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I had the 9mm objective on Jupiter & four moons and wanted to change the power, either by adding a Barrow lens or going to 24mm to find neptune. I changed lenses and started cranking on the focus knob -- now, nothing. What's wrong & how do I fix it?

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  • hoardlg Jul 12, 2009

    I took my telescope with both lenses out during daylight and found that I could focus either lens. It just took far more cranking than I expected.

    Your answer was no answer at all and should be priced accordingly.



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Do you mean you can see Neptune but it won't focus? Can you focus on anything else, just not Neptune or is your focus adjustment not working at all now?

Posted on Jul 12, 2009

  • Dick
    Dick Jul 12, 2009

    Often people posting a question do not include enough information to solve their problem. This requires the expert to ask a follow-up question in order to get the customer to provide more information and/or test their equipment. That testing process often solves the problem. That is exactly what happened here. Thank you for using FixYa.

    For future reference, the closer you get to the correct category the more likely you are to receive timely, correct assistance the first time. This question was in the binoculars section, but it is a question about a telescope.

    At any rate I was glad my follow up question prompted you to take the action needed to solve your problem. Thank you again for using FixYa.



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1 Answer

Can my canon ef 75-300mm f/4-5.6 iii lens take decent close ups of Jupiter

No it is too far for a 300mm lens. You would get a reasonable image of the moon with some digital zoom in post editing.

May 02, 2018 | Canon Optics

2 Answers

How many moons does jupiter have?

67 are known, although some are just big rocks. The ones you see in a telscope are the Galilean moons, Callisto, Europa, Ganymede and Io.

Mar 21, 2016 | Optics

1 Answer

Cant see anything through the view finder

1. During the day, use the 17mm eyepiece on a object outside (telephone pole, water tower, etc) then align the finder to what you see in the scope.
2. Put in the 7.5mm eyepiece and fine align the red dot finder.
3. At night, point the finder at the moon (less than half moon or the image is too bright without a moon filter) Use the 17mm eyepiece.
4. Once you see the moon, switch to the 7.5mm lens and enjoy.
5. Download Stellarium or any free astronomy software and see what is in your sky tonight. Your scope should be able to see Jupiter and its moons easily.(Saturn, Mars and Venus when the time is right) Open clusters like Pleiades will be nice is this fast scope.
5. If stars are not sharp, you may need to collimate the scope. Look online for general instructions.

Nov 14, 2011 | Optics

1 Answer

Not really a problem, but a question on expectations for a Venture RX-9 900mm reflector telescope. What should i be able to see on a clear night concerning Jupiter and Saturn? I am just getting started...

Is this your telescope?

If it is you can forget about 675 power magnification. The maximum magnification for ANY telescope is about 50 times aperture. You have about a 4 inch aperture mirror so 200 power is the highest it will go, and ONLY on perfect nights when the sky is very stable and if your optics are PERFECT.

Most of us only get 30-40 times aperture. You will not see color almost everything is shades of gray. If you are expecting a GIANT view you will certainly be disappointed. BUT-- the scope can show you many objects in the night sky.

Start with the moon and also Jupiter which is up shortly after dark. Download this free monthly star chart and read my tips on my profile page.

Jan 19, 2011 | Optics

1 Answer

I have a Barska telescope. Model: 60800. Diam: 60mm Focal length: 800 mm. I think I put it together correctly, but I can not see anything through it... just black. Yes, I have taken the cap off the...

The power of the scope will be the focal length of the main objective (yours is 800mm) divided by the focal length of the eyepiece, so a 9mm eyepiece will give a higher magnification (and be dimmer and harder to focus and find objects) than a 20mm eyepiece. It is usual to have two or three different focal length eyepieces for viewing different objects.

Starting out, you want to use the lowest power, so the highest number, eyepiece. Do NOT use the Barlow lens if one came with the scope. Try it out during the day (but never point a telescope anywhere near the Sun). This will make it easier to find the focus point. There is a very wide range of movement in the focus mechanism, because different eyepieces focus at different points, but the actual focus range for any eyepiece will be a small part of the overall range afforded by the focusing mount.

It is unlikely that the finder scope will be much use in pointing the telescope until you adjust it to precisely line up with the main scope. Most manuals recommend that you do this in daylight, by pointing the scope at an object on the horizon and adjusting the finder to match. Once you have a tree or mountain peak in the center of the main scopes image, you can then adjust the screws around the finder scope to get the crosshairs centered on the same object. It is very difficult to do this job in the dark, especially as objects in the sky are constantly on the move.

Remember that astronomical telescopes usually show an upside down image. There is a good reason for this- erecting the image needs more bits of glass in the light path, which reduces the amount of light and increases aberrations. Even if this is only slight, astronomers prefer to avoid it, and they don't really care which way up the Moon or Jupiter appear. It is possible to fit an erecting prism or eyepiece to most astronomical telescopes, and some of them come with one.

Dec 31, 2010 | Optics

1 Answer

I have a Meade EXT90. A black dot appears in the middle of every object I view (Jupiter, Mars, etc) with the exception of the moon. Any ideas on waht that might be? Thank you.

The black dot means you are way out of focus.

In an ETX90 Mars will always be a TINY disk, except under extreme magnification.

Jupiter is also a small disk but a little bit bigger.

Next time you try for Jupiter focus on the MOONS until they are tiny points of light like little stars.

Also certain eyepieces have this as an unwanted trait. Try another eyepiece -- start with the one with the largest number written on it which will be your LOWEST magnification.

