Venus Crossing Sun - 8th June

[megan_forbes]

Venus is crossing the Sun on 8th June - a once in a lifetime sight.

I'm interested in shooting this with my D70 and 70-300mm lens, but

would prefer not to fry it or my eyes in the process...

 

I have a x8 Hoya ND filter and a polariser, but imagine this isn't

enough? Should I get an eclipse filter? Or hold a piece of welding

glass in front of the lens?

 

Any ideas/experience gratefully accepted. Thanks!

[daniel rufer]

I am not sure about the 8xND and polarizer combo, I have the feeling that it might not be sufficient but I am not sure by far.<p>

However 2 points that you have to watch out for:<br>

- Never use drop in filters (at the rear end of the lens) as the focused sunlight will fry it in a very short time.<br>

- If you " hold a piece of welding glass in front of the lens" make ABSOLUTELY SURE that it cannot slide off!! If it does while you are looking through the 300mm lens you risk very serious eye damage. Do not "hold" it, attach it very securely! Besides, I remember I read somewhere that there are several types of welding glasses, some of which are not well suited for solar viewing.<br>

My personal opinion is that you would fare best with a solar filter.

<p>

Take care and I hope you get clear skies that day!<p>

Daniel

[megan_forbes]

Thanks, I'll look into the solar filter. Fortunately with a DSLR I can use the hit and miss method of reviewing on the LCD and not looking through the viewfinder at all (this will last for about 6 hours apparently), but I'd still prefer not to fry my camera :)

[david_debalko1]

Welder's glass or 2 pop tart wrappers

[david_debalko1]

Megan,

Depending where you are located- I am in the northeast US where the transit starts at about 1am and ends about 6am, the sun does not rise until about 5am so I will see the last hour-and you have to have a location where you will have a unobstructed eastern horizon.

And I think(not positive) you need a #3welder's glass.

David

[megan_forbes]

Thanks David - I'm currently in the UK, so I believe we'll see the entire thing - providing our eyes can survive it of course ;)

[robert_m3]

For reliable information on safely viewing the Venus Transit, have a look at this article on

the Sky & Telescope web site:

 

http://skyandtelescope.com/observing/objects/article_1258_1.asp

 

Please don't risk your eyesight using pop tart wrappers!

 

Most Astronomy stores sell what's called Baader film which is highly recommended.

Kendrick Astro sells the film mounted in holders in a variety of sizes.

[markci]

Don't expect a whole lot with a 300mm lens. Even with the smaller D70 chip, the sun will be about 1/10th the width of the frame, and Venus will be 30 times smaller than that. A few pixels, if it shows up at all.

[mark_peters]

I've been fortunate to view two total and several partial solar eclipses in the last several years and each time used shade 14 welder's glass. This is one of the few absolutely safe ways to view the sun. Please be wary of folklore about using any common household items as a filter. The damage to your eyesight can be catastrophic.

[blakley]

Don't use a ND filter - you have no way of knowing whether it is safe or not, and it probably isn't.

 

The most dangerous parts of the sun's spectrum (from the point of view of your eyes) are the IR and UV components, which many ND (and other) photographic filters won't block.

 

You really need #14 welder's glass, or a dedicated solar filter.

 

Make sure that you use a filter on the front of the lens, 'cause

drop-in rear filters will heat up and may shatter or melt.

 

#14 welder's glass should usually have a density of a bit more than

5; if you get a solar filter, you should look for one with density 5 also.

 

With a filter of density 5, your exposure should be about 1/500 sec. at f/11 on ISO 100 film - but of course you should bracket. I'd look for a 300mm lens with a 1.4 or 2 teleconverter - I wouldn't try to use a mirror lens for something which happens this infrequently for fear of poor image quality.

 

I'd also recommend a manual-focus lens, because you'll be able to set this reliably to infinity focus and get a sharp shot; many autofocus lenses will focus a bit beyond infinity if you rack them out all the way. Even with proper filtration, I don't really like looking through the lens to focus the image...

 

Another consideration will be camera shake - if your camera has mirror lockup (or if you can borrow a camera which has it) I'd definitely use it.

[blakley]

PS with a 300mm lens and 1.4x teleconverter (effectively 420mm lens) you will produce an image of the sun which is about 3.6mm in diameter - 1/10 of the wide dimension of a 35mm negative or slide. With a 2x teleconverter, you'll get a 10mm sun - almost half of the short dimension of a 35mm slide. Venus will of course be much smaller...

 

I don't know what the D70's magnification factor is, but the following formula will help you estimate how big your image will be is

 

((effective focal length) * 0.5) / 57

 

(0.5 is the angular size of the sun - about half a degree).

[raoul1]

Something simple to try:<P>

 

- take some binoculars and mount them on a tripod<BR>

- point them BACK TO FRONT at the sun (ie: eyepiece end points at the sun)<BR>

- hold a nice piece of reflective white cardboard or paper a little distance from the other end of the binoculars.<P>

 

 

Now you have a safe way to photograph and view the sun. This makes it easy to view sunspots or anything else interesting. No danger to your eyes, and you can have many people at once viewing the image.

[nikos peri]

May I have all the cameras belonging to soon to be blind photographers using pop tart wrappers as solar filters... please?<p>

<b>Seriously people, do NOT improvise when pointing long focal lengths at the sun: you WILL cause irreparable damage to your eyes.</b> You can purchase some new mylar foil from AstroSolar, Baader, Kendick... these are serious astronomy manufacturers used to dealing with solar filters. It's fairly cheap and the alternatives are going to get ugly.<p>

FYI, a 4x ND filter will (obviously) have a filter factor of 4. A proper (5 density Baader visual solar filter for example) will have a filter factor of 100,000. Anybody using ND filters is in for a painful surprise and I will collect their camera gear.<p>

As to apparent sizes, you will not see anything of Venus in a 300mm lens.

[blakley]

According to Barry Gordon, Venus becomes an "extended object" (that is, not just a point) at focal lengths of 500mm and over. Its diameter covers an angle of between 10 and 64 arc-seconds, so for estimating purposes let's say half a minute of arc. At 420mm, then,

its image on film will be (420 x .00833) / 57 = 0.6 mm, which is about 1/16mm. A sharp lens and a good sensor should be able to resolve at least 48 lp/mm, so the image of Venus should be visible on your picture - BUT...

 

Atmospheric instability is likley to be a problem, and flare will certainly be a problem. If you overexpose at all, the brightness of the sun will overwhelm Venus' tiny dark spot, and you won't see anything on the final image (so do some extra bracketing towards underexposure.) You won't be able to see if you got a good result on your camera's built-in LCD monitor, so do lots of bracketing to make sure you get a good result.

 

By the way, since you're using a digital camera, no matter how bad your filter is, you won't hurt your eye if you just look at the LCD and don't look through the optical viewfinder (unless LCDs have gotten A LOT brighter than I remember....) However you may fry your

chip.

[jonathan_laufersweiler]

500mm mirror lens + 2x teleconverter + solar filter IN FRONT of the lens. The lens

combo will be f/16 wide open, much less likely to accidently melt the inside of your

camera. Put it on an F(2,3,4,5) so you can take off the eye destroying prism and

focus/view on the ground glass. Dont lock up the mirror though, or you'll melt your

shutter.<p>Any thoughts on infrared film? HIE would halate Venus into oblivion, but

what about the others?