I'm looking at a camera for getting into astrophotography, and the DFK 41AF02.AS has a recommended retail price of US$575, which seems quite decent for a 1280x960 firewire colour CCD. THe DBK appears to be the same camera without the IR cut filter which may be the better option?
What sort of imaging would this camera be suitable for? I know most people go for the monochrome cameras instead of the one-shot colour, and I've read up on the reasons and that all makes sense, but wondering what the colour DFK would be capable of/best suited for.
The reason this one also piques my interest is that I have a need for a colour CCD of decent resolution to use in a film telecine rig (transferring Super8 and 16mm films to Bluray/DVD), and I could afford to spend the money on a camera if it solved two problems so to speak.
Imaging Source cameras (like the DMK/DBK/DFK etc) are great for taking piccies of the planets and the Moon, but aren't so hot for DSO's. Why do you want to by the camera with firewire?? If you have USB, you'd be much better off buying the USB version of the camera. The DFK 41 might be good for a film telecine rig, but if you're going to get one for astropics, you're much better off with a DMK 21 mono and a filter wheel. For planets and such, you want a camera that has a fast frame rate and good resolution. The DMK 21 is the best bet here....upto 60fps and 640x480 resolution. The fast frame rate will help you to "freeze" any unsatisfactory atm' conditions like tube currents, turbulent air etc, so you can get good frames to stack.
However, if you want to take piccies of DSO's as well, you'd be better off using a DSLR or buying a dedicated CCD camera.
Carl has it pretty well covered. I might add the 41 would be used mainly with solar or lunar imaging in mind. For planetary, the 21 is the one you want.
I have the colour one shot (DBK21) & it's a fantastic cam I reckon. I have the mono DMK21/filters/wheel as well, however in my mediocre seeing & very unpredictable weather, the DBK is better for me.
The only difference between the DBK & the DFK is the DFK has a factory fitted IR/UV cut filter whereas the DBK does not. I wanted to use my own filter so my choice was the DBK.
Imaging Source cameras (like the DMK/DBK/DFK etc) are great for taking piccies of the planets and the Moon, but aren't so hot for DSO's. Why do you want to by the camera with firewire?? If you have USB, you'd be much better off buying the USB version of the camera. The DFK 41 might be good for a film telecine rig, but if you're going to get one for astropics, you're much better off with a DMK 21 mono and a filter wheel. For planets and such, you want a camera that has a fast frame rate and good resolution. The DMK 21 is the best bet here....upto 60fps and 640x480 resolution. The fast frame rate will help you to "freeze" any unsatisfactory atm' conditions like tube currents, turbulent air etc, so you can get good frames to stack.
However, if you want to take piccies of DSO's as well, you'd be better off using a DSLR or buying a dedicated CCD camera.
All my current gear is firewire, it just gives me less hassles than USB, but I'd be happy to go the USB route.
I have a Nikon DSLR, so could use that for DSO, I mainly wanted to know if the DBK41 or DFK41 would be any good for astrophotography at all, as I can justify the spend if I can use it for telecine and astrophotography.
I get very dark skies here, and thought the 15fps would be fast enough for planetary playing, but I guess not!
Thanks everyone for the feedback, it was what I expected, but I was hoping that I might be wrong.
Carl has it pretty well covered. I might add the 41 would be used mainly with solar or lunar imaging in mind. For planetary, the 21 is the one you want.
I have the colour one shot (DBK21) & it's a fantastic cam I reckon. I have the mono DMK21/filters/wheel as well, however in my mediocre seeing & very unpredictable weather, the DBK is better for me.
The only difference between the DBK & the DFK is the DFK has a factory fitted IR/UV cut filter whereas the DBK does not. I wanted to use my own filter so my choice was the DBK.
For DSO work, better off with a DSLR I think.
A quick pic of the DBK's capabilities.
Wow! Nice shot of Jupiter. I've finally received the astrophotography book that I ordered, so am going to do some more reading before asking any more questions, I'm still a bit confused why a 640 x 480 camera performs better than a 1280 x 960 one for planetary, I thought with all that light that a higher resolution sensor would give better results. Thanks again, time for me to crack open the books!
Wow! Nice shot of Jupiter. I've finally received the astrophotography book that I ordered, so am going to do some more reading before asking any more questions, I'm still a bit confused why a 640 x 480 camera performs better than a 1280 x 960 one for planetary, I thought with all that light that a higher resolution sensor would give better results. Thanks again, time for me to crack open the books!
Technically it will, but practically, it boils down to the seeing conditions of your site and the image scale of your pics and the target. For any given FL and aperture of scope, the more pixels your camera has the larger the FoV of the image you will be able to capture. When you're targeting the planets, this is crucial because you're trying to image a small target as it is. The planets subtend true sizes of arcseconds in diameter, as opposed to arcminutes or larger for many DSO's. If you try and image, say Jupiter, through the average 10" newt at a typical F ratio of F4.5-6, the most you'll get with a camera like the DFK is a very small dot with little to see across its face except a few cloud bands. With a DMK in the same scope, because the chip is smaller, the FoV will be smaller but Jupiter will fill more of the whole image, giving you a better disk even though you're using less pixels. However, in order to get a pic like the one posted here, you need to increase the FR?FL of the scope to obtain a much larger image scale for the corresponding FoV. To do this you can purchase a good quality barlow lens or even a Televue Powermate, which will effectively boots the magnification of the image. If you were to boost the FR to F15-20 or even higher, your image scale would increase dramatically and give you a good image to play with.
