fuzzy saturn

[greyknight]

Hi all,

I can get nice close up views of saturn but not with any great focus or clarity. I'm using a Celestron 130eq with an 8mm through a 2 x barlow. I've got a 4mm which isn't great through the barlow and a 12mm which isn't too close, does anyone have any advice please or have I reached my 'scopes limitations?

Thanks guys

[Pappy Nick]

Hi Greyknight ...

I've got a Skywatcher 130p and I managed to get Saturn nice and clear with the supplied 10mm & 25mm eyepieces and a Barlow. Mind you that was going back a couple of months when it still quite cold, I'm not sure if the recent heatwave could be causing you viewing problems with heat-haze, humidity etc;

[umadog]

Your telescope has a focal length of 650 mm. So you're magnifying as follows:

650/12= 54x

650/6= 108x [barlowed 12mm]

650/4 = 162x [barlowed 8mm or un-barlowed 4mm]

650/2 = 325x [barlowed 4mm]

Useful magnification is limited by the atmosphere and by the aperture. Let's take aperture: http://www.cloudynights.com/item.php?item_id=547

At 325x you're at 65x per inch. That's unlikely to be useable: even you have the excellent optics needed to support it, the exit pupil will be very tiny. The 162x is 32x per inch. This is also on the high power end but it may be useable depending on optical quality. Exit pupil still small. The barlowed 12 mm is probably going to be the sort of power which will give you sharp images on most nights.

To get back to the atmosphere. Most nights it's not going to allow you to stray past 200x or 250x. This is due to atmospheric turbulence. The hazy nights are bad for DSOs because transparency is bad, but if the air is still they can be great for planets. Your scope is aperture-limited, though, since you're not going to be hitting those powers very often.

Finally: make sure it's well collimated. You will get a blurry mess if it's not. Your telescope is f/5 and that's fairly sensitive to being misaligned.

[damnut]

Hi Greyknight,

Umadog has it in one. The highest theoretical practical mag for your scope is 260x (2* aperture in mm). At anythig approaching this power you will need excellent viewing conditions and all your optics collimated, clean and a great ep!. Warm days and nights = poor seeing :-(..

Try coming down in magnification without using your barlow, in my 10" sct I rarely was able to use more than 250X which was half the theoretical practical power.

Clear Skies

[Tinker1947]

I think your find its just the conditions, i viewed Saturn last week (Wednesday) and could have driven a bus through the Cassini ring, just the one night, since then its been ok, but fuzzy and nowhere near that view, I have tried every night...Plus the type of EP your using as pointed out by Umadog.....

[Ad Astra]

Umadog is precisely correct. Most commercial (mass produced) optical systems won't perform much beyond 50x per inch of aperture. (2x per mm of aperture for the metrically minded!) This is sometimes referred to as the 'resolution limit'. At 3x per mm, you run into something called the 'visual threshold limit' - much above this, and the image becomes too dim for your retina to detect significant details.

Remember that you magnify everything - the image, the turbulence in the air, the light pollution problem.... You also reduce both contrast and image brightness as you push magnification toward its limit.

A couple of tips for high magnification viewing.

1. Steady air is a must. If the stars are twinkling a lot, this indicated unsteady air (poor seeing), and will limit your magnification. You can help somewhat by making sure you aren't looking over buildings or parking lots, which can radiate heat (and air turbulence!) for many hours after dark.

2. Dark skies are also a must. Getting your scope out away from city lights and buildings often helps solve both light pollution and turbulence problems.

3. Look to the Zenith! As your target moves toward the horizon, you look through more air, more turbulence, more pollution, dust, etc. Your best view at very high magnification occurs when your target is at least 60 degrees off the horizon. If you are tackling Saturn earlier in the evening, wait a bit until it rises higher in the sky.

Besides, viewing later in the evening has many benefits:

1. Fewer people hanging about wanting to have a go at your scope while you are trying to catch Cassini's gap or track down one of Saturn's pesky moons.

2. Fewer lights in your neighborhood. As people go to bed and automatic timers turn off lights, almost every area gets significantly darker after 10 PM, and again darker yet after midnight.

3. Steadier skies. As buildings, parking lots, and even the soil on the ground cools off, the waves of heat and turbulence they generate in the air drop off noticeably. You will often find that the wind calms down significantly in most locations as well (only to pick back up an hour or so before dawn).

The Saturn Observer's Log (attached) may also help. I give it to all my students to help them coordinate and record what they see at the EP as they pursue the ringed giant!

Cheers,

Dan

PS: Welcome to my astronomy class!

Your telescope has a focal length of 650 mm. So you're magnifying as follows:

650/12= 54x

650/6= 108x [barlowed 12mm]

650/4 = 162x [barlowed 8mm or un-barlowed 4mm]

650/2 = 325x [barlowed 4mm]

Useful magnification is limited by the atmosphere and by the aperture. Let's take aperture: http://www.cloudynights.com/item.php?item_id=547

At 325x you're at 65x per inch. That's unlikely to be useable: even you have the excellent optics needed to support it, the exit pupil will be very tiny. The 162x is 32x per inch. This is also on the high power end but it may be useable depending on optical quality. Exit pupil still small. The barlowed 12 mm is probably going to be the sort of power which will give you sharp images on most nights.

To get back to the atmosphere. Most nights it's not going to allow you to stray past 200x or 250x. This is due to atmospheric turbulence. The hazy nights are bad for DSOs because transparency is bad, but if the air is still they can be great for planets. Your scope is aperture-limited, though, since you're not going to be hitting those powers very often.

Finally: make sure it's well collimated. You will get a blurry mess if it's not. Your telescope is f/5 and that's fairly sensitive to being misaligned.

Saturn Observer's Log.doc

[umadog]

Lots of good advice from Dan. Certainly don't overlook dark skies for DSOs, but remember that for planets these don't make any difference. Heat from buildings will, of course, matter. Soil and grass gives off less heat than tarmac or concrete so you should not set up on these hard surfaces.

[greyknight]

Thanks everyone. Excellent advice as always on here. It really is a must for budding astronomers.