SkyWatcher AZ Pronto w/ EvoStar 90/660 or AZ3 w/ EvoStar 90/900?

[GeorgeP]

Hello,

I'm looking for a beginner, entry level AZ mount and these two caught my attention on FLO. I'm drawn more towards the AZ Pronto as I won't need to buy tube rings for my Heritage 130P as the head has a dovetail attachment. I will not be doing any photography, just simple viewing.

The scope is a little inconsequential for me. I don't own a refractor so an entry level one would be nice to have, especially the shorter one for grab and go. Does the focal length only really effect the chromatic aberration and FOV?

https://www.firstlightoptics.com/sky-watcher-az-pronto/sky-watcher-evostar-90-660-az-pronto.html

https://www.firstlightoptics.com/evostar/skywatcher-evostar-90-az3.html

Does anyone have any opinions on the two? I'm leaning towards the AZ Pronto at the moment. 

[vlaiv]

I think that AZ pronto will be more usable of the two.

AZ3 is really not very good mount. It is much more suited for terrestrial observing than for astronomy - as it's having tough time when the scope is pointing high up (OTA hitting tripod legs and in general poor motion).

Although it has slow motion controls - those are not fully usable. AZ motion is only limited to small section of "left/right" motion and needs to be "rewound" every so often (returned to center position).

Focal length will affect chromatic aberration, FOV but also general sharpness of the scope due to something called spherochromatism (also aberration and related to wavelengths of light - but different from simple chromatic aberration) which affects overall sharpness of the image.

Chromatic aberration is when not all wavelengths come to same focus - so when you bring image of star or planet to a focus - there some light (most notably purple being on far end of spectrum) - that is defocused and presents itself as "halo" around the object.

Spherochromatism on the other hand is spherical aberration that depends on wavelength. Even if color/wavelength is brought to focus - if it suffers from spherochromatism - it will be blurry and not sharp (like regular spherical aberration).

For this reason shorter (faster) achromat scopes are not suited for high power viewing. Having said that 90/660 is right there on the edge of not being overly fast and will probably show very decent high power images if stopped down to say 70-80mm (you can use aperture mask to stop down fast achromat and make it slower - which reduces chromatic aberration and sharpens up the view).

[GeorgeP]

Thank you, @vlaiv Wonderful explanation. I did see the AZ Pronto would do a full rotation and wouldn't need resetting, that is a nice feature.

I think it is the better option, I may look into getting the AZ Pronto by itself and a better refractor but £60 for the refractor seems a fair price given the Pronto is £175 on FLO.

 

[allworlds]

Just going by the pictures on FLO's website, if you buy an AZ-Pronto by itself it looks like you get the extension pillar and a better tripod?

https://www.firstlightoptics.com/alt-azimuth-astronomy-mounts/sky-watcher-az-pronto-alt-azimuth-mount-tripod.html

vs

https://www.firstlightoptics.com/sky-watcher-az-pronto/sky-watcher-evostar-90-660-az-pronto.html

[GeorgeP]

15 minutes ago, allworlds said:

Just going by the pictures on FLO's website, if you buy an AZ-Pronto by itself it looks like you get the extension pillar and a better tripod?

https://www.firstlightoptics.com/alt-azimuth-astronomy-mounts/sky-watcher-az-pronto-alt-azimuth-mount-tripod.html

vs

https://www.firstlightoptics.com/sky-watcher-az-pronto/sky-watcher-evostar-90-660-az-pronto.html

Looks like that is the case, good spot! I have never used a tripod so I don't really know if one looks better than the other, the extension does look a nice thing to have however. 

Hmm, need to weigh up if having a starter refractor for £60 is worth having. I do like the idea of taking that on trips and having my reflector for at home.

[Cosmic Geoff]

Depends what you want.  The AZ Pronto with 90/660 would make a handy starter outfit.  On the other hand, the 90/900 is a classic achromat design that should work well for its size on planets and double stars, but I wouldn't have the AZ3 even as a gift. 

[GeorgeP]

6 minutes ago, Cosmic Geoff said:

Depends what you want.  The AZ Pronto with 90/660 would make a handy starter outfit.  On the other hand, the 90/900 is a classic achromat design that should work well for its size on planets and double stars, but I wouldn't have the AZ3 even as a gift. 

I think the AZ Pronto and the 90/660 is a good little combo from what I have read. I don't do any astrophotography, I just want to look at stuff floating a long way away so think this will work. It is pretty cheap, good as a grab and go and doesn't need any faffing about like my reflector might. I think I will get my moneys worth.