Venus Transit- Day 8

Today we set up the refractor for mobile operations. Step one was to install a suitable dovetail plate for secure attachment to the dovetail bracket. For those not familiar with this concept, a 'dovetail plate' is a trapezoidal shaped metal plate which is a commonly used system for attaching scopes to mounts. The 'dovetail' slides into a similarly shaped clamp or bracket and this geometry enhances the stability of the connection.
This was not as easy as I thought. First of all, if you do have an ED80 OTA and it's an older model (mine was purchased in 2005), the dovetail Orion sells now for 20 bucks is not going to fit! I recommend this one from Scopestuff which is more robust and has plenty of slots in there to fit probably just about any scope. Plus it came with the proper screws and directions! I've never taken one of these refractors apart. It is kind of delicate inside and to get to the original screws holding the small mounting block you have to have small hands as the screws are set fairly far back in the tube! It's very easy to scratch the paint in there, so you have to be very careful. A long, thin needle nose plier can help, but if you have kids even better!

Inside the ED80 refractor. Mounting screw holes can be seen  at the bottom. One has been removed already. The far one is difficult to reach!

Final assembly showing the plate in place. The marker lines show the position of the dovetail rings for later repositioning back onto the Cave

The next step was mounting the scope. After researching the last couple of weeks, I settled on the Vixen Porta II mount. The mini porta was 100 dollars cheaper but felt to be too small for my scope. This one is still under 300 and very well built for that price. It comes with smooth slow motion control knobs for azimuth and altitude. I tested the assembly for about 2 hours and had no issues keeping it trained on the Sun with little effort. I'm using a 25mm eyepiece. This seems to get the whole Sun comfortably in the field! Now folks,  the hardest thing to do here is to find the Sun! I remember before I had a reliable pointing system I struggled for an hour to get the Sun in the field! You can buy a short mailing tube for $2 at the post office, drill a 1/8" hole at one end and cap the other with a piece of wax paper. Now you have a featherweight solar finder you can just tape on the top of the OTA! This saves me a ton of time. Today it took maybe 5 minutes tops to get the Sun in there!

Final assembly of refractor, homemade solar finder and HA filters mounted on Vixen Porta II

Homemade solar finder showing the Sun centered in the field

Close up of dovetail plate secured in the bracket

We are now officially ready for Transit viewing. Next we need to test the camera to see how it behaves on this portable set-up!

And by the way, the forecast is still sunny for June 5th!