I’m thinking about replacing my 72ED refractor with something nicer so I’ve started looking at what I might like instead. I’ve decided on a petzval astrograph of some description but can’t decide what focal length to go for. My 72ED is 420mm and there are plenty of options in that area, most of which can be reduced to around 300mm. Adding a reducer does require 55mm backfocus though so you loose the advantage of the petzval design, which makes me wonder whether I should just go for something at around 300mm. I’m currently thinking of the Askar FRA300, FRA400 or 65PHQ. I’d be using a ASI183MM Pro with the scope so not such a large sensor. I’d love a 2600MM Pro to pair with it but that will have to come later if at all.
I have another setup consisting of a SkyWatcher 190MN at 1000mm with a fairly small sensor (533MC Pro) so I’d like something wide field. Anything above 400mm or so is getting too close to my 190MN setup.
Anyway, I’ve looked on Astrobin for examples of images shot at 300-400mm with the IMX183 sensor. The trouble is, a lot of targets aren’t accissible from my location and it’s hard to tell at a glance if the image has been cropped, is a mosaic, etc. The astronomy tools FOV calculator doesn’t offer much in the way of targets. My next step was to look in Stellarium but even with it showing the deep sky stuff, it’s not really representative of what’s possible. As an example, here is a screenshot from Stellarium of the Heart and Soul. It doesn’t show much of the nebulosity around but there is so much there, as can be seen here:
https://www.astrobin.com/asmc87/B/
This leaves me feeling a little stuck as to where to go from here.
I don’t want to go too short (in the region of 250-300mm) and then not be able to reach many targets but then sometimes, these shorter focal lengths reveal so much more around the main target areas. A good compromise is get a 400mm FL and then a reducer to get the best of both worlds but you do loose some sharpness with a reducer so if the goal is to go wider, it’s best to get something that’s natively wide.
As a side note, I won’t be swapping and changing between scopes. I like to get everything set up and tuned in and then leave it all built up.
I have another setup consisting of a SkyWatcher 190MN at 1000mm with a fairly small sensor (533MC Pro) so I’d like something wide field. Anything above 400mm or so is getting too close to my 190MN setup.
Anyway, I’ve looked on Astrobin for examples of images shot at 300-400mm with the IMX183 sensor. The trouble is, a lot of targets aren’t accissible from my location and it’s hard to tell at a glance if the image has been cropped, is a mosaic, etc. The astronomy tools FOV calculator doesn’t offer much in the way of targets. My next step was to look in Stellarium but even with it showing the deep sky stuff, it’s not really representative of what’s possible. As an example, here is a screenshot from Stellarium of the Heart and Soul. It doesn’t show much of the nebulosity around but there is so much there, as can be seen here:
https://www.astrobin.com/asmc87/B/
This leaves me feeling a little stuck as to where to go from here.
I don’t want to go too short (in the region of 250-300mm) and then not be able to reach many targets but then sometimes, these shorter focal lengths reveal so much more around the main target areas. A good compromise is get a 400mm FL and then a reducer to get the best of both worlds but you do loose some sharpness with a reducer so if the goal is to go wider, it’s best to get something that’s natively wide.
As a side note, I won’t be swapping and changing between scopes. I like to get everything set up and tuned in and then leave it all built up.
