To Teleconvert or Not to Teleconvert

fmw · Jun 11, 2007

Alex_B said:
But with respect to final print size, the resolution of that lens in the sweet spot is reduced according to the crop factor. I have to admit that is a minor effect since you often have a very good resolution there to start with.

It also depends on how extended your sweet "spot" really is, this might vary and you will not get constant image quality over the whole APS-area with most lenses made for 35mm.

Quite the opposite. Issues like distortion, light fall off and corner sharpness affect mainly the corners or edges of the field of view. The crop factor for an APS digital crops off the corners and edges. The difference with average and poor lenses is dramatic. The difference with great lenses is minor as you say. You will get better performance (a more constant image, as you say) with an APS digital using a 35mm camera lens than with a 35mm camera. Every time. It is the laws of optical physics. The reason is simply that the corners are cropped off and you don't see them.

Alex_B · Jun 11, 2007

fmw said:
Quite the opposite. Issues like distortion, light fall off and corner sharpness affect mainly the corners or edges of the field of view. The crop factor for an APS digital crops off the corners and edges. The difference with average and poor lenses is dramatic. The difference with great lenses is minor as you say. You will get better performance (a more constant image, as you say) with an APS digital using a 35mm camera lens than with a 35mm camera. Every time. It is the laws of optical physics. The reason is simply that the corners are cropped off and you don't see them.

totally agree here! the minor effect i was referring to was the loss in overall resolution in the very centre, when you go from 35mm to APS digital, since you have to magnify more to get the same print size.

But that effect is very small compared to when you crop off the edges on not so great glass, true... and it is mostly negligible with good glass since the resolution in the centre will be very good to start with.

mysteryscribe · Jun 12, 2007

I ran the test this morning. I think i got it without any camera shake but I would not guarentee it.

The verdict was shoot it with the regular lens at a high resolution and enlarge and crop. I admit I'm surprised. There was a very noticeable amount of softness both ways, but more with the tele converter. Not really very scientific but it convinced me.

I used them mostly when shooting real estate and the house was too far from the gate to get a decent shot. I always knew there was loss just had no idea a crop would be less.

That's what my test with my glass showed. It there were to be different result it would be with a better converter the base lense is the same lense I would think.