Lens Problem, or Clueless User!?

[Kipling]

Hello everybody,
Firstly, please excuse me as this question may be absolutely ridiculous..

I am completely clueless when it comes to cameras, especially DSLRs, however i have acquired a Nikon D70s to play/learn with and a number of lenses.
The `problem` i have in particular is with a Tamron AF 28-200mm lens, now this appears to be a great size to use in general (i.e. could be ok for outdoors shots, but also close ups/portraits of people in doors for example), without carrying an arsenal of lenses with me.

The `problem` is, that outside the lens seems to work fine using autofocus (is a little slower than the Tamron 70-300 i have, or the nikon 35-70). Indoors however, if i try to zoom in and use autofocus on somebody say 3 meters away, the camera just does not seem to want to focus. It tries, and there is all manner of noises and movement but it`s as if the camera cannot quite seem to acquire a `lock on` (told you i was clueless!) on the desired object/person.
Now, is this simply a question of trying to use the wrong lens in the wrong conditions (the 70-300 seems so cope under similar conditions), or could there by a problem with the mechanism of the lens? The noises don`t sound too healthy, and the movement seems a little erratic when near to focusing point?

Please enlighten me, and thank you in advance if anyone finds the time/knowledge to assist!

[ian in lancs]

The camera needs contrast in the focus area to acquire 'lock-on'. Indoors in low light with a rather modest widest aperture all work against the camera. Is the little focus assist light coming on? You'll find it in the menu's that will help. Assuming you're not closer than minimum focus distance if it can focus on a light bulb or a tv screen there's nothing wrong - just lack of contrast in the target area and the lens 'hunting' for focus.

Edited by ian in lancs on Thursday 4th February 07:31

[Ed_P]

Might be worth checking what focus mode you have selected too. If you have "servo" or "tracking" mode on (or whatever Nikon call it), this will cause a noticeable "hunting" of the lens as it constantly re-focusses. This could be more apparent on closer than more distant objects. Just a thought.

[Simpo Two]

What they said. In critical conditions, use the central AF point, aim it at something with edges or contrast, semi-depress the shutter release to lock focus, then reframe. And as mentioned, enable AF-Assist in the menu. This means the litle white light on the front will help illuminate the target and so give the AF more to lock on to. Range is limited of course but in a normal room it can make all the difference.

I hit this wall at my first wedding, trying to photograph the (dimly-lit) first dance with a 70-300 AF-D lens - hunting all over the place. Next day a 70-200mm f2.8 was on the shopping list! With that, a Speedlight and the extra assist from an SC-29 synch cord I can work in complete darkness!

[Lambochick]

Another possibility is the minimum focus distance of that lens when zoomed in. I am not familiar with it, but if the minimum focus distance is greater than 3m, the lens will not be able to manage focus lock.

[Chicken Pox]

Lambochick said:

Another possibility is the minimum focus distance of that lens when zoomed in. I am not familiar with it, but if the minimum focus distance is greater than 3m, the lens will not be able to manage focus lock.

Tamron AF 28-200mm Lens Specifications: said:

- Focal Length 28-200mm
- Maximum Aperture F/3.8-5.6
- Angle of View 75°23’-12°21’
- Lens Construction 15 elements in 14 groups
- Minimum Focus Distance 0.49m (Over the entire zoom range)
- Maximum Mag. Ratio 1:4 (at f=200mm MFD 0.49m)
- Filter Diameter 62mm
- Overall Length 75.2mm
- Maximum Diameter 71.0mm
- Weight 354 grams
- Diaphragm Blades 7 blades
- Minimum Aperture F/22
- Standard Accessory Flower-shaped Lens Hood
- Compatible Mount Nikon AF-D, Canon AF, Konica Minolta AF-D, Pentax AF

low light/contrast more likely given the spec

[VxDuncan]

Yup. It's quite a slow lens, so doesn't let much light in. This means in low light there isn't much for the AF to play with. As said, the centre AF point is usually more sensitive.

[Kipling]

Hello again,
Just to say thanks to all who replied, and so quickly! I have been playing around with the lens some more, and it seems that as long as there is something else in the frame (e.g. not solely the object i want to shoot) then the lens seems to focus fine. I have been playing a lot with manual focus when indoors and this seems to be a more effective way to use it, but as i mentioned, i`m very new all this.
The photos occasionally appear almost grainy, is this just due to poor focusing on my part?
Also could anyone give me an idea as to what sort of scenario/tips as to when this lens would intended to be used, e.g is a lens of this size used for taking general photos? Or is that not the kind of questions that can really be answered?

Thanks again!

Edited by Kipling on Tuesday 9th February 19:53

Edited by Kipling on Tuesday 9th February 19:55

[GetCarter]

28-200 is a lens that is trying to be all things to all people. So it'll do landscapes to portraits to wildlife. The downside with these lenses is that they generally don't do any of them particularly well... and need good light to get good results, but the upside is you don't have to faff changing lenses all the time.

HTH

[TooLateForAName]

Kipling said:

Hello again,

The photos occasionally appear almost grainy, is this just due to poor focusing on my part?

What ISO are you using - or are you using auto? A high ISO setting will give you a grainy look.

It does sound as if you are using it in conditions which are too dark for it. On trick is to use a torch to illuminate the subject - that will often give you enough light for the AF to work reliably.

Are you using any filters on the lens?