585mc or a6000 for DSO with 8" F5 unguided?

[CraigT82]

Do the sorting/registration/stacking in AS3 rather than Pixinsight… might help a bit? Would still take a while though with the full sensor size of the 585.

[MichaelBibby]

1 hour ago, RolandKol said:

I just want to insert my 2 pence...
Short exposure DSO imaging is a real headache mate...

Just in 2 hours you may end up with the amount of 5k or more subs (16-32mb each), later stacking will take ages and software may even freeze or crash...
(not even talking about selecting best images, - blinking is not the option... Any other solution will also take ages, so you will end up dropping all images into the stack blindly).

Unless you have lots of patience and good hardware to process all of that.

You can read my experiences of a similar imaging below (process was done on MSI gaming laptop, with i7 9gen CPU, 16RAM and GPU GeForece 1050).

My suggestion, - go for the second hand cam which you will be able to use for guiding later, play with it on some galaxies and planets and if you decide to stay in hoby, later get the better mount or smaller scope and move from there.

 

 

Thats a lot of subs for 15 second exposures! (I've seen a lot of examples of astrophotography with 15 second subs on Astrobin, but never that many!). I do have a pretty good computer (similar to yours but 4gb gpu), and which already has 2 SSD hardrives in it (I use to process a lot of video footage from FPV drone flying). I presume part of the reason you had to take so many subs is owing to light pollution (I live under Bortal 4 skies)?

I have no experience with SharpCap but I want to play around with 'live stacking' (EAA). I still don't really understand what demands this will ultimately place on my computer, but I'll work through the problems as they arise.

As for for whether I will stay in the hoby, there is no doubt (I even intend on building an observatory enclosure at some point, but for now a permanent pier will have to do). As for second hand cams, there aren't many available here in Australia (I keep checking but its slim pickings).

Great result b.t.w.!

Edited October 5, 2022 by MichaelBibby

[Adam J]

1 hour ago, RolandKol said:

I just want to insert my 2 pence...
Short exposure DSO imaging is a real headache mate...

Just in 2 hours you may end up with the amount of 5k or more subs (16-32mb each), later stacking will take ages and software may even freeze or crash...
(not even talking about selecting best images, - blinking is not the option... Any other solution will also take ages, so you will end up dropping all images into the stack blindly).

Unless you have lots of patience and good hardware to process all of that.

You can read my experiences of a similar imaging below (process was done on MSI gaming laptop, with i7 9gen CPU, 16RAM and GPU GeForece 1050).

My suggestion, - go for the second hand cam which you will be able to use for guiding later, play with it on some galaxies and planets and if you decide to stay in hoby, later get the better mount or smaller scope and move from there.

 

 

16gb is not enough that'd for sure. I have 32gb on my laptop and can saturate that. But in terms of stacking I use app and it weights the subs by fwhm / star shape. 

[RolandKol]

28 minutes ago, MichaelBibby said:

I presume part of the reason you had to take so many subs is owing to light pollution (I live under Bortal 4 skies)?

Actually no.

The reason was, -  I simply could!

More data is always better than less, as you will want to get as much SNR as possible.
I had 2 clear nights, - and used them... Just keep in mind, I have not used all 6 or 7 hours on the target per night as my backgarden was very strickly covered with the treas and etc...
5k short subs, - can be done easily  during one night (depends how short they are), just count ~6h per night, usually DSO images are done per several sessions or even split into years... One night image is kinda, test image.
As per live stacking, - sadly, cannot advise... I am more than sure, it will be ok with 15 - 30sec, but cannot tell anything about the shorter ones.

P.S.

Thanks

Edited October 5, 2022 by RolandKol

[MichaelBibby]

I'

On 05/10/2022 at 01:50, vlaiv said:

Ok, so here are a few guidelines then. You mentioned that you are a technician, so I won't shy away from technical stuff then. I'll also be very brief and to the point as there is a lot to cover.

Regardless the fact you'll be using short exposures - anything expressed in seconds rather than milliseconds is long exposure as far as seeing is concerned. For long exposure, here is breakdown of what you can expect in terms of resolving the target.

There are three main components to the blur affecting the image.

