F/2 or two mono cameras?

[TareqPhoto]

Hi all,

It is just a simple question and hope i can get the answer as it is a decision according to budget/affordability somehow or the practical logic way.

Which one do you think is faster or you like to do the things assuming you have a target and you need to do for example 4 hours at least per NB filter at average focal ratio?

1. Using very fast scope such as RASA at f/2 [or similar, hyperstar is an example] and giving 2 hours for one filter so you do 2 filters respectively.
2. Having 2 mono cameras so you put one filter in each [one with Ha for example and the other with OIII] and image with each at 4 hours.

If it is my choice i really prefer 2 cameras, i have one already, so i can use those at any different two same scopes rather than i am stuck with one scope at specific focal ratio and focal length and aperture, but i feel like so many love a very fast scope these days, it is like they can afford 1 scope instead of 2 cameras maybe, i am not sure, but if you prefer one method or option above then please can you give me a reason or explain why so i know how to choose?

[wimvb]

A slower system with two cameras any day. F/2 requires special filters, and you'll be adjusting/tweaking the system so much, you won't have time to do any imaging. 

[TareqPhoto]

1 hour ago, wimvb said:

A slower system with two cameras any day. F/2 requires special filters, and you'll be adjusting/tweaking the system so much, you won't have time to do any imaging. 

I agree, i tried with my Canon 135mm F2 and it never made it shorter, i ended up with many issues and i still use one filter per time, so even with that i was dreaming about having another camera so i don't waste time with one lens or optics and camera for each filter, but i asked as i see that RASA and similar such as Hyperstar are getting popular, so i wanted to know the secret, the one who can afford a RASA should be able to get 2 cameras instead, so that i asked first.

In addition, how much slow is slow, is it because it isn't F2 then it is slow? I mean is F5 slow or F4 or even F3.5?

[wimvb]

I would feel comfortable with f/4 or above. But I have some experience with collimation, and I wouldn't care too much if stars weren't perfectly round in the corners. It depends on what you feel ok with. For me, the limit probably lies at around f/4. Filters otoh, especially narrow band, will have poorer performance in fast systems. The better ones may work down to f/3 at best. Below that, the light cone becomes so steep, that the filter characteristics are noticably affected. 

There is no one firm limit between fast and slow, and what is considered fast, depends also on the telescope model. A f/5 rc or sct would be considered a fast one. A f/5 newt not, even though they are equally fast.

With a faster optical system, you can shorten the single sub exposure time. After all, more light per unit time is collected on each pixel, either because of a larger aperture (yay!) or because of a lower "resolution". But I think that if you do a search on astrobin, you most likely won't find a substantially shorter integration time for "faster" systems. My guess is that people will still use the available time, but get better (higher snr) data.

[TareqPhoto]

3 hours ago, wimvb said:

I would feel comfortable with f/4 or above. But I have some experience with collimation, and I wouldn't care too much if stars weren't perfectly round in the corners. It depends on what you feel ok with. For me, the limit probably lies at around f/4. Filters otoh, especially narrow band, will have poorer performance in fast systems. The better ones may work down to f/3 at best. Below that, the light cone becomes so steep, that the filter characteristics are noticably affected. 

There is no one firm limit between fast and slow, and what is considered fast, depends also on the telescope model. A f/5 rc or sct would be considered a fast one. A f/5 newt not, even though they are equally fast.

With a faster optical system, you can shorten the single sub exposure time. After all, more light per unit time is collected on each pixel, either because of a larger aperture (yay!) or because of a lower "resolution". But I think that if you do a search on astrobin, you most likely won't find a substantially shorter integration time for "faster" systems. My guess is that people will still use the available time, but get better (higher snr) data.

Sounds for me that i should go with a second camera then and anther same scope i have and call it a "NIGHT", maybe i can't afford a very fast scope now from Celestron so i better not wait until that happen and go with second camera, and yes, you added a valid great point, i have Astrodon filters, i don't think i will replace those, so maybe those filters are still not good enough with very fast F/2 scope, means i have to forget about F/2 scope now.