Vignetting Question

[Tenacious Del]

What exactly is it, that causes vignetting in some images and not others? Google just confused me more.

[RSW]

I think all images have vigentting, it is just that the vigentting in some images is more prominent than others (I think).

[CanisMajorTom]

Optical systems that have lenses will always have vigentting. Basically, lenses are thinnner on the outside, and lenses also capture light from a different angle. These reasons are the causes of vigentting.

[AstroTasmania]

In the average camera lens the lens barely covers the 35 x 26mm field and in most outdoor shots it is not noticeable, Once you get into using wide apertures in low light levels, then the full lens coverage (or lack of) becomes very noticeable. You can always pick an astro shot taken with a the basic standard lens. brighter in the middle, Sad but true.

Once you move up into the real lenses of better quality, this effect is no longer a problem as they make the lens a little bigger than actually required. Have you often wondered why most good lenses cost so much!

My Nikkor lenses at f.2.8 apertures or better, cost much more than the camera body, a Nikkor 85mm f/1.2 lens cost me $700 S/H, and many of my good lenses start at $1500. These lenses do not have vignetting effects.

Over the years my pro gear has cost a fortune - one of the reasons that all pro hourly rates are so high!

My medium format Pentax 6 x 7 has 7 lenses, (and I need a trolley to cart them all because of their weight in quality glass) starting at the 180 degree fisheye, and I could go on an overseas trip on the cost of it alone.

Clear skies...

[Radar]

My medium format Pentax 6 x 7


I have never shot medium format film before but I am thinking about it. What are the ups and downs of medium format please Shev?

[AstroTasmania]

Camera's such as the Pentax 6x7 & Mamaya 6x7cm are used by the pro's, the larger film size produces very high quality prints and transparencies because they do not have to be enlarged as much as 35mm. In general they are a professional use camera, the cost alone puts them out of the reach of the happy snapper. My Pentax outfit cost me over $30K with its 7 lenses. They are heavy cameras, especially with the big lenses, it needs a monster scope to hang one of those on.

The Pentax has a focal plane shutter that goes up to 1000th second, whereas my Mamiya RB has leaf shutters in each lens which only go up to 400th second. An RB kit with extra film back, pentaprism, waist level finder and all the bits you need also put it in the high cost range.

I prefer my Pentax for some things, such as aerial photography, because of the faster shutter speed and its big pentaprism view finder. I also have a fisheye for the Pentax and is that some lens!

Film is 120 roll film which take 10 shots on a standard roll or 20 shots on the bigger roll. Film is only available through pro labs, as is the processing of.

Pro's:Top quality images, everything is first class etc.
Con's: Expensive to buy and to run.

I plan to take some decent wide sky shots with it when we get some dark winter skies. I might even make an adaptor to fit the Tak 180ED Astrograph once the new "Octadome" obs is finished and the big Alhena mount is installed etc.

Clear skies...

[Tenacious Del]

My Pentax outfit cost me over $30K with its 7 lenses.

Yikes!

How do you digitize a medium format slide though?

[AstroTasmania]

Again, it is an expensive process, about $30 a scan on a professional scanner!

Clear skies...

[Radar]

Shev, because medium format is larger than 35mm, doesn't that mean that the image has to be spread over a larger surface and as a result the F-ratio would go up slightly?


I might even make an adaptor to fit the Tak 180ED Astrograph once the new "Octadome" obs is finished and the big Alhena mount

Octadome sounds like it is going to be awesome.

[AstroTasmania]

No, the scope or lens has to deliver that size of illuminated circle, so in effect the f/ratio goes down. Draw a 100mm circle, within that draw a maximum size rectangle, pretend that the 100mm circle is sky, now draw 35 x24 mm rectangles inside the big one, that's the effect. The 35mm only records a small part of the 100mm field.

The Tak Epsilons are designed to cover large formats ( 6x7) & SLR plus DSLR's with ease.

This also illustrates why the f/10 SCT's need focal reducers for wide deep sky shots. So imagine a Meade DSI tiny, chip which is a mere fraction of a 35mm (I think maybe less than 1/15th) frame on a F/10 scope

Clear skies...

[Tenacious Del]

AstroTasmania, I take this to mean that a medium format camera sees a larger part of the sky than a normal film camera? If so, that is handy to know, though I'm a long way from ever trying medium format.