Optical window or just use the MFR-3?
Posted 10 January 2008 - 07:11 AM
My second question is, do you guys know what f ratio for my f/4.9 becomes with the MFR-3, then with the MFR-3 and the 5mm extension ring, then with the MFR-3 and the 5mm, and the 10mm extension rings? I've never been able to figure this stuff out, and this is actually the first time I've used a focal reducer on my DOB. Thanks for your help.
Still no sucker holes for my first light.
Posted 10 January 2008 - 07:19 AM
On my 8' f/4 Newtonian, I don't need or use an MFR-3. I do use the Optical Window to help isolate the cooled CCD sensor from the moisture in the air.
If you are using the MFR-3, you don't need the Optical Window.
Posted 10 January 2008 - 07:26 AM
Any Idea, of how to find out what my f ratio would be with the rings? Is there a chart or something?
Posted 10 January 2008 - 07:32 AM
Look at the graph I posted in the MallinCam Group Files section:
It shows the effects of adding the MFR-3 and spacers to the camera. Based upon Greg Stones measurements on images he took, I developed the graph.
Your f/4.9 scope changes to f/3.8 with just the MFR-3.
It becomes f/3.5 with the addition of the 5mm ring.
It becomes f/3.2 with a 10mm ring.
With 15mm of extension it becomes f/3.
Again this is all based on measurement data Greg obtained by taking images with different camera-focal reducer-ring combinations and then measuring the separation of certain stars on prints.
Posted 10 January 2008 - 01:14 PM