Skywatcher Apo 80 Equinox Pro ED refractor or 120 is it worth the extra cost?

[F64]

Hi

have been researching for a couple of months and really into photography would like to get in to astronomy with a scope that produces good quality images. If I were able to get money together what would be the practical advantage of getting the 120 over the 80?

Anyone got a 80 or 120 for sale?

Thanks

Janine

[ollypenrice]

None whatever, they do different jobs when used for imaging. The 120 has a longer focal length, the 80 a shorter, so when they are used for imaging they give a different field of view. It's no different form daytime choice of camera lenses, wide angle or telephoto. The 80 is shortish and the 120 medium in amateur imaging terms. Many of us have more than one focal length available.

Two things to consider; the mount is the heart of an imaging setup and the bigger the scope the bigger the mount. Also the longer the focal length, the better your tracking accuracy needs to be. For this reason the 80 might be a better way to start.

(Our most used imaging scope is an 85mm though we have larger ones available.)

Olly

[dmahon]

The 120 has a longer focal length, therefore you will take more "zoomed in" images.

The 80 has a faster focal ratio, so you will be able to taker shorter exposures.

The 80 has a shorter focal length, therefore you will take more "zoomed out" (widefield) images.

The 80 is lighter, and offers less cross-section to the wind, so will be more stable on your mount and there's less chance of needing to disgard images (and you may even get away with a cheaper mount than you would with the 120).

[Gary Parkerson]

Hi Janine,

If you plan to use the scope primarily for astrophotography, get the 80. The two scopes share a common focal ratio, but the 80 is far lighter. You'll spend far more on a mount that is truly capable of supporting the much heavier 120 under the rigors of astrophotography.

If you plan to use the scope for visual observing as well, the scales start to tip more heavily in favor of the 120 and the far greater resolution and shear light-gathering capacity of its much larger aperture.

For astrophotography with either scope, you will need a field flattener. There are two universal models available that don't also reduce effective focal length and several more that not only flatten the photographic field, but also reduce effective focal length.

Hope this helps.

Gary

[dmahon]

The two scopes share a common focal ratio

Not true for the Equinox series (but it is for the ED PRO series), as the Equinox 80 has a shorter focal length than the 80 ED PRO.

Equinox 80 = 80mm objective, 500mm focal length (F/6.25)

Equinox 120 = 120mm objective, 900mm focal length (F/7.5)

Have a look at this site for the effect that has on the image scale:

http://www.12dstring.me.uk/fov.htm

[Gary Parkerson]

Not true for the Equinox series (but it is for the ED PRO series), as the Equinox 80 has a shorter focal length than the 80 ED PRO.

Equinox 80 = 80mm objective, 500mm focal length (F/6.25)

Equinox 120 = 120mm objective, 900mm focal length (F/7.5)

Have a look at this site for the effect that has on the image scale:

http://www.12dstring.me.uk/fov.htm

dmahon,

You are, of course, correct. I should pay greater attention to such detail. Fortunately, your correction of my oversight would appear to strengthen the argument in favor of the faster 80 for astrophotography, unless image scale is your sole criteria.

I prefer having the benefits inherent to a faster focal ratio and addressing image scale by Barlow or tele extender as target warrants - assuming I can carry but one scope, as is often the case when traveling to remote dark sites. But your preference will undoubtedly vary.

Thanks again for correcting me.

Gary

[F64]

Hi guys

thank you so much for your prompt and knowledgeable replies. dmahon thanks for the link its in my favourites. So if I was to go for the 80 and wanted to increase the image scale then what would you recommend? I want to keep the quality so prepared to buy a quality lens. Also what other size lens do I need as scope does not come with any? Any recommendations?

Thanks

Janine

[astroimpulse]

Not true for the Equinox series (but it is for the ED PRO series), as the Equinox 80 has a shorter focal length than the 80 ED PRO.

Equinox 80 = 80mm objective, 500mm focal length (F/6.25)

Equinox 120 = 120mm objective, 900mm focal length (F/7.5)

Have a look at this site for the effect that has on the image scale:

http://www.12dstring.me.uk/fov.htm

If you change the 120s focal length to 765 you get f6.38 which is basically what the 120 reduces to when using the Skywatcher 0.85x focal reducer. Not as wide as the 80 still but a decent change for the purpose.

