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Meade 5000 Series 5x Telextender 1.25"

Horus

By Horus
in Discussions - Cameras

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Nexus 6

Nexus 6

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Hi Rich I would think your really pushing things at 5x, I would agree with what has already been suggested a 2 or 3x at most.

I myself prefer to leave out the barlow link and just use the ep increasing the power when I can if conditions allow. Your Meade has a focal length of 2034mm, a 7mm ep would give you 290x about as good as it gets for us in the uk due to the poor seeing and only on rare occasions.

As you are only going to want such power for observing the Moon or planets a decent 6 or 7mm ep for around the same price as the tele extender would, in my opinion, be a better chioce. :)

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r3i

r3i

Posted
Posted

I have both the 3x & 5x Meade TeleXtenders - I bought them to do planetary imaging with a webcam, so not sure if my comments are relevant if you are thinking about getting them for just visual use.

I've had some results with the 3x that I was pleased with. I think though, as others have mentioned, that the 5x is just pushing it too far - I haven't had much opportunity to use the 5x but so far haven't had any success with it. I think the both the collimation of your scope and the seeing would have to be top notch for the 5x to deliver a worthwhile view.

So IMHO I'd start with either the 2x or 3x TeleXtender and take it from there.

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michael.h.f.wilkinson

michael.h.f.wilkinson

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I have the 2x and 3x Series 5000 TeleXtenders, and both are excellent for planetary imaging. 5x might be stretching things, but the two lower ones are fine on both my C8 (at F/10) and on my new 80mm F/6 APO. In the latter I combined both with my 8 and 10mm Radian, and with the 14mm Meade UWA. The images remained crisp and free of any visible colour fringes on the moon.

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  • 8 months later...
michael.h.f.wilkinson

michael.h.f.wilkinson

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Just note that f/20 isn't a fixed value for planetary imaging. It's related to pixel size in the camera. In this case f/20 is for 5.6 x 5.6 pixels in most common planetary cams.

True, but it does not vary that much. Using a 3x at F/12 would require tiny pixels on the sensor (3x3 micron or thereabouts, with correspondingly small electron wells, leading to worse dynamic range)

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riklaunim

riklaunim

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MS Lifecams use 3 x 3 micron pixels in a modern CMOS sensor - they are more sensitive than the "old" ICX098 webcams and planetary cams, and can even challenge ICX618 in IR. Also newer designs are back illuminated. ICX445 in lunar cams is 3,75 x 3,75 too. Pixels are getting smaller and smaller... and planetary imaging doesn't need a lot of dynamic range. 8-bits will do.

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michael.h.f.wilkinson

michael.h.f.wilkinson

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MS Lifecams use 3 x 3 micron pixels in a modern CMOS sensor - they are more sensitive than the "old" ICX098 webcams and planetary cams, and can even challenge ICX618 in IR. Also newer designs are back illuminated. ICX445 in lunar cams is 3,75 x 3,75 too. Pixels are getting smaller and smaller... and planetary imaging doesn't need a lot of dynamic range. 8-bits will do.

Interesting. Back illumination helps a lot, and used to be very expensive. Good to see prices coming down. BTW, you need to separate the physical pixel size from the effective or logical pixel size. The SPC900NC can snap higher res pictures than 640x480, showing a smaller physical pixel size. What counts is the logical pixel size you get by dividing the physical size of the sensor area by the captured resolution.

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  • 2 weeks later...
jimao22

jimao22

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Thank you for answers, the problem is you cannot find anywhere the Telextender barlows, all are gone, disappeared... I understood that Meade will launch the new 6000 range and there will be the oldest (now) 5000 Telextenders.

Have anyone here one for sale?...

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jimao22

jimao22

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" It's related to pixel size in the camera. In this case f/20 is for 5.6 x 5.6 pixels in most common planetary cams."

It is a relationship between F ratio and size of the pixels, which I cannot remember now and I do not find it either. Who could help me?

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michael.h.f.wilkinson

michael.h.f.wilkinson

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" It's related to pixel size in the camera. In this case f/20 is for 5.6 x 5.6 pixels in most common planetary cams."

It is a relationship between F ratio and size of the pixels, which I cannot remember now and I do not find it either. Who could help me?

The F-ratio determines the size of the stellar image in the image plane (assuming diffraction limited optics). This is because the aperture determines the diameter in arc seconds of the diffraction disc (Airy disc). The focal length determines the magnification of that disc in the focal plane. If you double the focal length, you double the size of the disc. If you double the aperture, you halve the disc size. Together these effects mean that the focal ratio determines the size of the airy disc.

The pixel size must be matched to the Airy disc size to prevent loss of resolution: roughly 2 pixels in a disc diameter according to the Shannon sampling theorem (possibly multiplied by some constant, probably involving pi, but which I currently forget :)).

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Gina

Gina

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Interesting :) So, with an f5 scope and x3 Barlow (which I have) and MS LifeCam HD Cinema webcam (without lens) at prime focus, I should be fine for planetary imaging :)

Just gimme fine weather to finish my obsy then yet more of it with clear skies to get at it!! :)

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