Smaller sensor or longer focal length

[geordie85]

I'd like to start going deeper with my images and getting more detailed images. I currently image with a WO star 71 and atik 383l which gives me a nice wide-field fov but the detail can be lacking.

Would I be better off imaging with a smaller sensor ccd like the 314L or using my 383L with a longer focal length scope?

After a little playing around on a FOV calculator I really like the FOV with my current scope and a smaller sensor but would my images be lacking in detail still since the star 71 is quite a wide field scope? 

[gnomus]

You need to look at the imaging resolution.  X arcseconds per pixel is X arcseconds per pixel irrespective of your sensor size.  In fact the 314 pixels are a bit larger than the 338, so you would get more resolution from the camera you already have.  It would be a very expensive way of cropping, that's all.

[Alien 13]

Longer focal length would be best, most cameras have pixels far to big to get the best out of short fl like the star 71.

Alan

[Tim]

Lots of factors to consider here, and more than just what is immediately obvious.

What resolution in arcseconds are you imaging at with the 383?

Longer fl will take you closer, but you will only benefit if your target, and your mount, and your guiding, and your typical seeing allow you to make the most of the available increase in resolution. To iron out the fliers you need extra data, = more exposures. You need to target DSO's out of the worst of atmospheric distortion, or high overhead, again cutting your time on target and limiting some of them.

Personally, I find a focal length around 1000mm and imaging resolution in the 0.7 - 1 arcsec/pix region to be a useful compromise for typical (poor) UK skies. But as mentioned, there is more to it than simply looking at numbers in a FOV calculator!

Hope that helps

Tim

[ollypenrice]

As the others have said, a smaller chip is just a smaller chip. A given scope projects an image of a certain size in mm onto your chip. As long as the chip is big enough to accept all that projected image the chip size has no effect whatever on the level of detail, or resolution.

The way to get more detail is either to use a longer focal length or smaller pixels. If you use smaller pixels you will put more pixels under the projected image and, since at 'full size' screen presentation one camera pixel is given one screen pixel, you will get a bigger image on the screen.

Now, as Tim says, it may be bigger but will it be more detailed? That depends on whether the seeing and the guiding are allowing you to catch those details without them being smeared out.

Whatever you do, don't buy a smaller chip with bigger pixels to give you more detail than a bigger chip with smaller pixels. It will do the very opposite!

Olly

[geordie85]

Thanks for the advice. I guess I'll be in the market for a new scope soon.

[alacant]

Hi. I had 800mm as maximum fl and got to the stage where dsos looking like small blobs wasn't good. I got a 150mm f8 Newtonian with 1200mm fl. Well worth it; on nights when the seeing allows the guiding, it does the trick. On my dslr, you need no filters or correctors. HTH

[geordie85]

Thanks alacant. I'm busy looking into the skywatcher espirit 120ed at the moment, albeit a bit pricey. In fact a new 120ed costs more than my car. 

[Astrosurf]

Have a look at this thread. The SW150P-DS or 130P-DS look overall very good and are quite light. I love my 200P for imaging smaller DSOs but you need a very calm night! And it's at the limit of what my HEQ5 Pro mount can hold, with all the gear. What mount do you have?

Alex

[geordie85]

4 minutes ago, Astrosurf said:

Have a look at this thread. The SW150P-DS or 130P-DS look overall very good and are quite light. I love my 200P for imaging smaller DSOs but you need a very calm night! And it's at the limit of what my HEQ5 Pro mount can hold, with all the gear. What mount do you have?

Alex

I've viewed both of those threads from the beginning, thanks for pointing them out though.

I have an Neq6 so my load capacity isn't a problem, but wind is and since I have a west facing garden I get alot of wind. I also have a 200p that I mainly use for planetary imaging since I sold my coma corrector. I'm not a massive fan of the diffraction spikes a Newt produces. Although a new coma corrector will be a hell of alot cheaper than a new scope. 

But come on. A new scope is so much fun from answering the door to unpacking, first light to first finished image.