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#1
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Focal reducer placement...
I have a 10" F/10 LX200 I've been using for visual observing for a
year now and I've just purchased the kit I need for imaging. (Thanks for advice on the Digital SLR or cooled CCD thread folks! I bought an SXV-H9, True Tech filter wheel, Orion 80ED and SXV auto-guider). I'm keen to continue visual use and want a simple way to switch between modes (i.e. I don't want to reconfigure the optical train each time I switch between CCD and EPs). I understand that SCT-focuser-filter wheel-CCD is the best configuration but that's so long it prevents the OTA from swinging through the forks (no imaging around Polaris and a heart attack if the dec lock comes loose). So I have chosen to mount SCT-focuser-2" diagonal-filter wheel-CCD. I realise this is not the most stable configuration, but I can easily swap the filter wheel and CCD for an eyepiece, and both configurations swing through the forks. Ideal for now, except… I also bought a Meade 0.63 focal reducer. If I mount it on the SCT rear cell, besides being a pain to remove for visual work, it prevents both configurations from swinging through the forks anyway! Not a solution! So my main question is can I mount the FR between filter wheel and CCD or between diagonal and filter wheel? I assume I need adaptors as there's no obvious way to make the connections with what I have. In general, what is the best place to put a FR? Before or after the filters? Close as possible to CCD or close as possible to rear cell? Advice welcome – particularly from anyone else with a 10" LX200 Classic, 2" diagonal, Meade electric focuser, True Technologies filter wheel and SXV-H9 CCD. Cheers Beats |
#2
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Focal reducer placement...
"justbeats" wrote in message m... I have a 10" F/10 LX200 I've been using for visual observing for a year now and I've just purchased the kit I need for imaging. (Thanks for advice on the Digital SLR or cooled CCD thread folks! I bought an SXV-H9, True Tech filter wheel, Orion 80ED and SXV auto-guider). I'm keen to continue visual use and want a simple way to switch between modes (i.e. I don't want to reconfigure the optical train each time I switch between CCD and EPs). I understand that SCT-focuser-filter wheel-CCD is the best configuration but that's so long it prevents the OTA from swinging through the forks (no imaging around Polaris and a heart attack if the dec lock comes loose). So I have chosen to mount SCT-focuser-2" diagonal-filter wheel-CCD. I realise this is not the most stable configuration, but I can easily swap the filter wheel and CCD for an eyepiece, and both configurations swing through the forks. Ideal for now, except. I also bought a Meade 0.63 focal reducer. If I mount it on the SCT rear cell, besides being a pain to remove for visual work, it prevents both configurations from swinging through the forks anyway! Not a solution! So my main question is can I mount the FR between filter wheel and CCD or between diagonal and filter wheel? I assume I need adaptors as there's no obvious way to make the connections with what I have. In general, what is the best place to put a FR? Before or after the filters? Close as possible to CCD or close as possible to rear cell? Advice welcome - particularly from anyone else with a 10" LX200 Classic, 2" diagonal, Meade electric focuser, True Technologies filter wheel and SXV-H9 CCD. There is no 'best place'. The reduction from a FR, is dependant on the spacing between it's optical centre, and the CCD plane. You can mount it anywhere you like _provided this spacing is of the right order for the compression required_. The standard F*.63 reducer requires a spacing of about 3", from it's rear 'face', to the CCD. If you go much beyond this, the reduction factor rapidly increases, and the distortions on the image, also shoot up (it works quite acceptably with spacings perhaps up to about 20% 'long', but the effects become pretty uacceptable beyond this). Decrease the distance, and the reduction factor goes down (though more slowly). Why remove the reducer for visual work?. The F*.63 reducer works well with 1.25" eyepieces, to give a field close to that available using 2" eyepieces, that is flatter than the SCT otherwise manages. Now the problem is that with a normal 2" diagonal, and filter wheel, the spacing will be more than the design distance, and the results will probably not be acceptable. Given that your diagonal, presumably has 2" SCT threads on the 'scope' end, you could get the Ted Agos adapter, sold for the SBIG AO7 systems (He sells another design for 'normal' use, but it is the AO7 version that would suit your application). The SBIG cameras, when used with an AO7, have the camera, then a filter wheel (about 1" thick - you want this to be as thin as possible - hopefully yours is the 'thin' TT wheel?), then the AO7, which is effectively a 'diagonal', which ends at the front with a 2" SCT thread. This combination is too long to work properly with the standard F*.63 reducer. The Ted Agos adapter, allows the optics from the reducer to be moved 'into' the nose of the AO7 (in your case the diagonal), bringing the overall length, in line with the design requirements. With this, you should be able operate with the reducer, and simply replace the camera and wheel with an 1.25" adapter, and eyepiece. If you get one that is about 1" to 1.5" long, there won't even be much focus change. Putting the reducer after the diagonal will result in a very small reduction factor (probably only about *.8). If you want to do this, you would be better off getting a shorter focal length reducer (like the Optic *.5 unit), but this requires the spacing to the CCD, is exactly right (is is not as forgiving as the *.63 unit). Best Wishes |
#3
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Focal reducer placement...
The focal reducer is best placed before the filter wheel as shown in the
following illustration: http://www.astrovid.com/CustomWheel_...es/Config1.JPG You don't want the filters up front as they will be reduced in effective size by the focal reducer. Del Johnson "justbeats" wrote in message m... I have a 10" F/10 LX200 I've been using for visual observing for a year now and I've just purchased the kit I need for imaging. (Thanks for advice on the Digital SLR or cooled CCD thread folks! I bought an SXV-H9, True Tech filter wheel, Orion 80ED and SXV auto-guider). I'm keen to continue visual use and want a simple way to switch between modes (i.e. I don't want to reconfigure the optical train each time I switch between CCD and EPs). I understand that SCT-focuser-filter wheel-CCD is the best configuration but that's so long it prevents the OTA from swinging through the forks (no imaging around Polaris and a heart attack if the dec lock comes loose). So I have chosen to mount SCT-focuser-2" diagonal-filter wheel-CCD. I realise this is not the most stable configuration, but I can easily swap the filter wheel and CCD for an eyepiece, and both configurations swing through the forks. Ideal for now, except. I also bought a Meade 0.63 focal reducer. If I mount it on the SCT rear cell, besides being a pain to remove for visual work, it prevents both configurations from swinging through the forks anyway! Not a solution! So my main question is can I mount the FR between filter wheel and CCD or between diagonal and filter wheel? I assume I need adaptors as there's no obvious way to make the connections with what I have. In general, what is the best place to put a FR? Before or after the filters? Close as possible to CCD or close as possible to rear cell? Advice welcome - particularly from anyone else with a 10" LX200 Classic, 2" diagonal, Meade electric focuser, True Technologies filter wheel and SXV-H9 CCD. Cheers Beats |
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