81 replies to this topic

[John Tucker]

Hi All,
I have been looking into autoguiding my LX200 for some time and have spent a lot of time reading both recent and archived discussions of both SCTs in astrophotography and the relative merits of OAG vs guidescope based guiding on these long focal length scopes.  I’ve seen posts describing dramatically different personal experiences and correspondingly different recommendations.  As a chemist, it has often been my experience that the tiny details that no one thinks important enough to keep track of are often very important after all.  So I decided to document my experiences here in the same tedious fashion I do in my lab notebook.

 

I’m working with an 8” Meade LX200 classic on a recently purchased Skywatcher EQ-6 Pro mount.  I’ve never set the periodic error correction up on this mount.  I’m operating tonight with the tripod legs about 70% extended.  The polar alignment was performed using the mount’s polar alignment scope and without the benefit of further fine tuning using software, cameras, or drift alignment.  The guide camera is a NexImage 5 planetary camera and the guide scope is an Orion mini without the optional helical focuser.  It is attached to the OTA via a DSLR piggyback adapter attached near the “big” end of the scope. Guiding is via PhD2 using the “Windows WDM-style Webcam” camera type, the camera gain all the way up, 1 sec exposures, and the 2592 x 1944 (RGB32) camera mode. Pictures are taken with a Canon T5i DSLR under the control of Backyard EOS. 

 

As shown in the picture below, I’m shooting off my balcony in a very urban environment.  So I’m not trying to show nice pictures here but simply look for star roundness.  Historically I’ve usually been limited to about a minute with this setup unguided, though about one in five 3 minute exposures turns out semi-ok.

 

 

I took a series of 3 minute and 5 minute exposures, each about 35 degrees above the South or Eastern horizons.  The 5 minute exposures are shown below after conversion to monochrome and cropping to about 1/4th the original size. the total number of 3 minute exposures (not shown) was about 6 and all looked pretty good.

 

 

 

Also took a single 10 before the clouds rolled in fully.  At high brightness there is a long tail coming off the brightest star only that I believe to be an artifact of the clouds rolling in during this exposure.

 

I'm sure these fall well short of the expectations of real astrophotographers, but I suspect this will be good enough for me.  At least for a while. 

 

best,

JT

Edited by John Tucker, 31 August 2018 - 09:15 AM.

[Stelios]

If you're happy by all means keep at what you're doing and progressing at your own pace, but keep in mind that for guiding your SCT you should seriously consider an OAG. This will also avoid differential flexure issues which are inevitable with a guidescope. Today the cost of an OAG + suitable guidecam is about $427, not much more than a guidescope + guidecam. 

 

Some comments, please ignore them if they're unwanted:

 

1) Are you sure you're in focus? From the first 5-min image it appears you are significantly out of focus, which will tend to make the stars look rounder (the same way that an out of focus star on an SCT looks like a round donut even if it's significantly out of collimation when in focus).

 

2) The better focused stars on the 2nd 5 min exposure do display some coma.

 

One of the things to keep in mind is that good guiding not only avoids trailing and deformed stars (which you've mainly done), but, most importantly, bloated stars (to the extent allowed by seeing).

[John Tucker]

Hi Stelios, 

 

Yes, focus was bad, more so on one than the other. This limits the conclusions that can be drawn from these photos, but still they seem to exclude some of the extreme streaking some have encountered, so I'm happy with that. 

 

I think the coma is intrinsic to the OTA, which is quite old and predates anti coma designs. 

 

The real test will of course involve going somewhere dark and taking real pictures and seeing if I am happy with them, which probably won't happen till next month. But very pleased to have nominally round stars at 5 to 10 min at 2000 mm when 45 sec at 1200 mm has been dodgy hitherto.

[Walleye]

x2 for OAG, it just solves sooooo soooooo much.  I sold my guide scope and camera and got a ZWO OAG and ASI290MM Mini and will never look back.

 

It's also plug and play with the refractor I just bought... same mage train off of my 12" SCT onto the back of the ED127... easy peasy...

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Edited by Walleye, 31 August 2018 - 06:21 PM.

[John Tucker]

Hey John, congrats on getting to decent looking 5 minute exposures at 2000 mm.  The 10 minute exposure doesn't look bad either, crossing my fingers and hoping the streak is indeed just an artifact of cloud movement!

