<p>Greetings.<br> Here is my problem:<br> I was happy with my combination of D3 and D800 in usage and image quality. However, due to age and health condition my D3 is getting too heavy for me, e.g. with my 70-200 f2.8 zoom but even more when several lenses are in the bag. Like I would shoot fast and tele-zoom with the D3 and wide angle with the D800. <br> Mostly my D800 fulfils my need but when it comes to action the AF of the D800 is not fast enough.<br> For example: Yesterday I was shooting aerobatic flight displays of model plains and I lost several shots in a series and often had to refocus in a series.<br> My be I get out of practice too much but my memory is that the D3 was always spot on when following planes 1) approaching or leaving and 2) following the subject when in addition moving sideways in the viewfinder. <br> Now small planes are quite fast and the demand is high on focus tracking. <br> I did not follow the Nikon model updates but heard that the D810 improved quite a bit on focus tracking so would i just need to update to an D810?<br> Updating my D3 to a D5 is not worth the money for my non commercial use also in view of the weight.<br> For landscape and macro the D800 is fine for me with a good tripod and selected lenses like my Zeiss 100mm F2.0 Planar ZF2.<br> As a second question in terms of low light high ISO performance is there any less heavy replacement for the D3?<br> I always shoot raw, and process in PS btw, so in camera noise removal is of no concern and all my lenses are FX format.<br> Any suggestion would be appreciated.<br> Thanks<br> Walter</p> <p> </p>