The Leo Triplet

This is a group of galaxies in Leo, the Lion constellation that dominates spring nights. M65, M66 and NGC3628. At distances of 35, 42 and 37 Million light years, they form a fysical group in space  Tidal forces rip apart the extremities of NGC3628. The smallest galaxy identified in this image is PGC1423398 at a distance of 2 Billion light years: so glad those fotons travelled that distance in space & time only to get caught in my camera!! 

Picture with: C11 Starizona LF SCT reducer F 7.2 FL2010mm Nikon D750 FF Optolong L-Pro 2″ 800iso 27x600s

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The Horsehead Nebula in orion

This is a very familiar sight and thousands of pictures have been taken of this little “seahorse”  or horsehead in the sky.  Taken with the Celestron C11 on an EQ8 mount, Starizona LF corrector for Schmidt-Cassegrains, a Nikon D750 DSLR modified for extra H-Alfa sensitivity. 22 frames of 300 seconds each are combined in this image

Tri-Bahtinov Mask

We all know the classic Bahtinov mask: it allows to focus a bit more objective compared to visual star focusing.

The Bahtinov will produce Cross-shaped stars, with one clear line that moves along the cross as you focus. When the line is centered in  the cross, you should have achieved perfect focus.

So what is the tri-Bahtinov?

It essentially three Bahtinov masks in one, rotated over 120 degrees. It gives you three lines and three crosses to check collimation, along three axis simulteaneously.

In addition to focussing, the tri-Bahtinov so also indicates collimation status along three axis.

This is interesting for e.g. Schmidt-Cassegrain telescopes, where the collimation is done by push-pull screws of the secondary mirror along three axis.

When you position the tri-Bahtinov alongside these axis, it will give you insight not only per axis of the focus, but also how different these focus points are for each axis.

 

 

 

 

 

 

 

 

A picture of a star using the tri-Bahtinov and the ASI174 Webcam.  Very slight disalignement is visible.

You could basically do the same by turning your classic Bahtinov at 120° angles and check focus each time per individual axis.

Do i use the tri-Bahtinov very often? Not really. I believe it’s a great final check for a fixed SCT on a permanent mount. It will disclose the slightest error in collimation. But for every day use, with an SCT that is moved along and mounted for each session, it might be too cumbersome.

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