Can anyone identify this?

[MarkTownsend]

Hi all,

lovely to find this brilliant forum. I’m new to sky gazing - not in terms of interest but practise, having just bought a second hand 10” Dobsonian.

The guy who sold me it very kindly gave me a zoom eyepiece. Can anyone help me identify it please? Or give me any advice on what it might be in terms of its range of magnifications? Photo added. 

I have been looking at Jupiter but it is incredibly small, even at the highest magnification.

I would like to be able to see the larger planets clearly and some DSOs.

I am thinking of investing in a set of StarGuider eyepieces.

Thank you so much in anticipation.

Mark

[Franklin]

The zoom looks like a field scope eyepiece.

Jupiter is good at around x150.

Divide focal length of scope by focal length of eyepiece to get magnification.

[MarkTownsend]

Thank you,

Re. the zoom eyepiece, if it is a field scope, can it be of any use to me?

I think a skywatcher 8” will give me 150x 

 

 

[AstroKeith]

Almost definitely the eyepiece is from a spotting telescope (ie for bird watching etc) There is an Acuter model that has the same zoom range, and is specified as 8-24mm focal length range.

In astronomy our eyepieces are rarely marked as a magnification, since as Franklin says, that depends on the focal length of the telescope they are used in, which varies.

If it really is a 8-24mm zoom then at its highest power is should have been reasonable on Jupiter. Perhaps your expectations are too great (been looking at too many photographic images?) Your should see bands at least. How about on Saturn and Mars?

Being a Dobsonian you will need to ensure it is collimated well.

[badhex]

Hi Mark, welcome to SGL! 

You're definitely in the right place to start you astronomy journey - lots of sound advice to be found here 🙂

Regarding your eyepiece: I agree with @Franklin that it looks like the eyepiece from a spotting scope, so those magnifications listed will be relevant only to that scope (or another with the same focal length etc). What you need to understand the true magnification that it is giving in your scope are the focal lengths of that zoom eyepiece. Does it have any other markings on it that may help identify what scope it came from?

If you have any other eyepieces, you can also make a rough guess by comparing them with the zoom, although obviously this won't be super accurate. I know that it is possible to do more accurate tests to determine the focal lengths, but I've never had to dj it so I can't advise! There are others on here who will be able to suggest more accurate methods. 

[badhex]

14 minutes ago, AstroKeith said:

Almost definitely the eyepiece is from a spotting telescope (ie for bird watching etc) There is an Acuter model that has the same zoom range, and is specified as 8-24mm focal length range.

In astronomy our eyepieces are rarely marked as a magnification, since as Franklin says, that depends on the focal length of the telescope they are used in, which varies.

If it really is a 8-24mm zoom then at its highest power is should have been reasonable on Jupiter. Perhaps your expectations are too great (been looking at too many photographic images?) Your should see bands at least. How about on Saturn and Mars?

Being a Dobsonian you will need to ensure it is collimated well.

Agreed, it looks like this one but modified with a different eyecup and some o-rings (maybe as spacers), so 8-24mm fits. 

If this is true, at the highest setting it will be an 8mm eyepiece, so take the focal length of your scope, divide that by 8 and you will have the true magnification you are getting.

Do the same for 22mm and that's the true magnification you are getting at the lowest setting. You should also be able to then figure out the stops in between if you wish. 

What is the scope that you have out of interest? 

[MarkTownsend]

Thank you all for your responses. Super valuable advice. With regard to my expectations re. Jupiter, I’m aware that the stuff you see in magazines (and bad adverts) are well out of my scope, but I would hope to be able to see some of the markings on Jupiter. I can see the moons but the planet itself is a small bright circle with no definition. Obviously if this is a field scope lens then it’s not going to have the necessary coatings for skywatching so I think I’ll invest in a couple of Starguider eyepieces, maybe an 8 and a 25.

Really grateful to you all!

Mark

 

[MarkTownsend]

2 minutes ago, badhex said:

Agreed, it looks like this one but modified with a different eyecup and some o-rings (maybe as spacers), so 8-24mm fits. 

If this is true, at the highest setting it will be an 8mm eyepiece, so take the focal length of your scope, divide that by 8 and you will have the true magnification you are getting.

Do the same for 22mm and that's the true magnification you are getting at the lowest setting. You should also be able to then figure out the stops in between if you wish. 

What is the scope that you have out of interest? 

Thank you.

It’s a Skywatcher 250p

 

 

[badhex]

Okay, so if your focal length is 1200mm then the 8mm will give you 150x and the 22mm will give you 54x.

I observer Jupiter regularly at 159x with a 102mm aperture refractor, so you should be able to pick out some detail at that magnification. That said it's also possible that your scope is pulling in so much light that Jupiter is too bright and you're losing detail and contrast. You could try masking the aperture of your scope as an experiment. I think the 250p end cap has two smaller holes with caps you can remove? Try attaching the end cap but removing one of those smaller caps. This will temporarily reduce the aperture of your scope so the image will be significantly dimmer, but you might be able to pick out more detail. 

Regarding the BSTs, they are definitely good eyepieces but you might want to ask someone about their performance in very fast dobsonian scopes like yours - faster scopes are often more demanding of the eyepiece. 

