Well the forecast was for rain, the skies were clear and although the stars were twinkling, I decided to set up the rig for Jupiter, go to bed and get up again at 3:00am.
I actually awoke around 1:00am so crept out of the house and powered up the rig. Whilst waiting for Jove, I thought I’d try the DMK on a galaxy, M83 to be specific. A quick GoTo and crikey! There she was! Very dim and indistinct compared to the same exposure, 30 secs, using the cooled and more sensitive SBIG ST7 CCD camera.
I banged off an avi that comprised 10 x 30 sec frames and then headed for Omega Centauri. Just as the mount arrived after its slew, so did the clouds. A tantalising wait and I managed to squeeze off 10 x 15 sec frames. Hmm, I wonder how Registax will handle all those stars?
Anyhow, the time for Jove arrived, as did the clouds, so in the end, at 5:12am, I managed to grab the only ToUcam avi of the session.
Overall a very pleasing session, albeit a bit frustrating due to the clouds. The long exposures on the DMK are nice, but I'll stick to the more sensitive, cooled ST7 for DSO's.
Thanks guys. The DMK surprised me with the deep sky stuff, although even at 30 secs there were approx 6 to 8 hot pixels clearly visible, so I'm not too sure how it will perform for longer exposures?
It was good to be outdoors again Paul – but gee I was rusty, it took me ages to get going.
Mike – I am now even more impressed with your recent Jupiter images, after having attempted it myself this morning.
Still, the DMK is quite a versatile camera, whilst you are out there, waiting for the Planets or the Moon.
Very nice images Dennis.
I noticed on M83 that the middle to upper left seems lighter. I get that as well on some of my images, is that light pollution being captured as well or something else.
Very nice images Dennis.
I noticed on M83 that the middle to upper left seems lighter. I get that as well on some of my images, is that light pollution being captured as well or something else.
Cheers
Hi Ric
The M83 image has not been “reduced”, that is, Flat Fields and Dark Frames were not taken and applied. A Dark Frame (subtracted) removes thermal noise and a Flat Field (divided) removes light gradients, vignetting, dust spots, etc.
The light gradient would have been removed if I had taken a Flat Field. The DSO’s were captured using the Celestron F6.3 Reducer/Corrector. When using the F6.3 R/C, vignetting becomes quite apparent, even on a 640x480 chip.
Does your DMK have a maximum 30 sec exposure? That's the 21AFO4 right? Is that the astronomy long exp modded version?
Can it go any longer?
Hi Matt
Like Paul, I got the DMK21AF04.AS which is the firmware modded camera. I think that the unit is capable (in the software settings) of exposures of up to 1 hour? I only went as high as 30 secs on M83, just messing around really.
To take say, 3 minute + images, I would have to fit an auto guider, or acquire the patience and stamina of Scott and manually guide!
Thanks Dennis for the explanation.
I always take darks but haven't been using flats so that would explain the the same effect in some of my images.
Cheers
Hi Ric
Often at F10, I can get away without the need for Flats, but using the F6.3 Reducer/Corrector always requires Flats. EddieT has written a great article here which provides instructions on how to construct a Flat Field box.
I should have explained that I don't usually take flats (for vignetting) at F10 when using a small sensor such as the DMK 640x480. If I were using a larger sensor such as the 3000x2000 pixel Pentax *ist DS, I would always plan to take flats. Note the use of the word “plan”, for when I’m a little groggy at 4:00am, I sometimes forget - doh!
When imaging with the SBIG ST7 I always take flats, mainly for the dust bunnies rather than light gradients, which tend to be negligible at F10 over this relatively small sensor of 765 x 510 pixels.
The crucial thing part about taking Flats, is that you must take them at exactly the same camera/focuser configuration and orientation as your light frames. That is, you cannot change the focus or move the camera, otherwise you will get image artefacts when do the Flat Field division.
This is because the original light frame would have contained the data about the dust bunnies at certain X-Y pixel locations and if you have changed focus or rotated the ccd for the Flat, then the relative position of the dust bunnies will have changed so they no longer match up exactly with the original light frame.
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I gave it up as a bad joke. Cloud, Clear, Cloud, Clear, Cloud, Clear.
I'd give the DMK a shot at long exposure. Looks very promising. 
