Preparing for the transit

[stolenfeather]

Like many people out there, I am "all abuzz" about the Venus transit next week. I have never attempted to look at the sun with my telescope and with good cause since it is a 10" Dobsonian. I am told that any direct look at the sun would result with issues with my secondary mirror and since I was unable to find a pair of suitable glasses for the event, have decided to create a little concoction of my own using many different websites and sources.

Using elastics, I have affixed a pair of birdwatching binoculars to a camera tripod. It's not the best idea but it does give me some stability. I am thinking of leaning towards duct tape if my binoculars prove to be too heavy. Orienting the opening of the binoculars towards the sun, I will attempt to see the transit of Venus on a white sheet of paper.

I am also thinking of using a piece of cardboard at the back of the binoculars in order to create the necessary shadow so the transit appears on the paper. I found the following picture online that illustrates what I am thinking of doing:

Source: http://sternmann.livejournal.com/13831.html

Source: http://abaaonline.blogspot.ca/2012/05/last-venus-transit-of-century.html

As stated previously, I have never attempted anything like this before and would hate to encounter unforeseen issues during the transit. Like many of you know, it's a once in a lifetime thing right?

My questions to this helpful forum are:

1. Have you ever used this method before and how reliable is it?

2. Can you recommend anything that can help my experience go smoothly?

3. Have I researched the possibility of using my 10" Dobsonian telescope for the transit fully? Is there a way that I can do it safely (for both myself and the telescope)?

I thank you in advance for all the suggestions and encouragement for this project.

I wish you clear skies for the event!

Isabelle

[Skylook123]

Hello, Isabelle,

The projection method with binoculars or a small refractor (for ease of movement) is very easy to set up and use. My wife Susan and I used this method on an eclipse cruise in 1998 and it was a great way to watch the event. Once you get the binoculars in focus by looking at some terrestrial target very, very far away, then the only thing that will limit the size of the image projection will be distance from the eyepiece end to the projection surface, and the aperture and power of the binoculars. Keep moving the survace further away as long as the brightness of the image holds out.

We are supporting a public outreach event here, and one of our instruments is a 90mm refractor as a projector. Practicing with it gives us an image nearly 150mm across with sunspots clearly visible. Good luck with your endeavour.

It is incredible how much energy will be accumulated in your dobsonian. And all that energy is being brought to near focus at the secondary, so damage is entirely possible. I once was collimating a 10" f/4.5 tube newt on a dob, and had removed the secondary completely. I was near the open edge of the garage. Walking away for a few minutes to get the rest of the tools was long enough that the sun happened across the aperture and the garage door immediately began to char.

Back to your binoculars, it might help to have them as close to the ground as possible; the distance to the best image from the exit pupil to the surface will be quite small, perhaps less than half a meter. A few bricks or a small kitchen stool would make a workable stand for a white poster board or small white board as a display.

Have a pleasant sunrise observing time!

[JamesF]

To be honest, I see no reason why you shouldn't use the 10" dob for viewing the sun as long as the truss was suitably shrouded to prevent light getting in through the sides. If you made an off-axis 4" solar filter I'd have thought it would work fine. You'd also need to make a suitable finder or work out some other arrangement for locating the sun.

James

[Auntystatic]

You shouldn't use reflectors for sun watching, as Jim said it brings everything to near focus on the secondary and they have been known to explode on occasion.

[cotterless45]

I use a newt all the time for solar with a home made filter using badder film with a 10 inch do a 4 inch off axis one, as above and make sure the truss is closed in with a good thick shroud. As to damaging the secondary , you won't if you use a badder film apeture filter as only .0001 percent of the energy enters the tube.

[JamesF]

You shouldn't use reflectors for sun watching, as Jim said it brings everything to near focus on the secondary and they have been known to explode on occasion.

If you're using a filter made from Baader solar film or something similar I really can't see how that can possibly happen. Even more so if you've stopped the aperture down. The amount of energy reaching the primary is probably not that different from the amount involved when viewing the full moon. Sounds like urban legend to me.

