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Thread: Is there any difference?

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    Senior Member The_Cheat's Avatar
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    Default Is there any difference?

    Is there any difference in putting the filter in front of the front element of the lens, and putting it behind the real element of the lens?

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    Quote Originally Posted by The_Cheat
    Is there any difference in putting the filter in front of the front element of the lens, and putting it behind the real element of the lens?
    I don't think you can put a filter but the front of the lens as that's the only part with the threads to screw it into. Even for your gel filters, you put that in front because you mount the rear of the lens to the camera body.

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    Quote Originally Posted by The_Cheat
    Is there any difference in putting the filter in front of the front element of the lens, and putting it behind the real element of the lens?
    Yes, there is. How problematic the difference is depends on the circumstances. As an example, focusing may be affected.

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    Senior Member The_Cheat's Avatar
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    Quote Originally Posted by LittleWolf
    Yes, there is. How problematic the difference is depends on the circumstances. As an example, focusing may be affected.
    Can you elaborate more on that please?

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    Quote Originally Posted by The_Cheat
    Can you elaborate more on that please?
    The filter glass refracts the light, changing the apparent optical distance between the lens and the film. Since the filter glass is also dispersive, the filter also introduces chromatic abberations. There is a host of other small effects, too. In general, a filter is a disturbance to the optical system that will degrade image quality. For details, search on google for
    "planoparallel plate".

    This is true regardless of which side of the lens the filter is on. However, in standard situations, the distance between the lens and the film is much smaller than between the lens and the object. A focus difference of a fraction of a millimeter is normally negligible on the object side (unless you're doing macro shots), but on the film side may be quite significant.

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    Senior Member The_Cheat's Avatar
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    Quote Originally Posted by LittleWolf
    The filter glass refracts the light, changing the apparent optical distance between the lens and the film. Since the filter glass is also dispersive, the filter also introduces chromatic abberations. There is a host of other small effects, too. In general, a filter is a disturbance to the optical system that will degrade image quality. For details, search on google for
    "planoparallel plate".

    This is true regardless of which side of the lens the filter is on. However, in standard situations, the distance between the lens and the film is much smaller than between the lens and the object. A focus difference of a fraction of a millimeter is normally negligible on the object side (unless you're doing macro shots), but on the film side may be quite significant.
    Hmm... thanks for the elaborate explanation. I did come across that if one wishes to place two filters on one lens, it's better to put one on the front and one on the rear, as compared to two filters stacked on the front right? Any idea why this is recommended?

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    Quote Originally Posted by The_Cheat
    I did come across that if one wishes to place two filters on one lens, it's better to put one on the front and one on the rear, as compared to two filters stacked on the front right? Any idea why this is recommended?
    It doesn't seem like generally good advice to me. From a practical point of view, one possible explanation is that it might help to avoid vignetting. Also, ghost images and stray light from reflections off the filter surfaces will be different, but not necessarily for the better.

    I wonder if you're referring to large format cameras - since the distance between the lens and the film is relatively large in this case, the disturbance caused by a filter is probably much more tolerable.

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    Senior Member The_Cheat's Avatar
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    Quote Originally Posted by LittleWolf
    It doesn't seem like generally good advice to me. From a practical point of view, one possible explanation is that it might help to avoid vignetting. Also, ghost images and stray light from reflections off the filter surfaces will be different, but not necessarily for the better.

    I wonder if you're referring to large format cameras - since the distance between the lens and the film is relatively large in this case, the disturbance caused by a filter is probably much more tolerable.
    Yup... talking about large format lenses.

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