Exposure compensation the answer to Teleconverters??

[markj]

I'm going to the Nat'l Zoo tomorrow. I'll be bringing my nikkor 80-200mm lens along with my Kenko 2X teleconverter. Considering the fact that I will loose 2 stops of aperture when
I use them in conjunction, is it a simple case of boosting my EC setting to +2.0?

 

[MLeeK]

I am just subscribing because I am interested in the answers here! Sorry! I am no help and have probably just as many questions regarding TC's as you do! LOL!

 

[Overread]

Not exactly.

First off the loss of 2 stops of effective aperture is a real change of the lenses properties. It becomes a 160-400mm f5.6 lens from an 80-200mm f2.8 lens. You can't get those "lost" stops of light back as they are a physical part of the new lens that the TC makes of the setup.

Your camera should report this change to you through the viewfinder and you'll see that your max aperture setting is now f5.6. If it fails to do this (some 3rd party TCs don't always report well and some lens+TC combos can have errors with reporting) you've still lost the light so even if it said it was f2.8 it would really be f5.6

Metering wise because the meter itself is inside the camera the light loss from the reduced max aperture is already taken into account by the camera. As such even if you don't get the right reported aperture the real loss of light will still be factored into any exposure that the cameras meter gives you. So you won't need to use the exposure compensation any more than you would normally do in any given lighting situation.

Note that with the 2*TC you will want to stop down to f7.1/8 if you can as most lenses show marked improvement in optical performance when stopped down from wide open and with the 2*TC you will see a noticeable loss of sharpness.



In my experiences the only 70-200mm/80-200mm style lenses that can take a 2*TC well are the 70-200mm f2.8 IS MII from Canon and the 70-200mm f2.8 VR II from Nikon -I'm unsure where the 80-200mm stands on the scales, but whilst I've heard very good things of it I don't know/think its in the same league as the the MII versions.
This means you might find that the quality is "ok" but not really that outstanding. For a zoo I tended to use a 1.4TC all the time without fuss and on the Nikon side I've heard very good things of the 1.7TC.

 

[unpopular]

The only reason why you'd need to EC in this case is if you're using a handheld meter. But you'd set that in the meter, not the camera. As others have said, the meter is receiving less light and will recommend more exposure than if you didn't have the converter on in the first place.

It's essentially the same as if you had an ND filter ... or if a cloud passed over.

 

[Dao]

This is how I understand. Please correct me if I am wrong.

First of all, f number is the ratio of the effective focal length and effective diameter of the opening of the lens.

Let say you have a 200mm lens with max aperture of f/2 when you add a 2X TC with the lens, you are changing the effective focal length. But it does not change anything with the size of the opening. Hence the lost of f stops.

And that is the physical properties, adjust the EC has nothing to do with the physical properties.


For example:

Photographer A and B shoot with EF 200mm f/2L lens at f/2. Photographer A decided to change the lens from the 200mm lens to EF 400mm f/4 DO IS lens at f/4 while Photographer B add a 2X TC and also shoot at wide open. At the end, both are shooting with effective focal length of 400mm and guess what, about the same effective diameter. (Max diameter of 400mm f/4 DO lens is 128mm while the max diameter of 200mm f/2L is 128mm as well)

As you can see, both Photographers will need to shoot based on what the true f number. If the scene need ISO 100, 1/500 shutter speed and f/4, Photographer B need to set it to f/2 (it is actually f/4 due to lost of 2 stops) and Photographer A just need to set it to f/4.

 

[markj]

Thanks to you all for the explanations. I'm assuming, today being sunny it shouldn't be a problem. I'll post a pic of a tiger if I get one.

 

[TCampbell]

You can get away with a 2x teleconverter on an f/2.8 lens because the doubling turns it into an f/5.6 lens and the camera can still focus at f/5.6.

But suppose you had an f/4 lens. A 2x converter would turn that into an f/8 lens. It's EXTREMELY difficult (if not impossible) to get phase-detection auto-focus to work at f/8. Even cameras that can do it will be struggling (it wont be fast focusing and may take the camera a while to lock in. Find a really good contrasty point as a focus target.) If you had an f/5.6 lens then it wouldn't work at all. The 2x would turn that into an f/11 lens. Phase detect auto-focus absolutely will not work at f/11.... not on any camera I have ever heard of.

When the camera can't focus because the focal ratio is too high, you can switch to live-view and let the camera use contrast-detect AF (which probably will work if there's enough light) or you can focus manually.

Just for fun, I've picked up my old manual 35mm film camera (no auto-focus), looked through it with the aperture blades stopped down to f/8 just to see I could focus using the built-in split-prism focus target. It turns out that the target basically doesn't work at f/8 or higher.

Normally the split prism shows two half-circles which are out of phase when unfocused. For example if I were pointed at a flag pole. Instead of a nice straight pole in the center of the photo, I'd see part of the pole shifted to the left and part shifted to the right (in the upper & lower halves of the circle), and then turn the focus ring until those shifted halves all line up neatly (indicating correct focus.)

But at f/8 if I move my eyeball fractionally left in the viewfinder then I can see the top "half circle" but the bottom half is completely black. If I shift my eye fractionally right then the bottom half-circle is visible but the top half is completely black. There's pretty much nowhere that I move my eye where it's possible to see both the top and bottom at the same time so that I can line them up ... because the focal ratio is too high. If I just back off to f/5.6 it works again as long as my eye is well-centered. The better the focal ratio, the less critical it is that my eye be perfectly centered to get the split prism focus aid to work.

The phase-detect AF sensor in a modern camera basically has the same problem at f/8 or higher. It cannot "see" to align the phase on the focus target because the focal ratio is too high.

One last point about teleconverters: you will probably notice that the images are not quite as crisp when using the TC as they are when you use the lens by itself. This is why a lot of birders or other wildlife photographers prefer to just bite the bullet and get a nice long lens that doesn't require a TC (even though they can be ludicrously expensive.) For most of us who don't depend on taking those long shots every day, go ahead and use the TC. You don't need a 400mm focal length frequently enough to justify the investment in a dedicated 400mm lens. Sure your quality wont compete with the National Geographic photographer who owns the dedicated gear... that's ok. If you really NEED that tack-sharp quality for some special event, you can always rent a 400mm lens for the weekend.

 

[markj]

Got my tiger today. No PP, except cropping.

 

[3bayjunkie]

I like the second photo.

 

[gsgary]

Got my tiger today. No PP, except cropping.<img src="http://www.thephotoforum.com/forum/attachment.php?attachmentid=22626"/><img src="http://www.thephotoforum.com/forum/attachment.php?attachmentid=22627"/>

I bet you had to track that creature for hours

 

[fmw]

You may be happier with simply cropping your photos instead of using a TC. The biggest lens I ever had for 35mm was the Nikkor 500mm f4 EDIF. It was a big, heavy, expensive lens but performed quite well. On two occasions I wanted a little more reach and added a 1.5X TC - also an expensive one designed specifically for the lens. I was never happy with the results. I ended up cropping shots made with the prime lens instead and sold the TC to someone else. I would imagine a third party TC on a zoom lens might not be ideal. You can get to the point with long lense when even a tripod isn't enough to prevent blur. I would test it thoroughly before shooting anything meaningful.