Orion with astrotracer miscalibration fix

Started Dec 10, 2017 | Discussions thread
OP Polacofede Contributing Member • Posts: 980
Re: Congrats!

chris gunn wrote:

Polacofede wrote:

chris gunn wrote:

looks great to me!

I think I copy and pasted in Trapesium here!

definitely a lot to catch up for me, will re read an investigate about the topics you mentioned.

Here's another image by a guy who has been improving a lot recently, using 30s frames and 300mm (1.7 hours worth) at ~f5.1 (he used a step down ring).

wow looks impressive, and the exposure time is something i think i can reach, encouraging. Maybe it would be worthy to try with the DA*60-250 at 260mm @f5.1?.

i'm using much lower ISOs like 400 - 640. As you can bring things up later is there any need of higher?

If I understand it correctly, higher ISO helps separate your desired signal from sensor noise. With a large light range subject like Orion it can be nice to have the larger dynamic range of lower ISO.

RN Clark has a good section on this.

I have re read ClarkVision

"Use of lower ISOs than about 1600 on many camera does not amplify the weak signals enough to get them above downstream electronics noise (Nikon and Sony are exceptions--ISO 800 works well too).


It is best to image at the lowest ISO that gets above those noise problems from camera electronics and no higher. That gives the most dynamic range to keep star colors in the brighter stars. ISO 1600 is a good compromise on most cameras. You'll see that I use ISO 1600 for most of my nightscapes and astrophotos.


Often with Orion people use equal numbers of short and long exposures to get the dynamic range.

What is the step down ring for?

To get better star shape. I forget, but I think he had some internal reflections and unwanted spikes/shape from the aperture diaphragm.

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