100 or 120

[Simon P]

I am carrying on with my reading up but am gradually narrowing things down,

It has been suggested to me that to start I should just get the scope and mount, once I have got the hang of them, move on to a better camera and guiding. Camera wise the ZWO1600 mm would be the favourite so far for the step up.

Mount wise the SW EQ6 R pro would be the leader so far.

I have my eye on the Skywatcher Esprit pro 100 but could stretch to the 120, do people think I would get enough improvement to justify the extra cost?

Any comments and advice would be welcome.

[nfotis]

What's the expected weight of the scope?

If you expect around 11 kg with focuser, camera etc attached, the HEQ5 mount may be enough for your needs. If not, look into the NEQ6 mount *if* you can carry it easily.

 

Regards,

N.F.

 

[Padraic M]

Not sure that there will be a quality difference as such between the 100 and the 120 - both will be excellent - but a field of view difference, as they have different focal lengths. Check the various fov calculators online or input these scopes into Stellarium and see the difference the focal length makes to fov.

Many folks on here use the Esprit 80 or similar as their primary scope, matched with the ZWO ASI1600MM. The HEQ5 will carry this combination comfortably with the usual accessories e.g. focuser, filter wheel, guidecam and camera; and you'll save a heck of a lot of money over the 100 or 120. It just depends on what you want to image - large nebulae (go for the Esprit 80) or small galaxies/planetary nebulae (go for longer focal length). With the shorter FL at least you have the option of cropping. With a long FL you don't have that choice, and it makes guiding more difficult.

 

[teoria_del_big_bang]

Basically as @Padraic M says above it is the field of view that will differ not any quality as such (until you start cropping smaller targets).

Unfortunately there is no real ideal do it all scope. Below are some examples and shows the FOV for the Esprit 80, 100 and 120 with the ASI1600.

For a large target, such as Andromeda as below , or something like the very popular Orion Nebula, the ED80 wins hands down as the others cannot get the whole image without cropping part of it.

But for smaller objects, such as the Dumbbell Nebula the 120 would be better.

 

Now of course you can always crop any image to make the target look larger but the more you crop then the quality of that image is reduced.

And you can always do a mosaic if your field of view means you cannot get all the target into your image, but that adds complexity and means you need much more data to complete your image.

It's a difficult one to give advice on because if you are relatively new to all this then some of the popular targets for beginners are Orion Nebula, Andromeda, North America Nebula really you are better with the ED80 but obviously the smaller targets the 120 (or even the much more expensive 150) come into their own.

Personally if it was a first scope I would get the 100ED (or even the 80ED) and put the extra money into the best mount I could afford making it as future-proof as I can. A HEQ5 is fine for the ED80 and 100ED (although with all the other equipment such as filter wheel, focusser, camera etc the 100ED is about the limit for the HEQ5). If later you get something like a 120 or 150 and you invested in a good sturdy mount with a good payload capacity then you will not need to upgrade your mount.

Steve

 

 

 

Edited August 11, 2020 by teoria_del_big_bang

[ollypenrice]

I'm not entirely in agreement with your conclusions on priority. Mine would be mount-camera-scope, but not to worry.

The 120 is neither better nor worse than 100. If you want a wider FOV the 100 is better. If you want higher resolution the 120 is better. But, of course, it isn't that simple! (It never is.) If you went for the 120 what would your sampling rate be in arcsecs per pixel? If it were, say, 1 arcsec per pixel can you guide with an RMS of 0.5 arcsecs? If you can't there is no point in having the longer focal length with the given camera. Your guide RMS in arcsecs needs to be no more than half your image scale in arcsecs per pixel.

If you want a simple answer, the wider FOV of the 100 is likely to be more productive than the higher resolution of the 120 but the key variables are guiding accuracy and pixel size.

Olly

[Simon P]

Thanks for the advice, lots to ponder.