do lens-mount adapters effect focal length?

Started Jun 22, 2010 | Discussions
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supergong123 New Member • Posts: 2
do lens-mount adapters effect focal length?

So I'm waiting for my 7d to arrive in the mail and am researching lenses for it. I'm considering some lenses that are not canon-mount types and would need to buy lens adapters. My question is this; how does the adapter effect the focal length of the lens if at all. I'm assuming some adapters will set the lens farther out from the camera body. wouldn't this increase the effective focal length of the lens? I know that for practical purposes the difference is negligible, maybe only changing the focal length by a few mm, so this is more me being curious than me trying to decide whether or not to use an adapter. Unless there are other disadvantages I'm unaware of...

Also, I'm specifically looking for for f/1.4 lenses that are around the 30mm and 45-50mm range (for the apc-s sensor, so 18mm and 30-35mm for full frame lenses.) I'd like to not spend more than $450 if possible and I don't have a problem buying used. I know about the sigma 30mm (apc-s) and the canon 50mm (FF). You guys have any other recommendations on specific lenses or good places to buy? (either online, I know about keh.com, or at a store in the Los Angeles area.) Thanks!

supergong123 OP New Member • Posts: 2
Re: do lens-mount adapters effect focal length?

above is supposed to read "about" 18mm or "about" 30-35mm. auto formating turned the about sign into a strikeout apparently...

nokem
nokem Contributing Member • Posts: 729
Only the FD adapter

As far as I know only the Canon FD adapter will change the focal length

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Shoot.

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akin_t Senior Member • Posts: 2,923
Re: do lens-mount adapters effect focal length?

Don't.

Just use lenses of the EF or EF-S mount. There's really nothing I have to say on the subject. There is no sort of lens you are looking for that isn't available on the EF or EF-S mount from Canon, Sigma, Tokina or Tamron.

For goodness sake why all this extra trouble?

supergong123 wrote:

So I'm waiting for my 7d to arrive in the mail and am researching lenses for it. I'm considering some lenses that are not canon-mount types and would need to buy lens adapters. My question is this; how does the adapter effect the focal length of the lens if at all. I'm assuming some adapters will set the lens farther out from the camera body. wouldn't this increase the effective focal length of the lens? I know that for practical purposes the difference is negligible, maybe only changing the focal length by a few mm, so this is more me being curious than me trying to decide whether or not to use an adapter. Unless there are other disadvantages I'm unaware of...

Also, I'm specifically looking for for f/1.4 lenses that are around the 30mm and 45-50mm range (for the apc-s sensor, so 18mm and 30-35mm for full frame lenses.) I'd like to not spend more than $450 if possible and I don't have a problem buying used. I know about the sigma 30mm (apc-s) and the canon 50mm (FF). You guys have any other recommendations on specific lenses or good places to buy? (either online, I know about keh.com, or at a store in the Los Angeles area.) Thanks!

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guy schlacter Senior Member • Posts: 1,499
Re: do lens-mount adapters effect focal length?

If you buy the adapter, I suggest you buy the one that supports the AF confirm.

As far as focal length, it is negligible if anything. Also, I don't recommend the adapters with the screw set, but use the spring loaded tab instead.

-Guy

Lemming51
Lemming51 Forum Pro • Posts: 14,316
Most lens-mount adapters do not change focal length

Mount adapters for fitting Nikon, Contax/Yashica, Pentax screw and K, Olympus OM, Leica R lenses to EOS cameras do not change the focal length. The amount of "extension" applied is only to match the lens to sensor distance to the lens's "native" mount distance. The lens to film plane distance for all of these lenses is longer than EOS. If you want the full "old school" manual experience with inconvenient stop-down metering, have at it.

However, the Canon FD/FL lenses had a shorter mounting distance than the EF EOS design. So mounting these lenses to an EOS camera with a simple ring adapter does effectively apply extension, which makes them closer focusing (good for macro), but makes it impossible to focus beyond a meter or 2. Typical FD to EOS adapters have corrective lens elements to restore infinity focus, but these necessarily also act as a 1.26x teleconverter that results in the loss of 2/3 stop maximum aperture and degraded image quality. Unless you have an FD macro lens, or one of the FD super teles and Canon's own original high quality FD/EOS adapter (rare and $$$$ if you can find them used), FD/FL lenses are best left to the Four Thirds crowd who can adapt them without the optical corrective elements.

supergong123 wrote:

So I'm waiting for my 7d to arrive in the mail and am researching lenses for it. I'm considering some lenses that are not canon-mount types and would need to buy lens adapters. My question is this; how does the adapter effect the focal length of the lens if at all. I'm assuming some adapters will set the lens farther out from the camera body. wouldn't this increase the effective focal length of the lens? I know that for practical purposes the difference is negligible, maybe only changing the focal length by a few mm, so this is more me being curious than me trying to decide whether or not to use an adapter. Unless there are other disadvantages I'm unaware of...

Also, I'm specifically looking for for f/1.4 lenses that are around the 30mm and 45-50mm range (for the apc-s sensor, so 18mm and 30-35mm for full frame lenses.) I'd like to not spend more than $450 if possible and I don't have a problem buying used. I know about the sigma 30mm (apc-s) and the canon 50mm (FF). You guys have any other recommendations on specific lenses or good places to buy? (either online, I know about keh.com, or at a store in the Los Angeles area.) Thanks!

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Karl Gnter Wnsch Forum Pro • Posts: 11,408
Re: do lens-mount adapters effect focal length?

supergong123 wrote:

So I'm waiting for my 7d to arrive in the mail and am researching lenses for it. I'm considering some lenses that are not canon-mount types and would need to buy lens adapters.

With a lens budget of $450 this is like buying a Ferrari without wheels and then having to put bicycle wheels on it because you blew the budget on the body...

Unless there are other disadvantages I'm unaware of...

There are plenty of disadvantages.

First of all good non-Canon-mount lenses in your range aren't available for your budget. Only Minolta MD and Canon FD mount lenses are dirt cheap - because you can't mount them on any sort of decent DSLR without a teleconverter/adapter which costs you not only lens speed, but also increases focal length by about 1.25 and is of abysmal optical quality (coke bottle bottom has probably superior optical properties)...

Good fast manual lenses for other systems such as Nikon are still quite expensive and you don't have any automatic functions, so you have to focus manually with the aperture wide open, after doing so you have to close the aperture manually to the desired value and then take the shot. An awkward and convoluted routine which for little to no savings does make little sense to endure.

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regards
Karl Günter Wünsch

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