Planetary Imaging with 114mm/4.5" f/8 Reflector - Possible? - Forums

Topic starter

Sep 30, 2022 · Edited: Sep 30, 2022

Hi folks!

I know most planetary imagers have serious purpose-built setups, but my daughter has a Celestron Powerseeker 114, and I just upgraded my astrophotography mount and can accommodate the weight of her telescope. It's a spherical mirror, but it has pretty decent views of the planets with a 6-15mm eyepiece and 900mm focal length.

I image with a small refractor and have been doing deep sky imaging for a few years now. I don't think there's any point in me doing deep sky imaging with the 114, but I was wondering if it might be possible to use my ASI120MM guide camera to do planetary imaging with it. I checked the FOV in Stellarium and Jupiter and the Galilean moons would fit nicely even without a barlow.

I guess my main questions are:

- Would this venture be advisable or am I just heading for disappointment/frustration? I'm not looking for incredible results here.
- Should I purchase a barlow, and if so, how much magnification should I consider going up to before I max out the resolving ability of the telescope?
- Should I use my ASI120MM with some filters (and if so, which ones?) or should I consider purchasing an inexpensive colour camera?

Thanks in advance for any guidance here!

CS,
Mark

Well Written Respectful Engaging

James Tickner

Sep 30, 2022

Short answer - give it a go! I have a small 4” refractor and whilst it doesn’t produce the incredible images you get from large scopes, it nonetheless gives pretty satisfying pictures. It’s a good opportunity to learn about stacking, lucky imaging, sharpening etc.

To answer your specific questions:

- A 2x Barlow would be helpful. The usual rule of thumb is to image at a focal ratio about 5x your camera pixel size in microns (3.75 um for the ASI120MM). Currently you’re at about F/7.8 and want to be targeting 5 x 3.75 = F/18.75. A 2x Barlow will get you to F/15.6 which is close enough.
- To produce colour images with your camera you’d need a set of RGB filters (31 mm diameter would be fine) and a filter wheel. You then collect 1-2 min videos using each filter in turn, stack and sharpen and combine to make a colour image. There’s a bit of a learning curve here and you’d also need to use Winjupos to manage the derogation and combination. You’d probably be up for a similar cost to buying a cheap colour camera and the learning curve would be less - might be the easier way to go.

The Cloudy Nights site has a couple of long-running threads on ‘small bore’ planetary imaging using scopes of 6” or less that will give you a good idea of what you might expect to achieve. The Jupiter thread is https://www.cloudynights.com/topic/398608-small-bore-challenge-jupiter-w-6-or-less

Helpful Engaging Supportive

Mark Germani

Topic starter

Oct 1, 2022

Brilliant - thanks @James! Given the focuser is plastic and pretty weak, I'd probably skip the filter wheel and screw the filters in one by one, but maybe an OSC is a better approach after I factor in the cost and effort of LRGB.

I'll check out that thread!

CS,
Mark

Wouter D'hoye

Dec 17, 2022

Hi,

It for sure is possible. within the limitations of the aperture though.. I have a 6 inch which in the end is not that much bigger. The asi 120 is a great camera for lunar/planetary imaging. I'm asolutely positive that especially for lunar you could do some very nice things.

give it a go. You have all the gear.