I think my best advice to you is to quit fretting about your equipment
and go take some pictures. I've been taking pictures for about 40
years. I never had anything other than a standard 50mm lens for the
first 15 years. It didn't keep me from taking pictures of sunsets,
children, flowers or anything else. Your 35-70 Soligor CD is a good
quality lens which reaches from moderate wide-angle to moderate
telephoto. It's a fine, all purpose range and could conceivably be all
you'll ever need... but you have to go use it to find out.
One of the list members commented that the best sunset photo he'd ever
taken was done with an Olympus Stylus. The Stylus (Epic model) is a
point & shoot camera with an excellent 35mm f/2.8 lens. Note that this
prized photograph was not taken with a 300mm lens but with a 35mm lens.
Note that that happens to be exactly equal to the shortest focal length
of the zoom lens that you already own. Go take some pictures already!
Now for a practical lesson about f/stops, shutter speeds and film
speeds. You may remember that dreamoose told you that an "f/stop" was a
ratio between the size of the aperture of the lens and its focal
length. If you have a 50mm (focal length) lens and the aperture (or
diaphragm) control ring is set at f/4 then the size of the aperture is
50mm/4 = 12.5mm. If we close down one stop by setting the lens to f/5.6
then the size of the aperture becomes 50mm/5.6 = 8.9mm.
Now you might be asking, OK the markings on the lens are ratios but why
are they such odd numbers like 2.8, 4, 5.6, 8 , 11, 16 and 22? If you
remember your high school math for computing the area of a circle and
applied it to the size of the circles represeted by these ratios you
would discover that the area of the circle with diamter 8.9mm is half
the area of a circle with diamter 12.5mm. Likewise, the f/8 setting has
half the area of the f/5.6 setting and the f/11 setting has half the
area of the the f/8 setting. So, if each lens opening has either half
or double the area of it's neighbor's setting it will allow in either
half or double the light of its adjacent neighbors.
The same is true of shutter speeds. 1/125 second is twice as long as
1/250 second. 1/250 second is twice as long as 1/500 second. So,
increasing or decreasing the aperture by one marked stop has exactly the
same effect on exposure as increasing or decreasing the shutter speed by
one marked speed (also called a "stop" since they are equivalent in
temrs of amount of light). Changing either one up or down a notch has
the same effect on exposure. The aperture ring can halve or double the
amount of light by changing the size of the lens aperture by one stop.
The shutter speed ring can do the same by shortening or lengthening the
time that the film is exposed to the light by one "stop".
Assume that a proper exposure is determined to be f/5.6 at 1/250
second. Assume that I would like greater depth of field, ie, I would
like more things ahead of and behind the main subject to be in focus.
Inceased depth of field can be achieved by closing the lens down. The
smaller the aperture the greater the DOF. So, I decide to close the
lens down to f/8 for greater DOF. In doing so I just decreased the
amount of light that will strike the film by 1/2 since the area of the
lens opening at f/8 is only half as much as at f/5.6. In order to
compensate for loss of half the light we will increase the exposure time
by a factor of 2. Therefore, we need to decrease the shutter speed from
1/250 second to 1/125 second. That will double the amount of time that
the shutter is open and exposing the film to light. That will exactly
compensate for the smaller amount of light admitted by the smaller
aperture.
This notion of equivalence of "stops" also carries on to the film. A
200 speed film is twice as "fast" as a 100 speed film but only half as
fast as a 400 speed film. Note that halving or doubling the film speed
has exactly the same effect as changing the aperture or shutter speed
dial by one marked position.
Now for a slight anomaly of your particular lens. One stop faster than
f/4 is f/2.8 and one stop faster than that is f/2.0. On your lens you
will see the diaphragm control ring is marked at 2.5 rather than 2.8.
The reason is that the difference between 2.5 and 2.8 is only about 1/3
stop and there really isn't room to label the lens with both markings.
Third party lens producers generally competed with the camera
manufacturers by making a lens that was just a little bit "faster" than
the competition.
So, by using film of lesser or greater speed, apertures of lesser or
greater size and shutter speeds of lesser or greater time one can take
numerous pictures that are all technically equivalent in that they
control one or more of the variables used to properly expose the film.
But, that does not mean that these pictures are fully equivalent. The
correctly exposed shot taken at f/2.8 and 1/500 second will look
different from the correctly exposed shot taken at f/8 and 1/60 second.
At f/2.8 the lens will be operating in its less than optimal range and
might not be razor sharp all over. At f/8 (or perhaps f/11) it will be
operating in its sharpest range. The latter you might like for your
sunset. The former might be better for a portrait. Sometimes
exceptional quality can be a hindrance.
ps: I have about a dozen lenses. I have a 2000mm telescope and a 500mm
spotting scope but not a 300mm lens. Apart from the telescopes my
longest lens is a 250mm. I've only ever used the 250 once and have
never felt the need for a 300mm. Go out and take some picture!!!
End of lesson. Now take some pictures.
Chuck Norcutt
Woburn, Massachusetts, USA
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