Using a 120 magazine back dark slide as a shutter

[Laci Toth]

Hello all,

I’m planning to use a film back on an obscura and am wondering what are your thoughts about this.
If I use the dark slide as the shutter how will it affect the outcome? Probably because of the long exposure I won’t see difference on the negative not like when using fast shutter speed and the curtain closes slower than it should because of an error and then exposure issues can be seen on the negative.

 

[khh]

The bottom of the negative will be exposed more than the top. With a shutter the average exposure is the same across the frame, but with the slide your bottom is the part that gets exposed both first and last. Whether it matters depends on how large the difference is. I would calculate the difference in stops and see if it's acceptable for your application. My gut says anything with an exposure time above 30s is fine.

 

[tokam]

You may also be inducing camera shake as you try to remove and then insert the dark slide to complete the exposure.

How about using a dark cloth or a hand held hat over the lens to control exposure without shaking the camera. I.e. put hat over lens, remove dark slide, remove hat from lens and time your exposure, replace hat over lens and insert the dark slide. As long as you cover and uncover the lens quickly you should get fairly even exposure over the frame. (More reliable that a possibly sticky dark slide which was never intended to function as a shutter.)

 

[Laci Toth]

You may also be inducing camera shake as you try to remove and then insert the dark slide to complete the exposure.

How about using a dark cloth or a hand held hat over the lens to control exposure without shaking the camera. I.e. put hat over lens, remove dark slide, remove hat from lens and time your exposure, replace hat over lens and insert the dark slide. As long as you cover and uncover the lens quickly you should get fairly even exposure over the frame. (More reliable that a possibly sticky dark slide which was never intended to function as a shutter.)

Yes! That’s the solution I was looking for! Thanks for the suggestion!

 

[Laci Toth]

The bottom of the negative will be exposed more than the top. With a shutter the average exposure is the same across the frame, but with the slide your bottom is the part that gets exposed both first and last. Whether it matters depends on how large the difference is. I would calculate the difference in stops and see if it's acceptable for your application. My gut says anything with an exposure time above 30s is fine.

I’m about to make extra long exposures with a 10+ stop nd filter. As it was suggested by Tokam I’ll use a black hat and the slide to avoid camera shake and uneven exposure.

 

[Kino]

You could also just use a tight fitting lens cap like the old timers did on large format cameras...

 

[Laci Toth]

You could also just use a tight fitting lens cap like the old timers did on large format cameras...

I just found a push on cap at home which fits on the lens.

 

[Kino]

I just found a push on cap at home which fits on the lens.

Welcome to the 19th Century! Should work fine...

 

[narsuitus]

I carry a 12x12cm black foam board in my large format case and my medium format case to use as an emergency shutter when an unwanted vehicle with headlights enters the picture or when the mechanical shutter fails due to cold weather.

For my pinhole cameras, even if the camera has a mechanical shutter, I use a piece of black tape as a shutter.



120 Pinhole Cameras by Narsuitus, on Flickr

 

[Laci Toth]

an emergency shutter when an unwanted vehicle with headlights enters the picture or when the mechanical shutter fails due to cold weather

Great idea! Thanks!

 

[cliveh]

Hello all,

I’m planning to use a film back on an obscura and am wondering what are your thoughts about this.
If I use the dark slide as the shutter how will it affect the outcome? Probably because of the long exposure I won’t see difference on the negative not like when using fast shutter speed and the curtain closes slower than it should because of an error and then exposure issues can be seen on the negative.

As you don't mention how long your exposure is likely to be, it is impossible to give advice.

 

[Digger Odell]

Be Aware that rapid removal of the dark slide has been blamed for static electricity discharges, resulting in unwanted light damage to the film. Lightning like streaks I assume.

 

[Laci Toth]

As you don't mention how long your exposure is likely to be, it is impossible to give advice.

There’s the word ‘obscura’ in the first sentence and ‘long exposure’ two sentences later.
I also mentioned a 10+ stop nd filter.
But others already answered the impossible; a black hat or a push on lens cap then the slide.

 

[mshchem]

I’m about to make extra long exposures with a 10+ stop nd filter. As it was suggested by Tokam I’ll use a black hat and the slide to avoid camera shake and uneven exposure.

Reciprocity. You get over 10-20 seconds you will need to double check the film datasheet.

 

[Laci Toth]

Be Aware that rapid removal of the dark slide has been blamed for static electricity discharges, resulting in unwanted light damage to the film. Lightning like streaks I assume.

Okay, thanks for raising my awareness of this I wouldn’t thought about this. As this push on lens cap method seems a solution I don’t have to pull out the slide that fast.

 

[Laci Toth]

Reciprocity. You get over 10-20 seconds you will need to double check the film datasheet.

Yes, that’s fine. I make long exposures with 35mm format anyway.

 

[europanorama]

if possible get cosmos circle 18° Eighteen degrees shutter. it has B and multiples of 1/6 are possible. i measure using all kind of cable releases. pneumatic and standard. the same exposure time also on grundner shutter. M22-thread pinhole plates available. rafcamera made adapters for using them also on copal 0 and 1. soldering bras-filter-adapter to the 18° shutter is about to be made by me. will show later elsewhere.

 

[macfred]

I always liked this one ...

 

[Laci Toth]

I always liked this one ...

Thanks, that’s my idea also. I just need to find out the exact distance from the lens to the film.