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Is telescope balance THAT important?

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#1 Professor2112

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Posted 23 May 2020 - 05:48 PM

So about 3 weeks ago, I bought my first telescope (CPC 1100, regular, not the HD) after a couple years of research and saving. Originally I was planning on visual use only, but along with the scope I bought the adapters for attaching my canon 60D unmodded to dabble and see what I could get. Turns out I am now addicted to ap as the first shots I got were pretty good, to me anyway! So now I really wanna go all in, however I’m not rich so I don’t have the funds to go “all in” in one go. Plus I imagine it’s better to hone skill rather than have all this nice equipment you don’t know how to use! Now, with all that said my current equipment is as follows..

 

 CPC 1100 telescope

 Stock Canon 60D DSLR ( Canon 5D classic should be arriving sometime next week, so let’s go with that since it’ll be my primary AP camera once it arrives)

 

Equipment soon to be acquired..

 

Celestron f/6.3 focal reducer/corrector

Celestron HD pro wedge

 

Equipment I’ll acquire as soon as budget allows

 

Guide scope/camera or OAG (leaning towards OAG with the research I’ve done on long focal length SCTs)

 

Now for my actual question. Earlier this week we’ve been fortunate enough in New England to have a string of clear nights due to high pressure over the area… My first photo shoot on Monday night I tried taking 50 or so 30 second exposures at iso 1250 of the ring nebula and sombrero galaxy. They looked really good in the camera view finder, when I got home, I had spaghetti-O stars. Dang, I was out of foscus the whole shoot! Luckily the following night was also clear and dry with little to no wind so I used my cameras 10 times digital zoom and made sure I got the stars down to a nice small point.. collimation looks pretty dead on also. Nice. Time to shoot. Did the same thing, same iso, all 30 second long exposures. When I got Home to stack in DSS it turns out my picture quality wasn’t quite good enough for the program to recognize and use the stars.  I got the “can only stack one frame” deal. So, figuring the tracking wasn’t able to keep up with 30 seconds, I tried two nights later 15 second exposures at iso 1650. This is where I was able to get the shots you see posted of the Hercules star cluster and the ring planetary nebula... I stacked 5 15s exposures for Hercules, 7 for the ring nebula. Also added darks, bias, and flats. I think they came out pretty good for a first attempt, but I hear even with out a wedge I should be able to get up to a minute exposure time before field rotation is obvious, so the fact I could only go 15 seconds makes me wonder.. is the DSLR on the back of the scope throwing off my balance that much where it’s effecting my tracking making anything over 15-20 seconds undoable? Or am I just missing something? Thanks in advance for any feedback and/or advice!  Clear skys everyone!!

 

oh, and the picture of the sombrero galaxy I threw in there was just a single three minute exposure that I touched up in Lightroom that I thought came out pretty good considering...

 

 

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#2 xiando

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Posted 23 May 2020 - 06:03 PM

sorry i have no idea which thread I was responding to now. please ignore my post. weird...


Edited by xiando, 23 May 2020 - 06:15 PM.


#3 WadeH237

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Posted 23 May 2020 - 06:10 PM

...but I hear even with out a wedge I should be able to get up to a minute exposure time before field rotation is obvious, so the fact I could only go 15 seconds makes me wonder.. is the DSLR on the back of the scope throwing off my balance that much where it’s effecting my tracking making anything over 15-20 seconds undoable?

Before I answer the questions above, I want to say that I think that you've done a great job with these images!  Starting out with an 11" SCT - and on an alt-az mount, no less - is definitely diving into the deep end of astrophotography.

 

So here's the deal with the question above.  There is no single answer to how long you can expose a single sub on an alt-az mount.  Part of the answer has to do with image scale.  That is, how much sky is covered by a single pixel on my sensor.  For a given camera, a shorter focal length will cover more area of sky with a single pixel.  As such, it takes more tracking error for a pixel to "see" the error than it does for the same camera with a longer focal length.  Your C11 has a really, really long focal length, so it is going to show errors quite well (not a good thing).

 

The second factor is where in the sky you are pointing.  If you are pointing at the celestial pole, for example, your mount is going to be moving less physically, than if it were pointing at the celestial equator.  Another factor is your latitude.  If, for example, you are set up at the north pole, your alt-az mount would coincidentally also be an equatorial mount.  If you are set up at the (Earth's) equator, you will see the largest errors.

 

The acid test of how long you can go with your alt-az mount is just to give it a try.  In your case, it sounds like 15 seconds is about how long you can go.  If you mount your camera piggy back on the C11 and image through a short focal length lens, you will be able to go longer - but probably not more than a minute or two at the most.

 

Edit:  Oh, and regarding balance, your DSLR is not heavy enough to adversely affect the balance of a C11.  Keep in mind that the camera is just a few inches behind the mirror, which is where most of the weight is - which means that the mirror end of the scope is closer to the balance point.  If you were doing Hyperstar, with the DSLR mounted on the front of the scope, it would have a bigger affect.  But still, a C11 is a big scope and a DSLR is not very heavy by comparison.

 

On second edit:  Oh, and by the way, welcome to Cloudy Nights, and I like your user name.  I miss Neil.


Edited by WadeH237, 23 May 2020 - 06:14 PM.

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#4 Professor2112

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Posted 23 May 2020 - 07:21 PM

Before I answer the questions above, I want to say that I think that you've done a great job with these images!  Starting out with an 11" SCT - and on an alt-az mount, no less - is definitely diving into the deep end of astrophotography.

 

So here's the deal with the question above.  There is no single answer to how long you can expose a single sub on an alt-az mount.  Part of the answer has to do with image scale.  That is, how much sky is covered by a single pixel on my sensor.  For a given camera, a shorter focal length will cover more area of sky with a single pixel.  As such, it takes more tracking error for a pixel to "see" the error than it does for the same camera with a longer focal length.  Your C11 has a really, really long focal length, so it is going to show errors quite well (not a good thing).

 

The second factor is where in the sky you are pointing.  If you are pointing at the celestial pole, for example, your mount is going to be moving less physically, than if it were pointing at the celestial equator.  Another factor is your latitude.  If, for example, you are set up at the north pole, your alt-az mount would coincidentally also be an equatorial mount.  If you are set up at the (Earth's) equator, you will see the largest errors.

 

The acid test of how long you can go with your alt-az mount is just to give it a try.  In your case, it sounds like 15 seconds is about how long you can go.  If you mount your camera piggy back on the C11 and image through a short focal length lens, you will be able to go longer - but probably not more than a minute or two at the most.

 

Edit:  Oh, and regarding balance, your DSLR is not heavy enough to adversely affect the balance of a C11.  Keep in mind that the camera is just a few inches behind the mirror, which is where most of the weight is - which means that the mirror end of the scope is closer to the balance point.  If you were doing Hyperstar, with the DSLR mounted on the front of the scope, it would have a bigger affect.  But still, a C11 is a big scope and a DSLR is not very heavy by comparison.

 

On second edit:  Oh, and by the way, welcome to Cloudy Nights, and I like your user name.  I miss Neil.

First off, I’d like to say I am very pleased that someone on here got my username reference so quickly! Kudos! I also miss Neil!!

 

Second, thanks for the compliments on my images! I’d estimate around 20 hrs or so went into those! I’m just glad I actually have results to show that I can be happy with! But yes, the more I read on AP, the more I realized an almost 3m focal length is quite a beast to tame, so I’m trying to have as much patience and learn as much as I can and take things slow. I’m glad to hear the DSLR isn’t terribly effecting the balance. I’ll probably get that weight kit from starzona for the Cpc 1100 down the road though, especially if I plan to add a focal reducer and heavier camera plus OAG/guidescope.  I did notice that the ring nebula and Hercules cluster tended to come out more crisp than the sombrero galaxy as the sombrero galaxy is much further from Polaris than the other two. Great info. Thanks for the input! I’ll definitely keep those things in mind. Hopefully I’ll be able to order that wedge soon and go a bit longer as 15 seconds just doesn’t seem quite long enough for the fainter objects. 
 

edit: I shot those pics from a location on top of a mountain near North Adams, MA latitude 42.7009N to be exact. 


Edited by Professor2112, 23 May 2020 - 07:24 PM.


