Where to measure 55mm

[Stu Wilson]

I just need someone to clarify where I measure the 55mm back focus.

I'm also now not sure of distance to sensor.

It's a altair 294c pro tec cooled.

Hoping to sort this tonight for the clear sky.

Cheers

 

Stu

[StevieDvd]

As per here and here

You would need to add 37.5mm to the existing 17.5mm to make up the 55mm.

I've just learned myself and have spacers (due from FLO as soon as Royal Mail allow) for my latest setup.

[Stu Wilson]

1 hour ago, StevieDvd said:

As per here and here

You would need to add 37.5mm to the existing 17.5mm to make up the 55mm.

I've just learned myself and have spacers (due from FLO as soon as Royal Mail allow) for my latest setup.

dont suppose you know what i need to order?

 

cheers

stu

 

[StevieDvd]

12 hours ago, Stu Wilson said:

dont suppose you know what i need to order?

 

cheers

stu

 

Before you order you should check you need the back focus. I need the spacers as I will be adding a focal reducer that requires a 55mm back focus.

Is that an existing variable extender in the picture you have?

If you intend to use that then you only need a single reducer to allow you to get a 55mm length.  Rather than try for an exact size it might be better to get a larger size (21mm) so together with your variable one you can accomodate back focus  between a decent range (50-67 if I read your adapter as 29-46mm).

If it helps I have listed what I ordered from FLO below.  If you only need a single extender then of course there are cheap options on Ebay/Amazon etc.

I have gone for the exact sizes I need and had to include an M42/48 adapter. For some reason the 16.5mm only seems to come in the M48/42 fitting.

ZWO M48 to M42 Adapter Ring Qty: 1 Price: £14.00

ZWO M42-M42 Extender 21mm Qty: 1 Price: £16.00

ZWO M42-M48 Extender 16.5mm long Qty: 1 Price: £16.00

 

Hope that helps

Steve

 

 

[Stu Wilson]

It is a variable but its jammed solid and cannot adjust it without breaking it.

It's a bit of a codge up for my old cam. So I'll have to get new.

Are you same as me as in you need 42 mm male threads at 1 end and 48 mm female at other end?

 

Cheers 

 

Stu

[StevieDvd]

14 minutes ago, Stu Wilson said:

It is a variable but its jammed solid and cannot adjust it without breaking it.

It's a bit of a codge up for my old cam. So I'll have to get new.

Are you same as me as in you need 42 mm male threads at 1 end and 48 mm female at other end?

 

Cheers 

 

Stu

The reason I went with items from FLO was because of the number of times I've read about jammed adapters. I don't have m48 in my setup it's m42 both ends, hence the m48/m42 additional adapter - it appears to be a common requirement.

What's in your setup that needs the 55mm back focus?

 

[Stu Wilson]

Ts optics coma corrector