Beginner: low cost setup for planetary objects

Hi Simon97,

In reply to your inquiry regarding a low cost setup for planetary imaging, I'll be happy to give my opinion on the subject.

First I note your camera is a very fine Nikon J1. While I haven't seen any results except for yours in planetary imaging with that camera, I would expect it would do fairly well. That sensor, though a bit smaller than the APS-C size has considerably fewer pixels than many compact cameras, which is a good thing. Doing a bit of math on your sensor size (8.8mm X 13.2 mm) and resolution (2592 X 3872 pixels) shows that its pixel size is around 3.4 microns (294 pixels/mm). While not as large a pixel size as some other cameras, it is considerably better than most compact  P & S cameras. In general, larger pixel size enables higher dynamic range and less noise in low light conditions. I would expect some decent results with your camera.

As for your suggested optical tube for planetary work, I looked up the specs on the Orion Starmax 90. I haven't looked at any of the user reviews. But just based on the specs, its focal length of 1250mm would be a fairly good match for your sensor size with prime focus imaging of the Moon. With your sensor size (8.8 X 13.2mm) you would get an image field of 0.40° X 0.61°. While this would not allow for a full Moon disc to fit in, it would allow some nice partial disc shots. The full Moon subtends an angle of around 1/2° on average. As for the size of Jupiter, when it's closest to Earth, it's angular size is around 47 arcseconds or 0.013°. At prime focus with no amplification (Barlow lens or eyepiece projection) it would cover 0.286mm or 84 pixels. While this is not bad in itself, you would benefit from a larger image scale for the planets. This would be fairly easy to achieve by the above methods. So that optical tube could work out quite well for a start in lunar/planetary imaging.

Orion's website has several versions of that telescope, but all I saw were alt-azimuth mounts, which would be somewhat limiting except for the Moon. If your budget would allow an equatorial mount that would be an improvement, particularly if it was motorized for tracking. If it also was capable of slow-motion controls on both axes, it would make a decent guide/track platform for piggyback imaging as well. Used in that mode, a telescope would need some means to have a camera solidly fixed atop the optical tube. Some scopes have an accessory piggyback camera mount that is bolted to the top. Planetary imaging with the camera body using the telescope as its lens is easy to attain. Go to the following source for the adapters:

http://www.telescopeadapters.com/

If you start with a 90 -127mm aperture telescope, you'll find that lunar imaging will produce some nice results. Compared to refractors of that size, the Schmidt-Cassegrains or Maksutov designs are often less expensive. These types of scopes will be out-performed by an equal aperture refractor, but in "bang for the buck" they can't be beat. An added benefit for lunar/planetary work is that the two compound telescopes (S-C & Mak) usually have a much longer focal length than a refractor of equal size.

While I don't want to discourage planetary imaging, that type of work is much more demanding than with the Moon. This has mostly to do with the angular size of the subjects. The largest planet, Jupiter has the same angular size as a 60-mile crater on the Moon. This can be seen in the following link which shows the two at the same image scale.

http://forums.dpreview.com/forums/post/50735913

Note how Jupiter is about the same angular size as the dark-floored crater Plato, which is 109 km (68 miles) in diameter. Best results from the planets come from taking a large number of (highly magnified) individual frames and having a program like Registax sort out the best ones for stacking. I see that DPReview reports for your J1 camera a burst mode of 60 frames/sec. which could come in handy. Saturn makes a nice subject due to its interesting ring system, which is somewhat larger than Jupiter. In many cases the limiting factor will be the atmospheric seeing, although for a small telescope, its resolving power may come into play as a limitation as well.

I hope this information and opinion will be of use to you. If you need a more detailed explanation of the numerical results given above, I can give the details. If I missed any points or you have other questions, let me know - Wishing you success in your lunar/planetary imaging.

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Best Regards,
Russ