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Redcat 71 WIFD Image Train Length

William Optics Redcat 71 WIFD William Optics Redcat 71 Focuser Refractors
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Andyb90 avatar
Andyb90 avatar
Hi there,

I just got a Redcat 71 WIFD and I’m planning to attach the following on the scopes m48 connection:
m48 extension (10mm) -> m48 to m42 adapter (16.5mm) -> efw (20mm) -> camera (6.5mm)

So a total length of 53mm.

Could anyone tell me if this should be ok for achieving focus ?

I understand the scope is a Petzval design so there is no specific back focus, but I’m assuming there is a minimum and maximum image train length which you need to be within in order to achieve focus. Is that correct?

If the above is correct does anyone know what the min and max lengths would be?

Thanks,
Andy
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Oscar avatar
Oscar avatar
>>"I understand the scope is a Petzval design so there is no specific back focus, but I’m assuming there is a minimum and maximum image train length which you need to be within in order to achieve focus. Is that correct?"

yeah, that's right

but 2mm is nothing; it's a miniscule difference; if you can reach focus with 55mm, you can probably do the same with 53

but if you don't know if 55mm focuses, it's always handy to have an extra spacer or two just in case of an emergency
Robert Ray avatar
Robert Ray avatar
Andy,
I have a new Redcat 71 WIFD and have been imaging with it quite a bit lately at my New Mexico observatory.  I only added a filter holder and no additional spacers.  I did not bother measuring the focal distance.  I have had no trouble with achieving focus.  My advice would be to just try it out with your image train equipment.  I doubt you will have any major problems but it should be easy to adjust if necessary.

-Robert
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Andyb90 avatar
Andyb90 avatar
Robert Ray:
Andy,
I have a new Redcat 71 WIFD and have been imaging with it quite a bit lately at my New Mexico observatory.  I only added a filter holder and no additional spacers.  I did not bother measuring the focal distance.  I have had no trouble with achieving focus.  My advice would be to just try it out with your image train equipment.  I doubt you will have any major problems but it should be easy to adjust if necessary.

-Robert

Thanks for the response. That’s good to know. I’ll drop the additional m48 extension and just go with adapter -> efw -> camera.
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AstroMinden avatar
AstroMinden avatar
The RedCat 71 is a Petzval design which means that you don’t need to get to a specific backfocus distance. As long as you can get it in focus you are fine.

Clear skies.
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