None of us can make the decision for you, but you knew that already. But it's really fun to contemplate the idea with others, I fully get that
Whether you should get something
from Tak's current FC-100D line is the easy part: go for it, if you have the funds and see yourself using and enjoying a practically perfect, lightweight visual 4" scope! But whether DF or DC or DZ or DL is right for you, that will be a very subjective decision. The good thing about that decision is that you can't go awfully wrong with any of these. And while I only have experience with a DF, I bet that the biggest difference you'll see in the eyepiece in focus, will be a slightly different image scale with a given eyepiece due to different focal lengths. I still haven't been able to notice CA in focus in my DF, even on the moon at ridiculous magnifications. But perhaps some other people have, I don't know.
Some thoughts I've had, when deciding to get my DF, and later on when DZ became available and I had to decide whether to swap my DF for it:
- One of the strengths of a 4 inch APO is its ability to provide magnificent wide field views. DF and DC with 740 mm fl have the widest fields of the series, 3.6 degrees with Pan 41. Along the same lines, DF (as of course DZ and DL, albeit at slightly longer focal lengths) is natively capable of accepting a 2" diagonal, letting you easily enjoy those wide fields. I know that many people use their FC-100D's only with 1.25" EPs, but I truly believe that if you have access to dark enough skies, you owe it to yourself and to the scope that you take a peek with some big, honkin' 2" wide fields...
- If I were to make the purchase now, and if I had to/wanted to buy a new scope, I'd very likely end up getting the DZ. Focal length is not that much longer than in DF/DC, the sliding dew shield is convenient IMO, and at least theoretically it should be optically slightly better (again, I'm not sure how easy it is to see it in the eyepiece in focus), and the price difference when purchased new is not that huge. However, I'm so happy with my DF, that when DZ became available, I quickly abandoned the idea of making the swap. Too much hassle, and not worth the expense for me personally, at least at the moment. But I bet that there will be some DFs for sale second-hand at reasonable prices in the following months, and I'd be hard pressed to convince myself that the performance/convenience improvement that comes with the (new) DZ is worth the price difference over a well-kept, second-hand DF. So that's one option to keep in mind.
Good luck, and as said, no matter which one you choose, you'll likely be very happy with it!
Edited by Axunator, 11 January 2020 - 11:20 AM.