28 replies to this topic

[thornhale]

Hi community,

 

Last weekend, I spent an obsessive amount of time trying to make it so that the polar scope's axis aligns with that of the mount. Then I tried to do my best centering each alignment star into the center of my FOV. As a result, for once, finally, M51 stayed in view for more than 80 minutes.

 

My question is: Is that the result of a good polar alignment? Or star alignment? Or both? Was that good at all? What do really good good polar/star alignment enable in terms of keeping an object within the view of the telescope WITHOUT guide scopes? And how many minutes of exposure were you able to get astrophotography without guiding before the picture got blurry for you? What can I further do to improve upon my polar and star alignment?

[lee14]

Proper polar alignment of an equatorial mount is a requirement for achieving the best results, be it visual, or AP. Depending on the mount, and type of mount, you might achieve good 'star alignment', without perfect polar, and your target would remain in the FOV indefinitely. Long exposure AP would reveal that by field rotation, but it's likely to be unnoticeable visually. There are methods available to compensate for field rotation though. The long exposure days of film photography, where exposures could last many minutes or hours, until the sky fog limit was reached, are pretty much gone. With current technology and software, the best AP results come from stacking many relatively short exposures, so if your polar alignment is good, you might be able to skip guiding altogether.

 

Lee

Edited by lee14, 29 March 2021 - 12:40 PM.

[southerndandy]

Good polar alignment will keep the object centered better, longer.  Obviously the better the alignment and the less the object moves, the longer an exposure you can do.  Focal length plays a part too, though.  A longer focal length will show errors much more readily than a short one will.  Periodic error and seeing conditions can also affect things.   

 

Star alignments don't really play a part in tracking/guiding.  Those are really only for go-to operation.  But, a good star alignment can help when you're chasing faint fuzzies and you can put the object into the FOV each time. 

[alphatripleplus]

And how many minutes of exposure were you able to get astrophotography without guiding before the picture got blurry for you? What can I further do to improve upon my polar and star alignment?

If you are trying to do long exposure AP,  the length of time you can go unguided (even with "perfect" polar alignment) before you notice tracking errors will depend on a number of factors - focal length of scope, periodic error of the mount, flexure in the mount and OTA, etc. It can be as little as a few tens of seconds for lower end mounts with a floppy SCT, to perhaps 10 or 20 minutes for a rigid scope on a  high end mount that has a sophisticated pointing model and absolute encoders.  

[BlueMoon]

 

What can I further do to improve upon my polar and star alignment?

You can check it with the Drift Alignment Method. Drift alignment has been around for a long, long time and it's still one of the best techniques for getting precise polar alignment. It takes a bit of effort and practice but it's a worthwhile skill to have in your AP toolbox.

 

There are a number of good write-ups on the 'net. Here's a good article to get you started: https://explorescien...he-drift-method

[AhBok]

For my EQ6R Pro mount, I consider 5-10 arcmin to be a good alignment for visual use. For imaging, I strive for under one arcmin polar alignment and rely on guiding for the rest. 5-10 arcmin is easily obtained using a polar alignment scope. Less than one arcmin requires more accurate methods such as SharpCap, Polemaster, etc., or the old drift method which most consider too time consuming for simple visual observing.

[alphatripleplus]

One thing to keep in mind is that PA software tools, such as SharpCap, make it very fast (compared to drift alignment) to get accurate polar alignment within a couple of arcminutes. I usually spend just a couple of minutes using SharpCap for this purpose, and that includes a re-check.

[Tiago Ferreira]

I do drift alignment but i am very curious about sharpcap PA. I've tried a few days ago but i couldn't pass the 2nd part although it was a bad seeing night i couldn't figure if was that or simply the kind of set up i have in which i manually moved the 90º east. Will try again though.

[AhBok]

SharpCap is worth the effort to learn. I literally spend 2-3 minutes on average to get a <1 arcmin PA.

[alphatripleplus]

I went from using one of the quicker PA tools in PHD2 -  the polar drift align tool (not the standard drift align)  - to using SharpCap and it is faster and more accurate. The standard drift align took in PHD2 is still the gold standard, but it takes a lot longer than SharpCap to get comparable accuracy.

