Celestron C6-SGT

[thehasoe]

So if you think your main interest will be in DSO astrophotography, you may want re-consider your telescope choice for AP before spending more money buying more accessories for your C6 to achieve similar or better results.

As mentioned by other members above, totally agree with meeting up people for face-to-face chat/demonstration is the best way to approach AP.

Will definitely re-consider my telescope. Thanks for your advice

This computerised GOTO mount (and most GOTOs I suppose?) does not perform auto-guiding on its own. Only slewing to objects and then keep tracking it. But it does have an autoguider port for long exposure astrophotography. The more accurately aligned during setup and use, the higher the accuracy. But for serious DSO imaging, requires much more higher accuracy than that if you want pinpoint stars throughout the final image.

Understand now. Will start with Planetary photography first then next step DSO ..
Thank you

[thehasoe]

While I know that everybody recommends a small fast refractor for AP, the OP already has the C6 and the f6.3 reducer. These will work fine: the C6 is 1500mm focal length, and with the reducer is 945mm. Still a bit long for the CG-5 but definitely workable.

The OP will need to autoguide, however - that is a given. Or you can start with your Nikon DSLR. If you have a long lens like the 180mm f2.8 ED, or even the 70-200 f2.8 these can take very decent nebula photos, particularly of the larger nebulae. If you have a tripod collar already for your lens, all you need is a dovetail so that you can bolt the lens to the dovetail, then clamp the dovetail to the CG-5.

You will need a good polar alignment to take unguided photos with your camera lens. Master the All Star Polar Align routine in the CG-5, it will give you a good-enough polar alignment.

Hello, thanks for your advices.
I do not have the lens longer than 85mm as i am a landscape photographer and 16-85 is the longest i have. But i will give it a try by borrowing 70-300 from my friends soon.

Thanks

[cloud_cover]

Hello!
I think you have a decent setup especially when focally reduced. While the CG-5 is taxed when taking a C8 at 2000mm FL, it should be able to handle your lighter and shorter C6.
Don't worry about autoguiding just yet unless you really want to jump into it. For now, master Polar Alignment, which is the first all-important step in taking good photos. No alignment, no photo, even with autoguiding.
After that, you will be able to play with the various exposure times to see what your mount can reasonably do.
While there will always be better equipment, you have a decent setup to learn and do most of the brighter objects such as M42, M35, M6,7, 8 etc and that will keep you buys for a long time
Above all, have fun!

[orly_andico]

actually Kevin at 952mm (C6 with reducer) and a typical DSLR, the image scale will be sub 1" per pixel.

Guiding will be pretty much mandatory given the ~ 40" p-p periodic error of the CG-5.

[cloud_cover]

Hi Orly,
I fully agree there's no way to get pristine long exposure shots without guiding on a CG-5.
On the other hand, I'm also trying to offer advice to the OP about getting started without immediately bumping up the complexity, as guiding will entail guidescopes, guide CCDs and a laptop. While its true the CG-5 has a high PE, that PE occurs over a number of minutes hence a shorter exposure will result in a much smaller PE. While not pristine, the image that results may certainly be very acceptable especially to stoke the enthusiasm of a beginner.
For example, 30s exposures of a bright target such as M42 could well be acceptable, a total exposure of 1hr will bring out most of the nebulosity and during stacking the PE may well cancel itself out although it decreases the detail resolution. Not perfect, but still pretty
To the OP: Sorry for the technical discussion. periodic error is the inaccuracy of a mount as it tracks, assuming that you are perfectly polar aligned. This occurs because of imperfections in the RA axis's gear or worm screw. The result is stars that look like streaks, how much depends on how high the PE is. The only way to eliminate this is auto guiding or installing encoders(not an option on the CG5). However as the tracking error occurs over a period of time (usually a few minutes), you can employ shorter exposures to limit the error in each photo frame and your stacking software will realign each frame for you so that the error appears smaller. We're talking long exposure deep sky photography, of course. PE does not affect planetary imaging

[thehasoe]

Don't worry about autoguiding just yet unless you really want to jump into it. For now, master Polar Alignment, which is the first all-important step in taking good photos. No alignment, no photo, even with autoguiding.

Hi Cloud,
Thanks for your advices. I think i started to understand AP hehe.
Noted and will try to understand more about Polar Alignment now.

actually Kevin at 952mm (C6 with reducer) and a typical DSLR, the image scale will be sub 1" per pixel.
Guiding will be pretty much mandatory given the ~ 40" p-p periodic error of the CG-5.

Agreed! I have observed Saturn yesterday night and amaze by the details that can c6 produces.
But it moved tooooo fast! So i can imaging how much mandatory to have the autoguider and guidescope

For example, 30s exposures of a bright target such as M42 could well be acceptable, a total exposure of 1hr will bring out most of the nebulosity and during stacking the PE may well cancel itself out although it decreases the detail resolution. Not perfect, but still pretty
To the OP: Sorry for the technical discussion. periodic error is the inaccuracy of a mount as it tracks, assuming that you are perfectly polar aligned. This occurs because of imperfections in the RA axis's gear or worm screw. The result is stars that look like streaks, how much depends on how high the PE is. The only way to eliminate this is auto guiding or installing encoders(not an option on the CG5). However as the tracking error occurs over a period of time (usually a few minutes), you can employ shorter exposures to limit the error in each photo frame and your stacking software will realign each frame for you so that the error appears smaller. We're talking long exposure deep sky photography, of course. PE does not affect planetary imaging

There's no need to say sorry. I got knowledge from that T discussion.
Thanks you two.

