Tuesday, 29 May 2012

Coronado Telescope Photography

Taking pictures of solar eclipses and transits is a challenge. And it becomes even more challenging when using a hydrogen alpha telescope such as the Coronado PST (40mm). The problem is that you cannot simply attach the camera body to the telescope. The focal plane is below the image plane.

To fix that situation I use negative projection. A Barlow lens is used between the camera body and the telescope. The Barlow lens extends the focal plane out further (increasing the resultant magnification by making the focal length longer).

Here is what the Transit of Venus looked like in 2004 through the camera. I had only a 2x Barlow lens and the camera body attached.

Full frame view with Coronado 40mm telescope and 2x Barlow lens negative projection.


Transit of Venus 2004 in Hydrogen Alpha (Coronado 40mm)

An excellent description of negative projection is provided here.
http://www.licha.de/astro_article_barlow_lens_projection.php

What is needed is a DSLR camera body, a Barlow lens, a T-adapter, a good mount to hold it all steady, and a cable release.

Anyone attempting to use this type of set up is strongly recommended to practice as much as possible. Focus is difficult, the amount of light you see through the DSLR viewer is reduced, and the weight of the camera attached to the rear makes balancing a challenge.

So here are a couple of tips.
1) Use a dark color blanket or towel to cover your head and the view through the camera. The darker the better as it will greatly aid in focusing and centering the image.
2) Use a strong mount - as strong as you can carry to the site. And plan to add counterweights as needed.
3) Fine adjustments to focus will be needed through out the event. Check and re-check the focus.
4) Remember to adjust the etalon to see different views of the prominences and filaments that may not be clearly visible through the camera.
5) Vary your exposures and combine the images later with a computer.
6) Have fun and don't forget to enjoy the views.

A solid mount is essential when photographing. The Orion German EQ used here pushed the luggage limits.


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