Chuffed to bits with the eight-frame stack of M31 at 200mm, I couldn’t resist a quick grab at 300mm when the new lens arrived. Fixed focal length Nikon 300mm f/4.5, manual, donkey’s years old, bought second hand on ebay, it has that most precious of attributes – a focus ring that stops at infinity. That means you can focus on the night sky without needing to see what you are photographing. Priceless.
300mm f/4.5, ISO 3200, 180 sec.
Single frame of 3 minutes at 300mm.
This was at the end of a session experimenting with drift alignment alignment and imaging M42, I quickly turned the camera to M31 and took a single 3-minute frame as I was tidying up.
This lens is brilliant. There is almost as much detail in this frame as in the stack of 8 x 5 minutes taken earlier in the month. I will do more work on M31 with this lens when I get the opportunity.
Experience with tackling M31 using the fixed tripod and the 50mm lens made me realise that these objects (let’s not forget M31 is one of the most accessible) need longer exposure and longer focal length lenses.
That means using the equatorial mount, and all the issues of polar alignment and motor drives that go with it. The first kit upgrade is therefore a set of motor drives, one for each axis of the EQ3-2 mount.
200mm @ f/6.3, ISO 6400, 330 sec.
11 x 30 sec. frames stacked in DSS.
Polar alignment here was by eye (using the hole where the polar scope would go if I had one), followed by several phases of 2-minute drift alignment using the 500mm reflex lens. The whole process takes just over half an hour. This gives acceptable results with 30 seconds exposure at 200mm.
200mm f/6.3, ISO 200, 5 min.
Single frame of 300 sec.
Made bold by success with 30 seconds, I push the capabilities of the new motor and my skill at aligning to try five minutes per exposure.
200mm f/6.3, ISO 200, 40 min.
8 x 300 sec. frames stacked in DSS.
After a few tweaks in Photoshop, this stack of 8 frames of 5 minutes each looks pretty good.