 

The idea of providing detailed descriptions of exactly what you did and what your results look like is an interesting one. Perhaps it will help resolve some of the controversy in this area and be helpful to other beginners.

 

Looking forward to hearing more about your progress. Differences of opinion on how best to guide aside, it looks like you've got this to the point where you're ready to do some imaging, and that's a nice milestone!

 

Best Regards,

 

JT

Edited by John Tucker, 31 August 2018 - 08:10 PM.

[John Tucker]

Updating. 

 

Finally got a non-cloudy night here in Oakland, and reproduced the 5 minute and also ran a couple of 10 minute exposures.  Am getting consistently round stars across all of these though the RMS is still considerably higher than that posted by Walleye above.  

 

So far (but with experience that is still very limited) no signs of major streaking caused by mirror flop or flex of the sort that I have read about so often.  If the brightest star in the pic below is maximally expanded, it can be seen to be very very slightly out of round, but I'm really not sure at this point if my primary limitation is guiding and not the bad seeing that is typical of Northern CA near the coast.  Or for that matter, the limited quality of the optics of my 1980s era OTA.

 

Also, operating from my balcony, I am limited to calibrating the guiding on stars that are moderately close to the horizon, and PhD2 was complaining about that with a lot of messages.  So the results here may significantly underestimate those achievable in the open.

 

Obtained a significant reduction in RMS by binning the guide camera (thus increasing the ratio of the diameter of the star relative to FOV and am wondering if I might improve further by increasing the focal length of the guidescope from 150 mm (mini guide scope) to 250 or so.  Still shooting at 2000 mm.  Mostly unprocessed pic taken from downtown Oakland below. 

 

I'm sure lots of veteran astrophotographers can jump in here and tell me how much better their guiding is than mine, but I guess my goal is to keep things simple for now and takes some decent "snapshots".  Going to invest $120 or so in a longer focal length small guide scope to see if I can reduce RMS by half or so, but am reasonably happy with this for now. 

 

Another anticipated advantage of replaceing the mini guide scope is that it mounts to the OTA via a single bolt and I have to re-aim it every time I set up.  Also, the lack of a helical focuser (focusing is by moving the camera in and out of the eyepiece hole) is more of a hassle than I anticipated from comments I had read online. 

 

 

 

Curious as to why I am not having the problems described by some others.  Many of them used larger SCTs, and maybe the weight of the mirror was greater.  Or perhaps these old LX200s used a thicker grease on the focusing mechanism and are more resistant to mirror movement than some newer scopes

 

Edited by John Tucker, 07 September 2018 - 08:23 AM.

[StarmanDan]

You seem to be getting much better results with your setup than I (8" Meade SCT @ f/6.3, Orion Atlas, using converted Orion 9x50 RACI finder and ASI120MM).  Especially considering how you have yours mounted.  I'm using the Meade finder bracket for mine.  

Attached Thumbnails

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[John Tucker]

You seem to be getting much better results with your setup than I (8" Meade SCT @ f/6.3, Orion Atlas, using converted Orion 9x50 RACI finder and ASI120MM).  Especially considering how you have yours mounted.  I'm using the Meade finder bracket for mine.  

That's really interesting.  This issue about guiding, with three fourths of the responses to questions about guiding SCTs being people who adamantly insist that OAG is necessary and you might as well not guide as use a scope, and the other quarter saying "no, works fine for me" is what got me interested in posting about my experience in a detailed way.   It is very reminiscent of my experience as a chemist, trying to reproduce published procedures and learning on the 6th attempt that some little thing I didn't think mattered and that wasn't  mentioned in the publication was the key to everything. 

 

So given the interest and the divergent experience, I thought it would be interesting to get more detailed descriptions up here.  Haven't gotten many comments though. 

 

Some thoughts on our divergent experiences:

 

1) It may just be beginner's luck.  I've only done about a dozen exposures on two nights.  I once got a very nice 5 minute exposure unguided, and I've never come close to reproducing that.  Usually a minute tops unguided.  So I need to reproduce a few more times to see if I'm doing as well as I think I am.

 

2) All my exposures so far are no more than 35 degrees or so above the horizon given that I am on a roofed patio.

