Achromatic vs semi-apo vs apo

[Peter Drew]

Isn't the eye a single lens non achromat?

[ollypenrice]

Isn't the eye a single lens non achromat?

Yes, but check out the software...

lly

[laser_jock99]

Are you thinking about a 6" FSQ?

Pentax once made a 6" F6.4 150 SDP which can be reduced down to F4.9 with its 0.77x reducer.

The only price I managed to find for that scope was one dated to year 2000. 78600 Deutsch Mark for the scope + 2100 DEM for the reducer which translates to €41.3k!!! before adjusting for inflation.

http://www.astroopti...ntax_preise.htm

It makes Takahashi's TOA150's £10k price tag looks cheap.

No wonder I have never seen a photo of one in the wild. When you Google 150SDP, all you get is trade show photos.

6" is where refractors stop and mirrors take over (unless you have big money and an even bigger mount!).

[E621Keith]

Isn't the eye a single lens non achromat?

No, mammalian eye is a doublet with aspheric elements. The cornea and the aqueous humour is the first element, followed by a variable lens. The human cornea+AH is aspheric while the lens is a inhomogeneous element. This combination corrects for spherical aberration and maximise the resolution on axis, but at the expense of some off axis performance. (see page 12)

http://www.annualreviews.org/doi/pdf/10.1146/annurev.ne.15.030192.000245

Rats on the other hand have almost spherical cornea and a lens over corrected for SA. This gives it better all round vision but at the expense of on axis resolution

Evolution do some amazing trick and our eyes are surprisingly advanced.

[ollypenrice]

6" is where refractors stop and mirrors take over (unless you have big money and an even bigger mount!).

Seen those TEC200 images recently? But by and large I think you're right! Refractor nut that I am, I'm over and out with the TEC140.

Olly