aperture or focal length

[mason]

For planetary webcam imaging, what would be best, an f/4.7 10" newt on a eq 6 or a f/15 7.1" mak? would aperture be king over the higher focal length. i was also thinking of a 12" newt, but think that would be too much for the eq6 mount!

Apologies for asking this question again, but before spending a small fortune, i need all the advice i can get!!

mason

[E621Keith]

I'd go for the Mak. In theory the mak should have less secondary obstruction and don't have secondary spider to reduce contrast.

That's my opinion anyway, but since I haven't use either and don't do much imaging, please don't take my word for it.

Here is a review of the skymax pro Skywatcher 180 Pro–Mak - Review

[brianb]

More aperture gives you a brighter image at the same effective focal length which helps beat the seeing, as well as allowing more resolution. You'll want to be working in the f/20 - f/30 - f/40 region anyway, depending on the seeing and the camera, so you're going to have to use a barlow / tele-extender / eyepiece projection anyway. The larger central obstruction in a fast Newt will reduce the contrast slightly, but nowhere near as much as some people go on about, and in any case lost contrast can be got back in post processing when imaging.

Go for the Newt. Just make sure you collimate it accurately.

There's one big downside to the SW 180 Mak - it takes for ever to cool ...

[sixela]

For planetary webcam imaging, what would be best, an f/4.7 10" newt on a eq 6 or a f/15 7.1" mak? would aperture be king over the higher focal length.

mason

Yes, but it's going to be a lot more difficult to focus the f/4.7 scope (assuming the Mak has a focuser at the back, if you have to move its primary it's even worse than a fast Newt).

Of course the 10" Newt will be more of a beast to set up. With the seeing that we are "graced" with, it's not going to beat the Mak easily on most nights.

Both scopes need A-OK thermal management to deliver good planetary images. On the Newt, a ring baffle in front of the mirror (to force the air flow to come from over the mirror) and a baffle that closes the back with a fan that pulls air is ideal, but even just a fan that blows on the back of the mirror will help tremendously.

On the Mak, you need something like a Lymax or Geoptik cooler or it'll never cool down completely. And of course you'll also need dew prevention stuff on the Mak (or the corrector will dew over just when the tube currents have disappeared and you're ready to go ).

Lastly, there's also the quality of the optics. I think I'd take an Intes Mak over a Synta/SKywatcher 250mm mirror most of the time, but I'd take a 250mm Newt from Synta over one of their larger Maks.

[mason]

i have a x2 and a x4 barlow with a dfk 21auo4.as imaging source camera.

Does the chip size make a difference with such a long focal length on the 190mn?