SkywAtcher startravel st80 backfocus

[iwols]

Hi just using this scope for solar imaging but can anyone tell me what the back focus is as i can't find a figure anywhere thanks

[newbie alert]

If you're lucky imaging with a planetary camera then backfocus spec isn't a issue.. try it with or without a diagonal for focus. 

[Laurieast]

A Zwo Asi 224mc at prime focus is 60mm, if that's what you mean?

[iwols]

Thanks that's what I needed👍

[Laurieast]

5 hours ago, iwols said:

Hi just using this scope for solar imaging but can anyone tell me what the back focus is as i can't find a figure anywhere thanks

@iwols I have told you the wrong thing, it is 135mm back from the rear edge of the focuser.  🤦‍♂️
So if not using the diagonal you will need a ~ 36mm extension tube. I use the body of a 2x Celestron barlow.

 

 

 

 

Edited June 5, 2022 by Laurieast

[ollypenrice]

If you're not using a moving rear lens element such as a flattener or a reducer, isn't the back focus simply the focal length of the lens measured from its rear element? If the ST 80 is F5 then its focal length is 80 x 5 = 400mm.

Olly

[iwols]

21 hours ago, Laurieast said:

@iwols I have told you the wrong thing, it is 135mm back from the rear edge of the focuser.  🤦‍♂️
So if not using the diagonal you will need a ~ 36mm extension tube. I use the body of a 2x Celestron barlow.

 

 

 

 

Thanks where are you measuring to on your camera please 

[Laurieast]

7 minutes ago, iwols said:

Thanks where are you measuring to on your camera please 

That joint is about where the sensor is.

[iwols]

5 minutes ago, Laurieast said:

That joint is about where the sensor is.

Thanks for that

 

[Laurieast]