f/7.7 vs f/5

[Mezz]

Hi,

I am going to buy my first telescope and I can't make up my mind with the focal ratio. I have seen this two option within my budget

Skywatcher 130/1000 eq2 with a f/7.7 ratio

Meade 130 Polaris EQ with 650 mm focal length and f/5 ratio.

I read that a f/7.7 would be better to watch planets while f/5 would be better to watch galaxies and nebulae and will also give a brighter image.

 

As I am new and never looked through a telescope like those I don't know which to choose. The idea of looking at galaxies really excited me but I also wanted to see planets such as Jupiter or Saturn and it's moons, and at the moment I am not considering photography as I still need to get familiar with the telescope but in the future I would love to take some photos so brightness could be important.

My question is how much difference would I noticed between these two focal ratio when I looked at planets and galaxies. Would I get a much better view of Saturn with a f/7.7 or not really?

Thanks in advance for your advices

[John]

Hi and welcome to the forum

Both these scopes will show all the objects you are interested in (galaxies and the planets) and show them quite well.

Personally I would probably go for the 130mm F/5 but I would choose the Skywatcher branded version because I'm confident that its primary mirror is a parabolic one wheras I'm not sure about the Meade. This is the Skywatcher one:

https://www.firstlightoptics.com/reflectors/skywatcher-explorer-130p.html

The 130mm F/7.7 has a spherical mirror (thats the profile of it's optical surface rather than it's overall shape !) which can work OK but generally parabolic figured mirrors work best.

Hope that helps

 

[RT65CB-SWL]

Hi @Mezz and welcome to SGL. 

Good advice as above given by @John. 

Astrophotography is a steep-learning curve. Before you to get hooked, buy a copy of Make Every Photon Count. You will need a 'fast' 'scope to begin with. It will need to be perfectly stable & polar aligned mount, and you will need plenty of patience, plus other things.

[Demonperformer]

Hi, Mezz, and welcome to SGL.

For planets you want magnification (which is dependant upon the focal length [1000 vs 650], but the important thing for magnification is to have enough light, which is governed by the size of the mirror which is the same in these cases), but you can get the same magnification on the f5 scope ... just add a 1.5x barlow lens before the eyepiece.

For the same eyepiece, you will have a smaller brighter image on the f5 scope. This can be important for things like galaxies, whose light is spread over a large area, so lower magnification often makes them easier to find/see.

Enjoy the journey.

[alacant]

6 hours ago, Mezz said:

never looked through a telescope like those

I'd recommend going along to a nearby astro club where you can try them out. You then have first hand experience of what a galaxy will look like before you make a purchase e.g. even in big telescopes, galaxies show as little more than fuzzy blobs of light. If you're prepared for that then that's great.

HTH

[mikeDnight]

Hi Mezz,

At the price you're going to pay for 1he 130, I'd seriously consider this instead! It's a far better scope all round and very capable as a lunar, planetary and deep sky instrument.

 

[Demonperformer]

Although OP should be aware of the serious limitations of a dob when it comes to imaging (which has been stated as a future aim).

[Mezz]

12 hours ago, John said:

I would choose the Skywatcher branded version because I'm confident that its primary mirror is a parabolic one wheras I'm not sure about the Meade.

Hi John,

 

Thanks for your advice, I will go for  a f/5. I did a quick search and looks like the Meade has a parabolic mirror too. Also it is cheaper than the Skywatcher, would you still recommend the Skywatcher one? Is it a better brand?

[Mezz]

Thanks all for your comments, they really help! I am going to go for the f/5.

No my doubt is whether to get a Motor Drive one or not, is that worthy?

Also what about the finderscope? The telescopes I am looking at come with red dot but I have read it could be hard to find objects with a red dot, harder than with a 6x30 finder; is that true? What are the main difference between a red dot and a finder?

[Demonperformer]

If you want to image in the future you will need a driven mount. But I am not sure that the one that comes with this scope would be adequate, depending on what you want to image. The mount is the most important bit for imaging. 

Rdfs work quite well if you don't have any LP - particularly the orange lights are a problem. If going for a finder I would go for an 8x50 or 9x50 personally. 

[John]

48 minutes ago, Mezz said:

Hi John,

 

Thanks for your advice, I will go for  a f/5. I did a quick search and looks like the Meade has a parabolic mirror too. Also it is cheaper than the Skywatcher, would you still recommend the Skywatcher one? Is it a better brand?

I think both scopes are made by the same manufacturer. Recently a number of the lower cost Meade scopes seem to be identical to the Skywatcher ones apart from branding / colour scheme differences. So go for what seems to be the best value. Do buy from a reputable astro dealer though so you have access to some advice and decent service if you need it.

I don't think the mounts on these would be good enough for imaging (even if motor driven) but they are OK for visual observing.

Personally, if I had just one finder, I'd go for the red dot type over the optical type. I actually prefer to have both types on the scope but they are not supplied that way I realise that.

[Louis D]

1 hour ago, John said:

I think both scopes are made by the same manufacturer. Recently a number of the lower cost Meade scopes seem to be identical to the Skywatcher ones apart from branding / colour scheme differences.

Interesting.  I'm pretty sure Synta owns the Sky-Watcher brand and Ningbo Sunny owns Meade, and yet they get their cheaper telescopes from the same supplier?  If so, you might not be able to extrapolate Synta mirror quality from their larger scopes to that of their smaller scopes if they're outsourcing the production to a third party.