Big Focusers?

[billhinge]

I have a mix of telescopes and focusers from 3" to 2" but eyepieces and camera fittings are approx 2" so why would you need a 3" or even 3.7" focuser? (yes I appreciate there are M63, M68, M82 gizmo's but why)

In the old days is was simple 1.25" or  screw thread 🙂

I'm trying to sort out ext tubes, focusers, flatteners, adapters is why I'm asking

 

Edited September 6, 2020 by billhinge

[discardedastro]

On 06/09/2020 at 18:41, billhinge said:

I have a mix of telescopes and focusers from 3" to 2" but eyepieces and camera fittings are approx 2" so why would you need a 3" or even 3.7" focuser? (yes I appreciate there are M63, M68, M82 gizmo's but why)

In the old days is was simple 1.25" or  screw thread 🙂

I'm trying to sort out ext tubes, focusers, flatteners, adapters is why I'm asking

 

Basically only relevant for large format cameras, as I understand it. 2" will do you full frame with pretty minimal vignetting, though I suspect 3" and above wouldn't hurt for that, but for larger sensors like medium format you have to go beyond 2" - I think for medium format you'd have to be at at least 3.7". The FSQ-106 has an 88mm image circle and a 4" focuser and can support medium format sensors. So I think it's not so useful unless you're planning to hang a very expensive CCD/CMOS on the back!

[DaveS]

For imaging a big focuser usually provides greater rigidity, especially when hanging a heavy camera off the end. It doesn't even have to be a big sensor either, Moravian cameras for instance can be pretty heavy, even for the relatively small 16200 sensor.

Also, the 3.7" focuser on my 130mm apo allows me to sink my 0.75x Riccardi reducer into the barrel, so that it doesn't have the weight of the camera hanging off the end.

[billhinge]

OK thanks, I was thinking I may hang a G2-8300 off the back  of a M63 APM Riccardi with good quality 2" APM step down adapters to save replacing the  2"  Feather Touch. Do you  reckon that  would work?

There are dedicated step down APM adapters for the Riccardi, I assume  since they make them for the Riccardi  then they should  work?

I think a 3" focuser would require a custom adapter for my OTA