Sep 08, 2010 | Meade ETX-90EC (325 x 90mm) Telescope

1 Answer

Can't see anything through lens. I centered it on the moon. Light comes through but can't focus.

That all depends on what telescope it is, but generally you line it up with whatever you are trying to view, then you start with the biggest eyepiece you have (say you have a 9mm, 12mm, and 24mm; you should always start off with the 24mm) then gradually bring the mm size til u get to your lowest or however far you need to zoom into

Oct 05, 2009 | Optics

1 Answer

Not seeing a larger, more detailed image w/ Bushnell 78-8850.

Currently the rings of Saturn are nearly edge on so you won't see any details in them. Shortly the rings will appear edge on and the ring will disappear completely for a few months. Gradually, they will return and angle more towards Earth at which time you will be able to see some of the ring details.

There are many factors that can reduce your ability to see planetary detail. I had my Celestron 200mm out the other night looking at Saturn but saw no details because the atmosphere was too unstable. There are also limits to what a telescope can realistically view.

There is a general rule of thumb that states you can expect to view 50x per inch of aperture. Your telescope has roughly 5" of aperture. 5 times 50 equals a maximum of 250x. However, this is a guideline. On bad nights like I had you'll never reach that 250x since objects will appear blurry or unstable. On good nights, you can exceed this.

You can calculate your telescope power by dividing your telescope focal length by the focal length of the eyepiece ( that 4,9,20mm number).

An excellent object to look at when it comes back in view is Jupiter. It's always interesting and you can see four of it's moons.

Good luck and clear skies.


Mar 30, 2009 | Bushnell North Star 78-8850 Telescope

1 Answer

I am having trouble focusing in the stars and moon

I would recomend that you start with a low power then gradually work your way up. The best advice used to be and still is... "that for every inch of aperture of the objective should equal 50x." With advances in telescope technology this is still is a good rule of thumb.

The formula is focal length of the scope (in millimetres) divide by your chosen eyepiece (again, in millimetres. Based on my TeleVue Ranger (70mm objective) and a 6mm eyepice this is what I get. (see below).

telescope focal length: 480mm / eyepiece: 6mm = 80x magnification.

This is comforfable for observing of the Moon, Venus, Jupiter, Saturn and Mars (brilliant when it made its close approach in 2003). Mercury I have omitted is because it is always close to the Sun and I do not have it on a mounting which has setting circles.

However, if I add my 2.8x Klee barlow lens then it pushes it up to 224x. But word of advice here. To use that kind of magnification the end result is awesome, but you need a perfect sky (i.e. no thermal disturbances and debris up there).

Mar 23, 2009 | National Geographic NG70CA (225 x 70mm)...

1 Answer

Hardin Optical Deep Space Hunter model DSH-6

your telescope appears to be a newtonian reflector on a dobsonian mount. This type of scope is basically a point and shoot design, simplicity itself and many experienced astronomers swear by them, for there ease of use, set-up time etc.
The number 6 in the model number denotes the aperture (size of mirror) in inches. This is a good starter scope (much better than these small scopes that boast 525 X magnification) and with it tou will be able to clearly see Jupiters four main moons and the planets cloud belts. You will be able to see Saturn and it's ring system. Many nebulae, star clusters etc will become visable, that were invisible before.
Getting started with this kind of scope is pretty easy even for an absolute beginner. Set up the scope on a flat even surface, putting it all together should be self-explanatory. Insert the lowest power eyepiece (Usually the one with the biggest lens, and the one with the biggest number i.e. 40mm) and begin by pointing the open end of the scope at a bright object in the sky. To get you going with a bit of a buzz, I suggest Jupiter. Jupiter rises in the SE at 20.50, and is due South at around half past midnight, Look for a bright star that doesn’t twinkle to the right of the moon at about midnight, and that’s Jupiter!
Whilst looking through the eyepiece, carefully move the scope back and forth, up and down in the general direction of the planet. Remember, you are only looking at a very small part of the sky, probably about the size of a full moon.
It is unlikely your scope will be in focus at this stage so what you will find will probably look like a doughnut. When you find this “doughnut” you will need to focus. Adjust the focus knob until you see a crisp image of a small disk. If you are in Europe, you will see three bright moons (two on one side and one on the other) the fourth is hard to see tonight, but if you are lucky, you may glimpse a view of the shadow of this moon (Europa) as it crosses the disk. On the East coast of the US, you will also see three moons clearly, the fourth, Ganymede. Is still in Jupiter’s shadow at half past midnight, but by 1pm, it will become visible as it moves out of the shadow.
Keep looking for Ganymede during this half hour, it makes interesting viewing, and gives a sense of realism and motion to the whole event.
Try using different eyepieces as you become more accustomed to your scope, everything you see is upside down and back to front. Using different eyepieces will require re-focusing, but with a bit of practice, it will become second nature.
Finally, adjusting your finder scope. You will notice that the finder is held in place with two (sometimes three) adjustable screws. It may be best to set the finder scope up in the daytime. First find a distant object in the main scope (the further the better) a chimney pot on a distant roof etc. Then using the adjusting screws, centre the same object in the finder. It’s a bit fiddly at first, but you will get the hang of it. Then when night time comes, finding celestial objects is much easier. First locate the object in the finder scope, centre it, and the object should be in view in the main scope.
Hope this helps to get you going.

Kind Regards….Dave

Jul 16, 2008 | Hardin Optical Deep Space Hunter 6 (240 x...

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