Old 19-06-2008, 06:28 AM
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rick01 (Roman)
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DMK31 vs DMK21

Hello all,

I'm just newbie here. I'm thinking about new DMK's, especially DMK31 and DMK21. It's fifty-fifty. The DMK31 has bigger resolution, but slower frame rate and pixel size (and is more expensive than DMK21), on the other hand, the DMK21 has just 640x480 pix resolution, but 60fps framerate and bigger pixel size (lower noise??).

Which one is better mainly for planetary imaging? Isn't 640x480 pix too low resolution??

Thanks for answers


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Old 19-06-2008, 06:39 AM
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Roman, the number of pixels isn't important for planetary imaging. The size of the pixels may be. Your setup will project an image of a certain size on the sensor chip. If the pixels are smaller this image will cover more pixels and so there is potential to capture more detail.

If you want to capture larger areas of say the moon the bigger chip will be better, but otherwise for planetary where it's virtually impossible to cover the smaller chip you are better of with the 21. Speed in FPS is very important too in planetary imaging as it allows you to capture more data for better noise reduction etc.

If it's planetary you want to do get the 21.
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Old 19-06-2008, 06:41 AM
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Hello, Roman

Welcome to Ice In Space!

In terms of chip size, with the DMK21 at 640x480 and the DMK31 at 1024x768, I suspect that Jupiter will easily fit on either chip, although you will have a lot of (wasted) black space on the larger chip.

However, on the Moon, the larger DMK31 will mean that you can image larger areas whereas with the DMK21, you will have to make mosaics which is quite time consuming.

In terms of pixel size, the DMK is 5.6um versus the DMK31 at 4.65um. I’m not sure if this would make a huge difference in terms of image quality and the ability to resolve finer detail? I suspect the effects of the seeing (Earth’s atmosphere) would dominate here?

The DMK21 60fps versus the DMK31 30fps could be important if you are imaging Jupiter through RGB filters. Then, you need to collect as many frames as possible with each filter due to the rapid rotation of Jupiter.


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Old 19-06-2008, 07:25 AM
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iceman (Mike)
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Hi Roman

The advice above is perfectly sound.

What telescope will you be using it with? And what focal length will you be imaging at?

If you're going to use a 12" or larger telescope, and imaging at longer than 11m focal length, the largest of the planets (Jupiter) will still (just) fit in the FOV of a 640x480 camera, with Jupiter pushing the boundaries of the 480px high resolution.

So if you're using a smaller telescope, your focal length will be shorter, and so 640x480 will be plenty enough resolution to image the planets.

PLUS, the DMK21 has the faster framerate for freezing the seeing and larger chip which increases sensitivity.

For lunar imaging, the DMK31 definitely has the advantage in terms of resolution (capturing more of the moon in one go), and less need to do mosaics etc. For the larger resolution, most computers wouldn't capture that much data at 60fps and mine would only capture at 15fps without dropping frames.

My experiences comparing the DMK21 with the Astrovid Voyager X, had me leaning towards the DMK21 in terms of sensitivity (the DMK31 uses the same chip as the Astrovid Voyager X).

Either way you can't go wrong, but i'd personally go for the DMK21 for planetary imaging and if you can afford it, buy the DMK41 for lunar imaging
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Old 19-06-2008, 03:41 PM
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rick01 (Roman)
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Thanks all for advices!

Now I'm definitely decided for DMK21. I though, that higher resolution of DMK31 brings me more detailed image of planet, but difference is just in capturing larger areas.

Anyway, I'm using 8" Newton at f/10 approximate. In future I'm think about maximally 12" Newton.
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