5 replies to this topic

[StolenPotato]

So I'm very new both to this forum and to astronomy. I have owned a Celestron Powerseeker 70EQ (700mm focal length, f/10, 70mm aperture) for a while now and I never figured out how it worked because when I was younger me and my dad had assembled it incorrectly. I finally fixed it yesterday and I got a very nice view of the crescent moon. The next thing I wanted to do was to view Venus in the telescope, but it just looked like a tiny dot on my 20mm eyepiece. After switching to my 4mm I was able to see the phase of it, but it still looks tiny. With the 4mm it would be around 175x magnification, yet the few sources I found online say 120x should be plenty to see detail.

The last thing I could think of was to attach the standard 3x barlow lens that came with the telescope, and even though I notice a difference, I don't understand how it still looks so small with over 500x magnification. Am I doing something wrong? How could it still only look so small with over 500x magnification when sources say 120x should be enough?

 

That all said, even if what I am seeing is just how Venus looks through a telescope, the barlow seems to make everything really difficult to focus on. I have seen people talking online about how the focuser isn't long enough for their barlow, but that's not the problem with mine. The focuser has enough room, the problem is that everything seems more difficult to bring into focus, for example even the moon was very hard to get into proper focus without constantly overshooting it with the smallest movement of my hands, or maybe the old lenses are just dirty and cleaning them would fix it?

 

I guess my main worry is that I'm not sure if I'll be able to see more distant planets, or anything outside of the solar system with the telescope if even Venus looks so small and I struggle to bring anything into focus using a barlow.

 

I am very new to this so I'd appreciate any tips or advice on how to proceed!

[vtornado]

I have seen very subtle clouds on Venus with a 100mm refractor.  I can't recall what the magnification was, probably around 100x. I did have a polarizer in the telescope at the time.

 

I don't look at Venus very often because all that is typically available is the phases.

 

Jupiter and Mars are much more detail rich targets.

 

Many times the barlows included with low cost telescopes are low quality and are put in the box because it allows the box to say 500x.  I encourage you to look through the barlow with your naked eye at household objects and see if they look distorted.  In general, one should not magnify any more than 2x the diameter of the object lens.  In your case 140x.  Even 2x is pushing it.  I say more like 1.5 or 110x.

 

Everything you describe is normal.  At high magnification focus is more critical, vibrations are amplified, any defects in the optics are magnified.

 

Some things outside the solar system appear larger than Venus.  The Pleiades cluster for example occupies 2 degrees of the sky.  Venus is 120x smaller than that.  The Orion nebula is about 1 degree it is 60x larger than venus.

Edited by vtornado, 01 February 2025 - 07:17 PM.

[treadmarks]

Venus has two details that are probably the easiest to see of any planet: its phases and its terminator (boundary between day and night). I'm going to guess those online sources were referring to that when they said 120X was enough for detail on Venus. And it sounds like you did see them at 175X, so you should count that as a success. 175X is too much for a 70mm though. I have a much more expensive 70mm refractor and I usually stay below 120X. There's actually a lot of drawbacks to going too high in magnification.

 

To see more detail than day and night on Venus is an expert level task. For reference, I've been applying lots of expensive premium gear with quite a few tricks and observing skills over several years and it's amounted to something like this: https://www.cloudyni...1#entry13941486 I consider it a big success but I imagine most people would not consider such a view to be worth the effort.

[Sketcher]

Galileo observed a more or less full range of phases of Venus while noting that Venus appeared to be larger when seen as a crescent and smaller when seen as gibbous.  This was pretty strong evidence that Venus was orbiting the Sun.

 

It's been said that the highest magnification of any of Galileo's telescopes was about 30x.  The apertures of his telescopes were generally stopped down in order to reduce aberrations -- resulting in effective apertures somewhere in the neighborhood of 15mm.

 

In contrast, your telescope has a clear aperture of 70mm and can be used at magnifications considerably greater than anything achievable by any of Galileo's telescopes.

 

* * * * * * * * * * * * *

I suspect two potential difficulties in your experiences:

 

1) Expectations:  You were expecting Venus to appear larger than what you actually ended up seeing.  Galileo had no such expectations.  He saw what he saw -- and that was plenty good enough for him.

 

2) Experience:  Galileo observed Venus throughout its orbit about the Sun -- multiple observations over the course of a Venusian year, more or less.  You've just begun your telescopic journey.

 

It takes experience (practice) to learn how to see when it comes to visual, telescopic astronomy.

 

It's not unusual for beginners to be disappointed by the apparent sizes of planets -- as seen in their eyepieces.  But with increased experience, one becomes capable of seeing increased planetary details within those tiny images.  With increased experience, those previously "tiny" planetary images begin to look larger to the observer's eye-brain system.

 

* * * * * * * * * * * * *

What can be seen with any given telescope?  Well, the answer depends on a lot more than just the telescope, its aperture, and the magnifications used.  It is also heavily dependent on the observer as well as on one's sky conditions.

 

The below link is to a Cloudy Nights thread that contains multiple observations made with a 50mm f/10 telescope.  But the person making the observations has been using telescopes since the 1960s and the sky is in rural Montana, far from pollution sources -- both air pollution and light pollution.

 

Focus not on what you can't see.  Instead, focus on all that you can see.

 

https://www.cloudyni...e-observations/

 

It's not so much about what the telescope can do.  The telescope forms an image that the eyepiece magnifies, but it's up to the observer to "see" all the detail that's contained within that image.  And that takes practice -- experience.  One has to learn how to see.

 

With practice, one's eye-brain system develops "software" to enable the observer to discern details in a planetary view that's being compromised by less than perfect seeing conditions -- views where the planet might at first look like a featureless, boiling blob.

 

* * * * * * * * * * * * *

Drop the expectations.  Focus on all that you can see.  Push yourself to see more.  Take notes on what you see.  Make sketches.  Even Galileo made sketches of what he saw.  One tends to see more in the world of visual astronomy when one makes sketches.

Edited by Sketcher, 02 February 2025 - 03:07 AM.

[StolenPotato]

I have seen very subtle clouds on Venus with a 100mm refractor.  I can't recall what the magnification was, probably around 100x. I did have a polarizer in the telescope at the time.

 

I don't look at Venus very often because all that is typically available is the phases.

 

Jupiter and Mars are much more detail rich targets.

 

Many times the barlows included with low cost telescopes are low quality and are put in the box because it allows the box to say 500x.  I encourage you to look through the barlow with your naked eye at household objects and see if they look distorted.  In general, one should not magnify any more than 2x the diameter of the object lens.  In your case 140x.  Even 2x is pushing it.  I say more like 1.5 or 110x.

 

Everything you describe is normal.  At high magnification focus is more critical, vibrations are amplified, any defects in the optics are magnified.

 

Some things outside the solar system appear larger than Venus.  The Pleiades cluster for example occupies 2 degrees of the sky.  Venus is 120x smaller than that.  The Orion nebula is about 1 degree it is 60x larger than venus.

I checked the barlow and nothing seems distorted, at least to my eyes. Thank you for the info.

[Sebastian_Sajaroff]

Venus crescent is tiny -but visible- on my 70 mm F/6 refractor at 13x (32 mm Plossl)

I prefer to observe Venus at daytime (much less glare), 50x gives me a nice view.

 

I never saw any Venusian details or markings on my 70 mm, but I saw some on an old 6" Dobson of mine.

They're vague and elusive, nothing obvious like Mars polar cap or Jupiter bands. 

 

Jupiter disc -the biggest- is 50x smaller than Moon's, don't expect huge planetary discs !