[another] Which Wide Field Scope [question]?

[AstroGS]

I currently use a Redcat51 V2 OTA for any wide field project and it is doing a great job indeed. But, since i am using APS-C (2600MC & 2600MM) the stars at the edges/ especially corners are less round and sharp.

For that reason, i started looking for a new wide field scope - if money allowed i would definitely go for a Takahashi FSQ-85 + reducer but, new gets close to £4K and it is a definite no for me.

I have excluded also the RASA 8 as, i want the scope to be mobile and i can take it with me when i travel but, fast optics is a significant plus.

 

For that reason, i was looking into the below options - which from your experience could cover the whole APS-C and provide the sharpest image.

Borg 72FL F3.6 - £2.6K

RedCat61 F4.9 - £1.6K

Starfield Gear80 F4.8 (with reducer) - £1.4K

SharpStar 61EDPH III F4.5 (with reducer) - £810

Askar 65 PHQ F4.8 (with reducer) -  £1.3K

Askar FRA400 F3.9 - £1.5K

Edited July 6, 2023 by AstroGS

[Elp]

You'd have to look at each scopes specs for their illuminated imaging circle to see if they work with apsc, I'd assume so as a lot of scopes now also do full frame.

Question, what is your goal? You state wide field the scope list however tends toward a medium focal length so I assume youre after a bit more zoom? If that's the case most 60mm will be around 360mm focal length so won't really be that different from the redcats FOV. The Askar FRA are their top end so essentially eliminates the PHQ. I've been looking at Borg myself but most owner comments state not so good edge correction (it's expected the faster you go with a lens just like most camera lenses though the Samyang 135 is one of those rare exceptions).

As a general "upgrade" I'd look to 80mm+ refractor, the more lenses in its native construction generally the better control of focusing all rgb to one focus point, more so the larger the aperture you go.

Fast optics generally requires aperture which also offers a resolution boost. You could look at a Newtonian astrograph as another option but you still have the issues of getting one going with coma correctors, tilt, light leaks etc as well as the scopes size.

For a compact size and having a multitude of focal lengths to image with I went with a C6 (I have 3 focal length options with it, planetary at 1500-3000mm, f6.3 reduced at 1000mm and Hyperstar at 300mm), it won't however be as sharp as a good apo refractor but I'm happy with it so far due to its versatility.

[AstroGS]

Thanks @Elp - probably I should have said that I already have a Stellamira 90ED Triplet, which I will replace with an Esprit 120ED and I do have a SW 190MN as well (which I have not used yet).

 

What I want to achieve is to get a better to the Redcat51 wide field (between 250mm - 350mm), that offers better image circle, with better stars edge-to-edge. At the same time the f3.9 seems appealing too.

[Elp]

To be honest, the esprit will probably be better than your whole list from what I gather of it. F3.9 you'll get issues trying to get a flat field, I use a 0.65x Apex reducer with my Z61 making it around 250mm FL, even with the smallish 183 sensor I don't think I can get it flat so I just crop. If you want wider, just mosaic with your redcat leaving enough overlap to crop any elongated stars from the edges (use telescopius for planning).

I've been thinking along the same lines as you, I want a redcat for a flat field around 250mm, but I can just image with my Samyang 135 and mosaic, bonus is it's extraordinarily fast.

Edited July 6, 2023 by Elp