Change gear with our partner, MPB

Teleconverter Problems


devlin 11 653 39 India
6 Jun 2010 9:43AM
Just got a 2x TC (Digital) from a friend who's not using it anymore...hopefully if there;s a moon tonite i intend to use it with my Canon EFS 75-300mm lens will see / share how it turns out Smile
RichBrew 11 151 England
6 Jun 2010 12:00PM

Quote:I'm curious as to the problems with TCs on zoom lenses people keep alluding to on this thread... - AF worked fine.


If your primary optic is fast enough then AF issues may well never arise. It's optical quality that will suffer the most. Any flaws in the lens will be magnified by the converter.

RichBrew
devlin 11 653 39 India
6 Jun 2010 12:01PM

Quote:I'm curious as to the problems with TCs on zoom lenses people keep alluding to on this thread... - AF worked fine.

If your primary optic is fast enough then AF issues may well never arise. It's optical quality that will suffer the most. Any flaws in the lens will be magnified by the converter.

RichBrew



I guess that makes sense so in effect a lens with quality optics should not have many issues with a TC ??
Overread 13 4.1k 19 England
6 Jun 2010 4:54PM

Quote:
As has been said, no point, and not advisable to fit extenders/multipliers to zoom lenses. Save up and get a good prime if you need to "get up close" to your subjects.



We have to be carefull with coverall statements since they often get pulled apart by specific examples.

Here are my views on teleconverters:
1.4 teleconverters -- will take away 1 stop of light from your lens setup - this should be shown in your camera as your maximum (smallest number) f number (aperture) will decrease. For example
f2.8 becomes f4
f4 becomes f5.6
f5.6 becomes f8
Some of the 3rd party teleconverters won't show this through the camera as they don't properly report to the camera itself, but the lightloss and aperture change are real physical chances. Even if the camera does not report it they are going to affect your shot (note lightmeters will function the same with or without reporting).

A 1.4TC is the least magnification availble with teleconverters and generally will work on most f4 and f2.8 lenses with very minimuam degradation to image quality. If you fit them to f5.6 or smaller aperture lenses or lenses with a variable aperture range over its zoom length your results will vary depending upon the lens. In most cases the optical quality should remain decent to usable whilst you should lose auto focus on a canon camera body; unless the teleconverter does not report to the camera (eg a 3rdparty teleconverter or a canon one with tape placed over the reporting contact pin - a trick often used with the 400mm f5.6 for example).
The AF loss is because after f5.6 the AF speed and ability to lock focus degrades noticably and often as not even if you keep AF, be taped pins or none-reporting, you will still get degraded AF performance.

2*TC - this will take away two full stops of light from your lens setup - meaning that:
f2.8 becomes f5.6
f4 becomes f8
They also magnify the image a considerable amount and this even on pro end prime lenses the image degradation is noticable. On pro prime lenses like the 300mm f2.8 IS L the image degradtion, whilst noticable, still yealds very usable image quality for most purposes. On lesser lenses the quality quickly drops and for many will become unusable quality.
This TC is very much favoured for prime lenses only (since they are generally speaking always sharper than zooms) and there are only a very few zoom lenses that can take a 2*TC whilst delivering usable, good quality results - eg canon 70-200mm f2.8 IS L M2 can take the 2*TC and achive around the same level of image quality at 400mm as the 100-400mm L (A feat the original 70-200mm f2.8 IS L was unable to achive).


A final point about optical quality - quality of a shot and determining if its usable or not is highly (totally) based upon the output needs of the photographer for that shot. This can confuse things with teleconverters a little as peoples different output demands start to show up. Those who consider a 2*TC and a 70-300mm f4-5.6 lens unusable might have higher overall demands and output needs of their work than those who consider it a viable approach - the latter group might only use the net (for example) as their output and a 1000pixel (or smaller) image as the final works might be all they need. Which means their fullsize images can take being softer overall and then with sharpening methods and resizing still look decent on the net once processed.

Generally speaking though most people consider a 70-300mm f4-f5.6 lens not suitable for teleconverter use in general. The highest grade of 70-300mm lens might be able to take a 1/4TC but I would expect many would consider the 2*TC to degrade things too far.
dlegros 19 217 England
6 Jun 2010 7:38PM
Overread,

Many thanks, that all makes sense to me.

Dom
WilliamRoar 13 188 United Kingdom
21 Jun 2010 8:10AM
thanks,

so it'll work with a Canon EF 50mm F2.5 Grin

Will

Sign In

You must be a member to leave a comment.

ePHOTOzine, the web's friendliest photography community.

Join For Free

Upload photos, chat with photographers, win prizes and much more.