[teashea]

It depends if you are using the telescope for visual or AP.  For visual, that would probably be ok.

[Stelios]

Hi community,

 

Last weekend, I spent an obsessive amount of time trying to make it so that the polar scope's axis aligns with that of the mount. Then I tried to do my best centering each alignment star into the center of my FOV. As a result, for once, finally, M51 stayed in view for more than 80 minutes.

 

My question is: Is that the result of a good polar alignment? Or star alignment? Or both? Was that good at all? What do really good good polar/star alignment enable in terms of keeping an object within the view of the telescope WITHOUT guide scopes? And how many minutes of exposure were you able to get astrophotography without guiding before the picture got blurry for you? What can I further do to improve upon my polar and star alignment?

You *always* do the best you can--but devoting excessive time to it is counter-productive.

 

As others stated, using Sharpcap Pro you can get PA to under 1 arcmin in less than 2 minutes. Really. You can try for better than that, but 1 arcmin should be plenty good enough. 

 

Star alignment is *only* needed for GoTo. Nothing else. Most astrophotographers don't bother star aligning--they just plate solve. Star alignment does nothing for keeping a star centered. 

 

"Stayed in the FOV" is nothing special when it comes to astrophotography. It can stay in the field of view nearly forever and have your images be junk (the movement required to ruin your image would be imperceptible to your eye without high power and an illuminated reticle EP). Polar alignment reduces *one* source of drift--in the DEC axis (reduces, does not eliminate), but the *major* source of drift that guiding seeks to eliminate is the one in the RA axis, due to periodic error--inherent in the gears. Absolute encoder mounts that can overcome that (and often can still benefit from guiding) start around $10K. 

 

In addition to periodic error there are other disturbances, such as wind gusts, stomping feet, etc. Guiding helps minimize the effect of most of these. 

 

The best thing you can do is to accept that you will need to guide. With good polar alignment and guiding you can image for many minutes and get tight, round stars. Without guiding it will be much less, and it will be *variable*. Periodic error goes up and down but with plateaus, not like a sine wave. So when it is moving in one or the other direction, you will get bad stars, but at times (when it flattens) you will get decent ones (assuming relatively short exposures under 5'). This is why some people say "I got my [insert inexpensive mount here] to do 3' unguided. Sure they did--every once in a while. The subs lost to trailing they stay mum about. 

[thornhale]

In addition to periodic error there are other disturbances, such as wind gusts, stomping feet, etc. Guiding helps minimize the effect of most of these. 

 

The best thing you can do is to accept that you will need to guide. With good polar alignment and guiding you can image for many minutes and get tight, round stars. Without guiding it will be much less, and it will be *variable*. Periodic error goes up and down but with plateaus, not like a sine wave. So when it is moving in one or the other direction, you will get bad stars, but at times (when it flattens) you will get decent ones (assuming relatively short exposures under 5'). This is why some people say "I got my [insert inexpensive mount here] to do 3' unguided. Sure they did--every once in a while. The subs lost to trailing they stay mum about. 

 

 

 

That's what I was wondering about:

 

How much exposure time can I expect to get for a 150mm F.5 telescope on a Orion Sirious AZEQGT in EQ mode without guiding when my polar alignment is good? I am asking because guiding implies the purchase of another scope, and then hooking up a laptop. to it with software - ak spending more money. I wonder if I should first learn the basics better before jumping to that next step?

Edited by thornhale, 30 March 2021 - 03:01 PM.

[BlueMoon]

 

I wonder if I should first learn the basics better before jumping to that next step?

I'm an "old skool" astronomy guy so I'd say yes, learn the basics. Learning some of the "tried and true" techniques that have been around for years will teach you things no software solution ever will. Learn the "why" of problems and how to deal with them BEFORE adding the complexity of guide scopes, leased software and laptops. Get to the point where you have good and consistent results with what you have before moving on.

