RASA 11 ????

[Catanonia]

So back into the hobby after 10 years and typical of me, I go and buy big (lucky I can, although bank balance does not agree)

Well since June, I have been getting some great images on the rasa 8, but there is this nagging thought telling me I should have got the rasa11

So with a ZWO2600 MC Pro and a rasa8 in Bortle 6 skies, would I actually see any difference with the 11inch version of the rasa11 ?

If I would, what would the differences be other than the slightly longer focal length and F2.2 compare to the 8's 2.0

I understand that 3 inches more = more light gathered, but in my skies, is it actually worth it (ignoring the cost) ?

Thanks

 

[Whirlwind]

It depends on what you are trying to achieve.  Although it is larger the f ratio is similar; you are hence just spreading a similar amount of light per pixel (as the focal length is increased), you won't get brighter images because of it.  All you will be doing is increasing resolution at the expense of the field of view.  To capture the brighter image you would need to bin the pixels (but it is OSC camera so isn't really relevant here as you will lose the colour data). 

[Catanonia]

@vlaiv Any thoughts on this buddy as you are normally very hot on these topics

Thanks

Edited January 14, 2022 by Catanonia

[vlaiv]

I like bigger scopes as it usually leads to (potentially) faster system.

Although there is this notion that F/ratio of telescope is what determines the speed of system - that is not quite correct, and I like to view it like this:

Speed of the system is aperture at resolution.

Given certain resolution - or sampling rate - larger aperture simply wins. Problem starts when people try to compare two different apertures at two different resolutions. There is way to compare those as well - but it is a bit more involved.

If you don't change camera and just go for larger scope - in this case slower scope in terms of F/ratio - well, you'll get slower capture.

Another thing to consider is if scopes are diffraction limited in the first place and will there be some resolution improvement in if you switch the scopes.

8" scope at 400mm focal length will have diameter of airy disk of 2.5µm

In my view pixel size of 3.75µm of ASI2600 is simply wasted on RASA - you need to bin x2 at least.

RASA11 is corrected over larger field compared to RASA8 - that might be important for ASI2600 sized chip - which has diagonal of 28.3mm, however - there will still be a need for flat fielding which is not very feasible with RASA systems

At 11" F/2.2 Airy disk is 2.7µm - so again not diffraction limited and need to bin at least x2.

I'm not very big fan of RASA scopes for imaging, so I can't really advise properly - but for me it really comes down to FOV - do you like FOV of RASA8 or would you like slightly smaller FOV of RASA11 while keeping same number of pixels in the FOV without oversampling (~3000 x 2000 px)

[Catanonia]

On 14/01/2022 at 21:18, vlaiv said:

Loads of reading

Thanks buddy, will take a bit to read / re-read and process