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05-19-2009, 06:38 PM   #1
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F* 600mm f/4.0 question

Does anyone know whether there is a drop-in polarizer available for the F* 600mm f/4.0 similar to the one available for the FA* 600mm f/4.0?

05-19-2009, 07:15 PM   #2
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Jem, I am not sure what the answer is... they use the same 43mm diameter filter, but the holder is obviously different.

What means have you employed to find answers? Perhaps contacting Pentax USA parts/service would be a good idea if no one can answer this one for you.

Regards,
Marc
05-19-2009, 08:40 PM   #3
jem
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Hi Marc,

Just starting my quest for info. I've done a quick search via the internet with no luck. I thought I'd ask here to see if any other owners knew if it exists. I will check with Pentax parts next. If all else fails I'll machine one myself or have one made.

Best,
John
05-21-2009, 07:24 AM   #4
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The FA drop-in doesn't fit in the F model 600/4 so that won't work either...good luck on your quest...

05-21-2009, 08:15 AM   #5
jem
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QuoteOriginally posted by Ron Boggs Quote
The FA drop-in doesn't fit in the F model 600/4 so that won't work either...good luck on your quest...
Thanks Ron for confirming my suspicions. I figured there would be dimensional differences.

As far as I can determine, a drop-in polarizer does not exist for the F* 600mm. The manual does not list one as an optional accessory. I spoke with the nice lady at Pentax USA Parts who sent me a parts diagram of the only 600mm lens they sell parts for – the A* 600mm f/5.6. No help there – different size polarizer and holder. They don’t directly sell parts for the F* and FA* 600mm – they only do repair work using (I assume) their internal (not for direct sale) bench stock of parts.

This leaves me with manufacturing one myself. There are at least two ways I can go here:

One - cannibalize a FA* drop-in for the polarizer and thumb-wheel assembly. On the plus side I get a polarizer that should be suitable for the optical path of the F* 600mm. The machining should be minimized to only the holder itself. The minus is that the FA* 600mm polarizer is as rare as hens teeth and rather expensive.

Two – build the whole thing from scratch using a quality 3rd party polarizer. The minus here is the additional complexity. Doing gear work is a bit above my skill level so I would have to contract the task out. And one-offs tend to be pricy. Another factor is potentially screwing up the optical path with the 3rd party polarizer.

Anyway, still researching and thinking. Any thoughts?
05-21-2009, 09:43 AM   #6
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My thought is to make sure that the location of the filter glass is identical to the stock location. Moving the glass forward or back even a millimeter could affect focus integrity.

It's interesting that last week my shooting buddy and I compared filter slots on his F*600/4 that I sold him years ago and my current FA*600/4. Not only is the F* slot narrower, but the filter drawer pointer is designed to point the opposite direction of the pointer on the FA model. The F filter pointer (red line) is designed to point forward and this is diagramed in the manual for that lens. The FA pointer (black line) is designed to point back toward the camera and this is most clearly seen on the drop-in polarizer which has arrows directing which way is forward and which is back.

It appears to my unscientific eye that the filter in the FA drop-in is not directly centered which would mean that if the drop-in drawer is facing the wrong way, that focus could be affected. Because I started with an F version, I've been using my drawer the wrong way for years (when I paid enough attention to note a direction--I've used it both ways thinking it was interchangeable). This slight millimeter or so variation may help me pick up extra sharpness at f/4 and on the 250-600 at f/5.6. That's me, the forever optimist looking for a way to improve wide open performance which has in the past been noticeably softer than all the other stops on the ap. ring. Both lenses performed very well last weekend with the pointer facing the correct direction, but I didn't really test wide open as the subjects I was shooting were very challenging and somewhat rare, so I didn't take time or effort for testing...

Good luck on the drop-in, it's very nice for landscape extractions, but unless you own Marc Langille's FA* 300/2.8, you may want to keep the extra stop of light lost to the polarizer when using an f/4 lens. In other words, I pretty much never use the drop-in polarizer for critter work, only scenics. With the 2.8 lens, the extra stop lost to polarizing is less noticeable.
05-21-2009, 11:11 AM   #7
jem
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Thanks Ron for the very thoughtful and informative post.

