I am making a telescope at home whose front lens is off 500mm focal length and eye lens is of 1mm focal length so please help me to make it what should be the diameter etc....

[alankrit rajan]

500mm/1mm
Magnification≈500x

Edited September 1, 2023 by alankrit rajan

[AstroMuni]

13 minutes ago, alankrit rajan said:

500cm/1cm
Magnification≈500x

Hi,

Welcome to SGL. We will need more info on what you are trying to build this for etc. Do you have the lenses already? Or are you still at design stage.

Just a quick observation - 500cm FL is quite long (5m) ! Is this correct?

[alankrit rajan]

1 hour ago, AstroMuni said:

Hi,

Welcome to SGL. We will need more info on what you are trying to build this for etc. Do you have the lenses already? Or are you still at design stage.

Just a quick observation - 500cm FL is quite long (5m) ! Is this correct?

I want to see Saturn clearly that's why I am making this telescope.Write now I don't have any lenses I am still at design stage and from this formula 

Magnification = Focal Length of Objective Lens / Focal Length of Eyepiece Lens

I have choose the FL 500mm  for 500x zoom 

I am not a expert that's why I have come here for.

 

Edited September 1, 2023 by alankrit rajan

[alankrit rajan]

And 5m means 5 meters?? Please let me know 

[alankrit rajan]

 

Sorry for some calculation mistake it's 500mm

Edited September 1, 2023 by alankrit rajan

[alankrit rajan]

Please help me with your experience 

Edited September 1, 2023 by alankrit rajan

[AstroKeith]

To be honest, making a refracting telescope to see 'Saturn clearly' is not for beginners.

x500 is a very large magnification. It is unlikely that your atmosphere and mount would support it, even if your telescope was capable. Better aim for x300.

Now a good rule is that you can achieve x50 per inch of aperture. So x300 requires a 6" aperture. In practice a 4" or 100mm would be OK.

If you dont already have an objective lens, where is it coming from? It is unlikely to be of an advanced design which means you would need something around f10, which means a focal length of 1 meter for  100mm objective.

To achieve the x300, would mean an eyepiece focal length of 3.3mm which is just possible. 5mm is more realistic.

You are going to need a reasonable quality focuser, tube, objective lens mount, telescope mount, etc. 

Unless this is a particular project, for learning etc, I would look around and try to buy a telescope secondhand

[Astronomist]

why are you using a fixed eyepiece? most telescopes have a eyepiece holder (usually 1.25" or 2") so the user can use many different eyepieces for different magnifications. even in the very unlikely scenario that you could get hold of a 8" F2.5 lens (this is the minimum you will need for 500x at 500mm focal length) with acceptable chromatic aberration control, 500x is going to be tricky to aim unless you have a very excellent goto mount.

Edited September 1, 2023 by Astronomist

[alankrit rajan]

That means I should buy the objective lens of 6inch (15cm )aperture for 300x zoom and it's focal length will be?

and eyepiece of 3.3mm FL

[alankrit rajan]

I am not expert that's why I am asking you all 

[Mandy D]

2 minutes ago, alankrit rajan said:

That means I should buy the objective lens of 6inch (15cm )aperture for 300x zoom and it's focal length will be?

and eyepiece of 3.3mm FL

 

Objective FL is 300 x 3.3 mm = 990 mm

[alankrit rajan]

Okay 👍

[alankrit rajan]

With magnification of 300x can I see Saturn 🪐 clear

[Mandy D]

3 minutes ago, alankrit rajan said:

With magnification of 300x can I see Saturn 🪐 clear

Punching your numbers into http://astronomy.tools/calculators/field_of_view/

shows what you are likely to see in clear skies. Why not make a Newtonian reflector instead? It will be a lot easier and cheaper than trying to construct a refractor and the views you will get will far exceed anything from a simple homemade refractor.

[alankrit rajan]

Can you please explain me what is Newtonian reflector??

 

[Mandy D]

Just now, alankrit rajan said:

Can you please explain me what is Newtonian reflector??

 

It is a telescope which uses mirrors instead of lenses. A large parabaloidal mirror at the bottom of the tube with a small flat in front of it a short distance inside the focal point. Have a look at this link:

https://en.wikipedia.org/wiki/Newtonian_telescope

They are much easier and cheaper to make than a decent refractor. Plus, you can easily go to much larger apertures, say 200 or 250 mm or more.

[Cosmic Geoff]

I think you need to step back and do some basic research on the construction and use of astronomical telescopes, before you think of making one.  Also look at reflecting telescopes (Newtonians).

For instance, you mention buying an objective lens of 150mm (6 inch) aperture.  I think you should be sitting down when you check the price of this, assuming you can find one to buy.

If you have to buy the optical components, it will almost always be cheaper to buy a second-hand telescope than to make one.  A modest aperture will suffice to show Saturn with the rings projecting on each side, e.g. a 70mm aperture refractor.

[alankrit rajan]

Ok cosmic Geoff .

And Mandy D I think Newtonian reflector is too much complicated to make at home

[alankrit rajan]

And I have the lens of 70mm aperture

[Mandy D]

Just now, alankrit rajan said:

Ok cosmic Geoff .

And Mandy D I think Newtonian reflector is too much complicated to make at home

Yet, you imagine making a refractor would be simpler? OK, so you don't have to aluminise the glass in a refractor, but you have two surfaces to grind for each lens. You are going to have massive amounts of chromatic abberation to deal with, so will need at least two objective lenses to even begin reducing that. Sorry, I think building a large refractor at home without experience is far beyond what can be readily done, whereas a reflector is, by comparison, much, much easier. Are you buying all the lenses ready made? Where from? How much are they costing? What is the quality of them?

As @cosmic just said, you'd be better buying one ready made.

[Mandy D]

Just now, alankrit rajan said:

And I have the lens of 70mm aperture

70 mm aperture is not 150 mm aperture, so how does this help you?

[alankrit rajan]

As @Cosmic Geoff said 70mm aperture will be sufficient 

[Mandy D]

1 minute ago, alankrit rajan said:

As @Cosmic Geoff said 70mm aperture will be sufficient 

OK, so what is the focal length of this lens that you have? Don't forget if this is a singlet, you will have huge amounts of chromatic aberration affecting your view.

[alankrit rajan]

Around 500mm

Edited September 1, 2023 by alankrit rajan

[Mandy D]

Just now, alankrit rajan said:

Around 500cm

You mean 500 mm (millimetres)? Surely?