BolexSBM - Single Frame Sutter Speed

[Guest Brian Danin]

Hello,

 

So I have an issue with the Bolex SBM single frame (in I instentaneous mode). After reading the manual, nowhere does it actually say the shutter speed.

 

I was wondering if anyone had any information on this topic?

 

I was going to assume that it would be the same shutter-speed as the 24 FPS (which is about 1/60 second).

 

Thanks for your help.

 

-Brian

[Leo Anthony Vale]

I was going to assume that it would be the same shutter-speed as the 24 FPS (which is about 1/60 second).

 

Sorry, while I don't know the single frame shutter/prism speed offhand, don't assume it is the same as 24fps.

on the RXs it's the same as 8 or 12 fps. One would always see animation students doing which mixed single frame with 24 fps bursts. Yes, there was a very noticable exposure shift. Yet they never seemed to catch on.

 

---LV

[Clive Tobin]

So I have an issue with the Bolex SBM single frame (in I instentaneous mode). After reading the manual, nowhere does it actually say the shutter speed....

 

As the other reply states, the exposure time is longer since the shutter doesn't have time to fully get up to speed. So it is something like 1/30 or 1/40 second depending on how tightly the spring is wound, etc.

 

Also I assume you realize that at 24 FPS you have what Bolex calls the "adapted" shutter speed, taking into effect the prism loss to the finder, equal to 1/80 second.

[Guest Brian Danin]

As the other reply states, the exposure time is longer since the shutter doesn't have time to fully get up to speed. So it is something like 1/30 or 1/40 second depending on how tightly the spring is wound, etc.

 

Also I assume you realize that at 24 FPS you have what Bolex calls the "adapted" shutter speed, taking into effect the prism loss to the finder, equal to 1/80 second.

 

Great, thanks for the advice. When I was looking at the single frame shutter, it did look like it was going slower than when it's at 24fps. I think I'll just expose as if it were 1/30. I'm doing time lapse of a sunset anyways, so I'm going to have a hard time getting an accurate exposure metered. I want everything to be pretty hot (the sun about 5 or so stops over) when I start with the sun high in the sky; then only about 2 stops over right as the sun hits the horizon; and then for the sky to fall to about 1 stop under before I stop shooting: without changing my aperture. It'll be a fun endevour regardless.

 

I see, since the shutter is actually moving at 1/65 of a second and 25% of the light is reflected to the prism, it rates at 1/80 at 24 FPS.

[Sam Wells]

My experience with springwound Bolex - Rex 4,5 SBM etc - is that single frame "I" is ~ 1/32 so half the 1/65 exposure you'd get @ 24. These are actual not "adapted" speeds.

 

IOW same as shooting 12 fps.

 

I usually set the governor up near the top - 48 - 64 - so you're not "fighting" it when doing single frame.

 

(Just remember you did this when if you go back to 'normal' shooting on the same roll :o )

 

-Sam

[Boris Belay]

Hi, Just checked my SBM Manual and in my version (there are several) the single-frame shooting speed is indicated in the same table as the other shooting speeds (p. 13). Actual speed is 1/30th of a sec., corrected speed (which you should use with a regular lightmeter) is 1/40th of a second (with shutter fully opened).

I too would wind the spring up before it runs out... although in frame-by-frame mode, with about 650 frames on a full wind, it still means a lot of time between rewinds !

-B