Barlows

[Astro Imp]

As I understand it a Barlow doesn't alter the focal  length of the EP but increases the focal length of the OTA thereby giving greater magnification.

As the properties of the EP are not changed why does a Barlow extend the eye relief available.

[ronin]

I have no idea, but a year or so ago people said that the barlow effectively gave a shorter eyepiece (= longer focal length of OTA) while maintaining the eye relief, now I have noticed that it extends the eye relief in a few posts.

So there has been a change in the final result, from same eye relief to greater eye relief.

I am not sure where from.

[swamp thing]

I believe It changes eye relief because the Barlow lens alters the angle of the light cone hitting the field kens of the eyepiece.

Edit. It lengthens eye relief. Not quite sure how one calculates how much though, I believe its down to Barlow length, but not totally sure.

[Joves]

Is it that a Barlow extends the eye relief or that it allows you to use a longer focal length EP at higher magnification, which typically have longer eye relief, without changing its properties?

[swamp thing]

Is it that a Barlow extends the eye relief or that it allows you to use a longer focal length EP at higher magnification, which typically have longer eye relief, without changing its properties?

Barlows extend eye relief.

[Joves]

I didn't know that. Cheers.