 

My advice, take some time and just use what you have for now. Learn what it can and cannot do mechanically. Don't worry about how much exposure time you can get right now. Use it and find out. Then, perhaps, you may wish to look to "tuning up" your hardware first and see if you can improve it's performance before throwing $$$ money at a solution.

 

Anecdote: I'm using a 14yr CG-5 with just an RA drive. It doesn't get much more basic than that. I've tuned up the CG-5 so that it's smooth and silky in movement and adjusted the worm drives to minimize backlash. How much exposure time am I getting? Right now, 30 sec subs. Perfect subs. I'll methodically increase the exposure time until I start to see periodic error creeping in. At that point I'll know the accuracy limit of my mount and then decide what path I want to take. Frankly, I like taking shorter subs and stacking rather than long exposures so I may not do anything.

 

Clear skies and be well.

[Stelios]

That's what I was wondering about:

 

How much exposure time can I expect to get for a 150mm F.5 telescope on a Orion Sirious AZEQGT in EQ mode without guiding when my polar alignment is good? I am asking because guiding implies the purchase of another scope, and then hooking up a laptop. to it with software - ak spending more money. I wonder if I should first learn the basics better before jumping to that next step?

 

150mm F/5 (reflector I imagine). I would expect well under 1 minute, and you will probably lose frames anyway--and your "good" frames will be only good-ish.

 

If you have a laptop (it takes a very cheap one) then "hooking it up" costs nothing, and will save you money in batteries and storage cards for your camera as the laptop will do both cheaper and better. 

 

The cost of a guidescope + guide camera is $80 (Orion 50mm guidescope) + $149 (ASI 120MM-mini). They even provide the USB cable. 

 

Guiding *IS* the basics. Time spent avoiding it is, IMO, time wasted taking inferior images. 

[BlueMoon]

 

Guiding *IS* the basics. Time spent avoiding it is, IMO, time wasted taking inferior images.

Sorry, I couldn't disagree more with this. Perhaps its because I come from a time when we were shooting in 35mm film and one *had* to learn why images were poor or spend a lot of money on film and processing. Time is what experience is built on. My expectation is that folks would actually learn from the mistakes that created those "inferior images" and improve their techniques and skill set to avoid having more of them in the future.

 

Clear skies.

[Stelios]

Sorry, I couldn't disagree more with this. Perhaps its because I come from a time when we were shooting in 35mm film and one *had* to learn why images were poor or spend a lot of money on film and processing. Time is what experience is built on. My expectation is that folks would actually learn from the mistakes that created those "inferior images" and improve their techniques and skill set to avoid having more of them in the future.

 

Clear skies.

And I couldn't disagree more with your disagreement (about guiding, not about learning from mistakes).

 

There are many other components to good imaging: focus, proper (sub) exposure, framing, total integration time, how to shoot calibration frames etc., and a boatload of things to learn about processing, but *NONE* of those are impacted negatively by guiding. You will still have a lot to learn from your mistakes, but your mistakes will look better with guiding and you will be able to shoot longer frames which are usually optimal. 30" shots are very rarely optimal, even if they all are perfect. 

 

Guiding (with PhD2, truly a "Push Here Dummy" thing) is something that can easily be learned in part of an evening. You will never want to unlearn it. 

[BlueMoon]

 

Guiding (with PhD2, truly a "Push Here Dummy" thing) is something that can easily be learned in part of an evening. You will never want to unlearn it.

And when it doesn't work, what then? The 'Push Here Dummy" part sort of fails it seems and that is more the point I wanted to get across. When the technology fails, one spends more time troubleshooting their gear than falling back to basic AP skills and actually getting some shots in, inferior or not.

 

Clear skies.

[moonrider]

Guiding is definitely a necessity unless you are doing sub60sec imaging or you have the aforementioned 10k mount. To not use guiding would be like walking in pouring rain 10miles to work , leaving your perfectly maintained car at home because you didn't want to get it wet. Sure you could walk(not guide) but why? 

[Rollo]

Hi community,

 

Last weekend, I spent an obsessive amount of time trying to make it so that the polar scope's axis aligns with that of the mount. Then I tried to do my best centering each alignment star into the center of my FOV. As a result, for once, finally, M51 stayed in view for more than 80 minutes.

