Best DSLR or ILC for Night Sky Imaging?

Started Nov 8, 2017 | Questions thread
Trollmannx Senior Member • Posts: 5,467
Re: If you want the best, a dedicated cooled CCD cameras are far better than all the DSLRs and ILCs
1

kiwi2 wrote:

JimH123 wrote: One thing you are leaving out and that is stars are point sources of light, not extended objects. For them, the size of the objective, or mirror, is what is important, not the f-ratio.

Are the dpreview test scenes point source or extended objects? Perhaps you should explain the difference to Roger.

Migh be a good idea to read what Roger said one more time...

If anyone here is familiar with photons is is Roger - actually a real life astronomer!

rnclark wrote:
"DPreview changes focal length while keeping f-ratio constant. That means lens aperture area changes between cameras, thus the light delivered to the sensor is changing, and that means the amount of photon shot noise is different due to the lens, not the sensor.

Here is a shot of m31 taken with an Orion 8" Astrograph, a 800mm newton type scope with a f3.9 ratio. This image was done using the Sony Multi-frame Noise Reduction (6 images) for 25 sec each and ISO 3200 where the camera combines in camera with the result having much less noise. Since it is this Multi-Frame Noise Reduction, it could only be captured in JPEG. And because it was JPEG, it is not possible to do very much with the image and it is only lightly processed.

What you should see is that the 8" mirror does make the galaxy show up better than I was previously doing using the 300mm f2.8 lens at f3.2. Although I admit the the 300mm lens was using a lower ISO 800 for the same 25 sec. But it was heavily stretched.

So you went from 300mm f/3.2 to 800mm f/3.9. That's half a stop difference.

Yes - but there is another variable, aperture.

You then also went from ISO 800 to ISO 3200. That's two stops difference.

ISO does NOT change the sensitivity of the image sensor - just amplify the existing signal.

You are now recording more light with more magnification over a larger area of the frame. Of course it's going to look better.

The key here is more light...

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