C100EDR or Skywatcher 80ED Pro?

[samir_ansari]

Hi Guys and Girls,

Which of these scopes would you all say was best for imaging of DSO's? I have been offered a C100EDR second hand for a fair price but am unsure if I should go for it or just get a brand new Skywatcher. I understand the C100EDR has a slower F-speed but has more light gathering ability, will this help all that much?

[michael.h.f.wilkinson]

Both are good scopes. Visually, the C100EDR would be the clear winner, but in imaging a faster speed is useful. The Skywatcher requires 1.44 times less exposure time to image the same surface brightness objects. Also, the longer the focal length makes the guiding of the Celestron more critical. However, if you want to image smaller objects such as planetary nebulae, the C100 has the edge.

[samir_ansari]

So even with the extra 20mm of aperture it will still not really do much to close the gap between the F difference of the two scopes?

[michael.h.f.wilkinson]

The aperture makes a difference when imaging stars (which appear as points) but not when imaging extended objects. This is because the increased amount of light is spread out over a larger CCD sensor area. Of course, if you use a focal reducer on the Celestron, you may get the same F/7.5 focal ratio of the ED pro, and then you would require the same exposure time as the ED pro. However, the image would be larger. The increase in the number of photons will be reflected in the size of the image, not the brightness.

[samir_ansari]

ah ha, I see - that makes sense. Thanks very much for your help!

[samir_ansari]

In the end I went for the C100EDR. Still waiting on the cloud to clear before getting first light with it but just looking at it from across my sitting room is satisfying enough!

[michael.h.f.wilkinson]

Sounds nice. Let us know when you have first light.

[samir_ansari]

Ok, I didn't want the clouds to defeat me so instead I pictured a block of flats about 5 miles away.

I'm quite pleased with the result I must say. And sorry if you are one of the people who live in any of those two rooms!

[michael.h.f.wilkinson]

That's impressive! The result really looks excellent.