Is my math correct? In reading all the posts about tc's the constant is that they change the aperture as well as extend the focal length. This change in focal length is easy to figure...

jethro779 Loc: Tucson, AZ

In reading all the posts about tc's the constant is that they change the aperture as well as extend the focal length. This change in focal length is easy to figure, the aperture not so much. A 1.5 tc adds 150mm to the 200-500 f/5.6 Nikon. That is easy to figure. Is the aperture a change from f/5.6 to f/8, or is it actually f/8.4 and the camera just has that much variance in the ability to focus? Does this make the 1.7 tc change the lens to 850mm and f/9.52? and the 2.0 tc 1000mm and f/11.2? Math was not my strong suit in school, getting in trouble and visits to the Principal's office were much easier for me.

melismus Loc: Chesapeake Bay Country

TC does not add; it multiplies. Your lens becomes 300-750. There is approx. one stop loss, so its max aperture becomes 8.

jethro779 Loc: Tucson, AZ

melismus wrote:

TC does not add; it multiplies. Your lens becomes 200-750. There is approx. one stop loss, so its max aperture becomes 8.

That is well and good with a 1.5 tc, but I was trying to get figured out the 1.7 tc mainly since it was such an odd ratio.

NikonCharlie Loc: Kansas USA

At 500mm setting the 1.5 would be 750mm. Nikon does not have a 1.5, but a 1.4, which would equate to 700mm if lens is set to 500.
5.6 with 1.4 is f8, 1.7 f10 and 2X is f11

Mac Loc: Pittsburgh, Philadelphia now Hernando Co. Fl.

jethro779 wrote:

That is well and good with a 1.5 tc, but I was trying to get figured out the 1.7 tc mainly since it was such an odd ratio.

Multiply the focal length by 1.7.
A 200mm focal length with a 1.7 TC would give you 340mm. At 500mm it would be 850mm.

jethro779 Loc: Tucson, AZ

Mac wrote:

Multiply the focal length by 1.7.
A 200mm focal length with a 1.7 TC would give you 340mm. At 500mm it would be 850mm.

I was able to math the focal, it was the aperture I was questioning.

Mac Loc: Pittsburgh, Philadelphia now Hernando Co. Fl.

jethro779 wrote:

I was able to math the focal, it was the aperture I was questioning.

Sorry, I misunderstood.

jethro779 Loc: Tucson, AZ

Mac wrote:

Sorry, I misunderstood.

No problem, it was just when i did the multiplication I came up with inconsistent figures and wondered if the apertures did not come out exactly, since 5.6 multiplied by 1.5 came out to 8.4. 5.6 x 1.4 comes out to 7.84 so that is less than a full stop. 5.6 x2.0 comes out to 11.2 which is not exactly 2 stops.

NikonCharlie Loc: Kansas USA

jethro779 wrote:

I was able to math the focal, it was the aperture I was questioning.

Your comment: A 1.5 tc adds 150mm to the 200-500 f/5.6 Nikon- is incorrect. at 500mm it is a 750 equivalent lens. While 300mm at the 200 settng. Again, it would be a generic 1.5 as Nikon does not offer that unit.

Rongnongno Loc: FL

The lens aperture simply does not change because you place an extender in front of it.

You lose luminosity, gain in lens length but the dof characteristics stay the same. The extender is nothing more than a magnifier.

BHC Loc: Strawberry Valley, JF, USA

jethro779 wrote:

I was able to math the focal, it was the aperture I was questioning.

The f/stop increases quoted by NikonCharlie are correct. A 1,5 TC will only cost you about 1/5 to 1/10 stop more than a 1.4, which will yield f/8; a 1.7 on a 5.6 is technically 9.5. None of these minor differences is going to make any difference in your images; in fact, most cameras tolerances are looser than these estimations. Also, please note two other factors:

1. 200-500 can vary a few mm in the finest of lenses, and

2. Most lenses have trouble autofocusing beyond f/5.6; even the best AF degrades beyond f/8.

BebuLamar

jethro779 wrote:

No problem, it was just when i did the multiplication I came up with inconsistent figures and wondered if the apertures did not come out exactly, since 5.6 multiplied by 1.5 came out to 8.4. 5.6 x 1.4 comes out to 7.84 so that is less than a full stop. 5.6 x2.0 comes out to 11.2 which is not exactly 2 stops.

That's because the way they round thing off in photography.
f/5.6 is actually f/5.65689 and 1.4x meant to be 1.414X. f/11 is actually f/11.3137

Mac Loc: Pittsburgh, Philadelphia now Hernando Co. Fl.

Rongnongno wrote:

The lens aperture simply does not change because you place an extender in front of it.

You lose luminosity, gain in lens length but the dof characteristics stay the same. The extender is nothing more than a magnifier.

Since the f/number is a ratio of the diameter of the aperture to the focal length, does the f/number change when a TC is added? If so is that change reflected in the f/number reading on the camera?

BebuLamar

Mac wrote:

Since the f/number is a ratio of the diameter of the aperture to the focal length, does the f/number change when a TC is added? If so is that change reflected in the f/number reading on the camera?

The f/number does changes. The aperture diameter doesn't change but the focal length changes so the ratio or the f/number changes. I don't know if the TC can relay that information to the camera.

Rongnongno Loc: FL

Mac wrote:

Since the f/number is a ratio of the diameter of the aperture to the focal length, does the f/number change when a TC is added? If so is that change reflected in the f/number reading on the camera?

Take a capture. Whatever.
Crop it (magnifier effect) Does the dof changes? No.
Does it appear to have changed? Yes.
The same thing applies to the dof when using a extender.
An extender basically crop the scene to the center of the lens w/o modifying the lens characteristics.
Now does same amount of light hit the sensor? No.
Do you need to compensate? Yes. > ISO, < Speed or you open the diaphragm to keep the first two.

Always remember that the aperture controls the amount of light that hit the sensor at anyone time. dof is a 'side effect'. Since we are talking about dof, the amount of light is reduced when using the same aperture and you must compensate (ISO and or Speed) but its depth stays the same.

If you were changing the lens instead of adding an extender the dof depth would narrow due to the lens optical compression.