Edge 8 HD and Crayford focuser

[Stuartmyatt76]

Hi all 

i have an edge 8 hd which i am trying to get ready for first light. Does anyone know if i can fit a crayford focuser to my Edge and if i can will it affect my backfocus.

second question (sorry relative newby) would i put my reducer telescope side of the crayford or camera side. 

Thinking about this a little more looks like this wont work. Any ideas

[michael8554]

Hi Stuart

The Crayford won't alter your Backfocus, but it will eat into it.

The FR must be on the OTA side.

Otherwise when you alter focus with the Crayford, you will alter the FR Backfocus, which must remain at the correct setting for best star shape.

Michael

[beka]

On 04/05/2023 at 10:03, michael8554 said:

Hi Stuart

The Crayford won't alter your Backfocus, but it will eat into it.

The FR must be on the OTA side.

Otherwise when you alter focus with the Crayford, you will alter the FR Backfocus, which must remain at the correct setting for best star shape.

Michael

Hi Michael8554, you mean it should be on the camera side (of the focuser) - for the reason you stated?

Edited May 7, 2023 by beka

[michael8554]

"Hi Michael8554, you mean it should be on the camera side (of the focuser) - for the reason you stated?"

No.

OTA + Crayford + FR + Camera.

Because with OTA + FR + Crayford + Camera, the FR backfocus will alter when you focus the Crayford.

Michael 

Edited May 7, 2023 by michael8554

[beka]

On 07/05/2023 at 14:50, michael8554 said:

"Hi Michael8554, you mean it should be on the camera side (of the focuser) - for the reason you stated?"

No.

OTA + Crayford + FR + Camera.

Because with OTA + FR + Crayford + Camera, the FR backfocus will alter when you focus the Crayford.

Michael 

... so FR on camera side  

[fwm891]

@Stuartmyatt76 You will first have to lock the primary mirror focuser (see the Edge HD white paper on Celestron's web site) to produce it's optimum back focal distance before fitting your Crayford and focal reducer combination or you'll be fighting all sorts of aberation problems further down the line...

[michael8554]

"... so FR on camera side  "

Yes

Michael