lidl refractor telescope

Hi Neil,
First of all, I presume you'd be putting the webcam into a scope, if so you'll need a fill aperture filter that goes over the front of the telescope.
The field of view of the webcam is very small, so you wont be able to get the entire sun image in one go, you'd have to make up a mosaic of many images to get a complete image. A 35mm film camera or DSLR would be a much better choice for something as big as the sun.

You could always try using is a low power eyepiece and placing the webcam with its lens in place up to the the eyepiece of the scope, this will give you wider fields of view, but you'd want to practice this on the moon well in advance to make sure it works, you might get vignetting and a curved focal plane, i.e. the center of the field of view is focused, but away from the center its to focused.

Neill,

I have a couple of example images of sunspots on the Sun taken with a Philips webcam attached to the Lidl Skylux 70mm refractor on the Kerry Astronomy Club website including ones of the Venus transit .


This should give you an idea of the size of field of view possible. The ETX has half the focal length, so should see twice the field of view, but as Dave says you would still need at least four images to cover the whole event. Not something I would use the two minutes of totality to mess around with! Much better to use an SLR of DSLR at prime focus. Then you would need a Barlow to increase the image size. (Samples of these also on the same page)

Michael Scully

Hi,

This is going to sound like a stupid question, but I'll ask it anyway. On the lidl site it states that the focal length of the ETX is 350mm = 70mm*f/5. Thats okay, but it says that the focal length can be extended to 1050mm with a 3x Barlow lens. I always thought the barlow was there just to increase magnification ,i.e. 350mm focal length, 25mm eyepiece - mag 14x - stick in 3x Barlow - eyepiece length falls to 8.33 or something and mag increases to 42x. Thats right, isin't? Can the Barlow affect the focal length?

Does anyone know what eyepieces you get with the ETX - judging by the magnifications stated - looks like a 4mm upto a 25mm, whats in between?
Is a Barlow included?

Final question - in the previous post it states 'then you would need a Barlow to increase the image size' - what exactly is meant by this?

Apologies for all the questions

Neill

Included with the EXT 70 is a 25mm, 12mm, and 4mm Meade lens's. I 3X Telenegative Barlow Lens(1.25") and one erecting prism.

Deirdre Kelleghan
IAS
www.irishastrosoc.ie

Neill,

Barlows actually increase the focal length of the scope. A by-product of this is that it increases magnification which is dependant on focal length. So a 3x Barlow will increase the 350mm to 1050mm which in turn up the focal ratio to F/15 from F5.

Neil,
Magnification is derived by deviding the focal length of the telescope by the focal lenght of the eyepiece used.
For the etx 70 and the 25mm eyepiece, this gives,
350/25= a magnification of 14.

A barlow is a lens which "multiplies the focal length of the telescope, a 3x barlow on a 350mm focal lenght telescope gives you an apparent 1050mm focal length, so using the 3x barlow on the 25mm eyepiece now gives you a magnification of 14x3=42.

When it says the barlow increases the image size, this is true as using it increases the magnification of the image thus enlarging it.

For me, the eyepieces are the weakest link with this scope, they are series 3000 eyepieces. I found the the best view I get through this scope is with a 15mm series 4000 eyepiece, it gives me a sharper image.