problem you might be facing is that your imaging targets that are really faint. Your skies seem to be better then mine so I can't really comment on this with much accuracy but at my house I can't image the NA nebula because it is too faint. My 90 second subs are simply too short to distinguish nebulosity from noise. No matter how many subs I take it won't matter because I'm still not capturing any nebulosity. You might have something similar going on when you go after the faint nebulas. Just my $0.02.

Hayden

[SteveNickolls]

The recent clear dark night skies have allowed me to image M31 and M33 using the combination of Synscan SkyWatcher Alt-Az mount, 102mm Startravel refractor and Canon 600D DSLR. This season I have been trying out ISO 800 after finding ISO 1600 was producing images which on the camera histogram were well to the right hand side. I've also been using stock dark and bias frames. I realise I can't control the temperature of the camera chip but the dark frames do help with bad pixels. I am going to try using the kappa-sigma clipping in DSS as it's meant to be an alternative to using dark frames for removing rogue pixels.

The following two images were both taken using 60 second exposures since both objects were well placed in the East for field rotation mitigation purposes.

M31

x50 light frames, x50 dark frames, x60 flat frames and x50 bias frames. Stacked in DSS and subsequently processed using StarTools. Taken 29th August 2016.

M33

Again x50 light frames, x50 dark frames, x60 flat frames and x50 bias frames. Stacked in DSS and subsequently processed using StarTools. Taken 30.8.2016.

DSS was happy to accept 72% of the M31 exposures and 75% of the M33 ones. At sixty seconds I'm averaging 76% acceptable frames from all my exposures up until now.

This season I've obtained a Canon 75-300mm USM III lens to have some fun taking wide-ish piggyback shots using the Synscan Alt-Az mount and below is my first attempt at M31 in wide view taken on the 26th August this year. Taken with a camera lens setting of 200mm f/5.6.

The image is made from x50 sixty second light frames at ISO 800, x50 dark frames, x60 flat frames and x50 bias frames. Stacked in DSS and subsequently processed using StarTools. DSS was happy with all the light frames taken.

Cheers,
Steve

Edited September 1, 2016 by SteveNickolls

[The Admiral]

Steve, I may be mistaken but I think I've read that kappa-sigma clipping is used in association with dither. Whether the meanderings of an Alt-Az mount and/or field rotation is equivalent to dither I don't know, but it'll be interesting to see what effect it has. To be honest, I don't think I know exactly what kappa-sigma clipping actually does. I thought that using darks also has the effect of removing things like amp glow. Deary me, it's so long since I've done any astrophotography I'm pretty rusty on all of this

Looking back I see that I generally have used k-s clipping when stacking, but I haven't done a comparative study between using darks and normal stacking, and no darks and k-s clipping.

Ian

[SteveNickolls]

Hi Ian,

Thanks for your advice here, sadly I'm only repeating what I have read elsewhere regarding kappa-sigma as a means of removing pixels that are out of line with adjoining ons so I have no personal evidence either way. If I get chance I'll reprocess recent images in DSS using 'Kappa-sigma' in place of 'median' and leave out the dark frames as an experiment. The thought that the tracking limitations of our Alt-Az mounts can be used to advantage to 'dither' is intriguing. Will post what I find to help us all.

Best Regards,
Steve

Edited September 1, 2016 by SteveNickolls

[Stub Mandrel]

I did a comparison using kappa sigma and adaptive average and the kappa sigma appeared to have least noise.

I found leaving out darks made noise worse but 'your mileage may vary'.

[Herzy]

9 minutes ago, Stub Mandrel said:

I did a comparison using kappa sigma and adaptive average and the kappa sigma appeared to have least noise.

I found leaving out darks made noise worse but 'your mileage may vary'.

That's because averaging does far less work. Assuming your dithering property, any correlated noise or walking noise will be removed from a reject/sigma algorithm.

