I thought I'd have a go at doing my own version of David Malin's famous image of the colours of the stars in Crux, so this was taken and processed tonight.
Captured with the Oly E-510, 1600ASA, 15 sec (to limit star trailing), Zuiko digital 40-150 zoom at 40mm (80mm eq) and f/4, ICNR on (standard), IS off, manual focus using live view.
The image is a stack of 8 photos, stacked with blending mode "lighten", image flattened and saved for the web in PS CS3. No other processing.
I took 12 photos in 15 minutes, and had a few problems... like the remote ceased to work after the first image, so I had to go to cable release and start the sequence again, and it looks like I must've bumped to zoom on the second or third image in the sequence... there could be some movement in the tripod as well as I was too slack to get my big tripod from my binoculars to put the camera on... the lens was entirely dewed up at the end of the 15 minutes. It was -0.7C and 85%RH outside at the time.
I will have to do this again. Next time:
sturdier tripod
fixed focal length lens (Zuiko f/1.8 50mm)
try to take images at more regular intervals
Al.
Last edited by sheeny; 24-05-2008 at 09:20 PM.
Reason: Reload image
Wow that's awesome, Al!
I agree with Doug, next time that'll be very nice indeed. What you need is an computer/handpad controlled focuser on the camera lens though, so you can do it in one long exposure instead of several short ones.
I know Bert has a setup on his camera lens that could do that.
What's happening with Gacrux? why should it have a dark spot inside the out of focus star image? It's the only star in the image with this. In some of the less out of focus images it looks like it could be another close star, but why should the dark spot appear as it goes out of focus... I would expect it to lighten (ever so minutely)...
I do have a dew heater for my lenses, but I wasn't fully set up last night. It was really just a token effort after a big day working around the property... I just had to do something (but not too much).
It's not a dust bunny on the sensor because it moves with the star image. I suppose it could be dust in the lens, but I wouldn;t have expected this to show up as such a small dark spot... I just checked the lens... can't see anything front, back or looking through it...
In some of the less out of focus images it looks like it could be another close star,
Hi Al
Gacrux is an optical Double Star, the A/B distance is 110.6 arc secs and the Visual M is 1.6 for the A componant and 6.7 for the B star. There is also a 3rd star but it is fainter again.
Olympus E-510, Zuiko 50mm f/1.8 OM lens stopped down to f/2.8, 1600, 15s, ICNR on (high), IS off, manual focus, 21 frames stacked with blending mode "lighten" and saved for the web in PS CS3. No other processing. More robust tripod and no zoom to mess up.
I note the artifact on Gacrux is absent!
Just for fun (some might say art's sake) the second one has the sharpest 4 images hidden for that stylised look.
Thanks guys. It's such a simple technique to do with a dslr. I like it on nights when I'm too tired to set everything up... camera, tripod and a remote... ...15 minutes of data capture and some simple processing in PS.
Maybe I should right a little article for beginners....
Go for it Al, you've been a bit dry on that front lately
There has to be a simple way to constantly adjust focus so you get a smooth transition instead of the stepped transition.
Would having ICNR off make any difference to how it looks? Less gap?
I've been a bit dry on a lot of fronts lately, Mike... but that's another story.... Moving house and settling in does eat a lot of time!
I think a perfectly smooth transition would require a motorised focus adjustment and a single long exposure.
Turning ICNR off would reduce the turn around time between images, and so produce smaller steps, I'm just a bit wary of reducing the time so much that you lose the pin point star image in the blob of the first unfocussed image which will still be clipped for the brighter stars.
A method of moving the focus ring by the same amount every time would be a nice refinement.
A variation of the theme would be to do the same process but with a tracking camera. The star images would be circular discs of varying colour from centre to outer rather than the "conical" image.
I haven't decided yet about the ICNR... when it's off, random noise will be smoothed, but hot pixels will be amplified...
... like the remote ceased to work after the first image, so I had to go to cable release and start the sequence again, and it looks like I must've bumped to zoom on the second or third image in the sequence
Explain this
)
.
