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Tracking the moon for images at high magnification: Tips?

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#1 MachMike

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Posted 30 September 2020 - 12:57 AM

Hi,

 

I'm thinking about trying to capture some lunar details at higher magnification with DSLR video (or images) . I have questions just from thinking while viewing tonight. Frankly I got myself all turned around overthinking it.

I've taken plenty of cell phone / eyepiece 'images' at low (40mm) magnification with standard tracking without much issue. Tonight I started thinking about some magnified captures, then I started thinking about the difficulties.

 

  •  Egad...the moon moves/drifts fairly fast even with a proper calibration on my GOTO when at an extreme magnification. how to capture magnified images for stacking images?
  • Wedge or No wedge? (will it provide any benefit for this purpose with my particular gear).
  • Lunar Tracking rate in the Celestron menu (its an option I've never used) is this even functional to assist with the drift? is it basically a useless option?
  • Is a  series of stacked videos, or a series of single images better for stacking? Tracking at a high magnification must be quite difficult as the moon still drifts even when I'm doing pure visual.
  • single pass video or multiple pass on same region? (if video is better than images)
  • Should I just ignore the SLR / Barlow option, and attempt to use my cell with an eyepiece / Barlow (quality/benefit/time argument)

 

I'd prefer not to discuss the lack of a solar system imaging camera. I don't have one so....

 

Thanks in advance I'd love to hear any tips!

 

 

My equipment is simple:

CPC1100 Edge HD w/ or without Wedge

Explore Scientific 2x barlow

Telescope Accessories 2" Fujifilm SLR to 2" Barrel adapter

Baader Click Lock Visual Back

 

 

 



#2 sg6

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Posted 30 September 2020 - 03:03 AM

For whatever reason(s) the standard method for lunar images is "Get a video, and stack the good frames". Maybe a bit strange when you take long exposure images of M42 and M42 is twice the size of the moon. So not a size demarkation.

 

Lunar rate? Actually unsure. Years ago I set up a small scope for solar work. Couldn't align it properly - no stars - so North as best I could, Level as best I could and just said Yes to everything. The sun remainind in the field of view for around 2 hours. And it was on Sidereal rate. Ever had the idea they "offer" Sidereal, Solar, Lunar but just leave the rates actually unchanged? Select Lunar if it gives you a nice warm feeling.

 

For Lunar I would not bother with the Barlow. CPC1100 = 2800mm, moon = 0.5 degree, image = 24.5mm. Is that actually too big for the DSLR?

 

With the focal length and the general realistic nature of amateur scopes I would expect some drifting. They are good but still amateur hobby equipment.

 

The CPC1100 is easy to set up, found them very forgiving which doesn't help. People let the scope sort out all their poor setup's. Whatever the start up requirements are do them well and accurately. About level is not good enough, and all the rest. Spend the extra 10 minutes. My comment is all the corrections the scope is determining is a measure of how poor/bad the operator has done their bit.

 

After that go find the moon, focus the scope on the DSLR sensor and collect say around 1000 frames (nice round number other then that no reason) if 30 fps that would be 30 to 40 second capture. Could try 60 seconds so around 1800-2000 frames. Have assumed 30fps as "standard" on DSLR.

 

Then it is the transfer to software, select the "best" frame, stack the best 10% or 200 or whatever that closest match the "best" frame. The processing is for you to play with - I have read assorted recommended wavelet options for Registax. Limit the alignment points.

 

Moon problem is the atmosphere. If the air is turbulent you really do see the image "boil". And the moon (well for me) is generally low. The idea behind a video is rather simple - longer single exposures have too much turbulance so you collect a large number of short frames, and throw all the less good ones away (90% of them). Somewhere in that stream of 2000 frames there should be 100 or so good ones. They are the ones you want/use.

 

I don't think the moon will fit the DSLR sensor, have you a reducer? With the CPC1100 there are few dedicated solar work cameras that would be big enough, so a DSLR is likely the least cost option.



#3 spereira

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Posted 30 September 2020 - 07:28 AM

Moving to Solar System I&P ...

 

smp



#4 Alex McConahay

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Posted 30 September 2020 - 07:29 AM

>>>>>>Egad...the moon moves/drifts fairly fast even with a proper calibration on my GOTO when at an extreme magnification.

The moon should not be moving appreciably during the exposure. Even at high magnification with a properly aligned mount, properly operating, a target on the moon will stay stable enough to grab a short single shot, or record a 30 second video. If your rig is not, it is time to figure out why (balance, polar alignment, slop in gears, wrong tracking rate) and remedy that. 

  

 

>>>>>>>how to capture magnified images for stacking images?

 

Use your magnified LiveView (or not magnified) and record a movie on the DSLR. 

>>>>>>Wedge or No wedge? (will it provide any benefit for this purpose with my particular gear).

 

Not much at the exposure lengths we are talking about with the moon for single shot or video. 

>>>>>>>Lunar Tracking rate in the Celestron menu (its an option I've never used) is this even functional to assist with the drift? is it basically a useless option?

Again at the time of exposure/length of video, it will not enter into the picture. The difference between lunar and sidereal movement does not show up for a while. If you plan to have your scope on the moon for half an hour or so, use the lunar rate. But it won't affect the individual images probably. 

 

>>>>>>>>Is a  series of stacked videos, or a series of single images better for stacking?

 

Use video. 

 

>>>>>>Tracking at a high magnification must be quite difficult as the moon still drifts even when I'm doing pure visual.

 

Same response as your first issue. 

>>>>>>>>single pass video or multiple pass on same region? (if video is better than images)

 

I don't understand this issue. 

 

>>>>>>Should I just ignore the SLR / Barlow option, and attempt to use my cell with an eyepiece / Barlow (quality/benefit/time argument)

 

I'm assuming you mean Digital SLR, and you will get a better pic more easily (once configured) with the DSLR than with the cell phone. 

 

Note that there is a CN forum dedicated to solar system imaging. The people there specialize in the moon and planets. These present different challenges, and use different techniques that the Deep Space pretty picture stuff usually considered in this Forum. You may get better answers there. 

 

Alex

 

 

Alex


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#5 doolsduck

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Posted 01 October 2020 - 01:19 AM

A good dslr like a Nikon D5500/5600 is not very expensive and will give you superior images to a cell phone.  I do a lot of afocal imaging, first with an iPhone SE 1st generation and now a 2nd generation which is quite superior.  Cell phone cameras have terrible light sensitivity and they really suck at DSO, but when light levels are good, like on the Moon and planetary, they do ok.  I feel my new phone can record every bit of detail that seeing allows, seeing is now the limiting feature of the image quality I can produce.  It does help that I use a 14" reflector too, but yours would be superior.  I don't even bother to stack anymore (mainly because my dob is non-tracking), I just take a bunch of shots and choose the lucky ones.  But since you have tracking I would use it and stack video frames(4k vid if you can).  Alt/az is fine for the short 1-3min videos you would be taking.  Why not use your phone to begin and iron out the tracking problems.  A wedge for this is OTT I feel.

When seeing is good, I put my phone on a 5mm EP and a 2xbarlow I'm imaging at an effective f/l of ~2600mm, which reveals most features I could ever want to see down to ~1" (with my new phone I'm sampling ~~0.1arcsec/pixel at this focal length)  If you stuck that afocal setup on your scope, you'd be at an effective f/l of ~4500mm, so useful magnification afocally would be a doddle with your scope.  Once you've ironed out the process very cheaply, you could then make the decision to swap to prime dslr and be imaging at a similar focal length as what you'd done with the afocal setup.  As a guide to what a phone camera can do, the latest series of Lunar images with my new phone are in the gallery in my sig (bearing in mind Instagram compression).


Edited by doolsduck, 01 October 2020 - 01:27 AM.


#6 BrettD

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Posted 01 October 2020 - 04:25 AM

I can't speak from experience, as I image from an equatorial mount ... but if you have the wedge, I can't think why you would not use it ... if your alignment is good, it's one less motor to have errors in, and also, if you are planning on combining the results of multiple captures into a mosaic, you won't have field rotation to correct.

 

Regarding drift ... over the course of 30secs or so (a reasonable capture time) I would not expect more than 20 arc seconds of drift. How much magnification are you talking about?

 

Brett 



#7 Mirzam

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Posted 01 October 2020 - 07:46 PM

Even if the mount is aligned perfectly, a problem with tracking the Moon is that there is no “lunar rate”.  The orbit is very complex and the rate varies continuously.  30 second videos will be fine but then you will likely have to recenter.

 

JimC




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