Celestron C8 XLT with Meade 4000 F6.3 reducer

[IDM]

I recently obtained a secondhand Celestron C8 and Meade focal reducer/flattener and am now searching around to try an find details on the back focus for the Meade reducer. There are many posts saying its not the greatest reducer on earth but little on back focus. One post on Cloudy nights suggested 105mm. I had a look on the Meade website and despite listing the reducer I could not fins any instructions or guidance documents. Does anybody know the correct answer or have any guidance? I am interested in trying the scope with reducer as a reasonably fast scope for galaxy astrophotography.

Thanks,

Ian 

Edited March 26 by IDM
Typos due to using my phone!

[Cosmic Geoff]

The back focus (with the Celestron f6.3 reducer) is not that critical.  It's about 10 cm, which you can achieve, for instance, by fitting the camera on the end of the standard 1.25" diagonal. Or, if you have a mount with suitable clearance, fit the camera at the outer end of a flip mirror assembly or straight-thru extension tube.

[michael8554]

Hi Ian

Allegedly these Meade FR's come in two identical looking flavours.

Measure its focal length by focusing the sun (what sun ? 😆 ) onto a wall.

If it's around 210mm, adjust for best star shape in the corners, starting at 105mm Back Focus.

If the FL is about 135mm, start at 85mm Back Focus.

Michael

 

 

[blinky]

It should be 110mm if I remember correctly

[IDM]

9 hours ago, Cosmic Geoff said:

The back focus (with the Celestron f6.3 reducer) is not that critical

That's good to know as I guess the Meade is similar in design. I am just used to trying to be very precise with flatteners for refractors so it goes against the grain for approximate measurements! 

[IDM]

6 hours ago, michael8554 said:

Measure its focal length by focusing the sun (what sun ? 😆 ) onto a wall.

If it's around 210mm, adjust for best star shape in the corners, starting at 105mm Back Focus.

If the FL is about 135mm, start at 85mm Back Focus.

Rumour has it the the sun may come our here (briefly) tomorrow so I will try as you suggest.

Thanks for the help.

Ian

[IDM]

38 minutes ago, blinky said:

It should be 110mm if I remember correctly

I have currently set it at 105mm. Tomorrow I will try measuring the focal length as suggested by @michael8554

[michael8554]

I'd be interested to know:

If it is the short FL version, how bad was it at 105mm ?

Michael