 

My question is: Is that the result of a good polar alignment? Or star alignment? Or both? Was that good at all? What do really good good polar/star alignment enable in terms of keeping an object within the view of the telescope WITHOUT guide scopes? And how many minutes of exposure were you able to get astrophotography without guiding before the picture got blurry for you? What can I further do to improve upon my polar and star alignment?

The best way I know of to get a precise and permanent polar alignment is to build a observatory and put the mount on a pier.   Then it stays aligned.   To set up each time in the field and try to get a precise polar alignment is not easy to do,,, IMO.    You might consider shorter exposures,, like, less than 2 minutes and just keep stacking them.   

[BlueMoon]

 

To set up each time in the field and try to get a precise polar alignment is not easy to do,,, IMO.    You might consider shorter exposures,, like, less than 2 minutes and just keep stacking them.

+1 Another reason, at least to me, to do short exposures and stack them. And, easier to correct misalignment errors as well.

 

 

To not use guiding would be like walking in pouring rain 10miles to work , leaving your perfectly maintained car at home because you didn't want to get it wet. Sure you could walk(not guide) but why?

Interesting analogy. But first you have to learn to drive the car ...

 

Clear skies.

[AhBok]

And when it doesn't work, what then? The 'Push Here Dummy" part sort of fails it seems and that is more the point I wanted to get across. When the technology fails, one spends more time troubleshooting their gear than falling back to basic AP skills and actually getting some shots in, inferior or not.

 

Clear skies.

This seems to be a good illustration of how opinions regarding basic/essential skills change with time. I tried imaging with film 30 years ago when the basics were a driven mount and an OTA capable of focusing an image on a film plane. You could get an image, but for me it was pretty lousy (are stars supposed to be square, Lol? I found essential skills to be drift alignment and manual guiding. Nice to have skills included photo development and then scanning individual photos and stacking them. Some guys succeeded well at this, but most amateurs I knew found the results to not be worth the effort.

 

Today, many of us would include computerized polar alignment, platesolving and auto guiding to be basic/essential skills for imaging. Add to this post processing skills which many consider to be as important nas the other skills combined. I rarely have technology failure, but have the technical skills from using technology to quickly troubleshoot problems. If I did have a serious technical issue, I would never consider manual drift alignment, manual guiding or forgoing guiding altogether just to get some shots in. I could take very short exposures and stack them, but I would just have an image that I knew would be sub par. The answer to technical problems for me is to learn how to mitigate or solve them.

My last thought is this: I’ve ground mirrors, made my own eyepieces and built a driven EQ mount. I learned a lot that helped me with visual astronomy in the 70’s and 80’s. However, there is no practical carryover of that knowledge for the imaging I have done in the past decade. Times change and the basics change with it, IME. Of course others’ mileage . . .

[thornhale]

And I couldn't disagree more with your disagreement (about guiding, not about learning from mistakes).

 

There are many other components to good imaging: focus, proper (sub) exposure, framing, total integration time, how to shoot calibration frames etc., and a boatload of things to learn about processing, but *NONE* of those are impacted negatively by guiding. You will still have a lot to learn from your mistakes, but your mistakes will look better with guiding and you will be able to shoot longer frames which are usually optimal. 30" shots are very rarely optimal, even if they all are perfect. 

 

Guiding (with PhD2, truly a "Push Here Dummy" thing) is something that can easily be learned in part of an evening. You will never want to unlearn it. 

Guiding is definitely a necessity unless you are doing sub60sec imaging or you have the aforementioned 10k mount. To not use guiding would be like walking in pouring rain 10miles to work , leaving your perfectly maintained car at home because you didn't want to get it wet. Sure you could walk(not guide) but why? 

When I first looked (https://www.telescop...ord=guide scope), I thought that $499 is quite an expensive upgrade. But even if your suggested assembly will be cheaper (~$229). It took me 3 years to save together enough money for just the tripod (an Orion Sirius AZEQGT mount). One might say that this is all a matter of priorities, and it is: for me, I want to make sure that I save money for retirement and have money for my kids college education and cover the basics....and only then I can splurge. This will take me at least 8 months to save which is why I was wondering what I can do in the meantime to improve.