QuoteOriginally posted by Ron Boggs Quote
My thought is to make sure that the location of the filter glass is identical to the stock location. Moving the glass forward or back even a millimeter could affect focus integrity.
Yes, this is of great concern to me – do no harm to the optical quality of the lens.

QuoteOriginally posted by Ron Boggs Quote
It's interesting that last week my shooting buddy and I compared filter slots on his F*600/4 that I sold him years ago and my current FA*600/4. Not only is the F* slot narrower, but the filter drawer pointer is designed to point the opposite direction of the pointer on the FA model. The F filter pointer (red line) is designed to point forward and this is diagramed in the manual for that lens. The FA pointer (black line) is designed to point back toward the camera and this is most clearly seen on the drop-in polarizer which has arrows directing which way is forward and which is back.
A few questions:

Did it look like the FA* polarizer component (ignoring the overall filter mount width) was narrow enough to fit in the F* slot?

If possible, could you make a measurement with a caliper or micrometer of the width of the polarizer both with the overall housing and only the polarizer portion of the assembly?

Can you tell which side of the polarizer is the critical optical surface distance-wise - front (toward lens) or back (toward camera)? I assume you might be able to determine this by comparing the polarizer to your regular filter holder.

QuoteOriginally posted by Ron Boggs Quote
It appears to my unscientific eye that the filter in the FA drop-in is not directly centered which would mean that if the drop-in drawer is facing the wrong way, that focus could be affected. Because I started with an F version, I've been using my drawer the wrong way for years (when I paid enough attention to note a direction--I've used it both ways thinking it was interchangeable). This slight millimeter or so variation may help me pick up extra sharpness at f/4 and on the 250-600 at f/5.6. That's me, the forever optimist looking for a way to improve wide open performance which has in the past been noticeably softer than all the other stops on the ap. ring. Both lenses performed very well last weekend with the pointer facing the correct direction, but I didn't really test wide open as the subjects I was shooting were very challenging and somewhat rare, so I didn't take time or effort for testing...
Interesting. I wonder how much difference it does make. I remember your review discussing softness at F/4.0 along with another owner review discussing the same. Am I correct in assuming the review was written while you were using it the wrong way? Also, if you do a test I would be very interested in the results.

QuoteOriginally posted by Ron Boggs Quote
Good luck on the drop-in, it's very nice for landscape extractions, but unless you own Marc Langille's FA* 300/2.8, you may want to keep the extra stop of light lost to the polarizer when using an f/4 lens. In other words, I pretty much never use the drop-in polarizer for critter work, only scenics. With the 2.8 lens, the extra stop lost to polarizing is less noticeable.
Thanks! Yes I agree on usage. Typically I only use a polarizer on long telephotos when it is sunny and I’m around water – which we have quite a bit of both around here. It can be quite bright and shiny on the Gulf Coast.

Thanks again!
John
05-21-2009, 09:48 PM   #8
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QuoteOriginally posted by jem Quote
Does anyone know whether there is a drop-in polarizer available for the F* 600mm f/4.0 similar to the one available for the FA* 600mm f/4.0?
don't know if you are still looking for a drop in filter holder but saw one on e-bay Pentax 645 49mm Drop-In Circular Polarizer 600mm f5.6 - eBay (item 230339557365 end time May-26-09 08:11:14 PDT)

not sure if this is right for you but though il'd post it anyways...

have a good one!

Ben

05-22-2009, 05:09 AM   #9
jem
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QuoteOriginally posted by Ben Hunt Quote
don't know if you are still looking for a drop in filter holder but saw one on e-bay Pentax 645 49mm Drop-In Circular Polarizer 600mm f5.6 - eBay (item 230339557365 end time May-26-09 08:11:14 PDT)

not sure if this is right for you but though il'd post it anyways...

have a good one!

Ben
I'm looking for one that would fit the SMC Pentax F* 600mm f/4 ED(IF) K-mount lens. That one is for the 645 medium format 600mm. Same concept though - only I need one in 43mm. Thanks anyway!

