nikon mount not light tight

[geoff tompkinson]

I've been shooting in the field in Italy for the last three weeks using Dougs Nikon mount with a few Nikon manual lenses.

Everything works fine until you try to do some long exposure stuff in bright light.

If shooting at 1fps with a 1 second exposure the results can be completely fogged by light leaking into the sensor chamber from the area of the mount release mechanism.

For this to happen badly the sun needs to be in the right place to strike this part of the lens mount directly. Not difficult on a sunny day.

I have had to resort to using one of those black scrunchy things girls use for their hair. I wrap this around the lens and roll it back over the mount once my aperture selection is made. Works well if a little cumbersome.

Under normal 24fps shooting the effect is not noticeable but I suppose it might still impart some decay to the the contrast of the image.

Obviously the ratio of light levels between the leaked light and the lens transmitted light increases in favour of the leak the longer the exposure times are. This is why the effect is bad at 1sec but barely noticeable at normal exposure times.

I haven't had chance to send Doug and e-mail about this but hopefully he will pick up on this thread.

Geoff

[Damien Molineaux]

Thanks for the heads up. I'll be testing my Red Nikon mount in May, if my camera isn't rented out. I'll be sure to check for this.

Cheers,
Damien

[Sanjin Jukic]

I am planning to use Nikon adapter with the Birger EF on RED and later with the IMS PST.

[jbeale]

Obviously the ratio of light levels between the leaked light and the lens transmitted light increases in favour of the leak the longer the exposure times are.

That's not obvious to me. If you put ND filters in front of the lens and/or close down the aperture, you will change the ratio because you are attenuating only the through-lens light, and leaving the leak untouched. The shutter speed should affect both the same.

Is it true that 1-second exposures are now enabled? Last I heard, you could select down to 1 sec in the menu, but it did not actually take effect.

Build 15 Ops Guide 2.2.5, p. 29 (current as of April 26 2008)
---------------------------------------------------------
The additional exposure time presets are 1, 1/2, 1/3 1/4, 1/6, 1/8, 1/12, 1/16 second. Note: In Build 15 these additional exposure time presets are not operational.

[Douglas Underdahl]

Geoff - send me the mount and I will fix that. It sounds to me like you got one mount that didn't have the final step done to it to make it light tight as is standard. I can turn it around to you the same day, overnight it back to you.

[geoff tompkinson]

Is it true that 1-second exposures are now enabled? Last I heard, you could select down to 1 sec in the menu, but it did not actually take effect.

Build 15 Ops Guide 2.2.5, p. 29 (current as of April 26 2008)
---------------------------------------------------------
The additional exposure time presets are 1, 1/2, 1/3 1/4, 1/6, 1/8, 1/12, 1/16 second. Note: In Build 15 these additional exposure time presets are not operational.

set a project up as 24fps with a 1/24 sec exposure
Set shutter as relative
Go to Varispeed and enable it
Roll the varispeed frame rate down to 1fps

Voila. 1fps with 1sec per frame

[geoff tompkinson]

Geoff - send me the mount and I will fix that. It sounds to me like you got one mount that didn't have the final step done to it to make it light tight as is standard. I can turn it around to you the same day, overnight it back to you.

Okay thanks for that Doug !

[geoff tompkinson]

That's not obvious to me. If you put ND filters in front of the lens and/or close down the aperture, you will change the ratio because you are attenuating only the through-lens light, and leaving the leak untouched. The shutter speed should affect both the same.
.

That sounds about right but its only at longer exposure settings that you are going to ND/close down the light coming through the lens sufficiently for the leak to show up as a problem.

Best way to test if your mount leaks is to set up a 1sec exposure with the body cap in place and shine a powerful torch at the mount in the release trigger area. If it leaks like mine it will illuminate the whole right side of the frame.