First Jupiter from the C9.25

[tyco]

WOW, Great Image

[Christopher Davenport]

Good point James, though this short nosepiece and profile on the QHY5L-II does work to my advantage allowing me to image down to about 3.4x using the Revelation 5x barlow which is very close to the optimum F16.5 quoted for the 3.75um pixels.      The image train like this is considerably more solid and I have the option to slide the camera out to get 4.6x (F23) should we ever get some of the near mythical excellent seeing.

Jake,

Very interesting indeed. Makes me think I should get a 5x barlow for the same purpose.

Where did you get the F16.5 from for the cam?

I was reading on Damien peach website that f30 is ideal for Jupiter. If that's the case what size is the ideal cam UM?

And I bet that cam must cost a fortune!

[Christopher Davenport]

I meant 3x Barlow as my 127 is F11 already.

[rob0971]

Great work James. I am thinking of getting a sct for planetary/lunar & maybe a bit of tiny DSO work & the c9.25 keeps coming up. I have also thought about a c11 but the smaller scope seems to be the favourite at the moment.

[JamesF]

I believe the f/30 figure was relating to cameras with a 5.6um pixel size.  Martin Mobberley's webcam imaging book suggests IIRC that some people such as Damian Peach were even working towards f/40.  The figure comes from working out what is required for the resolution of the camera to match the resolution of the scope.  Somewhat unexpectedly to me when I worked through the maths for that it fell out that this is achieved at a given focal ratio regardless of the telescope in use; it depends only on the pixel size of the camera.

So, if f/30 is correct for a 5.6um pixel size then f/20 is about right for the 3.75um pixel size of an ASI120, for example.  I used to try to get to f/35 with my SPC900 (5.6um) pixels and anywhere from f/20 to f/25 with my ASI120.  A bit one way or the other is hardly going to make a lot of difference.  Michael Wilkinson and I have, well, I wouldn't even consider it as strongly as a difference of opinion, to be honest.  I used the diagonal size of the pixels in my calculations for what seemed to be good reasons and he uses the edge length in his, giving a lower figure than mine.  He's far more qualified in this area than I am; I just need to think it through to understand why he's right

If you're imaging with the QHY5L-II then I'd not worry too much about whether you're using, say, a 1.6x barlow and getting f/19 or a 2x barlow and getting closer to f/24.  Even a 2.5x wouldn't be that bad.  I'd choose a decent quality barlow with a slightly higher factor over lower quality one with a smaller factor any day.

Is there an "ideal" camera?  I'm really not sure.  Whatever gives most sensitivity for reasonable amounts of cash, I guess

James

[Space Cowboy]

I remember in my imaging youth I was shooting Jupiter at f50 with the 127 and spc900 but I would not recommend that as a rule of thumb. I do think the maks can be pushed more than a fast newt. Provided seeing is good enough you can attain better focus on a larger image I reckon, then downsize it after stacking. Mars is a good target to try this on.

[Christopher Davenport]

If you're imaging with the QHY5L-II then I'd not worry too much about whether you're using, say, a 1.6x barlow and getting f/19 or a 2x barlow and getting closer to f/24.  Even a 2.5x wouldn't be that bad.  I'd choose a decent quality barlow with a slightly higher factor over lower quality one with a smaller factor any day.

Interesting stuff, just did your FStop Calcs on my Jupiter image and I come just below F20 on my 127. (i.e my 2x Barlow is running at x1.6)

They way I have connected it is QHY5L -> Extension -> 2x Barlow lens (screws directly in same as a filter and rock solid)

I am thinking that I may extend the extension to increase the FStop upwards and experiment with Jupiter at higher F-stops.

My thinking is that a 3x Barlow (reduced due to the extension distance) will produce x2.6 

With my current F11.8 this will equate to F30.7, which I imagine will be right at the top of what UK seeing and my telescope will handle.

Till my next holiday up the volcano on the Canaries, where seeing is always perfect! 

[JamesF]

Interesting stuff, just did your FStop Calcs on my Jupiter image and I come just below F20 on my 127. (i.e my 2x Barlow is running at x1.6)

They way I have connected it is QHY5L -> Extension -> 2x Barlow lens (screws directly in same as a filter and rock solid)

I am thinking that I may extend the extension to increase the FStop upwards and experiment with Jupiter at higher F-stops.

My thinking is that a 3x Barlow (reduced due to the extension distance) will produce x2.6 

With my current F11.8 this will equate to F30.7, which I imagine will be right at the top of what UK seeing and my telescope will handle.

Till my next holiday up the volcano on the Canaries, where seeing is always perfect! 

I have been wondering if the Mak isn't set up so that the quoted focal length is correct when there's a diagonal in the optical train -- effectively as though you had another 60mm or thereabouts before the barlow.  I might try that one day.

James