Comparison of two SW

[igorigs]

Could someone tell me is SW 130/900 on EQ2 a lot better that SW 90/910 on EQ2 refractor? 

Primary for observing planets..

[Dave Lloyd]

Hi there and welcome. Someone with experience of these instruments will be along shortly. 

[sloz1664]

Hi and a very warm welcome to the Lounge

Regards your question.. are you asking if either a SW 130/900 or a SW 90/910 are better on an EQ2 mount I would go with the SW 90/910. The SW 130/900 would not be stable on the EQ2. To observe planets requires a stable mount.

Steve

[DaveL59]

Can't speak for the 90 but I have a 130/900 on EQ2 and while it can wobble it does a reasonable job of looking at the moon and planets. As steve has said though it's not the most stable and pretty much at the limit for the EQ2 mount. I found in use that you just need to minimise the physical contact with the scope and controls. Having the clockwork drive helps as once you have the target in view the motor will keep track reasonably well, tho you will need to have placed the mount so it is roughly polar aligned for that to work well.

I do find tho that placing a camera piggy-backed on the tube ring seriously affects balance with the one supplied counterweight, so if you plan on doing anything like that you'd want to consider adding an extra weight. 

[igorigs]

Thanks folks!

@sloz1664 Question is which one is better for observing, higher power... 

 

 

[vlaiv]

I'm not sure that anyone can answer that question if they did not have a chance to use both scopes side by side.

I can give you theoretical answer to that question, but it's probably not going to be very helpful. In the end, performance will be very close between two scopes without a clear winner.

Theory says that two things are important for "perfect" scope and planetary performance - or rather let's say potential planetary performance as atmosphere plays the most significant part and that is not instrument related.

1. Aperture size - larger aperture gives more resolution - more details can be seen on the planet

2. Central obstruction - larger central obstruction reduces contrast - planet looks more "dull" and this also impacts faintest features - as image gets "washed out" these small faint features get lost

90/900 has smaller aperture but has no central obstruction, while 130/900 is the other way around - has larger aperture and but has central obstruction - even spider support is very thick.

On top of that, 90/900 is achromatic refractor and it shows false color - chromatic aberration (although it has little of it being slow at F/10) and that impacts the view, while 130/900 has spherical mirror - although this has been debated:

In the end, there is sample to sample variation in both scopes and some will be better / some will be worse.

What I can do is show you that aperture with these small scopes does not make as much of a difference as one might think.

Here are images of Jupiter taken with 100mm scope and 130mm scope - in this case 130/900 Newtonian as I had that for my first scope:

vs

and

vs

Don't look at the size of respective planets - that depends on focal length, camera and barlow lens used - look at the level of detail.

Not much difference is there? Btw, images show better detail than ever possible visually - explanation is too technical, but it comes down to processing of the image - something that eye can't do but software does in processing of the image.

[igorigs]

18 minutes ago, vlaiv said:

I'm not sure that anyone can answer that question if they did not have a chance to use both scopes side by side.

I can give you theoretical answer to that question, but it's probably not going to be very helpful. In the end, performance will be very close between two scopes without a clear winner.

Theory says that two things are important for "perfect" scope and planetary performance - or rather let's say potential planetary performance as atmosphere plays the most significant part and that is not instrument related.

1. Aperture size - larger aperture gives more resolution - more details can be seen on the planet

2. Central obstruction - larger central obstruction reduces contrast - planet looks more "dull" and this also impacts faintest features - as image gets "washed out" these small faint features get lost

90/900 has smaller aperture but has no central obstruction, while 130/900 is the other way around - has larger aperture and but has central obstruction - even spider support is very thick.

On top of that, 90/900 is achromatic refractor and it shows false color - chromatic aberration (although it has little of it being slow at F/10) and that impacts the view, while 130/900 has spherical mirror - although this has been debated:

In the end, there is sample to sample variation in both scopes and some will be better / some will be worse.

What I can do is show you that aperture with these small scopes does not make as much of a difference as one might think.

Here are images of Jupiter taken with 100mm scope and 130mm scope - in this case 130/900 Newtonian as I had that for my first scope:

vs

and

vs

Don't look at the size of respective planets - that depends on focal length, camera and barlow lens used - look at the level of detail.

