Meaning of a 2 strength close-up diopter for macro

I asked this in another thread but didn't get an answer. Specifically,
I'm wondering what effect this would have on a 400mm zoom lense which is
only capable of getting as close as 7.5 ft. I don't understand what they
mean when they say "changes the closest focusing distance from infinity
to 9.9" My current 200mm zoom will get up to 1.3 ft away so I assume
this would end up having me a couple inches away. I don't know what
exact impact to expect.

paul wrote:
OK I found the item I was looking for.
$140 Canon 500D +2 77mm 2-element close-up diopter
http://www.adorama.com/CA77CU500D.html
More info:
http://www.earthboundlight.com/photo...-diopters.html
http://www.photo.net/bboard/q-and-a-...?msg_id=0005yN

The descriptions says "changes the closest focusing distance from
infinity to 9.9"

What exactly does that mean? Sounds like it will not focus on anything
beyond 9.9 inches away. It is supposed to have a very narrow depth of
field but I guess that's a given. Sounds not much quality difference
from a 'real' macro lense except the incovenience of having to unscrew
it for anything over 10 inches away.

On Tue, 04 Jan 2005 13:49:16 -0800, paul wrote:

I asked this in another thread but didn't get an answer. Specifically,
I'm wondering what effect this would have on a 400mm zoom lense which is
only capable of getting as close as 7.5 ft. I don't understand what they
mean when they say "changes the closest focusing distance from infinity
to 9.9" My current 200mm zoom will get up to 1.3 ft away so I assume
this would end up having me a couple inches away. I don't know what
exact impact to expect.


I just got a Hoya close up filter set, and it has +1, +2, and +4 element, and
they can be added up... for anything up to +7.

I use them on my Sigma zoom, since it can only focus from about 3 feet.

I just did a test using the +2+4 combination, and if I zoom to 300mm on a
subject 3 feet away with out the filters, I can then take the same picture from
about 7" away zoomed back to 28mm, with the +6 filters. This gives some
advantages...

I posted the example on alt.binaries.photos.original under "Glasses for my
camera".

The focus range with the +6 is very small, just a few inches back and forth. You
use the zoom to adjust the frame... but the camera MUST be about 7" from the
subject.

These filters are ONLY for macro work - you must take them off to take any other
type picture. But they work very well indeed! ($80 is a good price!)

+2 means it has a focal length of 1/2 meter. This is a diopter unit
(reciprocal focal length) as used in eyeglass prescriptions. It is very
handy for calculations, as this example will show...

You said your 400-mm lens focuses down to 7.5 feet without a close-up lens
attached to it. (This is something you have to know from the lens
specifications, of course; it has nothing to do with the 400-mm focal
length.)

7.5 feet is about 2 meters. We'll call it 2 meters from here on.

The reciprocal of 2 meters is 0.5. The reciprocal of infinity is
effectively 0.

So your lens currently covers a distance range (measured in diopter units)
of 0 to 0.5.

The close-up attachment will add 2 to this, making its range (in the same
units) be 2.0 to 2.5.

It will then focus from 1/2 meter down to 1/2.5 meter (i.e., from 20 inches
down to 16 inches).

That's how close you can get.

On Wed, 12 Jan 2005 19:57:25 -0500, "mc" wrote:

+2 means it has a focal length of 1/2 meter. This is a diopter unit
(reciprocal focal length) as used in eyeglass prescriptions. It is very
handy for calculations, as this example will show...

You said your 400-mm lens focuses down to 7.5 feet without a close-up lens
attached to it. (This is something you have to know from the lens
specifications, of course; it has nothing to do with the 400-mm focal
length.)

7.5 feet is about 2 meters. We'll call it 2 meters from here on.

The reciprocal of 2 meters is 0.5. The reciprocal of infinity is
effectively 0.

So your lens currently covers a distance range (measured in diopter units)
of 0 to 0.5.

The close-up attachment will add 2 to this, making its range (in the same
units) be 2.0 to 2.5.

It will then focus from 1/2 meter down to 1/2.5 meter (i.e., from 20 inches
down to 16 inches).

That's how close you can get.


That's useful info - thanks. Do most lenses have the diopter info for them
available? Or do you have to figure it yourself?

"Bob" wrote in message
...

That's useful info - thanks. Do most lenses have the diopter info for
them
available? Or do you have to figure it yourself?

You have to take the minimum focusing distance (given in the lens
specifications) and convert it to diopters by convering it to meters and
taking the reciprocal.

I need to make a web page about this. This system of measurement is
familiar to every eye doctor (which I am not) but photographers rarely
encounter it.

--
Clear skies,

Michael A. Covington
Author, Astrophotography for the Amateur
www.covingtoninnovations.com/astromenu.html

On Wed, 12 Jan 2005 21:46:55 -0500, "mc" wrote:


"Bob" wrote in message
.. .

That's useful info - thanks. Do most lenses have the diopter info for
them
available? Or do you have to figure it yourself?

You have to take the minimum focusing distance (given in the lens
specifications) and convert it to diopters by convering it to meters and
taking the reciprocal.

I need to make a web page about this. This system of measurement is
familiar to every eye doctor (which I am not) but photographers rarely
encounter it.

I think I'll make a spread sheet of all my lenses and my +1 - +7 diopter kit
for all the distances... right now I'm kind of guessing on which lens to pick
out!

Now, if I can just figure out the field of view... !

"Bob" wrote in message
...


Now, if I can just figure out the field of view... !

Not too difficult, but more than I can express in a short newsgroup posting.

On Thu, 13 Jan 2005 00:38:50 -0500, "mc" wrote:


"Bob" wrote in message
.. .


Now, if I can just figure out the field of view... !

Not too difficult, but more than I can express in a short newsgroup posting.


Is there a spec for distance for field of view with macro? I guess I should take
pictures of a yardstick in focus and get an idea that way...

I really am only concerned with taking product shots in focus for my site.

A direct experiment is the quickest way to find out.

Field of view is basic trigonometry. Just pretend your lens (of focal
length X) is a pinhole X distance from the film, and solve the triangles.

Adding a +2 close-up lens (or whatever) keeps your lens the same distance
away from the film, but lets you get an in-focus image of a nearer subject.
That's the simplest way to approach the calculations.

I've placed on my "to-do list" the making of a web page that explains all
this in more detail...


"Bob" wrote in message
...
On Thu, 13 Jan 2005 00:38:50 -0500, "mc" wrote:


"Bob" wrote in message
. ..


Now, if I can just figure out the field of view... !

Not too difficult, but more than I can express in a short newsgroup
posting.


Is there a spec for distance for field of view with macro? I guess I
should take
pictures of a yardstick in focus and get an idea that way...

I really am only concerned with taking product shots in focus for my site.

So an out of focus shot at the distance calculated is going to be what
you get, that's simple.

mc wrote:

A direct experiment is the quickest way to find out.

Field of view is basic trigonometry. Just pretend your lens (of focal
length X) is a pinhole X distance from the film, and solve the triangles.

Adding a +2 close-up lens (or whatever) keeps your lens the same distance
away from the film, but lets you get an in-focus image of a nearer subject.
That's the simplest way to approach the calculations.

I've placed on my "to-do list" the making of a web page that explains all
this in more detail...


"Bob" wrote in message
...

On Thu, 13 Jan 2005 00:38:50 -0500, "mc" wrote:


"Bob" wrote in message
...



Now, if I can just figure out the field of view... !

Not too difficult, but more than I can express in a short newsgroup
posting.


Is there a spec for distance for field of view with macro? I guess I
should take
pictures of a yardstick in focus and get an idea that way...

I really am only concerned with taking product shots in focus for my site.