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Thread: Filter use in 300/2.8 ais lens

  1. #1
    Senior Member JoelM's Avatar
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    Filter use in 300/2.8 ais lens

    Just received a 300 f2.8 lens. It had a large 122mm UV filter on the front, but no filter installed in the 39mm holder in the lens. I had thought that the 39mm filter was necessary for proper focus, but in researching, I get conflicting opinions. Of course, the holder must be inserted, but no consensus regarding the filter. Also, the holder can go in both ways so not sure which way is correct. I assume that it goes in with the filter screwed in from the front like a regular filter on the outside of the lens.

    All help is appreciated,

    Joel

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    Senior Member Swissblad's Avatar
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    Re: Filter use in 300/2.8 ais lens

    I agree, it seems confusing - at least what's circulating on the web.
    I don't have the AIS lens, but have the old Nikkor 300mm f4.0 lens, which also has a drop in filter. I would not imagine that it effects focus - but rather that it may have been useful in the pre-digital era to adjust colour tone ie warm or cold.
    In addition, some use a polarizer in this position.
    I would give your lens a thorough testing - it is one of the sharpest Nikkors around.
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    Member AreBee's Avatar
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    Re: Filter use in 300/2.8 ais lens

    Joel,

    Quote Originally Posted by JoelM View Post
    Just received a 300 f2.8 lens. It had a large 122mm UV filter on the front, but no filter installed in the 39mm holder in the lens. I had thought that the 39mm filter was necessary for proper focus, but in researching, I get conflicting opinions.
    Thom Hogan is a widely respected authority on Nikon. In his review of the Nikon 200mm f/2 and 400mm f/2.8 he states:

    As with all Nikon drop-in filters, the supplied plain filter is part of the optical formula; using a filter holder without glass is a slight no-no.

    In his review of the 300mm f/2.8 he states:

    Filters are the special 39mm drop-in variety. You get two drop-in brackets with the lens, and if you're not using filters, the one with the flat glass element in it should always be used (it's part of the optical formula).

    In summary, for optimum performance you should use a Neutral Clear (NC) that would have been included with the lens originally (I think the part number is 2478NASI), or a C-PL1S polariser filter available separately for the 300mm f/2.8. Instructions for Nikon drop in polariser filters is attached for your information.

    Also, the holder can go in both ways so not sure which way is correct.
    I have attached a photo showing the C-PL3L drop in polariser for the 200mm f/2, left, and the NC that was included with the lens originally, right.

    You can see "front" marked on the polariser (refer also to attached pdf of instructions) and also how the filter is closer to one side of the holder than it is to the other. Hence, an NC should be inserted into the lens such that it is closer to the front lens element ("front") than it is to the lens mount ("rear").

    I assume that it goes in with the filter screwed in from the front like a regular filter on the outside of the lens.
    In the case of an NC, no (refer to attached photo). In the case of a polariser, it is irrelevant because the filter is integral with the holder - if you purchase a drop in polariser the product you will receive is the filter built into an accompanying holder (due to the rotating wheel mechanism) - you swap filter and holder as one when inserting/removing a polariser drop in filter.
    Last edited by AreBee; 31st August 2013 at 13:12.
    Rob
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    Senior Member Swissblad's Avatar
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    Re: Filter use in 300/2.8 ais lens

    Thanks for posting that - very useful.

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    Re: Filter use in 300/2.8 ais lens

    Yep, you should use a clear filter. The thickness has to be right as well, so you're probably stuck trying to find the exact right Nikon item... Any air-glass surface by definition becomes a part of the lens, in this case when you change filters all you change is the tint or polarization of this (flat) element.

    A 2mm flat piece of glass shifts rear focus 2mm. Removing it effectively brings the lens in 2mm closer to the camera, like you shaved this much off the mount. It may still work but you lose some minimum focus distance since the max draw is reduced.

    Also, if the lens has floating elements (not sure if the 300/2.8 AI-S does, I suspect not) the exact mount distance matters for optimal performance.

    Edit: removing the filter increases draw. Sorry, I blame it being 8am on a Sunday and a low blood caffeine level...
    Last edited by Jan Brittenson; 1st September 2013 at 09:54.
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    Senior Member JoelM's Avatar
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    Re: Filter use in 300/2.8 ais lens

    That filter seems very hard to find. Can you use a Nikon L37C 39mm UV filter or some other 39mm clear filter? Since you can screw in any color filter for the effect you want, I would think that the particular clear filter would not make a noticeable difference.

    Thanks,

    Joel

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    Sr. Administrator Jack's Avatar
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    Re: Filter use in 300/2.8 ais lens

    The internal filter in Nikon teles is indeed part of the optical formula and should be there -- and you can use any Nikon (or similar) 39mm (or 52 on larger lenses) screw filter. Moreover, the front element is already a permanent flat protective element designed specifically to be relatively easy and relatively inexpensive to replace should it suffer damage.
    Jack
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    Senior Member JoelM's Avatar
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    Re: Filter use in 300/2.8 ais lens

    If I'm not mistaken, only the last iteration of the lens had the protective flat and no 122mm filter threads. I have the one right before that with the 122mm and 39mm filter threads. I had always thought that it was part of the formula, but I've always wondered what 2 more glass to air surfaces as well as glass thickness added to the formula would benefit. If anything, I would think that sharpness would be reduced.

    Joel

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    Sr. Administrator Jack's Avatar
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    Re: Filter use in 300/2.8 ais lens

    The front element has been flat for several generations in all the big teles, regardless of whether it's threaded or not. The filter drawer filter has been part of the optical formulae ever since it was introduced. A flat piece of glass changes (actually shortens) the total distance of the optical path. It does this when placed in front of the lens, but the effect is strongest at infinity and you're only slightly shortening what is basically already infinity, so it is for the most part irrelevant. However, when moved to the rear, it has a more significant effect -- leaving it out basically lengthens a relatively short path, hence a more significant effect.
    Jack
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