How does teleconverters and extension tubes affect lens aperture

[ah tong]

Hi,
Need some advice here,
If i use a telecoverter 2x on my 28-75mm f4.5 lens, knowing that the range is double now will it affect my aperture?

If the same lens using with an extension tube, will the aperture be affected?

Thank you in advance!

 

[Marmbo]

I think 1.4x TC's reduce the amount of light by 1 Stop and 2.0x TC's reduce about 2 stops. I don't know if it is directly related to the same way the aperture would reduce though.

 

[mpenza]

just multiply the TC multiplier with the aperture. so your 28-75/4.5 lens become 56-150/9.

 

[ah tong]

Thanks guys,
So its pretty straight forward with teleconverter.
How about those extension tubings? I know i have to overexpose by 1 or 2 stops to compensate for the extension length cos my pictures turned out dark.

 

[vinvin]

just multiply the TC multiplier with the aperture. so your 28-75/4.5 lens become 56-150/9.

just to clarify, so in the case above, the aperture on the lens would become F9? so to compensate for the lack of light, i should up the aperture size by 2 stops?