MicrobeHunter.com Microscopy Forum

I have a 10 mp Omax USB camera, which takes good stills of stationary objects, but distorts moving objects. A moving object will have each individual part in focus, but the whole image is bent out of shape. The front (say) is in one place, but the back has moved away from it's original position, relative to the front, even if the true shape hasn't changed.

I think that this is due to the time it takes to send 10 mp of data over a usb2 line, and that all of the image processing is done in the computer. In other words, the sensor updates continuously, so the data from the end of a scan represent a later time than one from the beginning.

The Omax camera works well for stationary objects, but distorts ones that move. I have a DSLR that makes better stills of moving objects, since all of the data are captured at the same time on the sensor, and then they are read and the data are transmitted to a monitor via an HDMI cable.

Two questions:

1) Am I right in my analysis that the problem is the relatively slow USB2 connection?

2) Omax has some USB3 cameras for sale. Would the shorter transmission time for USB3 reduce this problem? Has anyone had experience with the USB3 cameras?

I'd really like to know if replacing a USB2 camera with USB3 would worth the investment (about $300).

Some may be due to the USB 2 connection but do you know what the frame rate is for the camera? I am just guessing but I have USB3 and an Amscope 3MP USB camera and it was no good for video.

Have never tried my DSLR. Prefer stills.

JimT

I think most good DSLR's will take both video and stills. That's not my problem. I'm only interested in stills at the moment.
(BTW, my Canon T3i works very well for both.)

The problem is that stills are messed up if the subject moves; it looks like the CCD is being read sequentially at the rate the data can be transmitted over a USB2 connection, so you might see the front of the critter at one time, and the back a second later. This makes for a very odd picture.

Would USB3, with it's much faster transfer rate, remedy this problem?

JimT wrote:Some may be due to the USB 2 connection but do you know what the frame rate is for the camera? I am just guessing but I have USB3 and an Amscope 3MP USB camera and it was no good for video.

Have never tried my DSLR. Prefer stills.

JimT

Hi Jim, I'm thinking of a 3 or 5mp USB3 Toupcam at this time as the sheer convenience of this system beats the Canon 1200D for my particular type of image - i.e. stationary mounted slides. What do you think of your 3mp USB3 camera old chap?

Hi,
I myself have a USB 3 Toupcam (5MP). I was/am experiencing trouble connecting it with USB 3 speed, it will often connect only with USB2 speed. It is probably a driver problem. I wrote an article about it here: http://www.microbehunter.com/microbehun ... -issue-53/
The camera itself is fine.
Oliver.

Thanks Oliver for the link!...

BillT

I believe that this problem is probably due to the camera having a "rolling shutter", which means that each line of data on the camera chip is read out at a slightly different time to the next. Even very high end sCMOS cameras can have this feature, and it makes acquisition of live images problematic.

https://en.wikipedia.org/wiki/Rolling_shutter

The frame rate of USB 2.0 is certainly not the problem, at least not on cameras that capture the scene at the same time for the whole chip.

So. Using a USB camera can be complicated. Taking still images of moving critters (to use the scientific term) can be difficult because of the details of how the computer and the USB camera interact. The camera manufacturer has no control over the computer hardware and drivers, of course, which can make for confusion. Camera X may work with my Windows 10 desktop, but not a (nominally) similar laptop.

I gave up on the USB camera and bought a Canon EOS DSLR, which takes excellent video as well as still images. Since all of the processing is done in the camera itself, it gets done quickly. Also, the Canon has an HDMI output, so I mounted a monitor near the microscope and get a large real-time image.

One downside of of using a DSLR is the expense of the trinocular heads and the fancy adapters (the Meiji ones cost over $200).

Interestingly enough, I've found that video images of vorticella or stentor can show the cilia quite clearly, while they're still blurred in the still images. Are there any good USB cameras with both good spatial resolution and fast frame rate? In the $100 range, not $1000.

Can anyone suggest a USB3 camera for this work? If so, I may have some used Meiji adapters for sale at very reasonable prices.

Barlowax is spot on. It is most definitely a "Rolling shutter" phenomena. All DSLRs and other cameras experience this as it has to read the CCD/CMOS line by line and while doing so the object moves. Some advanced (and expensive) cameras have solved this by "stacked censors" or a global shutter. Normally, cameras have a buffer memory to at least buffer one or more images coming from the sensor, so USB2 or USB3 would make no difference. It is the cameras ability to read the sensor fast enough (to the buffer) that would determine how bad the rolling shutter effect will be.