1. Seeing - expressed in FWHM in arc seconds, and represents full width at half maximum of Gaussian profile approximation to seeing blur. It is measured with very large aperture on very good mount in course of 2 seconds for exposure (see - as soon as we step into seconds - seeing averages out).

2. Mount tracking / guiding performance. If you don't guide - this is nothing more than a guess. I'll give you some guides on what you can expect from HEQ5 type mount later on. If you guide - then you have measure of how good your tracking is and is expressed in RMS error in arc seconds.

Two are related by simple equation FWHM = 2.355 * RMS (for Gaussian profile). We always use Gaussian profile for approximation as it is fairly accurate approximation (central theorem) and easy to work with.

3. Aperture size. Here we approximate Airy disk with Gaussian profile. It holds true for perfect aperture but in reality, especially when using correctors (which correct over whole field but deteriorate on axis performance) this blur is somewhat bigger. When available spot diagram RMS is good alternative (and often more precise if one is using correctors or reducers).

Once we have all three values (measured or estimated) - total blur is square root of sum of their squares. This lets us get estimate for expected FWHM of stars in our image - which is in turn tightly related to sampling rate (as stars are point sources and their profile is directly representing PSF of blur).

Very simple relationship that you can use (but math behind it is not so simple) - is sampling_rate = FWHM / 1.6

Good seeing is 1" or below - that does not happen often. You have several websites that offer seeing forecast - and it is usually fairly accurate if you make sure you don't have any local influences (that can be very detrimental) - like properly cooled optics, no seeing disturbances around - like hot roads or large bodies of water or houses with heating and chimneys and so on.

More often seeing will be around 1.5"-2.0". That could be taken as average.

As far as mount performance goes - unguided performance usually depends on two things

a) periodic error

b) poor polar alignment

People always seem to blame poor polar alignment for star trailing - but in my view and experience - periodic error is much more responsible for star streaks and mount poor performance.

With either of the two you must estimate drift rate and limit your unguided exposure depending on wanted resolution (one you are aiming at).

For HEQ5 you can safely estimate that periodic error is about 35"-40" peak to peak. In fact, I once did recording of unguided performance of my HEQ5 and here is what it looks like:

Up down motion is periodic error (and you can clearly see how it periodically repeats - hence the name) - right to left drift is due to polar alignment. You can clearly see that PE is much larger in magnitude over shorter periods of time than PA error.

HEQ5 mount has period of 638s and if you have say 35" P2P periodic error - that means that mount will need to trail / lead - or drift in general for 70" (there and back again by Bilbo Baggins ). If drift is uniform (and it never is as seen from recording) then you would have drift of 70" / 638s = ~0.11"/s

This is important number - as drift due to periodic error will sometimes be more than this and sometimes less than this. If you take this to be reference then in 30s exposure - you will have ~3" of trailing on average. Half of frames will be less than this but half will be more.

You will probably discard worse than this (or even at 3" trailing). In fact in above recording you can clearly see how in some subs stars get elongated while in other are round. I think I used 1 minute exposures there on my HEQ5 (1200mm FL and 3.75um pixel size).

This is so that you can understand that there is percentage of subs that you will have to throw away if you don't guide and that percentage will depend on your tolerance for elongated stars and exposure length that you'll be using.

Back to resolution.

We have seeing that is around 2", when you start guiding - you can expect stock HEQ5 to guide at about 1 RMS, and we have 8" of aperture. If you use simple coma corrector - you'll get spherical aberration on axis and star bloat, but for sake of simplicity lets go with diffraction limited scope.

In those conditions - your final SNR will be ~3.14" FWHM or that will be about supporting 1.96"/px resolution. That is about 9.7um pixel size (so you know how much you'll have to bin based on initial pixel size - at least x3 if using 2.9um).

Further - most galaxies are rather small in size. Someone mentioned trying M82 - which is about 11' long or 660".

With 2"/px - that is only 330px. I'm just letting you know what you can expect. And that is with guiding (stock mount). Just tracked - you probably won't achieve 2"/px resolution due to additional blur.

I'm not saying this to put you off - but rather to prepare you.

If budget is tight - you might consider using simple web camera for guiding and modifying your finder scope for that role. Any sort of guiding will be better than no guiding at all.

On the other side of spectrum - when you tune and mod your HEQ5 - best you can hope to achieve is around 0.5" RMS guide error.

