Digital SLR Cameras Forum

Digital SLRs Forum Discuss digital SLRs, lenses, RAW conversion, or anything else related to digital SLRs. You may also want to see the Nikon, Canon, and Sony camera forums.
Digital Camera Pro Reviews >>
Read and Write Digital SLR Reviews >>
Digital SLR Buyer's Guide >>
Results 1 to 3 of 3
  1. #1
    Junior Member
    Join Date
    Mar 2011
    Location
    chester, UK
    Posts
    11

    using teleconverters?

    Hi

    I'm thinking on getting a teleconverter, but Im not sure if this is what I need.
    I have an 18-200mm sigma lens (with 72mm filter thread) so i dont have to carry around several big lenses with me just one mounten on the camera. The only thing is that it goes up to 200mm, and I like to take photos of wild animals and birds that always keep a distance to humans.

    So, is a 2x teleconverter what I need?

    Most teleconverters are with a 37mm thread. What is that mean? Most lenses have a 55mm-72mm filter thread.

    What is a diopter? Is it the same as the teleconverter? like this one: http://cgi.ebay.co.uk/Brand-New-Macr...item20b7b9dcf9

  2. #2
    Learning more with every "click" mjs1973's Avatar
    Join Date
    Jun 2004
    Location
    Mineral Point, WI, USA
    Posts
    7,561

    Re: using teleconverters?

    A diopter is basically a filter that you screw onto the front of your lens that acts like a magnifying glass. These are generally used for macro photography for increasing the size of a subject when it is really close to your lens.

    A teleconverter is a special type of "lens" that mounts directly to the camera, and then you attach your regular lens to the teleconverter. A 2x teleconverter will double the focal length of any lens that you attach to it. So your 18-200mm lens will act like a 36-400mm lens. This is what you would want in order to photograph wildlife from a distance, not a diopter.

    I'm sure that sounds great, but there are a few things you need to understand about how teleconverters work. First of all, teleconverters cause you to loose light. With a 2x teleconverter, you are going to loose two stops of light. I'm guessing that the maximum aperture on your lens is about f/5.6 at 200mm. By adding a 2x TC your maximum aperture becomes f/11. This loss of light may cause your camera's AF to not work very good, or possibly disable it completely, depending on the lens/camera combo you are using. (Most cameras need an aperture of f/6.3 to auto focus.) The two stops of light loss is also going to cause your shutter speeds to drop quite a bit so you are going to have to increase your ISO or shoot when it's really bright outside to get shutter speeds fast enough to freeze motion.

    Another issue with TC's is that they can cause a loss in image quality. Any problems with image quality your lens may have, will be magnified by using a TC. If your lens is soft without a TC, it's only going to get worse with one.

    TC's are a great way to increase your focal length without spending a ton of money, but they do come at a price. This is why most people who use TC's use them with very high quality lenses with fast apertures. This is really what they are designed to be used with. TC's on consumer grade zoom lenses generally aren't the best choice.
    Mike

    My website
    Twitter
    Blog


    "I thought that because fewer wolves meant more deer, that no wolves would mean hunters' paradise. But after seeing the green fire die, I sensed that neither the wolf nor the mountain agreed with such a view."
    Aldo Leopold

  3. #3
    Junior Member
    Join Date
    Mar 2011
    Location
    chester, UK
    Posts
    11

    Re: using teleconverters?

    thanks.
    this was a very comprehensive explanation.
    regards,
    Istvan

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •