9 replies to this topic

[RyanC]

Yes...the title is correct. F/90 telescope!

Last year I decided to have some fun and build a singlet refractor. The aperture is a mighty 27 mm with a focal ratio of 2500 mm. Singlet refractors have only a single lens (plano-convex, convex faces sky). This is nearly the optimal lens, but even still it has horrible aberrations. Hence the f/90 focal length. And it does successfully tame the chromatic aberration, mostly 

 

Here's my telescope "splinter" in all her glory.

 

 

 

I used my ZWO 1600mm over my 290mm for the larger sensor. But I still had to do a mosaic because of the immense focal length.

Binning 4x used and no filter.

 

Definitely happy with how it came out considering the rayleigh limit is around 4-5 arcseconds.

 

Ryan

 

[vtornado]

Did you process out the CA?  

If not that is really good.  A camera is very sensitive to unfocused blue light.

[RyanC]

Did you process out the CA?  

If not that is really good.  A camera is very sensitive to unfocused blue light.

No I did not. There really isn't much chromatic aberration to begin with. Through an eyepiece the moon is sharp and pretty much free of color. Chromatic aberration probably reduces the sharpness a bit, so next time maybe I'll use a green filter or something. I didn't think to use it last night.

[Sleep Deprived]

This is amazing!  Taking this idea to the n-th degree (which you did with this f90) is really interesting, yet none of us (???) have done it!  I can see the advantage of this approach.  Where did you get such a lens??  Is the lens home-made, too??

[RyanC]

This is amazing!  Taking this idea to the n-th degree (which you did with this f90) is really interesting, yet none of us (???) have done it!  I can see the advantage of this approach.  Where did you get such a lens??  Is the lens home-made, too??

I got the lens from OptoSigma. I am not good enough to make my own optics

[JohnBear]

I just love cute little table top Dobs!

[Look at the sky 101]

Fantastic image,  love the scope. 

[highfnum]

yea they work

[JoeyBaggo]

Wow!  Awesome ingenuity.  And great pic out of it too. 

[Stefano Delmonte]

My congrats to your fantastic job both telescope and image

 

Galileo, despite is not true, has been labeled the telescope inventor because understood that in order to reduce CA he must diaphragm and so enlarge the F ratio, his 20mm telescope was F50!  Since then the refractors start functioning

 

Ste