#5 xiando

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Posted 23 May 2020 - 09:00 PM

fwiw, personally speaking, I've found that the max stable length of an unguided sub on my mount is dictated by the precision with which I've polar aligned the mount. And for multiples, (a series of lights at that sampling rate) the polar alignment needs to remain precise over the imaging session (no sag on a leg from soft ground)

 

Does the CP 1100 have a polar scope? (I really have no idea) 

 

PS> I've gotten as much as 2-minutes (120s exposures), but it's pita to fine tune that much, since unless you get lucky on the initial tune, the longer you work on polar alignment, the more work you have to do, because the target for that alignment  is in continuous motion. ("chasing a moving target")

 

That's what finally made me shift to using PHD guiding.

 

edited for stuff


Edited by xiando, 23 May 2020 - 09:09 PM.

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#6 Professor2112

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Posted 23 May 2020 - 10:33 PM

fwiw, personally speaking, I've found that the max stable length of an unguided sub on my mount is dictated by the precision with which I've polar aligned the mount. And for multiples, (a series of lights at that sampling rate) the polar alignment needs to remain precise over the imaging session (no sag on a leg from soft ground)

 

Does the CP 1100 have a polar scope? (I really have no idea) 

 

PS> I've gotten as much as 2-minutes (120s exposures), but it's pita to fine tune that much, since unless you get lucky on the initial tune, the longer you work on polar alignment, the more work you have to do, because the target for that alignment  is in continuous motion. ("chasing a moving target")

 

That's what finally made me shift to using PHD guiding.

 

edited for stuff

Yeah that makes sense.. I was definitely planning on using some kind of guiding and hear PHD a lot so I’ll probably look into it sometime soon. But no, unfortunately the CPC does not have a polar scope. I’ve done a lot of research on the HD pro wedge and the instructions seem crude. First you’re supposed to do a rough polar align by eyeballing it, some have said a smartphone compass can come in handy for that part. Then after that, use the hand control to do an EQ North align.. just another learning curve I’ll have to deal with! But even if it only increases my stackable lights to a min.. I’d be happy with that hahaha. 
 

Ive just finished an imaging session as a matter of fact. Did 20 second subs of the black eye galaxy(about 40 or so) and 15 second exposures of bodes nebula (around 55 of them, 20 seconds seemed to get some slight blurring) Both at iso 1250. So wish me luck on that! 
 

oh, and I’m not gonna lie, I can’t wait for my 5D to arrive! I do have a question though about that… Since the crop factor on the 60 D is 1.6, wouldn’t that increase the focal length of my telescope by 1.6? If it works like that with camera lenses I assume it would work the same with the telescope being it’s acting as a giant lense. So if my math is right, that’s 2800mm x 1.6 = 4480?


Edited by Professor2112, 23 May 2020 - 10:42 PM.


#7 xiando

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Posted 23 May 2020 - 10:41 PM

Well if you can fill in that "gap" (polar scope)_ I'd recommend it, There are other gizmoes but the polar scope is kinda fundamental (to me anyway) 

 

PHD guiding is a definite plus (there's other software too but it's a popular solution) , but at least in this slowJoes' opinion, solid polar alignment can't be beat, with or without PHD guiding

 

good luck.



#8 Professor2112

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Posted 24 May 2020 - 04:34 PM

Well it turns out I got lucky and based off recommendations from this forum and others, I got the book “Making Every Photon Count” by Steve Richards. In it, there’s a whole chapter on how to align an alt/atz mount on a wedge. Definitely going to come in handy!

 

 In the meantime I shot this last night and processed it best I could being I was in heavy light pollution near downtown Springfield, MA last night with no light pollution filter. M81 - 35 fifteen second subs at iso 1650.  On top of that bringing the photo down to below 500kb took away even more quality. I’m impressed with what you can do with short exposures and stacking.. my original light frames had almost no data, basically the core of the galaxy looked like a bright star with a tiny bit of fuzz around it.  I stacked 35 frames and stretched the final image in Photoshop to reveal these gorgeous spiral arms and detail in the core.. only everything was orange from light pollution, had to correct the colors in Lightroom best I could. how could you NOT become addicted to this hobby?? Aww inspiring...

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