 

I was originally encouraged by astrobiscuit that one could do astrophotography on the cheap. His Jupyter for $100 (https://www.youtube....h?v=pYsgyL7I8RI) or astrophotography $600 vs $6000 video (https://www.youtube.com/watch?v=JRoFUj0cNt8) encouraged me to dive into this topic. He seemed to compensate money with skill. Am I wrong? This is the reason why I was asking what I can do in terms of technique improvement if I do not have a guide scope (and it will take me 8 months to save for this).

 

 

The best way I know of to get a precise and permanent polar alignment is to build a observatory and put the mount on a pier.   Then it stays aligned.   To set up each time in the field and try to get a precise polar alignment is not easy to do,,, IMO.    You might consider shorter exposures,, like, less than 2 minutes and just keep stacking them.   

Wow, that is indeed a cool idea! But I live in a red-white zone. My house  backyard is at the bottom of a steep hill, and the house is on the other side. Because of this, I only have access to things that are high in the sky facing the north side. The front of the house is facing the streets with lots of street lights. I don't know if it is worth building an observatory here - let alone the cost for doing so (see above....it will take me 8 months just to scrape together $200ish bugs).

 

Therefore, when I purchased a 6" F5 Newtonian with the tripod/mount mentioned above it was so that I could move the telescope/tripod/mount to a darker site on weekends when I actually have time.

[SonnyE]

Well, consider your Polar Alignment scope a very crude first step to aligning your MOUNT to the North Celestial Pole. Which incidentally, does not exist.

I nearly immediately gave up on my first Polar Scope as being worthless to my efforts. Because it was.

 

Over the last 6 years, I've refined and tried to perfect my Polar Alignment, and guiding.

Sharpcap is as perfect a program as I have found, because it Polar Aligns your entire mount using your optics.

So the actual device you are using, down to the Earth gets fine aligned to the North Celestial Pole.

It is a mechanical alignment that brings your mount and telescope as close to Zero as the atmosphere allows.

Personally, I have fun trying to get a zero error with it. Which is impossible, but fun to try.

 

Then I move into building my evenings model (Alignment). Which I do 10 or more stars for, just because I can.

After that (which I finally got a time for) the half hour it takes results in bullseye slews from Stellarium.

So my imaging gets underway immediately.

 

I don't consider a good Polar Alignment. I consider my results to measure success.

(For poopy stuff, there is the delete key.   )

 

You can get a free version, and a free trial, of Sharp Cap if you would like to play with it.

For me, it's well worth it. I just renewed, $13.86, I think it was, for another year, but got 14 months as a bonus.

 

It gives the best results I can recommend.

[thornhale]

Well, consider your Polar Alignment scope a very crude first step to aligning your MOUNT to the North Celestial Pole. Which incidentally, does not exist.

I nearly immediately gave up on my first Polar Scope as being worthless to my efforts. Because it was.

 

Over the last 6 years, I've refined and tried to perfect my Polar Alignment, and guiding.

Sharpcap is as perfect a program as I have found, because it Polar Aligns your entire mount using your optics.

So the actual device you are using, down to the Earth gets fine aligned to the North Celestial Pole.

It is a mechanical alignment that brings your mount and telescope as close to Zero as the atmosphere allows.

Personally, I have fun trying to get a zero error with it. Which is impossible, but fun to try.

 

Then I move into building my evenings model (Alignment). Which I do 10 or more stars for, just because I can.

After that (which I finally got a time for) the half hour it takes results in bullseye slews from Stellarium.

So my imaging gets underway immediately.

 

I don't consider a good Polar Alignment. I consider my results to measure success.

(For poopy stuff, there is the delete key.   )

 

You can get a free version, and a free trial, of Sharp Cap if you would like to play with it.

For me, it's well worth it. I just renewed, $13.86, I think it was, for another year, but got 14 months as a bonus.

 

It gives the best results I can recommend.

Do you need a guide scope, camera setup for this?