From: albe albo <richter1956@yahoo.com>
Date: February 11, 2010 2:25:28 PM MST
To: Astro_IIDC@yahoogroups.com
Subject: Re: [Astro_IIDC] Astro & DMK ROI?
Hi Alan,
yes, i already thought to buy a 640 x 480 TIS camera only for planets or small nebulas like M57, Snowball etc..
I asked here and there about the real increasing of sensibility due to the bigger pixelssize but i didn't receive satisfactory responses.
Did you find a real difference in sensitivity... at the same equivalent focal length ?
Of course the image scale is smaller since the pixels are bigger so i can't figure out what could happen if i would set the focal length in order to achieve the same planet size in pixels (varying the focal accordingly).
Sorry if i messed up... i meant that in order to get the same planet size in pixels i should use the DMK 31@ f40 and the DMK 21@ f50 (approx).
Question: In this case i will get the same equivalent brightness for both the cams or the DMK21 is still superior?
Another good side is the reduced firewire throughput and the smaller files.
I'll try to find a used DMK21 if possible.
Thank you for the suggestion.
Cheers
Da: Alan Friedman <alan@greatarrow.com>
A: Astro_IIDC@yahoogroups.com
Inviato: Gio 11 febbraio 2010, 18:42:50
Oggetto: Re: [Astro_IIDC] Astro & DMK ROI?
Hi Alberto,
You might consider purchasing a 640x480 TIS mono camera dedicated for your planetary imaging. After experimenting with various ROI settings, I think I am headed back to the DMK 21AF04. The pixel size and speed of this camera are just right for my 10" scope. I have yet to use 60fps on the planets - not enough light, though I might be able to if I were working at a shorter effective focal length. ROI is interesting, but sometimes too many options are just too much for my aging brain... especially if you happen across a few moments of steady seeing. Then you want to be able to think and move fast!
just a thought,
best,
Alan
On Feb 11, 2010, at 12:26 PM, albe albo wrote:
Ok Milton,
thank you fro the explanation.
I got the message.
When i said that the "disk" would work better i was thinking only to the data written to the disk and not to the data passing through the firewire.
I understood that the hardware part of the system will remain unchanged while the crop & save would be made by your software only after that the whole data arrived to the processor.
Anyway in my thoughts the space saving would not be a secondary result.
When grabbing 3.000 frames of Mars x IR-R-G-B (approx 8 giga bytes for a single composition) then every space saving would be really appreciated!
I confess that i often quit the grabbing because i have the feeling that i'm wasting something "physical" like water or so. LOL!
That's the age.
Should it be easier on monochrome cameras?
Cheers
Alberto
Da: Milton Aupperle <milton@outcastsoft. com>
A: Astro_IIDC@yahoogroups.com
Inviato: Gio 11 febbraio 2010, 01:06:03
Oggetto: Re: [Astro_IIDC] Astro & DMK ROI?
Hi Alberto;
On 10-Feb-10, at 4:54 PM, albe albo wrote:
Thank you Milton,
even the simple reduced disk space used is a nice and useful option, isn't it?
Perhaps it is very hard and time consuming to implement.
It isn't simple to do as there are lots of things that have to be worked through, especially when dealing with bayer video.
For the moon of course it's useless but for the planets it would be very precious.
Lately with Mars i'm wasting lot of gigabytes of black unused screen.
Since my mount is fairly precise the planet doesn't wander so much so i could easily set a smaller rectangle.
And if they had implemented Format 7 like many other companies, I would not need to do it.
Even if the bandwidth/framerate remain the same i guess that the disk would work better for the smaller amount of data that will be written.
It makes zero difference over the FireWire bus. The only thing it does is reduce the image size.
TTYL..
Milton Aupperle