Limitations when imaging the planets afocally

[Bokmakierie]

I have now spent many hours attempting to obtain decent afocal images of Venus, Jupiter and Saturn. Last night, Jupiter was in a perfect position and at its closest to the earth to really be able to get good images. In the Southern hemisphere it was as close to the zenith as it could get and at midnight the GRS was in a perfect position on the planet. But, alas, I had limited success as you can gather from the image I am posting here. Although reasonable surface markings can be seen, the image is a far cry from the fantastic images of Jupiter and Saturn that we have witnessed so far on the Forum.
The basic problem here is that too small an area of the CCD chip of the digital camera is exposed to the image. To expose a larger surface area one needs more magnification such as can be obtained with a 2 or 3X Barlow. But then it becomes almost impossible to position the image of the planet in the viewfinder of the camera. Believe me, I have tried and tried.
I have now realized that there really is no substitute for prime focus imaging with some system able to obtain longer exposures. For this you need a very stable mount, a good scope , lots of patience and software for stacking and optimizing image quality.
However, if you do not set your hopes to high, you can really get excellent images of the moon and reasonable images of the planets without incurring a lot of expense. Meanwhile, enjoy the wonderful images that some of our friends post on this Forum.
To obtain the image below, I manually stacked 5 of my best images using Microsoft Picture-It and optimized the brightness, contrast and sharpness of the image.

Phil

[AutoClub]

...The basic problem here is that too small an area of the CCD chip of the digital camera is exposed to the image. To expose a larger surface area one needs more magnification such as can be obtained with a 2 or 3X Barlow. But then it becomes almost impossible to position the image of the planet in the viewfinder of the camera. Believe me, I have tried and tried.

I have now realized that there really is no substitute for prime focus imaging with some system able to obtain longer exposures. For this you need a very stable mount, a good scope, lots of patience and software for stacking and optimizing image quality.

However, if you do not set your hopes to high, you can really get excellent images of the moon and reasonable images of the planets without incurring a lot of expense. Meanwhile, enjoy the wonderful images that some of our friends post on this Forum.

To obtain the image below, I manually stacked 5 of my best images using Microsoft Picture-It and optimized the brightness, contrast and sharpness of the image.

Phil

Hi Phil! I hope this finds you doing well. :)

I have tried prime focus photography of Saturn in the past with a DSLR (Canon 10D or 20D, can't remember which one I used), and it is an extremely frustrating (at least to me) experience. I still ended up with a pretty small image, even with the help of the 1.6x multiplication factor due to the camera's chip being smaller than a full-frame 35mm size. That helped my focal length by increasing the telescope's "native" focal length of 1180 to a "camera’s working focal length” of 1888 mm (still pretty small). I tried to "enhance" my viewing by using eyepiece projection using a 20 mm (or shorter) eyepiece. I don't know what my magnification ended up being with this, as the adapter I used was Meade's Variable Projection Eyepiece adapter, which basically is a sleeve that lets you move the camera closer to, or farther away, from the eyepiece, thus changing the magnification.

The problems that I've had using prime focus, and even with the "added benefit" of eyepiece projection, are at least three-fold. First, focusing becomes a major effort. I have found a great improvement using a Stiletto with a Ronchi screen, and focusing on a close star, then locking the focus tube so it doesn't move before slewing over to the main object. That definitely increased my odds. Secondly, the mount's stability gets even more critical the longer you get with the focal length, not only in being able to find your target (again) and get it centered on the camera's chip, but being able to keep it steady enough for the increased exposure time needed due to the longer focal length/dimmer subject. Third (and I tried this just the past weekend) was to add a Barlow and/or a Powermate. I added a Televue "Big Barlow" (2x Barlow) to my 5" refractor's 1180 mm focal length, and then added a Televue 2.5x Powermate on top of the Big Barlow. This arrangement gave me 5x the native focal length, resulting in the scope's “working” focal length now being 5900 mm. This is still almost too small for any kind of "decent" planet imaging with a DSLR, from what I've seen of others' images on this forum. I think iceman's setup is around 13,400 mm or so, with a 12” Newtonian bringing in a lot of light to start with, quite a step up from mine.

