solar filter

[Lloyd_Welch]

Ok...I am new to this and dont really know much but I have a canon rebel t5 and I am going down to TN to try my hand at photographing the eclipse. I bought a filter to fit my camera and dont know what 18 stop means. Can anyone enlighten me?

[kvbarkley]

It means it cuts the light by a factor of 2^18.

http://learn.usa.canon.com/resources/articles/2017/solar-eclipse/solar-filters-eclipse-photography.s...

[Lloyd_Welch]

Thank you sir.

[TCampbell]

18 stops seems an odd number... but it'll work.  

Most solar filters are "ND 5.0".  ND means it's a "neutral density" filter and the "5.0" is the density value.  Each "0.1" worth of density is exactly 1/3rd of a photographic "stop".  So "ND 0.3" would be just one photographic stop.  ND 0.6 would be two photographic stops, ND 0.9 would be 3 photographic stops, etc.  And by that math... ND 5.0 is actually 16 and 2/3rds of a photographic stop (just shy of 17 stops).  

The "stop" means it cuts the light exactly by 1/2.  So a 1-stop filter cuts light transmission through the filter so that only half of it can pass through.  A 2-stop filter means it's 1/2 of 1/2... or a total of 1/4.  A 3-stop filter is 1/2 of 1/2 of 1/2 (or 1/8th of the light can pass through).  

For an ND 5.0 filter, it means only one photon of light out of every 100,000 can pass through (it blocks 99.999% of the light).  If you were to attempt to hold the filter between you and ... say a desk lamp... you wouldn't be able to see any light from the desk lamp (it isn't nearly bright enough).  

Remeber that you only use the filter BEFORE or AFTER totality.  DURING totality you may look directly at the Sun (and your camera can directly photograph the sun without any filter).    It is the only time it is safe to look at the sun without proper protection.

Also... if the camera is on a tripod, you'll need to nudge the composition along to keep up with the apparent movement of the Sun & Moon (since the Earth is spinning).  You should do a final check of your framing and focus about 1-2 minutes before totality begins but do this WITH the filter still on the camera.  You may remove the filter about 20 seconds before totality (and no sooner than 50 seconds before totality).  Once totality ends, you should put the filter back on the camera at 20 seconds after totality.

The reason for removing the filter those few seconds before totality is because the "diamond ring" effect is usually visible about 9 seconds prior to totality and the "baily's beads" effect is usually visible about 1.5 seconds before totality.  You would want the filter off to photograph those.  Both of these repeat after totality ends but the effects would be completely over within 20 seconds of the end of totality.

You can find exposure guidance here:  http://mreclipse.com/SEphoto/SEphoto.html

[Lloyd_Welch]

I bought a 5.4 18 stop filter from Firecrest Filters Formatt Hitech. I bought this camera to photograph the sun and I also bought a tripod from Orion designed to hold a camera with a equatorial motorised tracker. And any advice I could get between now and then is greatly appreciated.

[TCampbell]

Get some practice in setting up your mount ... take advantage of any clear nights you have. 

The magic of a tracking mount happens when the axis of rotation (for the tracking head) or the "right ascension" axis (for an equatorial telescope mount) is exactly parallel to the Earth's axis of rotation.  As the Earth spins from West to East, the mount rotates from East to West at the same speed... and this exactly cancels out the perceived motion of the stars.  Objects are held in place and you can take very long exposures.

Your mount should have instructions on how to perform a good polar alignment.  Practice with that.  If you have questions, ask, but mention which mount make & model you own so I can give specific instructions.  (I've used a lot of telescope mounts).

If you are traveling for the eclipse, then you don't want to leave anything behind.  

Fred Espenak (Mr. Eclipse) suggests you set up everything at home and do a test-run.  Rely on only what you will have available at your observing site.  In other words if your observing site has no power, then don't plug anything into your house power... it all has to run on batteries for the test run.

The goal is to be able to do a test run without having to run back into the house to grab something you forgot.  

The other goal is to make sure your equipment will last (e.g. batteries wont die in the 3 hours of shooting... memory card will have enough capacity to hold all the photos, etc. etc.)

Once you declare success, Fred says to put a tarp on the ground next to your setup.  Disassemble all the gear and organize it onto that tarp.  Now... EVERYTHING on that tarp must go into your car.  Take an inventory.

I did a test run and my home has too many tall trees to get a clear view of the Sun.  So I setup at a nearby college campus.  When I did this, I thought I had everything.  I found that I forgot three items.  Two were "conveniences" (would have made setup easier).  But one was essential to photography (I forgot the teleconverter necessary to get the proper focal length for the Sun that I'll be using with my telescope.)  

I took notes on the gear I forgot.  I packed everything back into my car and drove home.  When I got home I grabbed the three missing items and put them with the rest of the gear.  

I then used a spreadsheet and some tags (they look like sales tags with wire twist-ties so I can attach them to soft-side bag handles, etc.) and tagged and numbered all my gear on the spreadsheet -- with descriptions.  Now I have a list of "everything" that must come with me when I travel to the eclipse.

[Lloyd_Welch]

I have a generator and have tested it. Believe it or not all I can get at ground zero may or may not have power and I am not going to depend on batteries and is only 12' x 12'. I ordered my tri pod from Orion. I am going to go with what I got and work with what I get. I have all the software and can make the shots from my lap top. I plan to take as many as possible at least 200 and more if I can. I have and will continue to practice.

[ebiggs1]

" I bought a filter to fit my camera ..."

What lens?  If you got it for the standard Rebel kit lens, you will not get a very good shot of the Sun.  The Sun is the same size as the Moon so you might try a few shots of it before to see what you may expect.

[Waddizzle]

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@ebiggs1 wrote:

" I bought a filter to fit my camera ..."

What lens?  If you got it for the standard Rebel kit lens, you will not get a very good shot of the Sun.  The Sun is the same size as the Moon so you might try a few shots of it before to see what you may expect.

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Taking a few shots of the Moon is a good idea.  It gives you a chance to practice focusing, because the focus for the Moon will be ideal for the Sun.  It also gives you practice at working in the dark, as well as, a chance to rehearse what you want to do during Totality.  You should figure out all of that stuff ahead of time.  Find out how long it will last, too.

I hope you have a robust, professional grade tripod.  They don't sell them at the Big Blue box stores, just plastic ones that shake and break.  When you use longer focal lengths, any camera shake becomes magnified, so a good stable platform is a must. 

Another "must have" is a remote shutter, so that you don't have to touch the camera to fire the shutter.  Using the camera's built-in 2-10 second shutter delay works, too, but  you may miss "the moment" of the diamond ring because of the delay.

[Lloyd_Welch]

Thank you for your input. I bought a Canon EF 75-300mm 1:4-5.6 III. I have been shooting the moon for practice and got the stacking software and have some pretty good shots so far. I have been practicing on the sun hoping to catch the sun spots but havent stacked them yet. Now I am hoping you are going to tell me it is at least adequate.