Dust BEHIND front element, how? at DVinfo.net

James Emory · December 7th, 2004, 12:11 AM

I saw some dust particles on a PD-150 lens and then noticed that they weren't blowing away with air. Upon further inspection, I realized that they were behind the glass of the front element. Now, how did that happen? These are rentals so there's no telling where all they have been and what all they've been exposed to.

Mike Rehmus · December 7th, 2004, 12:25 AM

A lens is not a closed system. Lots of openings for dust to enter. Especially if someone uses air to blow off the lens instead of a vacuum.

James Emory · December 7th, 2004, 12:38 AM

Thanks for the reply Mike. Now, that makes sense but I have never seen an AC cleaning lenses with a vacuum, only a soft cloth or canned air. Air is sometimes absolutely necessary for larger particle removal before wiping with a cloth.

Mike Rehmus · December 7th, 2004, 01:59 AM

That is the front surface and those tend to be fairly well sealed. The sides of the cheaper lens systems, and I place the Sony firmly in that camp are not so well sealed. The front element on the Sony may not even be a 'real' lens element but only a dust shield anyway.

Several people have removed the front element to clean it and may be able to better comment on its optical contribution to the lens, if any.

Tom Hardwick · December 7th, 2004, 09:06 AM

The front element of the PD150 is a plain, parallel sided piece of glass James, as so too is the second element in line. They form the outer limits of the vari-angle prism and contain and mould the wedge of fluid between them. This OIS VAP is simply placed in front of the zoom's true front element and you're probably seeing a foreign body on that surface. I'd not expect that it was too difficult to remove the VAP asembly, though like Mike says, there's lots of openings for dust to enter simply to allow the zoom's 5 moving elements room to zip about in there.

tom.

James Emory · December 7th, 2004, 09:37 AM

Thanks for the info. As far as disassembly, that's too invasive for me to do and is better left for the techs at the rental house.

Trying to remove the dust behind that element is like having your keys locked in your car in plain view but not being able to do a damn thing about it.

December 7th, 2004, 12:11 AM	#1
James Emory Regular Crew Join Date: Aug 2002 Location: Atlanta, Georgia Posts: 1,892	Dust BEHIND front element, how? I saw some dust particles on a PD-150 lens and then noticed that they weren't blowing away with air. Upon further inspection, I realized that they were behind the glass of the front element. Now, how did that happen? These are rentals so there's no telling where all they have been and what all they've been exposed to.

December 7th, 2004, 12:25 AM	#2
Mike Rehmus Wrangler Join Date: May 2002 Location: Vallejo, California Posts: 4,049	A lens is not a closed system. Lots of openings for dust to enter. Especially if someone uses air to blow off the lens instead of a vacuum. __________________ Mike Rehmus Hey, I can see the carrot at the end of the tunnel!

December 7th, 2004, 01:59 AM	#4
Mike Rehmus Wrangler Join Date: May 2002 Location: Vallejo, California Posts: 4,049	That is the front surface and those tend to be fairly well sealed. The sides of the cheaper lens systems, and I place the Sony firmly in that camp are not so well sealed. The front element on the Sony may not even be a 'real' lens element but only a dust shield anyway. Several people have removed the front element to clean it and may be able to better comment on its optical contribution to the lens, if any. __________________ Mike Rehmus Hey, I can see the carrot at the end of the tunnel!

December 7th, 2004, 12:38 AM	#3
James Emory Regular Crew Join Date: Aug 2002 Location: Atlanta, Georgia Posts: 1,892	Thanks for the reply Mike. Now, that makes sense but I have never seen an AC cleaning lenses with a vacuum, only a soft cloth or canned air. Air is sometimes absolutely necessary for larger particle removal before wiping with a cloth.

December 7th, 2004, 09:06 AM	#5
Tom Hardwick Inner Circle Join Date: Mar 2003 Location: Billericay, England UK Posts: 4,711	The front element of the PD150 is a plain, parallel sided piece of glass James, as so too is the second element in line. They form the outer limits of the vari-angle prism and contain and mould the wedge of fluid between them. This OIS VAP is simply placed in front of the zoom's true front element and you're probably seeing a foreign body on that surface. I'd not expect that it was too difficult to remove the VAP asembly, though like Mike says, there's lots of openings for dust to enter simply to allow the zoom's 5 moving elements room to zip about in there. tom.

December 7th, 2004, 09:37 AM	#6
James Emory Regular Crew Join Date: Aug 2002 Location: Atlanta, Georgia Posts: 1,892	Thanks for the info. As far as disassembly, that's too invasive for me to do and is better left for the techs at the rental house. Trying to remove the dust behind that element is like having your keys locked in your car in plain view but not being able to do a damn thing about it.