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12-14-2020, 03:13 AM   #1
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Infrared mark on old Pentax lenses

Because I have the bad habit that I never fully read manuals I suddenly noticed by doing so that there is a infrared mark (the red line) on the older Pentax lenses.
And I was wondering: is there anyone who has experience with taking infrared pictures (on film or otherwise) and this mark? It seems that it is used to correct the focal distance?

12-14-2020, 03:30 AM - 1 Like   #2
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When shooting infrared I just focus with liveview and get it right every time. That IR mark might have helped decades ago but these days you have modern focusing aids. You can focus in infrared as you do with any lens if there is possibility to use live view. And infrared mark does not guarantee good performance when it comes to hotspots.
12-14-2020, 05:42 AM - 1 Like   #3
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QuoteOriginally posted by Reciprocity Quote
Because I have the bad habit that I never fully read manuals I suddenly noticed by doing so that there is a infrared mark (the red line) on the older Pentax lenses.And I was wondering: is there anyone who has experience with taking infrared pictures (on film or otherwise) and this mark? It seems that it is used to correct the focal distance?
As MJKoski said, on DSLRs the best way to focus is with LV when shooting with an IR-filter on. But with film you would focus without filter, screw on the filter and correct focus by turning the position on the distance scale from the usual mark to the IR-mark.
12-14-2020, 09:53 AM - 1 Like   #4
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for film the process is you focus normally then shift that distance to the IR mark. So if you focus on something and the distance scale says 5 feet, you shift the 5 foot indicator to the IR mark. I used that back when I used IR film and a filter that filtered out all visible light. More recently I used Konica 750 film. Those pictures were IR and visible light using a red29 filter. I would split the difference between IR and visible and made sure the aperture was small enough to cover both.

12-14-2020, 10:17 AM - 1 Like   #5
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From the Pentax KX manual:

Phil.
Attached Images
 
12-14-2020, 08:13 PM - 1 Like   #6
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QuoteOriginally posted by Reciprocity Quote
Because I have the bad habit that I never fully read manuals I suddenly noticed by doing so that there is a infrared mark (the red line) on the older Pentax lenses.
And I was wondering: is there anyone who has experience with taking infrared pictures (on film or otherwise) and this mark? It seems that it is used to correct the focal distance?
As others have noted, it's not terribly useful these days, but I used it on film, and it worked great.

With infrared film, the filter killed so much light, metering was sometimes a trick, too...

But it's fun stuff if you can find it...

-Eric
12-15-2020, 12:00 AM   #7
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QuoteOriginally posted by MJKoski Quote
When shooting infrared I just focus with liveview and get it right every time. That IR mark might have helped decades ago but these days you have modern focusing aids. You can focus in infrared as you do with any lens if there is possibility to use live view. And infrared mark does not guarantee good performance when it comes to hotspots.
I see, thanks.

---------- Post added 12-15-20 at 12:06 AM ----------

I also notice that there are a lot of different filters, any idea which one I should use to start out with?For B&W mostly.

12-15-2020, 01:25 AM - 1 Like   #8
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Unfortunately my *istD cameras, with their CCD sensors, (which are quite sensitive to I/r without any modification), don't have LiveView, so I revert to "old-school" procedures and use the i/r index regularly.
I do find having a "square filter" holder fitted to the lens, so's the filter can be slipped in and out quite readily, to be a great advantage.
Older primes, the sort of lenses which are likely to have an I/r index, fortunately often have smaller filter threads, so there's no massive investment necessary in large filters and the screw-fitting ring can be swapped on the holder as necessary
For the (attempted) capture of a moving subject within a pre-framed scenario, or even as a "walk-around" snapshot camera with the lens pre-focussed at the hyperfocal distance, a separate wire-frame or optical viewfinder fitted in the hot-shoe can be very helpful
12-15-2020, 06:09 AM - 1 Like   #9
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830nm and 850nm+ are perfect for B&W IR. Results are mostly B&W straight out of the camera if WB is set correctly.
12-15-2020, 06:11 AM - 1 Like   #10
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I used it when using film 50 some years ago. It did work.
12-15-2020, 11:47 PM   #11
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QuoteOriginally posted by MJKoski Quote
830nm and 850nm+ are perfect for B&W IR. Results are mostly B&W straight out of the camera if WB is set correctly.
Thanks, I will look for a 850 nm one.
12-17-2020, 12:36 AM   #12
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QuoteOriginally posted by kypfer Quote
Unfortunately my *istD cameras, with their CCD sensors, (which are quite sensitive to I/r without any modification), don't have LiveView, so I revert to "old-school" procedures and use the i/r index regularly.
I do find having a "square filter" holder fitted to the lens, so's the filter can be slipped in and out quite readily, to be a great advantage.
Older primes, the sort of lenses which are likely to have an I/r index, fortunately often have smaller filter threads, so there's no massive investment necessary in large filters and the screw-fitting ring can be swapped on the holder as necessary
For the (attempted) capture of a moving subject within a pre-framed scenario, or even as a "walk-around" snapshot camera with the lens pre-focussed at the hyperfocal distance, a separate wire-frame or optical viewfinder fitted in the hot-shoe can be very helpful
Indeed, a square filter would be more convenient I guess, because of focusing. Any chance that Cokin has this?
12-17-2020, 06:27 PM - 1 Like   #13
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Very interesting thread. I have learned quite a lot here on the forums.
12-18-2020, 01:12 AM - 1 Like   #14
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QuoteOriginally posted by Reciprocity Quote
Indeed, a square filter would be more convenient I guess, because of focusing. Any chance that Cokin has this?
The filter holder I use is indeed a Cokin branded item, taking a 67mm square filter … not sure they're still available. Cokin also produced a frame for holding a sheet of gel or other filter material. I've got one with some Ilford SFX material in it (R72 equivalent, very dark red) and another with some Lee 87 fitted, (Wratten 87 equivalent, optically opaque). It's not difficult to make up card holders for sheet filter material, but sourcing the filter material itself probably isn't easy (or cheap) these days. I've had mine since the '70's
12-20-2020, 11:42 PM   #15
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QuoteOriginally posted by kypfer Quote
The filter holder I use is indeed a Cokin branded item, taking a 67mm square filter … not sure they're still available. Cokin also produced a frame for holding a sheet of gel or other filter material. I've got one with some Ilford SFX material in it (R72 equivalent, very dark red) and another with some Lee 87 fitted, (Wratten 87 equivalent, optically opaque). It's not difficult to make up card holders for sheet filter material, but sourcing the filter material itself probably isn't easy (or cheap) these days. I've had mine since the '70's
Yes, the Cokin sheet holder is probably a cheaper solution than a regular filter, but I'm wondering about lightleaks.
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