MichaelBibby

Hi, thought I'd reach out for some advice on building a housing to protect my Heq5 mount from the weather. My concern is with the wide temperature variations at my location, ranging from -1 degrees C right up to 45 degrees C, and the summers are very wet and humid.
My thinking is to completely house the mount in a plastic container to protect it from moisture and then to create another housing around that container (made of plywood) to shield it from the sun and allow air circulation (aided by a cpu fan powered by a solar panel) to keep the temperature inside the first plastic container down.

Here is the mount on the pier (the mount is orientated that way to fit inside the container):

A 'dry fit' of the inside plastic container (a bin):



And here are my plans:





Any suggestions or advice? Will this solution be adequate? One problem I can see is the base of the housing, which would extend around the pier, getting in the way of visual astronomy, but I'm primarily interested in EEVA. 

 

All finished, pretty happy with the results (apart from my shonky brick laying). Used a disc brake for the adapter. Ended up using a piece of pipe to prevent mortar filling in the holes while laying the bricks and then filled the cavities with concrete and the 1/2" threaded rods. And capped the whole thing off with some concrete.

On 07/10/2022 at 06:18, Hedlund said:

Around 500-600$ if its possible

The 585 is very well suited to your 750mm focal length (pixel size 2.9um). The 533 would also be a great option (I think the pixel size is about 3.88um, and a larger sensor than the 585), and ZWO are about to release an uncooled version which might just be within your price range.

Note: I don't have any experience with astrophotography, I've just been looking into similarly priced camera's, but for 1000mm focal length. I opted for the 585 because it seems well suited to my use case, which is video astronomy/EAA/EEVA.

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.


 

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.!

15 minutes ago, happy-kat said:

Was your other suggestion the sony because you already own it?

No, I could get a pretty good deal on one, thats why.

21 hours ago, vlaiv said:

Don't think so, but that is my opinion.

Since you are starting out, I would advise you to go for 1.8"/px resolution.

With focal length of 1000mm that translates into ~8.72um pixel size.

That would mean that you should get 4.3um pixel camera and bin it x2 or maybe 2.9um camera and bin that x3.

Now ASI585 might seem to fit the bill - with its 2.9um pixel size, but have you checked field of view on that camera with 1000mm of focal length?

First - since it has 3840 x 2160 with bin x3 you'll actually get 1280 x 720 image size. Second, and probably more important - you'll get very small field of view - only 0.64 x 0.36 degrees.

Ideally when starting you want something that is middle ground like 2x1.5 degrees or similar.

Thanks for your feedback vlaiv. I know the field of view of the 585 at FL 1000mm (I've been using this tool as well as Stellarium to get a sense of all that: https://astronomy.tools/calculators/field_of_view ). I'm most interested in imaging galaxies, which is why I opted for a 8" 1000mm over the more convenient 6" 750mm. I knew I was going to involve myself in difficulties, but I like challenges. I know that with guiding and careful balancing the Heq5 pro and 8" f5 can work quite well for exposures of a couple of minutes, but a lot of things have to go right for it to work out. I'll 'hypertune' my mount before I make any serious attempt at long exposures, within the limitations of an uncooled camera. And I do plan on exploring off axis guiding down the road too. Right now, I just want to play with some EAA with sub 30s exposures, and only intend on imaging when seeing conditions are quite good.

Money is a limitation, and right now I can't see a better camera option than the 585 for that price point. My main concern is that oversampling will be my biggest limitation, but my understanding is that under very good seeing conditions, using short exposures, this setup could work quite well.  ? But I am open to other camera suggestions (the uncooled 533 is probably a little too expensive for me, nearly twice that of the 585).

 

Thanks Adam, I understand that would have made a more reliable and versatile combination. I knew what I was getting myself into putting this hulking scope on this mount, and took it as a challenge to see what I can get out of this setup. It will be mounted on a pier, shielded from the wind, under Bortal 4 skies, so I have some things going for me. I'll only explore guiding once I've pushed the limits of my tracking setup first. I'd love to have a second telescope for widefield imaging, and longer exposures, eventually too.

Thanks guys, appreciate the time your taking helping me to understand all the variables. I'm a technician so capable of understanding all the details, just need to dedicate more time to it. And now you've given me some more lines of inquiry to follow up.

44 minutes ago, vlaiv said:

https://www.teleskop-express.de/shop/product_info.php/language/de/info/p15858_.html

Not translated into English yet.

There is also official ASI version, but won't be available from TS for next 12 days:

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p15856_ZWO-Farb-Astrokamera-ASI533MC-ungekuehlt--Chip-D--16-mm---3-76--m-Pixel.html

Thats great! I know that a lot of people would be interested in an uncooled 533. Given my FL of 1000mm the 3.76um pixel size would be perfect.

So now I wonder: would the larger pixel size of the 533 offset the lower read noise of the 585?

17 minutes ago, Adam J said:

You want low read noise, note that the ASI533mc is now available uncooled. But I believe you will get lower read noise with the Uranus C. 

I can't see any information about an uncooled version of the 533 anywhere, I imagine that would be big news if true.

Something else I only just learnt is that the a6000 doesn't work with SharpCap, which is a problem...
 