[Don Pensack]

5 hours ago, MarkTownsend said:

Thank you all for your responses. Super valuable advice. With regard to my expectations re. Jupiter, I’m aware that the stuff you see in magazines (and bad adverts) are well out of my scope, but I would hope to be able to see some of the markings on Jupiter. I can see the moons but the planet itself is a small bright circle with no definition. Obviously if this is a field scope lens then it’s not going to have the necessary coatings for skywatching so I think I’ll invest in a couple of Starguider eyepieces, maybe an 8 and a 25.

Really grateful to you all!

Mark

 

It's so small!  These are the words we hear from every beginner.

First, the planets are small--possibly the smallest objects you will ever look at in a scope.  Even Jupiter is only about the apparent size of a large crater on the moon.

Let's do the math:

The moon is about (it varies) 30' in diameter to us here on Earth.  That is half a degree, or 1800 arc seconds.

Would you like Jupiter in the telescope to appear the same apparent size as the Moon does to the naked eye?

How much magnification would that take?

 

Well, Jupiter is 46 arc seconds in size right now.

So it would take 1800 / 46 = 39x to make Jupiter in the telescope the same size as the full moon to the naked eye.

Your zoom yields 150x at the high power end, which makes it 3.8x as wide as the full moon to the naked eye when you look at it in your scope, and almost 15x the area!!

Imagine if the Moon were that large!  

 

So why does it appear so small to your eye?

Primarily it is because there is no context, no horizon or trees or anything familiar to compare it to.

Just be aware that Jupiter at 150x is very large in the scope.  That doesn't mean you can't use a higher power ever, merely that you should see details on Jupiter at that magnification.

 

So why don't you?

1) Expectations.  You expect a photographic image and that's not what we see in a telescope except in larger aperture scopes under exceptional circumstances.

2) You might be not paying enough attention to the circumstances that will give you a better view.  To wit:

--collimation of the scope.  How are you collimating?  What tools are you using?  Precise collimation is critical to get sharp high power images.

--cooling of the optics.  A 250mm scope won't give sharp images when it is first taken outside.  It takes 2 hours or more for the optics to cool down to the ambient temperature

   and that is necessary before the scope will see sharp high power images.

--conditions of the atmosphere.  Seeing conditions (the steadiness of the air and the lack of scintillation) need to be good before you will see sharp high power images.  You can't do anything about this,

   but if you view often, you will encounter stable air from time to time, and maybe even from hour to hour.  How can you maximize the potential for good seeing?

   a. don't set up on asphalt or concrete.  Set up on grass or dirt.  You don't want heat wafting up from the ground below to ruin your images.

   b. don't view a planet directly over a roof.  Roofs leak heat all night long and it makes the air above the roof turbulent.

   c. don't view the planet below a 30° altitude.  Wait for it to be higher in the sky, preferably when it crosses the N-S meridian in the sky (a line that runs through the zenith from N to S), when it is highest above the horizon.

      At 30°, the air is 2x as thick as the zenith.  At the horizon, the air is 10-12x as thick as the zenith.  The more air you look through, the blurrier the image will be.

   d. When viewing planets, it actually helps to NOT be dark adapted.  You can leave outside lights on and use a white flashlight.  That is the exact opposite of what you'd do for deep sky objects, but it will prevent

       the planet from appearing so bright in the eyepiece and dazzling your eye with bright light.  And, even then, look for a few minutes and the planet will seem less bright as you completely lose your night vision.

   e. in many places, the air is calmer and less turbulent after midnight.  Try observing later (which you'll do anyway to see Jupiter up high, at least right now) and you will see a better image.

 

The 2 equatorial bands vary in visibility over time.  Right now, one of the bands has lost a lot of contrast and is hard to make out.  One of the dark EQ bands is still quite visible.

Here are 2 pics of Jupiter:

https://www.cloudynights.com/topic/843981-saturn-and-jupiter-saturday-1-october-2022/?p=12186925

https://www.fox13news.com/news/jupiter-opposition-2022-closest-approach-earth-when-how-to-see-it

Note how the 2010 pic only has one equatorial band and how the 2022 photo is close.

Compare that to an image from a few years longer ago in 2005:

https://www.cloudynights.com/topic/28450-jupiter-426-perfect-night-with-the-c11/?p=359187

 

Yes, Jupiter has weather!.  In the '90s, if I recall correctly, both EQ bands faded out and then came back strongly.

So, watch over time, and you'll probably see the South Equatorial belt come roaring back and get darker.

 

Don

 

Edited November 5, 2022 by Don Pensack

[Louis D]

It's a Celestron Regal Zoom 8-24mm that has had the original eye cup screwed off and replaced with some aftermarket bits and pieces.  It was sold with Celestron Regal spotting scopes.  I've measured the actual focal lengths to be 8.2mm to 21.2mm.

It's step up from the standard Celestron 8-24mm zoom, but not quite as good as the Baader Hyperion Zoom.  The biggest issue for astro usage is that there are no filter threads.  The lower lens group goes right to the end of the barrel at one end of the zoom range.

Here's some photos of mine.  The upper two are from a 65mm spotting scope.  The bottom one was the version sold à la carte with markings for all three spotting scope sizes.  Yours must have been sold with a 100mm spotting scope.

[MarkTownsend]

Thank you so much for the excellent advice,