Forgot Password
Pentax Camera Forums Home

Show Printable Version Search this Thread
10-05-2011, 11:36 AM   #1
New Member

Join Date: Aug 2011
Posts: 9
Understanding zoom distance/range

I'm in the market for a telephoto zoom lens. Before I spend my unborn child's savings on it, I need help understanding the range of a lens relative to its zoom specs. For example, at what maximum distance can a 50-135mm lens shoot a portrait of a person's face? Is there a link somewhere in this wonderful internet world that explains this? If not, would someone please educate me about it? I've already googled up several permutations of the words range, zoom, distance, how-to, etc. but I haven't found anything that answers this question plainly.

The purpose of the lens is to eventually take some pictures of folks dancing in a social dance studio/club. I currently have the kit lens, 18-55 and a fast 50 prime. I'd like to get the 60-250 f4 cause it'll fulfill my long range needs and the reviews for it seems great. However, the dance environment I plan to shoot in will be relatively dark so I'm thinking the faster 50-135 f2.8 might be needed. I just don't know how far 135mm can zoom in on a couple on the dance floor, thus my question.

Thanks in advance!

10-05-2011, 12:05 PM   #2
Just1MoreDave's Avatar

Join Date: Feb 2007
Location: Aurora, CO
Photos: Gallery | Albums
Posts: 4,863
At 135mm, one person's face starts to fill the frame at 7 feet or so. I'd say 10 feet if you want a little space around a face, 6 feet is kind of extreme close-up. Unless you have to be really far away, the 50-135 will be OK, and the extra speed will be useful.
10-05-2011, 09:42 PM   #3
Veteran Member
sterretje's Avatar

Join Date: Dec 2008
Location: Roodepoort, South Africa
Photos: Gallery | Albums
Posts: 3,534
You can use the following calculators to get an idea

Lens focal length calculator (scroll down to 'Dimensional Field of View Calculator')

And if you have been shooting the dancers with your fast 50mm prime, 135mm will make the subject about 2.5 times bigger on the photo (135/50) and 250 will make the subject 5x bigger on the photo (250/50)

Example for the first calculator above:
dancer being 1.8meter tall
camera in portrait (so 24mm for the image size)
distance 5 meters
==> focal length is 65 mm

double the distance and you will have to double the focal length
10-06-2011, 07:09 AM   #4
Veteran Member
steve1307's Avatar

Join Date: Mar 2010
Location: Sydney
Photos: Gallery | Albums
Posts: 1,129
Image size = Object size x Focal length / Subject Distance

To use offline I downloaded this "Barnack" program & have on my desktop. Its similar to the DOF calculators but also give the image size.
Download from this site: Barnack

You can also load up an image youv'e shot, and it will read the exif and load those variables into the application, however the focus distance isnt in the exif data though (for Pentax anyway) so it doesnt get the image size right unless you know the approximate distance to the subject.

EDIT: oops! corrected formula (thanks Mr Goudge). It was was right in my head but the fingres got it wrong.

Last edited by steve1307; 10-12-2011 at 03:37 PM. Reason: correction
10-07-2011, 11:33 AM   #5
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,400
Steve you have a little error in your formula

for distances >> focal length, the formula is

image size = subject size x focal length / subject distance

When I say distance is >> focal length, this means typically distance is more than 10-20 x focal length. for example with a 50mm lens between 1/2 and 1 meter and above. when you move in close there is a more accurate formula but....
10-12-2011, 12:02 PM   #6
New Member

Join Date: Aug 2011
Posts: 9
Original Poster
Thanks for the links to the calculators and the other explanations.

  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
camera, dance, distance, lens, pentax help, photography, question, range
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Similar Threads
Thread Thread Starter Forum Replies Last Post
best mid to long range zoom lens sany Pentax SLR Lens Discussion 28 06-08-2011 07:59 AM
Budget mid range zoom ~ 28-105mm tim_kayak Pentax SLR Lens Discussion 12 03-20-2011 03:08 PM
which one is going to be a more useful zoom range for events on an APS-C? techmulla Pentax SLR Lens Discussion 13 01-07-2011 01:36 AM
Rambling mid-range zoom comments pacerr Pentax SLR Lens Discussion 2 10-17-2010 08:25 PM
Question About Zoom and Focal Distance Ari Pentax SLR Lens Discussion 17 10-23-2009 04:38 PM

All times are GMT -7. The time now is 09:44 PM. | See also:, part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]