For each my optics- scopes and SLR Photolenses - I have determined the Field-of-View.
I used my FOV measuring method to find out the real Field-of-View per optics in combination with my cameras and made the following table.
Please note that I made this table for my own use and it might not be applicable for your setup, so I strongly recommend that you make your own table !

I use the table to select the appropriate optics for a celestial object, depending on the size of that object.
Note: meanwhile I have made a similar table based on my Canon EOS 1000D DSLR Digital Camera

Meade Bresser Skylux 70mm f/10 Telescope [Lidl] Meade LX200 10" f/10 Telescope SLR Photolenses William Optics Zenithstar 80 ED II APO	Focal Length	Width in arc minutes with SC3 and/or ATK16IC camera	Height in arc minutes with SC3 and/or ATK16IC camera
ToUcam lens	5.8mm	2807	2105
TV Zoom lens at 10mm	10mm	1357	1017
TV Zoom lens at 40mm	40mm	441	331
SLR Photolens 29mm Note for myself: use 7mm extension ring (T2<->M42) to reach focus with filterwheel/ATK16IC combo.	29mm	542	407
SLR Photolens 35mm	35mm	465	349
SLR Photolens 50 mm	50mm	313	234
SLR Photolens 35mm with 2x teleconverter	70mm	232	174
SLR Photolens 85 mm	85mm	193.85	145.37
SLR Photolens 135mm	135mm	125.48	94.11
SLR Photolens 200 mm (SOLD)	200mm	83.49	62.62
ATK16IC camera + WO Zenithstar 80ED with Meade 3.3 FR	240mm	67.84	50.88
William Optics Zenithstar 80ED II APO with Mogg 0.6 FR	245mm	66.45	49.84
SLR Photolens 135mm with 2x teleconverter	270mm	66	49
SLR Photolens 300 mm (SOLD)	300mm	57.13	42.85
William Optics Zenithstar 80ED II APO with Meade 3.3 FR	290mm	56.14	42.11
Coronado PST with Trust WB-5400 webcam	400mm	46.2	36.96
SLR Photolens 400 mm (SOLD)	400mm	40.7	30.5
Meade Skylux 70mm f/10 'Lidl scope' with 0.6 Focal Reducer	435mm	37.43	28.07
William Optics Zenithstar 80ED II APO Prime Focus	545mm	29.87	22.41
TAL-2M with Focal Reducer (SOLD)	690mm	22.55	16.91
Meade Skylux 70mm f/10 'Lidl scope'	700mm	23.26	17.44
LX200 10" f/10 with f/3.3 Focal Reducer SC3 camera in combination with Scope Teknix Filter Wheel	912mm	17.85	13.39
LX200 10" f/10 with f/3.3 Focal Reducer SC3 camera mounted with custom made M42 ring and extra spacer ring	1015mm	16.04	12.03
LX200 10" f/10 with f/3.3 Focal Reducer SC3 camera mounted via 1,25" eye piece adapter	1030mm	15.81	11.86
LX200 10" f/10 with f/3.3 Focal Reducer SC3 camera mounted via 1,25" eye piece adapter and Astronomik H-Alpha filter	1140mm	14.28	10.71
LX200 10" f/10 with f/3.3 Focal Reducer ATK16IC camera in combination with Scope Teknix Filter Wheel	1270mm	12.82	9.61
LX200 10" f/10 with f/3.3 Focal Reducer SC3 camera mounted with custom made M42 ring (distance between optics and CCD too small)	1420mm	11.47	8.60
TAL-2M Prime Focus (SOLD)	1200mm	13.57	10.18
TAL-2M 2x Barlow (SOLD)	2400mm	6.78	5.9
LX200 10" f/10	2500mm	6.41	4.88
LX200 10" f/10 with Trust WB-5400 in 1280x1024 pixels frame format	2500mm	7.39	5.91
TAL-2M 3x Barlow (SOLD)	3600mm	4.52	3.39