maximum magnification for a 70 mm refractor, please help

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maximum magnification for a 70 mm refractor, please help

Postby mufalak » Wed Apr 05, 2006 8:53 pm

Hi all.
Ive got a question (again), what do you think would be maximum bearable and still watchable magnification with my meade 70mm, 700mm focal length refractor? As I want to update meade MA eyepieces that I got with the scope and Idwouldnt like to get something which id end up unhappy with. What is the max for planetary viewing? Max for deep sky? Doubles?
Thank you very much. Sorry for being such a trouble.
Pat.
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RE: maximum magnification for a 70 mm refractor, please help

Postby les » Thu Apr 06, 2006 12:13 am

HI Mufalak,
No trouble at all![:)]I think the rule of thumb is that the optimum power is X2 per mm of apature.So a 70mm scope you should aim for a high power of 140X.This will only be usable at good seeing.A mid power (the one youll probably use the most) of about 70X ,and a low power for general veiws of around 40X.Im sure other will have there own power combinations.
Regards and clear skies Les.
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RE: maximum magnification for a 70 mm refractor, please help

Postby mick » Thu Apr 06, 2006 12:13 am

Hi Pat
I see there are two options for your scope as follows.
1. Meade 4000 plossl 12.4mm 56Xmag + 2x Barlow 112X mag
2. Meade 4000 plossl 9.7mm 72xmag + 2x Barlow 144x mag
my thoughts are option 1 is the better one as option 2 you will need good sky conditions, you will get more use out of option 1 in average conditions i have a 66mm scope with a shorter focal length and i find 80 to 100x mag is ok for me hth.

Mick.
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RE: maximum magnification for a 70 mm refractor, please help

Postby mufalak » Thu Apr 06, 2006 11:36 am

Mick and Les. Thanks for your replies, youve been a great help!
Cheers!
Pat.
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RE: maximum magnification for a 70 mm refractor, please help

Postby andrew short » Thu Apr 06, 2006 4:36 pm

Hi Pat,
I've pushed my son's 70/700mm refractor to 155x magnification(9mm and x2 barlow)and it worked well providing detailed planetary views for the aperture.
However seeing conditions were excellent and I would generally agree with Les and Mick and keep the magnification to a high of around 140x,and even then as they both said,depending on seeing conditions.
If the optical quality is good and in with your Meade it is,and the conditions are just right then you can get away with a bit more.The highest mag I use with my 90mm reflector is x180 when conditions permit.

Rgds
Andrew.
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RE: maximum magnification for a 70 mm refractor, please help

Postby barnardstar2 » Thu Apr 06, 2006 6:16 pm

Don't know is this advice helps or not but I have a 90mm ETX and I have used a 9.7mm on a shorty X2 Barlow a couple of times and as far as I'm concerned (and as Mick suggests) that really is pushing it, the seeing has to be really good to make it worthwhile. Because of that the fact that my scope has a slightly larger aperture than yours I'd be tempted to say stick to the 12.4mm eyepiece.

I'm sure I have seen somewhere on the internet a programme that shows you the maximum theoretical limit of eyepiece magnification you can use with a given objective, perhaps somebody else knows where it can be found.

Hope it helps.
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RE: maximum magnification for a 70 mm refractor, please help

Postby les » Fri Apr 07, 2006 12:06 am

HI All,
Though the optimum limit of a my 8" f5 Newtonian is about 400X,I rarely go over 160X. In fact my favourite eyepiece for the planets is a 10mm Plossl ,that gives a power of 100X.Many will disagree but I find a small sharp image is far better than a large fuzzy one.I use a 6mm EP (160X) for close doubles.
Regards and clear skies Les.
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