Not much difference is there? Btw, images show better detail than ever possible visually - explanation is too technical, but it comes down to processing of the image - something that eye can't do but software does in processing of the image.

Oh, now I understand it a lot better, thanks! 

Last night went out of town (btw I live in Kikinda) to observe moon and just to check Jupiter and Saturn. Was astonished how bright the Moon is under a scope. Saw Jupiter much better then from my pavement as the temperature was a lot colder then in town. Could see Saturn much clearer also. I know that I won't be able to see them that close with this scope and that you actually see them like a dot having 1cm radius.. Still I am in love with it. 

Will Andromeda be visible (the shape) under very low light pollution? And will I be able to distinguished the two rings around Saturn? Right now I see them as one.. 

[John]

I was observing last night with a 90mm refractor very similar to the Skywatcher one and I could see the Cassini Division in Saturn's rings, Jupiter's Great Red Spot, the Andromeda galaxy and also split the "double double" stars Epsilon Lyrae.

I have been observing for many years with many different scopes which makes it easier to find and observe these targets but the 90mm refractor is certainly capable of performing to the limit of it's aperture.

I have only used the Skywatcher 130mm F/7.8 newtonian once or twice (a friends scope) but that worked pretty well too. As @vlaiv says, there is very little to pick between these in terms of capability and performance.

The refractor might be a little more rugged and maintenance free. The reflector will show fainter objects better because of it's larger aperture.

 

[igorigs]

@John Could you tell me which eyepieces you use? Observed them last night but the Moon was so close to them that I couldn't see  GRS and Cassini Division. At least I think it was because of the Moon... 

 

The question of comparison of these two was just to make me satisfied of what I bought. Wanted to buy the 130/900 but not a single shop had it at this time in my country so I found a used 90/910 refractor. Was just curious if it would make any huge differences. Thanks for both of your answers and now I can observe in peace. 

[John]

Last night I was using a 7.2mm - 21.5mm zoom, the Baader 2.25x barlow to get higher magnifications (I used up to 180x lest night) and a 25mm 58 degree Skywatcher eyepiece for low power, wider views. These are my travel / out reach eyepieces rather than my regular ones but they worked well in the refractor last night.

 

[vlaiv]

14 minutes ago, igorigs said:

Will Andromeda be visible (the shape) under very low light pollution? And will I be able to distinguished the two rings around Saturn? Right now I see them as one.. 

As John above said - you should be able to see Cassini division in your scope. I certainly saw it from my balcony few days ago with 100mm scope - a day before above images to the left were taken.

You just need practice to spot those things now. As you gain experience - first thing that you will notice is that not each night is the same in terms of quality of the views. This is key for planetary - you need to recognize a good night with steady atmosphere.

Good way to tell is to just look at the stars with naked eye - many stars twinkling - probably not a good night for planetary observing - few stars twinkling - probably a good night for planetary. No stars twinkling? Either grab your scope and go if you can see them, or stay inside because it's cloudy

Moon is now very bright because it is almost full moon - larger area of it is illuminated and it really shines. Don't try to observe deep sky objects now because the moon causes bright sky and contrast is lost. Moon itself is best observed when it is not full first / last quarter and few days prior and after that are best.

In order to know what to expect with Andromeda galaxy / M31, here is field of view of your telescope with 25mm eyepiece:

You won't be able to put all of it into your eyepiece - and you'll probably only see central bulge. Look for M32 and M110 as markers - two gray blobs.

If you get GSO 32mm eyepiece, view will be a bit better like this:

You can use this website to check what sort of field of view you can expect from a telescope + eyepiece combination:

https://astronomy.tools/calculators/field_of_view/

[igorigs]

31 minutes ago, John said:

Last night I was using a 7.2mm - 21.5mm zoom, the Baader 2.25x barlow to get higher magnifications (I used up to 180x lest night) and a 25mm 58 degree Skywatcher eyepiece for low power, wider views. These are my travel / out reach eyepieces rather than my regular ones but they worked well in the refractor last night.

 

Thanks, will definitely save this for future!

 

@vlaiv Once again, thanks mate! I know for this website and I've used it to compare some settings.. Wish that in real life the weather conditions were perfect for seeing as they are on the website 😅

I will definitely save some money for a better eyepiece as these ones are good for an amateur as I am but would be really nice to improve it as it is possible to do it..