Quote:
Originally Posted by janoskiss
No need for "apo" barlows. My Televue "achro" barlow has less off-axis false colour (ie none) than the Orion Shorty Plus "apo" I used to own (which is very simular to the Ultima). AFIU, having an apo or ED lens in a barlow is either solely for marketing purposes or perhaps sometimes to allow the use of a very short barrel while still maintaining good colour correction.
Powermates are not necessarily as good as well made more basic 2-element long barrel barlows like the TV barlows. Have a read of this comparison from someone with a fair bit of experience:
http://www.cloudynights.com/ubbthrea.../Number/523562 |
Interesting Steve. I'm still wading thru the CN link above. From what I understand so far, for on axis sharpness, contrast and transmission, you can't beat simpler 2 element designs, of course, as long as they are designed well and made with good glass/coatings, etc. Off axis performance may be a different issue though, and it could be that a well designed apo barlow may perform better off axis? And then, when it comes to imaging (though not my pursuit so far) , it could weigh towards the apo type barlow as well.
It's a bit like comparing simpler design narrower field eyepieces, to wide field complex/many element types. What do you think? I noticed you said your "acro" barlow was still better off-axis for colour than the Orion Shorty plus.
Clear skies.