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omega3

F5 scopes and 5mm eyepieces

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Hi,

Last night, I tried using a 5mm BST Explorer with my F5 scopes. Jupiter was fairly low early in the evening and I was just able to make out one band. The image wasn't crisp, maybe the scopes were not sufficiently cooled, last evening was quite cold. When they were cooled I looked at Castor, though I could split the double the stars were fairly spread out.

Are 5mm eyepieces generally too much for F5 scopes for our skies? Will I have more joy using them on the moon?

Alan

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I don't think the SEB has fully returned yet so one band sounds right. Jupiter is way past best though and the seeing will have a big effect. The thing with f5 scopes is that glass quality matters. I don't know much about the BST's but my TV 5mm and Hyperion 8mm are pretty clear when I use them - so I know any vagueness of image is down to atmosphere, cooldown, collimation, etc. Hope that helps :)

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Jupiter is pretty low now so getting a crisp view is a bit of a challenge. I use a 5mm eyepiece in an f4.5 scope but only when the seeing allows.

Hope this helps

Adrian

Edited by JAO

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I'm interested in this as currently thinking on what ep's or barlow to get for my f5 150p other than the 8mm and 24mm hyperions i have.

At 5mm on f5, looking at your sig I assume you're at around 250x mag - that should be good for planetary work inc. Jupiter, moon etc

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I found 240x was too much for Jupiter with my 10" newtonian, even when it was better placed for viewing a few months ago - I'm sure with the planets current low altitude it's not going to give good views. I find 150x - 180x perfectly adequate for observing the planets features and having them crisply defined.

I observed Jupiter a couple of nights ago with a 5" refractor and the South Equatorial Belt (SEB) was really well defined - almost as dark as the NEB. I was using 156x then.

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The Skyliner 10" has FL of 1200, so 5mm will give 240x, whilst the Celestron 102 has FL of 500, so that would be 100X.

I think the dob is collimated, defocussed stars are perfectly circular.

Looks like I will have to try it on many more nights to see if there are occassions when I can get sharp bright stars, to know the cause of the blurry Castor last night.

Alan

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My 8mm hyperion gives 188x mag with 2x barlow - saturn looks good with detail clearly visible, I'm thinking of 14mm FTR to give me option of 125x & 250x mag

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If 240x is too much for the 10" dob on Jupiter, would it also be too much on the moon?

Alan

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If 240x is too much for the 10" dob on Jupiter, would it also be too much on the moon?

Alan

No, I think it would be OK on the moon, although you should always back off the power if the views are not crisp. Jupiter just does not seem to "take power" that well. Saturn, on the other hand, seems to respond better in that respect.

I expect the Jovians have erected a force field to protect their privacy wheras the Saturnians have not got around to that yet :p

On a more serious note, the trick is to judge what the conditions on a particular night will allow - there are some nights which look OK but the seeing is so rotten that you can't go much above 100x - our human nature leads us to blame our equipment on such occasions but 99% of the time it's the observing conditions :)

Edited by John

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Although too much for Jupiter on all but the best nights you will probably find 240x fine on the moon on most nights.

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240x is not going to flatter a planet that is close to the horizon - the image will be a boiling mess - but just wait until October / November when Jupiter will be riding high - I'll be surprised if you don't find a use for that 5mm then.

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No, I think it would be OK on the moon,

[snip]

On a more serious note, the trick is to judge what the conditions on a particular night will allow - there are some nights which look OK but the seeing is so rotten that you can't go much above 100x - our human nature leads us to blame our equipment on such occasions but 99% of the time it's the observing conditions :)

Taking this latter point, unless you were very lucky last night, the Met Office infra-red satellite pictures suggested that there was a thin layer of high cloud over most of the UK, as there has been for several nights; I gather some places seemed pretty clear (Cheshire, so I'm told... as I sit in Cambridge :p), but it didn't look it on the sat shots...

Maybe that was a factor?

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err, and of course if you are prepared to wait up a bit until Saturn is a reasonable angle above the horizon you might find you get a good view with your 5mm on that now, although the seeing would have to be decent.

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