[LargeFormat] Silica Packs to avoid the Fungus

[Clive Warren]

At 7:38 pm +0000 7/11/01, philip Lambert wrote:
>  Actually I admire your courage: stripping and cleaning lens elements is not
>for the nervous. My 210mm was sent to a professional for dust-removal and he
>wrecked it.  I got the second hand price.  Incidentally is there any way to
>improve a lens with a broad  mark on the rear glass coating? I did hear that
>a mark on the rear coating does not affect the image but I doubt it.  Philip
>

I have stripped down many lenses and as long as you are careful and 
have the right tools (eg appropriate lens spanners) then it is a 
relatively satisfying process unless the fungus has been in the lens 
too long.

Before my last photo trip to the US I stripped down all the lenses 
that had any dust in them and gave 'em a good clean.

Marks on the rear element will have an effect on the final image - 
much more so than any mark on the front element. My favourite story 
about marks is one about a non-technical government chappy inspecting 
a huge lens that the gov. had paid to be ground. He was appalled to 
discover that there were bubbles in the glass and threatened to chop 
the funding. The wise techy peops placed a coin on the lens and asked 
him to inspect the image made by the lens and point out any problems 
caused by the coin - there were of course none visible :-)

Lots of marks on the front element will reduce contrast - a deep 
scratch can be easily dealt with by painting the scratch with matt 
black paint and will not affect the image.

As for the mark on your back element - is it a scratch or a coating problem?

I have had a similar experience to your own with a lens sent in for 
shutter CLA - the soft coating on the front lens element came back 
with a number of small scratches. This had no real effect on image 
but did irritate me......

Cheers,
        Clive