NOTE: This article was originally published on April 9, 2012.
As it is now May 18, 2012 it is almost It is now just hours before the Transit of Venus beginning at 3:02 PM PDT, June 5, 2012. If you’re just now trying to get a solar filter chances are extremely thin of doing so. Try a telescope store if there is one near you. Trust me, most of them are sold out. PLEASE DO NOT attempt to photograph or observe the sun if you are not properly prepared. PERMANENT BLINDNESS or DAMAGE TO EQUIPMENT may result.
I have been asked a lot about solar filters and why I was strongly encouraging people to get them. First let me explain how you might use them, then I’ll talk about the different kinds of solar filters and their costs.
Here are several shots of the sun rising behind Lick Observatory on Mount Hamilton, San Jose, CA. All shots are without any filter.
The upper exposures are pretty conventional. The exposures at the bottom, however, are clearly MUCH shorter and exhibit excessive flaring mostly due to IR light. Indeed, here are the settings from upper left to lower right:
- ISO 200, f/11, 1/80
- ISO 200, f/11, 1/640
- ISO 200, f/11, 1/8000
- ISO 100, f/36, 1/2000
What is probably immediately obvious is the glare / flare and color fringing. Compare the above shots to this one:
This is NOT a single shot, it’s a blend of two shots. The thing to notice is how much better tamed the violently bright sun is. Another important consideration is that a solar filter provides a boatload of protection to both the eyes and the camera equipment more on that in a moment. The bottom line is that the flare is well controlled and the sun exposure is sufficient that if there were a large sunspot on it, you’d be able to see it.
What Can I Do With A Solar Filter?
So glad you asked. Consider these:
- Safely capture the Annular Solar Eclipse coming on May 20, 2012.
Why: Because it’s cool and solar eclipses visible from any given area are relatively rare.
NOTE: Don’t be fooled when you see a date of May 21 – that’s Universal Time (London Time). 1:30 May 21 in London is 6:30 PDT, May 20.
- Safely capture the Transit of Venus on Tuesday, June 5, 2012.
Why: Because this event won’t repeat for another 105 years! It’s rarer than Halley’s comet and it’s visible from everywhere in the continental United States.
- Capture sunspot activity.
Why: We are approaching the solar maximum where sunspots and coronal mass ejections are at their most active.
- Composite a nicely formed sun into your shots. You can use my “Easy HDR” method described in a prior column.
- Seek solar alignments where the sun forms the back light to silhouette a foreground object.
- Catch the International Space Station (or other spacecraft) as it hurtles across the face of the sun.
- Use the solar filter as an “ultra stopper” to make extremely long daytime exposures.
For some good background on how to observe an eclipse, see here.
Do I Need Protection?
For your eyes, absolutely. For your camera, HIGHLY recommended. People often go “over the top” in their worry that a big lens will burn an instant hole in the sensor or camera body should they aim it at the sun. The image projected is onto a broad area at least as big as your sensor. In a short period of time i.e. a 1/4,000 of a second exposure nothing horrible is likely to happen to the sensor at least. The combination of a mirror and shutter in a DSLR provides SOME protection to your camera and sensor from “certain doom” however if you were to ask my advice, I’d say DON’T use your camera to photograph the sun unless you have a SOLAR FILTER. Most especially do not use live view (or a point and shoot camera) pointed at the sun. That tactic is very likely to damage your camera.
When I zoom in on the sun, isn’t that concentrating the light even more?
Well actually, just the opposite. Instead of focusing all the energy on one spot, you’re spreading it over the sensor surface. So in fact, the sunlight is more concentrated when you don’t use a telephoto lens.
DO NOT look through the viewfinder to compose your shot unless you have a proper solar filter! Permanent eye damage may result. Even then be careful. And we just figured out that it’s not a good idea to use Live View to compose a shot.
What Kinds of Filters Are There? What Do They Cost?
Protection For Your Eyes
There are filters that you can wear or hold over your eyes. I highly recommend you get a pair. These are rated “ND 5″** and allow only 1/100,000 of the energy to pass through. Alternatively you can use a welders mask (though I bet not many of you have one!) #13 or greater. Cost of wearable / simple filters ranges from $1 or so to $20 and more depending on the type. Wearable filters are usually made of black polymer which blocks all wavelengths of light (important to prevent eye damage from non-visible light) and renders the sun a yellow-orange color. Most locations only sell the personal filters in bulk (10 or 25 are the usual minimums). I purchased a stock of 60, for example and have sold them all.
**IMPORTANT NOTE: There are at least FIVE different standards for measuring the transmissiveness of filters: “Neutral Density: ND, Optical Density – also often called ND, Shade Number – for welders glass, transmissiveness, and stops). For a photographer who is familiar with the ND scale used to rate Neutral Density filters this is NOT the same scale as the “Optical Density” scale used to rate solar filters! An ND3.8 (photo solar filter) in the optical density scale is equivalent to the ND8192 neutral density filter! An ND8 filter for your camera is 3-stops of light. For safe visual viewing you need about 14 stops! So an ND8 is woefully short of light snuffing capabilities. Moreover neutral density filters used with cameras may or may not extinguish harmful Infra-red and Ultraviolet radiation.
