Evostar vs Star travel

[MattGP]

Morning all

So I have a Canon 500d which am currently using with a Star Adventurer, with the plan always being to buy a better scope to go with it in time.

My plan and budget was for an Evostar 72ed, but was just looking at the Skywatcher Star travel range and that the 80t is a third of the price. Now am going to guess it’s 3 times not as good as the evostar, but could anyone confirm why?

 

many thanks

matt

[happy-kat]

Hi

One is an apochromatic and the other us a achromatic lens. Both are doublets but the ED72 is better corrected for chromatic aberration.

[ollypenrice]

The ST80 is utterly hopeless for imaging. (I have two and use them for autoguiding, which they do brilliantly, but that's an entirely different task.) There are three problems.

1) The chromatic aberration is extreme. Different colours come to different points of focus. This will affect your camera particularly badly because, being one shot colour, you cannot refocus between filters so some of your colours will always be out of focus and you'll get big blue halos around stars.

2) The focuser is too primitive for imaging. It will not hold your camera chip square to the light beam so one side may be in focus while the other is not. This is called 'tilt.'

3) The lens has significant spherical aberration and your camera has quite a large chip. Stellar images away from the centre will be distorted.

It's a worthy little scope, good value, but for budget imaging get a Newt or the Evostar.

Olly

Edited April 14, 2020 by ollypenrice
Typo

[MattGP]

Cheers for the super fast replies

Funnily enough was just reading an old thread on here pretty much saying the same thing 😉

72ed it is - unless there’s something better for the money (which I don’t think there is)

[johninderby]

Another one worth considering. Not a bad price at the moment and a good R&P focuser.

https://www.teleskop-express.de/shop/product_info.php/info/p1151_TS-Optics-70-mm-F6-ED-Travel-Refractor-with-modern-2--RAP-Focuser.html

[vlaiv]

1 hour ago, johninderby said:

Another one worth considering. Not a bad price at the moment and a good R&P focuser.

https://www.teleskop-express.de/shop/product_info.php/info/p1151_TS-Optics-70-mm-F6-ED-Travel-Refractor-with-modern-2--RAP-Focuser.html

That one also does not have very good correction of CA. It is very good travel scope / small visual instrument, but SW 72ED is going to be much better for imaging.

There is TS photoline 72mm model that uses FPL53 and lanthanum glass that has much better color correction and is well suited for AP purposes (as the name of line suggests):

https://www.teleskop-express.de/shop/product_info.php/info/p8866_TS-Optics-Doublet-SD-APO-70mm-f-6---FPL-53---Lanthan-Objektiv.html

Btw, while I fully support the notion that ST80 is not imaging instrument, has a loads of CA and poor focuser - I have to say that with some careful application it can be used for imaging:

This image was taken with ST102 - bigger brother of ST80, and purple fringing was not removed in post processing. It was done with color camera (although small planetary cmos type - ASI185) and only tricks used were aperture stop and wratten #8 yellow filter stacked with UV/IR block filter.