I once managed to go as low as 0.36" RMS and have a screen shot to prove it

But list of modifications that I did to my mount is:

1. All bearings replaced for SKF high quality ones

2. Mount cleaned, regreased, tuned

3. Periodic error correction recorded and applied (in EQMOD)

4. Saddle replaced for Geoptik dual Vixen/Losmandy variant

5. Rowan belt mod

6. Berlebach planet tripod

If we have diffraction limited 8" scope, 0.5" RMS guiding and happen to image in 1.5" FWHM seeing - we can hope to achieve about 2" FWHM or about 1.24"/px.

Even at this resolution - most galaxies will be just few hundred pixels across, and that is about as good as you can get (maybe down to 1"/px - in ideal conditions and with better mount and larger aperture).

In the end - I want to explain one more thing - when I say that you should aim for say 2"/px because that what your setup / sky can support - that does not mean that you can't image at 1"/px or even 0.5"/px. Sure you can, but two things will happen:

1. you will record image that is very devoid of detail when viewed at 100% zoom - since you are over sampling

2. As soon as you start over sampling - you are starting to have slower system than if sampling properly. Light is spread over more area and each pixel receives less photons / less signal. Less signal means less SNR, and astrophotography is all about SNR.

If you want large galaxy image (devoid of detail) - then I advise you to sample it properly to get best SNR and them simply enlarge image in software - result will be the same as far as detail goes - neither can pull detail out of thin air.

 

Excellent information, thanks, you've given me a good headstart on getting my head around all the relevant maths, especially as it applies to my use case.

Re the mount, its already got the belt mod, and I started sourcing all the upgraded bearings before I even bought the mount, knowing that I'd have to put a bit of work in to squeeze the most out of it. And it will be permanently attached to a pier (which I've nearly finished building) so that polar alignment shouldn't be an issue (one less variable to worry about), and shielded from the wind. While I've got your attention @vlaiv, what grease did you use on your Heq5 pro?

I guess I'm realizing the need for guiding (your animation demonstrates the problem of periodic error beautifully), and will probably pursue that sooner rather than later as I initially imagined. I understand that very good seeing conditions are quite rare (it wasn't until many outings with my 8" dob, under Bortal 3 skies, that i eventually experienced extremely good seeing conditions and realized for the first time the joy of visual astronomy-- that moment when the optics and atmospher disappear completely from view and reveal, in their perfect transparency, the glory of the heavens with a crystalline clarity, ah!).

I think I'm just going to give this camera a go. Others are getting pretty good results with this camera at similar magnification and short exposures (EAA/EEVA) on mounts that are less than perfect. Worse case scenario I will on-sell the camera, loose only a small amount of money, and would have benefited from the learning experience. Right now, I just want something to play with so I can get started. And if I leave it any longer I wont have the money to buy a camera. I'll update this thread after I've had a play with it (will probably take a while though, firstly because of the wet weather were expecting in the months ahead here in Australia, and secondly because I need to learn all the programs and processes).

Michael.


 

Edited October 6, 2022 by MichaelBibby

[vlaiv]

10 hours ago, MichaelBibby said:

While I've got your attention @vlaiv, what grease did you use on your Heq5 pro?

I really don't remember. It was nothing special - just some decent (but rather no name) lithium grease.

Mechanical parts in mount don't really experience any sort of extreme - no very high temperatures, no high pressures, no high speeds. Maybe worst extreme is sub zero temperatures in winter - but that is probably no concern for you given your location.

That means getting just decent lubricant that will mostly stay in place (no oils or runny stuff).

10 hours ago, MichaelBibby said:

I think I'm just going to give this camera a go. Others are getting pretty good results with this camera at similar magnification and short exposures (EAA/EEVA) on mounts that are less than perfect. Worse case scenario I will on-sell the camera, loose only a small amount of money, and would have benefited from the learning experience.

Sure, why not. You might even decide not to sell it.

At some point I made similar decision and purchased ASI178mmc. It is versatile little thing - can do planetary, can do guiding, although it is very bulky for guiding as it has cooling. I did some long exposure imaging with it (but on much shorter focal lengths of 380mm), and it is now in wide field role (well actually waiting for me to be in the mood to go actively out again and do some imaging).

