Teleconvertors in a digital world - Why?

What does a telcon give that moderate interpolation doesn't?

Personally, I retired my telcon along with my Velvia and Reala. All a telcon does is pull up the centre of the lens' image, but at a cost of light loss (potential for camera shake) and puts extra glass in the light path (potential for image degradation). So, is the final result really superior to a crop from the unconverted lens with a touch of intelligent resampling?

Has any measurbation been published that makes real-world comparisons between telconned and Genuine Fractal-ized image pairs

I've done any comparative work in the comparison of cropping and/or upsizing versus using a teleconverter at the time of shooting.

I must think that you had bad experience with teleconverters in the past if you have totally retired them. I used them in film and continue to use them in digital. I can honestly say that the images taken with my 1.4TC and any of my long glass (see gear list) are absolutely great. Even the 2.0 is more than acceptable but it definitely is not as sharp as the 1.4. Intuitively, I have to think that using the teleconverter is better than cropping the image in post production.

Example: One of my bodies gives me an image size of 3328 X 4492. If I want to bring something up in the image to be larger in the viewing area I can crop it. Using an test image in the background here, I cropped an image to 2334x2476. I am throwing alot of usable data away. However, if I want that same subject matter to be more visible in the image I can put my teleconverter on get it to approximately the same size in the image but it remains at 3328X4492 which results in much more data to work with.

I have Genuine Fractals and while it is good it can still only do so much with the data. You are performing a destructive routine on the image.

I will continue to use my teleconverters as I get better images than cropping. This however is a personal choice and one should do whatever works for them and makes them feel comfortable.

As Ssim says, using a teleconverter maintains resolution. Cropping kills resolution.

It is exactly equivalent to the difference between optical and digital zoom on a P&S. The basic rule is that digital zoom is only good for one thing: marketing to the ignorant.

Of course, if all you want is a 4×6 print or a web shot, cropping will usually do nicely.

If you compare a 1.4x crop from a frame vs. using a 1.4x telextender on a lens, you will clearly see an advantage to the purely optical solution over the limited resolution imposed by pixels.

I'm still using TC's. As ssim said, Genuine Fractals can do a lot, but you're still throwing away data when you crop and up-rez.

Mark

I think there was an online article about this on Luminous landscapes.
Digitally cropping was actually better on a cheap zoom than a TC, but on a pro telephoto, a TC was sharper than cropping.

Here is a nice comparison by Bob Atkins.