We’ve had reports from customers of a black or blank preview screen, or “no frames in preview mode” particularly with the high-megapixel cameras.
This is usually due to USB bandwidth limitations on the PC or laptop you are running the camera on, and is not necessarily a defect in the camera.
The frame rate appears “stuck”:
When it should be incrementing like this:
Tip: If your exposure duration is set too long it may appear as if the camera is stuck when it’s actually waiting for the next frame. First try reduce the exposure time to about 30ms and see if the frame rate changes.
We’ll explain the solution shortly but first we should explain what’s going on. The Hypercam 183C for example, has a 20mp sensor which by astronomy standards is very large. What makes this camera special is that it can be used for solar system imaging in video mode (outputting a video file) as well as deepsky imaging (subframes). The video data is not compressed like a DSLR (which is a good thing) and the camera produces .FITS files too (a very good thing) but this can put a high demand on your USB bandwidth, because each RAW frame contains a lot of data about the object you’re imaging – a lot more than a conventional camera.
Here’s an example of frame size with the Hypercam 183 camera:
Hypercam 183C has a resolution of 19,850,560 pixels. In RAW8 and MONO8 mode, (planetary imaging) that would equate to 19,850,560 bytes (at 1 byte per pixel). In 12 bit RAW and MONO modes (although, the sensor ADC can only produce 12bits), the final frame is stretched to 16bits to work with standard image processing software. Therefore it could be up to 39,701,120 (2 bytes per pixel for anything more than 8 bit depth). In RGB mode it would be 59,551,680 (3 bytes per pixel) in .FITS file format.
That’s a pretty big frame by any standards. Therefore, in some situations, the PC cannot accept the current frame, before the next frame is due.
Symptoms: This causes the preview window to show a blank black square in video mode, dropped frames, or a halt in the capture sequence in deepsky image sequence mode. Often you’ll be able to “jog” the camera back into action by disconnecting other USB devices on the same Host controller (an internal device which manages your USB connections) or by reducing the resolution using the ROI, or resolution dropdown menus for example. If reducing the resolution results in the camera restarting, then you know it’s a bandwidth issue. Tip: Bear in mind the longer the exposure and the higher the bit depth, the slower the frame rate in video mode! If nothing ever appears in preview, no matter what settings you try, we recommend you check you’ve got the latest drivers running, try swapping cables, or try another PC, just to make sure there isn’t a larger issue.
The solution: There is a Frame Rate control panel in AltairCapture, which reduces the USB speed. If you’re getting a black screen, dropped frames or halts in imaging sequences, reduce the Frame Rate until the camera is operating smoothly and the frame counter starts to increment again. You can do this in video mode. As an experiment, try increasing the speed until the camera preview halts. This speed is the most your computer can handle at that resolution. Reducing the resolution, using ROI or binning can get the camera running at a higher frame rate than normal full resolution. Removing other USB devices and making sure the PC is not in USB standby mode can also solve the problem. Tip: Remember that if you choose a faster frame rate, or less “gaps” between your images in a sequence, you are putting more “pressure” on the computer to download the frame before starting the next one, so testing in video mode should be done with the fastest possible exposure time.
Computers and hardware: Generally but not always, machines made in 2013 or later, with an Intel xHCIv1.0 USB3.0 host controller are the fastest and the most error-free. Helpful astronomy enthusiasts have been gathering data for various machines on the Altair Google Technical Support Group. Check out the sticky post here.
As a general rule, machines with the Renesas v1.0 and v0.96 host controllers (pre 2013) have been found to have to USB bandwidth issues. Avoid them if possible. Here’s how they appear in Device Manager:
This is because the USB3.0 device drivers only came out in 2012. Many older PCs can have their device drivers updated to 1.0 which helps. Some but not all. For example, in our experience Lenovo W250 workstations with Renesas host controllers can have updated drivers installed which improve compatibility with high bandwidth USB3.0 devices, but Lenovo W510 workstations cannot, because the updated drivers do not exist for that model.
This Intel USB Host controller is a better bet:
With desktops, it’s cheap and easy to update your PCI card with a more modern chipset and drivers, and even a £10-15 unit can outperform a laptop costing a couple of grand on a cheap desktop, so that’s another thing to mention!
There are also many cheap machines which work extremely well with no issues, for example a Toshiba laptop costing £150 on eBay! Please help fellow astronomers post your experiences on the USB speed/compatibility thread in the Altair Google Technical Support Group.
Note: Additionally we’ve found that machines with multiple host controller architectures appear to work better than single host architectures. Perhaps they have better bandwidth.
Using the free USBTreeView software (opens new window) you can get a picture of what they look like: