Telescope Set-Up: Objective & Eyepiece Combination

[deppfx]

I am trying to prepare a telescope with the following lens combination. Can someone suggest if it is any good? I am intending to notice the planets and the moon in detail.

Objective: Plano convex - 50cm focal length
Eye-piece: The lens supplier suggested I use a Ramsden's eye-piece for this. Any other suggestions?

Also, would the thickness [diameter] of the objective lens make any difference to the telescope?

Regards
Depp.

 

[bapowell]

I am intending to notice the planets and the moon in detail.

...
Eye-piece: The lens supplier suggested I use a Ramsden's eye-piece for this. Any other suggestions?

I would not recommend a Ramsden eyepiece: they have a tiny exit pupil, narrow field of view (FOV), and suffer from several aberrations. Obviously it depends on your budget, but I would recommend Plossl eyepieces (around $50). These come in a variety of focal lengths and typically have a wider field of view than Ramsdens and good eye relief (for longer focal length eyepieces.)

 

[KrisOhn]

I second Plossl eyepieces, they are relatively cheap and high quality.

The diameter of the objective lens will make lots of difference to the telescope, you will collect more light if you use an objective lens with a diameter of 8 inches than you are using an objective lens with a diameter of 2 inches.

I'm not very familiar with refracting telescopes but I would recommend that you increase your focal length. For planetary observing you want a long focal length telescope and a short focal length eyepiece to get the highest magnification possible, so you can clearly inspect Jupiter's clouds, Saturn's rings, Mar's ice caps, etc. Note that if you are going to be observing deep sky objects you want a larger aperture and a mid to wide field eyepiece; the smaller the focal length of the eyepiece, the less light is going to get through.

 

[Chronos]

Is the objective a single element lens? Single element lens suffer from chromatic aberation. The lens maker's eyepiece suggestion makes sense in that regard. The view will only be acceptable near the center of the FOV with a single element objective lens. Spending money on a better eyepiece will not help.

 

[bapowell]

Is the objective a single element lens? Single element lens suffer from chromatic aberation. The lens maker's eyepiece suggestion makes sense in that regard. The view will only be acceptable near the center of the FOV with a single element objective lens. Spending money on a better eyepiece will not help.

If the OP is using a refractor, doubtful the chromatic aberration will be all that different between the Ramsden and Plossl. I have an f/10 100mm achromatic refractor and use Plossl and Celestron X-Cel eyepieces. When viewing planets I only begin to have (minor) problems with chromatic aberration at very high magnification (250x or more).

 

[deppfx]

I do want to make a DIY telescope and am on a low budget. I see that the Plossl and Celestron X-Cel eyepieces are a little expensive for a home project. Without much hassle, can someone suggest a basic/good combination for a beginner? I gathered a couple of combination of lenses from the internet.

* Primary Objective lens: Convex-Concave 25mm diameter with a 300mm focal length
* Eyepiece lens: Plano concave 25mm diameter with a 50mm focal length

# Primary Objective lens: A plano-convex lens of +2 diopters with diameter of 2 inches.
# Eyepiece lens: A microscopic eyepiece of 10x power.

Thanks in advance
Depp.

 

[chemisttree]

Buy http://www.cloudynights.com/classifieds/showproduct.php?product=37733&sort=&cat=26&page=1" lens.

Buy this http://www.cloudynights.com/classifieds/showproduct.php?product=18746&sort=&cat=26&page=1"

Buy this http://crawmach.com/TelescopeAcce.aspx" Call him and tell him you are going to put it into a Carton 60mm tube from Sheldon Faworski.

Buy any eyepiece you want at this focal length. Plossls are higher quality than Ramsdens.

Be very happy... as I am with mine!

 

[Chronos]

OK, it's not a single element lens - good. I bought a single element 50mm lens for like $0.95 about 40 years ago. It was disappointing. I mounted it in a spiral wrapped paper tube and achieved astoundingly horrible results. Of course that was like 20 years before I was born so I didn't know any better . . .