[Herzy]

6 hours ago, SteveNickolls said:

The recent clear dark night skies have allowed me to image M31 and M33 using the combination of Synscan SkyWatcher Alt-Az mount, 102mm Startravel refractor and Canon 600D DSLR. This season I have been trying out ISO 800 after finding ISO 1600 was producing images which on the camera histogram were well to the right hand side. I've also been using stock dark and bias frames. I realise I can't control the temperature of the camera chip but the dark frames do help with bad pixels. I am going to try using the kappa-sigma clipping in DSS as it's meant to be an alternative to using dark frames for removing rogue pixels.

The following two images were both taken using 60 second exposures since both objects were well placed in the East for field rotation mitigation purposes.

M31

x50 light frames, x50 dark frames, x60 flat frames and x50 bias frames. Stacked in DSS and subsequently processed using StarTools. Taken 29th August 2016.

M33

Again x50 light frames, x50 dark frames, x60 flat frames and x50 bias frames. Stacked in DSS and subsequently processed using StarTools. Taken 30.8.2016.

DSS was happy to accept 72% of the M31 exposures and 75% of the M33 ones. At sixty seconds I'm averaging 76% acceptable frames from all my exposures up until now.

This season I've obtained a Canon 75-300mm USM III lens to have some fun taking wide-ish piggyback shots using the Synscan Alt-Az mount and below is my first attempt at M31 in wide view taken on the 26th August this year. Taken with a camera lens setting of 200mm f/5.6.

The image is made from x50 sixty second light frames at ISO 800, x50 dark frames, x60 flat frames and x50 bias frames. Stacked in DSS and subsequently processed using StarTools. DSS was happy with all the light frames taken.

Cheers,
Steve

You really need more integration. Integration is key. Especially on M33, where the spiral arms aren't very well defined in your image and there isn't much detail to be had. That is because the noise is just too strong relative to signal. You need at least 4x the integration to improve the sharpness by 2x and reveal details half as bright (due to diminishing returns) and that is well worth the effort. You would be surprised how much detail you could pull out of a 4hr stack vs a 1hr stack. I was certainly surprised with the results of M16 (1hr vs 9hrs). It was a HUGE difference.

Also, your color balance is a little off. Not sure what is causing that.

At the end of this day, the images are great. They would impress almost anyone you showed. Good job!

Edited September 1, 2016 by Herzy

[Nigel G]

Steve,  great images plenty of detail, I was wondering how M 33 would turn out, it's not quite in my field of view yet.

I have always use kappa sigma in dss, something I had thought about but not experimented with. Perhaps I should. 

I  too have been building my camera lense collection,  I have a 135mm a 210mm and a x2 adapter . 

Using M31 as a target I have images with a 55mm and 135mm lenses and my 150p scope. Just waiting for good sky's  to get images with the 210mm and 420mm lenses before I  post them.

For the first time ever I'm looking forward to the nights drawing in ☺

Nige.

[The Admiral]

15 minutes ago, Herzy said:

You really need more integration. Integration is key. Especially on M33, where the spiral arms aren't very well defined in your image and there isn't much detail to be had. That is because the noise is just too strong relative to signal. You need at least 4x the integration to improve the sharpness by 2x and reveal details half as bright (due to diminishing returns) and that is well worth the effort. You would be surprised how much detail you could pull out of a 4hr stack vs a 1hr stack. I was certainly surprised with the results of M16 (1hr vs 9hrs). It was a HUGE difference.

Also, your color balance is a little off. Not sure what is causing that.

At the end of this day, the images are great. They would impress almost anyone you showed. Good job!

Trouble is, a 4 hour or 9 hour stint using an Alt-Az mount does create other problems!

Ian

[SteveNickolls]

Hi All,

Thanks for the comments Herzy, the colour issue is down I think to the data not being enough for StarTools to properly handle in its COLOR module, hence I skipped that out plus I tried just using the green channel hence the tint. I agree on more photons but as Ian makes the point 4-9 hours would require a number of imaging sessions, do-able at a pinch but we don't get lots of decent clear nights in the UK? Will see how it goes though-thanks.

Nige, good to hear you use kappa-sigma in DSS, I'll post my results as soon as I can. You have a nice collection on lenses and it will be great to see your images before too long.

