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Old 18-02-2005, 11:13 PM
rowena
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focul reducer

Is anyone using a focul reducer when they are doing astro pics? do you prefer to use it or not? are u using the F/6.3?
Did you buy it in australia or from overseas? I see they are around the $275-300 AU mark in australia, but $115 US, which equivlates to around $150-160AU plus postage.

(Focul reducers reduce the amount of exposure you do for a photo as it reduces your focul length)

Rowena
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Old 18-02-2005, 11:35 PM
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[1ponders] (Paul)
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Hi Rowena.

For the few deep sky I've taken I've used a 6.3 focal reducer. It has a considerable effect on exposure time. This is a quote from Astro Photography by HJP arnold.

:quote:
To give an example: an exposure of f/8 at 1/125 of a second is equivalent to one of f/11 (one stop less light) at 1/60 of a second (one shutter speed more time), And also to one of f/5.6 (one stop mor light) at 1/250 of a second (one shutter speed less time). :end quote:

So everytime you double your f/ratio (5.6 to 8) you double the exposure time., or halve your ratio (8 to 5.6) you halve your exposure time. From f/10 (if tha's what your telescope operates at?) to f/6.3 is a strange ratio as it doesn't conform to the standard camera f/ratios the results are very similar (though it is a common astronomical/telescope ration). That is you will end up roughly halving your exposure time. Hence the benefit of a 6.3 reducer.

However if you're using an already fast scope (f/6 or 5 or faster) the focal reducer may have strange effect on your images, depending on your type of scope.
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Old 18-02-2005, 11:54 PM
rowena
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mine is a F10, the celestron G5, 5" scope.

i figured the reduced exposure time is a good thing!
specially as i'm still learning to set up the south celestrial pole correctly, and even if its slightly off, then you still get movement! the joy of doing everything manually!


Rowena
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Old 19-02-2005, 12:10 AM
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Hi Rowena, There are a couple of guys in our club that would be glad to help out, if you like. One is a prof. photographer, but loves Astronomy as well.
*www.rudiphoto.net*
His name is RUDI.
Just the facts m'am.
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Old 19-02-2005, 01:10 PM
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I know what you mean about the polar aligning. Fun/frustrating/challenging isn't it. Try it using a Meade where you have to sit on the ground under the telescope (cause its upside down at -90 degrees dec) trying to align through the finderscope until its very roughly aligned. Wht alignment technique are you using?
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Old 19-02-2005, 01:41 PM
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Hi Rowena , I use the Celestron F6.3 reducer on my C11 and C8
it works well with one small problem you will find with 35mm film that you will get some vignetting, this is when the corners of the frame don't get enough light, but it's not a problem you just crop the image. I bought mine from OS cost about $169.00 .
Another hint to get a good polar alignment start with a compass , I have the compass on a length of wood so it's about 1m away from the mount, as long as you have the deviation set right on the compass you should be able to get very close to the pole within 1degree at least.It's simple to do just find a flat spot on your mount and then place the wood against it and move the whole mount till the compass arrows point north or south whichever you use.
When you get this far you then use your polar finder if you have one or do a drift alignment.

regards
David
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Old 20-02-2005, 11:36 AM
rowena
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Hi David,

It sounds very similar to what I'm doing.

I think I will get the focul reducer. very worst, if i dont like it i can sell it on ebay

Rowena
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Old 20-02-2005, 12:34 PM
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hI Rowena, I don't think you can go wrong, they work well and allow you to get those large DSO's on the film plane,the f6.3 is also good for visual, makes my C11 a different scope. should give you a nice FOV in the 5"
beware the F3.3 is only for CCD and not film or visual.

David.
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Old 20-02-2005, 01:17 PM
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Rowena.
If you haven't already committed, perhaps consider the Mogg. It is made for a 2" focuser (not sure what you are going to use it on), and it has a T thread at the rear, for a DSLR (again not sure what you will use it on).
They are made in Aus, and are priced at about US$75.
Gary
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Old 20-02-2005, 01:23 PM
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Dave I'd be interested in knowing how you attach your eyepieces to the reducer. Mine is threaded both ends. Is there an adapter available for this purpose?
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Old 20-02-2005, 01:35 PM
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Rowena, I have purchased the Focal reducer for my LX200 from overseas...it should be delivered early this week...it cost me $129 USD.......cant wait.
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Old 20-02-2005, 02:06 PM
westsky
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Hi Paul the visual back from the C11 just screws onto the FR , then your diagonal or straight through whichever you use .
so it's scope /FR/visual back/diagonal/EP

David.
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Old 20-02-2005, 02:08 PM
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Hi,Tony how much was shipping?

David
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Old 20-02-2005, 02:12 PM
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Ok so I'll have to go "scope - FR - microfocuser connector ring - microfocuser - star diagnal - eyepiece" Hope I've got enough room in the back yard That's on of the things with the meade, I'm not sure how that will affect the overall back focus. Guess I'll just have to try that oldest of scientic principles - suck it and see :/

thanks
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Old 20-02-2005, 02:15 PM
westsky
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Hi Gary I have the 1.25 Mogg FR, unfortunatly it doesn't work on SCT's as well as on other scopes.
The SCT FR also flatens the field ,its a reducer and correcter designed for SCT's.
The Mogg FR I have is great on refracters and newts but I get too much curviture on my SCT.

David.
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Old 20-02-2005, 02:18 PM
westsky
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Paul the difference in focusing should be around 4 full turns of the focuser, don't know about the microfocuser as I don't use one.
I guess you will have to try it and see.
David.
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Old 20-02-2005, 02:23 PM
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David do you notice much difference visually using the FR and is there much vignetting/reduction in the real field of view?
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Old 20-02-2005, 02:53 PM
westsky
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Paul, Visually the FR is fine it's only on 35mm that I see vignetting.
the change in FOV is substanstial, at F10 on Eta Carina I see maybe 2/3rds of the Neb, at F6.3 I can fit it all in the fov with a 20mm ep

David
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Old 20-02-2005, 03:08 PM
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Right, if this cloud will only bugger off I'll give it a try tonight
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Old 20-02-2005, 03:11 PM
westsky
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Be carefull you will get hooked on the F6.3 view, I seem to use the FR visually more and more.

David
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