Planetary Imaging

[Gina]

Spreading my wings again   I've done a bit of planetary imaging in the past but only with my first cheapo scope (Celestron AstroMaster 130 Newt) and a webcam.  Now I think I would like to try again.

Best scope I have ATM is the MN190 and best webcam the MS Lifecam Cinema HD with 3.3micron pixels.  I also have 2x and 2.5x Barlows.  The image size with this arrangement is tiny   BUT would I do better with a longer FL scope with the poor seeing in the UK?

[ChrisLX200]

Well for sure with planetary imaging you are hostage to getting excellent seeing - if only for moments. Lots of people use longer focal length with success. I think a lot depends on local conditions and where I am such seeing is rare indeed. The cheapest way to find out may be to buy a 5x Powermate s/h for your MN190 and try it (rather than go to the expense of a dedicated MakCass or something).

ChrisH

[johnrt]

The 1000mm focal length of the 190mn is midrange DSO, you need to go longer, much, much longer. The Celestron 9.25 is 2350mm. A good barlow may be a good place to start as Chris says.

[riklaunim]

You don't need a long focal length in the telescope, as Barlow will do it for it. 190 mm telescope is already quite good aperture. Lifecam Cinema should give good sizes, especially if you are at max around f/15 for those small pixels. In SharpCap there is subframe to pick and "zoom" which then should be at max (anything less is camera shrinking the image from bigger part of the sensor to fit on the smaller subframe output).

I have some lunar images taken with Lifecam Studio here.

[Gina]

Well for sure with planetary imaging you are hostage to getting excellent seeing - if only for moments. Lots of people use longer focal length with success. I think a lot depends on local conditions and where I am such seeing is rare indeed. The cheapest way to find out may be to buy a 5x Powermate s/h for your MN190 and try it (rather than go to the expense of a dedicated MakCass or something).

ChrisH

Thank you Chris   That sounds a good idea.  I'll try with MN190, best Barlow I can find and webcam and see what I get.  When I do DSO imaging I'm lucky to do better than FWHM of 3 with 4.5micron pixels and no Barlow but I guess there are short periods of good seeing amongst all the bad   TBH I'm not expecting much from here.

[Gina]

Thank you John and Rik   Two conflicting views there   I can see that increasing magnification in the telescope might mean less glass and easier optics than a Barlow, resulting in a cleaner image perhaps.

[Gina]

I find I have a Tal x3 Barlow so I'll give that a try

[neil phillips]

What I think Rik means Gina is that shorter focal length scopes are not as much a disadvantage as what might be assumed.

Because even long focal length scope users will likely still use a barlow. When I used my old Meade  MAK  native focal length F15 I still used a 2x barlow to get enough focal length to see very fine details on the moon and planets.

I am currently using two scopes a F5 and F6.3 Both are actually better at lunar and planets than my old F15 Mak Cass was.

Which can confuse newbies, and experienced alike

The  Reason being is aperture. Which is more important. for the most part than Focal length.

If one had a massive mount, a f8 10" Newtonian might well perform better than a 10" F4.5 " Newt. For a few of reasons.

Collimation errors are less troublesome in longer focal length scopes. Also Making good primary mirrors is easier at longer focal lengths.

But the downside is, as Telescope mirrors get larger and larger, a 12" F8 Newtonian would be so long and heavy, it could flex.

In the wind it would jolt more, as the see saw effect of long tubes react worse under windy conditions. The mount needed to hold such a beast well. Would be very expensive. So for the most part those on a budget have to compromise, and those shorter length scopes can be made to work well on planets and lunar. Regardless that higher power Barlows are needed to achieve it. in the range of 3 to 5x Barlows. Some truly Stunning images can be got with shorter length Scopes. Of course its one reason why SCTs are widely used on lunar an planets being more compact and lighter than long focus Newtonians. Best of both worlds. The contrast issues with large secondary's on SCTs are overstated in my opinion.

That's not to say A 6" F4 Newtonian would be as good as a 6" F11 Newtonian on lunar and planets.

My money would be on the  F 11  Contrast will also be slightly better on the F11 as the secondary mirror will be smaller. But a 12" F5 for imaging purposes would kill stone dead that 6" F11 Newt. For all the reasons outlined. Its often aperture that is king.

 Its all these considerations that confuse a lot of people, when it comes to focal lengths, scopes and planets.

I would have thought the MN 190 would be excellent with a 4 or 5x barlow  on lunar and planets.

[RAC]

The MN190 should be good. I've been using my 10" f4 newtonian for planetary imaging and its been great with a 5x powermate. IMO Saturn is hard work at anything slower than f20 so you may find a 3-4x barlow better for that one.