I paired it with Samyang 85mm F/1.4 lens on AZGti mount that was converted to EQ (just added wedge, CW bar and firmware with EQ mode). I think it will be cracking combination for wide field.

[Enceladus Dan]

@MichaelBibby hiya Michael, did you get the ASI585mc? If so how did you find it.

Im looking for a first dedicated astro cam as a stepping stone from my DSLR. Ive seen youtube reviews which make this camera look like a good starting point, without breaking the bank on larger cooled versions. 

At some point I aim to end up with something like the ASI294 Pro, be it the OSC or mono, but this will be further down the line. While looking at the ASI585mc I did see the ASI533mc uncooled. Double the sensor size, which I'm liking the idea of, as I'm not using goto a wider Fov would be easier to find my targets, but it also seems to offer similar low read noise, zero amp glow and low dark current as the ASI585mc. 

I tried to find a compassion of the 585 & 533 which brought me to this thread. But I've not found anything which really shows the 533 uncooled other than the pro versions, I'm hoping it's as good as the 585, meaning I can use it as a good first dedicated cam. 

If anyone has seen or used the uncooled ASI533mc, could you let me know your opinions. 

Thanks

Danny

[RolandKol]

20 minutes ago, Enceladus Dan said:

@MichaelBibby hiya Michael, did you get the ASI585mc? If so how did you find it.

Im looking for a first dedicated astro cam as a stepping stone from my DSLR. Ive seen youtube reviews which make this camera look like a good starting point, without breaking the bank on larger cooled versions. 

At some point I aim to end up with something like the ASI294 Pro, be it the OSC or mono, but this will be further down the line. While looking at the ASI585mc I did see the ASI533mc uncooled. Double the sensor size, which I'm liking the idea of, as I'm not using goto a wider Fov would be easier to find my targets, but it also seems to offer similar low read noise, zero amp glow and low dark current as the ASI585mc. 

I tried to find a compassion of the 585 & 533 which brought me to this thread. But I've not found anything which really shows the 533 uncooled other than the pro versions, I'm hoping it's as good as the 585, meaning I can use it as a good first dedicated cam. 

If anyone has seen or used the uncooled ASI533mc, could you let me know your opinions. 

Thanks

Danny

Are you planning to use it for DSO or Planets (short exposure imaging only?).

If DSO, - maybe check the second hand cooled cam market also.

[Enceladus Dan]

Hello Roland, it will be for DSO imaging. I use a dslr so far and looking for a good starter dedicated cam to learn with. 

I have a smaller asi462 I use for planetary. 

[RolandKol]

24 minutes ago, Enceladus Dan said:

Hello Roland, it will be for DSO imaging. I use a dslr so far and looking for a good starter dedicated cam to learn with. 

I have a smaller asi462 I use for planetary. 

Just, trying image myself in your shoes... Once I would get un-cooled cam, few months later, I will want to test the cooled one... Curiosity... I would not be able resist...

At the end, I would spend twice...

Not sure about you.

P.S.

And even further more... Goodness... The same would happen about Mono and Colour...

Not pushing, but just think about it... 

As far as I know, all people in astro hobby are curious....

My suggestion would be, the most painful, but the cheapest in the long run... Jump to cooled mono.... maybe not today... maybe in April.. But if money is an issue... 

it is probably the best way in a Long run.

 

Edited October 18, 2022 by RolandKol

[Enceladus Dan]

I put away each month, and next month I'm buying Pixinsight. I've just on a trial and i find it way better than DSS and Gimp. Maybe more so because I don't fully understand gimp. 

I have thought of the jump in deep end approach to save in the long run, but I get carried away and before I know it there is £2-3k in the basket for a cooled mono with all the filters and wheel. 

I'm gonna take a small step with a smaller OSC to get to grips with them, I tried it out with my asi462mc on M57( took some finding without goto on a 6x3mm sensor), I didn't know quite what I was doing and the subs were all blown out. Now I've read up and a bit more aware about the bit depth and full well capacities. It's a bit more obvious I was going to over saturate. 

I know that I will probably soon after want the mono, but while saving ( aprox 10-15 months) I can enjoy the colour while learning. 

Thanks 

Danny

[RolandKol]

1 hour ago, Enceladus Dan said:

I put away each month, and next month I'm buying Pixinsight. I've just on a trial and i find it way better than DSS and Gimp. Maybe more so because I don't fully understand gimp. 

