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Barlow purchase. Want a quick bit of advice please


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I have a 2 x barlow and want to get a 3 x to give me more imaging options with my SPC900.

I'm looking at a Televue 3 x. Can anyone confirm this is the ideal candidate? I don't mind spending good money if the results will be worth it.

I have found it online at £100. Wanted to get confirmation before I pull the trigger on the purchase.

Thanks in advance guys.

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James, I plan to use I for planetary imaging, but also to give me more viewing options.

I sold my 200p dob along with the 25mm and 10mm eps that came with it. That leaves me with an 18mm,28mm and a 7mm. I have a 2x Barlow, but it's very low quality.

So a bit of both really.

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My concern with a 3x barlow is that you're not giving it much aperture to work with. Obviously the barlow makes the image three times larger, but that means any individual pixel on the camera sensor receives 1/9th of the light it would have had without the barlow. Unless someone comes along and says "yes, I've used one and it works fine" I think I'd be more tempted to look for a decent 2x barlow and play with extensions to get a bit more image scale if I wanted it.

James

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Just whack a couple 2X barlows together, thats what I'd do, making sure they have coated optics & you'll be fine! That's what they say to do against planets like Saturn anyway, some web-cam barlows go up to 5X for example, the image is just supposed to go a bit wobbly is all......

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Just whack a couple 2X barlows together, thats what I'd do, making sure they have coated optics & you'll be fine! That's what they say to do against planets like Saturn anyway, some web-cam barlows go up to 5X for example, the image is just supposed to go a bit wobbly is all......

There are times when a 5x barlow (or even more) works. Equally there are times when it's utterly pointless. If you increase the focal length too much then you end up with an image too dim for the camera to function properly. Raising the gain to get a brighter image increases the noise and you can end up with a lower quality image as a result. It's a balancing act. Using a 3x barlow might work for Mars or Venus, or even Jupiter at opposition, but if you're going after a target that's dimmer to start with it might just leave you with unusable data.

Adding an extension behind a barlow will increase its effective power, so if you start with a decent quality 2x item you may well be able to push it to close to 3x with an extension (or somewhere between 2x and 3x if you use a shorter extension) and see how it goes.

James

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