 

3) Sorry if this is obvious, but when I choose my camera in PhD2, it brings up a whole list of modes of the sort small number x small number, medium number x medium number, and large number by large number.  I think the small numbers are something like 400 or so and the large numbers 4x or so larger.  I got much better results in small number x small number mode. 

 

4) Since we use the same OTA, it would be interesting to compare their age.  I'm on a trip to Dallas right now but will look at the serial number and try to figure out the age.  I wonder if it could be something as simple as different viscosity grease on the focusing mechanism modifying the mirror flop.

 

5) I got the mini guide scope because someone told me it had worked for them after a larger scope failed.  Maybe someone who is much smarter than me could explain whether there is any possibiilty at all that the positioning of the scope at the front rather than the back of OTA could be a favorable thing. 

 

I will try mounting the mini scope in the finder mount when I get back to California and tell you how that works for me. 

 

6) I don't know much about what the inside of these instruments looks like, but is it possible that the (considerable) weight of the DSLR is stablizing the mirror position?

Edited by John Tucker, 07 September 2018 - 01:24 PM.

[Stelios]

 

2) All my exposures so far are no more than 35 degrees or so above the horizon given that I am on a roofed patio.

 

That's it. You are much more likely to see differential flexure and mirror shift as the scope rises towards (and goes past) the meridian. Even with a refractor I would get it (admittedly the guidescope mount wasn't perfect). 

 

Most people would rather not image that low since you're going through more of the atmosphere. I've also found guiding to be worse when lower than 30 degrees and improve as the scope rises.

[John Tucker]

That's it. You are much more likely to see differential flexure and mirror shift as the scope rises towards (and goes past) the meridian. Even with a refractor I would get it (admittedly the guidescope mount wasn't perfect). 

 

Most people would rather not image that low since you're going through more of the atmosphere. I've also found guiding to be worse when lower than 30 degrees and improve as the scope rises.

That may well be it.  Unfortunately it will be at least 2 weeks before I can test that idea.  

 

I appreciate the input.  As I noted in the original thread, the reason I bought this package was to explore the dissonance between posts like yours and many, many other posts in which people say they have guided very successfully with a system similar to this.  I'm trying to figure out why this works for some people and not others.  And while my own experience is at low altitude only, others have reported more general success. 

 

http://uncle-rods.bl...otta-guide.html

 

https://www.cloudyni...-sct/?p=5211578

 

 https://www.cloudyni...-oag/?p=7635942

 

So, my thought is that assuming the physical constants of the universe don't vary between Austin TX, Clearwater Fla, and Brisbane, Australia, the folks who make it work must be doing something slightly different from the people who have tried it and insist it is a disaster.  

 

For me worthwhile to spend $150 and a couple evenings to see if I can figure it out. 

Edited by John Tucker, 07 September 2018 - 06:03 PM.

[AstroBruce]

Are you sure your camera is set to BULB, and not 1/30 sec.?

 

Bruce

[John Tucker]

Are you sure your camera is set to BULB, and not 1/30 sec.?

 

Bruce

Yes. Took pics in Backyard EOS, did 3 min exposure followed by two 5 min exposures followed by 10 min exposure. Back Yard EOS puts the exposure time in the filename also.aThis one was massively overexposed as I live in a white zone. Pushed the brightness down as far as I could in my JPEG editor before posting.

Edited by John Tucker, 11 September 2018 - 05:34 AM.

[spokeshave]

That's really interesting.  This issue about guiding, with three fourths of the responses to questions about guiding SCTs being people who adamantly insist that OAG is necessary and you might as well not guide as use a scope, and the other quarter saying "no, works fine for me" is what got me interested in posting about my experience in a detailed way.   It is very reminiscent of my experience as a chemist, trying to reproduce published procedures and learning on the 6th attempt that some little thing I didn't think mattered and that wasn't  mentioned in the publication was the key to everything. 

I doubt that you will find some fundamental factor that the 1/4 have discovered that the other 3/4 don't know about. Differential flexure is a real, and well-understood phenomenon. A shift in relative position between the guide camera and imaging camera on most imaging trains that will result in measurable star training will typically be on the order of a a small number of ten-thousandths of an inch. While mirror shift in SCTs is a huge contributing factor, there are other factors as well, such as thermal expansion and contraction, compliance in connections, and simple bending due to gravity. Since a perfectly rigid system does not exist, every guide scope system experiences flexure. That is indisputable. The question then becomes simply one of degree - how much flexure is an imager willing to tolerate. As you mentioned, your experience is limited  - both in number of experiments and in sky location for the experiments. Additionally, you haven't controlled other variables well (your test images are out of focus) so you don't really have enough quality data to draw any firm conclusions.

