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Will I able to see Mercury transit with a f/4-5.6 200mm lens (on APS-C)?

I do not have solar filter and I don't have time to buy as transit will be on 9th May 2016. I'm wondering if I can use my UV and neutral density filter to shoot Mercury transit when sun is pretty much dim (around 6:30PM) with help of DSLR display. Will this be ok?

I got this today at 6:51 PM IST only sun spot, no mercury(might be there)

Safety: ND filter 2,4,8 + UV filter + pointed the camera at sun always less than 10 sec.

sun mercury

  • If you have more pictures taken some time apart then you can try to detect mercury by subtracting the pictures. – Count Iblis May 9 '16 at 20:01
  • i tired searching for 3 pixel dot near sun edge. can not find the mercury. I might have messed up in focusing. – editinit May 10 '16 at 7:16
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Field of View

The sun is approximately 0.5° across in the sky. At 200mm on a DX (1.5 crop factor) body, the field of view (FoV) is 6.9° (wide) / 4.5° (high) / 8° (diag).

In terms of Sun diameters (☉), the 200mm FoV is 13.4 ☉ wide by 9 ☉ high.

According to Wikipedia, Mercury's diameter when viewed from the earth during May transits is 12 arcseconds. In terms of Mercury diameters (☿), your FoV is

FoV (☿) = FoV (degrees) * 60 (min/degree) * 60 (sec/min) / 12 (sec/☿)

This comes to 2060 ☿ wide by 1374 ☿ high. Using a Nikon D3300 (with 24.1 MP — 6000px by 4000px), Mercury would be approximately 3px across.

ND Filter for Photographing the Sun

I DO NOT RECOMMEND DOING THIS. I can't stress that enough. Certainly, it is possible to reduce the sunlight using an appropriate amount of ND filters to maybe, possibly safely take pictures of the sun without damaging your camera's sensor.

In my opinion, the only proper recommendation for photographing the sun (telephoto) is to reduce the strength of the incoming light to be safe to use at the widest aperture of your camera. That is to say, the aperture should not be relied upon to reduce the intensity of the light before it gets to the sensor. The reasons for this "rule" are:

  1. To keep a simple safety rule simple. Analogous to the firearm-handling rule "the weapon is always loaded" (even if you think you know it's not), this rule is designed to keep your eyes and your camera sensor safe.

  2. When photographing events such as transits and eclipses, the camera is most likely pointed at and focused on the sun for at least several minutes. The sun's intense light concentrated to some degree or another in multiple places in the lens. These places can become hotspots in the lens and damage glass elements, adhesives, etc., even before the aperture.

The correct, safest method to reduce the solar light intensity is to use a solar filter designed for photographic/telescopic use (see also Star Circle Academy's article on solar filters).

The sun requires about 16-17 stops of light reduction (around 1/1000 of 1% light transmission). If you have 17 stops of ND filters (this is darker than most welding glass. Only a welding shade number of 14 is enough), you'd probably be fine. However, I'm a strong proponent of "the right tool for the job", so I still do not recommend it.

Now, you mention you will be observing the transit around 6:30pm. Depending on your longitude, the sun will be 15°-20° or so above the horizon. This will help reduce the amount of light reduction by a couple stops at most.

Having said the above, you will find examples on this site and others of great pictures of the sun with a Venus transit or sunspots, taken with something like a 10 stop ND at ƒ/22 or so. I think every one of these pictures should have a "Don't try this at home" caption.

Oh, and your UV filter would contribute to the safe ability to shoot the sun about as much as mosquito attacking a fighter jet.

  • My 200mm lens was already Dx. I guess this will make mercury much smaller than 3px. – editinit May 23 '16 at 7:08
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Probably not. But it depends on just how dark and what type your ND filter is. It can be very dangerous to both your equipment and your eyes to try and take photos of the sun without the proper precautions!

The most damaging portion of direct sunlight to the internals of your lens, camera, and eyes are in infrared, not in the visible spectrum. The UV filter reduces non-visible ultraviolet light on the other end of the visible spectrum, but does nothing for infrared. Most ND filters are designed primarily to affect visible wavelengths of light. So you're not really doing as much to reduce the infrared energy from the sun as much as you are reducing the visible light portion of the energy radiating from the sun. If a filter is not documented with regard to UV and IR light you should assume that it does not filter these as well as visible light!

Neutral density filters made specifically for solar viewing through telescopes are much darker than most ND filters used by photographers. A typical "white light" solar filter only allows about 0.001% of the sun's energy that fall on it to pass through. That is the rough equivalent of a 16 2/3-stop ND filter. In the different notation systems it would be an ND100000 (NDnumber notation used by B&W, Coken, etc.), ND 5 (ND.number notation used by Lee, Tiffen, etc.)(NOT to be confused with a 1-stop ND 0.3 or 2-stop 0.6 filter!), or ND 117 (ND1number notation). More importantly, "white light" solar filters also attenuate for UV and IR light as well as the visible spectrum.

Once the sun drops to near the horizon you can relax those requirements a little as the sun's angle through the earth's atmosphere absorbs more of the sun's energy. What is safe for photographing a sunset should also apply equally to a sunset that includes the silhouette of Mercury in front of the solar disc.

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DO NOT ATTEMPT THIS WITHOUT A SOLAR FILTER which is metal that absorbs harmful levels of electromagnetic radiation that will damage your EYES and maybe your equipment (which can be replaced, unlike your eyes).

ND Filters use dyes which do NOT cut the radiation in the dangerous areas of the spectrum.

Further, the size of Mercury will be minuscule.

  • Point of technicality: metal film solar filters achieve their light blocking by reflecting the light back. ND filters and other "dark" filters that use dyes like you mention block the light by absorption. – scottbb May 11 '16 at 11:40

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