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Focusing with a filterwheel
Guys
Sometime ago, I asked a few questions about imaging with a DMK21 and getting it into focus with a filterwheel, etc. Well, I purchased the filter wheel and I thought I would share some stats with you. Maybe someone will find it interesting. Then I will have some questions.
I have an 8 inch Skywatcher, with a Crayford focuser
There is a total of 40mm draw on the focuser
Now with the DMK at prime focus I have 10mm of inward travel remaining on the focuser.
with a 2x barlow - 19mm of inward travel remaining
with 3x barlow - 34mm of inward travel remaining
with 5x powermate - 35mm of inward travel remaining
When I include the filterwheel (the Orion advertised as requiring an additional 20mm of focus travel), things don't work out as expected.
With the 2x barlow, I move the focuser in by only 6mm, leaving 13mm of inward travel
With the 3x barlow, I don't need to move it much at all - in by about 1 or 2 mm.
I would have thought that in each case I would have had to move the focuser in by 20mm at least. I don't understand.
The equipment was configured as
telescope; barlow; filterwheel; dmk
Darrell
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