Tele convertor question

TheNissanMan

TheNissanMan

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Ryan
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From my understanding a tele convertor is a cheap way of extending your current lens lineup by boosting it's zoom capabilities...

Now If I have a Canon 500d would any canon TC work with any Canon compatible lens or are they lens specific ?

If I'm right with my thinking I would planning on using this with the Tamron 70-300 which you get with the Canon bundles until I upgrade the lens to a better zoom and then be able to use it with that as well...
 
A Canon branded teleconverter won't fit but offerings from other manufacturers should. Whichever one you choose will require you to focus manually and quality is likely to be degraded.....don't expect the earth from the combination.

Bob
 
A 1.4x TC loses you 1 stop of light, so an f4 max aperture lens becomes an f5.6, a f5.6 becomes an f8 etc. A 2x TC loses you 2 stops of light, so an f4 max aperture lens becomes an f8, a f5.6 becomes an f11 etc.

By magnifying the light from the lens you use it with, you also show up any deficiencies in the original lens. If the lens is already only just sharp enough to produce detail at a level that the sensor can make use of, adding a TC won't allow you to see any more detail, it'll just be magnifying blur.

Given lenses tend to sharpen up when you stop them down (i.e. use them at an aperture a bit below their widest), you may find the combo of the lens and the TC is just too 'dark' at the aperture required to give a sharp image.

This is why TCs are best used on already very sharp lenses (usually primes, i.e. single focal lengths or very exotic zooms) that are also bright (low f number) to begin with.

I would not hold out much hope for great images from a Tamron kit zoom...

Whichever way, don't push it, get the 1.4x TC rather than the 2x if you really want to use a TC.

Andy
 
My Canon 2xTC will not fit on all my Canon lenses - you need to check before purchasing.
For example, it wont fit the 24-105 but will fit the 70-200

Also - most Canon DSLRs will not auto-focus with a 2xTC unless you are using an f2.8 lens.
 
DuncanDisorderly said:
My Canon 2xTC will not fit on all my Canon lenses - you need to check before purchasing.
For example, it wont fit the 24-105 but will fit the 70-200

Also - most Canon DSLRs will not auto-focus with a 2xTC unless you are using an f2.8 lens.
Click to expand...

I believe you can 'get around' this by applying a small bit of tape to disconnect a couple of pins - but the AF is not very reliable. Centre point-only is the recommendation.

Andy
 
On certain Canon bodies, when you apply a TC, you lose autofocus also. I have a 2x Canon TC, which I find I rarely use on my 70-200L, due to previously mentioned, loss of a stop or two, manual focusing, and it also becomes a fairly lengthy combination to hand hold. There is also I bit of a loss in image quality.
 
AndyElliott said:
I believe you can 'get around' this by applying a small bit of tape to disconnect a couple of pins - but the AF is not very reliable. Centre point-only is the recommendation.

Andy
Click to expand...

Tried this, but all it did was hunt around the focus point, never achieving focus.

I was thinking of selling my 2xTC but it works superbly on my 24mm TS-E, so long last it is getting some use :)
 
DuncanDisorderly said:
Tried this, but all it did was hunt around the focus point, never achieving focus.

I was thinking of selling my 2xTC but it works superbly on my 24mm TS-E, so long last it is getting some use :)
Click to expand...

I've not experienced it directly - not having Canon - but two Canon shooter mates do this - same issue - lousy AF. Nice of Canon to fix the issue by disabling it..
 
Canon Bob said:
You'll have to explain that one Andy?

Bob
Click to expand...

There are two ways to solve 'poor AF performance'. One is make it better, the other is say it will never work and force you to use MF. That's what I meant! :D

Edit: I suppose it was nice they allowed such an easy way to remove the second solution, even if it does result in poor AF!
 
Hmmm - not sure about the lousy AF thing - I hear a Nikon axe being ground
I'd be surprised if 'normal' Nikons do anything different....
An f4 lens with 4 times less light reaching the camera is going to give anybodies AF a struggle.
The Canon 1 series will just cope, but the lesser models will not......

The other challenge is that the 70-200 is very quick to focus.
I don't think the camera says 'focus closer' and watch till it looks right, I think the camera tells the lens to jump by X. When you mask the magic TC pins the camera no longer knows about the TC. Hence when the camera says jump by X, the lens effectively jumps 2X and sails swiftly past the actual focus point. Then the camera re-thinks and tells the lens to jump X back in the other direction neatly landing back at the start point. And this repeats until the battery goes flat....
Hence the hunting is due to the camera not knowing about the TC because we masked the pins.
 
AndyElliott said:
There are two ways to solve 'poor AF performance'. One is make it better, the other is say it will never work and force you to use MF. That's what I meant! :D

Edit: I suppose it was nice they allowed such an easy way to remove the second solution, even if it does result in poor AF!
Click to expand...

The AF sensors use phase detection and aperture diameter and mirror box size becomes a limitation. Contrast detection doesn't have this problem but is more at the mercy of the subjects composition until technology improves. AF using contrast detection beyond f/5.6 is not disabled but is less practical in high speed situations.
I guess that they solved the AF phase detection problem by offering lenses with the appropriate aperture sizes...in short, you pay for a better body (1Dsrs) or a better lens (f/2.8 or faster). The only real fly in the ointment is why they limit the 5D...probably to avoid hitting 1Ds sales too hard.

Bob
 
Canon Bob said:
The AF sensors use phase detection and aperture diameter and mirror box size becomes a limitation. Contrast detection doesn't have this problem but is more at the mercy of the subjects composition until technology improves. AF using contrast detection beyond f/5.6 is not disabled but is less practical in high speed situations.
I guess that they solved the AF phase detection problem by offering lenses with the appropriate aperture sizes...in short, you pay for a better body (1Dsrs) or a better lens (f/2.8 or faster). The only real fly in the ointment is why they limit the 5D...proably to avoid hitting 1Ds sales to hard.

Bob
Click to expand...

They are valid technical reasons, but other manufacturers can get their 2x converters working on f5.6 lenses with AF. Phase detection on just the centre point, if the AF sensor is sufficiently sensitive can work just fine. On the Oly bodies, even going back to the dinosaur bodies with only 3 AF points, the less-bright lenses (albeit not very quickly) could phase-detect AF with the 2x converter (they didn't have contrast-AF!).

I suspect it is more a commercial reason on the later bodies for the reason you suggest!

Andy
 
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