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Old 01-01-2012, 05:31 PM
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BlackWidow (Mardy)
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Position of focal reducer in image train

I have an LX200GPS with a Meade Electric Focuser, Eyeopener, and F6.3 Focal reducer with a QHY8 Camera. Currently I have been using the focal reducer after the electric focuser just before the camera. I did not have the adaptor to connect the focal reducer at the visual back of the scope.

That has now changed and I am able to move the focal reducer back to the visual back of the scope. However before I do,, I would like to ask what is the best? An I correct in thinking that the further back I place the reducer the more I will increase the F:stop, hence reducing my field of view. I know I cn do some trial and error, but would like to ask the question to make sure I understand the process. I have read that moving the focal reducer back away from the visual back effects (increase) the F:ratio


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Mardy
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Old 01-01-2012, 05:42 PM
gbeal
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Distance, reducer to chip, will affect the amount of reduction yes. BUT............... most reducers or correctors have an optimum distance that they like to be, and this is what you should be working towards. Depends what the reducer is, and from there you can enquire as to the distance.
Trial and error could work though, as the main thing is image quality, and trial and error is perfect for establishing the quality of the image, laborious but works.
Gary
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Old 01-01-2012, 06:11 PM
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BlackWidow (Mardy)
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Thanks gary

Thanks Gary for the info. I have a hersh (? Spelling). its the same in every way to the Meade and Celestron. All made in the same factoy IMO



Mardy
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Old 01-01-2012, 06:38 PM
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lepton3 (Ivan)
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And a related question if I may, is it better to have the OAG after, or before, the focal reducer?

What are the pros and cons?
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Old 01-01-2012, 06:56 PM
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rogerg (Roger)
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Much as what Gary said... I've found the distance between reducer and chip to be quite critical. Varying the distance will affect the amount of reduction but will also affect edge distortions, field flatness and vinyetting. I would expect the focuser to be before the reducer, not between reducer and camera.

For my Meade (LX200 classic) I have the reducer positioned inside the focuser such that its position in the optical train is similar to as if there was no secondary focuser at all. Doing this seems to be common for LX200's. To do this required having a 2" tube machined to transfer the optical elements of the reducer in to, and that sliding in to the 2" focuser drawtube.

Roger.
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Old 01-01-2012, 07:47 PM
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BlackWidow (Mardy)
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Very interesting

Rodger i would love to see a picture of what you have done. Are you using the meade focuser? I am guessing the reducer is in the front part of the focuser. What part gets machined? I appreciate you assistance.


Mardy
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Old 01-01-2012, 09:42 PM
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rogerg (Roger)
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Quote:
Originally Posted by BlackWidow View Post
Rodger i would love to see a picture of what you have done. Are you using the meade focuser? I am guessing the reducer is in the front part of the focuser. What part gets machined? I appreciate you assistance.


Mardy
Does this explain it clearly? http://www.rogergroom.com/items/focal_reducer

I am using the optics from the Meade F/6.3 reducer, but not the metal housing from that unit.

Happy to answer questions you have from the above..

Roger.
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Old 02-01-2012, 01:41 AM
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Moonlite focusers have the FR mounting option built into the drawtube if you order it that way. Problem is it is not always good for accurate sensor to FR distance which can be fixed if you have XS but not if it is too short which means it has to come out and be mounted the traditional way.

Mark
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