What influences lens size?
My Nikon 50mm lens is a lot smaller
than my brother-in-law's Sigma 50mm. Why is that when they both have the same
focal length?
Nikon
Lets Slip New 50mm ƒ1.8G Silent Wave Lens
Focal length is only one factor that
influences the physical size of the lens, and it's not the main one. The
maximum aperture also plays an important role because the larger the aperture,
the bigger the lens has to be to accommodate that aperture. A 50mm f/1.8 lens
will be physically smaller and lighter than a 50mm f/1.4 and that, in turn,
will be much smallerand lighterthan a 50mm f/1.2. Allied to maximum aperture is
optical design; the wider the maximum aperture, the more glass elements there
tends to be in the lens, which also increases size and weight.
Finally, if the lens has any specialist
characteristics this also results in a size increase. Is the Sigma 50mm a basic
standard lens or a macro version? That could also explain the size difference.
Cropping to create close-ups
I enjoy shooting close-ups of
everyday objects and have been thinking about buying a macro lens. But they're
expensive, and I don't have cash to burn, so I'm wondering if I could just crop
the shots taken with my 50mm prime lens. Printed to A4 or viewed on-screen,
will I really notice the difference in quality? My DSLR is a 16.2-megapixel
Nikon D7000.
Cropping
to create close-ups
It all depends how much you crop them. A
proper macro lens allows you to focus very close and fill the frame with tiny
subjects. At 1:1 (life-size) repro, you can fill the frame with an area the
same size as your D7000's sensor, so around 25x16mm. Cropping an area out of a
shot taken with a 50mm lens to match that isn't feasible as you'd be enlarging
a fraction of the image area. However, for everyday details, cropping 50mm
images to enlarge the subject is perfectly acceptable.
The output size of an image from your D7000
is approx 12xl6in at 300dpi. You could crop a quarter of that image and still
have an output size of 6x8in at 300dpi. However, by interpolating the file
you'd be able to print bigger than 6x8in - easily up to A4 at 300dpi and bigger
if you dropped the print resolution to 240dpi or even 180dpi. All you do to
interpolate is go to lmage>lmage Size, enter the new dimensions of the
image, click on Bicubic Smoother at the bottom of the window, then click OK.
For images to be viewed on your computer
screen or put online, you can crop in closer because screen images only need to
be at 72dpi. So, if you enlarge one of your 50mm images to 100%, crop an area
that measures only 4x3in (Vi6th the total image areal), then convert the
cropped image from 300dpi to 72dpi - it would measure around 16xl2in and look
great on screen.
Moody skies
I have a Nikon D3100 and have started
shooting landscapes, but have been having difficulty getting to grips with the
Bulb mode. Even using graduated filters I am struggling to capture moody,
moving clouds and instead keep getting overexposed skies. What am I doing
wrong?
On most DSLRs, 30 seconds is the longest
automatic exposure possible. To exceed this, you will need to use your camera's
Bulb mode, allowing you to manually lock the shutter open. However, an exposure
upwards of 30 seconds is normally only possible in low light. If you are
getting blown-out results, too much light is reaching the sensor. You could try
using a lower ISO and smaller aperture to help rectify this, but I suspect you
are simply trying to achieve an exposure that is too long for the conditions. Try
waiting until the twilight hours when light fades, or buy a solid Neutral
Density filter. While a grad is designed to just hold back the sky, a solid ND
will lengthen overall exposure. They are available in varying strengths, with a
three-stop ND filter a useful buy. If you're wanting exposures of a minute or
more, you will need an extreme ND such as Lee Filters' Big Stopper or Hitech’s
Pro Stop, both of which offer ten stops of filtration. When shooting, review
the monitor and histogram regularly to judge whetheryour exposures are correct.