But 80s do seem a very popular choice for AP

[Gary Parkerson]

Hi guys

thank you so much for your prompt and knowledgeable replies. dmahon thanks for the link its in my favourites. So if I was to go for the 80 and wanted to increase the image scale then what would you recommend? I want to keep the quality so prepared to buy a quality lens. Also what other size lens do I need as scope does not come with any? Any recommendations?

Thanks

Janine

What camera do you plan to use with the scope, Janine? The dimensions of the camera's sensor will effect your choice of Barlow or tele-extender, although a 2-inch 2x Barlow such as that produced by Skywatcher (ED Deluxe) will handle most sensors without vignetting.

As for eyepieces, there is an excellent sticky thread entitled "Eyepieces - the very least you need" in the Beginners Help and Advice forum.

Best of luck.

Gary

[dmahon]

You don't need any additional lens for photography (other than a guidescope), just the right camera(s). Problem with increasing the scale is you make the scope slower (a 2x Barlow = 2x slower). You would probably be better choosing a different camera or a different scope to change the image scale appropriately, or just cropping in photoshop.

As for visual use, click on that link again (and on "switch to visual view") to see what you will be able to see with various eye pieces. I have 35/22/9/6 mm EPs. I would like a 3 or 4mm EP to finish off my collection, and the 35mm EP is probably superfluous.

I also have a TRF-2008 which is a 0.8 focal reducer / field flattener that is suitable for the Equinox 80.

[Gary Parkerson]

You don't need any additional lens for photography (other than a guidescope), just the right camera(s). Problem with increasing the scale is you make the scope slower (a 2x Barlow = 2x slower). You would probably be better choosing a different camera or a different scope to change the image scale appropriately, or just cropping in photoshop.

You are again correct Dmahon: every scope represents compromises of one aspect or another. But for a photography enthusiast who wishes to explore astrophotography and has narrowed the selection of scopes from between an 80- and a 120-mm refractor, I suspect the 80 would be the most accommodating initial platform for the various reasons explored in this thread. In the end, Janine will be well served by and enjoy imaging and viewing with whatever first scope is selected. Until then, we are fortunate that you are here to share your far-greater experience to which I, of course, must defer and therefore humbly withdraw.

Thanks again.

Gary

[dmahon]

I am afraid that far greater experience only equals 2 months - I am simply regurgitating advice given out on these fora before in many other threads.

I still haven't got my camera yet (but hope to do so at the weekend).

[ollypenrice]

I do an awful lot of astrophotography both for myself and with guests and I would not consider extending the focal ratio of any of these scopes except under very, very exceptional circumstances. I have never yet found the circumstances in which I would do so, either! I can only think of a couple of images on the DS boards which were taken with extenders recently, though I may well have missed some. Steve took his f5 Mak Newt to f10 for a stunning M13 and Rob extended his big refractor on a target as well. It is not what imagers normally do. Normally we want fast f ratios to get good signal to noise and more data in the time available. Time is always limited, however good your sky. The sun, the moon and the seasons put us under constant pressure.

I think the thing to remember is that many glorious targets are large on the sky and need a wide FOV. When you add to this the fact that guiding is difficult (so making short focal lengths and fast exposures an advantage) the advantages of the Equinox begin to assert themselves. If I had to lose either my 85mm f5 or my 140mm f7 it would be the big one with which I would part. (Horrors!)

As an eg of an 85mm scope in action, here are Andromeda and M42, two contrasting targets. An Equinox 80 would get very close to this indeed in my view, despite the cost of the Takahashi used here.

Olly

http://ollypenrice.smugmug.com/Other/Galaxies/M31best-v1/1056334673_daDu7-X2.jpg

http://ollypenrice.smugmug.com/Other/Nebulae-and-clusters/M42CCBOV2010/1100345185_HHd4m-X2.jpg

[Euan]

Anyone got a 80 or 120 for sale?

Shameless plug: For Sale: Skywatcher Equinox 80 with Moonlite Focuser & DC Option

[Gary Parkerson]

I do an awful lot of astrophotography both for myself and with guests and I would not consider extending the focal ratio of any of these scopes except under very, very exceptional circumstances...Normally we want fast f ratios to get good signal to noise and more data in the time available.

