AFC tracking a bit slow?

[wider]

just wondering about the tracking/focus speed on the d70s... i have been taking some slow shutter (1/50-1/80) panning shots at a racetrack recently, as the car gets closer to me i need to pan quicker, but am noticing that alot of shots are not quite spot on. im using a sigma 70-300 lens.

are there known issues with the afc tracking/focus speed on the D70s or is it more likely me? when i muck around with it at home sometimes it takes a half second to react to a change in distance...

[mark]

It's probably not the fastest of lenses and that may be part of the problem, are you noticing it moreso when the light is low?
Perhaps you could post one of your shots, there are some great motorsport shooters here who would be able to take one look at your shot and tell you whether it's technique related or not.

[wider]

mark, i do have some small doubts in this lens (hey they're pretty cheap anyway) but it was taken in midday sunlight. its the camera body which determines the focus correct? (not the chip inside the lens?)

a good suggestion there, i will post some good vs. bad images when the sun is up later on.

[rangie]

I had the D70s and the with my 80-200 the focus was pretty quick, I also had an older 70-300g and the focus was terribly innacurate and slow.

[gstark]

its the camera body which determines the focus correct? (not the chip inside the lens?)

Neither.

It's the chip behind the camera.

[Grev]

D70 with a Sigma 70-300 = recipe for disaster.

I'm sure it'll be the same with my D70 and the Tamron 70-300, I wouldn't think it's slow, it's just getting by.

[Glen]

Wider, most AF systems are not rated to work above f5.6, though they usually do. They need light to work. That lens can only just provide that much light at the long end, which is why a faster optically lens will also usually have faster AF, due to more light and often better (AFS) motors.

[mark]

its the camera body which determines the focus correct? (not the chip inside the lens?)

Not always, some lenses, contain Silent Wave Motor, and this combined with VR (Vibration Reduction) not only helps with focus, also helps eliminate vibration cause by shakey hands, resulting in more sharp and in focus photos.

Silent Wave Motor : The Silent Wave Motor focuses internal lens elements using ultrasonic traveling waves which are converted to rotational energy. This advanced, high-torque motor system is extremely powerful, driving autofocus elements with instant startup, and with exceptionally effective stopping action for superb total response, resulting in high-speed autofocusing with added accuracy, it works and combined with newly designed Nikon autofocus of Focus Tracking as well)

That being said, you can, with paitence and practice get good shots from your 70-300.
As a quick tip, I always pre focus the spot where you have envisaged taking the shot, that way when your subject arrives, the focus will be close and your lens won't hunt so much to find focus.

Cheers

[Pehpsi]

Throw a 70-200 f2.8 on there and you'll see the difference..

[wider]

Grev: its not as bad as you make it sound, but the only reason i took that lens is because with the points system in Biccamera i picked the lens up for AUD$20 (no, not $200)

Glen: even if i were to pick up a 80-200 f2.8, i would still have to shoot at a F10 ish to get the shutter speed i want (1/50-1/80). regardless i want a brighter lens and it is the next thing on the cards

mark: the reason why i ask about the location of the focus detector thing is because if that part were slow, then no matter what lens i put on it i assumed the camera would still focus at the same speed. but as Glen mentioned and I realise, there are many more variables than this

i usually find i dont need to prefocus as i just run AF-C mode and half press the shutter button as the car comes, then press the button when i feel i have matched panning speed with the car. the lens has no trouble keeping up for most of the shooting, except when the car comes really close (probably easily going more than 120km/h) and goes from 30m away to 4m then 30m away in over a second. this is the critical part and maybe to get ultra sharp images i need to take a single shot pre-focused instead of sequential.

Pehpsi: if you can 'throw' one of those lenses my way, i'll be happy to use it i'll just settle with the 80-200 f2.8 for a while i think

sharp image:


not so sharp image (same location):


cool image (18-70mm):


would VR actually be any help in panning shots like these?

[Glen]

Grasshopper, time to learn about Auto Focus, F stops and life As I mentioned before, your lens is f5.6 at the long end, the 80-200 2.8 is as you think, 2.8. AF systems need light to work. The F stop range works on a doubling (or halving) of the light at each stop. So F4 allows half as much light through as the stop before it, f2.8. F5.6 allows through half as much as F4, or viewed the other way f4 allows double as much light as f5.6. In the comparison of the two lenses here, the f2.8 allows four times as much light through as the 5.6.

The Auto Focus system works while the mirror is down and diaphragm is fully open, eg at the largest opening (smallest f number). So when your 80-200 is set to f10, the AF works first at f2.8. When your 70-300 is set to f10, the AF is working at F5.6, with 1/4 the light the 80-200 provides. No wonder it works slower, you are making it work in the dark by comparison! You have probably seen this for yourself if you use the Depth Of Field Preview button on the D70 (located under the lens within easy reach of your index finger when your hand is on the handgrip). As an example set your lens to its largest numerical f stop, eg f29, etc. Look through the viewfinder then press the DOF button. You will see the viewfinder darken up, which is the real amount of light getting to your sensor. So now you can see why a faster lens also focuses faster

Life. I hadn't mentioned this and I hate the fact it is so, but like many things which are fun in life, you often have to pay to play. Digital SLRs unfortunately are one of those things. That said many can get excellent results with the 70-300 by applying good technique, shooting on sunny days and working within its limitations. It is just easier and able to handle more difficult conditions with a 80-200 or easier again with a 70-200 which also has AFS (motor in the lens).

Good luck.

[wider]

thanks for the info glen, or should i say 'big grasshopper?'

although this lens is 'working in the dark' compared to the 2.8 versions floating around, numerous times i have seen people mention how much faster their lens focuses on a more expensive camera body. eg going from a d70 to a d200. i doubt you would see much difference with a sigma lens though.
i agree with you that my lens is darker, slower, and relies upon the camera's af motor instead of an integrated one. but the fact remains that other bodies and also a few other variables do also have an effect on focus speed ie.the fact that i was using a polarising filter in the images supplied so i would probably assume that my lens would have been working with 1/8 or less light compared to a 2.8

regardless, im happy to know that i can get faster AF with another lens and its not the camera body's direct fault. as you can see in the 2nd image i took, i'm going have to re-evaluate how i take photos with this lens until a bigger one becomes available

this 70-300 sigma lens has less flexibility compared to others, i do not feel restricted to sunny days and quite enjoy working outside of its limitations. playing and not paying

[Glen]

Your lens will be faster on a more expensive body if it is a big enough jump, eg D70 to D300 because of a bigger motor but there are also better and more efficient focussing system and algorithms eg the D300 uses Cam3500 and the D70 uses Cam900. It sounds like you know exactly what you are doing and are quite happy with your 70-300.

[wider]

thats exactly what i was thinking and a nice combo would be the 70(80 in my case)-200mm and a d300. all in due time.

for $20 ($150rrp japan) the clarity and colours on the 70-300 arent up there with the pro stuff but i enjoy people questioning me 'what lens do you use?'

i just have to put up with not getting as many successful shots as others do. which is the heart-wrenching part of photography: missing that moment sometimes

for the hell of it, does anyone know off the top of their head what the clearest apeture is on these things (if it has one ). i would guess around the f8-11 mark??

[gstark]

for the hell of it, does anyone know off the top of their head what the clearest apeture is on these things (if it has one ). i would guess around the f8-11 mark??

I would guess around the paperweight mark ...

[cobby1]

I would guess around the paperweight mark ...

What does that mean

[Grev]

f8 will do, f11 would the limit.