Question on a 2x teleconverter lens

[xentinel2]

Hi, I don't know if this have been asked before but say I have a 2x teleconverter lens. Surely this means that the focal length is doubled say from 105mm to 210mm. But for the picture does this mean that the half of the picture have been zoomed up by twice as well?

For example, if I have a 2"x2" picture, with a 2x teleconverter lens should I be able to zoom at the 1"x1" of that picture?

A confused mind :confused:

[blacksmurf]

uhm :shock:
try to explain it again.

What do you mean with "the picture"? You'll always get a picture measurable in pixels. The same X*Y pixels with or without the converter. But with the converter, you'll have a result as if you've used a lens with double focal length.
:confused:

[glowluzid]

I think he is asking for macro fotos. If whether the field of view or field of angle will cover half as much with twice the zoom.

2x2 to 1x1 is a fourth in reduction. The reduction would at most be divided by SQRT(2), not 2.

So from 2x2, you'd at best get 1.414 x 1.414...

[xentinel2]

Hi tnx for the replies and the info for the macro. Its not for macro shots but for telephoto lenses like kenko 2x telephoto lens and the likes that is attached to a lens adapter + G5. I don't know if macro and telephoto lenses would have the same principles.

Anyway, I did some experimenting and comparison with copies the full zoom photos with and w/o telephoto lens from lensmateonline.

What i did was.
1. let full zoom photo without telephoto as pix1 and with 2x telephoto as pix2. I also added 1.75x telephoto as pix3. all of them were of the dimension 14.4"x10.8" w/ a resolution of 180pix/in
2. I cut out the portion of the pix1 that would be exactly the same as pix2 and copied it to a new file. I only concentrated on the lenght since it was easier to distinguish where to cut and I am assuming the factor would be the same for height. The new image size have a length of 7.95" at 180pix/in. Somehow I got ~55% zoom from the original or ~45% from the picture was removed.
3. I did the same with pix3 and got a ~57% zoom from the original.

This almost coincides with what I was thinking. Say for a 2x2 picture, the 1x1 get zoomed when there is a 2x telephoto lens. I don't know if I did the right assumptions but maybe there are better answers out there.

Unfortunate for me, the infocus 2x telephoto lens that I bought only zooms up to 75-70%. This led me to the question does a 2x telephoto lens zooms only so much... and then I asked the question here. I felt I was sooo duped. :cry:

thanks,
Julius

[rpolitsr]

Hi, xentinel2.
I read your posts and I think you are correct in all your assumptions.

I prefer to think in terms of the subject in front of the camera or in pixels for the pictures instead of translate to inches and dpi, but with the correct calculations you will arrive to the same results in either way.

We were talking about sensors, sizes and angles in another thread and I read the G5 user guide to compare values. (I am a Pro1 user).

It is interesting: if you use your G5 zoom lens at full wide angle, the subject captured at 10 feet from your camera will be also 10 feet wide. Easy figures to remember!

I will add some theoretical calculations performed graphically in AUTOCAD with the G5 data:

From the G5 user’s guide:
sensor size= 1/1.8” or 9mm. diagonal (7.2mm x 5.4mm)
lens: 7.2mm to 28.8mm. (35mm. to 140mm. equivalent)

Field of view of the G5 at 10 feet (120 inches):

7.2 mm (35mm equiv.): 10'x 7' 6" or 120' x 90'
28.8mm (140mm equiv.): 2' 6"x 1' 10 1/2" or 30" x 22 1/2"
2x at full optical zoom: 1' 3"x 11 1/4" or 15"x 11 1/4"

Field of view of the G5 at 3m. (300cm.)

7.2 mm (35mm equiv.): 3m. x 2.25m.
28.8mm (140mm equiv.): 75cm. x 56.25cm.
2x at full optical zoom: 37.5cm. x 28.125cm.

Both sets of data are really the same set, the first one with distances in feet and inches and the second one in meters and centimeters.

As you did, I focused in horizontal sizes because the vertical measurements conform to the 4:3 aspect ratio.

It would be great if you perform the measurements described in your post but comparing your LCD with a suitable subject at 10 feet (3 meters) from your camera to compare theoretical and practical results.

I did a similar test for my Pro1, and all the theoretical and measured data were pretty close.

[xentinel2]

Hi rpolitsr,

Thanks! This is great info. I really liked the full wide at 10ft will show a 10ft wide shot.


As you did, I focused in horizontal sizes because the vertical measurements conform to the 4:3 aspect ratio.

I never thought of it that way :o but my thought process was since the only difference was the telephoto lens I would think the same factor applies. But the biggest reason was I find the the details was easily identifiable along the longer side making the cuts easier. :D


It would be great if you perform the measurements described in your post but comparing your LCD with a suitable subject at 10 feet (3 meters) from your camera to compare theoretical and practical results.

Hmm I should try it out with my telephoto lens and get the actual results from it.

thanks!
Julius