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Author Topic: Alternate uses uses for solar eclipse filters  (Read 14371 times)

jabbott

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Re: Alternate uses uses for solar eclipse filters
« Reply #15 on: May 09, 2012, 10:45:37 AM »
THIS IS A RECIPE FOR DISASTER.

If you're exposing either your eyes or your camera to dangerous sunlight such that you need protection in the first place, photographic filters of any kind and in any combination will NOT provide said protection.
Here is a description of the B+W Neutral Density Filter 113, which has an optical density of ND4.0:

With its light reducing capability of 13 f-stops, this B+W Neutral Density Filter is used in astronomy for photographs of the sun and for recording the relative movements of heavenly bodies as light traces in extremely long exposure times. For photographs of the sun, this filter must be positioned in front of the lens and under no circumstances should it be located near the primary focus in front of, or behind the eyepiece because of the intense heat at those locations. It must not be used for observation of the sun (danger of blindness) due to its greater transmission in the infrared range. The filter factor is 10000x.

The optical density I've used is ND3.9, which is ~8000x light reduction.  ND4 is 10000x.  Because of this difference I only use a highly stopped down aperture and a fast shutter speed when photographing the sun.  My camera appears completely fine after doing this, as do my lenses.  My eyes were protected because I exclusively used Live View for framing, focus and the shot.  While I would agree that lower optical densities would certainly cause damage, in my own experience ND3.9 or greater optical density provides sufficient protection for very short framing/focus time and exposures.  The biggest danger in my opinion is that Live View continuously exposes the sensor to the sun, so the time spent framing and focusing must be minimized.

Quote from: TrumpetPower!
If the camera or your eyes are going to be pointed at the sun for more than a second more than once or twice, you need some sort of real protection. For your eyes, that means welding glass or eclipse glasses or the like. For your camera most especially if you yourself will be looking through the viewfinder that means either comparable protection or covering the front element (with the lens cap, etc.) when you're not actively making an exposure.
I already said in an earlier post that it would be unsafe to look through a viewfinder at ND3.9, and this echoes Drizzt321's comments.  Only use Live View instead.  I agree that minimizing framing/focus time is important, as well as using eclipse glasses if you are actually going to look at the sun at all.  Also essential is to use manual focus because the camera can't do phase correlation auto focus with black glass in front.  Here is what happens when you point a 600mm lens at the sun without adequate protection (see the section titled "Don't Try This at Home"): http://www.the-digital-picture.com/Help/Flare.aspx
« Last Edit: May 09, 2012, 11:50:02 AM by jabbott »

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Re: Alternate uses uses for solar eclipse filters
« Reply #15 on: May 09, 2012, 10:45:37 AM »

Drizzt321

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Re: Alternate uses uses for solar eclipse filters
« Reply #16 on: May 09, 2012, 12:21:44 PM »
THIS IS A RECIPE FOR DISASTER.

If you're exposing either your eyes or your camera to dangerous sunlight such that you need protection in the first place, photographic filters of any kind and in any combination will NOT provide said protection.
Here is a description of the B+W Neutral Density Filter 113, which has an optical density of ND4.0:

With its light reducing capability of 13 f-stops, this B+W Neutral Density Filter is used in astronomy for photographs of the sun and for recording the relative movements of heavenly bodies as light traces in extremely long exposure times. For photographs of the sun, this filter must be positioned in front of the lens and under no circumstances should it be located near the primary focus in front of, or behind the eyepiece because of the intense heat at those locations. It must not be used for observation of the sun (danger of blindness) due to its greater transmission in the infrared range. The filter factor is 10000x.

The optical density I've used is ND3.9, which is ~8000x light reduction.  ND4 is 10000x.  Because of this difference I only use a highly stopped down aperture and a fast shutter speed when photographing the sun.  My camera appears completely fine after doing this, as do my lenses.  My eyes were protected because I exclusively used Live View for framing, focus and the shot.  While I would agree that lower optical densities would certainly cause damage, in my own experience ND3.9 or greater optical density provides sufficient protection for very short framing/focus time and exposures.  The biggest danger in my opinion is that Live View continuously exposes the sensor to the sun, so the time spent framing and focusing must be minimized.

Quote from: TrumpetPower!
If the camera or your eyes are going to be pointed at the sun for more than a second more than once or twice, you need some sort of real protection. For your eyes, that means welding glass or eclipse glasses or the like. For your camera most especially if you yourself will be looking through the viewfinder that means either comparable protection or covering the front element (with the lens cap, etc.) when you're not actively making an exposure.
I already said in an earlier post that it would be unsafe to look through a viewfinder at ND3.9, and this echoes Drizzt321's comments.  Only use Live View instead.  I agree that minimizing framing/focus time is important, as well as using eclipse glasses if you are actually going to look at the sun at all.  Also essential is to use manual focus because the camera can't do phase correlation auto focus with black glass in front.  Here is what happens when you point a 600mm lens at the sun without adequate protection (see the section titled "Don't Try This at Home"): http://www.the-digital-picture.com/Help/Flare.aspx

The other issue with standard ND filters (even the B+W one) is that it still passes a lot of IR through, which can easily damage your eye. Only the special Solar filters that are rated to filter out enough IR/UV will be safe to use visually. Even if you stack standard ND filters up to 20+ f-stops light reduction, it's still not safe to with your eyes because of the IR transmission. As someone said earlier, the sensor usually has an IR filter over it (unless it's been converted for IR photography), and so the sensor will generally be fine unless exposed for extended periods of time such as being left in LiveView for the entire time, or for extremely long exposures.
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squarebox

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Re: Alternate uses uses for solar eclipse filters
« Reply #17 on: May 11, 2012, 02:17:17 AM »
For what it's worth, I'll be using a ND5 filter rates at 100,000x.  It is specifically for use during the eclipse and on the back of it is all kinda of warnings not to use it it with anything else besides liveview because it doesn't filter out IR. 
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PeterJ

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Re: Alternate uses uses for solar eclipse filters
« Reply #18 on: May 12, 2012, 03:51:39 AM »
For what it's worth, I'll be using a ND5 filter rates at 100,000x.  It is specifically for use during the eclipse and on the back of it is all kinda of warnings not to use it it with anything else besides liveview because it doesn't filter out IR.
The one I bought was rated for IR blocking / viewfinder use but originally I intended to use liveview regardless. One blindingly obvious thing I overlooked (if you'll excuse the pun) is that I was standing in direct sunlight while trying to frame / focus initially and reflections made the LCD just about impossible to see, so given the above I ended up using the viewfinder.

Anyway given it's a rare event just in case you hadn't thought about that it's worth having a dark cloth sheet or something on hand just to make sure you can see the LCD properly. I normally only use liveview for indoor or low-light tripod shots so hadn't given that much thought.

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Re: Alternate uses uses for solar eclipse filters
« Reply #18 on: May 12, 2012, 03:51:39 AM »