- What about using an 8-stop Vari-ND (ND2-400 Filter)?
At the maximum 8-stop setting (ND400) the filter is passing 0.4% of the sun’s energy. That’s more than 40 times the recommended energy for PHOTOGRAPHIC use. A photo filter should transmit less than 0.01% (1/10,000). Even a 12-stop reduction in light (ND4096, Optical Density 3.6) passes too much energy for safe and effective photographic use. 13-stops which is the same as Density 3.8 or ND8192 is preferable.
- What about the “Big Stopper” by Lee or Hitech?
10-stops sounds like an impressive reduction in light but the resin filter (Hitech) passes quite a lot of IR and UV light. And 10-stops still really isn’t enough. I haven’t see the response curve for the Big Stopper. It would be UNWISE to assume the Big Stopper or any filter is safe if it isn’t solar specific – especially if you plan to try to take more than a few shots. These filters certainly aren’t visually safe.
In addition to not reducing the light to safe levels, having an insufficient energy reduction means that you’ll have problems with flare / glare.
Photographic and Visual Filters
There are several varieties of solar filters that can be used for photography.
- Black polymer screw-in solar filters – pre-made you order them to screw in on the end of your lens(es). There would be little point in getting such a filter for any lens that is less than about 200 mm effective focal length. It might be worth making your own from an existing UV filter.
- Black polymer “covers” or black polymer solar sheets from which you can make filters.
- Silver solar mylar sheets (make your own) which render the sun a more natural white to a blueish cast. Mylar is less durable than polymer.
- Glass solar Filters in a housing to fit over a lens hood or dew shield (ND 5.0)
- ND 3.8 (Photographic) solar filters which are NOT suitable for visual observing. This type generally only comes in sheet form and you must make your own filter. Not suitable for visual use because it allows too much of the suns energy to pass through to your eyes.
- Tuned solar filters (also called Hydrogen Alpha) – like those found in the Coronado solar telescope. I don’t have a background in these, but normally you will need a set of filters and they are primarily designed for use with telescopes. The cost is upward of $600.
Normally when you buy a solar filter, you select a size that will cover your lens hood (or for a telescope the “dew shield”). Fit on filters should be snug so that they cannot come off if bumped or buffeted by wind. You really do NOT want your eyesight destroyed by a gust of wind! The filter should also seal out light leaks since most solar filters are reflective.
Since the upcoming events all require solar filters, they are in short supply. It may take literally MONTHS to get a filter from some suppliers.
Costs depend on the size and quality of the filter. For the average telephoto lens expect to pay from $60 to $100 for the glass type filters. For very large lenses or for telescopes that cost could reach up to $200 and more.
Black polymer or silver mylar sheets will run you about $35 not including shipping. The ND 3.8 Baader photo filter is about $90 for a 19 x 39″ sheet. I also ordered a “natural color” Mylar polymer sheet (12″ x 12″) for about $30 from RainbowSymphony. RainbowSymphony also has the solar glasses at minimums of 25 pieces. Finding things on the RainbowSymphony site is a bit tedious.
There are many references on the web for building your own solar filter if you choose not to buy a glass filter.
As with all things, quality varies quite a bit. I do not have the resources to exhaustively test all filters, but so far my best photographic results have come using the Baader Astrosolar Film (PHOTO) and hand made filters. This filter passes enough light to keep the exposures fast at low ISOs and is optically superior to any other mylar or polymer material I’ve tried. The glass (visually safe) filter I have darkens the image to make it visually safe and renders the sun an orange color (which it isn’t by the way). Somewhat longer exposures are needed for this.
I’ve placed these in order according to my experience surfing and buying from the company.
- OPT Really fast to ship. Also has smaller sheets of ND 5 and ND 3.5 films available. Shipping is about $10, however.
- Thousand-Oaks Optical A little slow to ship (due to demand) and you have to know what you want exactly to use their website.
- RainbowSymphony Difficult to navigate website, but efficient and inexpensive otherwise.
- Orion Slowest to ship, least communication. Note this link is to a specific filter, you may need to find a different size – which is, unfortunately, not as easy to do as it should be.
- Astro-physics.com - Large sheets of Photo density filters (ND 3.5) – placed an order but Astro-physics lost my payment information. They have an excellent reputation for high quality scopes, but I am worried about a process that “loses” payment data. There are also some significant flaws with their website / ordering process.
If your goal is photos, get a Baader Astrosolar filter. It is not eye safe, but it does allow higher shutter speeds and versatility. Practically this means you’ll have to make your own filter from sheets as there are few resources with pre-made photo transmissiveness filters. Making your own filter is not that hard.
Second choice based on quality is a glass filter that seals well over your lens hood (you do have one, right?). The “outside diameter” of your lens hood must be about the same as or slightly smaller than the inside diameter of the glass filter you’ll put over it. Since most glass filters are designed for visual use, you’re shutter speeds will be a bit slower but good quality glass will keep your photo sharp.
Get a pair of solar glasses for your eyes regardless of what else you do.