 

Nonetheless, your images do not show obvious indications of trailing for as long as 10 minutes. That does tell us something. If your imaging intent is to continue imaging in one direction only and below 35 degrees, you will probably have few frames rejected due to flexure and won't need an OAG. However, you should also recognize that your imaging paradigm is significantly different from most. I venture to say that the majority of imagers will tend to be imaging the entire sky, with the OTA and mirror being subject to dramatically different orientations over the course of a night's imaging. Those are the people who have concluded - many from direct experience - that an OAG is necessary. If you want to challenge this conclusion, then your next experiment should be to take your gear to a site where the entire sky is visible and then take a full night's worth of images on a single target (including a meridian flip - which tents to cause fairly extensive flexure). I suspect at that point, you will move from the 1/4 cohort to the 3/4 cohort.

 

Tim

[John Tucker]

I doubt that you will find some fundamental factor that the 1/4 have discovered that the other 3/4 don't know about. Differential flexure is a real, and well-understood phenomenon. A shift in relative position between the guide camera and imaging camera on most imaging trains that will result in measurable star training will typically be on the order of a a small number of ten-thousandths of an inch. While mirror shift in SCTs is a huge contributing factor, there are other factors as well, such as thermal expansion and contraction, compliance in connections, and simple bending due to gravity. Since a perfectly rigid system does not exist, every guide scope system experiences flexure. That is indisputable. The question then becomes simply one of degree - how much flexure is an imager willing to tolerate. As you mentioned, your experience is limited  - both in number of experiments and in sky location for the experiments. Additionally, you haven't controlled other variables well (your test images are out of focus) so you don't really have enough quality data to draw any firm conclusions.

 

Nonetheless, your images do not show obvious indications of trailing for as long as 10 minutes. That does tell us something. If your imaging intent is to continue imaging in one direction only and below 35 degrees, you will probably have few frames rejected due to flexure and won't need an OAG. However, you should also recognize that your imaging paradigm is significantly different from most. I venture to say that the majority of imagers will tend to be imaging the entire sky, with the OTA and mirror being subject to dramatically different orientations over the course of a night's imaging. Those are the people who have concluded - many from direct experience - that an OAG is necessary. If you want to challenge this conclusion, then your next experiment should be to take your gear to a site where the entire sky is visible and then take a full night's worth of images on a single target (including a meridian flip - which tents to cause fairly extensive flexure). I suspect at that point, you will move from the 1/4 cohort to the 3/4 cohort.

 

Tim

Well, thanks for the input Tim.  We will certainly have an unambiguous experimental answer in about 3 weeks when I get back to Oakland.  

 

Until then all I can say is that for every 2 or 3 notes like yours, I see one that says exactly the opposite. Being really, really adamant doesn't change that.

 

In either case I will document my results in detail here, so that whatever the outcome, people doing searches on the subject will have detailed data to use in forming their judgment and not just  comments with no detailed description of what was tried.

 

As a chemist I found that details can make or break any experiment. Of course some experiments can't be made to work at all. I'm not convinced that the naysayers have shown as much appreciation for the former as the latter.

Edited by John Tucker, 11 September 2018 - 04:38 PM.

[spokeshave]

Well, I certainly didn't mean to come off as "really, really adamant". I'm just providing a counterpoint. This is a beginner's forum and I think we have a responsibility to steer beginners in the right direction - or at the very least, let them see both sides of an issue.

I think you are overstating the number of people who successfully use a guide scope with an SCT and get good results. People like me are "naysayers" because we (or at least I personally) have tried it and found that flexure was an insurmountable problem. I spent months trying to get my EdgeHD 14 and ST-80 to work well. Even with mirror locks, and extremely rigid attachment for the guide scope and camera, and after spending a lot of time and money to get it to work, I still experienced flexure that ruined images. Not every image every time, but enough to cause a lot of frustration. I bit the bullet and got an OAG and immediately realized that I wasted a lot of time, effort and money trying to eliminate flexure in the guide scope. I, along with a lot of other people, learned this the hard way. It is very difficult to eliminate flexure with an SCT and guide scope. In fact, of the accomplished imagers that I have followed here over the years, I do not know of a single one who uses a guide scope to guide an SCT. That is not to say that it is completely impossible. But the probability of success is far greater with an OAG that with a guide scope. So while you may be getting good results in your limited experimentation, I definitely would not advise beginners that they too could expect good results.