However, with my set up, when I get to a 5900 mm focal length, I'm ending up with an f/ratio of about f/46.5, which is extremely slow (!) for photography. Plus, when you couple this slow an f/ratio with a small 5" aperture, the amount of light you end up with that gets to the camera is pretty small, thus requiring much longer exposures. If there were "perfect seeing conditions" with no turbulent atmosphere to look through, and assuming you could keep your mount stable enough for the longer exposure needed, then things may work pretty well. Unfortunately, my experience has been that every shot taken with a DSLR is significantly different from the previous one(s), and I need to take a gazillion images to end up with enough “good ones” for RegiStax to work with. It is very frustrating!

I am constantly amazed at the quality of images you get with your set up! I think what I'm finding more and more (and concurring with others who have posted on this forum and other websites), is that for planetary and lunar imaging, there apparently is no other "best" approach than to use video cameras, such as the Toucam or other types. The ability to take a "non-stop" video of perhaps many thousands of individual frames, and then have software select the best, stack them together, and allow you to apply some "tweaks" to enhance the image, gives you much greater control over the problem with turbulent air in the atmosphere, and apparently also helps compensate for the reduced amount of light getting to the camera.

I know it is frustrating to spend a lot of time setting up equipment and getting a camera to give something that we think it should, but I keep trying. I’m beginning to play a little more with my Meade Lunar Planetary Imager (which needs a computer unfortunately to work), and have tried a couple of times to use the software package called K3CCDTools to take a video, instead of Meade’s software, which just takes multiple “still” images. I’m using the trial version of K3CCD now, and don’t know if I’ll buy it after my 30-day trial expires. It just seems like there is no limit to the amount of hardware/software/accessories to this “hobby”, and the required set-up time for all these gadgets to get what I want keeps getting longer. Bummer :(

Well, anyway, I’m not sure I’ve said much here, other than hope you keep at what you’re doing so well. I appreciate your efforts, as others on here do as well. Each image posted here is a different man’s (or woman’s) efforts, and not only are we all learning this “as we go”, but I for one am seeing how much effort each little improvement requires. And it shows!

Thanks for all your great images, Phil! And to the others on this forum who have bothered to read all the way to the end of this lengthy post, thanks to you as well!

By the way, Phil, I intend to post an image I shot of Jupiter this past Saturday from my backyard, using the Meade LPI and K3CCD. I ended up with a couple of videos, and chose to process the one that only used the 2.5x Powermate. The larger image obtained with the additional 2x Big Barlow was too dim, and the atmospheric turbulence was, IMHO too severe to warrant further work. :(

Cheers, and Clear Skies! :)

Paul

[Bokmakierie]

Thank you Paul for your comments and for highlighting the problems one finds when attempting to do prime focus imaging. I must say that the images that you have been posting recently are really of a very high standard and I appreciate the dedication and perseverance you have put into your efforts.
I also appreciate the kind words about my own efforts. Unfortunately my physical condition precludes becoming involved in more than my afocal efforts. I am not doing poorly health wise at the moment and the fact that I spent 3 hours in the cold trying to get decent Jupiter images testifies to this. Meanwhile I drool over the fantastic images that some of our friends post on this forum.

All the best, my friend.

Phil

[JAICOA]

Hi Phil, Paul I concur with both of you anything new or just the intent is a milestone for me there are times you have to be persistent but not to the extreme where it would create a negative situation. I myself having a hard time just to image Jupiter this year it sits low and the turbulance here in the tropics is severe and the humidity is way up there and the rain is almost daily but i continue to try, to see if by chance that one momment shows up if not keep on trying and not get discourage by the odds. So Phil you have a Great Photo there it is sharp some cloud structure could be seen and the color a slight saturation for it's size but still an Excellent shot! Well done and looking to see more from you. Clear Skies

[Bokmakierie]

Thank you, Efrain, for your encouraging words. Clear skies my friend.

Phil