I am sorry to ask yet another version of such a question. However, after having done all possible homework, I am still undecided and I would really appreciate some help/suggestion. Also critical comments on my reasoning to come down to the scopes I am debating about, is more than welcome.
What I am interested in?
DSO photography. As my eyesight is not so good, I do not care, in general, about visual.
As I live in central Europe (about 50 deg North), planets are never such a great target.
I like to photograph the moon, though but it is not a driver (and in any case I have a Mak 127 that I can use for that).
Which mount and setup I use right now?
I use an AVX that I need to move to my backyard every time I use it. The mount was chosen for its weight.
As much as I may like a better mount, I am not prepared to carry around more weight or at dismounting everything in bits every time. So, changing mount is not an option for the foreseeable future.
I guide by using PHD2 on an ASI224 with an ASI 60/260 guide scope.
My main camera is an ASI183MM with an EFW8. Currently, imaging is done with a Nikon AI-S 200mm f/4 (front stopped to 37mm). Both systems are mounted on a dual mount plate. The lens is nice and I'll continue using it, but it is substantially a good achromat so I would like to make use of the L filter as well as to have some more reach for smaller objects.
Due to the small pixels of the ASI183, I want a fast scope, not much slower than f/5, possibly faster.
An f/4 newtonian would be perfect but, again because of my eyesight, I am not too sure of nailing collimation as required for such high resolution camera (I have never done it in practice, so I do not know how demanding it is).
So, I would like to upgrade to a triplet apo (as I understand a doublet would not suffice for AP) and I came down to the following models:
For guiding. I would most likely use an off-axis system, especially for anything longer than 400 mm main scope.
1) WO GT 71/420 with 0.8x reducer (FL 336mm f/4.7) - about 2.2 kg
2) TS Optics 80/480 with 0.79x reducer, maybe 0.75 Riccardi (FL 380-360 f/4.5-4.7) - about 3.1 kg
3) TS Optics 90/600 with 0.79x reducer, maybe 0.75 Riccardi (FL 474-450 f/5-5.3) - about 4 kg
4) Esprit 80 ED with flattener (FL 400, f/5) - about 4 kg - it may be even used with a reducer for NB work..
5) Esprit 100 ED with Riccardi 0.75 reducer (FL 412, f/4.1) - about 6.3 kg
6) TS Optics 107/700 with 0.79x reducer, maybe 0.75 Riccardi (FL 553-525 f/4.9-5.2) - about 6.5 kg
7) TS Optics 115/800 with 0.79x reducer, maybe 0.75 Riccardi (FL 632-600 f/5.2-5.5) - about 6.4 kg
Cost-wise, they roughly rank as 1), 2), 7), 4), 3), 5), 6).
I very much like 5) but I am afraid the load could be too high (about >7.5 kg with camera, efw and guiding).
7) uses FPL-51 and is sold at a very good price (less than the esprit 80). There are amazing images taken with it on astrobin, some of them with an AZEQ5... and I would get rid of the Mak in this case (as well as in the case of 5) and 6)).
However, 7) is heavy and also starts to be quite long so it may be too much and starts to be on the slow side. 6) is the most expensive, probably just too much for me. So it boils most likely down to the first four.
I have not listed the ES 102 triplets. The essential version would be great, really. However, I have read about possible issues with the focuser and, more important, I have not found any information on a suitable reducer as it would be too slow at f/7 (ideally a 0.7x reducer would be needed).
At the end, despite I would have preferred mounting rings, I am giving an edge to the Esprit 80 followed by the 90/600.
Any comment, suggestion, would be extremely welcome!! Many thanks in advance!