As a physicist, I try to give due consideration to the opinions and experimental results of my colleagues and certainly would not dismiss them as really, really adamant naysayers because my noisy, very limited results do not agree with theirs.

Tim

[billc2016]

 

 

1) Are you sure you're in focus? From the first 5-min image it appears you are significantly out of focus, which will tend to make the stars look rounder (the same way that an out of focus star on an SCT looks like a round donut even if it's significantly out of collimation when in focus).

 

 

Ahhh . that may be a clue that I never knew  .. an issue has developed that I am having a bear of a time tracking down .. perhaps I should look a little closer at some in focus stars instead of believing the out of focus round image . I would do a quick test like that and say no .. its collimnated ok . perhaps not so much . thanks for the clue!

[John Tucker]

So I will say this. I've been extremely pleased with the response of this group when I've had problems and asked for help.  But I genuinely do not understand the current response. 

 

I clearly stated that I had two goals.  

 

1. To resolve discrepant advice that I've seen on this subject. 

 

2. To address my own concern that "that won't work" isn't enough information, and given #1, may be an overgeneralization. 

 

Someone tried putting "a guide scope" on "an SCT" and "it didn't work".  Uh uh.  I want to know was it a 3 lb guide scope on an 11 inch SCT or a 1 lb guidescope on an 8 inch SCT.  How was it attached?  And which brand SCT.  And whether you used a 2 lb DSLR or a little astronomy camera.  How long of an exposure were you attempting? And some pictures please.  Maybe your failure is good enough to meet my criteria for success.  

 

That's how I was taught to make progress on difficult problems.  And that is what has worked for me over a 30 year career that consisted mainly of troubleshooting problems.  

 

 

So what are some of the responses have I received?

• "Oh no, that will never work."
• "You'll just end up agreeing with me"
• "You're wasting your time"

How are these comments helpful in any way?  Gee whiz, my roster has now gone from 25 comments against and 10 in favor to 28 against and 10 in favor.  Is this going to convince me to change my mind? Did anyone listen when I said 3 times that I'm getting conflicting advice?

 

And suggesting that I drop it at this point when I've gotten attractive preliminary results, already spent the required funds, and have only a 2 hour experiment left to do?  Because its 28 instead of 25 to 10 now? 

 

How is this helpful?

 

I think its pretty cool that I got a 10 minute exposure without streaking.  You guys can find all kinds of things to criticize about it I'm sure.  But it vastly extends my capabilities even if it doesn't work for "a full night's worth of images on a single target (including a meridian flip)"  because all I've been able to up to this point is 45 seconds, and that doesn't get you much of anything at all.  And I only spent $75. 

Edited by John Tucker, 11 September 2018 - 07:57 PM.

[pedxing]

If it works for you, fine. No need to endlessly argue the point.

 

I've been there, done that, gone OAG so I guess I'm number 29. As far as I'm concerned, my guidescope was a waste of money and time.

 

I'm not sure what the argument even is at this point. You have had success in a limited application. Bully for you.

[Mike7Mak]

This is my non-adamant, matter of fact voice...

 

It's simple physical reality that the mirror of a SCT moves as the OTA changes orientation with respect to gravity. No amount of added rigidity, to the imaging train or guidescope mounting addresses this issue. The only thing that does is guiding on a star image produced by the moving mirror.

 

Tuning an imaging rig involves a series of plateaus. As each one is reached it feels like a quantum leap has been made...for a while. Like getting a 10 minute exposure free of guide and mount errors. That's great, the next hurdle is getting 3 in a row and the next getting 7 out of 10. All the way up to losing only 1 or 2 frames a night, if that. That progression is a mount/guiding thing that can overshadow the relatively minor issue of differential flexure...for a while.

