If there's such a thing as a usable, cheap massive Dobsonian I've never come across it. And for what it's worth I also own a Tak, as well as a pretty respectable stable of Unitrons, Meades, Celestrons and a few quality home brew optics. Despite this, I have friends; so add in Astrophysics, TMB, Zeiss, Questar, Zambuto and even the obscure Suching
to the list of products I've been able to assess objectively over time. Resolution and visual limiting magnitude are a function of aperture. End of story. Get over it. Contrast is pretty much a function of good instrument design and maintenence.
I spent the money on the Tak to get the flat field and good aberration control for photography with a full-frame DSLR. In the world of astrophotography there are plenty of great images online taken with 'lesser' scopes, although once you've stumped up for the upgraded focuser and field flattener you may have been better off with the Tak...
For visual use, which is what this thread is all about, the eye is far more tolerant of field curvature and chromatic aberration than a sensor, and I would imagine that there are few people more qualified than a master optician who owns an ED120 to comment on whether it's as good visually as a reflector of equivalent cost.
I've heard plenty of Tak and AP owners claim that their scope regularly outperforms a scope of twice the aperture, but have yet to see it for myself. And to returen to the topic of this thread, my APO Tak is no better than either of my 30 year old achromatic Unitrons visually, but I love the digital images it produces, and there is no way I could take them through an f15 Unitron.
Cheers!
Andrew.
Quote:
Originally Posted by issdaol
I don't think anyone is claiming that their scopes defy the laws of physics. But there is more to scopes and image quality than just how Big the Aperture/Mirror is. A crappy 20 inch mirror will most probably be worse than a 5 inch APO. Similarly a excellent 20 inch mirror scope that is poorly mounted and aligned in a poorly designed tube/truss will require a lot of effort and maintenance to use.
Also not everyone has small trucks, trailers or wagons to cart around some of the massive "so called cheap" dobsonians
The other thing that I find interesting is the armchair critics that provide seemingly expert comments/advice on scopes that they have never owned or used. ( Not to mention the scope owners that love to try and say that Tak, TV, TEC or AP owners were ripped off or stupid for having paid more than their cheaper Chinese scopes ). |