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Old 07-03-2012, 03:37 PM
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gregbradley is offline
Join Date: Feb 2006
Location: Sydney
Posts: 16,936
Martin another point may be the spacing between your lens and the camera. I am sure the Canon engineers designed the lens to be a certain distance away from the sensor. Perhaps you should measure that and make sure your lens is in that zone.

Also I think the Pentax 67 lenses are good bang for buck here. They have outstanding backfocus at around 89mm (among the highest of any camera lens).

I use FLI PDF focuser, FLI CFW and Proline and an adapter made by Precise Parts that fits on the PDF.

I am using Pentax 67 55mm F4, 165mm F2.8 and 300mm F4.
All are non-ED and relatively cheap and plentiful on ebay.

The 55mm I use at F5.6 and 2x2 binning. The 165mm can be done wide open at F2.8 and on a demanding Proline 16803 chip is sharp corner to corner. The 300mm also is sharp.

Examples of the 55mm at F5.6 and the Proline 16803 are here:

There is some chromatic aberration that shows up as a bit of magenta around brighter stars but its easily fixed in Photoshop.

Also at 2x2 the stars are a bit larger than at 1x1( needs a small amount of deconvolution) but I was getting awful seagull outer stars at 1x1 on the Proline. 2x2 though magically stopped that.

There is also a 45mm F4 Pentax 67. They go for a few hundred US dollars on ebay.

An 8300 chipped camera would be a piece of cake for these lenses.

Your Canon F1.2 is probably worth a lot and is best used on a 5D mark iii!

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