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Old 09-09-2011, 01:25 PM
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MortonH
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Confused about flatteners and spacing

I have a 70mm f/6 ED scope that I'd like to try some imaging with. I understand that a flattener is pretty much essential, but don't quite understand what spacers, if any, I would need (I haven't even decided which flattener I would get).

Can anyone give me some examples of their own gear? I'd be using a Canon 30D.

Thanks

Morton
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Old 09-09-2011, 02:55 PM
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DavidTrap (David)
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Most flatteners have a recommended distance between the flattener (usually measured from the the thread starts, not the edge of the flattener) and the imaging plane. The distances for Canon's are ~45-46mm (have a look on google). You need to allow the thickness of the T-adapter as well (usually about 10mm). Therefore a standard DSLR & t-adapter will give you a minimum of 55mm from back of the flattener to the imaging plane.

Varying this distance changes the "focus" of the flattener and usually the degree of "reduction". Get it right and you'll be a happy astrophotographer. Get it wrong and you'll look like you're in the cockpit of the Millennium Falcon
as hyperdrive is engaged.

DT
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Old 09-09-2011, 02:56 PM
gbeal
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Might pay to be a bit more specific about the 70ED Morton. If it's the Stellarvue, then maybe ask Vic himself, he should know.
In my case, as far as flatteners go I've had good success with an AstroTech AT2FF, and have used it on a variety of refractors, currently on a W/O GT-81, and a Lomo 102/650. For a reducer I have had success with the Televue TRF2008. AT2FF is happy about 56mm, the TRF2008 seems to like being about 50mm, weird I know.
Gary
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Old 09-09-2011, 07:00 PM
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hotspur (Chris)
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re flattners

Would like to learn more about these too,and how to install them etc,I am using a F 7.7 103mm refractor.Tony did a very nice image of 'coat hanger' and comet,recently-so would like to try something like that one day-If I can ever get my AG working properly.

How much are the flattener things and what do the look like?

Alternatively-I could use a 400 mm lens I have for those wide shots.but it would mean a lot of stuffing around taking main scope off and putting stuff back on a plate etc.
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Old 09-09-2011, 07:31 PM
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MortonH
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Quote:
Originally Posted by DavidTrap View Post
Most flatteners have a recommended distance between the flattener (usually measured from the the thread starts, not the edge of the flattener) and the imaging plane. The distances for Canon's are ~45-46mm (have a look on google). You need to allow the thickness of the T-adapter as well (usually about 10mm). Therefore a standard DSLR & t-adapter will give you a minimum of 55mm from back of the flattener to the imaging plane.

Varying this distance changes the "focus" of the flattener and usually the degree of "reduction". Get it right and you'll be a happy astrophotographer. Get it wrong and you'll look like you're in the cockpit of the Millennium Falcon
as hyperdrive is engaged.

DT
So if a given flattener requires a certain distance (or small range of distances) and the distance from flange to sensor is obviously known for any given camera (plus width of T-ring) then the 'spacer requirement' should also be known. Seems like there should be a list of cameras and required spacing with each flattener, but they don't have them with any online adverts. They simply show a picture of flattener + T-ring + camera. Should it be that simple???
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Old 09-09-2011, 07:37 PM
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Quote:
Originally Posted by MortonH View Post
Seems like there should be a list of cameras and required spacing with each flattener, but they don't have them with any online adverts.
The Astro-Tech flattener ad has this information on the Astronomics website. Finally it makes some sense.
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Old 10-09-2011, 11:23 AM
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DavidTrap (David)
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The Televue flattener/reducer tells you the distance ~55mm. Problem is, unless the scope and flattener match, the degree of correction may not be what is required for your scope. I've not tried it, but varying from the recommended distance might achieve better correction of field curvature. What we need is a "variable spacer" - like a helical focuser?

Unfortunately buying a flattener for a scope (unless their a matched pair) is a bit like Forrest Gump's box of chocolates!

DT
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