Astrophotography

russ_watters

M-13 from a few nights ago...

Attached Thumbnails

 

The_Professional

I love the pictures russ, wonderful images. Especially the one on thread 38. They're very clear and quite detailed, did you shoot them with a digital camera attached to the telescope.

russ_watters

Starting with post 38, all pics are with the MEADE Deep-Sky Imager.

I'm still having some tracking problems, so I'm not having much luck with deep-sky objects, but the planets will keep me occupied for a while... (tonight: Ganymede transit of Jupiter).

turbo

If you will describe your tracking problems, I will try to help. I have probably managed to replicate every tracking problem imaginable over the past 30 years or so. They are all tractable to some extent, depending on the equipment you own and the amount of attention that you are willing to expend on addressing its limitations.

If you do not have a permanent mount, you are constrained by having to set up every night, and your tripod can shift throughout the session when you are working on ice and snow, especially if you have a light scope and you just touch a tripod leg with a boot! You've got to polar align the mount (easy to gloss over with a cheap PA mount - you've got to PA through the primary), and then supply adequate degrees of guidance to each type of exposure. Back when I had a lot of opportunity to do this in dark sites, each exposure had to last at least 20 minutes to capture usable images of faint deep-sky objects on Konika 3200 film through a 6" f:8. These aren't snapshots, and they can feel like forever when it's -20F or lower (the clearest nights for this kind of work).

Without accurate polar alignment, field rotation errors can ruin your exposures. Atmospheric refraction can make getting sharp images impossible, especially close to the horizon. Periodic errors in your scope's drive can be infuriating, and are impossible to detect unless you have the troubleshooting skills to ferret them out. Guidescope flexure can ruin every image in an entire night, if you are not cognizant of it, and they are prevalent when working with short-tube scopes with inadequate guidescope mounts. Working through a variety of telescopes, I have experienced all of these, and would be willing to help troubleshoot any guiding problems that anybody here has.

By the way, if anybody here is imaging through a SCT or any other similarly-designed telescope that uses a moving primary, let me offer a very basic piece of advice. You must get a high-power guiding ocular with an illuminated reticle and after aligning your scope and activating your drives, focus out, then bring the focus slowly back in until the stars are crisp. Then:

1) set the reticle on a star
2) run the focus slightly in and out.
3) observe the position of your chosen star both in and out from correct focus to see any perceived shift.
4) focus out and then critically focus the star and see if the star at focus is at the original position in the reticle. If the position is sufficiently accurate, you can (in the future) hope to focus out, then in to critical and retain alignment.

You can repeat these steps (reversing in and out) and determine in which mode your scope most repeatably keeps alignment. Whichever procedure gives you the most repeatable position for the guide star is the procedure that you must use to have any chance to keep your scope useful for astrophotography.

If you cannot get repeatable results in either mode, your telescope will sabotage your efforts at astrophotography, and you likely own a scope that can never properly be collimated either, because this type of image shift implies excess mirror tilt. If you want to pursue astrophotography, especially with film, sell the scope and get a decent newtonian or a refractor with optics that are in relatively fixed locations and alignments.

russ_watters

I'm out of the country for a couple of weeks, but I'd be greatful for the help.

Jeff273

Russ,

Nice photos. Are you shooting from Philly? What are your skies like? I'm in rural south-central PA and I have maybe mag 5.5 from my yard. Have you done any deep-sky work? If so, I'd be interested in your results given the high light pollution in Philly.

russ_watters

Jeff, I'm just outside of Norristown, about 20 miles from center city. All of the photos I have posted so far are from this area. As for deep-sky: everything I have taken so far I have posted here. I haven't put much effort into figuring out my limiting magnitude, but I'd have to guess about mag 5 or even a little worse. The combination of bright skies, a small scope, and unreliable tracking for lengths of time over 30 seconds has limited what I've been able to do deep-sky. I'm still working on it....

russ_watters

Ok, I finally got a chance to break out the scope last night and attached is a fairly typical 45 second exposure. About half of them come out OK and half look something like that. The pic is about 25 arc min across, which makes the oscillation about 20 arc sec across. Like I said, it happens every 30-45 seconds and it is very consistent - it does not get better or worse with better or worse alignment.

Alignment (I'm doing polar) really hasn't been an issue (yet) - last night, for example, the image would move down through the field of view over about half an hour. That's an alignment issue obviously, but since I can't go over 30 seconds because of the oscillation, it hasn't hurt me. I have had better alignment nights, where the image would stay roughly centered for a long time, except oscillating back and forth.

