Lunt 60PT B1200 - QHY5-II Mono

[Robny]

I have finally got around to using this camera with my Lunt after having the camera so long. I used a calculator (sky at night) and it indicated that I should achieve full disc images, I was using sharpcap and was unable to achieve a full disc, I was clipping top, bottom and sides quite significantly. Is the fov calculator wrong or did I not have the software configured correctly, I ensured it was the correct camera selected first.

My other is question is, I noticed lots of dropped frames while recording, could this be due to the USB cable? I was using the cable supplied with the camera, do I need a powered hub to overcome this or could it be some other reason for dropping frames?

Could the two issues I'm having be related?

Will pay a beginner PIC soon.

Many thanks.

Rob

[Davey-T]

Never had a QHY5-11 but the sensor may not be big enough for a full disc in the Lunt LS60, I bought a Skyris 274 to achieve a full disc with mine.

Just checked the QHY5-11 should achieve a full disc, I use Firecapture are you sure you haven't got a ROI selected ?

Dave

[JamesF]

The QHY5L-II sensor is about 4.8x3.6mm.  The Lunt 60 looks to have a focal length of 500mm.  At 500mm you'll get an image scale of 513 arcseconds per mm, giving you a field of view of about 2460x1845 arcseconds.

The angular diameter of the Sun varies from around 1900 (northern hemisphere summer) to 1950 (northern hemisphere winter) arcseconds so it's never going to fit by the looks of it, especially if you want a reasonable amount of room around the disc for picking up proms and so on.

Doesn't sound right that you should be clipping the image as much as you think though.  I'd have thought a two-pane mosaic should be possible.  Perhaps the focal length is longer, or perhaps you're not operating the camera at full resolution?

I'm not entirely surprised you're getting dropped frames if you are running the camera at short exposure times and relatively high resolutions though.  There's just not enough bandwidth on the USB2 bus to transmit that much data without something going wrong occasionally.  The ZWO ASI120MM (using the same sensor) is the same, whereas the USB3 version of the same camera has no real problems at all.

James

[JamesF]

Never had a QHY5-11 but the sensor may not be big enough for a full disc in the Lunt LS60, I bought a Skyris 274 to achieve a full disc with mine.

Dave

Yup, the 274M sensor is 8.5x6.8mm, giving a field of view of 4360x3490 arcseconds which is clearly plenty big enough.

James

[michael.h.f.wilkinson]

Curious. My old ASI130MM had the same sensor as the QHY5-II, and it should fit. The QHY5L-II has a smaller sensor (is this perhaps your camera?)

[Davey-T]

If you look at the FLO FOV calculator the QHY5-11 shows as plenty big enough to capture the full disc.

The QHY5L-11 clips the sides a bit and top and bottom a lot.

Dave

[JamesF]

Curious. My old ASI130MM had the same sensor as the QHY5-II, and it should fit. The QHY5L-II has a smaller sensor (is this perhaps your camera?)

I made that mistake, Michael.  Well caught.  I'm a bit lacking in sleep due to the rather humid weather

James

[JamesF]

Hmmm.  I wonder if you're not right though.  I wouldn't personally bother adding "mono" to "QHY5-II" because that's all there is.  I might with the QHY5L-II though, as it comes in both colour and mono.

James

[Davey-T]

Here from FLO calculator

Dave

[JamesF]

That suggests that even with the QHY5L-II you should be able to get about 2/3rds of the disc in a single frame, so it may well be that the camera isn't at full resolution?

James

[David Smith]

Were you capturing using the full res of the sensor (1280 x 1024)? I don't use sharpcap so not sure how you check or alter the setting but you can use the camera at several different settings from something like 400 x 400 up to 1280x1024. I use mine with a PST (FL=400mm) and the full disk easily fits in the frame at the 1280x1024 setting.

Cable that came with mine has been adequate, how fast is your pc? At low res the camera can spit out some fairly high frame rates (170fps).

[michael.h.f.wilkinson]

Quite apart from whether or not the camera gets the full disk, you will be losing resolution by working at prime focus (many aren't worried, but I am a resolution junky). By using a Barlow or tele-centric lens, you can match the focal ratio to the pixel size of the camera. I then stitch multiple images into a whole disk image. Not only does this give you a better resolution (at the expense of more data capture and processing time), but sweet-spot issues are much reduced, due to the smaller area of the image plane being used.

[Robny]

Thanks for all the feedback, it has given me something to go of at least

Curious. My old ASI130MM had the same sensor as the QHY5-II, and it should fit. The QHY5L-II has a smaller sensor (is this perhaps your camera?)

It is definitely not the L version as at the time I decided not to pay the extra money as I had planned to be using it as guide camera only, things changed.

Were you capturing using the full res of the sensor (1280 x 1024)? I don't use sharpcap so not sure how you check or alter the setting but you can use the camera at several different settings from something like 400 x 400 up to 1280x1024. I use mine with a PST (FL=400mm) and the full disk easily fits in the frame at the 1280x1024 setting.

Cable that came with mine has been adequate, how fast is your pc? At low res the camera can spit out some fairly high frame rates (170fps).

I was capturing at full res, but the most amount of FPS achieved was around 15 max down to 6 min

Quite apart from whether or not the camera gets the full disk, you will be losing resolution by working at prime focus (many aren't worried, but I am a resolution junky). By using a Barlow or tele-centric lens, you can match the focal ratio to the pixel size of the camera. I then stitch multiple images into a whole disk image. Not only does this give you a better resolution (at the expense of more data capture and processing time), but sweet-spot issues are much reduced, due to the smaller area of the image plane being used.

Interesting, I did not know that - need to read further into this, any interesting links you recommend on this?

I'm not entirely surprised you're getting dropped frames if you are running the camera at short exposure times and relatively high resolutions though.  There's just not enough bandwidth on the USB2 bus to transmit that much data without something going wrong occasionally.  The ZWO ASI120MM (using the same sensor) is the same, whereas the USB3 version of the same camera has no real problems at all.

James

Is there anyway around this or just something I have to live with?

Additional Info

I am using a VERY sturdy pro photo tripod and video head, okay for observing but not ideal for imaging, I know that.  I think if the if it is very tight to get the full disc then this may have been my problem not being able to move the mount smooth and in small enough movements to actually get it in the frame, and besides if I did it probably would have moved out within a few seconds.  I realise that I'm not going to great results like that but at the moment until I get some spare cash I'm just playing with what I have.

As promised here is what I have been able to achieve at what essentially is my first attempt at using the QHY5 to image with the Lunt with some REALLY DODGY processing can only get better right?

This was taken 30th June taken of the prom on the NE limb as you look through the scope

Rob

[JamesF]

Is that the full resolution of the video you captured?  You've not cropped it down?

James

[Robny]

Is that the full resolution of the video you captured?  You've not cropped it down?

James

No, that is cropped - in fact I had to crop it because I only managed to get the image captured at the bottom of the screen (my fault I guess), because when I saw that prom I was set on capturing that instead of the full disc.

[Robny]

Is that the full resolution of the video you captured?  You've not cropped it down?

James

This was pretty much raw from the video

Capture 30_06_2015 16_01_09_pipp.tif

[JamesF]

That looks like there's plenty of room to get the full disc if you have the image properly centred on the camera sensor.

James

[Robny]

I think so too now looking at it, the difficulty is having video head I think and trying to keep it there, the movements required are not intuitive and it ends up all over the place. 

[Robny]

Okay feel a bit of a fool, I had not had the view on Sharpcap zoomed out, so it looked like it was cropped but I just need to scroll the screen, now I have found where to adjust the zoom