2" Eyepieces

ariefm71 · Post by **ariefm71** » Tue Oct 10, 2006 11:29 am

A cheap dob requires an expensive eyepiece

Expensive fast dob also requires expensive ep.

Btw, I have a 34mm 70-degree Siebert Observatory, on my f/5 scope, i can't see any differences with 35mm Pano. Can try again when the sky clears up.

rlow · Post by **rlow** » Tue Oct 10, 2006 1:16 pm

Btw, I have a 34mm 70-degree Siebert Observatory

Yes, I have noticed that for some time... can we do some test together when the sky gets clear?

Canopus Lim · Post by **Canopus Lim** » Tue Oct 10, 2006 1:50 pm

Aiya.. was just making a comparison that buying a cheap fast scope would mean buying a more expensive eypiece to correct the steeper light cone. Expensive scopre surely got expensive eyepiece right?

rlow · Post by **rlow** » Tue Oct 10, 2006 2:04 pm

Btw, cheap fast scope need NOT use expensive eyepieces! There are also effective cheap EPs for cheap fast scopes. But there are trade-offs, of course...

Robin Lee · Post by **Robin Lee** » Sat Oct 28, 2006 3:03 pm

I have tested that the Meade Series 4000 SP 40mm isn't better than the 32mm. It's even worse. As it's a 1.25" eyepiece, it can't benefit from the wider fov. The 32mm produces much more contrasty view.

Post by **Airconvent** » Sat Oct 28, 2006 6:19 pm

Kim Miau wrote:I have tested that the Meade Series 4000 SP 40mm isn't better than the 32mm. It's even worse. As it's a 1.25" eyepiece, it can't benefit from the wider fov. The 32mm produces much more contrasty view.

My favourite is the 32mm for DSO. The 40mm has a slight vignetting which I find a little irritating.

Robin Lee · Post by **Robin Lee** » Sat Oct 28, 2006 6:23 pm

Airconvent wrote:
Kim Miau wrote:I have tested that the Meade Series 4000 SP 40mm isn't better than the 32mm. It's even worse. As it's a 1.25" eyepiece, it can't benefit from the wider fov. The 32mm produces much more contrasty view.
My favourite is the 32mm for DSO. The 40mm has a slight vignetting which I find a little irritating.

I assume that the vignetting is caused by the 1.25" barrel. You won't get this with a 2" 40mm. Your visual back has to be 2" as well. Most of the SCT's visual back is just 1.5" (Am I correct?). Peterson EyeOpener is quite a hot product.

ariefm71 · Post by **ariefm71** » Sun Oct 29, 2006 12:51 am

The vignetting is caused by sct's central baffle (see pic). The diameter of this baffle for 8" sct is around 38mm. This will limit the max field of view of your sct to only 1 degree (at f/10) or 1.7 degree (if using 0.63 focal reducer). If you're using an eyepiece that exceeds this max fov, you'll get vignetting (you may or may not feel the vignetting, depends on your flight hours).

See detailed explanation in this thread: http://www.singastro.org/viewtopic.php?t=1651

The Peterson can be used only for 10" or above meade sct or 11" and above celestron's. It won't fit into an 8" sct thread.

Robin Lee · Post by **Robin Lee** » Sun Oct 29, 2006 1:55 pm

Thanks for the detailed explanation.

Post by **weixing** » Sun Oct 29, 2006 8:19 pm

Hi,

This will limit the max field of view of your sct to only 1 degree (at f/10) or 1.7 degree (if using 0.63 focal reducer).

Hmm... from what I read, the maximum field of view for C8 is around 1.3 degree with 2" eyepiece and you won't get anything wider even you use a focal reducer because it will increase the amount of vignetting.

Have a nice day.