Saturday, May 12, 2012

Neutral Density Filter & Sun Photography

I bought a variable neutral density filter for my Pentax, so that I can safely photograph the annular eclipse from near Reno next weekend.  The filter works perfectly--I can see the really massive sunspot that is currently visible on the face, left of center, quite clearly through the viewfinder--but when I take a picture, the camera refuses to produce an adequately sharp focus to see the sunspot.  It isn't even a blur.  I've put it on manual focus (at infinity, of course).  I've adjusted the filter from relatively dark to a little brighter than I would want to look at for long, and nothing seems to matter.  Any suggestions?  I suspect that it will be sufficient to catch the progression of the Moon across the Sun, but not sufficiently sharp to catch sunspots--and I would like to do that.

I also tried to buy some solar filters for my 11x70mm binoculars--and are you surprised to find that they are all back ordered, a week before an eclipse that will be visible across the U.S.?  Plan ahead for 2017!  The solar eclipse glasses I bought for our trip to Britain in 1999, amazingly enough, I was able to find without difficulty, and you can even see this massive sunspot just with these on.

I do have a solar filter for my refractor, made by Kendrick Astro in Canada, and I was using that earlier to look at that sunspot--and wow! At 46x, it is pretty impressive; at 127x, wow.  I may try to get some pictures tomorrow afternoon.

A word of caution: never, never, never trust any solar filter for a telescope that goes on the eyepiece end.  These filters overheat, crack, and can cause permanent blindness.  You should never use a solar filter unless it the kind that goes over the objective lens of the telescope.  If you can see anything except the Sun through such a lens, it is almost certainly inadequate on an optical device that likely gathers more light than your naked eye.

UPDATE: There is no "mirror lock" on my camera, but setting the camera to wait two seconds before opening the shutter seems to help.  You can at least tell where the sunspots are, although realistically, taking much of a picture with a 200mm focal length lens is optimistic.  This image is cropped, of course; if the Sun filled the frame this effectively, it would be like that Twilight Zone episode about the Earth falling towards the Sun.


5 comments:

Darrell said...

Does your camera have a mirror lockup?

Clayton said...

Probably, but I am sure that they don't call it by that name. Remind me what a mirror lockup does?

Darrell said...

If you're using an SLR, (at least the old film ones) have a mirror lockup. You try for best focus, then flip the mirror out of the way and fire the shutter. The mirror cycling as with normal photography can induce a good bit of vibration in the camera, ruining critical focus, especially when using a telephoto lens, which a telescope basically is.

Paul Cunningham said...

Don't trust the "infinity" setting without testing it. Autofocus lenses have to be able to 'go past infinity' in order to work their magic. Try testing various settings just slightly to either side of infinity. Good luck!

Anonymous said...

If you're using a Nikon there is a MUP setting. This stands for Mirror UP. Try this mode. I plan to shot the eclipse with a D7000, in MUP mode with a remote shutter release. I have a circular ND filter... which I've read is both safe and not safe. Hopefully I won't go blind....