Friday, July 27, 2012

Saturn and the Moon with the Tamron 500mm BBAR Mirror Lens

I’ve been chomping at the bit, waiting for clear skies. And tonight we finally got them when the moon and Saturn were both up. They set by midnight, so you have to be really on the ball to get a slice of time with quality skies.

I started with Saturn since it was much further west and dropping fast. I had the Tamron 500mm Mirror BBAR on its own tripod mount on the Feisol tripod with Markins head. I added the Kenko 300 2x teleconverter onto it and then the Nikon D7000. This combination has proven to be surprisingly sharp on macro detail. Micro detail is a little less impressive. But wait and see … I was a bit surprised at the outcome.

Remember … this combination is fixed at f/16 (f8 with 2 stops light loss) … that makes focusing difficult. But here is the fun part … the magnification of this combination is so high at 1500mm (longer than the 1325mm Celestron NexStar 4 SE Maksutov-Cassegrain telescope) that, at full live view magnification Saturn traverses the LCD’s field of view in about 20 seconds. It is stunning to actually watch celestial bodies moving on the back of your camera :-)  Jon came out when I was shooting the moon and was completely blown away at watching craters go by … it felt a little surreal seeing that for the first time.

So anyway … slow lens with manual focus that is not assisted by quality focusers as are telescopes. This was me twisting the lens back and forth and guessing if it was good enough.

And without further ado … Saturn.

Nikon d7000 + tamron 500mm bbar + kenko 2x tc
800iso  f/16 (effective)  1/4  1000mm (1500mm EFL)

Ok, that’s a tad underwhelming. I’ve shown some more impressive shots from the HS25 for example. However, that camera auto focused using contrast detect, which is far better than I can do. And I increased that magnification considerably, whereas this is a straight 100% crop. And you have to admit, that’s a big Saturn on the sensor. In fact, I was able to see the rings in the view finder for the first time. That was very cool :-)

And now, beelaba moonaba …

I shot it several times, but in two configurations. One with the Kenko, and one without. Normally, it is a wash between the two as the Kenko adds sufficient blur to bring the quality down. But tonight it is decidedly the opposite. Of course, it could easily be that I had a bad seeing moment, where the air disturbed the shot. That happens, and I certainly did not shoot enough images to really be safe from that.

Anyway … the shot with just the Tamron …

nikon d7000 + tamron 500mm BBAR  100iso  f/8  1/160  500mm (750mm EFL)

And now with the Kenko …

nikon d7000 + tamron 500mm bbar + kenko 2x tc  100iso  f/16  1/125  1000mm (1500mm efl)

The previous shot makes my eyes see very subtle blur while this shot is perfectly clear wit wonderful acuity for a hacked together cheap telescope :-)

Click on the image to see the Apennine mountains in all their glory. I remain pretty stunned by how good this shot really is.

So … an $80 used mirror lens and a used Kenko 2x teleconverter gave me a great night of shooting our solar system. I missed a chance at Mars, but perhaps tomorrow …