Identifying a couple of odd filter discs

Marcus Rowland · 10-15-2018, 12:29 PM

I'm trying to sort out a lot of old filters and there are two that have me a bit baffled. They're glass discs without holders, I'd guess intended for 62mm filter mount, and both are very thick and very dark - I put one in front of a camera pointed at a bright light, the meter reading went from 1/320th f5.6 to 1/6th f5.6, e.g. 6 stops (ish). One has a slightly grey/brown tint, the other is blue, both seem to cut down light by roughly the same amount.

Anyone got any idea what they might be for?

Unregistered User · 10-15-2018, 12:51 PM

Lenses for welding goggles?

**Alex645** · 10-15-2018, 01:15 PM

Originally posted by Marcus Rowland

I'm trying to sort out a lot of old filters and there are two that have me a bit baffled. They're glass discs without holders, I'd guess intended for 62mm filter mount, and both are very thick and very dark - I put one in front of a camera pointed at a bright light, the meter reading went from 1/320th f5.6 to 1/6th f5.6, e.g. 6 stops (ish). One has a slightly grey/brown tint, the other is blue, both seem to cut down light by roughly the same amount.

Anyone got any idea what they might be for?

If you posted a photo, it would help. If it wasn't so large, it could be for a rear mount mirror reflex telephoto or for a telescope (moon viewing, not the sun), but at 62mm and without a ring, it's hard to say. For a spot light, they would use gels, as the glass could easily break from heat. Where did this come from?

photoptimist · 10-15-2018, 01:32 PM

Might they be IR-pass (visible-block) and UV-pass (visible-block) filters? Those would be useful for pictures with a camera with a full spectrum conversion.

(P.S. If you are measuring the attenuation of very dark filters, make sure you cover the eyepeice to get an accurate reading.)

Marcus Rowland · 10-15-2018, 02:20 PM

The trouble with taking a photo is that they look pretty much like black disks - I could take a picture through them, I suppose, I'll try it in daylight tomorrow. Maybe the light curve would tell me something.

I wouldn't have thought they were cutting out part of the spectrum completely - if I look at e.g. a computer screen it looks like some light is coming through across the visible spectrum. It's more like one is like an old-style A to D filter and the other D to A, but with a huge reduction in light level.

Marcus Rowland · 10-16-2018, 12:32 PM

Here are some photos:

The two disks together

Holding them up to the light

Effect when used as a filter (no filter, then blue, then greyish-brown)

Unfortunately I forgot to switch off auto ISO setting. Exposures are 1/160th f9 at ISO 100 for the one without a filter, 1/40th f5.6 at ISO 400 for the blue filter, 1/20th f5.6 at ISO 400 for the grey one

If I'm working this out correctly it looks like approximately a 7-8 stop decrease plus colour changes for each of the filters. I'd say the last one looks warmer than unfiltered daylight.

TaoMaas · 10-19-2018, 12:51 PM

Originally posted by Cipher

Lenses for welding goggles?

That was my first thought, too, when I read this the other day. I would think that if they were intended for use in photography, they would have some means of attaching them to a lens. Maybe there's some kind of holder for them that's missing or they're drop-in type filters for some specific lens or telescope.

Marcus Rowland · 10-21-2018, 09:04 AM

OK, if the general consensus is goggles I'll leave it at that, and keep them in case I ever need an extreme ND filter for some reason.

10-15-2018, 12:29 PM	#1
Marcus Rowland Pentaxian Join Date: Dec 2016 Location: London Photos: Gallery Posts: 1,079	Identifying a couple of odd filter discs I'm trying to sort out a lot of old filters and there are two that have me a bit baffled. They're glass discs without holders, I'd guess intended for 62mm filter mount, and both are very thick and very dark - I put one in front of a camera pointed at a bright light, the meter reading went from 1/320th f5.6 to 1/6th f5.6, e.g. 6 stops (ish). One has a slightly grey/brown tint, the other is blue, both seem to cut down light by roughly the same amount. Anyone got any idea what they might be for?

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10-15-2018, 12:51 PM	#2
Unregistered User Guest	Lenses for welding goggles?

10-15-2018, 01:15 PM	#3
Alex645 Site Supporter Join Date: May 2015 Location: Kaneohe, HI Photos: Albums Posts: 3,526	Originally posted by Marcus Rowland I'm trying to sort out a lot of old filters and there are two that have me a bit baffled. They're glass discs without holders, I'd guess intended for 62mm filter mount, and both are very thick and very dark - I put one in front of a camera pointed at a bright light, the meter reading went from 1/320th f5.6 to 1/6th f5.6, e.g. 6 stops (ish). One has a slightly grey/brown tint, the other is blue, both seem to cut down light by roughly the same amount. Anyone got any idea what they might be for? If you posted a photo, it would help. If it wasn't so large, it could be for a rear mount mirror reflex telephoto or for a telescope (moon viewing, not the sun), but at 62mm and without a ring, it's hard to say. For a spot light, they would use gels, as the glass could easily break from heat. Where did this come from?

10-15-2018, 01:32 PM	#4
photoptimist Pentaxian Join Date: Jul 2016 Photos: Albums Posts: 5,127	Might they be IR-pass (visible-block) and UV-pass (visible-block) filters? Those would be useful for pictures with a camera with a full spectrum conversion. (P.S. If you are measuring the attenuation of very dark filters, make sure you cover the eyepeice to get an accurate reading.)

10-15-2018, 02:20 PM	#5
Marcus Rowland Pentaxian Join Date: Dec 2016 Location: London Photos: Gallery Posts: 1,079 Original Poster	The trouble with taking a photo is that they look pretty much like black disks - I could take a picture through them, I suppose, I'll try it in daylight tomorrow. Maybe the light curve would tell me something. I wouldn't have thought they were cutting out part of the spectrum completely - if I look at e.g. a computer screen it looks like some light is coming through across the visible spectrum. It's more like one is like an old-style A to D filter and the other D to A, but with a huge reduction in light level.

10-16-2018, 12:32 PM	#6
Marcus Rowland Pentaxian Join Date: Dec 2016 Location: London Photos: Gallery Posts: 1,079 Original Poster	Here are some photos: The two disks together Holding them up to the light Effect when used as a filter (no filter, then blue, then greyish-brown) Unfortunately I forgot to switch off auto ISO setting. Exposures are 1/160th f9 at ISO 100 for the one without a filter, 1/40th f5.6 at ISO 400 for the blue filter, 1/20th f5.6 at ISO 400 for the grey one If I'm working this out correctly it looks like approximately a 7-8 stop decrease plus colour changes for each of the filters. I'd say the last one looks warmer than unfiltered daylight.

10-19-2018, 12:51 PM	#7
TaoMaas Pentaxian Join Date: May 2007 Location: Oklahoma City Photos: Gallery \| Albums Posts: 3,574	Originally posted by Cipher Lenses for welding goggles? That was my first thought, too, when I read this the other day. I would think that if they were intended for use in photography, they would have some means of attaching them to a lens. Maybe there's some kind of holder for them that's missing or they're drop-in type filters for some specific lens or telescope.

10-21-2018, 09:04 AM	#8
Marcus Rowland Pentaxian Join Date: Dec 2016 Location: London Photos: Gallery Posts: 1,079 Original Poster	OK, if the general consensus is goggles I'll leave it at that, and keep them in case I ever need an extreme ND filter for some reason.