what should I be able to see with an 8" sct

[Emdeejay]

I just got an 8" nexstar evolution and it's great I love it. But I feel like I should be able to see more than I am seeing, I can't see any nebulae to speak of, granted I know I would see orion since I could see it in my 4" refractor quite well, but its not out at night right now. But I can't see any nebulae at all. I'm wondering is this cause the moon is so bright r.n.? Is my scope just still not big enough? Or is it possible this area is more light polluted than I previously thought. It gets pretty dark out here but I am near a larger well lit city, however my entire neighborhood has 0 street lights, just porch lights and backyard lights that people put in themselves, so it is quite dark here. However I feel I should be able to see more nebulae, I'm not expecting colors and all that I know that's not realistic at this level of aperture(or any really unless it's like a 14"or 16" literal light bucket and even then...)however I still think I should be able to see some. Andromeda is a light fuzzy patch in the sky, I can see some star clusters and planets and stars obviously and the omega nebula shows up just barely as a hardly noticeable gray patch that no1 would notice unless they knew what to look for. 

Is my scope just too small still, is the moon too bright right now? Or am I suffering from a case much worse light pollution than I even knew I had. Please lemme know, cause I'm feeling a big discouraged, like what must one spend to be able to see up there. I'm not going into this with unrealistic expectations either, I know I'm not gonna see stuff like you see in pics or even close to it for that matter. But I feel like this scope should be providing some better views than this. Lemme know your thoughts please. I just wanna know what I should be able to be seeing so I know if its the scope or what. Thanks. All input is appreciated.

Edited June 29, 2021 by Emdeejay

[Padraic M]

You have two concepts to consider with your 8" SCT. Firstly, even though it's got more aperture than your 4" refractor, it's got an f10 focal ratio. Your 4" may well have been an f5, which has twice the light-gathering power. Objects will appear half as bright in your SCT. This means that your skies had better be dark, and your eyes had better be dark-adjusted, especially for any faint deep-sky objects. SCTs really are better for planets than for nebulae or galaxies.

The second concept is field of view. With such a long focal length, you will need to use a wide eyepiece on a small target to fit everything. Andromeda won't fit, nor will Orion. Both of these will be better in your 4" frac.

At this time of year, you could try M13 the Great Globular Cluster in Hercules. It's a small, compact and very bright object that is high in the skies at this time of year. There are other clusters in the same area too.

Also get some planetarium software for your PC and use it to check what field of view you will get with your scope and your eyepiece. Stellarium is excellent and free. You can enter in your scope details and your eyepiece details and the software will show you what you will see.

Here's an example of M31 in a C8 SCT with a 26mm eyepiece - it will be nowhere nearly as bright as this but you can see that all you'll fit is the core as a fuzzy white patch. You won't see any detail.

 

 

On the other hand, here's what M13 will look like:

[Cosmic Geoff]

Without a measure of the light pollution in your area, it is hard to comment, but you may have to manage your expectations.  It is hard to see more than a handful of galaxies from a moderately light-polluted area, even with an 8" SCT.  And a near full moon will not be at all helpful.

In darkest Devon, I found that I could see lots of galaxies with my 8" SCT, and I got tired and cold before I ran out of galaxies to look at.  But generally they look like faint grey smudges.  I deliberately visited at a time with minimal interference from the Moon.  The Spring is the best time for galaxy viewing.

I have found that electronically assisted astronomy is a much better way of seeing galaxies, as a 4" refractor with planetary camera and laptop attached, showed about as many galaxies at my home site as the bigger telescope did at a dark location. I went through a list of galaxies down to mag 10 to 11 and it picked up every one.

[Clarkey]

Good advice above. Just a little addition

I am really an imager more than an observer, but you could consider some filters to improve visibility. These could be used with both the SCT and refractor. Maybe something along the lines of a UHC filter or even an OIII filter might help with with the views. Again, the effectiveness will depend on the LP.

[jonathan]

Check this map for your area's light pollution, click a point to get detailed info including the Bortle rating - a rating of 4 or lower should afford you plenty of nebula viewing capability, although I'm sure people will tell you they've observed nebula probably up to Bortle 6, assuming there isn't a porch light ruining your night adapted eyes or causing very localised light pollution.  Nebula are among the faintest objects so need to be observed when the moon is either below the horizon, a thin crescent or new.

Be sure that your SCT has a suitable dew shield in place, this will help to cut down any stray light and also is a necessity on everything but the dryest of nights to help keep dew from forming on the front glass corrector plate.  Dew heater tapes will probably be necessary as well during the damp autumn / winter nights.  Use a dimmable red LED torch to see by (a rear bicycle light is probably too bright IMO), and make sure there are no white light sources, windows with lights on, etc visible from your observing location.

Also make sure the goto system is functioning correctly, it might be that it's not pointing directly at the target so with a narrow field of view you're just missing it.  Test it out on bright objects such as Polaris or the moon with a low power eyepiece to check how accurate the alignment is.

[Emdeejay]

I always make sure all lights are off in my yard and house and it's usually pretty dark in NY immediate area but go a few miles and I've got some pretty brightly lit areas. Also would a focal reducer help or would I be better off using a 40mm wide angle eyepiece. I tried a focal reducer but I wasn't caring much for the view through it, it was severely vignetted whereas imo the 40mm gave as much of a wide view as the f.r. did, but with the 40mm ep I got a big crystal clear view as opposed to the small vignetted view of the f.r. maybe I need to add the space between it and the e.p. it's just one of those ones that screws on the e.p. I couldn't spring for the expensive f6.3 celestron f.r. not yet anyways.... I could see andromed better with sct imo it didn't look much different from the 4", and the 4" is an f6.5 so I had really good views with it. I got the 8"sct cause I wanted some bigger aperture with better zoom capabilities and then I thought with a focal reducer it would be good for dso's as well so it seemed like the best choice but the focal reducer so far isn't working how I was hoping, I have no spacing between it and the eyepiece though.... I would have preferred a slightly bigger Dob with goto but the whole world seems to be experiencing a quite literal telescope famine right now, so I didn't have as many choices as I would have liked. I originally had wanted an AVX 8" newt with f/5 but after ordering it and waiting 3 weeks I was told it wouldn't be in stock again till June 2022 so I canceled that order and this was one of the only telescopes I could find that I really liked. Stupid covid freaking ruining the world man. But I digress... I love the sct and with the 40mm e.p. I think it's pretty much as wide an angle as the 4" f6.5 scope. I'm gonna check that light pollution chart. Thanks for that.

[Emdeejay]

It says my area is 5 on the bortle rating. But going by the colors on the rating it looks somewhere between 5 and 6 so it's definitely quite light polluted here, I've never seen the milky way or central galaxy as it calls it, I didn't know you were supposed to be able to see it with the naked eye haha. So yea apparently my area is much more polluted than I originally thought. I'll have to go outside next time the power goes. Not that I want that to happen either, it's too damn hot for that. It's a shame that's the only time I'd be able to see most of that stuff.... so apparently I'll have to go camping somewhere if I wanna get a glimpse of anything real well. 

[Cosmic Geoff]

TBH I think focal reducers are mainly intended for imaging. And a 0.5 reducer seems rather extreme. If a f5, 6" or 8" scope is what you really want, perhaps you should think of getting a f5 Newtonian instead.   However in a light polluted area there is not much you can do with a f5 scope visually that you can't do with a f10, other than look at wide star clusters.

At your home site you should concentrate on looking at smaller objects of high surface brightness: planets, double stars, planetary nebulae, globular clusters, rather than low surface brigtness objects like galaxies and nebulae that will not show up well.