Telescope advice - goto with tracking

[john10001]

I just wondered if anyone knows what the weight of the different mounts are that go with the Skywatcher telescopes? E.g. the EQ2, EQ3-2, NEQ3, EQ5, HEQ5, EQ6 and what the maximum size and weight of telescope they and the motors can accommodate? I'm also not sure who manufacturers these mounts? Is it all the same company that makes the Skywatcher telescopes? I was just trying to gauge what the portability of these mounts would be including motors, goto functions, power pack etc.

My next question is just about the telescopes in general. I quite like some of the Skywatcher telescopes like the Explorer 150 and 200 and I also like the telescopes that Orion make.

Regardless of whether tube length is better for one type of observing or not e.g. near sky objects like the moon and planets or Deep Space Objects, isn't it always better to have the lowest F number possible for photography and imaging? If so then an F4 or F5 is going to be way better than F8, F10 etc?

I also just wonder which if any telescope you have or are thinking of getting if you are new to this like me and don't yet have one? If you have one already I just wonder how you find it with the mount you have for weight and portability?

I am thinking of getting a 6 or 8 inch telescope at some stage, I can't afford just yet but I am just doing a lot of research for when I can. I'm trying to weight up what a good mount would be in terms of balancing its weight but still having something sturdy and portable to get the best cost and value of the both?

In order to do astrophotography you really need to have a dual axis motor don't you so that it can accurately track an object through the night sky for its ascension and declination during that time? Would you still be able to track effectively by only having a goto scope if you kept hitting a button to keep it aligned? Or if you only had a single axis motor?

Last question is, would you say any of the Dobs that Orion make that now also have tracking as well as goto are worth considering given their price point or is it always going to be better to get a Newt. Reflector on an EQ mount?

Thanks very much for your help and advice.

John

[brantuk]

Hi John - I'll try and answer most of what you ask:

There's no such list of mount/scope weights - usually it's stated on the spec of each scope but some don't. Synta I think it is, own SW and Celestron - all operate through dealers in the UK.

There's no all rounder so some folk have more than one scope. Generally big dobs for observing dso's (due to light gathering power), Catadioptrics for planets (for sharpness of long focal lengths), and appochromatics for widefield fast dso photography.

You'll find a 6" or 8" is a great start - the beefier the mount the better. I'd suggest a minimum EQ5 or CG5 for these, much over 8" look to the EQ6 and above. The 5's are very portable the 6's are starting to get very heavy. Anything under a 5 tends to rely on design to make them stable rather than weight.

For astro photography alt/az mounts can't easilly produce the same accuracy of tracking as eq mounts. Goto scopes usually go to the object and track for you automatically (wether al/z or eq).

Alt/az tracking is fine for observing anything, but limited to solar system objects for short exposure photography, unless you polar align them on a wedge. For imaging dso's, a polar aligned eq mount allows you to track in one plane (RA) allowing the longer exposures required to capture very faint light. However you also need to use guiding and two motors (ra and dec) for best results.

Tracking with ra motor only requires odd tweaks in dec - fine for observing but would ruin a long exposure.

Imaging is very expensive - a fast wide field short tube appo on an EQ6 will set you back the best part of three grand by the time you add cameras, guide scope, and ancilliary bits. Or you could maybe save a grand doing it second hand.

But a webcam on an auto tracking dob can be as little as £300-£400 for some nice shots of planets. You really need to know what you want to image, the appropriate type of scope, and the best type of mount to drive it. So set a budget, do the research and choose wisely.

Hope that helps

[dmahon]

Most important rule: the mount must be sturdy.

Focal ratio is important for imaging, the lower the better. You also require a flat field with no coma and no chromatic abberation (there are addons to help reduce coma, flatten the field and reduce the focal ratio [and focal length]).

Focal length, together with your chip size, decides the size of image you will get at the end of the day.

Play with this - http://www.12dstring.me.uk/fov.htm

Shorter focal lengths are easier to start imaging with.

Any goto scope will be able to track - it will have the motors in to do the goto. If it is not polar aligned, however, there will be field rotation apparant in exposures over 30 seconds or so. You can image with a plar aligned GEM mount that only tracks in RA, however to get good images you will want to use a seperate guidescope and issue corrections in both axis, so you'll end up selling it and buying something else later on.

The most commonly recommended startup kit for astrophotography when someone is beggining from scratch is:

HEQ5

ED80

Canon dSLR camera (preferably a model with liveview)

Look at the website of OVL (the distributors of Skywatcher kit in the UK), which has the weights listed for most of the mounts (and scopes). Stick to half the maximum weight to get the best out of the mount for imaging.