Thanks Olly,

The dynamics of forum threads have long been of fascination to me and this one does not disappoint. The 80-mm refractor was recommended largely because its shorter native focal length arguably makes it physically easier (and less expensive) to use for astrophotography and eventually because it does indeed have the fastest focal ratio of the two options under discussion. But, it was then objected that this faster scope of shorter focal length will produce less image scale than the 120-mm option and so the discussion reverted to methods of increasing image scale should occasion arise, for example when imaging a very bright solar-system or even a terrestrial object. And now the thread is back to a discussion of the fact that increasing image scale by extending effective focal length defeats the advantages inherent to the faster focal ratio that first recommended the 80-mm scope. I get dizzy just repeating the tale:-)

All of this is great fun! Thanks. As already confessed, I'm clearly out of my league here, although not totally unfamiliar with imaging. But I'm wondering what Janine is to make of all this. Is the 80-mm with its faster focal ratio and smaller payload profile the best first-imaging-scope choice, or is it the 120-mm with its slower focal ratio and longer focal length resulting in greater image scale? I assumed the 80-mm offered greater overall advantage to a beginning astrophotographer, but am now very interested to know what others of much greater experience recommend. While at it, I'd be curious to know why the Powermates have been so popular with astrophotographers. I've assumed it was to gain desired image scale when photographing the brighter solar-system targets when conditions permit, as I used one when photographing the moon just a few days ago, but I again appear to have been mistaken in that assumption. If it's just not done then I should put my time to better use as well.

Anyway, thanks again for your patience with my attempts to follow this discussion. I'm learning a lot and sincerely appreciate the lessons, although I regret highjacking Janine's thread.

Gary

[dmahon]

I think you're right about the powermates (and barlows0 - they are useful for increasing the image scale when taking pictures of bright (i.e solar system) objects. Some people use x4 and x5 devices, with focal ratios of F/30+, when taking pictures of the moon and planets.

As to what to buy as a beginner - well, that's me, and after asking here for some time I bought the Equinox 80. Not only is it faster, it's lighter (so easier to set up), shorter (so less affected by the wind and easier to guide) and can be mounted on a smaller (cheaper) mount without suffering as much. You'll also probably save around a £1000 going for the 80 on a HEQ5 instead of the 120 on an NEQ6 - which definitely swung it for me.

[Gary Parkerson]

I think you're right about the powermates (and barlows0 - they are useful for increasing the image scale when taking pictures of bright (i.e solar system) objects. Some people use x4 and x5 devices, with focal ratios of F/30+, when taking pictures of the moon and planets.

As to what to buy as a beginner - well, that's me, and after asking here for some time I bought the Equinox 80. Not only is it faster, it's lighter (so easier to set up), shorter (so less affected by the wind and easier to guide) and can be mounted on a smaller (cheaper) mount without suffering as much. You'll also probably save around a £1000 going for the 80 on a HEQ5 instead of the 120 on an NEQ6 - which definitely swung it for me.

Thanks again Dmahon. I'm surprised to learn that you've only been at this for just a couple of months. You've advanced well beyond beginner status in a very short time, which I assume is in large part due to the excellent resources of this community, but mostly the result of your shear enthusiasm and innate talent for this stuff. I'm pleased for you that you found astronomy just as I'm happy for astronomy that it attracted you. As for you choice of scopes, I work regularly with a fellow who's become one of the "rock stars" of astrophotography and he still does much of his nightly imaging through small apos.

What camera are you planning to match with your Equinox 80?

Gary

[dmahon]

I'm hoping to finally pick up my promised second hand Canon 450D this week, from a (non-astronomically inclined) friend who has upgraded but lives the other side of the country.

I have an SPC900 webcam for lunar / planetary (with Barlow) imaging.

I keep considering a CCD, but will give it a go with the DSLR first.

[svetimas]

Hello, you had a nice discussion about 80 and 120 so maybe someone would have advise where to look for used Skywatcher Evostar 80ED DS-PRO or Equinox 80?

[Demonperformer]

DELETED ... didn't read the 'used' bit!