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Steve_meg

Help with heat wave effect

29 posts in this topic

Just been outside to look at Jupiter through me 8se and became very frustrated. I can get to a point were I can see markings but the is constant heat wave effect, even at 25mm.

Tried the moon and the same thing??

Nothing's changed with the telescope and only has a few bits of dust on the corrector so I can't see that being an issue.

I took it outside from a 25 degree room but it's been outside 45 minutes so surely enough time to cool down.

Lastly the seeing condition look good tonight

So I'm really confused as to what it is???

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It could well be that your scope just needs more time to cool. SCT's take quite a while. Stick with it as it will keep improving. I have just been looking at the moon with my dob, and managed 720x mag. It had been out for some time though. If you are looking over houses this can give localised heat ripples too.

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How long should it take to cool down? It's about 3 degrees outside

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SCT's can take 40-80 minutes to cool fully. The seeing is really not great here tonight, despite the clear sky and it may be similar where you are. Jupiter is also still quite low in the sky - it may get steadier as it rises higher.

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Well it's about 23-25 degrees difference between inside and out. But after 6 mins still lots of heat wave.

Just so I can check things off, what list of things can cause this effect?

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are the bright stars you can see with your eyes twinkling like mad?

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Jupiter is drifting in and out of focus here as well. 10 seconds of white blur to 1 second of glorious colours and bands galore! Got frustrated and started looking at the moon through my new (delivered today) MaxVision 68deg 24mm eyepiece. The texture that it brings out (paired with Baadar moon filter) was quite stunning. M45 looked great too.

Happy viewing.

Paul

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Well it's about 23-25 degrees difference between inside and out. But after 6 mins still lots of heat wave.

Just so I can check things off, what list of things can cause this effect?

Do you mean that you have left the scope to cool for 6 mins ?

As I said above, you won't star getting decent higher power views until the scope has fully cooled and that could take an hour or more with a 25 degree difference to adapt to.

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Sorry I meant 60 minutes. Even then it still hadn't improved.

Would anything like a dirty eyepiece cause this? Also to note when out of focus a bright star will appear as a nice round donut so I think the collimation is ok.

Just starting to get the feeling like the se is more hassle than its worth. And that I should have stuck with my dob

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I can't get decent views at high power with my 12" dob tonight (it's been out for hours !) so I feel it's likely that the conditions would be affecting your scope too. My 120mm refractor is faring much better as does the dob when I stop down the aperture to around 4" which seem to me to be other indicators that the conditions favour smaller aperture scopes tonight.

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the stars here are having a fair old dance around

transparency is good now 2 am but seeing still poor

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Ay, I'm not sure if it helps but I've been out tonight (and this week in general) and this end of Europe also seems to be suffering from a fair amount of bad layers in the atmosphere. The nights have been crystal clear, cloud free but there is a lot of turbulence about making seeing rather rough. I managed to see Io's shadow passing over Jupiter tonight but couldn't really tweak much from the GRS's transit.

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I agree with all the above about poor seeing later last night. When I looked at the Moon earlier on, the air was quite stable. As the night went on the sky was inky black and clear, but the seeing was very lumpy. Like Qualia, I managed to see Io's shadow transit, but not much detail in the bands. Also like john, the planetary views where better with a stepped down aperture.

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I'm probably not far from the OP location-wise; until about 23:00, the seeing here was poorish, although quite a lot of detail could be seen every now and then. It got a bit better later on, but frostbite was setting in so I headed in for the red stuff.

I think the OP should have seen more therefore.....my guess is (as above) that he was looking over a warm object like a roof, or was downwind of, or looking through, someone's central heating duct or chimney.

Chris

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Tube currents cause the image to wobble, seeing causes the image to lose sharpness. SCTs take a long time to cool, you might be better off leaving it outside for 2 hours or so (probably better in a shed where it will be at outside temperature permanently.

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My 150 Mak (similar to SCT) takes around 5 minutes per degree difference to cool fully, and I leave the ep off to allow the warm air inside to escape (with a peice of old tights to stop unwanteds getting in)

So your 8 inch will probably take longer than mine, its usually a good 90 minutes before I can up the mag.

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My mak was rubbish a little while ago. It was out for hours, but I had not sorted out running the fans so I think it was just not equalising properly. If the temperature is falling still then the tube sometimes doesn't keep up so you still get poor views.

Stu

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It's an 8" scope under UK skies. You will almost always be able to magnify more than the skies can deliver. Some nights the seeing is bad and you can't hit any sort of decent power. Seeing will be worse near the horizon and better near the zenith. Below 30 degrees elevation stuff is nasty. Wait for your target to get high and, as others had said, cool down the scope.

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It was probably just the conditions last night.

I had the same trouble, everything looked like it was boiling, even at longer focal lengths.

Just try again another night.  :embarrassed:

Cheers

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I live our in the sticks so no other houses around. Even at 25 mm it was bad.

I will try putting it out for a few hours next time and hope for a better outcome.

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It was all wobbly wobbly here, usually bad when warm air rises from town. That and humidity spoilt what looked like a dark night after Moonset,

Nick.

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Just to set my mind at rest is there anything that could be wrong with the telescope or eyepiece that would cause this?

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No, it was just a combo of all the points raised. Fear not, your scope is fine :smiley:

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Sounds like ropey seeing last night but just for the sake of discussion:

I know you're out in the sticks so it's not heat plumes from houses but you could check different directions to eliminate another heat source - cattle shed / muck heap / natural swampy area / sub-station.

A bit off the wall but worth a thought if you're not in a standard suburban garden like all too many of us.

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I have a Celestron C11 SCT so I know the problem.  If you point at a bright star and then seriously defocus until you see a big "doughnut" then you can actually watch the tube currents passing across the doughnut.  It's difficult to describe but it will be obvious when you see it.  Observe the tube currents as soon as you take the scope outdoors and then again after 60 minutes.  Once those tube currents are no longer visible then the quality of the observed image is much better.  2 hours of cooling time for the C11 is not uncommon and if the ambient temperature is still dropping it can take longer.  That's why some folk do the "cooling fans" mod.

Here's an SGL thread with an example image of what I mean:

http://stargazerslounge.com/topic/132922-collimation-error-or-tube-currents/

Mark

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