DMK21au618

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Merlin66
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DMK21au618

Post by Merlin66 » Tue Mar 18, 2014 10:42 pm

I know the response curve for this camera shows a much better QE at Ha....
but, is it REALLY worth the extra $$$$$
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Re: DMK21au618

Post by thesmiths » Wed Mar 19, 2014 1:10 am

It's a good camera for Mars and Jupiter, which have a large red/IR component. I have not found it particularly useful for solar since it's chip is so small and there is no shortage of photons from the Sun. The DMK51 is far more useful for solar. Actually, the chip in the DMK21AU618 is falling out of favour with planetary imaging since it has such poor blue sensitivity. The ASI 120MM seems to be the best all rounder these days (for planets). I bought one recently and have been impressed. I haven't used my DMK21AU618 since.

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Re: DMK21au618

Post by Merlin66 » Wed Mar 19, 2014 5:17 am

-1, +1......
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
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"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

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Re: DMK21au618

Post by thesmiths » Thu Mar 20, 2014 12:14 am

If frame rate is really a serious issue (and normally for solar, I don't think it is since the features do not change all that quickly compared to planetary rotation) then the ASI 120MM leaves the DMK21 in the dust. And it has smaller pixels, more of them and you can do ROI. And also do more than 8 bits. The only draw back I've noticed with the ASI 120MM is the incredible amount of dust the workers in China leave on the chips versus those scrupulously clean Germans.

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Re: DMK21au618

Post by solarchat » Thu Mar 20, 2014 12:55 am

the entire background surface "canvas" of the Sun, granulation, mottling, etc... recycles about every 5 minutes so I would say that it changes at an extreme rate and quite a lot faster than any planetary rotation. Not to mention that every magnetic feature on it is churning and moving about at around 40-50 thousand miles per hour. :) Hard to see at the full disk scale, but its there. Very easy to see at F45 or so.
Generally, I feel that any info gained on an imaging run over about 90 seconds is pointless with the Sun at any focal length. I would say that 12 fps is minimum needed for full disk and an optimal 60fps or higher for high magnification.
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Re: DMK21au618

Post by thesmiths » Thu Mar 20, 2014 1:46 am

Actually, the Sun rotates once every 24.5 days at the equator while Jupiter rotates once every 9.9 hours and Mars every 24.6 hours. So the angular rotation of the planets is considerably higher. High quality planetary videos really need to be taken in 20 or 30 seconds.

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Re: DMK21au618

Post by solarchat » Thu Mar 20, 2014 2:10 am

Maybe I wasn't being clear. The features you are imaging are not solid and unchanging. The surface is a churning gas which changes completely every 5 or so minutes with the granulation cell recycling. The rotational period is irrelevant as it is the surface itself that is changing, not its position that dictates the need for high frame rates.
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Re: DMK21au618

Post by solarchat » Thu Mar 20, 2014 2:14 am

I used both the 21 and the 51 when I used to use PCs. They are both great but for very different applications. The 51 is far superior for full disks while 21 is much better for high mag work.
Stephen W. Ramsden
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Re: DMK21au618

Post by sullij1 » Thu Mar 20, 2014 2:15 am

As Stephen said, rotation is pretty much a non issue. It "is" how quickly the minute features are changing that becomes the challenge. The DMK 21 is a good lil cam for isolating close in. Yuh its getting older and receiving more competition but it is one of those cams that you can still truly plug and play and still land some fine images. Alll the DMK line up is reliable and still producing fine solar images. As stated the only draw back is the tiny lil chippie! IMHO. Herb produced some of the finest Ha images I have seen with his lil 21.

If its all you can afford the 21 is a thumbs up. I think the mentioned ASI type offer more chip real-estate for the price.

And yuh, cuz the surface is changing so dramatically, normally I never shoot more than 400 frames for an image, ~ 20 -30 seconds and stack no more than 10-50 now days.

BTW, it was the first real cam I owned. It sees less use now days but will remain in my kit of goodies.
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Re: DMK21au618

Post by Merlin66 » Thu Mar 20, 2014 4:06 am

I appreciate all the comments....
My question could probably been put better-
"Is the DMK21au618 so much better than a DMK21 au - enough to justify the significant price differential"
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

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Re: DMK21au618

Post by sullij1 » Thu Mar 20, 2014 4:40 am

Difference between the 21 AU04 and 21AU618 Maybe, the difference is ~100 in the US. Here is a ~comparison article on the 618:

http://www.astronomycameras.com/blog/ar ... ang-paech/

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Re: DMK21au618

Post by alex » Tue Mar 25, 2014 10:28 pm

Ken i have the DBK21 with the ICS 098 and i also use the DMK with the ICX618.

I haven't used the DMK with the mono ICX 098, but i've heard that it has some artifacts at 60fps,that the ICX version doesn't have.

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