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Difficult tracking object with Barlow lens.

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#1 arshadwm

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Posted 05 May 2021 - 11:23 PM

I bought Televue 4X Barlow and used it with my Celestron CPC EdgeHD 1100 Alt Azm Mount with Wedge.

I have noticed that it’s nearly impossible to track the object. In my case it was Saturn which was moving super fast and I tried my best to keep the tracking under control but failed. I used Eq North with sidereal. Polar Alignment was accurate. Both through camera and eye piece it was not possible.

How to tackle this issue.

#2 havasman

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Posted 05 May 2021 - 11:32 PM

That's expected. When you increase the effective focal length by 4x and up the mag, you decrease the field by a similar factor. There's no "free ride"


Edited by havasman, 05 May 2021 - 11:32 PM.

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#3 ButterFly

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Posted 05 May 2021 - 11:33 PM

Solar rate is better than sidereal rate for planets.  Each planet has its own rate, but solar is close enough to all and better than sidereal.  Time and location are critical for planets and alt/az mounts, so check those as well, despite the wedge.


Edited by ButterFly, 05 May 2021 - 11:34 PM.

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#4 ButterFly

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Posted 05 May 2021 - 11:36 PM

That's expected. When you increase the effective focal length by 4x and up the mag, you decrease the field by a similar factor. There's no "free ride"

A 4x barlow on an SCT is insane power!


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#5 gnowellsct

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Posted 05 May 2021 - 11:42 PM

I bought Televue 4X Barlow and used it with my Celestron CPC EdgeHD 1100 Alt Azm Mount with Wedge.

I have noticed that it’s nearly impossible to track the object. In my case it was Saturn which was moving super fast and I tried my best to keep the tracking under control but failed. I used Eq North with sidereal. Polar Alignment was accurate. Both through camera and eye piece it was not possible.

How to tackle this issue.

 

Well the usual thing is that it is very had to get a wedge *really accurately* aligned. 

 

4x Barlow is also of interest.  If we assume in the usual case that a 40mm is your lowest power, then you were tracking at 280x.  The scope should be able to handle this. 

 

If on the other hand you were using a 10 mm eyepiece, you would have been north of 1100x and at that magnification you might be encountering backlash problems (for example).  With backlash you get the object positioned and then before the scope begins tracking the gears have to "catch up".  You see this often on Dobsonian mounts with tracking, it is hard to keep the object centered because it takes awhile for the gears to "catch up."  There is supposed to be a software compensation for this effect in the Dobs...doesn't work that well IME.  I have also seen it in equatorial mounts equipped with servos. 

 

One of the tricks might be looking for the object at lower powers, letting the "drift" happen, then the drift should stop.  Once the drift stops, position the object at center and increase magnification.   There may be backlash settings as well. Check the manual.

 

Another technique is to slow down the speed of the slew for final approach.  At a slower speed it takes less energy for the mass to be stopped and so, less overshoot.

 

There are other things that go wrong.  People sometimes think they are in sidereal but they're not.  Maybe lunar or solar.  

 

More remote possibilities include a defective paddle.  

 

 

Greg N



#6 gnowellsct

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Posted 05 May 2021 - 11:49 PM

I agree with everyone including myself that the 4x barlow indicates very high powers and that this is a major "stress test" on the accuracy of the tracking.  

 

On the other hand my mounts pass the test (G11 with steppers, AP900QMD with steppers).  If you step away for twenty minutes at 800x yes there might be some drift but not so you would get on a group and say this mount is not working.  

 

Whether the CPC 1100 is made to this standard I can't say, don't have one.  I do use SCTs though.

 

I'm not going to say that this is crazy high magnification because it is not uncommon for planetary imagers to use a 4x barlow or stack two 2x barlows.   Of course they don't need super-accurate tracking.  They take a string of 800 frames at 20 frames a second and then reposition and do it again.  Then they take all the frames and stack them.  The software compensates for any drift so long as the image is landing on the chip.

 

People on reddit get good planet images using hand cell phones and hand dobs, they just let the planet drift across, then reposition, collect a bunch of frames and then go process.  It's a little freaky actually, how good some of them are.  So I would like to think a C11 with tracking could do at least as well.

 

Greg N  



#7 gnowellsct

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Posted 05 May 2021 - 11:52 PM

I should mention I practically never mess around at 800x or higher.  But, you know, sometimes.  When the sky is cloudy with some empty spaces one might mess around with un-serious stuff.

I pushed the moon up to 2200x once.

 

Greg N



#8 Padremo

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Posted 06 May 2021 - 03:10 AM

With my Celestron scope at high powers I have to center the object using the up and left arrow keys only, this eliminates the backlash on the drives. This is built into the drives when using goto - the scope will always fine tune centering the object by approaching the same way.
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#9 spereira

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Posted 06 May 2021 - 08:02 AM

Moving to Celestron Computerized Telescopes.

 

smp



#10 KBHornblower

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Posted 06 May 2021 - 09:39 AM

Solar rate is better than sidereal rate for planets.  Each planet has its own rate, but solar is close enough to all and better than sidereal.  Time and location are critical for planets and alt/az mounts, so check those as well, despite the wedge.

My calculations show that Jupiter and Saturn are much closer to sidereal rate throughout their synodic cycles.  Mars around conjunction with the Sun, along with Mercury and Venus around superior conjunction, are closer to solar rate.  In any case the planets will not move fast enough to be a serious problem at sidereal rate.


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#11 KBHornblower

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Posted 06 May 2021 - 09:52 AM

I bought Televue 4X Barlow and used it with my Celestron CPC EdgeHD 1100 Alt Azm Mount with Wedge.

I have noticed that it’s nearly impossible to track the object. In my case it was Saturn which was moving super fast and I tried my best to keep the tracking under control but failed. I used Eq North with sidereal. Polar Alignment was accurate. Both through camera and eye piece it was not possible.

How to tackle this issue.

I have used my old Celestron 8 at over 600x for close double stars, and the simple clock drive tracks without difficulty.  It should be easy for a modern computerized system, especially if accurately polar aligned on the wedge.  This sounds like defective equipment and/or user error.

 

What eyepiece were you using with the 4x Barlow?  Did you try centering Saturn with low magnification before trying the Barlow?



#12 arshadwm

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Posted 06 May 2021 - 10:54 AM

@KB

I even removed Barlow and used televue negler type 12 mm but problem remained same.

#13 KBHornblower

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Posted 06 May 2021 - 01:20 PM

@KB

I even removed Barlow and used televue negler type 12 mm but problem remained same.

That is about 230x, which should not be a problem if the mount is aligned correctly and is in good working order.



#14 Angeles

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Posted 06 May 2021 - 02:55 PM

The goto should work at 230x
Something is wrong with your scope or alignment or tracking
Heck i have gone to 350x on a manual mount without tracking and it worked sure from edge to edge was only 20 sec but i keeped using the knobs and was ok
Maria


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