Re: [APML] 6x7 single exposures (was: new technique?)

[Chris1011@aol.com]

In a message dated 11/13/2001 12:26:36 PM Pacific Standard Time, matt@starmatt.com writes:


> Mike used a 130 f/6?
> What film did he use?
> Do you know what his typical deep exposure durations were?
> At what resolution were the frames scanned?
> What digital processing did you (or he) do?
> Were you able to use the entire frames?
> Did you (or he) do anti-vignetting?


Hi Matt,

In the original letter, Mike sent the following info:

Scope - AP 5" F6
AP 80mm Guide scope
Losmandy Mount
Film - Kodak PMZ1000 medium format film
Camera Pentax 6x7

There is no indication of exposure times. 

I did a bit of processing. The original image showed a greenish background illumination which I adjusted using Channels and Curves. I brought the contrast up a bit which revealed some vignetting in the corners. Using the original image, I made a pseudo-flat field with Gaussian blur and some blending. The resultant image looks striking.

The scan size is 2.656 wide at 1700 pixels per inch. At full size, it is 62" wide. When reduced to full screen size (approx 9"X11") at about 16.7% enlargement on my screen, the grain is not really noticeable. Picking one image, Small Megallanic Cloud + 47 Tuc, at full 100% enlargement, the grain pattern measures approx 0.06" and stars are nominally 0.10" to 0.15" in diameter. There are a few very bright stars which measure 0.18" diameter. 

I had asked Mike if he could take a number of images of the same object for stacking the next time he goes to Australia. I believe with 3 or 4 stacked, the grain would pretty much disappear.

Roland Christen