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Old 28-07-2008, 04:52 PM
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Tilt (Michael)
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Is f/7.5 too slow for imaging? - ED80

What do you think?

Or should I get a WO 0.8x FR/FF.

I intend to use a 350D with this scope.

Michael
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Old 28-07-2008, 05:05 PM
Ian Robinson
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With low noise , high sensitivity DSLRs and CCD camera , it should be OK.

The 0.8x FR/FF wont hirt the image quality and will get you a wider FOV.
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Old 28-07-2008, 05:49 PM
gbeal
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No way, not at all. I sometimes image with my ED80/840 refractor, so f10.
Try it, with and without the reducer.
Gary
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Old 28-07-2008, 06:22 PM
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iceman (Mike)
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The WO is handy to have. You don't HAVE to use it every time.

But helping to flatten the field is a big plus.
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Old 29-07-2008, 04:00 PM
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Tilt (Michael)
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Quote:
Originally Posted by iceman View Post
The WO is handy to have.
I'll get one so I have both options available.

<what's that over there? wife looks yonder while I quickly make the order for the WO 0.8x>

Thanks for the feedback guys


Michael
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Old 29-07-2008, 06:17 PM
TrevorW
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A smaller f ratio allows a greater amout of light to be gathered in a shorter period of time but the amount of light gathered overall is dependent upon aperture. So in answer to your question no a f/7.5 lens is not to slow to do imaging
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Old 29-07-2008, 11:03 PM
Zuts
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Hi,

Mike at Bintel gave me an interesting article which says for a given aperture, the F ratio makes no difference to the amount of time it takes to take a sub of the same brightness. The article states that for film this is not the case. For CCD's however the brightness of the image is purely dependant on the number of photons hitting the CCD. Since this only changes with aperture the F ratio doesnt matter as far as brightness is concerned.

This means you can wack a 2 by powermate on your F7.5 and go to F15. This will give you a very good image scale and you can continue to take the same number of subs as you took at F7.5 or F6 with the reducer. Of course it will be far harder to guide and you cant increase the resolution.

However it is an interesting experiment for a small scope; and may negate the need for moving up to say a VC200L. When the weather clears this is an experiment I would like to try out.

Guiding at F28 on a Televue 85 with a 4 by powermate will probably be horrible. However a TV85 is a light scope, it's unobstructed and no harder to guide at F28 or 2.4 meters than say a VC200L.

Cheers
paul
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Old 02-08-2008, 12:47 PM
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Tilt (Michael)
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However it is an interesting experiment for a small scope; and may negate the need for moving up to say a VC200L. When the weather clears this is an experiment I would like to try out.
Interesting indeed, let us know how you go with that.

Meanwhile, I just got the focal reducer 2 days ago and maybe, just maybe I will be able to have a go tonight. Depending on the clouds.

Michael
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