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Expert advice would be appreciated


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Hi guys,

I have a 150P Dobsonian and my father has just purchased a CPC1100 (which I have to take outside for him because of the weight, so he can't use it unless I'm there :) ).

Anyway, we were looking at how best to get clearer/larger images on either scope of a) planets and :rolleyes: deep sky objects. I assume there are better eye pieces for each scenario. Our thinking is that if we pool our money we can hopefully find the best solution to view both (when we finally get a clear night again of course!)

Any advice from people's experience on here?

Many thanks

Chris

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Tempted to say buy the set of BST/Skyguiders.

Not necesarily all at once but a couple every month or so.

The sizes are 5mm, 8mm, 12mm, 15mm, 18mm, 25mm.

Presently £47 a piece, were less a while back, so you are looking at close to £300.

Suspect the CPC will not use the 5mm or 8mm, but the 150 will.

So all will get used.

The field of view is 60 degrees so reasonable with the 25mm in the CPC.

Others are the TMB planetarys, or plossls - Vixen plossl's are good and £30 a piece. The BST's and TMB's have the advantage on the eye relief.

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Both scopes will need different eyepieces due to the large difference in focal lengths of the scopes (750mm vs 2600mm), the CPC giving 3.5x more magnification for the same eyepiece. That said, due to the larger aperture of the CPC, it will allow more magnification without the image being any darker than the 150p.

Planets need high magnification and most are bright. The 150p should allow up to 300x magnification on a good night and you'll need 200-300x for Saturn for example. 200x will require a 750/200=3.75mm (4mm) eyepiece. 4mm eyepieces get quite difficult to look into, so maybe a 8mm with a 2x barlow would be better. The Baader Genuine Ortho's are considered to by very good for high magnification on planets.

On the CPC, 200x will need a 2600/200= 13mm eyepiece, so you can see the difference.

On the CPC at the same magnification, the image will be much brighter, maybe too bright, so you can push up the magnification. A 6mm eyepiece will give 2600/6=433x which will still be easy to look into and Saturn would be nice and large.

DSO's are different again. Most a dim, some large, some small. Aperture wins here. You don't want too much magnification, as they will be too dark to see. Best to start with a 25mm lens (30x mag) on the 150p (which you probably already have) and maybe a 30mm on the CPC (86x mag). You can get some nice 2" wide angle eyepieces, like moon fish 38mm 80 degree, which have huge glass and you can really immerse yourself in the image and look around the view! Again the CPC will allow more magnification before the image becomes too dark (but low is best), with the 150p, I'd stick to low magnification.

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There has been some recent threads concerning the Explore Scientific range of eye pieces at 82° FOV, they are often on offer in the States and Ocean Photo and Telescope has them at between $119 and $150 at the moment, with the Pound gathering strength against the Dollar ( exchange $1.6 to the £ to-day ) it may be worth considering importing. You can read about them in the Telescope Houses website. These are excellent products and at a very reasonable price, without going to the extremes of expenditure on eps costing much more only to give you the same visual result :)

John.

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n.b we already have TAL 2x barlow, and a 10mm, 25mm and 40mm Celestron eye pieces with it (and a light pollution filter because of the darn streetlight down the side of the back garden)

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