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Requesting I.T. wiz's advice on laptop capability for planetary imaging.


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I currently own a 6" maksutov on a tracking mount and have had some pretty decent views of Jupiter & Saturn, despite their low altitude. This lead me to thinking I'd like to try a spot of "lucky" planetary imaging and I recently came very close to purchasing an astro-modded DSLR (Canon 550D with movie crop mode) on the basis that I could also use it for DSO imaging.

I received some pretty solid advice in another thread suggesting the 550D wasn't up to much and a dedicated astro camera would be a better bet. However, this put the stops on things for a while as I didn't class myself as owning a laptop........

Well, that was not quite accurate, more that I didn't own a "capable" laptop. I have now recovered, from the darkest depths of the back of "the cupboard" an ACER netbook I purchased a few years back which I basically never used because it was DEATHLY slow.

The netbook is of such low spec that Windows could not even update due to a lack of storage space available to download the updates! However, I used the Windows media creation tool to install the latest version of windows vis usb to get around this and normal updates seem to be completing successfully since. I think the latest version of windows also supports downloading updates to external storage, so hopefully this issue is resolved.

I have also run Windows10 de-bloater, updated the BIOS and all windows drivers. I installed a few programs on the SD card and they run fine, but the card kept un-mounting (a common W10 issue I believe) - rolling back the SD card reader driver to an earlier version seems to have resolved this and the SD card now seems stable.

 

Lets throw some specs down.......

Intel Celeron dual core 1.6GHz N3050 (2.2GHZ turbo)

2GB DDR3L SDRAM (not upgradable)

32GB SSD (not upgradable)

1X SD Card port

1X USB2 port

1X USB3 port

 

My concerns are mainly about data transfer rate.....

 

The internal SSD @ 32GB only has about 6GB of usable space after removing everything other than critical windows components. From what I have read, planetary imaging generates a LOT of data so writing to the internal SSD is not an option. As such I have been investigating other storage options and have done some data transfer rate testing using Crystaldisk benchmark.

1. Internal SSD write speed for reference - 70MB/s

2. Internal SD Card port - Write speed with a 10MB/s card was 10MB/s. I don't know what the upper write speed limit of the port is though, so buying an expensive SD card could be a waste of money and I'm not sure if it shares the same BUS as the USB3 port.

3. USB3 pen drive in USB3 port - 17MB/s

4. USB3 External HDD in USB3 port - 100MB/s

 

I have a few options. 

1. Sink a good few £££'s into a high speed large capacity SD card to use in the SD card reader hoping that the port is capable and it runs on a different BUS to the USB3 port. 

2. Use external storage via the USB3 port, but the camera will also use that port necessitating a hub. My assumption is that using a HUB will bottleneck data transfer as the camera will be trying to write through it and the external drive trying to read through it.

 

The problem I have is that I do not know, nor can find, the sort of data transfer rates that typical planetary cameras such as the ZWO's require to operate at full speed. FYI - I am considering the ASI178MC or ASI385MC.

 Can anyone with decent I.T. knowledge/planetary imaging experience shed some light on the transfer rates required and using the camera and external drive via a hub? 

Does the internal SD card port have an upper write speed limit, or is that just dictated by the card specification?

Does the PC actually have to do much processing during imaging or is it just shifting data between the camera and storage device?

 

Thanks for taking the time to read such a long post - I'd appreciate any advice as I don't want to sink £300 in to a camera only for the laptop to be useless.

Cheers,

Jon

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A Pi4 8Gb would be faster & much more capable than the Celeron PC, but it would necessitate learning about some new OS/software etc.

Personally, I'd have a look out on eBay for a used laptop, with an i7 processor, at least 8GB memory, 300-500 GB hard disk and at least 2 USB 3 ports and USB 2 ports, also wired (ethernet) / Wifi connectivity...  e.g. https://www.ebay.co.uk/itm/144251216148?epid=16036394839&hash=item21960ae114:g:i80AAOSw2gphO4--

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I should have mentioned in my original post - I don't want to/can't spend on another laptop at this time. I'm  on the verge of a career change that come with a 40% pay cut in the short term so I really should be saving 😈 The purpose of my post is to understand whether what I have got is capable, if not the whole idea will have to go on hold unfortunately.

Edited by parallaxerr
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I believe that what you already have, will only cause you frustration as it tries to cope with the load you are trying to put on it, so no it would not be capable....  Start saving for a new/used laptop, or go balls out for the Pi4 route !!

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You really need to invest in a new(er) laptop, as your old one is clearly inadequate. I recently bought a Dell Vostro 7th gen I5, 8GB memory, 250GB SSD (mainly brand loyalty as I already had an older Vostro).  It is decidedly quick and has enough storage for several night's imaging, and it has three USB3 ports, which match the later ZWO cameras with their USB3 ports.   Also wifi and Internet port. It cost about £130. No need to buy any hubs or SD cards.