[cloud_cover]

Agreed! I have observed Saturn yesterday night and amaze by the details that can c6 produces.
But it moved tooooo fast! So i can imaging how much mandatory to have the autoguider and guidescope

I'm glad you enjoyed your view of Saturn
Actually the movement you saw causing Saturn to drift out of your field of view was not Periodic Error. That was "Declination drift" which was caused by polar mis-alignment of your mount. (The mount was actually on, ya?) Periodic error is usually only visible if you have a cross-hair reticle eyepiece as the movement is very small visually. It will appear as a slow oscillation from one side to the other but the center of the oscillation should remain the same so the object won't drift out if the field.
Generally if you're reasonably aligned (i.e. used a compass and pointed your mount North, tripod was leveled), for visual use your normal GOTO alignment should correct for declination drift and the movement of your target in the eyepiece should be minimal.

[thehasoe]

I'm glad you enjoyed your view of Saturn
Actually the movement you saw causing Saturn to drift out of your field of view was not Periodic Error. That was "Declination drift" which was caused by polar mis-alignment of your mount. (The mount was actually on, ya?) Periodic error is usually only visible if you have a cross-hair reticle eyepiece as the movement is very small visually. It will appear as a slow oscillation from one side to the other but the center of the oscillation should remain the same so the object won't drift out if the field.
Generally if you're reasonably aligned (i.e. used a compass and pointed your mount North, tripod was leveled), for visual use your normal GOTO alignment should correct for declination drift and the movement of your target in the eyepiece should be minimal.

As Mariner said, now m started to learn how to swim first.
I was trying to learn how to locate the object using the finder scope and iphone apps then manually adjust the mount that why Saturn is out of field of view very fast.

I don't have autoguider/guide scope yet.
In this case, what u want to say is if i power on the mount and point the scope to the Saturn and polar alignment is correct, then the movement of my target in the eyepiece should be minimal?
It is happen with or without of autoguider? Because what i understand is goto mount only find the objects but not guide along right?

I am really sorry for my another noob question

[Gary]

Hi thehasoe.

I think you are confusing "tracking" with "guiding".

If you align the telescope correctly and relatively accurately, once located, the object (e.g. Saturn) should not move out of the field-of-view (FOV) so quickly. The telescope system should automatically start tracking (not guiding) the object until a new one is being selected. Maybe your alignment is not accurate enough and you also use a high magnification narrow FOV eyepiece which create this effect of Saturn moving quickly out of view. Try a lower power wider fov eyepiece initially to check how good is your alignment and keep improving it until it still stays within the fov as you use higher power and narrower FOV eyepieces.

If you do not have access to a person to guide you face-to-face, take and enjoy your time to read and understand your telescope system by reading and following the manual. Especially the alignment procedures from page 19:
http://www.celestron.com/c3/images/file ... cedsgt.pdf

Congrats on seeing Saturn! Try observing it through a binoviewer in the future.

[cloud_cover]

Ah! So the power was off!
In that case the drift you saw was merely drift... no error or declination anything The reason the object moved is because its of the earth's rotation. what you experienced was what you would see if you used a completely manual mount.

The term "guiding" refers to using a separate CCD and (usually) guidescope to enhance the trackign accuracy of a mount in order to take long exposure pictures. Its unnecessary for visual use.
"Tracking" refers to the mount moving in tandem with the sky, by means of its gears and motors. very different.

GOTO mounts like the CG-5 are able to track objects as the earth rotates around you so you will find it much more enjoyable to power up the mount. Even if you fail to align, as the mount tracks at the sideral rate (the rate at which objects in the sky appear to move), you should experience significantly longer view times before adjusting. The days of GOTO only without tracking are long over

Simple GOTO alignment is easy. Ensure your mount is level and pointed north (use a decent compass or a known landmark). Connect battery and power on. Next, command your mount to slew to your intended target (preferably a star or planet). At this point it will probably point off. Correct using the slewing commands on your handpad until the object is centered in your eyepiece. Now hit whatever command on your handpad tells the mount that you are aligned with your target. You have just done a one-star align and your mount will be significantly more accurate than if you had not powered it on at all! as you continue your viewing session, you can slew to and align each consecutive target to enhance the GOTO accuracy. You needn't do it all at once so instead of thinking of aligning as a task, think of it as a process throughout the night of observation

Autoguiding uses a CCD to detect the tiny errors in the mount tracking and is not needed for visual work. For example, in a 10mm plossl eyepiece (with 50deg apparent field of view), you would have a true field of view of about 1/3 degree (50/150x mag), which is about 20arcmin or 1200arcsec. Now if your PE is 40arcsec over a period of say....6 minutes, you would expect to see your target oscillate a distance of 1/30th of the field of view (40/1200) over 6 minutes, an imperceptibly small amount to the eye. To a CCD though, each pixel represents about 1 arcsec so this movement is obvious and a long exposure picture becomes ugly. Since your eye isn't bolted to the eyepiece (ouch!), it makes no difference when using it visually