Excuse any spelling mistooks as I'm on the hudl with it's tiny keys and random spelling :-)

Cheers,

Steve

 

[happy-kat]

You should try swipe for typing on your hudl of you haven't yet

[Herzy]

2 hours ago, The Admiral said:

Trouble is, a 4 hour or 9 hour stint using an Alt-Az mount does create other problems!

Ian

Why would it? Sorry, I don't know too much about altaz.

[SteveNickolls]

8 hours ago, happy-kat said:

You should try swipe for typing on your hudl of you haven't yet

Ha, for that you need some typing skill, knowing where the keys are laid out. I often don't know where the hudl is ;-). I will put that down as an aspirational achievement, but thanks for the idea happy-kat.

 

[SteveNickolls]

10 hours ago, Stub Mandrel said:

I did a comparison using kappa sigma and adaptive average and the kappa sigma appeared to have least noise.

I found leaving out darks made noise worse but 'your mileage may vary'.

Thanks for this, will see what happens! Fingers crossed.

Cheers,

Steve

[The Admiral]

9 hours ago, Herzy said:

Why would it? Sorry, I don't know too much about altaz.

Unlike a finely tuned EQ mount, there are two main problems with the Alt-Az mount: field rotation and tracking performance. In order to minimize the manifestation of field rotation on one's images one needs to use short exposures, only a few tens of seconds, so a total exposure of 4 hours or more will produce hundreds of subs. Star streaking will be evident in a percentage of these subs, the more as the exposure time is increased (even if that time is acceptable from a field rotation point of view), and DSS will reject them, so the integrated exposure will be less than one might hope for. I think it's also true that the overall tracking performance of Alt-Az mounts is somewhat below that of the correctly adjusted EQ mount, so if one did embark on a long exposure session it would have to be done in a number of shorter bites with mount realignment in between.

I'm not saying that all this couldn't be done, but the reason I'm using Alt-Az imaging is that I have to set up the gear each time I use it so it needs to be simple and quick to set up (and I can't see the Pole star from my observing position). As Steve alluded to, this is because here in the UK the weather seems so unpredictable that often the decision to image is a last minute one. Personally, I'm not striving for salon-quality images, but just to reveal the glory of what I can only see as a grey smudge when viewed by eye. That is not to say of course, that I don't want the best output that I can achieve within the constraints imposed by this style of imaging. But one has to be realistic about the law of diminishing returns.

Don't forget also that much of the UK is blighted by light pollution, so that is yet another issue we have to contend with.

Ian

Edited September 2, 2016 by The Admiral

[SilverAstro]

Hi Steve very interesting very nice images, amazing in fact

The two of Andromeda - are they full frames or cropped ? Reason I ask is, are the scales of the images as presented comparable ?

[Nigel G]

Field rotation over a long session will leave the final image to be cropped quite a considerable amount to reduce stacking artifacts.  With M31 this crops out wanted details so it would be better to gather the subs over a few nights .

Nige.

[SilverAstro]

1 hour ago, Nigel G said:

Field rotation over a long session will leave the final image to be cropped quite a considerable amount to reduce stacking artifacts.

Or divide one nights set into two or three batches, stack each, rotate each by hand in software of choice, and then stack the resulting two or three combo frames ? ? ( been there, Tshirts etc, also helps with jogged tripods )

Edit : put the above on "hold" I'll have to re-think that, it may not have been my problem, perhaps it was just lens distortion in my camera lens , , , or jogged tripods !  my head hurts

 

Edited September 2, 2016 by SilverAstro

[jimbo747]

Took my first image for over a year, and first ever with my modded DSLR. Moving house and cleared shed as far as my telescope and it just so happened to be a clear night. 

Dumbell nebula and some cluster at the bottom of the image. Stars look bloated because 1) its a full spectrum mod and I have no IR or UV filter 2) its a cheap £30 200m zoom lens 3) I'm rubbish at processing, did some levels and curves tweaks.

Used SLT alt az mount. 

1 hours worth of 60s exposures. The image is completely uncropped and the mount kept the nebula bang in the middle for 2 hours - never managed this level of accuracy before. No calibration frames of any kind, vignetting reduced in photoshop.

