From: "Raoul Schlesser" <gr842@yahoo.com>

Date: January 18, 2006 7:58:19 AM MST

To: Astro_IIDC@yahoogroups.com

Subject: DMK 21BF04 & DSOs: a few pics and thoughts

Hi Folks,

it's been a while since I last stopped by here, so I'm sure I must have missed some 

interesting posts. I just saw Alan's superb M27 shot... very nicely done!

It is amazing how deep one can go with an 8-bit mono, uncooled firewire, even with an 

exposure limit of just 30 seconds. I have been playing with a DMK 21BF04 for a while... so 

I thought I'd share some of my thoughts regarding DSO imaging with this thing.  To 

illustrate some of the DSO targets that can be recorded without  too much trouble I 

uploaded 3 DSO images I took toward the end of 2005, have a look under Files > DSO >

NGC7331_20051017_RS.jpg

NGC891_20051126_RS.jpg

StephansQuintet_20051014_RS.jpg

All 3 images were taken from my rather light-polluted backyard (typ. VLM 4.5) with a tiny 

80 mm f/6 refractor (further details are on the images) and a DMK 21BF04 (8bit mono, no 

binning).

I found it rather interesting that Stephan's Quintet showed up in the first place, with all 5 

(well, 6, really) galaxies visible, and with hints of structure after only 12.5 min of total 

exposure time (more would definitely have been better here, I know :) 

In some test shots I reached mag 18-19 with the same setup and within 15-30 min worth 

of exposures. While it's certainly nice to have 16 bit depth, I think that stacking of multiple 

8bit images does lead to acceptable results, probably at least in part due to the low read-

out noise of these cameras... and, of course, cooler fall/winter temps do help a lot as well 

to reduce thermal noise. 

From discussions with folks who don't (yet?) own a similar Firewire cam, the 30 sec max 

exposure  time is often considered too short to record any of the dim stuff... and that's 

kinda correct, in principle. It's clear that these cameras are not optimized for the *real* 

dim stuff. On the flip side, the good thing is that even a PE-challenged mount may be 

sufficient to do the trick for short, 15-30 seconds exposures, unguided. Also, since these 

cameras are very sensitive, much longer exposures may not even be practical under 

heavily light polluted skies.

The 21BF04 certainly does not compete with a dedicated, cooled Astro cam, but for its 

price it does a whole lot and it's fun to use (and it really does more than just planets and 

moons).

Clear, dark & cold nights,

raoul