Modifying Newtonian For DSLR

[wooleybull (MICHAEL)]

Hi all I modified my 130/650 scope today from the article by Alchemy.
it worked perfectly, from F5 to F4.6, I can now focus my DSLR and use my 2 x Barlow, of course the clouds have rolled in, sorry everyone.
thank you for the article Alchemy!
cheers Michael

[RyanJones]

Originally Posted by wooleybull

Hi all I modified my 130/650 scope today from the article by Alchemy.
it worked perfectly, from F5 to F4.6, I can now focus my DSLR and use my 2 x Barlow, of course the clouds have rolled in, sorry everyone.
thank you for the article Alchemy!
cheers Michael

Can you provide a link to the article Michael, I’m intrigued.

[Eldest_Sibling (Alan)]

Methinks all you have to do is shorten the optical-tube; but then, by how much?

[RyanJones]

Originally Posted by Eldest_Sibling

Methinks all you have to do is shorten the optical-tube; but then, by how much?

But that doesn’t change the optical length of the mirrors it just moves the focal point further out of the tube.

[Eldest_Sibling (Alan)]

Originally Posted by RyanJones

But that doesn’t change the optical length of the mirrors it just moves the focal point further out of the tube.

Yes, and to enable the tip of the light-cone from the primary-mirror to reach a camera's sensor. An eyepiece can sink down into a draw-tube, but a camera cannot, therefore you have to move the primary-mirror forward a bit.

Granted, this case does seem to differ, and I couldn't find an article by "Alchemy" online. Is "Alchemy" an individual, or a publication? Did the OP use a focal-reducer of some sort, or did they have the primary-mirror re-figured? I doubt the latter.

[RyanJones]

Originally Posted by Eldest_Sibling

Granted, this case does seem to differ, and I couldn't find an article by "Alchemy" online. Is "Alchemy" an individual, or a publication? Did the OP use a focal-reducer of some sort, or did they have the primary-mirror re-figured? I doubt the latter.

This is the bit I’m interested in. Moving the focal point I get and is pretty straightforward. It’s the change of focal ratio I’m confused about ( as a simple DIY at least ) and also going from f/5 to f/4.6 is a shortening of the focal length which would only exacerbate the difficulty in achieving DSLR focus.