Magnification on Celestron Advanced VX 9.25

[Neiman]

Hiya, I am a complete novice at this - I’ve managed to see both Saturn and Jupiter on two consecutive nights and I’m just made up to be honest. It’s just awesome. My question is - can I increase the magnification on this scope while viewing ? Or would this only be possible by using a camera and magnifying in software ? Probably a bloody stupid question but if you don’t know - you don’t know lol. 

Many advice would be gratefully received.

Thanks

Neil

[Stu]

Hi Neil,

No such thing as a daft question.

You change the magnification by using different focal length eye pieces. Magnification is calculated as focal length of scope/focal length of eyepiece, so a 25mm eyepiece in your scope gives 2350/25= 94 times magnification. A 10mm eyepiece would give x235.

So, what eyepieces do you have?

[Neiman]

2 minutes ago, Stu said:

Hi Neil,

No such thing as a daft question.

You change the magnification by using different focal length eye pieces. Magnification is calculated as focal length of scope/focal length of eyepiece, so a 25mm eyepiece in your scope gives 2350/25= 94 times magnification. A 10mm eyepiece would give x235.

So, what eyepieces do you have?

I’ve got a 40mm Celestron Plossl on it at the moment.

[Stu]

3 minutes ago, Neiman said:

I’ve got a 40mm Celestron Plossl on it at the moment.

Giving you x59. Worth adding a few more to the collection.

[Neiman]

3 minutes ago, Stu said:

Giving you x59. Worth adding a few more to the collection.

So the smaller the eyepiece focal - the higher the magnification ? Is that right ? So a 10mm will magnify it by  X 235 ?

[Rob Sellent]

Aye, that's it

I don't want to overload your initial enquiry, so will simply throw this out as a little more unnecessary information for you to take account of as you wish.

On occassions, I think it's an error solely to pick eyepieces based strictly on magnification. Exit pupil is also an issue. Briefly, your average adult eye will dilate to about 6mm or 7mm in diameter. So, an exit pupil of say more than 6mm is passing more light to the eye than is necessary or useful. On the other hand, as exit pupil decreases, so does the light entering your eye. As exit pupil decreases to less than 1mm, viewing becomes evermore uncomfortable and observers start seeing weird floaters drifting in front of their eyes. By the time you get to 0.5mm and less, exit pupil is so small that for all but the most bionic of eyes the experience is quite uncomfortable.

I mention all this because in a significant way, exit pupil is linked to magnification. You can work out your exit pupil with your scope by either: i) scope's aperture in mm / magnification or ii) eyepiece's focal length / telescope's focal ratio.

Your SCT has an aperture of 235mm and its focal ratio is f10 (scope's focal length / scope's aperture). So your 40mm Plossl is giving you an exit pupil of around 4mm and a 10mm Plossl would give you a 1mm exit pupil. It follows that the smaller the exit pupil, greater is the magnification.

Ultimately, your eye and local seeing conditions will set the boundaries but as a general rule of thumb, with the exception of double stars, it is only on the better nights of seeing will you be using more than 200x magnification. Starting from the low power end, exit pupils of less than 4mm to about 6mm are best kept for dark skies looking at large and faint objects, surfing star fields, the milky way and observing large clusters. 2mm to 4mm is good for everyday general viewing, they're great for most DSOs you will encounter, for the Moon and for the planets when seeing conditions are rough. A 2mm exit pupil is a general sweet spot for observing. 2mm and below is good for double stars, planets when seeing is good, the Moon, and for getting up close and examining brighter DSOs. 

From this, for general skies and general everyday viewing in your f10, I personally think it would be interesting to check out wide-field eyepieces at 3mm, 2mm and something around 1.5mm. You could get away with just the 3mm and 2mm if you also sought out a Barlow. After experimenting for a while with these ranges, you will then be in a better position to decide on where there might be gaps in magnification/exit pupil suiting your skies and viewing dispositions.

Hope that helped a little 😀

[Stu]

Great post Rob. Exit pupil is a very useful concept which relates aperture, magnification and focal ratio. It can take a while to get your head round it but it is worth it. I used to think that exit pupil was the same as magnification, but it is not. x200 in a 100mm scope gives a 0.5mm exit pupil, great for planetary in an apo scope but about as small as you want to go except for lunar, solar and doubles, but in a 400mm scope it gives 2mm exit pupil which is great for DSO contrast, which helps explain why people who chase small faint galaxies use big scopes under dark skies.

So, in your f10 scope a range of eyepieces from 10mm which would give x235 and a 1mm exit pupil, all the way up to say a 55mm Plossl which would give you x42 with a 5.5mm exit pupil and would be useful for filtered views of Nebula under darker skies. A 30mm widefield 82 degree would be nice giving a 3mm exit pupil and x78 mag.

Loads of options out there though so with these parameters in mind I'm sure plenty of people will chuck in ideas.

[Star101]

Disclaimer- I'm an imager, not a viewer

Just so as you know..

 

Congratulations on finding and seeing such great interesting planets

 The 40mm eyepiece gives a great all round image of the area and makes it easier to find objects. When one moves to 20mm/10mm/3mm the field of view (FOV) will diminish. Use the 40mm to find the object then centre the object before moving to the higher magnification.

When you decide to purchase a Barlow, to get an even closer look. Be aware that there are 5x Barlows !!! WOW!! ....Not as great as one would think!!. I Have a 2x Barlow and a 5x Barlow. I never use the 5x Barlow! I also have an excellent mount. Finding an object/planet using the 40mm is easy. Insert the 5x barlow....spend 30 minutes looking for a planet? I have yet to find it... I stick with the 2x barlow. Much easier to find the object/planet. Also, the magnification reduces the light...so 40mm very bright...3mm with 2x Barlow...Not so bright  

[bingevader]

15 hours ago, Neiman said:

My question is - can I increase the magnification on this scope while viewing ?

 

14 hours ago, Neiman said:

I’ve got a 40mm Celestron Plossl on it at the moment.

The answer to your question is a very definite, "YES YOU CAN!"

Good advice above.

I'd take your time though.

For me, the greatest limiting factors in the UK, regardless of magnification or exit pupil, are light pollution and the conditions.

You can't see through clouds!

A streetlight in your FOV doesn't help much.

And with the planets so low at the mo, we're seeing them through a bubbling, boiling gloop of an atmosphere!

I wouldn't rush out and buy a kit, but you will end up with a range of eyepieces and more in the shorter focal lengths.

As you do the maths above you'll see that a small change in focal length in a short focal length eyepiece gives a larger difference in magnification (or exit pupil) than in a longer focal length eyepiece.

It's why I have 4, 5, 6, 7 and 8mm at the shorter end, but 18, 24 and 30 at the other end (and some others in between).

Have you had a look at this thread?

 

[celestron8g8]

I agree , add some eye-pieces to your collection and a good barlow whether it be 2x or higher . You should get some great views with higher mag. 

[John]

A good quality zoom eyepiece such as the Baader 8-24mm can work very well with these SCT scopes. In your 9.25 inch the zoom would give you from 97x to 294x all in one eyepiece. Add a longer focal length eyepiece, such as your 40mm, for lower power observing and you have a really useful range of magnification in just 2 eyepieces. All you need for most observing circumstances.

[Stu]

Given that the scope is 2350mm focal length, a Barlow is not really than necessary unless as part of a carefully planned set which avoids duplication of effective focal lengths. With a slow scope like that, you can achieve the higher powers without the need for a Barlow though.