Optics coverage on 7x17inch - my math is wrong

I recently shared some email with a gentleman who said that a Schneider
150mm Super Symmar XL might adequately cover 7x17inch format. I did a
little math and calculated that it would take a 150mm lens that covers
100 degrees to do the job. But when I look at the specs for the 105
degree 150mm SS-XL is that its rate to cover 398mm, not the 466mm needed
by the 7x17.

OK. I must be making a mistake in my math. I used right angle trig to do
my calculations. Can someone please correct me?

1) 9.19inches opposite side (diagonal from center of the 7x17inch format
to the corner) divided by 5.9inches adjacent side (150mm lens length)
equals 1.55

2) Tangent 1.55 equals 50 degrees

3) 2 times 50 degrees to get the full angle equals 100 degrees

This means several super-wide angle lenses might cover and be useful on
7x17. These would include:

* Schneider 150mm Super Symmar XL

* Schneider 165mm Super Angulon

* Nikkor 150mm SW

* Rodenstock 155mm Grandagon

But somethings not right. Where did I goof?

OK. I found my mistake. Tan 1.55 is really 57 degrees. I read the
table wrong.

To work on 7x17 format, a Schneider 150SS-XL will need to cover 114 degrees.

By comparison, I use a 110SS-XL on 8x10. To accomplish this, the lens
needs to cover 112 degrees. I've confirmed that while there's some
fall-off toward the edge of the frame, the image remains acceptably
sharp in contact prints in the 8x10inch format.

I may, therefore, be possible for a 150SS-XL to work acceptably well on
7x17. If anyone has direct experience in this matter, could you share
your thoughts?

Regards - Chris


Christopher Perez wrote:

I recently shared some email with a gentleman who said that a Schneider
150mm Super Symmar XL might adequately cover 7x17inch format. I did a
little math and calculated that it would take a 150mm lens that covers
100 degrees to do the job. But when I look at the specs for the 105
degree 150mm SS-XL is that its rate to cover 398mm, not the 466mm needed
by the 7x17.

OK. I must be making a mistake in my math. I used right angle trig to do
my calculations. Can someone please correct me?

1) 9.19inches opposite side (diagonal from center of the 7x17inch format
to the corner) divided by 5.9inches adjacent side (150mm lens length)
equals 1.55

2) Tangent 1.55 equals 50 degrees

3) 2 times 50 degrees to get the full angle equals 100 degrees

This means several super-wide angle lenses might cover and be useful on
7x17. These would include:

* Schneider 150mm Super Symmar XL

* Schneider 165mm Super Angulon

* Nikkor 150mm SW

* Rodenstock 155mm Grandagon

But somethings not right. Where did I goof?

1) 9.19inches opposite side (diagonal from center of the 7x17inch format
to the corner) divided by 5.9inches adjacent side (150mm lens length)
equals 1.55

2) Tangent 1.55 equals 50 degrees

3) 2 times 50 degrees to get the full angle equals 100 degrees

This means several super-wide angle lenses might cover and be useful on
7x17. These would include:

* Schneider 150mm Super Symmar XL

* Schneider 165mm Super Angulon

* Nikkor 150mm SW

* Rodenstock 155mm Grandagon

But somethings not right. Where did I goof?
--------------------------------------------------------------------------
-------------------------------------
To just cover the 7x17 format you need a circle of diameter = sq root of (7
squared + 17 squared) inches = 18.4 inches or about 467mm.

The diameter of the circle of coverage of a lens is (simple trigonometry):

C = 2 F tan (angle of coverage / 2)

Given an angle of coverage of 100 degrees, you would need a focal length:

F = C / [ 2 tan ( angle/2) ]

The tangent of 50 degrees (100 / 2) is about 1.19, therefo

F = 467mm / (2 x 1.19) = about 196mm

That is, a lens with an angle of coverage of 100 degrees would need to be at
least 196mm in focal length to cover the 7x17 format.

That eliminates every single lens in your list.




Bob G

Christopher Perez wrote:
OK. I found my mistake. Tan 1.55 is really 57 degrees.

Your terminology is not right. You want the arctangent or inverse
tangent, not the tangent. It is sometimes denoted ATan. Also with a
scientific calculator, you get it if you first press the inverse button
and then the tan button. The tan function is applied to an angle and
gives you the value of the tangent of that angle. The atan function
takes a number and gives you the angle with that number as tangent. But
that is not quite correct because many angles have the same tangent. So
the atan function gives you the angle with that tangent in a certain
predetermined range. You sometimes have to add a multiple of pi to get
the right angle for your application. For lens calculations, you can
usually ignore that subtlety.

I read the
table wrong.

To work on 7x17 format, a Schneider 150SS-XL will need to cover 114
degrees.

