1.4x converter

[darcy_cheung]

<p>I recently purchase a 1.4x tele-converter, I don't quite understand that if I use a 100mm lens and the aperture is set to f2.8, then the converter will make me lost 1 step exposure. So, should I need to increase the exposure +1 or not. Secondly, about the depth of field. Is my picture's depth of field still same as 100mm or it is same as a 140mm lens? See anyone can help me to understand this. Thanks</p>

[pturton]

<p>If you are using a modern camera, the camera will meter the light coming through both lens and TC to give you the proper exposure.<br>

If you are setting an exposure for a camera that does not have through the lens (TTL) metering and use a handheld light meter, you must take the lost stop into consideration when setting the lens' aperture.<br>

The DOF will be the same as the effective focal length; in your example, 140mm</p>

 

[SteveH]

<p>Your camera may take care of some of this for you. For example if you have an f4 lens and put the 1.4 teleconvertor on it your camera will record the maximum aperture as f5.6, or one stop smaller, and you don't have to do any manual correction. Below the maximum aperture you won't notice any changes: in aperture priority, f8 will be f8 and the shutter speed will adjust to allow for the one stop less light through the convertor. </p>

[darcy_cheung]

<p>Thank you to answer my question for both gentleman. So, my focal length is 140mm in this case, And if I set the aperture to f5.6 in AE mode. My DOF still f5.6 not f8.0. And my shutter speed will automatic slower to justify for the correct exposure. Am I right?</p>

[mark_pierlot]

<p>Hi Darcy. Effective depth of field varies inversely with both focal length and aperture size. That is, the longer your lens or wider your aperture, the shallower your depth of field. So, following your example, while your aperture size will stay at f/5.6 while you're using the 1.4x teleconverter, the focal length will increase from 100mm to 140mm, and consequently reduce the depth of field. This is one reason why photographers like to use short and medium telephotos for portraiture.</p>

[derrickdehaan]

<p>Yes, your shutter speed will still automatically expose the scene correctly. Everything will function just like normal. You basically won't even notice that it is on there. The camera still funtions in the same ways. The meter in the viewfinder still works the same. And very generally speeking, centering your meter without the extender (like normal) means you still center the meter the same way with it attached. The only differences you will see are that you would no longer be able to get to 2.8 aperture and the viewfinder my be slightly darker to view through.</p>

<p>Derrick</p>

[photographicsafaris]

<p>Hi Darcy;<br>

The 1.4 extender makes the 100mm lens a 140mm lens. Thus being a longer focal length the depth of field is more compressed, giving better out of focus isolation.</p>

<p>But</p>

<p>The extender will increase the actual aperture, from f2.8 to say f4, consequently the out of focus depth of field range is going to be less than an equivalent f2.8 lens at 140mm</p>

<p>So the nett result would be focus depth of field would be more or less the same.<br>

However<br>

Cunningly the focus distance remains the same so using the (hypothetical) 100mm lens (as canon dont make a 100mm compatible with the extenders) with the extender means that you will get more of your subject matter filling the view making your depth of field out of focus separation more exaggerated.<br>

Does that make sense?<br>

So to answer your question Yes err No, no yes!<br>

The camera reads the lens as the lens becomes, so it would record a f4 100 mm lens.</p>

<p>BUT last bit<br>

In order to obtain sharp results you will need to shoot with the aperture stopped down so instead of shooting at f4 you would need to shoot at about f6.3 to get acceptable results, so the final answer is that the out of focus depth of field would be about the same.</p>

<p>sorry thats a bit long winded<br>

G</p>

[darcy_cheung]

<p>Thank you to all of you guys. Graham, that's is exactly what confuse me, since the focal length and the aperture, they all affect the DOF. At the beginning, I think 140mm focal length will give me better out of focus effect, but on the other hand, it step down my aperture to increase my DOF. That's what I don't understand. After you explain, I will try again. I haven't got any good chance to try it yet. Anyway, photograhgy is a really interesting thing, and a lot of things to learn. Thanks again.</p>