crossed polarising filters to reduce light?

bugbear wrote:
Jeff R. wrote:
I suspect it may be difficult to get a set that will not introduce a
strong colour caste.

Not a problem in the digital era, of course.

The same problem (only worse) will be evident with welder's goggles or
solar filters (e.g. Thousand Oaks or Baader film).

Hmm. Not heard of those. I'm trying to go from
(around) 1/125 exposure to 10 secs, which is

1/125, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2, 1, 2, 4, 8

11 stops. Any know of a ND22 filter?

1/1000... that's 99.9%
Try to look for optical equippment for lasers and optics for example. At
work I have a set of filters which goes up to 99.8% (but I usually only
use the 50% and the 75%).

Marco

--
Dimage A2, Agfa isolette
http://flickr.com/photos/kruemi
http://profile.imageshack.us/user/kruemi/images

bugbear wrote:

I suspect it may be difficult to get a set that will not introduce a
strong colour caste.

Not a problem in the digital era, of course.


When I put a couple of my filters in front of each other with polarisation
set as such there is a very deep purple-blue caste - suspect that it is
just too far gone to correct.

--
http://www.petezilla.co.uk

In rec.photo.equipment.35mm bugbear wrote:

Hmm. Not heard of those. I'm trying to go from
(around) 1/125 exposure to 10 secs, which is

1/125, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2, 1, 2, 4, 8

11 stops. Any know of a ND22 filter?

You can get most of the way there with an ND 3.0 filter.

http://www.bhphoto.com/?O=productlist&A=details&Q=&sku=8110&is=REG

They used to have filters up to 6.0 listed, but it seems the
catalogue is getting smaller.

Peter.
--

Peter Irwin wrote:
In rec.photo.equipment.35mm bugbear wrote:
Hmm. Not heard of those. I'm trying to go from
(around) 1/125 exposure to 10 secs, which is

1/125, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2, 1, 2, 4, 8

11 stops. Any know of a ND22 filter?

You can get most of the way there with an ND 3.0 filter.

http://www.bhphoto.com/?O=productlist&A=details&Q=&sku=8110&is=REG

Surely that's only 1 1/2 stops worth?

BugBear

timeOday wrote:
I can't comment on the polarizing filters, but couldn't you just put a
piece of cardboard with a hole punched in it over your lens?

Might introduce vignetting?

BugBear

In rec.photo.digital bugbear wrote:
Peter Irwin wrote:
In rec.photo.equipment.35mm bugbear wrote:
Hmm. Not heard of those. I'm trying to go from
(around) 1/125 exposure to 10 secs, which is

1/125, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2, 1, 2, 4, 8

11 stops. Any know of a ND22 filter?

You can get most of the way there with an ND 3.0 filter.

http://www.bhphoto.com/?O=productlist&A=details&Q=&sku=8110&is=REG

Surely that's only 1 1/2 stops worth?

No, density 3.0 cuts out 99.9% of the light - 10 stops.

0.3 - 1 stop
0.6 - 2 stops
0.9 - 3 stops

Peter.
--

/

Peter Irwin wrote:
In rec.photo.digital bugbear wrote:
Peter Irwin wrote:
In rec.photo.equipment.35mm bugbear wrote:
Hmm. Not heard of those. I'm trying to go from
(around) 1/125 exposure to 10 secs, which is

1/125, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2, 1, 2, 4, 8

11 stops. Any know of a ND22 filter?
You can get most of the way there with an ND 3.0 filter.

http://www.bhphoto.com/?O=productlist&A=details&Q=&sku=8110&is=REG
Surely that's only 1 1/2 stops worth?

No, density 3.0 cuts out 99.9% of the light - 10 stops.

0.3 - 1 stop
0.6 - 2 stops
0.9 - 3 stops

Hmm. I think there's more than one
scale of units being used:

Here's a Hoya "ND4" filter

http://www.jessopsbusiness.com/Product/?Prod=18837

Hoya HMC ND4 Filter 72mm

Filter - Factors & F-stops

Filter Factor = 4 f-stop = 2

I'm now (officially) confused.

BugBear

In rec.photo.equipment.35mm bugbear wrote:
Peter Irwin wrote:

No, density 3.0 cuts out 99.9% of the light - 10 stops.

0.3 - 1 stop
0.6 - 2 stops
0.9 - 3 stops

Hmm. I think there's more than one
scale of units being used:

Here's a Hoya "ND4" filter

http://www.jessopsbusiness.com/Product/?Prod=18837

That is a 4x filter which has a density of 0.6.
It would be fine to call it a 4 times ND filter,
a 4x ND filter or a two stop ND filter, but Hoya
is using bad terminology if they call it an ND4
filter. Density is a well defined term in photography
and B+W, Heliopan, Kodak, Tiffen and Lee get it right.

Peter.
--

In rec.photo.digital Matt Ion wrote:
bugbear wrote:
Nicholas O. Lindan wrote:
"bugbear" wrote

[I need v. dark] ND filters
A thought struck me from my school physics
days. 2 polarising filters, at 90 degrees
(in theory) block all light.

Works. With the following caveats:

(lots of good info)

Wow! Thanks for all that; above
and beyond what I need to know,
but interesting in its own right.

Remember too that a polarizer typically drops light around 2 stops on
its own, so two polarizers stacked is going to get you down 4 stops
right off the hop.

No, because a polarising filter will have no effect on light already
polarised in its direction of filtering.

--
Chris Malcolm DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
[http://www.dai.ed.ac.uk/homes/cam/]

Don McC wrote:
"Peter Irwin" wrote:
Here's a Hoya "ND4" filter
That is a 4x filter which has a density of 0.6.
It would be fine to call it a 4 times ND filter,
a 4x ND filter or a two stop ND filter, but Hoya
is using bad terminology if they call it an ND4
filter. Density is a well defined term in photography
and B+W, Heliopan, Kodak, Tiffen and Lee get it right.

Here is a Web page that explains the difference between
the Hoya and other manufacturers' nomenclature.
http://www.cs.mtu.edu/~shene/DigiCam...filter-ND.html

Excellent info - thanks for that.

I will add that Jessops in the UK follow
Hoya's nomenclature.

BugBear