Go Back   Steve's Digicams Forums > Digicam Help > Newbie Help

Thread Tools Search this Thread
Old Apr 30, 2010, 7:47 PM   #1
Join Date: Dec 2009
Posts: 64
Default zoom calculation

If I have 2 lens that has 10x zoom and put them end to end, all at 10x zoom, how much total zoom do I get?
chengbin is offline   Reply With Quote
Sponsored Links
Old Apr 30, 2010, 8:33 PM   #2
Senior Member
TCav's Avatar
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,395

I don't think you can do what it is you're talking about.

When a manufacturer quotes a 10X zoom, that is the ratio of the smallest focal length to the longest. That is, the lens has a focal length of, for instance, 5mm at the wide end and 50mm at the tele end. ( 50mm / 5mm =10 ) You can't stack those types of lenses. They are attached to the camera and can't be removed.

If you're talking about a 2X teleconverter, for instance, mounted on a camera's lens, it would double the focal length of that lens, but at both ends. That is, instead of being a 5mm-50mm lens, it would be a 10mm-100mm lens, which would still be a 10X zoom. ( 100mm / 10mm =10 )
  • The lens is the thing.
  • 'Full Frame' is the new 'Medium Format'.
  • "One good test is worth a thousand expert opinions." - Tex Johnston, Boeing 707 test pilot.

Last edited by TCav; Apr 30, 2010 at 8:47 PM.
TCav is offline   Reply With Quote
Old May 3, 2010, 8:14 AM   #3
Senior Member
BillDrew's Avatar
Join Date: Jun 2002
Location: Hay River Township, WI
Posts: 2,512

TCav has it right.

I don't want to think about what that kind of stacking would do the the effective f/stop. Could be forced to do using something like ISO 1600 to be able to get a shutter speed much faster than a quarter second in bright sunlight. Even if the magnified distortions didn't stop you from using it, that would.
BillDrew is offline   Reply With Quote
Old May 9, 2010, 8:29 PM   #4
Senior Member
RioRico's Avatar
Join Date: Aug 2008
Location: In mountainous California or Arizona or Guatemala or somewhere.
Posts: 224

For better answers, we'd need to know: what camera, what lenses?

Usually when you see a zoom described as 10x or 20x or whatever, it's attached to a P&S (point-and-shoot) camera, and it's difficult to stack another superzoom atop it. A zoom for a dSLR will carry numbers like 18-250 or 50-500, and while it may be *possible* to stack another zoom atop it, the results won't be pretty.

With a dSLR, you can stretch a tele or zoom by adding a TC (teleconverter) behind the lens, but those beyond 1.4x generally suck. With a point-and-shoot, you can add a tele adapter in front, but these ALWAYS suck. Stacking zoom-upon-zoom will REALLY suck. The optics just aren't made for this abuse.

If you need tremendous reach with a dSLR, mount it on a telescope. If you need great reach with a P&S... well, too bad. Get a dSLR.
RioRico is offline   Reply With Quote

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

All times are GMT -5. The time now is 12:17 AM.