Parabolic Mirrors

[Ganymede12]

There are two telescopes I am looking at upgrading to.They are both the same but one has parabolic mirrors. The one with parabolic mirrors cost £10 more than the one without. Are parabolic mirrors worth the extra money?

P.S the two scopes are the SKYHAWK-1145 and the SKYHAWK-1145P

[mdstuart]

A parabolic mirror is only needed at short focal lengths. The f1000 version can get away with a spherical mirror as it has a long light path..but this is via a cat design.

The parabolic version is "non cat" and has a shorter focal length...

They both gather the same light and will be broadly the same to use but personally I would go for the pb one..In fact I would go further and say I would go for a dob mounted 130mm scope which will get more light in and be easier to use from a visuall point of view. The 114mm will allow basic astrophotography if you get the motorised version but a dob will not.

So many choices!

If you buy one second hand you can easily sell it on when you want to go for a bigger scope anyway!

Mark

[JamesF]

I'd certainly always go for the one with a parabolic mirror. If a scope has a spherical mirror it requires additional correction to bring all of the light to focus at the same point. A parabolic mirror does this anyhow. I don't know if the spherical mirror version has any corrective lenses, but at that sort of price I'd be surprised if it did. If there's only £10 difference I have to admit that I struggle to see why they'd even offer two options. I see FLO only appear to list the parabolic mirror version, but it doesn't look like they have it in stock at the moment.

James

[assasincz]

As below

[Tiddles]

As below

This is very true for the extremely short focal length shown in your diagrams, the longer the focal length, the less significant this will become.

The difference between a spherical versus parabolic mirror at longer F/L's will be insignificant compared to quality of the profile and other items in the optical path.