10 Stop ND filter for Venus Transit? School me.

[bloodhound31]

I've had a lot of people asking me if it is safe to use a 10 Stop ND filter on their lens for eclipse and transit photography.

I don't know anything about such filter but I am guessing it would not be sufficient?

What's the story? Can anyone educate me?

Baz.

P.S. Let's see how the knowledge base on this forum fares against the same question on other fora. Clock's tickin'.....

[Octane (Humayun)]

Only if they have a decent implemetation of Live View.

ND filters don't block UV/IR light.

H

[bloodhound31]

Originally Posted by Octane

Only if they have a decent implemetation of Live View.

ND filters don't block UV/IR light.

H

YAY!!! IIS wins!

Can you elaborate H?

Baz.

[naskies (Dave)]

An OD5/99.999% solar filter used for visual observing (e.g. the Baader solar film) is like a ~16 stop filter, and an OD3.8 filter is about ~12.5 stops.

Furthermore, if you look at the transmittance charts for most photographic ND filters you'll see that they typically allow a very high amount of UV and IR light to pass through. The OD5 solar filters block virtually all UV and IR light.

It's not a problem photographically since digital cameras have a UV/IR filter over the sensor, but unfortunately it's the kind of light that burns your eyeballs (without you knowing it)...

[bloodhound31]

Originally Posted by naskies

An OD5/99.999% solar filter used for visual observing (e.g. the Baader solar film) is like a ~16 stop filter, and an OD3.8 filter is about ~12.5 stops.

Furthermore, if you look at the transmittance charts for most photographic ND filters you'll see that they typically allow a very high amount of UV and IR light to pass through. The OD5 solar filters block virtually all UV and IR light.

It's not a problem photographically since digital cameras have a UV/IR filter over the sensor, but unfortunately it's the kind of light that burns your eyeballs (without you knowing it)...

So live view would protect your eyes, but is the sensor safe? What about heat inside the lens? Does a 10 stop ND protect from that?

[gregbradley]

I have a variable ND filter. Plus you can make your own out of 2 circular polarisers. Spin one around agains the other and they get very very dark.

I left my purchase of solar film too late so if the sky is clear (by no means sure) I intend using the variable ND plus a Ha filter on my DSLR.

I can't even experiment due to the wet weather.

Hopefully it works!

Greg.

[Octane (Humayun)]

The sensor has a UV/IR filter on it.

H

[naskies (Dave)]

Originally Posted by bloodhound31

So live view would protect your eyes, but is the sensor safe? What about heat inside the lens? Does a 10 stop ND protect from that?

They would probably want to tape over the view finder, though, to prevent accidental exposure to the eyes.

I have no idea about the sensor... but if it were me, I probably wouldn't be exposing the sensor to 6 hours of sunlight in LiveView mode.

It's up to them, I guess?

[gregbradley]

You'd want to make sure. Pehaps put your finger at the focus point and see if it is hot. Like checking the hot water in a bath first.

Greg.

[bloodhound31]

It all sounds very risky.

[Poita (Peter)]

Originally Posted by gregbradley

I have a variable ND filter. Plus you can make your own out of 2 circular polarisers. Spin one around agains the other and they get very very dark.

I left my purchase of solar film too late so if the sky is clear (by no means sure) I intend using the variable ND plus a Ha filter on my DSLR.

I can't even experiment due to the wet weather.

Hopefully it works!

Greg.

I wouldn't greg, let me know your address and I'll send you a piece of solar film, it will get there by tomorrow and save your gear from harm

[von Tom (Tom)]

If the ND filter lets through IR and UV, and even if the sensor is protected from IR somehow, what would happen to the temperature of the glass of the lens, and the temperature of the air between the lens and the sensor?

[Octane (Humayun)]

Greg,

The two polariser twisty thing is so dodgy! Why would you want to do that even in normal terrestrial photography? In front of all the elements/groups in your lenses, you're introducing two more layers of glass that the lens designers never fathomed you'd use. Every time we use a polariser or a screw on filter of some kind, we're deteriorating the quality of the lens. Spend big and buy yourself a proper neutral density system!

H

[iceman (Mike)]

I wouldn't be using any ND to point directly at the Sun. Just sounds too risky, the chance of someone putting their eye up to the eyepiece

[traveller (Bo)]

For my $0.02's worth, it would be dedicated solar filter or solar film (Baader) or nothing.
Two NDs don't make it right.
Bo

[rally]

Greg,

What is the spectral response curve of your particular film ?
Ask your supplier for a copy.

Most polarising film is rated between 400-700nm and they often dont even show the spectral response beyond say 850nm
You are looking for the crossed response above 900nm right into the infrared

Most curves start increasing (logarithmically !) above 700nm making me think that at above 950-1600nm ++ you might have a real problem ?

I dont know for sure, (I haven't seen your spectral transmittance curves) but even at 10-20% transmittance you might be likely to damage your CCD after some time, depending on the aperture in use.

It might work, it might not, I really dont know, if you do proceed, maybe consider just using a CCD you can afford to throw away and dont risk your eyes !

Rally

[mplanet62 (Michael)]

No camera sensor is completely immune to IR and UV. I can shoot pictures in IR with my non-modified camera and black IR filter. ND10 is a sure-fire way to destroy the camera if pointed to the sun for long. Two polarisers even more so. To avoid cooking the sensor you need something that blocks out IR and UV almost completely. Like solar filter or solar film. Or, as worst case scenario, shade14 welders glass. Make sure to use live view only, and put a cap over the visual finder. Even with that, very long focus , well-stopped (manually) lens would be better than anything else. And I don't take any responsibility (leave alone blame) for the results of this idea...

[bloodhound31]

Originally Posted by iceman

I wouldn't be using any ND to point directly at the Sun. Just sounds too risky, the chance of someone putting their eye up to the eyepiece

I think I'll go along with this Mike. ^^^^