Is using the video mode on my DSLR as good as a webcam?

[evilgeenius]

Is using the video mode on my DSLR as good as a webcam? My DSLR (well, technically a Micro four thirds camera - GH1) has a higher resolution and can do 60fps. Should I be able to get better results on lunar/planetary targets?

[RobH]

I have wondered about this myself....looking forward to some answers

Rob

[JohnnyD333]

At Prime Focus you should get great shots of the moon. Planetary might be out of range, unless you go the afocal method. Webcams are convenient because they fit right into your focuser, are comparable to a 3mm EP, and can be adjusted and viewed from the computer. I have gotten some descent results holding my DSLR up to the eyepiece and taking a video. But at Prime Focus you dont get that zoom that the webcam provides. Also, webcams are much cheaper than even a point and shoot camera.

[bigal1]

I have tested this out with my canon 1000d and once in video mode you can use the zoom function on the camera which at 5x is quite good and helps to bring in the targets and very helpful for live viewing / outreach .

[RobH]

It seems to me that a DSLR should be fine in video mode, even for planets. If you want better image scale, simply use barlows like you would with a webcam.

I'd assumed that there was some reason it wasn't done, as I don't remember seeing any high frame rate planetary or lunar images done with a DSLR in video mode.

I haven't tried it so stand to be corrected of course

Cheers

Rob

[Mike Hackenbacker]

i use my compact camera to shoot video and stills.without a remote start i use the 10sec countdown timer,as it takes about 5 secs for vibration to stop,as i use a camera bracket i can preset the zoom before shooting movies,then its hands free for shoot,i am not sure about DSLR'S as i have only had mine a couple of months and still figuring it out.maybe some of the other experts here can answer your question..

[RikM]

Isn't the file size huge from a DSLR video out? A 4 min avi from a little Philips webcam is about 2Gb.

[virtualpilot45]

I'd have thought it would be smaller, as webcams don't compress the data, cameras may.

[26Left]

I tried video mode on my DSLR without much success. The problem is that, even at it's highest resolution, my camera only makes 1280 x 720 videos, but the sensor is over 4000 pixels wide. So, the effective pixel size becomes quite large. I tried Barlows, but this brings its own problems - focussing is very difficult because I could not see the image on the live view.

In the end, I gave up, because I could not get the image scale good enough.

[THome]

The videofiles from you GH1 are practically unsuitable for stacking because this uses an AVCHD compression codec. This has two major problems for astro use:

- Firstly, AVCHD is a so called "Long GOP" codec. This means that while you think you are shooting with 60 frames per second, only one in n frames is actually stored entirely in the video stream (i believe one in 15). The frames in between are derived from the differences with these reference frames. In the proces compression will discard most of the subtle changes you would want to retain for stacking.

- Secondly, AVCHD uses "chroma subsampling". If i'm not mistaken of the 4:2:0 type.

This indicates that for every four pixels of luminance data, only two pixels of chroma data are recorded horizontally and only one vertically. Instead of a 1280x720 video you thus have 1280x720 luminance, and only 640x180 chroma.

In some cameras the HDMI output is less compressed, and you could use this to record the videostream with lossless recorders. But these are very expensive.

[evilgeenius]

I am using a hack for my GH1 so I can get data rates upto 100Mbps, compared to to the unhacked rates of 17Mbps. This uses a GOP rate of 12. The hack also allows me to use 4:2:2 chroma for the mpeg codec.

There is a "Fast Action 3-Frame GOP" patch that I could use which would increase the GOP rate, with peak bit rates upto 60Mbps.

[THome]

As long as you can edit these custom videofiles (which may be out of standard specifications) and convert them to separate frames or uncompressed AVI, I would say give it a go ! The 4/3 system has a cropfactor of two i think. Image size on the sensor would be a little larger relatively than on a Canon DSLR.

Does this hack also allow you to increase your video bit-depth from the standard 8 to 10 (or even more) ? This would improve your dynamic range significantly.

[philwright66]

i have found the video crop mode on my canon 550d to be excellent on jupiter,but not very good on saturn.here is a jupiter image from last autumn,taken through a w.o. flt110 + 1.4x teleconverter.