I was under the impression that most field flatteners were only useable for AP use because they change the focus position drastically. But I looked up the product on-line and it seems to be advertised for visual use too. Very interesting... . So.... if I add a field flattener, all the field curvature I see would be caused by the eyepiece alone?
Yes, and that's not going to be significant. Many field flatteners are AP-specific but not all. The TSFlat2 is flexible. The key is getting the working distance to the sensor right (in this case the eye-facing ocular lens). From the TS web site:
In principle this rule applies: the shorter the refractor´s focal length, the longer the working distance to the sensor has to be.
♦ focal length < 450 mm: 128 mm
♦ focal length 450-490 mm: 123 mm
♦ focal length 500-550 mm: 118 mm
♦ focal length 560-590 mm: 116 mm
♦ focal length 600-690 mm: 113 mm
♦ focal length 700-800 mm: 111 mm
♦ focal length ab 800 mm: 108 mm
For an 80/480 you can pretty much screw the TSFlat into the nosepiece of most 2" mirror diags and you'll be spot-on or close enough. At longer focal lengths, the TSFlat will *be* the nosepiece for the diag. And there are workarounds in between. For visual there is at least a 5% error factor. It works! I am amazed how many times I have to post this. It ought to be common knowledge. But generally, between the option to buy flat field quad telescopes or use TSFlat 2 or 2.5 with triplets and doublets, there is no reason for most refractor users to be putting up with telescope FC.
Eliminate that and get eyepieces that leverage flat fields, and you're done with FC forever. The two phenomena that baffle me most on astro forums are 1/ FC complaints, and 2/ undercut rants about eyepieces. Both of these are easily solved. And if people bought more quads or more TSFlats, the market would get the message. Flat field scopes solve pernicious observing problems, so however you get there -- buying a quad or using something like a TSFlat with a triplet or doublet -- makes your astro life much easier. I've known this for decades because I started buying astrographs for visual use over 30 years ago. I'd have thought more observers would have caught on. But no. Ban FC from your astro observing life. You have multiple ways to do it, and you won't regret removing FC as an observing concern.
Edited by 213Cobra, 25 July 2019 - 01:58 AM.