I have thought of the jump in deep end approach to save in the long run, but I get carried away and before I know it there is £2-3k in the basket for a cooled mono with all the filters and wheel. 

I'm gonna take a small step with a smaller OSC to get to grips with them, I tried it out with my asi462mc on M57( took some finding without goto on a 6x3mm sensor), I didn't know quite what I was doing and the subs were all blown out. Now I've read up and a bit more aware about the bit depth and full well capacities. It's a bit more obvious I was going to over saturate. 

I know that I will probably soon after want the mono, but while saving ( aprox 10-15 months) I can enjoy the colour while learning. 

Thanks 

Danny

yep, sadly this hobby does not bring money!  and works in opposite manner...

Out of curiosity, I've checked both cams (585 & 533), and as you already stated ,  -  main differences are resolution and pixel size, slight difference of Full Well, which you will not notice unless you will go for EAA. (for example, one of the most famous ASI1600 full well capacity is more than twice less and most people are happy with it)

However,  you missed, - it is 14bit vs 12bit...  Asi533 (14 bit ) will have around 4 times more dynamic range... 

for  additional $100 I would take 14bit for DSO for sure, I would even test it for EAA

Plus, in my personal opinion, it has much nicer FOV with 150PDS than 585

As per scaling, both cams will perform almost the same.

P.S.

@vlaiv can make much better comparison on the paper, I just hope I have not missed much.

[Enceladus Dan]

Yes I forgot to mention the 14bit, was another factor that I favoured the 533 for. 

I don't really understand how all the charts will impact the end result, but the 533 to me seems better at a slight cost of higher dark current noise. How it will impact me? I have no clue, but for sure it's got to be better than my 600D. 

I see plenty of videos and images for the 585 as there seems to be a hype for it at the moment, but all I get when I look for 533 examples is the pro cooled. If it is pretty similar I'm gunning for the 533 i think. 

I did read vlaiv comments in this thread too on oversampling. I kind of get it, trying to work out the seeing was a whoosh over my head moment. So I googled seeing forecasts and cheated. My area at the moment shows seeing as 1.2-1.8. So guessing this is particularly good example I'll be very slightly under sampling, if it goes to anywhere from 2-4 I'll be in the green according to the calculator on astronomy tools. 

[MichaelBibby]

Just on the price, I can get the 585 for $615 Australian (which I have purchased directly from Player One), but the uncooled versions of the 533 are nearly double that price.
 

2 hours ago, RolandKol said:

yep, sadly this hobby does not bring money!  and works in opposite manner...

Out of curiosity, I've checked both cams (585 & 533), and as you already stated ,  -  main differences are resolution and pixel size, slight difference of Full Well, which you will not notice unless you will go for EAA. (for example, one of the most famous ASI1600 full well capacity is more than twice less and most people are happy with it)

However,  you missed, - it is 14bit vs 12bit...  Asi533 (14 bit ) will have around 4 times more dynamic range... 

for  additional $100 I would take 14bit for DSO for sure, I would even test it for EAA

Plus, in my personal opinion, it has much nicer FOV with 150PDS than 585

As per scaling, both cams will perform almost the same.

P.S.

@vlaiv can make much better comparison on the paper, I just hope I have not missed much.

 

[Enceladus Dan]

What did you think of the 585?

Here in the UK it's £430 for the 585 and £670 for the 533, so extra £240 for double the sensor, which I hope will be just as good. 

[MichaelBibby]

1 hour ago, Enceladus Dan said:

What did you think of the 585?

Here in the UK it's £430 for the 585 and £670 for the 533, so extra £240 for double the sensor, which I hope will be just as good. 

Haven't had a chance to test it yet (clouds as far as the eye can see, extending infinitely far into the future, gah!). And I have no experience with astro, so I am not the person to ask. I know its not the perfect camera for my use case, but it seems like no such camera exists right now, but I do think that it should be a good compromise.

[Enceladus Dan]

Thanks, I may just go for it. The 533 looks good from the little I know. Only one way to find out by the looks of it. 

Hopefully you get some clear skies some time soon. For me it seems the clouds know when I'm working and tease me on days I can't get out at night.