13 hours ago, PeterC65 said:

Both the ZWI and Player One IMX585 based cameras have High Conversion Gain mode. With the ASI585MC it kicks in a a gain of 252 and with the Uranus-C it kicks in at 180. From what I understand, the accepted wisdom is to operate the camera at a gain just above the HCG / LCG switching point as this is the best compromise between read noise (reduces with gain), dynamic range (reduces with gain), full well depth (reduces with gain) and the overall SNR of the image (increases with gain).

I chose the Uranus-C over the ASI585MC as a result of the difference in the HCG / LCG switching point. There is a longer discussion here. I've only been able to use the camera once so far, so I'm not yet decided on the pros and cons, but the Uranus-C is a well-built camera and I prefer the hexagonal body as it allows me to know how the sensor is aligned.

 

 
Thanks Peter, I have been following that thread. I guess what I am realizing is that what I am wanting to do is EAA (live view, live stacking, short exposure times, etc.,). And it seems like the 585 might be a good fit ('compromise') for my setup (whereas the a6000 would cause me a lot of headache's owing to Sony's incompatability with Sharpcap).
But I thought I saw you say somewhere in that threat @PeterC65 that the P1 version would have better s/n performance than the ZWO version, is that still your assessment? For very short exposures at high gain would you recommend one over the other?

2 hours ago, Adam J said:

You would use it at gain 400 but the player one version looks better for this type of imaging. As above though 1000s of subs are required. 

I suppose your talking about the 'High Gain Conversion' mode on the Uranus-C which kicks in when the iso is >180 and helps to reduce noise while preserving dynamic range.

Thanks, that might be a great option.

I've created a separate thread to address the specific question of 585mc vs a6000 for my setup here:

Zwo asi585mc or Sony a6000?

I have a 8" F5 (1000mm) Newt on a belt modded Heq5 pro and am interested primarily in DSO.
Given the fact that I'm pushing the weight limits of my mount, and I aren't using a guidescope, I will be limited to short exposures (between 1 - 30 sec). Which camera will make the most of these limitations: the Zwo asi585mc/player one Uranus C or the Sony a6000? And why? I know the 585 has 2.9um pixels and the a6000 has 3.88um which would be more suited to my focal length, gather light faster and be more forgiving of tracking problems, but what other factors/specs should I consider?

Fortunately where I'm building my pier will be relatively shielded from the wind so that shouldn't be too much of a problem 

26 minutes ago, Adam J said:

Honestly I think that would be a great combo for galaxy imaging at high gain / short exposures ~1s to mitigate seeing. 

I didn't think such short exposures were possible with the 585mc at gains with low s/n. My understanding is that the ideal gain setting for the 585mc is about 252 (from what I've read). I was thinking more along the lines of 30 second exposures? Would the a6000 produce better results at these sort of exposure times? Could I expect reasonable tracking with my setup over 30s exposures? (Note: I do intent do 'hypertune' my mount at some point, and really squeeze the most out of it).

Seems like the Sony a6000 might be a good choice-- its pixel size is 3.88um (which is really in the 'perfect' range for my focal length, and more forgiving of tracking errors, especially if using under 30s exposures).

Or if I were to stick to exposures under 30s would that largely mitigate most tracking problems, and produce good results with the 585mc? I wonder how these camera's would compare with that sort of exposure time...

I just discovered this online tool which matches your focal length with ideal pixel size under various seeing conditions:

https://astronomy.tools/calculators/ccd_suitability

This seems to indicate that the 2.9um pixels might make a good match for my focal length in good seeing conditions, but in worse seeing conditions it would tend to fall on the side of oversampling, and from what I understand, oversampling is less forgiving of guiding problems.

I should have said that I live under (about) Bortal 3-4 skies.

(Thanks for the replies, I'm learning alot as I go).

I recently bought a belt modded Heq5 pro mount and 8" f5 (1000) Newtonian telescope and am wanting to get into astrophotography (I have previously owned an 8" Dob, so I am not completely new to astronomy, and I understand the need to maintain good collimation). I'm more interested in DSO than planetary imaging.

Now, with this setup I am probably going to be limited to relatively short exposures owing to the fact that my scope is pushing the weight limits of my mount, that, and the fact that I'm not using a guidescope at pretty high magnification. My main interest is imaging galaxies, and nebula.

Given these restrictions would the zwo asi585mc be a good option? I understand its not ideal (my first preference would be for the 533mc, which, besides being cooled also has a sensor twice the size of the 585), and that its a 'planetary camera', but I have seen people getting great results with it using short exposures on DSO with smaller apertures and comparable focal lengths. Is there a better camera for the same price that you would recommend for my setup?

Any help is greatly appreciated.

I forgot to ask: what do you use the Playstation controller for Roger? Is it to slew the telescope?

Thanks for sharing your project RogerTheDodger. I'm in the process of making a brick pier right now, and I have a very simple question which I'm hoping you can help me with. When you embedded the threaded rode into the bricks did you use the brick mortar or did you use concrete? I'm using bricks with three large holes (like yours it seems) so as to give me enough room to fit the galvanized 1/2" rods I'm using to secure my pier adapter (a disk brake), and my initial plan was to fill the cavity around the threaded rod with brick mortar, but my concern is that the brick mortar might not be strong enough and that concrete might be a better option. Can I ask how you did it? Did you use brick mortar and then some concrete to 'cap' it off with?

Thanks in advance.