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+++ATH0
Guest

Sat Aug 25, 2018 11:45 pm   



On 2018-08-14 09:08, nospam wrote:
Quote:
In article <9LKdncSlBe9dVu_GnZ2dnUU78a_NnZ2d_at_brightview.co.uk>, NY
me_at_privacy.net> wrote:

One other factor to bear in mind: the depth of field varies with lens focal
length, not field of view of the subject.

actually, it's aperture.


actually, it's the ratio of focal length to aperture.

nospam
Guest

Sat Aug 25, 2018 11:45 pm   



In article <ZYGdnUsaBKCjTRzGnZ2dnUU7-TednZ2d_at_supernews.com>, +++ATH0
<news_at_ringpiece.local> wrote:

Quote:
One other factor to bear in mind: the depth of field varies with lens
focal length, not field of view of the subject.

actually, it's aperture.

actually, it's the ratio of focal length to aperture.


nope. depth of field is a function of physical aperture.

what you describe is f/stop, which is used for exposure purposes, and
in some cases (usually movies), t/stops are used, which is actual light
transmission through the lens, not a simple ratio.

+++ATH0
Guest

Sun Aug 26, 2018 12:45 am   



On 2018-08-25 15:06, nospam wrote:
Quote:
In article <ZYGdnUsaBKCjTRzGnZ2dnUU7-TednZ2d_at_supernews.com>, +++ATH0
news_at_ringpiece.local> wrote:

One other factor to bear in mind: the depth of field varies with lens
focal length, not field of view of the subject.

actually, it's aperture.

actually, it's the ratio of focal length to aperture.

nope. depth of field is a function of physical aperture.

what you describe is f/stop, which is used for exposure purposes, and
in some cases (usually movies), t/stops are used, which is actual light
transmission through the lens, not a simple ratio.


Are you claiming that focal length has no bearing on depth of field?
That's an interesting viewpoint.

nospam
Guest

Sun Aug 26, 2018 12:45 am   



In article <s7ednbBkJLg4QxzGnZ2dnUU7-audnZ2d_at_supernews.com>, +++ATH0
<news_at_ringpiece.local> wrote:

Quote:
One other factor to bear in mind: the depth of field varies with lens
focal length, not field of view of the subject.

actually, it's aperture.

actually, it's the ratio of focal length to aperture.

nope. depth of field is a function of physical aperture.

what you describe is f/stop, which is used for exposure purposes, and
in some cases (usually movies), t/stops are used, which is actual light
transmission through the lens, not a simple ratio.

Are you claiming that focal length has no bearing on depth of field?


for the same subject size and same image quality (coc), no.

> That's an interesting viewpoint.

not really. it's just math.

Tim
Guest

Sun Aug 26, 2018 2:45 am   



+++ATH0 <news_at_ringpiece.local> wrote in
news:ZYGdnUsaBKCjTRzGnZ2dnUU7-TednZ2d_at_supernews.com:

Quote:
On 2018-08-14 09:08, nospam wrote:
In article <9LKdncSlBe9dVu_GnZ2dnUU78a_NnZ2d_at_brightview.co.uk>, NY
me_at_privacy.net> wrote:

One other factor to bear in mind: the depth of field varies with
lens focal length, not field of view of the subject.

actually, it's aperture.

actually, it's the ratio of focal length to aperture.

That is correct. For any given focal length, the smaller the aperature, the
greater the depth of field. That is why pinhole cameras focus from closeup
to infinity without a lens.

Tim
Guest

Sun Aug 26, 2018 2:45 am   



nospam <nospam_at_nospam.invalid> wrote in
news:250820181923372947%nospam_at_nospam.invalid:

Quote:
In article <s7ednbBkJLg4QxzGnZ2dnUU7-audnZ2d_at_supernews.com>, +++ATH0
news_at_ringpiece.local> wrote:

One other factor to bear in mind: the depth of field varies with
lens focal length, not field of view of the subject.

actually, it's aperture.

actually, it's the ratio of focal length to aperture.

nope. depth of field is a function of physical aperture.

what you describe is f/stop, which is used for exposure purposes,
and in some cases (usually movies), t/stops are used, which is
actual light transmission through the lens, not a simple ratio.

