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Hi folks....bit of a stuttered start


wooah62
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Hi all

I've been lucky enough to buy a Skymax 90 as my first scope with a 10mm and 25mm lens. For father's Day I got a Skywatcher 2x deluxe Barlow and because we've had cloud for days went outside to focus on some TV arials..fascinating...and done leaves on trees...less fascinating?. However cutting to the chase saw a pigeon with my 10mm lens about 150 metres away and clearly saw him blink..buy using my new Barlow...a cloud of blurriness. Now is it because im trying to focus on something too close with a Barlow or should I be seeing something other than standard grey. Don't laugh...it maybe a stupid question but I was always told there's no such thing as.....(,this may be the exception). So hello to all and thanks in anticipation. All best Wooah 62

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Welcome wooah!  If you used the 10mm EP, then a x2 Barlow, you'd have a mag of x250, which is high!  At high mags, focusing gets more critical and brightness drops, which could explain the poor view.  High mags are generally over-rated - lower mags give clearer, sharper views.

Pigeons - have you noticed they seem to sense you are looking at them!!

Doug.

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With a 2x barlow and the 10mm you are getting 250x magnification! With a 0.36mm exit pupil, I'm not surprised you can't see anything through it!

Keep the barlow, but I suggest only using it on "faster" scopes (like if you went with an f5 newtonian dob later down the road) or with your 25mm eyepiece to get a 12.5mm eyepiece with longer eye relief.

You seem new, so mishaps are expected. There is no stupid question here.

 

Generally, people advise you do not use exit pupils outside the range of 0.75mm-6mm. Less than 0.75mm is bad because you will only dim your image for no gain in sharpness, and floaters and dust in your eye becomes increasingly pronounced even under 1mm. More than 6mm because (generally) your eyes cannot expand to use the whole circle and light is wasted. Your 10mm gives you 0.72mm (acceptable high power), your 25 gives you 1.8mm which is considered a medium or high-medium magnification.

Your exit pupil is defined as: your aperture (90mm) divided by the magnification used (magnification is focal length of telescope (1250) divided by focal length of eyepiece (10 or 25 in your case))

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The friends are right! A 90mm maksutov can't do more than 180x. The rule of thumb says the maximal power of a scope is twice the diameter; don't close your mind to - many! - other possibilities that you can learn later on, but for now it's simpler to remember twice the diameter.

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If my memory is correct that SW 2X de luxe Barlow is versatile. You can unscrew the lens cell & screw it directly into the filter thread of your eyepiece.

In this location it  magnifies by about 1.5X because it is closer to the eyepiece lenses. So your 10mm EP would have a Mag of about 180X, which is coincidentally the rule of thumb max for your scope.

 

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Wow...many thanks to all of you who replied ....nice to know that there is support there for a newbie. All we need now in the North of England is a cloudless sky ?.  I guess I might have been a quick to "mention" how useful it would be to get a Barlow lend from my daughter in"passing" to my wife ? although from what I've read it may be useful with the supplied super 25 wide angle long eye relief lens....I guess making a 12.5 mm? Can I ask why it is particularly called long eye relief? Tanks again and any advice given is most welcome! ?

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6 hours ago, wooah62 said:

Can I ask why it is particularly called long eye relief?

Eye relief is the distance you need your eye from the glass to see the image properly.

 

Somewhat a matter of preference as to whether long or short suits you best...

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