help with telescope

[jayconnor]

ok needing a little advice.

I have a Bintel BT200 f/5 scope that's quite banged up.
I have moved house 3/4 times over the 5-year period I have owned it and it's needing to be replaced.

Now im looking at buying the BT200 f4. is there a big difference between the f/4 and f/5 scope in terms on astrophotography wise?

just can't get my head around it all at the moment.

Thanks in advanced.

[jayconnor]

i take it the f/4 lets more light in?

[Merlin66]

Jay,
It's the size of the main mirror that defines how much light gets in.
So, both the 200mm f5 and the 200mm f4 will receive the same amount of light.


Simplistically, the difference is that the f4 "concentrates" that light into smaller images, hence they can look brighter.


"Faster" optics like an f4 put demands on the eyepieces - better eyepices are required, which usually means $$$

[jayconnor]

thanks kindly

[Startrek]

Jay
Collimating the f4 will require more skill and effort than the f5, there’s no argument about that
I’ve used my Bintel 200mm f5 for over a year now and has plenty of light grab , can image magnitude 9 to 10 galaxies
I was awarded image of the month for April across Australia by Bintel using my Bintel 8” f5 newt
Image attached
Go for the f4 if are worried about a little bit of extra weight on your mount ( 2 kg ) but my recommendation as a beginner go for the f5 mate you won’t regret it

Cheers
Martin

[astro744]

Visually f4 is very demanding on eyepieces and you definitely need a coma corrector, (and at f5 if you are picky). However the OP did not ask for a visual recommendation, rather a photographic one. Put simply f4 is faster than f5 and in photography and astrophotography speed is desired, (f2 seems to be a goal of many).

An f4 telescope is photographically faster, is capable of a wider true field for the same aperture, is lighter, but does requires a better structure keep it in collimation. It is perhaps a good choice once some experience is built up with an f5 telescope first. Photographically both require a coma corrector.

I found the following discussion on this forum some years ago. See http://www.iceinspace.com.au/forum/showthread.php?t=88094

[jayconnor]

thanks all so much for the comments.

i went with the F4 i have a Baadar coma corrector already also.

So now all that im struggling to get my head around is these f***ing clouds :lol: can anyone help with them? :lol:


P.S Martin that is such a nice image and what im aiming to achieve

[jayconnor]

great thread you sent me too. thanks for that mate.