New teleconverter.. Few questions

413x · 12 Sep 2014 at 20:11

Got a 1.4x sigma tc for my 120-300mm sigma
It's waiting for me at the DO

With the tc on I loose stops
Will the camera adjust for this or will it still read a max aperture of 2.8?
I will he using it on Sunday (weather permitting) I'm guessing with something so simple there isn't anything else I need to know about?

Phal · 12 Sep 2014 at 20:16

Aperture should adjust itself yes so it'll change to F4

You'll probably notice the AF is a bit slower but other than that it's pretty straight forward

413x · 12 Sep 2014 at 20:27

Thanks phal

Yeah the AF is the unknown for me.
As this is going to firstly be used at duxford I'm hoping this wont be too much of a problem. I will see
Birds in flight might be harder!

It would be lovely if it means I don't need a 400mm f5.6 despite being so much heavier and probably worse in IQ

Phal · 12 Sep 2014 at 20:35

Yeah I guess you'll need to decide about the IQ hit and whether you're ok with it. I don't think the AF will slow enough to be a problem with planes but birds in flight could be an issue if they're close etc. Those are never easy at the best of times so any AF speed decrease is meh.

413x · 12 Sep 2014 at 20:47

I'll just try it for a bit. I may well be too fussy and not like the results.
When I get back, maybe next weekend, I'll do a crop vs Tc test somehow and see the difference

Amp34 · 13 Sep 2014 at 12:10

I've found that using the sigma 1.4 has a negligable hit on the IQ, to the point I think it still outresolves my D7000 sensor wide open...

The 2x is significantly worse though and if you get that you will see a fairly significant degradation. it's still a little odd the massive difference in performance between the 1.4 and 2x...

Energize · 13 Sep 2014 at 13:51

Well at 2x you've got 1/4 of the light hitting the sensor so your throwing away a lot of resolution and you'd expect significant degradation.

413x · 14 Sep 2014 at 19:00

Yeah definitely not even going to attempt a 2x

Amp34 · 14 Sep 2014 at 20:44

Energize said:
Well at 2x you've got 1/4 of the light hitting the sensor so your throwing away a lot of resolution and you'd expect significant degradation.

I understand the physics behind it, just the the difference in sharpness is a lot worse than with other lenses and TC combinations.