I had a chance to test drive a new camera from Point Grey Research, the Dragonfly2. This camera was introduced a few months ago, and it's specs have made me curious to try it for myself.
The PGR people were kind enough to send me an eval unit, and after trying it for myself I've decided to buy one :-)
This camera uses the Sony ICX424AL ccd, the same one as in the Lumenera LU075M. This ccd is known to be low noise and high sensitivity.
In addition, this camera has 16 bit data output, giving much more accurate data when used with a short shutter, and also the non-standard "format7" modes that allow you to roll up arbitrary framerate and shutter settings.
The only downside that I found is that the gain maxes out at 24db, meaning that the image is not as bright as my Dragonfly Express camera that has a max gain of 30db.
In side-by-side tests the Dragonfly2 clearly beats my DMK21AF04 in image quality, likely due to the 16 bit data mode.
Here is a set of three raw frames from one of my test sessions that show the relative images from the three cameras. Please ignore the image quality itself, these tests were done from suburban Canberra and the seeing was not very good :-(
However it is useful to compare the relative brightness and noise present in each image. I think that gives a good idea of the relative merits of each camera.
I hope you don't mind the image dimensions, it's actually a small image so that ok :-)
Pricewise the Dragonfly2 is about $750 US, and the Dragonfly Express is $1100 US. The DMK21AF04 is something like $390 US.
Which one will you use though? I can't see why you'd use the DF2 over the DF Express? The DFEx image is much brighter, and still 16bpp.
I guess it's starting to come down to price and how much you can afford. The DFEx is certainly looking to be the best in terms of sensitivity and noise, but it's also 2-3x the price of the DMK.
Do the dragonfly's come in large format versions with resolution higher than 640x480? It would be interesting to compare these versus the SkyNyx range.
Mike, if you correct for the brightness differences in each image it seems like the DR2 may have less noise than the DX, even though the image will be dimmer.
So the possibility remains that if you boosted the brightness of the DR2 images (in software) to equal the DX then you'd end up with an image with less noise.
Noise is the real limiting factor in these cameras - 16 bit cameras make life a lot better since you still get a reasonably accurate image with very short exposures, but even so it takes a lot of frames to suppress the noise.
The DFE is certainly brighter, but the DF2 seems a lot smoother and containing less noise. I find this attractive for my needs.
The real choice for me now is as you would say Anthony "future proofing".
The DMK has served me well, but I need something with speed, good well charge and image brightness. DF2 looks attractive in price, but it can't deliver the frames I need for the SDM imaging.
It seems that for next year I will be using the DFE at this stage, although I would like a larger format. 640x480 is a bit limiting when it comes to imaging the sun in Ha.
Paul, the DR2 is capable of about 60fps @ 640x480 16bpp, about half the data rate of the DX but still not too shabby.
Your scope would probably be able to use all of that bandwidth, and maybe more - so the DX with it's ability to reach 130fps might be the other option. Some calculations I did a while back show that you could easily use 75fps.
Worth remembering though that using all the bandwidth available , even on normal firewire cams like the DR2, will require a pc that can write to disk at 40Mbytes/sec reliably, and that's still tough to do unless you buy an high performance drive.
And using the DX at higher rates again will mean data coming in at something like 50Mbytes/sec.
I remember DP saying something in a post awhile ago about recording to RAM (or memory) (I could be wrong and I can't find the post) so he was able to get his write speeds up and then when download was finished he then wrote to his HDD.
Can anyone expand on this or have I got it way wrong?
Bird with the Laptop I have now I won't have any trouble downloading at that rate. Well at least that is what seems to be the case. 2Gig of 667mhz of DDR2 RAM, Dual Core 1.87, 5,500 RPM drive; that downloads 30fps from the DMK without even thinking.
So it looks like the DX is the camera for me. The only thing that erks me a bit is that the pixel sizes reduces the size of Jupiter a little. Although this might be advantageous when imaging with the SCT at home (I am looking at getting a C14 for home)
That method Paul tends to cause delays of the same amount of time, which is ok for planets like Mars and Saturn, but not in the case of Jupiter.
as bird said, i have tested the lu075m and 8 bit i can get good rates on my 7200rpm hard drive, but bump it up to 12 bit or 16 bit and 26fps is as fast as i can write.
capture to ram and get 60fps easy, but unfortunately with filter wheels, you need to change runs and each run from memory needs to be written to disk...........something for software to address. bird has accomplished most of this ram capture in linux
How do you do your capture to RAM Dave? While it might not be filter wheel friendly, I could certainly give it a big shove for Ha imaging of the ol' Sol.
the lucam recorder software for the skynyx and lu075m cameras allows for straight to disk or straight to ram, depending on the amount of ram you have spare....it is very quick........
30fps on the DMK is equal to 15fps on the DX or DR2, assuming you'll use 16 bit data on those cameras (which you will, of course).
Bird
Yes this might make some difference, although with 2 gig, I should be able to download most of a video to RAM and while I am capturing the next video it should be writing to disk.
I don't think this machine will take more RAM. ie 2x 2gig RAM modules.
NOTE: I haven't tried this yet, but it sounds interesting. I read a couple of the comments and it seems it works great for some and for others it doesn't work at all.
thanks andrew......i had a quick read through and 32mb as the limit may be a little small.......Birds recent blue channel is 1 gig of data for a single run, but he is capturing at 45fps, most of us are 1/2 that....
So we need to try and get roughly a 1.5g - 2g ram drive setup.....worth some more investigation
Heard back from th PGR guys this morning, looks like they have one of these cameras in stock and will be shipping it to me asap, hope to have it in a week or so...
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