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Film lens AF

Discussion in 'Sony Chat' started by 5872, Jan 17, 2009.

  1. 5872

    5872 Well-Known Member

    I have been told that film lenses have an AF that is slighty out of focus when they are mounted on a Digital SLR (Such as my 28-200 on my Sony A300).

    Has anyone got any ideas?.
     
  2. Fen

    Fen Well-Known Member

    Hogwash!

    May I ask who told you that?
     
  3. RonM

    RonM Alpha Napper

    Unless Fen he's talking about Back Focus issues that have been seen with some DSLR's, but, that is not to do with the lens it is as we know to do with the body
     
  4. Fen

    Fen Well-Known Member

    As you say, Back focus isn't to do with the lens, whether be an old one or a new one.
     
  5. Roger_Provins

    Roger_Provins Well-Known Member

    I beg to differ. Lenses can and do back-focus or front-focus (nothing to do with if they were originally made for film or digital) this is why the more expensive digital cameras are equipped with some form of Micro-AF adjustment capability for individual lenses. So if one lens is found to focus wrongly then the camera can be programmed to always make a previously ascertained adjustment when this lens is fitted.

    The camera can also be at fault but then the same degree of back or front focus would be found with with all lenses.

    There is a fairly good explanation here.
     
  6. 5872

    5872 Well-Known Member

  7. Fen

    Fen Well-Known Member

    Train moving...
    - not fast enough shutter speed
    - poor technique

    Could be lots of different reasons, but doesn't mean that your lens won't focus on a new camera
     
  8. RonM

    RonM Alpha Napper

    ^^^WHS^^^

    I'd reckon that Fens nailed it for that shot, looking at the wall behind the train, where I think the plane of focus is, the static wall looks sharp whereas the moving train is 'soft' indicating as you think poor focus, but, in this case unless the shutter speed was in excess of 1/250th then I would suggest that it's the movement within the plane of focus that is causing the 'softness'
     
  9. 5872

    5872 Well-Known Member

    Thank You Gentlemen, So Shall I experiment with the Shutter speed?
     
  10. El_Sid

    El_Sid Well-Known Member

    I looked at the image you linked to and a few things sprang to mind...

    Have you applied any sharpening to the picture? I added a bit of Unsharp Mask and it improved it quite a bit...

    Was the image taken at the long end of the 28-200? Superzooms like this, especially older ones, can be a bit soft at the extreme ends of their range.

    Did you prefocus and wait for the train to pass or attempt to use continuous focus? Older lenses tend to have much slower AF than current. I have an early (ca '87-90) Canon EF 70-210 which while capable of accurate and sharp focusing on stationary objects is simply far too slow to use continuous focusing with any expectation of accuracy.

    It's difficult to tell from the picture whether the train was moving with much speed but the longer the focal length of the lens the faster the shutter speed needs to be to ensure a crisp image.

    If you want to quickly check focus accuracy put the camera on a tripod and focus on stationary objects at different distances (ideally you need to release the shutter with a remote or by timer to avoid possible camera shake from pressing the shutter button). If the pictures come out properly focused then the AF is OK. If they tend to come out out of focus then there may be an issue with AF accuracy that needs further investigation. As far as the 'advice' you were given originally goes then I'm afraid it's a myth. I have several AF film lenses of varying ages for my digital Canons and they all generally focus fine - low light and low contrast subjects can sometimes fool them though...
     
  11. 5872

    5872 Well-Known Member

    Thank You mr El Sid, How do I change the Sharpness on the Camera? (Sony A300) - the train was moving at about 20mph.

    I did have it at 135 on the 28-200.
     
  12. El_Sid

    El_Sid Well-Known Member

    I'm not familiar with Sony's system but generally there is a page in the menu system which deals with image processing parameters such as sharpness, contrast saturation etc. There will be something about it in the manual (or someone with more Sony familiarity may be able to help) that explains where to find it.

    I'm not sure if you are aware of this but the images from digital cameras tend to be naturally a little soft because of the way they work. 'Unsharp Mask' is a filter found in most good image editing packages that locally increases edge contrast in the image to put back the sharpness that the capture method loses.

    At 135mm even 20mph can be enough to induce a little blur in a moving subject if the shutter speed is low. At 135mm your minimum shutter speed for handheld work ought to be at least 1/200th to prevent image softening camera shake happening. On a tripod obviously you can get away with a slower speed but I'd suspect even then you'd need to keep the shutter speed up to freeze motion. If necessary increase the ISO setting to keep speeds up - a sharp if slightly noisy image is generally preferable to a soft blurry one.

    Incidentally how much of a crop is that picture? Obviously you've cropped it down to the 'letterbox' format but does the train still occupy the full width of the frame in the original. Heavy cropping means that the resultant image is a much greater enlargement of a smaller portion of the image and this can lead to an apparent loss in sharpness...
     
  13. LargeFormat

    LargeFormat Well-Known Member

    Roger will be able to give a definitive answer (he has an a350 which I guess is similar to the a300) but for what it's worth on my a900 you can adjust the in camera sharpening by FUNCTION / IMAGE STYLE / SHARPNESS. However I'd leave the in camera setting at zero and adjust on the computer. That keeps the file pristine and gives you flexibility. As El Sid says images straight from the camera are usually soft and benefit from a bit of sharpening but don't overdo it!
    If you aren't already, try getting into RAW. It's the route to the best results, you can tinker about without the progressive deterioration of multiple saves of JPEGs and I find it strangely satisfying. Now wait for the response by JPEG fans. :)but please don't explain to me that there is no connection between RAW and shutter speeds, it's just that the OP was writing about trying different things.
     
  14. Roger_Provins

    Roger_Provins Well-Known Member

    Camera menu 1 > Creative Style > choose which you prefer then > right on multi-function pad into that style where you can alter brightness/contrast/sharpness. Only applies to jpegs.
     
  15. 5872

    5872 Well-Known Member

    Thank You all for your help.
     
  16. 5872

    5872 Well-Known Member

    So it should be fine to use the 28-200 (film lens) or should I stick to my Sony DT 18-70 (Kit Lens) ?
     
  17. LargeFormat

    LargeFormat Well-Known Member

    I'm sure your 28-200 will be fine and if you want the extra reach over the 18-70 there's no other way. Take some test shots to see which you prefer for the overlap lengths.
     
  18. 5872

    5872 Well-Known Member

    Thanks, I did that and found that the focus is largely the same... I'm confused now.
     

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