parallaxerr

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"

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.

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.

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.

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.

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.

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!

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.

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 - 

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

On 01/10/2021 at 21:25, david_taurus83 said:

Why not just buy a colour planetary camera in the first place? Be much better frame rate and will work no problem with 1.25" focuser.

On 02/10/2021 at 00:34, paul mc c said:

As David says can't compare to a dedicated planetary camera. 

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....

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 😂

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

12 minutes ago, michael8554 said:

If only the #LPF-2 filter has been removed to increase Ha response, the remaining #LPF-1 will filter IR.

Only the white balance will have altered, easily corrected in PS etc.

Michael

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.

Another question for anyone that may know - When using the movie crop mode of a Canon DSLR, am I right in saying the framing/scaling changes as in the image below? 

The green FoV is with the camera sensor at full frame and I adjsuted the the red Fov to 640x480 pixels (movie crop mode). Is this right?

15 minutes ago, CraigT82 said:

For planetary you can always stick a uv/ir cut filter in the imaging train somewhere. 

Thanks for the info Craig.

In hindsight, I think I've read this before, but as usual I have melted my brain with research!

So I can use an astro modded DSLR for planetary with a UV/IR cut filter and without for DSO.....bargain 😀

I'm pondering a new (to me) DSLR for planetary imaging with my 150mak. I don't wish to use a laptop, so I have identified the relevant Canon models with movie crop mode to access the 1:1 pixel ratio.

The question is - should I wish to image DSO also (with my refractor), it would be best for the camera to be astro modded to increase red/Ha sensitivity. Would this affect the planetary imaging? Is this a done thing or do the planetary and DSO imaging disciplines require different cameras?

TIA, Jon

Reaching for the 🍿 🤣

Well John, you read my mind.....

I just flocked the baffle tube and did rather a good job, if I do say so myself. Removed the backing so it's stuck in there nice and straight and even.

I switched out the 2" diagonal for a 1.25" which has re-established a good balance, actually slightly front end heavy with the dew shield on.

More to your point John, I couldn't find stock of the baader, so I ordered the cheaper option of a ZWO microfocuser and 1.25" nose piece. Should look quite snazzy with the red Altair diagonal.

3 minutes ago, Pixies said:

Flocking the baffle tube shown here:

I did similar for a Mak90. I removed the backing and stuck it against the inside of the baffle tube, rather than letting it rest in place. I found the best way was to wrap it around a pencil, sticky-side out, and then press it against the inside of the baffle tube and run the pencil in the opposite direction that you rolled the flocking material, pushing outwards as you go. The FLO flock isn't too sticky and makes this easy. Didn't need much!

 

That's great, thanks. Looks like the flocking offers a significant improvement in contrast too!

4 minutes ago, Louis D said:

That's usually caused by reflections off of the interior of the rear baffle tube.  Try putting flocking material in it.  Generally, just roll it up in a tube after cutting it to length and push it up in there without removing the sticky backing covering.  Friction will tend to keep it in place.

Thanks Louis. As luck would have it, I recently ordered a fresh roll of flocking material, I'll try this tonight 👍

I've been lucky enough to get 1st, 2nd & 3rd light with my new Orion 150mm Maksutov this week. Had some great views of Jupiter so far when the seeing allowed, managing to catch both Io and Ganymede transit shadows and re-apperances on the limb

Optically, I am very impressed but I have identified a few small issues with the scope I wish to resolve:

1. The focuser is not great. There's a reasonable amount of mirror shift but more importantly a horrid little notch right around the point of focus. This is leading me to consider a crayford focuser.

2. Balance - it's already back end heavy with a 2" diagonal so adding a focuser will just make this worse. I am also considering a dovetail clamp mounted counterweight for the front.

3. There's a small floating donut shaped ghost reflection on bright objects - assuming it's the primary reflection.

Given that I am considering the focuser upgrade which will exacerbate the balance issues, a lighter diagonal may be in order.

Would a 1.25" prism diagonal (Tak) help with the reflection I am seeing, as the prisms are often touted to reduce scatter etc?

Well, an order has been placed for a new planetary scope.....

The only 180 Mak I could find was a Celestron, which I very much would have liked, but came in at £1450 🤯

Found C8's at £1099 but I've been there and done that. Best view of Jupiter was with one, but still over budget.

Considered the 8" CC but think the mount would have been stressed with the weight and couldn't get over the CO of the 6" (not that it would likely be a problem in reality).

I do like a lens scope and always wanted to try a mak (I did briefly once when I was new to astro but didn't really know what I was doing), so having watched and waited for stock to arrive over the last few weeks, I just plumped for one of these 6 inchers....

With the left over budget, a Baader Steeltrack may very soon find it's way onto the back. But I'll hold out until I've tried a bit of lunar first.

Excited 😀

26 minutes ago, badhex said:

Now I'm worried that only taking lower quality gear means I won't be getting the best of a rare opportunity to observe under really dark skies

I would actually say quite the opposite. What you will do is squeeze every last bit of performance out of the inexpensive gear and likely will be so impressed with the views that ED glass, for example, wouldn't make much difference.

My very best views EVER were under very dark skies in Southern France using a WO 66mm refractor and a 32mm plossl, that's literally all I took! I ticked off more of the Messier list that night than I had managed before, or since for that matter. Image scale was small but the contrast made up for it!

Thanks John, you have certainly helped me along my astro journey!