[APML] Long Exposures (was: Recent Images)

[Matt BenDaniel <matt@starmatt.com>]

Jon Kolb wrote:

> Matt,
>
> Your September images are excellent.  I especially like the Veil shot with
> its distinctive O-III regions.

Jon,

Thanks!

> Groton, NH must be pretty dark to allow 90 minute exposures at f/6.7.

Yes, LVM 6.5+ is pretty dark. Even at 90 minutes on unhypered PPF 400, the
corners were a bit underexposed due to light falloff. You can see it in the
Veil image as a thinning out of stars in the corners. That image is already
full anti-vignetted. There's just less information the corners because less
light got there. With my setup, if I want to utilize the entire frame, I have
to expose long enough to get the sky glow over the response toe in the
corners. This is one reason why I like print film over slide film. Print film
records a larger dynamic range (an additional 2 stops). My M31 shot was two
hours long, and the core was not burnt out. The longer exposure helps record
the faint areas and results in less grain there.

I have the notion that medium format (MF) also supports more resolution and
larger dynamic range than 35mm film. You get 4 times the film area to absorb 4
times as many photons per unit sky, which yields yet another 2 photographic
stops. For example, I shoot MF at 875mm focal length, which has similar
angular coverage to my previous TV-85 setup (35mm film at 480mm). Note: film
noise comes primarily from film grain.

The problem is that I do not know of good 120 print films in production that
perform well unhypered.
--
Matt BenDaniel
http://starmatt.com



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