 

Everyone's idea of what's an acceptable image for the effort/money expended is different. I must have 3 times the number of images in my AstroBin gallery flashing away on a digital picture frame in the living room. Most from a time 'before OAG' and I still get a great sense of satisfaction looking at them, egg shaped stars and all.

 

So if it seems like the OAG crowd is piling on it's because many of us have been where you are and gone down the same road you seem intent on going down. If you're enjoying the trek that's all that matters.

[John Tucker]

 

So if it seems like the OAG crowd is piling on it's because many of us have been where you are and gone down the same road you seem intent on going down. If you're enjoying the trek that's all that matters.

 But respectfully (and I mean that literally and not in the snarky way that phrase is usually used), I'm not going down any roads. 

 

Did anyone hear me say 

 

"OMG, my new Orion Miniscope just came in and so I'm driving to Montana for 2 weeks of astrophotography doing 1 hour exposures"

 

I said that I was doing some experiments and specified that I had gotten several acceptable 3 minute exposures.  I went out a second night and reproduced that and did several 5 minute exposures.  And then I very tentatively tried a 10 minute exposure.  Somebody suggested that it wouldn't work as well if I went further up from the horizon and I said I would try that. 

 

What I'm objecting to here is the nitpicking criticism that what I'm doing is not going to get me to the point where I can achieve someone else's goals.  And the superfluous predictions of failure in experiments that will hardly take more time to do than was spent writing out those predictions of failure. 

 

The kindest remark I got here was apparently unintended.  Someone asked me if my 10 minute exposure had actually been a 1/30th second exposure due to failing to remember to switch the camera setting to Bulb.  

 

Not one of my better experiences here.  But I will come back and post the results of my next round of experiments.  However they turn out. 

Edited by John Tucker, 11 September 2018 - 11:54 PM.

[DavidW]

It is good that you got a good 10 minute exposure, on an EQ6 that means your exposure time included the full cycle of the gear. From memory that is about 6 or 8 minutes. You could have exposed for 30 minutes or 60 minutes if you wanted to. Try to make that exposure repeatable and you are well on your way. That exposure also would have given you some idea of the periodic error for your mount from which you can decide if you want to try refining the PEC. I think your 10 minute exposure looks good.

 

When I was starting my guide scope setup was in the 7-9lb range in both side by side and piggyback configurations of refractors as I had setup balancing and flexure issues, I was also pushing the weight capacity of the EQ6 then. I moved to OAG which simplified equipment setup a lot saving time and solved a few issues I was having. Later, getting the Mach1 mount with the polar scope to figuratively "automate drift alignment" saved a good amount of time and I worried less about the mounts alignment. At this point the physical mechanical setup was mostly handled and I was able to spend much more time on rest of the system. Since then guide scope setups have gotten a lot smaller and you are likely benefitting some from that. I still have that guide scope available for widefield imaging. I was using refractors but have the opinion that this mechanical part of the setup is what makes learning with an SCT seem harder as the longer focal length makes the issues more noticeable, both scope types can have focuser issues, the SCT also has a couple mirrors. The other aspects of the imaging system are largely the same for an SCT as a refractor. Parallax might factor in to your guiding with the longer focal length, I don't know as I haven't really thought about it but it can probably be calculated.

 

When I started learning one of the difficulties I had was learning what all of the necessary steps and required settings were for the system and - when something(s) was not right, not being able to assign a symptom to a requirement, and not knowing the correct way to solve the issue. There were more than a few nights when simple things like incorrect equipment settings, time, and location settings in software gave me issues elsewhere in the system and cost me time. It took a while to get a good understanding of my system and learn what setting dependencies a task had to make diagnosing things easier. When you think about the system you have right now, in how many places are the time and location stored? How many sky location settings are in the system, which one is driving and when - and when do they become out of sync, and then how do you realign them? When starting out this logical part of the system is active and precisely identifying an issue as logical or mechanical can be difficult, sometimes both are contributing factors.

 

With your background I think you have the temperament to enjoy figuring it out and getting it to work. Hope this post helps your thread.

[View2]

I have a basically u used celestrin OAG I'd sell ya

[John Tucker]

It is good that you got a good 10 minute exposure, on an EQ6 that means your exposure time included the full cycle of the gear. From memory that is about 6 or 8 minutes. You could have exposed for 30 minutes or 60 minutes if you wanted to. Try to make that exposure repeatable and you are well on your way. That exposure also would have given you some idea of the periodic error for your mount from which you can decide if you want to try refining the PEC. I think your 10 minute exposure looks good.

