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Barlow Lens x3 - not focusing

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10 replies to this topic

#1
darlingtonskies

darlingtonskies

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I have waited days to use it and it wouldn't focus. it didn't focus down.
I know magnification would be 270 with the 10mm lens but even in 25mm which would be about 235x mag still dint work. i am gonna try again on a clear clear night but just waited for a break in the clouds.

Managed to see saturn and mars again :)

hope you all got a chance.
Skywatcher 130m
EQ 2
10mm and 25mm
Barlow lens x2 and x3

#2
skye at night

skye at night

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are you using it with a diagonal?

if so, before or after?

what scope?

Steve
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#3
Cornelius Varley

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Did you run out of focuser travel inwards or outwards before the image came into focus ? The image would start to become smaller as it came into focus. If it is a lack of outwards travel you might be able to slide to barlow out slightly to achieve focus. A short extension tube would help here. If you have run out of inwards travel, things get a bit more complicated moving the primary mirror up the tube to compensate). It could be that you were moving the focuser too quickly and went through to point of focus.

ps. Your calculations for the magnification using the 25mm eyepiece + 3x barlow are wrong. 900x3 = 2700, 2700 / 25 = 108

Peter

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#4
darlingtonskies

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Yes sorry CV - worked it later that it was 108 which means it should easily work.,

As I focus out it has a yellow mark and the four lines in it. I moved it a fraction at a go and would not focus. now it was a cloudy night but the light pollution is not a problem on a clear night.

Sky at night - sorry diagonal?
i basically placed it in the scope and wouldnt work but worked perfectly fine with the x2 barlow i have.

Could it be that it is too much for my scope, however if it was it would still work on 108x mag wide angle.

Sorry everyone. only new to it. Please help

DS
Skywatcher 130m
EQ 2
10mm and 25mm
Barlow lens x2 and x3

#5
ashenlight

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Hello DS :) I have the same scope as you, and often use the 3x barlow with a high mag eyepiece for planetary viewing, or splitting doubles.

You will find that, as the magnification goes up, the 'sweet spot' for focus - the best focus you can get for that magnification, will get very tight, and hard to come by. Of course, if the image you are seeing is distorted because of the seeing (the conditions in the atmosphere that effect the quality of viewing) it will be harder to get good focus, and a good image.

Sometimes it can be easy to think 'this is the scope's maximum useful magnification, so at this much below that, I should easily get a good image' - but it just doesn't work like that alot of the time. It all depends on the object, the seeing, and transparency - alot of things come into play.

My advice would be to knock down the magnification a bit when you find it hard to focus with the 3x barlow - perhaps use the 2x barlow instead, and see what the image is like then. If you can get a decent image at lower mag, I find it fairly safe to say, in my own experience, that the seeing just can't 'handle' higher magnification on that particular night. It's a guessing game, and a game of chance. You just have to play it by ear.

Here's an article on the atmosphere and observing, if you would like to read up on it to understand ;) The Atmosphere and Observing - A guide to Astronomical seeing. - How To

Don't feel disheartened, and remembe,r the longer you observe an object for (say, in one night, or on consecutive clear nights) you have more of a chance of getting those glimpses of good seeing and conditions that will let you push the scope to its limit.

edit: as you take the magnification higher, the light that you are seeing from the object is 'spread over' a larger area - making the object bigger, or magnified. You might get a sharper image at lower magnification, but as you 'zoom in' adding other eyepieces, these details are stretched out and so become less crisp, an dmaybe a little blurry. This could also account for the problem (it has in my experience) particularly if the seeing was shoddy too.

HTH

Edited by ashenlight, 09 February 2010 - 04:15 PM.

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#6
Cornelius Varley

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As I focus out it has a yellow mark and the four lines in it

Where is the yellow mark and four lines ? On the focuser or is this what you are seeing down the eyepiece ?


Peter

Edited by Cornelius Varley, 09 February 2010 - 04:15 PM.

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#7
darlingtonskies

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When i look down focuser i see the yellow circle with a + in middle.
I focus down and gets better but is still not right. normally this happens with the 2x barlow lense but finally focuses easily. but wont go small enough. its not that i can see the object and its blurry, i see a massive object that is not focused.

Ashlen - how big do you see saturn and mars at moment with the same scope
Skywatcher 130m
EQ 2
10mm and 25mm
Barlow lens x2 and x3

#8
pvaz

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When i look down focuser i see the yellow circle with a + in middle.
I focus down and gets better but is still not right. normally this happens with the 2x barlow lense but finally focuses easily. but wont go small enough. its not that i can see the object and its blurry, i see a massive object that is not focused.

Ashlen - how big do you see saturn and mars at moment with the same scope


There is a chance you don't have enough outward travel on the focuser to get this in to focus.

Try to untight the locking screws and pull the balow+ep slowly out to see if you can reach focus that way. If you do reach focus that way then you'll need an extension tube.
Paulo
Observations: Messier: 110/110 | Herschel: 399/400 | Caldwell: 52/109 | Color Doubles: 24/41 | Lunar: 5/100 | Planets: 7/7 | Limit mag: 5.5+ @ 38ºN 27ºW
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#9
darlingtonskies

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oh ok, i understand that. this would mean looking for an extention to the barlo lens so it can focus. however its more focused when its rolled it (shall we say) than when its rolled out.
Skywatcher 130m
EQ 2
10mm and 25mm
Barlow lens x2 and x3

#10
Cornelius Varley

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The cross ypu are seeing ius the spider vanes holding the secondary mirror, it is usual to see them when an eyepiece is out of focus. It appears that you have a lack of inwards focus, you can compensate for this by moving the prmary mirror up the tube but I don't recommend this. What make of barlow are you using ? You may find that another brand mighht work with your telescope or someone here might have the same telescope as you and a 3x barlow that works and can advise you.

Peter

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HEQ5 Pro / ADM saddle upgrade, IM603, Skywatcher Skymax 150+JMI EventHorizon motorised crayford, Meade Series 5000 80 APO, etx105 ota, ST80, Heritage 130P
CG4 with EQ3-2 Synscan, AZ4 (steel legs). DMK21, QHY5v, Pentax 12x50, eyepieces, filters etc etc. some other stuff in big boxes.


#11
darlingtonskies

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kewl thank you. i will have a look at which one. would the light polution make it worse. as it was bad that night?
or is it literally the focus
Skywatcher 130m
EQ 2
10mm and 25mm
Barlow lens x2 and x3




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