James

[JamesF]

Ah, it strikes me that perhaps you're only considering solar viewing by projection. Using a large reflector at full aperture without a filter for that purpose probably isn't smart, no.

James

[stolenfeather]

Thank you for your suggestions Jim, I will surely take it into consideration since I really have caught the "transit bug". Mind you, in my neck of the woods the experience will be more of a sunset thing than a sunrise one.

I am unfamiliar with using filters James and since I live in a very remote community (the nearest city is 8 hours away, driving in nothing but forest), it is extremely hard to obtain the equipment needed. Yes, I am thinking of using projection to see the transit which is why I opted for the binocular method. Let's just say that I've had many issues with my eyes in the past. Thank you for you input.

I hate to expose my lack of knowledge but what exactly is "a badder film aperture filter". Up till now, I have only been interested in deep-space objects and planets so i guess sophisticated equipment never really came up. Like I have said previously, this is my first time trying anything with the sun.

Thank you so much for all of your help. I hope you all have a wonderful view on the day of the transit. So far, the weather in my region looks fine with no clouds in sight!

Isabelle

[carastro]

Baader solar filter is a sheet of specially made "film" that you can put over the aperture and it will filter out the harful part of the suns rays and can be used as a white light solar filter. It needs careful handling so you don't damage it. From what has been said previously it sounds like you can buy a baader solar filter already made as well.

There are two different qualities, one for visual and one for astrophotography.

I made myself a couple.

Carole

[Skylook123]

Sorry, Isabelle, I had you on the wrong side of the Atlantic!

When we did the annular eclipse at the Grand Canyon (on eclipse day the park had a visitor count 10,000 higher than normal for that day), at my spot we had about 30 telescopes up to 16" apertures and 1400 visitors, with glass filters and Baader film equally represented. Prior to the event I built six Baader film filters for Rangers' scopes and my own 90mm short tube refractor, and for the event I used my 10" SCT with full aperture glass filter and a Lunt 60mm solar scope. My comments about the effect of the sun with your 10" was assuming unfiltered since you did not say anything about having a filter available.

With all of the instruments available, one of the most popular setups was a Ranger with her personal 90mm spotting scope doing projection. When you project an image the image size is much larger than the eyepiece view, but it needs to be unfiltered. Larger apertures grab too much energy for projection.

Good luck with your project!

[stolenfeather]

Thank you Carole for the information about filters. I might look into this farther down on my astronomical journey but for this particular project (with time limited now) I will keep my projection project alive and well. I realize that what I will see will not compare to other more professional set-ups but my small binoculars will give me the sense of "dirtying my own hands" when it comes to experiencing the transit. This combined with a webcast and a well deserved bottle of red will be my own personal celebration of the event!

Jim, to be at the Grand Canyon and experience the stars there with your group would be amazing. As you know, the Grand Canyon has a very special place in my heart. There's a part of my brain that relives my hike down and up the Bright Angel Trail everyday. With your encouragement, I am now sure that my project will be successful! I promise to post the results!

Mind you, let's hope the weather predictions remain as they are,.. still bright opened skies ahead! I hope the same for you!

Isabelle

[JamesF]

I think there's a lot of sense in sticking with the projection route at this stage, Isabelle. It's fairly easy to make a solar filter, but not something that should be rushed.

James

[cotterless45]

Yep,

there's going to plenty of solar activity over the next year. Enough time to get kitted out and solar safe.After today's deluge ,we'll be lucky to see the Sun in Middle England.

Nick.

[Skylook123]

Personally, since I do not do photography, I enjoy solar viewing by projection through a 90-120 mm refractor since the image is so much larger than in an eyepiece and if not alone, it is more fun to share the view rather than immerse myself alone in the eyepiece.

I hope some day you can return to the Canyon and join us on the South Rim, Isabelle.