The SSD had enough space for a suite of astro programs as well as Win 10. Win 10 needs at least 4GB of RAM (8 Gb preferred).

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I was really hoping to hear some actual empirical observations and some actual information around the camera data transfer rates. If, for example, someone could state that a transfer rate of 20MB/s is enough to sustain 60FPS at a certain resolution, I'd be better informed because I can measure what I've got.

To be clear, I'm not being obstinate, but I'd like to make a decision around trying my laptop first based on real data and weighing up the risks with regards to expenditure. This is after all just an initial toe dipping into planetary imaging.

So often I see threads advise new gear as a first response and the OP questions never get answered. Perhaps someone else will chime in with some data, otherwise I guess it's down to me to take a punt!

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Unfortunately it's nigh on impossible to give you empirical data, as stand alone figures would be meaningless.

Without having your equipment to test with, and knowing what other events/applications/buffering that the PC is doing, will greatly influence any results etc. 

Manufactures sometimes offer data transfer rates, but this is only from the device under test to the receiving computer and not writing to any local/remote storage.

So by all means, give it a go with what you have, to see if it will work...  one of the reasons it may be perceived that we only offer 'equipment upgrades', is that we do have the experience of trying to do what you want, and have found that in the end, for useable performance, especially with modern hi res cameras etc., the easiest route is also to upgrade the computing devices as well as the imaging devices.

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Thanks Julian. You're right in as much as there are many other contributing factors that affect performance. 

I have mailed ZWO to ask what the transfer rate from the camera is at a certain bit depth and FPS. I'd just like to have a feel for something - if it's 200MB/s for example, then I know my lappy is a non-starter. 10MB/s on the other hand may mean it's worth giving it a go.

 

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For the ASI294MC camera, ZWO publish the specs (below) and even selecting the lower bit rate, the highest transfer rate, under IDEAL conditions, is 19fps, but in REAL world conditions that will drop significantly especially when adding in mount control/guiding etc.

Sensor: 4/3″ SONY IMX294 CMOS
Diagonal: 23.2mm
Resolution: 11.7Mega Pixels 4144X2822
Pixel Size: 4.63µm
Bayer Pattern: RGGB
Exposure Range: 32µs-2000s
ROI: Supported
Non-volatile memory/On camera storage: Build-in total 192K byte user-accessible space(image size up to 480X320)
Interface: USB3.0/USB2.0
ST4 Guider Port: Yes
Focus Distance to Sensor: 17.5mm
Shutter Type: Rolling Shutter
Protect window: AR coated window
Operating System Compatibility: Mac, Windows, Linux
Interface: USB3.0/USB2.0
Bit rate: 12bit output(12bit ADC)
Adaptor: 2″ / 1.25″ / M42X0.75
Dimension: φ62mm X 36mm
Weight: 120g or 4.2 ounces (without lens)
Working Temperature: -5°C—45°C
Storage Temperature: -20°C—60°C
Working Relative Humidity: 20%—80%
Storage Relative Humidity: 20%—95%
Max FPS at full resolution:
12Bit ADC
4144×2822 19fps
14bit ADC
4144×2822 16fps
More resolutions can be user defined

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I've asked about transfer data rate in MB/s in order to assess my storage options, not frames per second. This should help me to understand how far off I will be from achieving the quoted FPS.

Edited by parallaxerr
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As a concrete example, taking a 5000 frame shot of Jupiter with an ASI224MC camera and C8, Sharpcap and a USB2 port laptop results in a 350Mb file recorded in about 20 secs at around 250 frames/sec. That's for a 320x240 px reduced frame.  Exposure per frame is about 2ms.

Recording a full frame of 1304x976px takes proportionately longer.

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1 minute ago, Cosmic Geoff said:

As a concrete example, taking a 5000 frame shot of Jupiter with an ASI224MC camera and C8, Sharpcap and a USB2 port laptop results in a 350Mb file recorded in about 20 secs at around 250 frames/sec. That's for a 320x240 px reduced frame.  Exposure per frame is about 2ms.

Recording a full frame of 1304x976px takes proportionately longer.

Excellent, thanks Geoff! So that's 17.5MB/s transfer rate, something solid to work with.

If I extrapolate out your quoted resolution vs what I intend to run with my intended camera, I get 280MB/s @130FPS.

I'm seeing 100MB/s with my external USB3.0 HDD, so that would be bottlenecked to 46FPS and maybe halved if using a hub, so 23FPS.

I'm prepared to be shot down on those calcs as there are so many other factors that affect things, but it gives me something to consider!

