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02-01-2009, 01:07 AM   #1
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Which filters for Pentax-FA* 300mm f2.8 ?

Long shot getting an answer but where better to ask ?

I've only had the Pentax-FA* 300mm f2.8 for a little less than 12months and haven't often used it in anger, but I have a stupid question in preparation for an upcoming outdoor event I'd like to shoot.

The FA*300 f2.8 has the 43mm drop in filters as well as allowing for 112mm screw on filters. At the moment I have UV filters on both the front and for the drop in. Most of my other lenses are nude as a preference but is there any reason to have both of these UV filters on the lens, (aside from protecting the front element) ?

Just wondering what other owners of this lens, (or other Pentax lenses that cater for drop in filters), may be doing.

bazz.

02-01-2009, 05:52 AM   #2
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Hey bazz,
I think the rear filter is part of the design and should always be used (like my tamron was) They show it in the diagram:

http://www.bdimitrov.de/kmp/lenses/primes/_optics/300f2.8-ii.gif

You don't really need that old lens do you? I would gladly take it off your hands so you'll have more room in the cupboard.
02-01-2009, 08:20 AM   #3
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the front filter was listed as a PF (protective filter) when I bought mine. You can take it off if you want.... but I'm sure not going to.

I have only changed out the rear filter once - an an airshow when it got a bit hazy and I planned to shoot b&w. Otherwise i have not taken out the rear filter
02-01-2009, 01:59 PM   #4
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What Tom wrote about the rear filter is correct - it is part of the computation and should be in place all the time. If you shoot without a rear filter you may get a slight focus shift and induce some spherical aberration - but that might get unnoticed on a APS-C camera. For the front filter: leave it on, it will degrade the IQ, but this is in my personal experience completely unnoticeable. And these large front lenses (112mm thread?) are really prone to get damaged (my Tamron has a "nice" scartch on the front...)

Ben

02-01-2009, 04:05 PM   #5
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If you have the 112mm Pentax PF (protective front) filter in place and then added a UV filter, I believe you've gone too far. The PF and the rear drop-in are both part of the optical formula, so you need something in place, but adding a UV up front isn't needed and could in-fact be a problem.

I have noticeable problems with my M*400/4 for 6x7 format if I add too much stuff out front. For example, it won't work with the 112mm PF and a 112 Circular Polarizer plus split neutral density grads. Take off the polarizer and grads work fine. Take off the grads and the polarizer works fine. I've since obtained a drop in circular polarizer (and sold the 112mm Kasemenn Cir. Polarizer to another forum member for his A*300/2.8).

I highly recommend playing with the cloudy filter for the drop-in, I'm presuming you have the 6 filter drop-in kit that comes with all the 35mm * teles that take drop-ins. For many outdoor situations, the cloudy is just the right amount of warming. The cloudy filter built-into the Pentax digi bodies is way too warm for everyday shooting, the cloudy is not.

I also recommend that you try to find a copy of the drop-in circular polarizer for FA* lenses. Several forum members have one and like it. I like it very much...
02-02-2009, 01:23 AM   #6
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Hmmmm...interesting. Thanks to all who replied.

I just double checked and it is infact the standard PF on the front and not a UV filter.

Avalon Air Show is in mid March and is the event I was referring to. Think I'll try and hunt down one of those drop in CP's over the next few weeks.

I did also note that the lens formula posted borno, (thanks), shows the drop in filter as a flat element which kinda implies that there's no corrective properties to the filter. Who knows, I might just get bored enough to do some testing with/without to satisfy that lingering sprinkle of curiosity.

cheers all,
bazz.
02-02-2009, 05:10 AM   #7
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QuoteOriginally posted by sir_bazz Quote
Hmmmm...interesting. Thanks to all who replied.

I just double checked and it is infact the standard PF on the front and not a UV filter.

Avalon Air Show is in mid March and is the event I was referring to. Think I'll try and hunt down one of those drop in CP's over the next few weeks.

I did also note that the lens formula posted borno, (thanks), shows the drop in filter as a flat element which kinda implies that there's no corrective properties to the filter. Who knows, I might just get bored enough to do some testing with/without to satisfy that lingering sprinkle of curiosity.

cheers all,
bazz.
A plano-parellel glass plate, like the drop-in filter always has optical properties, the minimum being to induce a slight focus shift. According to Ray (Applied Photographic Optics) the focus shift is equivalent to 1/3 of the glass thickness. For converging rays (i.e. those not paraxial) a glass plate can also introduce aberrations (as I mentioned before) and thus has to be part of the overall lens computation, so that it is a corrective element and not a destructive one.

Ron is ofcourse right, when he suggests to always only use oine filter at a time in front of the lens. Combining several filters will in many situations visibly degrade IQ. I think, this filter-combination-thing lead to the bad reputation of Cokin filters. If you had just one in place, they were (are) not too bad...

Ben
03-28-2009, 09:54 AM   #8
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Would anybody know where I could get my hands on a drop in polarizer for the FA*300 f2.8???

03-28-2009, 10:57 AM   #9
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QuoteOriginally posted by borno Quote
Would anybody know where I could get my hands on a drop in polarizer for the FA*300 f2.8???
You should be able to get one from Pentax, as the lens was listed until recently (9 months ago or so).

Ben
03-28-2009, 11:08 AM   #10
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Thanks Ben,
I'll ask them when I call about my lens. I bought it second hand and though it was not used by the previous owner something is out of adjustment. Back focus and the images are soft so I'm hoping they can get it tuned up for me. I guess an element or lens group was out of whack from the factory.
03-28-2009, 12:01 PM   #11
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Hey Tom,

I purchased mine (drop in Polarizing filter) used via B&H for $219. It was like new condition. The images of that FA* CPL in the lens review DB are mine. It's worked very well in certain situations!

Regards,
Marc
03-28-2009, 01:09 PM   #12
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Thanks Marc,
I'm going to keep my eye out for one when I get my lens back, The wildlife photographers I talk to say it's a "must have" and I trust their judgement (on that anyways)
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