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 Post subject: Focal ratio/reducer
PostPosted: Tue Apr 28, 2015 10:35 am 
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Joined: Tue Apr 11, 2006 11:42 pm
Posts: 126
Hello

I wonder if anyone can confirm if I have this right please.
I used to own an 8" Newtonian with a focal ratio of 4.92, I now have an 8" schmidt cassegrain with a focal ratio of 10. Looking back over images I took (some years ago) with the f4.92 Newtonian, it shows a very wide rich field of stars in the pictures using a Meade DSI, now im starting over with the f10 Schmidt cassegrain its showing far, far less stars in the images, its also more of a challenge to get the images to look half decent. So (and im probably stating the obvious I know) is the difference because of the change in f-ratio ? and if I purchased a 0.5x focal reducer does the f-ratio go from 10 to 5 thereby getting back to the view had with the Newtonian ?
And apart from vignetting, would a reducer reduce any picture quality or make it slower to catch light.
Hope that makes sense, thanks.

Below is the focal reducer I was considering for the DSI and eyepiece
http://www.telescopehouse.com/acatalog/ ... 1.25-.html

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 Post subject: Re: Focal ratio/reducer
PostPosted: Tue Apr 28, 2015 6:43 pm 
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Joined: Fri Dec 03, 2004 9:58 pm
Posts: 3258
Location: Wellingborough
This should work for you. I think I'm correct to say that Forum member smerral uses one of these reducers with his Celestron 8SE system, and he has posted a number of images in the Gallery over the years.

I'm sure Brian (smerral) could give some more info and advice on this,

Regards,

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 Post subject: Re: Focal ratio/reducer
PostPosted: Tue Apr 28, 2015 6:58 pm 
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Joined: Tue Apr 11, 2006 11:42 pm
Posts: 126
Hi Brian
Thankyou for taking the time to reply, I will take a look and see how things look.
Thanks again.

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 Post subject: Re: Focal ratio/reducer
PostPosted: Tue Apr 28, 2015 7:02 pm 
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Joined: Tue Apr 11, 2006 11:42 pm
Posts: 126
Sorry bad English

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