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 03/18/2010 06:20:42 PM · #1
Anyone experienced with sunspot photography?

I need advice from an experienced photographer.

What I'd like to know is whether or not it is safe to take a direct photograph of sunspots with an equivalent 24X neutral density filter on a 300mm lens using a digital camera.

The "equivalent 24X neutral density filter" means I have 4 neutral density filters - 10X, 8X, 4X and 2X - stacked. I have no problem looking directly at the sun with the naked eye. Brightness is not an issue.

My concern is ultraviolet or other high energy invisible radiation damaging the lens or sensor.

Can anyone tell me if that is a significant concern? Thanks.


03/18/2010 06:40:27 PM · #2
I once was told by an astronomer than some high-density graphic arts film was dark enough. It had a density reading of about 4 on a logarithmic scale, meaning (I think) that it transmitted 1/10,000 of the incident light. You'll have to do the math with your ND filters to see if you come to that or more (that is, less).

If those "X"s are actual multiplier values, I think you fall short. If they are f-stop values, then you should be OK.

As for UV, if you're stacking all that glass, why not put a standard UV filter in front?
 03/18/2010 06:57:56 PM · #3
Why risk damaging your camera or, worse, your eyesight? Get some of the aluminized mylar film designed for solar observation. Look Here to start.

I'll tell you that unless there's significant solar spot activity, the sun basically looks like a big ping pong ball.

If you're interested in making some dramatic images of flares and other solar activity, you should investigate Hydrogen Alpha filters...then you can see matter being dramatically ejected from the sun...it's really cool.
 03/18/2010 06:59:48 PM · #4
Originally posted by GeneralE:
I once was told by an astronomer than some high-density graphic arts film was dark enough. It had a density reading of about 4 on a logarithmic scale, meaning (I think) that it transmitted 1/10,000 of the incident light. You'll have to do the math with your ND filters to see if you come to that or more (that is, less).

If those "X"s are actual multiplier values, I think you fall short. If they are f-stop values, then you should be OK.

As for UV, if you're stacking all that glass, why not put a standard UV filter in front?


Good points... first off, a ND8 neutral density filter reduces light by 4 (FOUR) f/stops. In total I have 3 ND filters totaling ND14. That reduces light by 7 total f/stops or to about 1/16,383 if I calculated that right. :)

Lastly I have the B&W 1000X filter. I don't really understand what that is supposed to mean, but I do know that it cuts out a lot more light than the other three filters combined.

I forgot to mention I had a standard UV filter on the lens since I have UV filters on all my lenses. I don't often take them off so forget about them. :)

So, based on what you said I'm guessing I might be OK.

I'd like independent confirmation of that, though. :)

Message edited by author 2010-03-18 19:00:37.
 03/18/2010 07:04:57 PM · #5
Originally posted by Bader website:
... in optical density 2.5! Baader AstroSolarĂ¢„¢ safety film has been approved for eye safety by the National Bureau of Standards in Germany, the PTB.

So my 4.0 density film may even be overkill ...
 03/18/2010 07:06:25 PM · #6
Originally posted by Spork99:
Why risk damaging your camera or, worse, your eyesight? Get some of the aluminized mylar film designed for solar observation. Look Here to start.

I'll tell you that unless there's significant solar spot activity, the sun basically looks like a big ping pong ball.

If you're interested in making some dramatic images of flares and other solar activity, you should investigate Hydrogen Alpha filters...then you can see matter being dramatically ejected from the sun...it's really cool.

I thought about mylar. I've used that before for solar photography just before totality during solar eclipses. But that was with a film camera and I just don't happen to have any of it handy. I figure if my ND filters will work then there is no need to scout out mylar. ;)

Though we were at an extended solar minimum with hardly any sunspots at all for the last few years that time is now over. Sunspots are returning with a vengeance... hence, my interest. :)

Message edited by author 2010-03-18 19:07:01.
 03/18/2010 07:09:27 PM · #7
Originally posted by GeneralE:
Originally posted by Bader website:
... in optical density 2.5! Baader AstroSolarĂ¢„¢ safety film has been approved for eye safety by the National Bureau of Standards in Germany, the PTB.

So my 4.0 density film may even be overkill ...

