FOV

[Guest dindy]

As mentioned in the welcome forum I do not have a telescope as yet and as usual going round in circles as to choice.

 

I will be observing only and no plans to do photography.

 

 

What I am not sure of is how accurate is the Field of View Calculator in Astronomy Tools? I know the viewing site, dark skies or polluted is a factor but what about the magnification? A 8†sct with say a 10mm eyepiece for example gives far greater mag than a 200 dob with same eyepiece. I know the 8†sct has twice the focal length of a 200 dob and therefore you will get greater magnification but does the FOV calculator give a realistic comparison? I only have the FOV calculator to go on a guide as to what the 8" ota below will show me.

 

 

I am currently looking at the Celestron C8 SCT Advanced VX Goto or possibly if funds allow the Celestron Nexstar Evolution 8. I know in the early days of release the VX mount (2013-14) had a lot of problems so I read associated with the power connection, tracking etc. true most have to do with user error, experience, but was wondering if any of the earlier faults if that is the correct word have been corrected by Celestron. I also did read that someone pointed out Celstron say only use their powertank to fire up the mount, that may have been sales talk.

 

Not a great deal on reviews or problems with Evolution 8 apart from one battery problem and again user errors which were sorted. So for the time being wait for a clear night then out with binos & Planetsphere.

 

So much to consider & think about, I am sure your input & experience will be greatly appreciated.

 

[Guest CodnorPaul]

Hi dindy - welcome to the forum!

 

I use an 8" sct and have never found the FOV a problem - true they are not as wide as an F5 reflector however there are very few DSOs that do not in with a 2" EP and diagonal fitted, plus the long focal length is very easy on EPs meaning that you do not have to spend a fortune to get very well corrected EPs.  They are great OTAs and you wont go far wrong with one, the views are incredible on planets and DSOs.

 

I am very much an sct man after comparing my views with other designs, but others will be along shortly that are reflector or refractor people - it really is a personal choice.

 

As for mount I would suggest the AVX being an EQ mount is preferable but I had bad experience with my OTA on the old SE mount which was the single fork arm version before the Evolution.  If you can find one I would prefer it instead on an NEQ6 or HEQ5 mount - they are a bit quieter than the Celestron ones, but I haven't heard an AVX running.  I have hear an evolution, and my previous SE mount, and for me the amount of noise was a problem in the dead of night.

 

As for the FOV calculator I will leave that to someone who knows a proper answer...

[Daz Type-R]

Hi Peter,

 

Don't get too hung up on magnification, in any telescope, approximately 200x magnification is as high as you want to go except on the very rare 1-2 nights a year when the seeing is exceptional.  Remember, an eye piece magnify's  everything that is in front of it, so the object you are viewing as well as light pollution, atmosphere ETC.

 

If for example, you are interested in the planets, then a wide FOV is not really required as you will be focusing entirely on the planet in the center of the EP, so a wide FOV is just a waste.  A scope with a focal ration of F8 upwards would be preferable here.

 

If for example, you want open clusters, wide DSO's ETC, then a wide FOV will help, coupled with a low power, 2" ep like Paul said above, so a scope with a fast focal ratio of F4 or lower would be beneficial.

 

This is why I opted for a 200P (one of many reasons) as its focal ratio is F6 so sort of in the middle, and with the right kind of EP gives nice wide views but is also OK on the planets.

 

The scope you have mentioned above is nice, will give good views and you should enjoy using it, perhaps a little more info on what you plan to observe, coupled with a budget and if you would like to cart it around to dark sites, want a manual setup or GOTO ETC, would help us to advise.

 

Good luck in your search and let us know how you get on.

[Tweedledee]

Welcome to EMS Peter.

Yes, the FOV calculator is accurate.

The angular size of the FOV is not affected by the viewing site or light pollution, although that will limit how good a view you get. The parameters you input for the focal lengths of scope and eyepiece and its apparent FOV are what affects the results, so just make sure you input those correctly. The magnification is calculated within the program and used in calculating the other results.

Just to complicate matters slightly, when you focus an SCT by moving the primary mirror relative to the secondary, which is the usual way for n SCT, the focal length of the system changes slightly. Therefore the actual FOV may be slightly different from that shown on screen, but it will be near enough and maybe only several percent different. So don't worry about that it will be as near as makes no difference.

Don't expect to see such detailed views of nebulae and galaxies as shown in those views. The FOV will be correct but those photographs bring out a lot of detail which cannot be seen at the eyepiece. This can be made worse due to light pollution and poor skies.

Enjoy the hobby

[Guest dindy]

Thank you all for your advice ,much appreciated. My observing will be done from the backyard. Got 2 street light problems but in process of thinking of a way to block them out.The normal way would be  2 poles with a say a tarp spread between them. I got a pair of 10 x 50 binos and the lights are a pain in the back..... for my night vision. I was amazed when I just held my hand up to block out the street lamp what a huge difference it made. It would be good to get that sorted out before I start using a scope.

 

No doubt once I get  confident in setting rig up I will want to go to a dark site to experience what it is like, but that is for the future. As far as what I am going to observe I admit that is always a difficult question as apart from some bino observing not done any scope viewing. I may just be a planet person but I very much doubt that as there is so much to see even if just a fuzzy blob it would be great.

 

 I have to admit that seeing Jupiter & Saturn with its rings has always been a desire/must for me. I suppose that really is one reason I am looking a t the 8" sct as I have read they are good for planetery. Not so good for dso`s although again from what I read a reducer would help. Maybe later when I am in a position to I would perhaps buy a 200p for the dso`s ?? Going by the  2 telescopes I mentioned £1300 + for VX or if I save a bit longer the Evolution 8 around £1600.

[BAZ]

I would hang on to your horses for a while, Saturn is very poorly placed for the next fifteen years or so. yes you will be able to see it, but it right down low in the murky stuff.

 

If you go purely down the planetary route, you are really limiting your options, you have seven objects plus the moon to view. True you are able to see the brighter DSO's, but have a think what you want to be looking at every night. The major planets are all visible at around five in the morning at the moment.

 

You are looking to spend a fair wedge of money here, just ask around and see what answers you get before rushing out and buying a scope.

It's only with the benefit of 20/20 hindsight I say this.

 

Feel free to ask folks what they think in the Beginners and help section, you will get sensible advice, well mostly anyway.