Deep Bit of SMC

[avandonk]

Finally a clear night almost without Moon.

Camera Canon 5DH, Canon 300mm F2.8L at f/5, Hutech LPR filter. Fridge at -10C.

Exposures 20x( 1m, 2m, 4m ) and 24x8m at 1600 ISO.

Twice native resolution 8MB

http://d1355990.i49.quadrahosting.com.au/2009_10/smcdeep.jpg

I will worry about the residual gradients when I get the second panel as deep for a mosaic.

Bert

[AlexN]

Fantastic effort Bert.. Looks great! Sure is plenty of data in there... 24x8m @ 1600 = HEAPS of light! especially with the massive objective of the 300mm F/2.8L...

Well done... Looking forward to the second panel.

[avandonk]

Actually Alex I have two apertures inside the lens hood. These apertures are baffles from an achro refractor. The one nearest the lens is 56mm diameter and the one at the entrance to the lens hood 84mm diameter.

This effectively makes the lens f/5.2 and there is no diffraction spikes from the len's iris. This way all light passes through the 'allmost perfect' center of the len's optics. Another benefit is no light not contributing to the image even enters the lens to be scattered. No light even hits the lens's internal baffles. This would lower contrast.

As usual it is all about signal to noise not brute force. It took me a while to figure this out. I can also use the lens the same way at f/3.5 but the f/5.2 configuration has stars almost perfect to the corners and vignetting is less of a problem. This is a real plus for mosaics.

The proof is in the image. If you look closely you can see dark dust starting to appear.

If I used the lens wide open at 1600ISO the aberrated and scattered light just swamps the image. This has the effect of losing all dim stars and bright haloes around all the brighter stars.

Bert

[AlexN]

Great idea.. I do sometimes think the diffraction spikes given by these lenses is very nice, but only in the right image of the right target, you know? like an image of crux would look nice with the 9 pointed diffraction pattern from the lens, however a shot like this shot of the SMC would not...

True, these pre-objective aperture stops would give more contrast, and lessen the amount of stray light and off-axis scattering experienced when imaging in the vicinity of either street lights or with very bright stars just out of the FOV...

Very clever!

Alex.

[multiweb]

re:stopping lens- Clever. Nice image btw. :thumbsup:

[Hagar]

Very nice Bert. The full image should be very interesting once you capture the other half.

Very nice