FS: William Optics Zenithstar 66SD Doublet APO - SOLD

Post by **Airconvent** » Sat Oct 28, 2006 6:33 pm

Upz...still looking for an astro cum birding owner...

Robin Lee · Post by **Robin Lee** » Sat Oct 28, 2006 7:06 pm

Airconvent wrote:upz..
Price adjusted to $600. Final.
Thanks for reading.

Is this the ZS66 Petzval ED? Just realised that we both are horses.

Post by **Airconvent** » Sat Oct 28, 2006 9:28 pm

Kim Miau wrote:
Airconvent wrote:upz..
Price adjusted to $600. Final.
Thanks for reading.
Is this the ZS66 Petzval ED? Just realised that we both are horses.

No.The Petzval is a 66mm "semi-apo" scope.
William Optics uses this term to describe their achromats that have better colour correction than normal.
The one I am selling is true APO scope. Price difference is substantial.
You can check out the difference on the WO website.
We may be horses but I think you should be at least one cycle younger than me! cheers

Robin Lee · Post by **Robin Lee** » Sat Oct 28, 2006 9:33 pm

Do you mean that the Petzval has better optics than the APO? Yeah, I am younger than you by 2 cycles.

Post by **Airconvent** » Sat Oct 28, 2006 9:38 pm

Kim Miau wrote:Do you mean that the Petzval has better optics than the APO? Yeah, I am younger than you by 2 cycles.

Actually the other way round. The Petzval is not an APO scope, that is why it is so much cheaper. I think the design was primarily optimised for astrophotography, not visual.

APO scopes uses a mix of quality optics and design to achieve as little chromatic aberration as possible. Inspite of this , though, WO has amongst the cheapest APO scopes around.

Robin Lee · Post by **Robin Lee** » Sat Oct 28, 2006 9:39 pm

If Petzval is optimised for astrophotography and visual use, it should be better than a APO, I am confused...

Post by **Airconvent** » Sat Oct 28, 2006 9:43 pm

Kim Miau wrote:If Petzval is optimised for astrophotography and visual use, it should be better than a APO, I am confused...

sorry, I just edited my earlier post due to error.

Robin Lee · Post by **Robin Lee** » Sun Oct 29, 2006 1:51 pm

I got it. Is APO designed for both astrophotography and visual?

Post by **weixing** » Sun Oct 29, 2006 3:02 pm

Hi,

If Petzval is optimised for astrophotography and visual use, it should be better than a APO, I am confused...

The Petzval design is use to reduce the effective focal length and to reduce or eliminate curvature of field of a telescope. Since it produce a flat field (CCD sensor surface is flat) and short focal length ("fast" focal ratio), it is very suitable for Astrophotography. Also, it can be an APO scope if design to do so (eg. Televue NP-101, NP-127 & Takahashi FSQ-106).

I got it. Is APO designed for both astrophotography and visual?

IMHO, any scope can be for Astrophotography... the only question is it more convenient to do so??

A scope design for Astrophotography will have "fast" focal ratio, flat field and produce a large image circle... it may not need to be an APO.

A scope design for visual use can also be use for Astrophotography, but it'll not as convenient as a scope design for Astrophotography... you may need a separate field flattener, a focal reducer and the may have some vignetting if use on large CCD sensor.

Anyway, please create a new thread if you have more question on this in the "Equipment Discussions" section. This section is for "Buy and Sell", so is limited to enquiry only.

Thanks and have a nice day.

Robin Lee · Post by **Robin Lee** » Sun Oct 29, 2006 3:10 pm

Oh ok, thanks for your information. Sorry for disturbing your thread.