HI,
Firstly I'll apologise for the long winded post. I am interested in buying the Tamron or Sigma 100-400mm as a lighter alternative to my Tamron 150-600mm on my D850, however I'm trying to find out if all of the AF points work all of the time on the D850 (or D500). The reason that I ask is that my Tamron 150-600mm VC doesn't play nice with the D850 and D500 in that beyond around 520mm only these focus points work, ie those for a lens with the equivalent of f4 with a 1.7TC (so I guess f6.9 ish)
Now my assumption is that it's due to the Tamron being an f6.3 lens at the long end. However, there are two confusing things. Firstly the Tamron stops down to f6.3 long before 520mm so if it was truly aperture limited then you'd expect the limited AF points from that time, and secondly the Tamron worked fine on my D750 at all focal lengths. I did briefly have the D500 and this exhibited the same problem as the D850 so I'm assuming the issue lies with the new 153 point AF system and maybe the AF sensors aren't as sensitive, or light is restricted more? Obviously while the lens stops down to f6.3 at around 450mm (IIRC) as the lens continues to 'zoom out' there will be a little more light loss, and I guess at around 520mm this is enough loss for the 153 point system to revert to the restricted AF points. I did ask around and apparently the Sigma 150-600mm also has the same issue with the D500 and D850.
As the 100-400mm lenses are also f6.3 I am wondering if they will exhibit a similar issue, ie at 400mm on the restricted AF points will work on the D850 (and D500). Does anyone have either of these lenses and used them on the D850 (or D500) and can confirm whether all AF points work all of the time please?
Cheers, Toby
Firstly I'll apologise for the long winded post. I am interested in buying the Tamron or Sigma 100-400mm as a lighter alternative to my Tamron 150-600mm on my D850, however I'm trying to find out if all of the AF points work all of the time on the D850 (or D500). The reason that I ask is that my Tamron 150-600mm VC doesn't play nice with the D850 and D500 in that beyond around 520mm only these focus points work, ie those for a lens with the equivalent of f4 with a 1.7TC (so I guess f6.9 ish)
Now my assumption is that it's due to the Tamron being an f6.3 lens at the long end. However, there are two confusing things. Firstly the Tamron stops down to f6.3 long before 520mm so if it was truly aperture limited then you'd expect the limited AF points from that time, and secondly the Tamron worked fine on my D750 at all focal lengths. I did briefly have the D500 and this exhibited the same problem as the D850 so I'm assuming the issue lies with the new 153 point AF system and maybe the AF sensors aren't as sensitive, or light is restricted more? Obviously while the lens stops down to f6.3 at around 450mm (IIRC) as the lens continues to 'zoom out' there will be a little more light loss, and I guess at around 520mm this is enough loss for the 153 point system to revert to the restricted AF points. I did ask around and apparently the Sigma 150-600mm also has the same issue with the D500 and D850.
As the 100-400mm lenses are also f6.3 I am wondering if they will exhibit a similar issue, ie at 400mm on the restricted AF points will work on the D850 (and D500). Does anyone have either of these lenses and used them on the D850 (or D500) and can confirm whether all AF points work all of the time please?
Cheers, Toby