JohnH
07-08-2008, 10:44 AM
Help please!
I want to get an FR to use with my 127mm F7.5 refractor mostly for use with my OpticStar 145m camera which has a smallish chip and pixels (6.45um), ideally the FR could also be used with my Canon20d.
As I understand it the FR to chip distance is critical to getting the reduction right but this will limit the focus range quite substantially. This might be an issue with the Optictar CCD fitted as it is a mono system and I therefore have a filter wheel in line which limits available in focus to about 2cm.
The 145m has a C thread and I have a 1.25" nosepiece and a C to T adapter. I have a T ring for the Canon also so ideally I want to use a T thread mounted FR as the last step before the sensor.
I am considering the following units:
WO : http://www.williamoptics.com/accessories/flattener3_features.php
Lumicon : http://www.lumicon.com/telescope-accessories.php?iid=LG1080&cid=6&in=2+inch+Thread-In+Focal+Reducer&hn=
Optec : http://www.optecinc.com/optec_029.htm
There is also a Televue unit available but I am confused. Is the multi element design going to give me (much) better performance. I have a single element FR (Vixen) previously and was not that impressed with it. How can I work out the amount of in (or out) focus that will be required. Finally there seems little point in paying for a large format FR to put in from of a 1.25" filter wheel - are the good 1.25" FR options out there ?
Most suppliers are not willing to let me have a unit on sale or return and I do not want to spend $300 without being sure it will work.
I want to get an FR to use with my 127mm F7.5 refractor mostly for use with my OpticStar 145m camera which has a smallish chip and pixels (6.45um), ideally the FR could also be used with my Canon20d.
As I understand it the FR to chip distance is critical to getting the reduction right but this will limit the focus range quite substantially. This might be an issue with the Optictar CCD fitted as it is a mono system and I therefore have a filter wheel in line which limits available in focus to about 2cm.
The 145m has a C thread and I have a 1.25" nosepiece and a C to T adapter. I have a T ring for the Canon also so ideally I want to use a T thread mounted FR as the last step before the sensor.
I am considering the following units:
WO : http://www.williamoptics.com/accessories/flattener3_features.php
Lumicon : http://www.lumicon.com/telescope-accessories.php?iid=LG1080&cid=6&in=2+inch+Thread-In+Focal+Reducer&hn=
Optec : http://www.optecinc.com/optec_029.htm
There is also a Televue unit available but I am confused. Is the multi element design going to give me (much) better performance. I have a single element FR (Vixen) previously and was not that impressed with it. How can I work out the amount of in (or out) focus that will be required. Finally there seems little point in paying for a large format FR to put in from of a 1.25" filter wheel - are the good 1.25" FR options out there ?
Most suppliers are not willing to let me have a unit on sale or return and I do not want to spend $300 without being sure it will work.