Are you claiming that focal length has no bearing on depth of field?

for the same subject size and same image quality (coc), no.

That's an interesting viewpoint.

not really. it's just math.


No matter what the focal length of the lense is, the further away the
focal plane is, the greater the depth of field will be for any aperature.

As an example, if one is taking a head and shoulders portrait with a
large aperature, it is quite likely that part of the subject will be out
of focus slighty. Moving back a few feet with the same lense and
aperature will result in a deeper depth of field, so that all of the
subject should be in focus. The drawback is that the image size will be
smaller, and thus require more enlargement to obtain the same size image,
with the resulting loss of resolution with the enlarged image.

Phil Hobbs
Guest

Sun Aug 26, 2018 7:45 pm   



On 08/25/2018 06:06 PM, nospam wrote:
Quote:
In article <ZYGdnUsaBKCjTRzGnZ2dnUU7-TednZ2d_at_supernews.com>, +++ATH0
news_at_ringpiece.local> wrote:

One other factor to bear in mind: the depth of field varies with lens
focal length, not field of view of the subject.

actually, it's aperture.

actually, it's the ratio of focal length to aperture.

nope. depth of field is a function of physical aperture.

what you describe is f/stop, which is used for exposure purposes, and
in some cases (usually movies), t/stops are used, which is actual light
transmission through the lens, not a simple ratio.


For an ideal optical system, the depth of _focus_ (on the image side) is
a function only of wavelength and numerical aperture, i.e. the sine of
the half-angle of the cone defined by the rim rays (i.e. the illuminated
cone). That's where wave properties come in.

On the object side, the depth of _field_ equals the depth of focus
scaled by the square of the magnification. Magnification is of course
the ratio of the object distance to the image distance.

Aberrated optical systems degrade a bit more slowly because they're not
as good to begin with.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

aioer
Guest

Fri Aug 31, 2018 6:45 pm   



Blue light is bad for your eyes. that includes monitors and leds.
They suggest making sure you have UV blocking glasses at all times and
blue blocking glasses too.

default
Guest

Fri Aug 31, 2018 11:45 pm   



On Fri, 31 Aug 2018 10:20:11 -0700, aioer <aioer_at_aioer.com> wrote:

Quote:
Blue light is bad for your eyes. that includes monitors and leds.
They suggest making sure you have UV blocking glasses at all times and
blue blocking glasses too.

I expect that's true to some extent. Fluorescent light and sunlight
is bad for beer, and anything that's bad for beer...

Some quack made the rounds of the place I was working trying to sell
us, or sell the guy handling maintenance of our buildings, on the idea
that switching to these ghastly super "cold" (high color/temperature)
fluorescent lights would improve visual acuity and were more
efficient. (lumens/watt)

I was a guinea pig and got them in my office and workshop. They may
have improved acuity slightly, but they weren't what we were used to
and very unpleasant to work under. I switched the lights back to
"daylight" ones and put the kibosh on the salesman's dreams.

They were thinking of switching the chemistry labs over to the new
lights. We tested drugs that degraded in fluorescent lighting - in
fact it was one part of our degradation studies: subject the drugs
and packaging to bright fluorescent lights, high temperature, and high
humidity to come up with practical expiration dates on pharmaceutical
products.

The instruments I worked on contained deuterium light sources (a full
spectrum light that went into the "vacuum UV range," very short
wavelengths are absorbed by air) Not something you want your eyes
exposed to. Quartz glass passes short wave UV, borosilicate glass
passes light in the near-ultraviolet range. Plastic tends to absorb
UV so I'd use plastic safety glasses around the exposed light sources.
We scanned them in one of our scanning spectrophotometers to determine
the UV cut-off before hand.

