10 stop ND filter ok for sun? - Page 2
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Old 03-20-2015   #11
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Default Re: 10 stop ND filter ok for sun?

I will point out to photographers who may
not speak telescope jargon that the filters
listed as being for "finders" are NOT to be
used on your camera's optical finder. On a
telescope the "finder" is a small telescope
mounted parallel to the main scope [with
wider FOV, and cross hairs] and the finder
filter is for the FRONT of that small scope.

I realize I seem to be the nagging "safety
warden" of this thread. It's cuz I care.


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Old 03-21-2015   #12
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Default Re: 10 stop ND filter ok for sun?

It is both unnecessary and very unwise to look through the viewfinder of any camera when doing solar photography. The shadow of the lens barrel can be centered on the lens mount for positioning. White paper or cardboard surrounding the lens mount makes this easier than chasing shadows on black camera bodies.

DSLR bodies that accept old film camera lenses can be useful for solar photography. A few of the inexpensive 400mm f/8 four element telephotos were sharp. Even better is my Vivitar 400mm f/5.6 in Nikon mount, sharp when wide open. Stopping down too much to reduce exposure limits sharpness due to diffraction.
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Old 03-22-2015   #13
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Default Re: 10 stop ND filter ok for sun?

Quote:
Originally Posted by Jim Jones View Post
It is both unnecessary and very unwise to look through the
viewfinder of any camera when doing solar photography.
The shadow of the lens barrel can be centered on the lens
mount for positioning. White paper or cardboard surrounding
the lens mount makes this easier than chasing shadows on
black camera bodies.

..........
That inspires an innerressing accesory. It would be double
threaded like the mount around a camera lens filter but it
would have an "outrigger" structure that projects a pinhole
image of the sun down a "shadow tube" onto white target
surface ... needs an opening in the target end of the tube
to allow viewing the target.

The attachment via the filter threads assures parallelism
to the lens axis. But a cheaper version could be the same
pinhole imaging device on an under-camera bracket. This
requires some visual alignment before tightening up the
tripod screw of the bracket into the camera body. More
work, but less need for manufacturing precision, prolly a
sturdier device, and more universally adaptable.

This idea is soooo stoopid simple and do-able that I won't
be too sooprized to see someone post links to an existing
similar device already on the market.


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Old 03-22-2015   #14
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Default Re: 10 stop ND filter ok for sun?

Quote:
Originally Posted by Jim Jones View Post
...........
A few of the inexpensive 400mm f/8 four element telephotos
were sharp. Even better is my Vivitar 400mm f/5.6 in Nikon
mount, sharp when wide open. Stopping down too much to
reduce exposure limits sharpness due to diffraction.
The ubiquitous and oft maligned front-cell-focus 400/6.3 and
500/8.0 sold under 20 brand names, usually house brands, are
great lenses when focused at infinity and stopped down one
or two stops. They are long focus designs, not true telephoto
[e.g. physically/optically compressed designs like the typical
135/2.8] which are less challenging to design for quality, and
they tend to have built-in rotating tripod collars. If it hasn't
gone missing, they usually come with a long snoot lens hood.

Basically they're rather well corrected 2-1/2" f/8 telescopes
adapted to cameras via T-mount. Their terrestrial-use focus
system is questionable, but for celestial use you don't use it.

`


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