[jdou]

I have tried using the pentax 1.4 multiplier on a pentax 150-450 mm lens on a full frame K! camera and noticed that the image was cropped! In fact when using the lens alone the image size was 7360 x 4912 while with the multiplier the image size is 4800 x 3200 and you will also get a black rectangular box in the viewfinder. I never read anything that this would happen with a multiplier on a full frame camera. I asked a fried of mine who uses a multiplier on a different camera make and he told me that it keeps its full frame function.

[KiloHotelphoto]

If it's the DA 1.4 AW converter it is not full frame. You can use it and select FF in the menu, but you will get some vignetting in the corners.

[Adam]

I have tried using the pentax 1.4 multiplier on a pentax 150-450 mm lens on a full frame K! camera and noticed that the image was cropped! In fact when using the lens alone the image size was 7360 x 4912 while with the multiplier the image size is 4800 x 3200 and you will also get a black rectangular box in the viewfinder. I never read anything that this would happen with a multiplier on a full frame camera. I asked a fried of mine who uses a multiplier on a different camera make and he told me that it keeps its full frame function.

Yup, the 150-450mm is one of the many lenses which will produce heavy vignetting when paired with the DA (crop) teleconverter. Virtually all other teleconverters out there are full frame, but with a few notable exceptions I'm not sure they will do much to improve the image quality.

[jdou]

If it's the DA 1.4 AW converter it is not full frame. You can use it and select FF in the menu, but you will get some vignetting in the corners.

thanks
j

[zosxavius]

The tamron is full frame and according to pentax forums nearly as good as the DA 1.4x. I think it loses a bit in the corners over the DA, so that might be worse on a full frame camera. That said corners might not matter in most cases you would be using a TC anyways. edit: I don't know if the tamron has the powerzoom/AF pins. Something to possibly consider.

edit: Looks like the MC4 has the connectors. I wonder if it passes lens information correctly and would support electronic aperture since the pins are all simple pass through.