9 replies to this topic

[Scott Rose]

I am looking for eyepieces for planetary viewing in a C8 SCT with tracking.   Trying to use Astronomy.Tools to get an idea of what to buy.  What is more important, more magnification or smaller FOV to see a larger more detailed object. 

[donniesoprano]

For planetary observing, since you have a tracking mount, you want the right magnification.  FOV is not really important for you with a tracking mount for the planets.  If you're tracking well, you’re not looking near the edge of a wide fov for a planet that’s centered.

 

“Right magnification” = the correct magnification for the given sky conditions.  Buying a 7mm eyepiece for 300x only makes sense if you have the skies to support 300x. More often useful for most people will be a 10mm for 200x or 15mm for 135x.  Those will be used much more often.

Btw, the object will be the same apparent size at 200x, regardless of the FOV, whether it’s 35*, 55*, 82*, 100*, or any other number of degrees.  It might appear larger in a smaller FOV, but it’s an optical illusion.  200x is 200x.  Using an eyepiece calculator, the size looks different because the box showing the output doesn’t change size for the FOV, so they change the image scale.  Using a calculator like that doesn’t give you an idea of image size, it only shows you how much sky you will see for a given FOV. For planets, those calculators also don’t take into consideration the current apparent size of the planet.

 

ds

[Scott Rose]

Great explanation.  Really appreciate it.

[Cpk133]

I am looking for eyepieces for planetary viewing in a C8 SCT with tracking.   Trying to use Astronomy.Tools to get an idea of what to buy.  What is more important, more magnification or smaller FOV to see a larger more detailed object. 

More important is to find some eyepieces with comfortable eye relief, especially if you wear eyeglasses.  I’d highly recommend getting a binoviewer.  I’ve been using a william optics kit that I see is still sold for about $300.  It comes with a pair of 20mm 66 degree apparent field of view eyepieces and a 1.6x barolw/ nosepiece.  The C8 will focus without the nose piece (may slightly clip some aperture but you wont notice), you can screw the barlow into the bino nose for 1.6x or in front of the diagonal for more magnification.  They also sell a 2x so you have a fair bit of flexibility in terms of power.  I prefer the binoviewer for just about all of my planetary viewing and there are lots of choices and opinions about them.  You really don’t need to spend a lot of money on eyepieces when you have an f10 system.  I’d try to find some used at various fl’s from 14-5mm to see how you get along with them.  Maybe join a local astronomy club and try out other peoples stuff if you’re patient.  

[quilty]

for better detail you need higher power. Wide angle eyepieces are the only solutions like ES 4.7 and 6.7 at 82°

[ButterFly]

The sky is the limit as to how far in magnification you can go - and it's always changing.  That's where a zoom eyepiece is helpful.  It's ready to dial in when the sky lets up, and back away while waiting.

 

A Baader zoom does nicely with tracking.  It's not parfocal, so tracking helps you ride both the focuser and the zoom, without having to also track.  The APM zoom is more parfocal, and has less glare, but it only has a 2x range rather than the Baader's 3x range.  That extra low end will help with an SCT's long focal length.

 

FOV only really matters for the moon.  200x is 200x, but twice the field at 200x means four times as much moon at 200x!  The air never gets calm enough to let Jupiter get big enough that it won't all fit into a reasonable eyepiece.

[Cajundaddy]

I did planetary observing for 30 years with a nice C8.  Most nights a 10-12.5mm was the best choice after the scope was fully cooled down. On those rare magical nights of exquisite seeing I might enjoy a 7mm.

[ABQJeff]

For planetary on a tracking mount it is all about magnification, exit pupil, seeing and good eyepiece that minimizes light scatter.

Seeing: average best seeing across US is ~300x, some can do only 200x, but where I am at I can regularly do 450x, people on the Gulf can do 1000x. That leads to exit pupil…

Exit pupil: most people’s eyes can go down to 0.5mm exit pupil before eye issues (floaters) become an issue or image becomes too dim. Some can only do 1mm. I can do 0.3 mm on the Moon.

So with that in mind and knowing little of you or your conditions: For an F/10 2000mm scope, a 5mm (400x) is a good max magnification eyepiece then get a 7mm and a 9mm or 10mm and you will be set for varying seeing conditions.

TV Delite, Pentax XW, Baader Morpheus are some good ones to look at (thru!)

[12BH7]

My most used planetary EP's with my 8" SCT are a 19mm Panoptic and a 15mm TV DeLite.

[quilty]

not only on a tracking mount

My C9 does best with ES 6.7 mm and goldline 6mm. For Ganymede it's the Omegon 4 mm Cronus when seeing allows.
Mars nothing longer than 6 mm