Strong UV light also produces ozone, so for health reasons I tried to
minimize exposure.

Mr. Man-wai Chang
Guest

Sun Sep 02, 2018 6:45 pm   



On 9/1/2018 1:20 AM, aioer wrote:
Quote:
Blue light is bad for your eyes.  that includes monitors and leds.
They suggest making sure you have UV blocking glasses at all times and
blue blocking glasses too.


If they were really that bad, shouldn't all eye-glasses have blocked
them by default?

Legislation or regulatory action? :)

--
@~@ Remain silent! Drink, Blink, Stretch! Live long and prosper!!
/ v \ Simplicity is Beauty!
/( _ )\ May the Force and farces be with you!
^ ^ (x86_64 Ubuntu 9.10) Linux 2.6.39.3
不借貸! 不詐騙! 不賭錢! 不援交! 不打交! 不打劫! 不自殺! 不求神! 請考慮綜援
(CSSA):
http://www.swd.gov.hk/tc/index/site_pubsvc/page_socsecu/sub_addressesa

knuttle
Guest

Sun Sep 02, 2018 7:45 pm   



On 9/2/2018 1:03 PM, Mr. Man-wai Chang wrote:
Quote:
On 9/1/2018 1:20 AM, aioer wrote:
Blue light is bad for your eyes.  that includes monitors and leds.
They suggest making sure you have UV blocking glasses at all times and
blue blocking glasses too.

If they were really that bad, shouldn't all eye-glasses have blocked
them by default?

Legislation or regulatory action? Smile

I don't see why not legislation and regulation is the solutions to all
problems. Wink

default
Guest

Sun Sep 02, 2018 8:45 pm   



On Mon, 3 Sep 2018 01:03:16 +0800, "Mr. Man-wai Chang"
<toylet.toylet_at_gmail.com> wrote:

Quote:
On 9/1/2018 1:20 AM, aioer wrote:
Blue light is bad for your eyes. that includes monitors and leds.
They suggest making sure you have UV blocking glasses at all times and
blue blocking glasses too.

If they were really that bad, shouldn't all eye-glasses have blocked
them by default?

Legislation or regulatory action? Smile


Not necessarily. It is a perfect example of capitalism and marketing.
You create the need (using fear as the motivator in this case) then
sell the solution.

Oops. I forgot, they already did it:

"The BluBlocker experience all starts when you first put on a pair.
The world will change and you'll never want to go back to ordinary
sunglasses again. The high-definition Malenium lenses block 100% of UV
and blue light, giving you a level of protection and clarity that only
BluBlocker sunglasses provide."

"Why is Blocking Blue Light So Important?

Blue light doesn't focus on the retina which is the focusing screen of
the eye whereas other colors focus close to the retina. When you
"block blue light" with BluBlocker sunglasses you eliminate this
problem. Objects appear clearer, sharper, and well defined. You get
amazing clarity and the best protection with BluBlocker's
high-definition Malenium lenses."

I think Malenium is right next to Unobtanium in the periodic chart; it
is really good shit and very, very exclusive...

Mr. Man-wai Chang
Guest

Sun Sep 02, 2018 9:45 pm   



On 9/3/2018 1:51 AM, knuttle wrote:
Quote:

If they were really that bad, shouldn't all eye-glasses have blocked
them by default?

Legislation or regulatory action? :)

I don't see why not legislation and regulation is the solutions to all
problems. Wink


Other than kids, I think grown-up eyes should really avoid too much blue
and UV light.

--
@~@ Remain silent! Drink, Blink, Stretch! Live long and prosper!!
/ v \ Simplicity is Beauty!
/( _ )\ May the Force and farces be with you!
^ ^ (x86_64 Ubuntu 9.10) Linux 2.6.39.3
不借貸! 不詐騙! 不賭錢! 不援交! 不打交! 不打劫! 不自殺! 不求神! 請考慮綜援
(CSSA):
http://www.swd.gov.hk/tc/index/site_pubsvc/page_socsecu/sub_addressesa

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