By comparison, I use a 110SS-XL on 8x10. To accomplish this, the lens
needs to cover 112 degrees. I've confirmed that while there's some
fall-off toward the edge of the frame, the image remains acceptably
sharp in contact prints in the 8x10inch format.

I may, therefore, be possible for a 150SS-XL to work acceptably well on
7x17. If anyone has direct experience in this matter, could you share
your thoughts?

Regards - Chris


Christopher Perez wrote:

I recently shared some email with a gentleman who said that a
Schneider 150mm Super Symmar XL might adequately cover 7x17inch
format. I did a little math and calculated that it would take a 150mm
lens that covers 100 degrees to do the job. But when I look at the
specs for the 105 degree 150mm SS-XL is that its rate to cover 398mm,
not the 466mm needed by the 7x17.

OK. I must be making a mistake in my math. I used right angle trig to
do my calculations. Can someone please correct me?

1) 9.19inches opposite side (diagonal from center of the 7x17inch
format to the corner) divided by 5.9inches adjacent side (150mm lens
length) equals 1.55

2) Tangent 1.55 equals 50 degrees

3) 2 times 50 degrees to get the full angle equals 100 degrees

This means several super-wide angle lenses might cover and be useful
on 7x17. These would include:

* Schneider 150mm Super Symmar XL

* Schneider 165mm Super Angulon

* Nikkor 150mm SW

* Rodenstock 155mm Grandagon

But somethings not right. Where did I goof?

Christopher Perez wrote:
OK. I found my mistake. Tan 1.55 is really 57 degrees.

Your terminology is not right. You want the arctangent or inverse
tangent, not the tangent. It is sometimes denoted ATan. Also with a
scientific calculator, you get it if you first press the inverse button
and then the tan button. The tan function is applied to an angle and
gives you the value of the tangent of that angle. The atan function
takes a number and gives you the angle with that number as tangent. But
that is not quite correct because many angles have the same tangent. So
the atan function gives you the angle with that tangent in a certain
predetermined range. You sometimes have to add a multiple of pi to get
the right angle for your application. For lens calculations, you can
usually ignore that subtlety.

I read the
table wrong.

To work on 7x17 format, a Schneider 150SS-XL will need to cover 114
degrees.

By comparison, I use a 110SS-XL on 8x10. To accomplish this, the lens
needs to cover 112 degrees. I've confirmed that while there's some
fall-off toward the edge of the frame, the image remains acceptably
sharp in contact prints in the 8x10inch format.

I may, therefore, be possible for a 150SS-XL to work acceptably well on
7x17. If anyone has direct experience in this matter, could you share
your thoughts?

Regards - Chris


Christopher Perez wrote:

I recently shared some email with a gentleman who said that a
Schneider 150mm Super Symmar XL might adequately cover 7x17inch
format. I did a little math and calculated that it would take a 150mm
lens that covers 100 degrees to do the job. But when I look at the
specs for the 105 degree 150mm SS-XL is that its rate to cover 398mm,
not the 466mm needed by the 7x17.

OK. I must be making a mistake in my math. I used right angle trig to
do my calculations. Can someone please correct me?

1) 9.19inches opposite side (diagonal from center of the 7x17inch
format to the corner) divided by 5.9inches adjacent side (150mm lens
length) equals 1.55

2) Tangent 1.55 equals 50 degrees

3) 2 times 50 degrees to get the full angle equals 100 degrees

This means several super-wide angle lenses might cover and be useful
on 7x17. These would include:

* Schneider 150mm Super Symmar XL

* Schneider 165mm Super Angulon

* Nikkor 150mm SW

* Rodenstock 155mm Grandagon

But somethings not right. Where did I goof?

"Christopher Perez" wrote in message
. ..

You can save yourself a lot of grief and go with the Super-Anglon 210mm. 100
degrees. 500mm circle of coverage.

"Christopher Perez" wrote in message
. ..

You can save yourself a lot of grief and go with the Super-Anglon 210mm. 100
degrees. 500mm circle of coverage.

"Christopher Perez" wrote in message
. ..

You can save yourself a lot of grief and go with the Super-Anglon 210mm. 100
degrees. 500mm circle of coverage.

You can save yourself a lot of grief and go with the Super-Anglon 210mm. 100
degrees. 500mm circle of coverage.


At six and a half pounds.

Bob G

Never one to avoid grief (you know how it is with Italian motorcycles
:-) I thought about the shorter 150mm SS-XL. Alas, I'm affraid you may
be right. But it means a potentially larger cash outlay for the longer
210mm SS-XL. :-(

Since equipment is seldom the limiting factor to realizing one's vision,
I'll just sit on this a bit and ponder before making my next move.

- Chris

jjs wrote:
"Christopher Perez" wrote in message
. ..

You can save yourself a lot of grief and go with the Super-Anglon 210mm. 100
degrees. 500mm circle of coverage.