 

When I was starting my guide scope setup was in the 7-9lb range in both side by side and piggyback configurations of refractors as I had setup balancing and flexure issues, I was also pushing the weight capacity of the EQ6 then. I moved to OAG which simplified equipment setup a lot saving time and solved a few issues I was having. Later, getting the Mach1 mount with the polar scope to figuratively "automate drift alignment" saved a good amount of time and I worried less about the mounts alignment. At this point the physical mechanical setup was mostly handled and I was able to spend much more time on rest of the system. Since then guide scope setups have gotten a lot smaller and you are likely benefitting some from that. I still have that guide scope available for widefield imaging. I was using refractors but have the opinion that this mechanical part of the setup is what makes learning with an SCT seem harder as the longer focal length makes the issues more noticeable, both scope types can have focuser issues, the SCT also has a couple mirrors. The other aspects of the imaging system are largely the same for an SCT as a refractor. Parallax might factor in to your guiding with the longer focal length, I don't know as I haven't really thought about it but it can probably be calculated.

 

When I started learning one of the difficulties I had was learning what all of the necessary steps and required settings were for the system and - when something(s) was not right, not being able to assign a symptom to a requirement, and not knowing the correct way to solve the issue. There were more than a few nights when simple things like incorrect equipment settings, time, and location settings in software gave me issues elsewhere in the system and cost me time. It took a while to get a good understanding of my system and learn what setting dependencies a task had to make diagnosing things easier. When you think about the system you have right now, in how many places are the time and location stored? How many sky location settings are in the system, which one is driving and when - and when do they become out of sync, and then how do you realign them? When starting out this logical part of the system is active and precisely identifying an issue as logical or mechanical can be difficult, sometimes both are contributing factors.

 

With your background I think you have the temperament to enjoy figuring it out and getting it to work. Hope this post helps your thread.

Thank you!  That was explicit and helpful.   Knowing which OAG and camera you are using would be helpful in the event I need to switch over. 

 

The 10 minutes exposures have been reproduced several times without losing star roundness, though as pointed out by others, the focus was very slightly off on some of them and they were all taken at modest elevations relative to the horizon.  Next test is to see what I can do closer to the zenith. 

Edited by John Tucker, 12 September 2018 - 07:03 AM.

[John Tucker]

I would also like to add here that some of the friction may have been due to poor communication on my part.  

 

I am not a seasoned astronomer hoping to produced publication quality photos at this point.  I have been doing this for about a year, and living in Oakland, that mostly means getting in the car once or twice a month and driving 1-2 hours to someplace where the light pollution is low enough that I can see Polaris.  And coming back when I am still awake enough to drive. Aside from very basic technique practice off my patio, I've probably logged about 50 hours total.  

 

My goal in using a camera is to see details too faint to see through an eyepiece.  I want the stars to be round enough that things don't look obviously distorted.  If they are better than that, its all gravy.  With the caveats that have been discussed already, I seem to be achieving that.  

[John Tucker]

As a physicist, I try to give due consideration to the opinions and experimental results of my colleagues and certainly would not dismiss them as really, really adamant naysayers because my noisy, very limited results do not agree with theirs.
 

 

I guess the problem is that no one here has told me what their experimental results are in sufficient detail for me to evaluate them.  That's what I'm trying to do here.  

 

Agree the results thus far are very limited.  I've been very explicit about that.  Noisy?  I dunno.  Maybe by your standards.  I'm pretty happy with the fact that someone asked me if I was sure my 10 minute exposure was really 10 minutes or if I forgot to set the exposure to "Bulb" and took a 1/30th second exposure instead. Using a setup that everyone keeps telling me can't be made to work. 

 

Focusing is pretty difficult here in N. CA because the seeing is bad.  When I was playing with planetary photography I learned to aim for the setting that put my target in focus 40% of the time and not one of the settings that put it in focus 18% of the time.  Maybe a lot of problems will show up if I go somewhere that has decent seeing, but for now seeing seems to be the limiting factor.

 

For me the most important test going forward is too see how this works further above the horizon.