4 replies to this topic

[Robby9newbie]

Happy New Year everyone

I have an 8" Meade LX200 with Meade's microfocuser and Meade's f6.3 fr/ff and I am doing some research regarding an off axis guider. From what I understand the spacing between the fr/ff to the camera sensor is quite critical however I cannot find what this spacing should be for my setup. I will be using a Canon T5i camera for imaging and a ZWO ASI224MC for a guide camera. 

 

What I would like to know is what the spacing should be for this fr/ff as well as possible suggestions for an OAG. I did see another post where the Orion TOAG was coupled with the same guide and imaging cameras that I will be using and there was an issue with the hockey puck shaped ZWO camera hitting the Canon camera. It appears that they could only mount the guide camera so that it was pointing to the lower right corner possibly introducing the prism into the image with Orion's TOAG.

 

Any suggestions and guidance is appreciated

Robin in Ottawa

 

[einarin]

Celestron reducer should be placed 105mm from chip.

I thought that Meade had different fl (some mention 95mm), but I'm not sure.

http://www.cloudynig...ducer-question/

[Robby9newbie]

It looks like 95mm is the magic number for f6.3 reduction.

Thanks

Robin

[Hicks]

I have the Meade f6.3 and believe* 85mm +- a few mm is the correct spacing. I spent a bit of time trying to calculate the spacing but as the focal ratio of the SCT changes as you move the primary, I gave up and just took some images and plate solved, results are:

105mm gave 25.8×19.3 arcmin = EFL 1197. f5.89
90mm gave 24.2831 x 18.1401 arcmin EFL 1271, f6.27
59mm gave 21.7×16.2 arcmin = EFL 1422, f7.0

I didn't have the correct spacers to try @ 85mm but f6.3 is clearly just a little below 90mm and a fair bit above 59mm so 85mm give or take looks like a good target imo.

 

I've since moved to a moonlite focuser with the reducer mounted inside it so my minimum spacing I can hit is now 87.5mm, I just haven't had a chance to get an image and measure the final f ratio.

 

That said, the images I took at 90mm looked fine to me and I've heard others using it spaced even further. If you have a variable spacer, it'll be easier to just test and get as close to f6.3 as you can and whatever spacing that happens to be, that'll be the correct one

 

I have read there's a bad batch of focal reducers out there from a few years ago and that meade made some shorter (55mm?) spacing ones, but that's just based on what others have said.

 

*: Depending where you measure from, I based it on the rear shoulder (ccd side) of the reducer where any adapter will thread up against.

Edited by Hicks, 04 January 2017 - 03:05 PM.

[Robby9newbie]

Any suggestions for an OAG to achieve this spacing of 90mm? See above regarding the Orion TOAG issue.

Thanks again

Robin