Nocton at Night

Started Feb 7, 2013 | Discussions thread
Vittorio Fracassi
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Re: Same with me!
In reply to Bob Tullis, Feb 8, 2013

Bob Tullis wrote:

Vittorio Fracassi wrote:

Compliments, Vittorio

PS adressed to Bob: do you use F0.95 often or do you take advantage of the stellar resolving power at slower settings? difficult to tell from the DOF of the photographs.

At night like this wide open gives more the defined but soft circular halo about the lights. Stopped down to 1.4 they start to transition from globes to stars, and the overall softness starts to fade as well. So far the shots that had to be .95 are then affected by necessary NR, so I try to avoid it and seek f1.4-2.0 as much as possible.

But it's time to leave this on during daylight too and start stopping down. As well, I should shoot the f.95-2.0 at ISO 200 at night to work a clean exposure for comparisons. But I'm not carrying tripod right now, and it's too cold to linger out there even with the Cullman Copter. . . but it's due.

Your reply(ies) triggered thoughts (of the dangerous midnight type)

1-      Halos:  you have gotten me curious about their shape and the influence of aperture, type of diaphragm, resolving power of the lens, position with respect to the focus plane.  Must investigate this.

2-      F n. from F0.95 to F2: I have always been suspicious of the effective utility of this range.  The loss of resolving power as aperture increases becomes exponential and the benefit from lower ISOs and lesser need of NR with consequent blur is smaller than the penalty.   With sensors smaller than FF the OOF effect is hardly worth the effort,  unless ...

3-      Engineering:  lenses capable of F0.95 to F1.8 max aperture are usually very sharp at the sweet spot, these days  well below F8, better between F2.8 and F5.6, that’s where I suppose they should be used.   I had a lens which was ridiculously bad from F1.4 to F3.5 but at F5.6 it was the champion of sharpness,  the modest  Zeiss Planar T*1.4/50 ZE, cheapest of their MF lenses.

4-      Why does Bob Tullis go out with the Nokton 17/0.95 to take pictures with long DOF at F0.95?  Instead of composing with principal subject in forefront and equally important but subtly blurred background?   Why no monopod or tripod?

And what is a Cullman Copter? (off I go in a web hunt to look this up in order not to appear the ignorant that I am...imagine speaking of wines..what? you don’t know what a Brunello di Montalcino is?)... He’s probably found a compromise of blur and sharp which is particularly suitable for PP.

5-      And what’s that “field curvature” ? something to do with the theory of relativity? Wait, I read something about that in http://diglloyd.com/index-zf.html  (a subscription site with a great Zeiss MF lenses review and advice section), so after spending some time to recover ID and password I found out.  It’s not about relativity it’s about focal plane.  Here is an extract with my excuses to the author for not asking permission to show it here:

the author describes a vertical landscape image of a broken tree: “...A curious fact emerges: sharpness is absolutely outstanding (speaking of the image at F4 rather than F1.4, my note), from the center to the bottom (closer) but extends only a short distance from the point of focused to the background.   This sharpness behaviour suggests a field curvature at the edges that extends forward,which would have the effect of blurring the top (background), and sharpening the foreground, which is what occurs in this image...”

I beg tolerance for my cheeky ponderings,   Regards,  Vittorio

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