Deep sky astrophoto with the GM 100-400 mm lens

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Magnar W
Magnar W Veteran Member • Posts: 5,080
Deep sky astrophoto with the GM 100-400 mm lens

How good is the Sony GM 100-400 mm telezoom lens for astrophoto when mounted on a small tracking platform? In fact pretty good, with smaller and rounder stars than the Minolta 400 mm f:4.5 apo telephoto lens. Not as fine results as with a small apo refractor telescope made for astrophoto, though, but good enough to get respectable results.

This setup, the A7rIII and the GM long zoom lens wide open at 400 mm, attached to a first generation Astrotrac star tracker, is my choice for low end deep sky astrophotography - possible on a pretty tight budget if you already have the camera and the lens.

I was a bit abot worried about how manual focus would turn out with this "focus by wire" lens, but after a test with the M13 global cluster, I have to say it was pretty easy to get good focus with magnified view at highest magnification. At least focus was within how much stars are smeared out by turbulent air at my location.

Up here north we also have to fight the cold nights. During exposure everything was soak wet by dew after a short period, and I lost some frames because dew froze to ice and blocked the tracker drive ...

What else to say? Great fun!

Andomeda galaxy. About 60 frames, each 30 sec., to a total exposure of 30 minutes.

The Pleiades, with a lot of dust and gas. 60 exposures, each 30 sec. stacked to a total of 30 minutes.

A nice focus test, the M13 globular cluster in Hercules. 60 exposures, each 15 sec., stacked to a total of 15 minutes.

And one taken with the 85 mm Loxia lens of the Nort America nebula/Cygnus region of the Milky way  (the brightest star is Deneb) - just for those who want to find out the exact number of stars framed here.

 Magnar W's gear list:Magnar W's gear list
Sony a7 Sony a7R III Sony FE 90mm F2.8 macro Zeiss Loxia 21mm F2.8 Zeiss Loxia 35 +2 more
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