Pherdinand
the snow must go on
merciful said:
) yes we realize that this represents no problem for you, the Tri-X Pusher.
The problem is also worse with wide-angle lenses. They are more likely to pick up the sun in their field of view and they will focus it into a smaller dot. I used the 5cm F1.4 Nikkor as a "magnifyng glass" yesterday to see what I could burn. The image of the sun was fairly broad and I could not burn through a leaf within a reasonable amount of time; it was late in the day and the leaf became "scarred". I suspect that my 28mm F2 Nikkor would burn through it readily. Should be 1/2 the light (F2) focussed into 1/4 the spot.
Pherdinand
the snow must go on
As kids we played alot with lenses and trying to burn holes on different stuff. It depends alot on the material you use as screen. A white sheet of paper is almost impossible to burn with a lens; as soon as you draw a coloured line on it with a pen, it can burst into flames in a second. Wood is also a very good absorber unless it's very light coloured+polished or not dry enough. Never tryed with black shutter curtains but i'm sure i could get some smoke at least.
Biber
Established
I tried to burn a piece of paper with my 50/1.5 at different apertures, focused at infinity. At f/1.5 it burned through the paper in 10s, at f/16 didn't leave a mark even after 3 minutes in the sun. I didn't try any longer times or close focus since it was hard to keep it steady (hand held), but it does support the claim that stopping down makes it harder for the sun to damage the shutter.
Roger Hicks
Veteran
I tried this with black card and a Summilux 35/1.4. What follows is is from memory, and under English sun -- mauybe subtract a stop for India or even Arles. It may also be that shutter material burns easier than black card but I doubt it.
At small apertures -- f/8 and below -- you NEVER burn the card because the sun moves too fast. This is with the lens and card locked in lab clamps (Climpex).
At f/1.4 it still takes several seconds. Carrying the camera around your neck will jiggle it enough so you don't have to worry. Likewise driving on almost any normal; road.
No, it won't burn faster at smaller apertures because the speed of burn is a function of the amount of energy passing through the lens and focusing on the shutter. At f/8 this is 1/32 the energy admitted at f/1.4.
When I stop at an outdoor cafe, etc. I take good care to point the lens away from the sun; I may stop down to 16 too, but I usually don't. In about 35 years of using Leicas I have yet to burn a hole in the shutter. Of course this means I'll probably do it tomorrow but I haven't yet.
Cheers,
Roger (www.rogerandfrances.com)
At small apertures -- f/8 and below -- you NEVER burn the card because the sun moves too fast. This is with the lens and card locked in lab clamps (Climpex).
At f/1.4 it still takes several seconds. Carrying the camera around your neck will jiggle it enough so you don't have to worry. Likewise driving on almost any normal; road.
No, it won't burn faster at smaller apertures because the speed of burn is a function of the amount of energy passing through the lens and focusing on the shutter. At f/8 this is 1/32 the energy admitted at f/1.4.
When I stop at an outdoor cafe, etc. I take good care to point the lens away from the sun; I may stop down to 16 too, but I usually don't. In about 35 years of using Leicas I have yet to burn a hole in the shutter. Of course this means I'll probably do it tomorrow but I haven't yet.
Cheers,
Roger (www.rogerandfrances.com)
laptoprob
back to basics
I will try an experiment on the remains of a FED2 I have lying around fully ruined. It used to eat film. tear through the holes and stop transporting. Terrible.
On a next sunny day I will positon the camera in the sun and aim my collapsible elmar 4/90 wide open at infinity into the sun. That is about a worst case scenario.
Depending on the result I can try my summicron.
The screwmount is already off the FED body so I should be able to tape or mount the M lenses on it.
Anyone ever seen the TV programme Mythbusters?
To be continued...
Rob.
On a next sunny day I will positon the camera in the sun and aim my collapsible elmar 4/90 wide open at infinity into the sun. That is about a worst case scenario.
Depending on the result I can try my summicron.
The screwmount is already off the FED body so I should be able to tape or mount the M lenses on it.
Anyone ever seen the TV programme Mythbusters?
To be continued...
Rob.