Last edited by jem; 05-22-2009 at 05:13 AM. Reason: Clarity
05-22-2009, 01:12 PM   #10
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Gosh, I have a couple measurement tools around here somewhere, but honestly I wouldn't trust my results to do a $500 tinker. You should be able to measure filter location--front of glass and back of glass as it fits into your F* drop-in and then try to match those figures with a custom polarizer for dropping in.

You know, the old school way was to use polarizers with 360 degree labeling and tick marks around the edges. Then you hold it up in front of your eyes to determine the best setting, then screw it into the stock drop-in filter holder and match the setting you determined in front of your eyes. Not very artistic but workable. And I'm pretty sure there are still tick-marked degree labeled polarizers available on the market, but probably not 43mm. You may want to simply add your own labels to a standard 43mm polarizer and try this method. The only cost is the polarizer--you can get a heliopan or something else really good for under $75. Using it in the stock drop-in holder will remove the risk of poor alignment or poor placement.

I believe this may be the way old school rangefinder users added polarizers as well (before the advent of dual polarizers that fit one in front of the viewfinder and one in front of the lens--turn one wheel to adjust both simultaneously...adjust exposure for the lost light due to polarizing and shoot.

Your drop-in would be easier than adding polarization to rangefinders, but the old-school method is probably discussed on some rangefinder forums somewhere? That might give you some direction other than the custom idea you are thinking of.
05-22-2009, 05:14 PM   #11
jem
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QuoteOriginally posted by Ron Boggs Quote
Gosh, I have a couple measurement tools around here somewhere, but honestly I wouldn't trust my results to do a $500 tinker. You should be able to measure filter location--front of glass and back of glass as it fits into your F* drop-in and then try to match those figures with a custom polarizer for dropping in.
No worries - I was just looking for a guestimate to see if the FA* version is worth pursuing for further info, not purchase as yet. I’m not sure if I can even find one anytime soon.

The reason I ask about front/back surface comparisons is that due to their construction some polarizers tend to be thicker than a standard filter such as a UV or Sky. The thickness varies from manufacturer to manufacturer and quality of the polarizer. This is why I want to use a standard filter in its holder as a baseline. Ideally, the FA* polarizer is the same thickness as the standard filters and I can cross out that variable. But if it is not, then I have to factor in which surface is the critical surface in the optical path. Thus the FA* polarizer versus the standard filter comparison is the only way I can determine this piece of information. This will be needed information especially if I use a 3rd-party polarizer. For example, I measured a few of my 49mm polarizers and the variance in thickness was from approximately 2mm to nearly 5mm versus 2mm typical for a couple of UV filters.

QuoteOriginally posted by Ron Boggs Quote
You know, the old school way was to use polarizers with 360 degree labeling and tick marks around the edges. Then you hold it up in front of your eyes to determine the best setting, then screw it into the stock drop-in filter holder and match the setting you determined in front of your eyes. Not very artistic but workable. And I'm pretty sure there are still tick-marked degree labeled polarizers available on the market, but probably not 43mm. You may want to simply add your own labels to a standard 43mm polarizer and try this method. The only cost is the polarizer--you can get a heliopan or something else really good for under $75. Using it in the stock drop-in holder will remove the risk of poor alignment or poor placement.
Indexing is always a solution. I don’t even need to mark the filter. Just pull the holder out keeping the orientation the same, adjust the polarizer by eye, insert, inspect the view and repeat if necessary. But unfortunately for me sometimes, I’m too much of an engineer to not try to finesse the problem. Just a little background: I work for an infrared camera company and my group builds cameras for a living so I like to get my hands dirty so to speak. Anyway, I can’t help myself – I want the elegant solution – even if it is hard.

QuoteOriginally posted by Ron Boggs Quote
I believe this may be the way old school rangefinder users added polarizers as well (before the advent of dual polarizers that fit one in front of the viewfinder and one in front of the lens--turn one wheel to adjust both simultaneously...adjust exposure for the lost light due to polarizing and shoot.
Ah, that brings back memories of my father teaching me photography with his rangefinder and all the little gadgets he had to simplify/complicate the task. Thanks for the memory!
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