Coating variation on 2 copies of same lens (Pentax F 35-70)

Lititz · 05-22-2013, 06:23 PM

I've got two copies of the Pentax-F SMC 35-70mm f3.5/4.5. I've noticed that their coatings have very different reflections, even when side-by-side under the same light (and regardless of how I hold or move them around). One is cool, tending toward blue, while the other is red/magenta (see attached image). Did SMC coatings vary this way over time (even on the same lens model)? Or did a previous owner over-clean and remove a layer (though I'd be surprised that ta layer could get removed so uniformly by an amateur cleaning). FYI, the "red" lens is about 40,000 later in its serial number, so I assume it is later production. Does anyone have any knowledge about this? Thanks much.

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Eulogy · 05-22-2013, 10:30 PM

I believe early F lenses used A series coatings, while later F series used their own variant (Which overlapped into the FA lenses briefly). It could also be finish wear, as in some of the coating as worn off on one over time.

**ashurbanipal** · 05-23-2013, 09:19 PM

Originally posted by Lititz

I've got two copies of the Pentax-F SMC 35-70mm f3.5/4.5. I've noticed that their coatings have very different reflections, even when side-by-side under the same light (and regardless of how I hold or move them around). One is cool, tending toward blue, while the other is red/magenta (see attached image). Did SMC coatings vary this way over time (even on the same lens model)? Or did a previous owner over-clean and remove a layer (though I'd be surprised that ta layer could get removed so uniformly by an amateur cleaning). FYI, the "red" lens is about 40,000 later in its serial number, so I assume it is later production. Does anyone have any knowledge about this? Thanks much.

Out of curiosity, what are the serial numbers? What kind of lighting was the picture taken under? Mine (serial 1313773) seems to be more like the one on the right, at least under the daylight CFLs I have here.

Lititz · 05-24-2013, 06:16 AM

Originally posted by ashurbanipal

Out of curiosity, what are the serial numbers? What kind of lighting was the picture taken under? Mine (serial 1313773) seems to be more like the one on the right, at least under the daylight CFLs I have here.

The lens on the right (magenta reflection) is #1413582. I gave the other lens (on left) to a family member, so I don't have it in front of me, but the serial number was somewhere in the range of 105xxxx to 115xxxx. The photo was hastily shot under a 100 watt "soft white" incandescent bulb.

**ashurbanipal** · 05-24-2013, 07:09 PM

Originally posted by Lititz

The lens on the right (magenta reflection) is #1413582. I gave the other lens (on left) to a family member, so I don't have it in front of me, but the serial number was somewhere in the range of 105xxxx to 115xxxx. The photo was hastily shot under a 100 watt "soft white" incandescent bulb.

Checking under incandescent, mine's definitely more magenta than blue. Hopefully someone will chime in with a definitive answer about the coatings.

Lititz · 05-28-2013, 06:13 PM

Originally posted by ashurbanipal

Checking under incandescent, mine's definitely more magenta than blue. Hopefully someone will chime in with a definitive answer about the coatings.

I looked at a number of photos of this lens for sale/sold on eeekbay, etc. Some show the magenta coloration, some the blue. Of course, there's not much of a clue as to what kind of lighting was used to photograph them.

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05-22-2013, 10:30 PM	#2
Eulogy Veteran Member Join Date: Feb 2012 Location: Fredericton, New Brunswick Photos: Gallery Posts: 632	I believe early F lenses used A series coatings, while later F series used their own variant (Which overlapped into the FA lenses briefly). It could also be finish wear, as in some of the coating as worn off on one over time.

05-23-2013, 09:19 PM	#3
ashurbanipal Loyal Site Supporter Join Date: Nov 2008 Location: Lincoln, Nebraska Photos: Gallery \| Albums Posts: 515	Originally posted by Lititz I've got two copies of the Pentax-F SMC 35-70mm f3.5/4.5. I've noticed that their coatings have very different reflections, even when side-by-side under the same light (and regardless of how I hold or move them around). One is cool, tending toward blue, while the other is red/magenta (see attached image). Did SMC coatings vary this way over time (even on the same lens model)? Or did a previous owner over-clean and remove a layer (though I'd be surprised that ta layer could get removed so uniformly by an amateur cleaning). FYI, the "red" lens is about 40,000 later in its serial number, so I assume it is later production. Does anyone have any knowledge about this? Thanks much. Out of curiosity, what are the serial numbers? What kind of lighting was the picture taken under? Mine (serial 1313773) seems to be more like the one on the right, at least under the daylight CFLs I have here.

05-24-2013, 06:16 AM	#4
Lititz Forum Member Join Date: May 2011 Location: greater Philadelphia area Posts: 83 Original Poster	Originally posted by ashurbanipal Out of curiosity, what are the serial numbers? What kind of lighting was the picture taken under? Mine (serial 1313773) seems to be more like the one on the right, at least under the daylight CFLs I have here. The lens on the right (magenta reflection) is #1413582. I gave the other lens (on left) to a family member, so I don't have it in front of me, but the serial number was somewhere in the range of 105xxxx to 115xxxx. The photo was hastily shot under a 100 watt "soft white" incandescent bulb.

05-24-2013, 07:09 PM	#5
ashurbanipal Loyal Site Supporter Join Date: Nov 2008 Location: Lincoln, Nebraska Photos: Gallery \| Albums Posts: 515	Originally posted by Lititz The lens on the right (magenta reflection) is #1413582. I gave the other lens (on left) to a family member, so I don't have it in front of me, but the serial number was somewhere in the range of 105xxxx to 115xxxx. The photo was hastily shot under a 100 watt "soft white" incandescent bulb. Checking under incandescent, mine's definitely more magenta than blue. Hopefully someone will chime in with a definitive answer about the coatings.

05-28-2013, 06:13 PM	#6
Lititz Forum Member Join Date: May 2011 Location: greater Philadelphia area Posts: 83 Original Poster	Originally posted by ashurbanipal Checking under incandescent, mine's definitely more magenta than blue. Hopefully someone will chime in with a definitive answer about the coatings. I looked at a number of photos of this lens for sale/sold on eeekbay, etc. Some show the magenta coloration, some the blue. Of course, there's not much of a clue as to what kind of lighting was used to photograph them.