Carina at f/3.5

[avandonk]

I did this with the lens stopped down to f/3.5. I actually used a baffle out of a refractor to stop the lens down by placing it inside the lens hood. The iris in the lens causes diffraction spikes on the very bright stars. This time took some care with focusing. Also the fridge by keeping the camera at constant temperature has the added advantage that focus now only changes by factor of about 1/3 with ambient temperature change compared with the uncooled system.

Details
Canon 5DH, Canon 300mm F2.8L at f/3.5. Hutech LPR filter.
Exposures 5x( 1m, 2m. 4m and 8m) at 160 ISO. Fridge at 0.0C. The usual hdr method. I have not used any enhancement. As you can see this is a vast improvement over f/2.8.

Full resolution 4.5MB
http://members.optusnet.com.au/~chee...f3p5%20(1).jpg


Earlier thread here
http://www.iceinspace.com.au/forum/s...ad.php?t=41517



Bert

[strongmanmike (Michael)]

Well, I think you have your formula for that lens Bert?

Lots of nice sharp stars all over the field corner to corner.

Mike

[avandonk]

Jeez Mike I thought I had the formula a few years ago! You are correct we are getting closer. Time to get some apertures made to find the 'sweet' spot and then a set that are a stop apart.

The field is very good from corner to corner. This image is slightly cropped to get rid of noisy corner bits due to too much vignetting. It is a big ask for a lens to produce an aberration free field with a diagonal FOV of 8.5 degrees!

These lenses were not designed for very long exposures with very faint objects. They lack the extra baffling needed for this task. I must put up an image of a spider web taken from thirty feet away with this lens at f/2.8. The depth of field is about 3mm! The lens is rectilinear across it's field within about 1%. Its MTF is second to none.

Thanks for your constructive criticisms Mike.

If you look very hard you can see a vestige of 'my wifes best friend'. You may have to squint.

Bert