 

I read a post on CN where a user got the same transfer speeds to internal SSD and external HDD via a hub with camera also connected, so I think it's feasible. He said he suspects that the internal SSD was connected to the same USB3 controller as the external port, which makes sense.

 

In my case, it's interesting how my external HDD beats the internal SSD on write speed. Maybe the internal SSD is on the same USB2.0 BUS as the SD card reader.

 

 

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For a comparison, the 550D on raw video movie crop mode will write at 21mb/s regardless of card (camera limitation), so i would assume your write speed is good enough.

51 minutes ago, parallaxerr said:

Excellent, thanks Geoff! So that's 17.5MB/s transfer rate, something solid to work with.

If I extrapolate out your quoted resolution vs what I intend to run with my intended camera, I get 280MB/s @130FPS.

I do wonder why you have the need for increased resolution if this is the limiting factor? ADC bitrate also plays a large part in file size, you can lower this in many cameras to increase framerates. 

 

Really what concerns me is the capabilities of the laptop, it might not be able to handle high framerate video of really any resolution.

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32 minutes ago, ONIKKINEN said:

I do wonder why you have the need for increased resolution if this is the limiting factor? ADC bitrate also plays a large part in file size, you can lower this in many cameras to increase framerates. 

I chose the ASI178MC based on the usual recommendations of working to certain sampling rates etc. It has small pixels hence the higher resolution, but I would reduce the frame down using ROI most of the time, saving full resolution for times of exceptional seeing where it could be used with a barlow (laptop permitting).

This actually suits better than a larger pixelled camera which would need to be barlowed on normal nights, reducing the amount of cropping available. I calculated the ASI385 would need to be barlowed for critical sampling and would thus actually run slower because the ROI would be bigger.

32 minutes ago, ONIKKINEN said:

Really what concerns me is the capabilities of the laptop, it might not be able to handle high framerate video of really any resolution.

Likewise this is my concern hence the questions. Most posts I have read suggest the laptop is doing very little processing during capture, it's just a data throughput. Note that the laptop will not being doing anything else, no guiding or mount control for example.

I'd be interested to hear what CPU loads people experience during capture with programs like ASICAP, Sharpcap, FireCapture etc.

Edited by parallaxerr
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For the data rates the camera is outputting you can think of it like this:

  • When capturing in RAW8 (which is what you should be doing for planetary), 1 pixel = 1 byte.  So say you have a 400x400 RoI that's 160,000 bytes which is 0.16MB for a single frame. 

So if you have 10MB/s of transfer rate capability you'll get 10/0.16 = 62 fps.  Obviously other factors may affect this.

Don't think that a camera with smaller pixels will have a smaller RoI than a larger pixeled camera, and hence will have smaller files to transfer.  The smaller pixels mean a smaller RoI (in terms of square mm) but there's still the same number of pixels within that RoI, and it's the number of pixels which dictates file sizes.

In terms of costs and affordability, have a look at used kit.  I recently sold on here a QHY462C for £175 and a rather good USB3/SSD laptop for £125.

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1 minute ago, CraigT82 said:

For the data rates the camera is outputting you can think of it like this:

  • When capturing in RAW8 (which is what you should be doing for planetary), 1 pixel = 1 byte.  So say you have a 400x400 RoI that's 160,000 bytes which is 0.16MB for a single frame. 

So if you have 10MB/s of transfer rate capability you'll get 10/0.16 = 62 fps.  Obviously other factors may affect this.

Don't think that a camera with smaller pixels will have a smaller RoI than a larger pixeled camera, and hence will have smaller files to transfer.  The smaller pixels mean a smaller RoI (in terms of square mm) but there's still the same number of pixels within that RoI, and it's the number of pixels which dictates file sizes.

In terms of costs and affordability, have a look at used kit.  I recently sold on here a QHY462C for £175 and a rather good USB3/SSD laptop for £125.

Good stuff, thanks Craig. I thought pixel size may be an influencing factor!
So each frame in my case would be 1.2MB, with the external HDD running at 100MB/s, most likely half that with a camera sharing the port. Certainly gives me some confidence to give it a go.

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Further testing with my laptop and a much newer external 10TB HDD I use for bulk storage returns transfer rates of ~250MB/s. However, using dummy cameras in Sharpcap and FireCapture I'm only seeing 30-40FPS, so as many of you have said, there are other factors at play. Interesting point to note was that CPU load was minimal during these tests, but a "real" camera may change that.

 

I also received a response from ZWO on how to calculate the transfer rate in MB/s which some may find useful......

 

"Here is the formula for your reference, it's only in theory.

If you choose RAW8,

Transfer rate = resolution's width* its height*1*max fps/1024/1024

RAW16:

Transfer rate = resolution's width* its height*2*max fps/1024/1024"

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