Now the image isn't anything special, but the reason I post is interestingly, most (90%) of the images when the object was high in the sky showed star streaks, however I think thanks to kappa sigma it averaged them out giving them a far more round look compared to any single raw file. I took 2 hours worth and stacked 50% thinking the image would be ruined, maybe I could try adding more of the remaining 50%. When I'm setup at new house and can see far more of the sky I'll try some 90s-120s subs and see how DSS fairs. 

 

[SilverAstro]

26 minutes ago, jimbo747 said:

Now the image isn't anything special, but the reason I post is interestingly, most (90%) of the images when the object was high in the sky showed star streaks, however

I cant see it !

You are right, I cant see frame rotation, interesting !

Perhaps you could post a streaky one because I dont think I have seen a picture of this frame rotation wot everyone is on about   (people dont generally post their duds, but they can often be as informative, like what not to do ! as the good ones ) As you say, high in the south is supposed to be the poor direction, very interesting.

Nice dumbell, nice image.

[Stub Mandrel]

I would have thought an ordinary skylight or UV filter as used for 'taming the sky' with an ordinary lens would help with star bloat, I'm going to use one next time I use the 135mm lens to reduce the 'violet haloes' although the process out easily enough.

[The Admiral]

2 hours ago, SilverAstro said:

I cant see it !

You are right, I cant see frame rotation, interesting !

Perhaps you could post a streaky one because I dont think I have seen a picture of this frame rotation wot everyone is on about   (people dont generally post their duds, but they can often be as informative, like what not to do ! as the good ones ) As you say, high in the south is supposed to be the poor direction, very interesting.

Nice dumbell, nice image.

Well by my reckoning at an altitude of 60° and due South, it would take about 20s for a 0.1° rotation, which is what I use as a basis for acceptable limits. So for a 1 minute sub you are talking of a 0.3° field rotation, and I don't know what that would be in terms of pixels. I can't see any rotation in jimbo's image, so perhaps my criterion is a little too strict? What do others feel?

I can't help thinking that if DSS was morphing the streaked stars into one rounded one, then we'd see a noticeable increase in star size towards the edges. And I don't see why it should because it's not as though the 'streak direction' is random, they'd all point in the same direction.

Interesting!

Ian

[The Admiral]

3 hours ago, SilverAstro said:

Or divide one nights set into two or three batches, stack each, rotate each by hand in software of choice, and then stack the resulting two or three combo frames ? ? ( been there, Tshirts etc, also helps with jogged tripods )

 

My emphasis. Why rotate in software, why not rotate the camera at the beginning of each set so that you get back to roughly the same starting position for each set? Presumably DSS would stack them all as one set?

You may need to do flats for each position if the field uniformity is not axially symmetric, in which case I guess you'd need to stack each set separately.

Ian

[dobbie]

On Monday, January 25, 2016 at 12:33, ollypenrice said:

Some impressive results and a good idea for a thread. 

Erm, would it be considered unsporting of me to go and beg some time on this Alt-Az instrument up the road from me? 0.8M Ritchey Chrétien, direct drive, field de-rotator and a price tag of 6 million Euros...

Well it isn't an EQ!!! 

(There's always one...)

lly

 

 

Nope..your not getting away with that one olly

[SteveNickolls]

Jimbo747,

A most interesting phenomenon you have imaged there for over an hour. Can I ask if you were imaging at 200mm with your DSLR? My thoughts would be that at that FL the percieved field rotation on the chip was insufficient to cause a streak to appear. When I process images in StarTools I often bin the original image by 50% or 65% as my 18M pixel camera image is mostly wasted (oversampled I think the term is). I know in his book, 'Using Short Exposures with Light Mounts..' Joe Ashley has a  technique for overcoming field rotation  based upon calculations involving 0.125 degree over 20 seconds which is close to Ian's value. You also need to remember that even if you can 'overcome' field rotation (using a tracked Alt-Az mount) by using a short FL lens your mount performance might limit your maximum duration of exposure from a mechanical viewpoint. Very interesting phenomenon though and well worth exploring more.

Cheers,
Steve

Edited September 2, 2016 by SteveNickolls