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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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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. 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.
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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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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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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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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.
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By way of a follow up - thanks for the advice guys, I decided against the 550D. I have revived an old laptop so a dedicated camera is on the cards, but I am concerned over the specs and performance, so I started a more specific thread to address those questions here -
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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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The reason for choosing the DSLR is because I don't have a laptop to run a planetary camera. Nor, to be honest, do I have any other reason to own a laptop so by the time the cost of one is added in, the DSLR becomes the cheaper option. However, @ONIKKINEN has pointed out some real drawbacks that I was unaware of, thanks for the info. More thinking time required....
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Hi Tomato, The camera will be running at 640x480 in movie crop mode, so I believe tor FoV will be more like this.... As you can see, any vignetting at this FoV may affect the image. However, given that this is the central ~40% of the chip by pixel area, I kind of think the 1.25" nosepiece will be OK. Just wondered if anyone had any first hand experience. I can always try with a 1.25" and a 2" nose peiece. The 2" option just leads me down a more expensive filter route and possibly a new focuser....and I don't need much encouragement to buy one of those 😂
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I'm planning on purchasing a Canon 550D for planetary imaging with my 150MAK. For a few reasons I would like to stick with a 1.25" nosepiece, mainly so that I can use my 1.25" micro-focuser and also to keep the cost down on a UV/IR cut filter. The question is, will I experience any vignetting with this setup? POINT TO NOTE - the camera will be operating in movie crop mode, so 640x480 pixels. For this reason, I think it will be OK, but I am not 100% sure. TIA, Jon
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Modified DSLR for planetary imaging?
parallaxerr replied to parallaxerr's topic in Imaging - Discussion
Thanks Michael. The particular camera I'm considering has the hot mirror removal mod leaving only the clear protector over the sensor, so I think that basically means it's full spectrum.