Guider Download Speed.

[multiweb]

What are the requirements to maximize subs download on a guider?
Fast CPU, Minimise USB cable length, not using a USB hub but a dedicated line? Just shooting in the dark here. What do you guys reckon? :question:

[Terry B]

I don't think that the USB cables will make any difference really. The only thing that is significant is the size of the frame being downloaded. Using a subframe selected around the guide star meaning that only a few pixels need to downloaded. This makes guiding possible even through a parallel port camera.

[Octane]

Marc,

A USB issue I had with the STL -- USB cable through USB hub and then to netbook -- the system was having a hard time coping with the amount of data coming down. I removed the hub from the equation, and everything started working smoothly.

H

[Bassnut]

I found the QHY5 download speed fine at 2 sec exposures, why the question?, are you having trouble with it?.

[multiweb]

QHY5's fine. I got a SX-Lodestar to drive my AO. I need to optimise transfer rate in order to send the maximum amount of corrections per second. The lodestar is sensitive enough to pick up a faint star at F/10 on the C11 with an OAG at 0.2 or even 0.1s exp, so now the bottleneck is the cables, hubs, etc...

[Alchemy]

I see my question is answered, hope you don't get a bottleneck, I find 0.1 sec updates unlikely myself...... Still you never know.

[Bassnut]

Ahh, I see. Tried binning?. Can you drag a small box around the star or something to select a smaller downloaded image?.

[multiweb]

Yes I bin 2x2. I use the SX software at this stage. I haven't managed to get the AO detected in MaximDL yet. Got v5.10 over the week-end. I also ordered a new USB Serial adaptor see if it makes a diff. Fail this and I might have to update the AO firmware. Shame coz I'm so close now.

[JohnH]

Marc, I think you have hit the nail on the head - use subframes for this guide rate. It also seems that short usb cables no hubs and a fast PC are in order (a netbook is probably not an option for AO) binning 2x2 might be a good idea as well depending on the arcsec/pixel ratio of imaging to guide frames.

[multiweb]

Last night was clear but a nightmare . USB/Drivers conflits.. in the dark. Just what I needed ... NOT! Turned out one 5m USB2.0 extension I bought is what's known as an active cable. It is detected by the laptop as a USB device when plugged on it's own in any port. All sorts of bells ringing... GBUSP dropping when guider's plugged in or when imaging camera was downloading subs. Packed up at 8:20pm :P All sorted out now trying again tonight.

[Barrykgerdes]

Oh dear!

That will ensure clouds tonight!

Barry

[multiweb]

Hope not. :)

[bert]

Just to throw a spanner in the works. On wednesday night I got a very bright guidestar and I was sitting on .01 second exposures and 32 hertz correction rate using the internal guide chip on my sbig camera and AO8, bin 2.

My sbig camera is usb 1.1, uses a belkin powered hub and an active 5m usb cable. Processor is dual core 2.4ghz. I did notice a slow down in the correction rate when the cpu is in use by some other application.

Marc I am not sure if the lodestar does subframe exposures... I know that my ssag does not.

Brett

[multiweb]

Wow! 32Hz? Smokin'! :lol: :thumbsup:
Subframes? You're asking me too much. I don't have a clue. At the moment I'm barely getting the AO to talk to the mount still. Using the SX software. Maxim DL doesn't play nice with me as yet.

I did a session last night with the AO at 10Hz and kept the guidestar within the Lodestar FOV by hand guiding 120s subs in Ha. Was in moderate to high wind and at F/10. 0.70asp . Got round stars. Nice.

Tonight I'm doing it again but this time I have PHD/QHY5 guiding on a finder through a separate port and the AO/lodestar doing their thing independently on another hub. It worked on the bench so tonight will be first light hopefully. Hand guiding is definitely not for me. 15min of it drove me nuts. :P

[bert]

Marc, if you do get it to work in maxim you can set the threshold that bumps the mount. I have it set at 5% deflection, so the mount gets bumped once the tilt passes 45 or 55%.

Maxim also allows for dithering via AO. Very handy for noisey cameras.

[multiweb]

I think the maxim thing is a driver issue coz I can connect and poll the AO from the COM port with a range of different utilities. It's just MAXIM DL that chucks a fit. I'd be interested to see how any other MAXIM users connect their AO.

[marki]

Thanks for pointing out the issues with maxim Marc. Just last night I was thinking about the starlight setup but will put it on hold until I see if you get it sorted. Best of luck :thumbsup:

Mark

[Bassnut]

With DL (and SBIG anyway), when guiding starts, the image frame is automatically reduced around the selected guide star to a settable size just big enough for the star to stay in the tiny frame so that the download speed is much higher. You can also drag a box around an object to manualy select a smaller image.

Im guessing a subframe like this is required for any fast AO. SX must have a way of doing this somehow, do they mention that on there site, or in the manual?.

[multiweb]

When I have it working in DL I can't see why not but I have some drivers issues with DL and the AO at the moment.

Well last night I finally got a good run and everything worked as intended.

I got the AO/Lodestar working on one hub and guided the scope with PHD/QHY5 on a separate hub, same laptop. All worked together fine. Did a couple of test fields and stars were nice and round(ish). Still some camera tilt and minor collimation issues.

Couple of things I gathered along the way that might be of interest to other users about USB cables, Hubs, etc... I did some speed measurements so here it goes:

1_ USB hubs powered or unpowered don't seem to have an effect on data transfer speed. The only issue is if a device down the chain is power hungry but most cameras have a separate power supply and guiders don't need much to run. A 4 port hub's fine. Haven't tested on a 7 port hub. Might need to be powered.

2_ Cable length and quality do have a major impact on USB speed. Two cables might look similar and be branded USB2.0 but when you actually time the amount of data going through you'll see difference up to 20% improvement on a good quality shielded USB cable. So don't skimp on cable quality. Spend the money there, no on the hub.

3_ USB active cables tend to conflict with other devices when plugged in a hub. Passive cables don't. Took me a while to figure out but active cables when first plugged in are detected by the OS as USB device and drivers are installed. A passive cable will plug outright just as a connector with no bells and chimes. Might be why there's no conflict.

4_ Active USB cables have less packets drop out when talking to serial devices via USB to serial adapters. On inititial connection as well. So that's why maybe it's best to use an active cable over long distances.

[bert]

Marc,

Did you get the subframes to work with the lodestar?

Just out of interest how does the AO work with the starlight system in maxim. With the sbig AO, I simply connect the camera as 'Sbig usb with AO'. Maxim brings up a ao control window as well as the camera control window. Is this the same as with the sx system?

Brett

[multiweb]

I have used it only with the SX software. It does render only a portion of the guider window maybe 50x50pixels that the AO uses to move. I haven't been able to connect the AO in Maxim DL 5.10 with the SX universal drivers. I am not sure if it's a driver problem or a limitation of Maxim at this stage for not using a SX camera with the AO.