Hmmmmmm... perhaps that explains the unusually high incidence of German blindness. ;) ;)

Just kidding... sorry, I could not f/stop myself from saying it. LOL!!!
03/18/2010 07:09:29 PM · #8
Originally posted by Artifacts:
Good points... first off, a ND8 neutral density filter reduces light by 4 (FOUR) f/stops. In total I have 3 ND filters totaling ND14. That reduces light by 7 total f/stops or to about 1/16,383 if I calculated that right. :)

Not if you've described them right. I thought each f-stop is halving/doubling the exposure, so 2 to the 7th is only 1/128. Your 1/16,384 is 2 to the 14th.
 03/18/2010 07:11:17 PM · #9
I think I have a bunch around here. I'll look if you want and I can send you some in the mail. Just PM me.
 03/18/2010 07:21:31 PM · #10
Originally posted by GeneralE:
Originally posted by Artifacts:
Good points... first off, a ND8 neutral density filter reduces light by 4 (FOUR) f/stops. In total I have 3 ND filters totaling ND14. That reduces light by 7 total f/stops or to about 1/16,383 if I calculated that right. :)

Not if you've described them right. I thought each f-stop is halving/doubling the exposure, so 2 to the 7th is only 1/128. Your 1/16,384 is 2 to the 14th.

You are right, now given that I have a total of ND24 reduction then it should reduce light by 12 f/stops or 1/2 to the 12th power or by 1/4,096.

According to what you said earlier I'm under half what I need. Hmmmmmm...
03/18/2010 07:42:04 PM · #11
Seems like I should be able to stop down my telephoto an f/stop or 2 to get where I need to go.

What do you folks think?
 03/18/2010 09:00:38 PM · #12
That will help protect the sensor, but what about the person looking through the camera. Unless you hold the DOF preview button or have a lens that's not controlled by the camera, you don't look through the lens when it's stopped down.
 03/18/2010 09:10:52 PM · #13
Originally posted by Artifacts:
Seems like I should be able to stop down my telephoto an f/stop or 2 to get where I need to go.

What do you folks think?


You will be fine with the with the 1000x filter. I have the exact same filter. The solar filter I have for my telescope is 10,000x, so 1/10 the transmittance of the 1000x, but the aperture of that telescope is 8 inches (200mm), so the light collecting power is about 7x greater.

Edit to add:
Solar cycle 24 is just getting underway, and is promising to be a rather mild one. The best sunspot activity will come in a year or two.

Message edited by author 2010-03-18 21:12:09.
 03/19/2010 12:01:30 PM · #14
Originally posted by kirbic:
[quote=Artifacts]
Edit to add:
Solar cycle 24 is just getting underway, and is promising to be a rather mild one. The best sunspot activity will come in a year or two.

A Sunspot Aside:
NASA's next prediction will give a clearer picture. Their last prediction was April, 2009.

Almost every sunspot cycle begins with a very sharp spike of growth in sunspot numbers. This one is shaping up to mimic past behavior. Should that happen this next year should be pretty exciting.

In May, 2009 in the middle of the extended minimum I conducted my own less-than-rigorous analysis of the previous 23 sunspot cycles to make my own prediction for cycle 24 based on past behavior rather than physics. I predicted the peak would occur in 2013 and that the peak would reach a comparatively high sunspot number of 130. So far this year I've seen short term sunspot numbers as high as 41 at Spaceweather.com.

The cycle has begun, but how high it will go is unknown.

I recently read an article published in a credible science journal analyzing the measured Gaussian strength of sunspot magnetic fields over the last 15 years. It shows a very striking linear decline. Why that is happening is unknown. But if continued Sunspot Gaussian strength will decrease to ZERO in 2015 and sunspots will completely disappear again.

What that means for us in the here and now is that Cycle 24 would have a very small peak and that sunspots would go away indefinitely after that. We could go into another extended period of sunspot inactivity such as occurred in the 1600s and early 1700s. That period is called the Maunder Minimum.

I'm still holding out that my prediction is right, but I say photograph sunspots now as soon as you can while they are still here! LOL!!!
 03/19/2010 12:39:24 PM · #15
Interestingly, old 3.25" diskettes work really, really good...

The inner material was simply PERFECT to stop almost all of the light coming from the sun, and by their very nature, they are exceedingly consistent in thickness.
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