My tracking is not yet good enough that I've had to deal with periodic errors. A lot of the other things you talked about are beyond my basic problem: getting rid of this oscillation so I can at least get ~2 min exposures.

I have worked out a similar system to what you describe for dealing with image shift when focusing - essentially, I always focus clockwise.

Attached Thumbnails

 

turbo

Your troubleshooting is accurate. This has nothing to do with alignment, it has to do with a flaw in your RA drive train. The frequency with which this occurs is very high - perhaps too high to attribute to a faulty RA gear, but we've got to look at that first. What is the model and vintage of your scope? Is there a drawing of the RA gear layout that I can access on-line or is there one in your owner's manual that you can email me? Depending on the gear ratio and the fineness of the hobbing, it's possible that you have a burr on the smaller gear that is causing this problem, but still, a 30 second period seems really short.

Please also tell me if your drive is AC or DC driven and whether the drive incorporates a transformer or power inverter to deliver the final juice to the drive motor. This should be in your owner's manual (I hope!).

It's good that you have established a focus procedure that gives repeatable results. Little things like this can seem insignificant, but they are critical to successful astrophotography. If you intend to step up to photography of faint objects, you will encounter much longer exposure times and these "little things" will become big pretty quickly.

russ_watters

Ok, so I have my scope on my coffee table, pretending to align itself. After its finished and tracking, I'll open up the drive and have a look (something I really should have done before. I'll post some pics too....

russ_watters

Attached is a photo of my RA drive. Its an ETX-105. The only visible problem is too much grease, but that's not a fatal issue. There are no chipped teeth, burrs, or anything else visible that could cause the problem.

I watched run it for several minutes, then turned the scope off and moved it by hand. Moving it by hand, everything appears smooth. When electronically driven, every now and then, for no reason I can see, it starts oscillating back and forth for about a second, then resumes moving (and corrects itself). It does not happen at regular intervals - sometimes it happens 5 times in 10 seconds, sometimes the drive runs smooth for minutes at a time. Seems to me like it could be an electronic issue.

Do you know much about the new Autostar feature, "[drive] percent"? It corrects for backlash and "looseness" (the gears have to move a little before they start moving the scope) in the drive when manually slewing. I've gotten good results with it fixing issues like "creep after beep" and slow response times, but could that have anything to do with the tracking rate? Perhaps I need to play with those values some more....

I think I'll call Meade tech support to see what they have to say.

Attached Thumbnails

 

turbo

Since you have looked at the drive train while it was operating, did you notice if any of the gears have a period of 30 seconds or so (or any period that could divide evenly into the minimum period of the oscillations)? There could be a very tiny piece of plastic or nylon floating around in all that grease causing some binding periodically. BTW, that IS quite a bit of grease in there and I would be a bit surprised if the scope did not give you drive troubles on cold nights.

russ_watters

I've cleaned off some of the more critical surfaces (a greased clutch plate? c'mon ), but I guess I'll clean out the whole ra drive gear assembly.

turbo

That's probably a good idea. On colder nights, you could easily get ropes of grease forming (like taffy) and feeding into one or more parts of the drive train, and causing periodic binding. You might want to check with Meade before trying this, but in cold weather situations, that entire train would probably be better lubricated with a light coating of silicone. It would give less loading (requiring fewer corrective guiding measures) on the RA drive, and would make your scope's drive last longer. If you ever observe in a COLD environment, and your RA drive has to pump cold stiff grease, you can bet that those little nylon gears will get sloppy PDQ. If the RA drive is being stressed, the scope will soon be useful for little more than bird-watching and casual sky-gazing.

dekoi

Could anyone suggest good equipment for astrophotography?

What is the most cost-effective digital camera and (digital camera compatible) telescope?

dekoi

My hope for a reply is slowly diminishing.

Another question: What will a decent 4-6" aperature refractor/reflector telescope allow me to see? What viewing distance is allowed (considering a little city light and smog)?

russ_watters

Sorry...

I have an ETX-105 (4 inch) and I like it. The tracking is a little sketchy as you can see from my previous posts, but as a beginner-intermediate scope with real go-to capability, its pretty good.

With the naked eye, a scope of this size will allow you to see planets in pretty good detail with the naked eye and the brighter nebulae and galaxies. Attached is an unprocessed photo of Jupiter and its comparable (though a little higher contrast) to what you can see through the eyepiece. The processed pics are a good twice the detail and you can get pictures like that with a $20 webcam. For more than just faint-fuzzy pics of galaxies or nebulae, you need a camera that'll do long exposures.

Attached Thumbnails