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Advice on 2 scopes pls?

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Hello All.

I'm more than likely buying a 200p dob, but also I have in mind the skywatcher st120 short tube refractor.

The reason I need some guidance and I know there two different things but I want the most suited to me.

The short tube appeals to me because it's easier to move in and out the house.

I may fancy doing some basic astrophotography at sometime, is it doeable with both or easier with one of them?

Will I see alot more with the 200p? I know aperture is everything but is the difference alot?

Could I get good planetary views with the st120?

Any help guidance and points of view welcomed.

Thanks Gary 

Edited by stafford_stargazer
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8 minutes ago, stafford_stargazer said:

I may fancy doing some basic astrophotography at sometime, is it doeable with both or easier with one of them?

Neither of the two scopes is suited for astrophotography, or maybe I should phrase it like this:  both scopes require extensive measures to be able to take even simple astro photos.

200p is massive beast and you'll have to purchase something like EQ6 mount and some rings to be able to track the skies.

Alternative is using EQ platform - which just simply tracks and can't be guided. It is also not very precise and special technique needs to be employed in order to get anything decent (lucky type DSO imaging). That also requires special type astronomy camera with low read noise for best results (DSLR won't quite cut it).

Upgrade to focuser will also be needed to be able to steadily hold imaging equipment.

I actually imaged with 200p on Heq5 mounts - but quickly abandoned it as rather unsuitable imaging platform.

ST120 is short achormatic refractor and it suffers from large amount of chromatic aberration. This will affect your imaging. I also used ST102 for imaging and here is example of result of that:


yep, that is crescent nebula. You can see blue halo around bright stars - but also red halo around all other stars. This is spherochromatism - spherical aberration depending on wavelength of light. You simply can't get sharp image from this scope unless you do again some serious things that make imaging less than enjoyable.

If you want to start with astrophotography - maybe it would be best to start another topic and ask for advice depending on your budget (it can be really costly enterprise).

15 minutes ago, stafford_stargazer said:

Will I see alot more with the 200p? I know aperture is everything but is the difference alot?

More, but not a lot more. Difference is really hard to quantify and it will depend on your observing experience. Beginner might not notice a lot of difference, but seasoned observer will say that it is night and day :D simply because 8" scope will show some small very faint galaxy while 5" will fail to render it visible.

View will be much more different (dramatically so) on planets. 200p will be planet killer compared to ST120.

18 minutes ago, stafford_stargazer said:

Could I get good planetary views with the st120?

Not really. As is - it will provide very poor view of planets. Fast achromats are simply not suited for high power views. You can however do couple of things to improve views - namely stopping the aperture and using filters. This will improve views somewhat at expense of other things (filters make colored view and aperture mask resolves less than full aperture without aberrations), but it will never reach what is possible with 200p.

Out of the two 200p is much more all around scope and is better unless you have very specific observing as a preference. ST120 is better at wide field views and is lighter and easier to carry and store.

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Many thanks for you concise replies, pretty much what I thought, imam more of a visual bloke just thought I'd throw astrophotography into the equation just in case.. I am going to go for the 200p dobsonian mounts reflector as I think for visual stuff it's going to be great and planets too.

Thanks again Gary 

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For photography you're best off with something like an 80ED or 72ED to start with - which is also a nice visual scope but there is a step up in price and that price will just be for the OTA so expect to pay around twice as much again for a mount - a minimum of an EQ-35M really.

The Dobsonian already has a mount built-in and they are the go-to as a visual scope for many, particularly those on a budget.  Planetary imaging with a Dobsonian is possible and I've seen some manage it manually but it's not really a photography platform.  Great for visual work though, especially with a lower-power eyepiece.  They are bulky but very easy to set up (it takes seconds).

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A newt reflector around 8" is regarded by many as a keeper scope - even when others are chosen for other tasks.

My first proper scope was an 8" on EQ5. Since then I have always had a reflector in the 8" or 10" range.
wouldn't be without one.

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