2x Teleconverters

[mant01]

I know that my f/2.8 sigma 70-200mm with a 2x converter will drop to f/5.6 but will the image be the quality of 2.8 or 5.6 without the converter? The reason Im asking is because at 2.8 the images arent sharp anyway and I have to stop down to at least f4 to keep it sharp. Because 5.6 will then be the largest I can go to will it be as soft as the 2.8 or as sharp as the 5.6 was without the converter. Not sure if Ive said it clearly lol
Thanks for any help

 

[Chappers]

I understand what you mean. As the converter "effectively" increases the focal length, the effective aperture becomes smaller. That's why you go from f2.8 to f 5.6. However the diameter of the aperture stays the same so you still get the definition of f2.8. Dropping down to your preferred aperture of f4 means your "effective:" aperture is now f8

 

[mant01]

Thank you thats a great help

 

[HoppyUK]

I know that my f/2.8 sigma 70-200mm with a 2x converter will drop to f/5.6 but will the image be the quality of 2.8 or 5.6 without the converter? The reason Im asking is because at 2.8 the images arent sharp anyway and I have to stop down to at least f4 to keep it sharp. Because 5.6 will then be the largest I can go to will it be as soft as the 2.8 or as sharp as the 5.6 was without the converter. Not sure if Ive said it clearly lol
Thanks for any help

What a teleconverter does is magnify the centre of the image. As such, virtually all aspects of image quality are decided by the mother lens, not the TC. With a 2x, the image is made 4x larger in terms of area, hence the two stops reduction in brightness. This is an actual change to the optical specification, not an 'effective' one, ie a 200mm f/2.8 lens becomes 400mm f/5.6 in every respect.

At f/5.6 with the 2x, you're using the lens at its widest aperture (normally f/2.8 of course) so image quality will be significantly worse than without the TC at f/2.8. So if you're not happy with IQ as it is at f/2.8, you're not going to like it with the TC attached at all

 

[mant01]

Yeah Ive kinda decided to not bother with one at the minute. Seems pointless to get one and do images Im not happy with.

 

[andyred]

Yeah Ive kinda decided to not bother with one at the minute. Seems pointless to get one and do images Im not happy with.

Why not see if you can borrow one / hire one or try one in a local shop you were thinking of buying from ?

At least it would answer the uncertainty, but as has been said, if your not happy with your lens at present on F2.8, then your not going to be happy with a TC on...