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Is this the best the ETX90 can do?

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#1 HaroldC3

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Posted 17 August 2019 - 01:34 AM

Purchased an ETX90 OTA just for photographing the moon and I'm kind of disappointed.  I expected somewhat sharp images but these aren't even close.  Is is because of the atmosphere and it being warm (mid 90's for highs and upper 60's for lows)?  I've tried focusing and refocusing over and over but I can't seem to get the moon perfectly sharp.  

 

Any tips?

 

I'm using two-second delay with a wired shutter cable.

 

Here's a link to the full image.

https://flic.kr/p/2gYLLFn

Attached Thumbnails

  • IMG_0292-Edit-Crop.jpg

Edited by HaroldC3, 17 August 2019 - 01:34 AM.


#2 Joe1950

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Posted 17 August 2019 - 01:53 AM

I’m not an AP expert. But let me ask. Is the image at the prime focus of the scope? I would guess it is if you captured the whole moon. 

 

Your enlargement is of a smaller image scale and wont hold detail.

 

I would suggest to get a much larger image scale with eyepiece projection so that you are in closer to begin with and don’t have to enlarge the image after the fact. That’s where it gets soft.

 

Also, due to seeing and other factors, you would want to take many images and choose the best one. 

 

Then there is stacking, but I don’t want to advise on that. I had a C-90 (same as ETX basically) and was able to get very sharp images with it.

 

Hope this makes sense. I’m sure others in the know will comment. 



#3 HaroldC3

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Posted 17 August 2019 - 01:59 AM

Thanks for the reply.

 

I’m not an AP expert. But let me ask. Is the image at the prime focus of the scope? I would guess it is if you captured the whole moon. 

 

 

Yep I'm using prime focus.

 

 

Your enlargement is of a smaller image scale and wont hold detail.

 

 

It's a full resolution crop of the overall image.  I didn't enlarge it at all.

 

 

I would suggest to get a much larger image scale with eyepiece projection so that you are in closer to begin with and don’t have to enlarge the image after the fact. That’s where it gets soft.

 

Also, due to seeing and other factors, you would want to take many images and choose the best one. 

 

Then there is stacking, but I don’t want to advise on that. I had a C-90 (same as ETX basically) and was able to get very sharp images with it.

 

I was hoping for sharp images.  I rack the focuser back and forth and images come out of and in to focus but never get perfectly sharp.  I do see atmospheric distortion so my guess is that is the culprit.  

 

Hope this makes sense. I’m sure others in the know will comment. 


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#4 Joe1950

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Posted 17 August 2019 - 02:05 AM

Often, I’ll look at the moon and looks like it’s under a running stream. That will definitely ruin things.

You’ll get it to work! As I say, more will chime in with good info.



#5 Tapio

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Posted 17 August 2019 - 02:10 AM

Let scope cool down - an hour or so.
You target should be high in the sky - 30 degrees or more.
Take many many images, video even better and stack the results with Registax or Autostakkert.
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#6 sg6

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Posted 17 August 2019 - 02:16 AM

I guess the image is a single one of a second or more?

If so then it will be atmosphere and thermals etc. There are "classic" video's of the moon that when displayed show the surface as if viewed through moving water.

 

The "solution" is to take a video, 30 fps, and say 30-60 seconds. So you gather 1000-2000 individual frames. The idea being that say 1 in 10 of those frames are actually sharp(ish). Then you stack just those sharp frames into a final image which is itself sharp, well hopefully.

 

In a way the longer the single image then the more movement the camera collects and so the single image gets worse.


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#7 HaroldC3

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Posted 17 August 2019 - 02:30 AM

Thanks everyone.  I guess I was hoping for results like the below which were taken back in 2014 using a Canon FD 400mm f4.5 lens.  The above and below were a single image.

