So, I burned a hole through my shutter...

[Xmas]

Magus

You wanna try this on paper first. A Noct is real fast lens, fast to burn f1 is half the time for f/1.4... just like on the exposure guide, unless my physics is wrong again...

Noel

 

[Magus]

Post deleted by posters request

 

[kinoglass]

At F1 the lens is transmitting, lets see, 50mm (focal lenght) divided by the diameter of the front element (50mm for the Noctilux) equals 1. So, fully open the Noctilux, transmitts as much light as it receives. At F8 the focal lenght (50) is divided by 8 and the diameter of the opening of the diaphragm becomes 6.25mm and the light transmitted is then 1/32 of what the lens transmits fully open. The F number system is important because it allows to regulate exposure regardless of the focal lenght of the lens. In other words the light reaching the film plane is the same with a lens of 21mm of focal lenght than with a lens of 500mm FL provided that both lenses are set at the same F stop.

Mind you, you can burn a hole in your shutter curtain with both lenses, just the size of the initial hole will be different and perhaps other components besides the curtain may burn as well. Any one interested in a little experimenting?

So I stand by my previous set of necesary conditions in order to burn a hole in a cloth shutter curtain.

 

[FrankS]

Yep, wide open is more dangerous than stopped down due to there being more light (energy) transmitted. Also if the focus is set closer than infinity, that'll focus perfectly on the curtains which are in front of the film plane.

 

[kinoglass]

XMAS, You're absolutely right. Focusing on the ccurtain itself is the perfect heat concentration to start a fire, never mind a hole. Super wide angle lenses give you a choice of locations where the pin holes can be placed. Actually moving the camera in small angular increments can provide many little holes on a 24x36mm area. The 1000mm lens should burn at least half of the curtain in one single shot and I think we at this forum should recommend it as the preferred lens for "curtain burning"

Curtain material is silk and rubber. Both ingredients were at one time only available in Asia. Germany was cut off from both during the war (ww2) but they had plenty of stock. Then shortly after war the allies took control of industrial production and the worst shutter curtains ever in Leicas were produced: many years later IIIf's do show the "non natural" rubber cracking and dried up of their curtains.

 

[raid]

This thread is making me switch my 7.5mm lens from the M6 with a cloth shutter curtain to the Canon P with a metal curtain. Sorry for your "accident", and thanks for reminding us about such possibilities.


Raid

 

[edodo]

XMAS, You're absolutely right. Focusing on the ccurtain itself is the perfect heat concentration to start a fire, never mind a hole. Super wide angle lenses give you a choice of locations where the pin holes can be placed. Actually moving the camera in small angular increments can provide many little holes on a 24x36mm area. The 1000mm lens should burn at least half of the curtain in one single shot and I think we at this forum should recommend it as the preferred lens for "curtain burning"

Curtain material is silk and rubber. Both ingredients were at one time only available in Asia. Germany was cut off from both during the war (ww2) but they had plenty of stock. Then shortly after war the allies took control of industrial production and the worst shutter curtains ever in Leicas were produced: many years later IIIf's do show the "non natural" rubber cracking and dried up of their curtains.

The rubber on the IIIa is still in good shape, on mine it is even after 70 years.