Barlow eyepiece

[daf1999]

Is there a huge difference between different models? I've seen some for £8 and some for £40 - wondering how much difference they make and what the actual differences are? clarity? robustness?

[John]

They can cost up to £300 and there are major differences. Adding anything into the optical path has to be done with a bit of care if the image is not to be degraded so the barlow lens needs to be accurately figured (a normal barlow has two lens elements but some have as many as 5) carefully matched and quality coated. The interior of the barlow must not allow stray light to bounce around so needs blackening and baffling accordingly.

The best "budget buy" barlow seems to be the TAL (Russian) at around £35.00. Some of the low cost ones are not even achromatic, ie: they are just a single lens and will introduce false colour an other optical aberrations.