Step 6: (3) Increase your eyepiece collection (if necessary)
Now we arrived at the most critical point for a scope : eyepieces. Are they enough? How do they perform?
In the case of a 70mm/700mm scope one needs magnifications in the range x20-140. A higher magnification is not so usefull because the resolution is limited from the size of the objective lens anyway. You may magnify but you are not getting any more information from the image. The rule for finding the maximum useful magnification is to multiply the diameter of the objective in mm x2 or in inches x50.
If the scope had no eyepieces at all, I would buy at least three of them, the best quality I could afford :
1. A wide field 24mm or larger
2. A 10mm (70x) and
3. A 5mm (140x) or a Barlow Lens x2 to use with the 10mm.
The scope included three eyepieces a 20mm, a 12mm both adequate but not optimal and a 4mm (too much distortion and aberrations). I intended to buy a Barlow but the nice people at the shop advised me differently and I am glad I listened to them. I got an 8-24 zoom Celestron wide field which has become my main tool, since it covers the 20mm and 12mm eyepieces with a much better performance. Furthermore it has a 42mm threading so that you can mount a DSLR camera and photo using the "projection" method (see step 13 for discussion on this).
Still, I intend to get a 5mm in the future.
In the case of a 70mm/700mm scope one needs magnifications in the range x20-140. A higher magnification is not so usefull because the resolution is limited from the size of the objective lens anyway. You may magnify but you are not getting any more information from the image. The rule for finding the maximum useful magnification is to multiply the diameter of the objective in mm x2 or in inches x50.
If the scope had no eyepieces at all, I would buy at least three of them, the best quality I could afford :
1. A wide field 24mm or larger
2. A 10mm (70x) and
3. A 5mm (140x) or a Barlow Lens x2 to use with the 10mm.
The scope included three eyepieces a 20mm, a 12mm both adequate but not optimal and a 4mm (too much distortion and aberrations). I intended to buy a Barlow but the nice people at the shop advised me differently and I am glad I listened to them. I got an 8-24 zoom Celestron wide field which has become my main tool, since it covers the 20mm and 12mm eyepieces with a much better performance. Furthermore it has a 42mm threading so that you can mount a DSLR camera and photo using the "projection" method (see step 13 for discussion on this).
Still, I intend to get a 5mm in the future.
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