Now, this is where frame rate and pixel count/size come into it. The larger your image and image scale become, the more prone your shots will be to any atmospheric turbulence both inside your scope and outside in the environment. You've basically magnified them as well as your piccie. So, in order to counter those effects, you need the camera to be able to take as many snapshots in a given amount of time, so as to catch those moments when your seeing is clear and stable. Consequently, the faster the frame rate of your camera, the better it will be at doing this. However, because of the larger FR/FL with the barlow/powermate added to your image train, it will reduce the amount of light getting to your camera because the FoV light cone entering the scope becomes effectively narrower. Having a camera with many pixels in this case will be more of a burden than a blessing because only a certain amount of light will be registered by the camera and the dimmer the light, the less that will strike each pixel in turn and therefore your image will be dim. Having less pixels might sound counterintuitive, but because of the smaller number of pixels, in the dimmer light it's actually a case of more photons striking the smaller numbers of pixels and your image will be correspondingly brighter. The faster frame rates of the smaller pixels chips will also compensate far better for tube currents and such and make it easier to process any of them out of your image.
In other words, the higher resolution camera might not necessarily be the best camera for the job, depending on your scope and setup, plus the seeing conditions under which you normally image.
I have both the DMK21 and the DMK41 firewire versions.
Other than the hassle of getting 6 pin firewire connections to the laptop and external 12V supply - they are very good.
I usually image Ha solar and spectroscopy.
To me the frame rate is nice but can be over riden by exposure settings.
ie if you want a stack of exposures for DSO's etc (or in my case faint spectra) you can pump up the exposure to minutes per frame.
For Ha solar I find most of my exposures are around 1/120s for the surface detail and up to 1/11s for the proms.
Ahhh, I think I finally understand the missing piece that is bugging me.
It isn't so much that the DBK 41 has more pixels than the 21, it is more that the sensor is physically larger on the 41 than on the 21?
So the planet doesn't take up enough space on the sensor so you need more magnification to fill 'er up, and that means less light.
So would that mean that the larger the scope the larger sensor/higher resolution you could use as you have more light?
I imagine turbulence is less of an issue in the scope if you have been outside for a lot of hours and everything has stabilised. It seems that way when I am viewing, but I'm not sure if it is just because seeing always seems better at 2am when I should be in bed
Hmmm
Not really.
The image for the same focal length will be the same size on the chip.
You need to consider the plate scale ( sec arc/pixel)
The rule of thumb is you need two pixels to record data.
If the pixel is 5 micron, then the minimum data size is 10micron...
Depending on the plate scale ( 1.2 sec/ pixel)this could be equivalent to say 2.4 sec arc, the image is then made up from "blocks" of 2.4 sec arc bits.
The physical size of the sensor doesn't really come into play until you start imaging large objects ie moon, sun DSO etc etc
HTH
Ahhh, I think I finally understand the missing piece that is bugging me.
It isn't so much that the DBK 41 has more pixels than the 21, it is more that the sensor is physically larger on the 41 than on the 21?
So the planet doesn't take up enough space on the sensor so you need more magnification to fill 'er up, and that means less light.
So would that mean that the larger the scope the larger sensor/higher resolution you could use as you have more light?
I imagine turbulence is less of an issue in the scope if you have been outside for a lot of hours and everything has stabilised. It seems that way when I am viewing, but I'm not sure if it is just because seeing always seems better at 2am when I should be in bed
Tell you what to do....the best way to visualise what I've mentioned is to see it for yourself. Nothing like experience
Go and crab this little app...CCDCalc. Enter your scope's details and the chip size for whatever camera you want to use. Then vary the focal length/focal ratio and see what you get. You can also do that with a variety of scopes, cameras and numerous targets you may want to look at. It's a nifty little piece of software
Planetary imaging is really all about speed and frames per second. The faster you can get your well exposed frames the better. The smaller sensors fill this need quite well, whereas the larger sensors are not fast enough to record enough frames.
Excellent thread this !!
Thanks for the excellent explanation Carl, I have wondered what frame size, ppixels, barlows etc all had to do with the DSO vs Planetary imaging requirments and now I get the picture.
Should be written up as a tutorial and saved forever..
So the wider aperture the scope, the brighter the image and the more light hitting the sensor, so the faster you can grab images to 'freeze' the few moments of great seeing?
Is there an issue with bigger scopes having more internal turbulence or is that not an issue?
Peter that is essentially right. The main reason why Anthony, Trevor and myself use objectives over 14" is for light gathering capacity. There is a significant resolution difference to a 10" of course, but the main objective is light. More light means more frames per second and a faster exposure which freezes the seeing at any one moment.
Large scope do have cool down issues but this can be worked around with TEC (peltier cooling), just like I did here a few years ago. And then you can get results like this and this and this and this. Seeing permitting of course.
So the bottom line is that large sensors have trouble with high download speeds and the DFK41 just does not have the frames per second to be useful as a planetary camera. It is fine for the moon and the sun because the sun does not rotate quickly and the moon remains static and you can go for several minutes collecting data. The planets on the other hand need a smaller sensor to fill the roll. These will have a fast frame rate with smallish pixels. Something like the DFK21 or DBK21 or the DMK21 are perfect for this job at present. Until large well depths and large sensors can be downloaded at fast frame rates these cameras will have to do.
