AboutScott Valentine Expertise Most anything about digital post processing (Photoshop, etc), effects, and image restoration, some technical information about digital imaging systems, light and electron microscopy, optical physics and image analysis. I can help with shooting basics, lighting setups, and getting the most out of your digital camera. I am also an 'expert' here for Photoshop (Computers/Technology > Software > Graphics Software > Photoshop).
Please - NO operating, trouble-shooting, or purchase questions on point-and-shoot or video cameras.
Experience Author, "Real World Compositing with Photoshop CS4" (available January 2009 from Peachpit.com). I've been an image analyst and advanced amateur photographer for over 6 years. I run an Adobe user group, focusing on digital media, and have lectured on digital image capture systems. Currently, I am an administrator for a rather large instructional Photoshop forum
Organizations Adobe User Groups, National Association of Photoshop Professionals, Advanced Imaging Specialists
Publications CommunityMX.com, Real World Compositing with Photoshop CS4 (Adobe Press)
Education/Credentials Bachelor of Physics, University of California, San Diego
Awards and Honors Winner: Best in Show and several category first place awards - Imaging Professionals of the Southwest Print Competition (multiple years)
Question Hi, I currently have a digital Canon Rebel XT with a 70 - 300mm 1:4-5.6 telephoto lens on it.I recently saw an ad for a lenses doubler that said it could be used with any size lense. Having the need for greater zoom capabilities without having to buy a whole new lens I was interested to find out more. I was curious if you had ever used such a lense, and if so does it distort the quality of the photos at all? Any insight on the matter would be greatly appreciated because I can't find a whole lot of general information on this specific type of lense.
Answer Thanks for a great question, Crystal.
Lens doublers sound like a fantastic bargain at first, and in many cases they are very useful. However, the biggest drawback is that they 'slow' your lens down. The way doublers work is by extending the focal length of your existing lens, but they do so at the cost of the amount of light that gets through to your sensor. That means you have to increase your shutter time or the sensitivity/ISO. Longer shutter times mean you have to keep the camera more steady, and higher ISO means you are risking more noise in your images.
So, when are doublers a good idea? When you have extremely high quality telephoto lenses (not zoom lenses) and a lot of available light. I've seen great results from 300mm lenses with doublers, but the lenses themselves are typically very expensive and very fast (meaning, they have large apertures so can capture a lot of light).
A better choice for you might be a teleconverter. These are usually around 1.2x to 1.6x and have less of a problem with losing light. They still aren't perfect, but are a much better solution, especially if you want to increase the range of a zoom lens. Keep in mind that neither doublers nor teleconverters are 'matched' to your lens unless you buy specialized sets from the same manufacturer that are meant to work together. This translates into degraded lens performance, though you may not notice it all the time.
A 70-300 lens with an aperture range of 4-5.6 is not a good match for a doubler, so if you decide you really want it, make sure you purchase from some place that has a good return policy. Test it out in a variety of situations to see whether it's worth the trade-offs to you.
I hope this helps - if you have further questions, please don't hesitate to ask!
