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Old 17-01-2020, 02:54 PM
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traveller (Bo)
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Back focus (again)

Just reaching out to the IIS brains trust.

I have a Vixen PH corrector, the stated back focus distance is 56.6mm
https://www.skypoint.it/en/ota-refle...-095x-f38.html

I am using a ZWO ASI1600, which has a 55mm back focus.

Question: Which one should I be aiming for?

I am inclined to go with the corrector spacing (56.5mm) as that would achieve the stated flat field.

Over to you!

thanks
Bo
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Old 17-01-2020, 03:14 PM
Imme (Jon)
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Sensor window to chip face on the asi1600 is 6.5mm from memory.........so you need a 50mm spacer from the corrector to front window (thread) of corrector
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Old 17-01-2020, 03:18 PM
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Merlin66 (Ken)
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As Jon says, it's 6.5mm from the T thread body connection.
See:
https://astronomy-imaging-camera.com...asi1600mm-cool

The mating thread on the corrector is M56 x 0.75 - Ideally a 50mm spacer with female M56 on one end and a female M42 T thread at the other.
Don't know where you'll get a "special" like that......
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Old 17-01-2020, 03:26 PM
Imme (Jon)
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Quote:
Originally Posted by Merlin66 View Post
As Jon says, it's 6.5mm from the T thread body connection.
See:
https://astronomy-imaging-camera.com...asi1600mm-cool

The mating thread on the corrector is M56 x 0.75 - Ideally a 50mm spacer with female M56 on one end and a female M42 T thread at the other.
Don't know where you'll get a "special" like that......
Joshua....that's where you get a special and very well made adapter like that for a reasonable price.

.....if he can pull himself away from building the new Ob's
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Old 17-01-2020, 04:20 PM
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traveller (Bo)
Not enough time and money

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Thanks,
So am I right in assuming to go with the 56.5mm and not the 55mm?

The camera is a mono with a filter wheel (26.5mm used up), so that will take me down to 30mm spacer with m56 female and m42 male.

Any bidders for the 55mm spacing?

Bo
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