 

https://flic.kr/p/2gYMgPm



#8 Chuckwagon

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Posted 17 August 2019 - 02:43 AM

What camera are you using?  Does it have a live view shooting mode?  If so, use that, so that it doesn't get vibration from the shutter opening.  Also, seeing will limit your sharpness.  If the edges of the moon were "boiling" when you shot this, your seeing was not good enough for a truly sharp image.  You will need excellent seeing to get a truly sharp image.  And as noted, the best way to get moon photos is to take high-frame-rate video and allow a program such as Registax to piece together a good image from all of the unsteady ones.  DSLRs are, generally speaking, not the best cameras for lunar photos, though you can get excellent results in the right circumstances.  It will take patience and some good luck, but it can be done.


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#9 44maurer

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Posted 17 August 2019 - 02:58 AM

I have an etx125. I’m assuming the quality of the images would be similar. You can expect to do much better than that image.

 

example 

8C5F39F2 9D80 4917 9018 78DFED465A20

 

This is first attempt, so I am by no means good at planetary imagining. I didn’t have any of my moon shots to show, but these scopes are very good at doing moon/planets. (Disclosure: my etc is an older model,  it I would expect the newer ones are equivalent).


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#10 james7ca

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Posted 17 August 2019 - 05:38 AM

A properly functioning ETX90 should be able to take much better images than that shown by the OP. It looks to me like the focus was not very good or you had some vibrations when the image was taken. The activation of the focal plane shutter itself can cause vibrations, so you generally want a camera that has a so-called first-curtain electronic shutter or a completely electronic shutter. If you have a DSLR with a liveview mode or a mirrorless camera then it may have an option for using a first-curtain electronic shutter mode (if so, then you should enable that feature when using your camera for astrophotography).

 

In any case, if the seeing conditions were poor then you aren't going to be able to get sharp images and you should follow some of the other recommendations that have been made in this thread. Also, as has been previously mentioned even these little Maks need a good hour or more of cool down (or warm up) once they are taken outside.

 

Below is an image that I took of the crescent moon with a Celestron C90 using a dedicated CMOS astro camera (the QHY5III-178C) which uses an electronic shutter. Also, some additional links showing other results with the same scope (which should be almost identical to you ETX90).

 

  https://www.cloudyni...dpost&p=8098565

 

  https://www.cloudyni...dpost&p=8095307

 

  https://www.cloudyni...dpost&p=7734355

Attached Thumbnails

  • Crescent Moon C90 and QHT5III-178C.jpg

Edited by james7ca, 17 August 2019 - 10:57 PM.


#11 HaroldC3

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Posted 17 August 2019 - 07:46 AM

Thanks again for the replies.  I am using a Canon M6 mirrorless camera.  I used a 2-second delay using a wired remote.  

 

Based on information here my seeing was not good.  The moon was "boiling" or "running through a river" as others have described, which was my hunch as to why my images were not good.  I guess I'll have to wait until it cools down to get better seeing.  

 

It also sounds like using something with 4k movie mode would be best so I can then stack high resolution images.  Certainly I could use 1080p but they would not be very high res but I may try it just to see the results.  

 

Unfortunately I don't have a tracking mount (or even one with a simple clock motor) so the moon only stays in frame for a few seconds and then moves on.  



#12 james7ca

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Posted 17 August 2019 - 09:51 AM

I did a search of the M6 manual and unfortunately this camera doesn't appear to have a first-curtain electronic shutter mode and that means you are always going to have some vibration before the picture is taken from the shutter closing and then opening again to begin the exposure. Whether this will make a significant difference in the sharpness of you images I can't say, but it would be better if your camera did support this feature. However, I don't believe that is the principal cause of your unsharp images (although it certainly doesn't help).

 

As for using video, that could help but it is offset by the resampling that happens when the video is resized and compressed from the raw image that is read directly off of the sensor (which is what you get when you capture using a RAW, still image at full sensor resolution). So, try some video and stack only the best frames.


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#13 RedLionNJ

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Posted 17 August 2019 - 11:54 AM

 

As for using video, that could help but it is offset by the resampling that happens when the video is resized and compressed from the raw image that is read directly off of the sensor (which is what you get when you capture using a RAW, still image at full sensor resolution). So, try some video and stack only the best frames.

The importance of this paragraph cannot be over-stated. Too many people rave about "I recorded in 4k - isn't that resolution enough?".  No. It's not. It's not really 4k unless you genuinely have one of the very, very few sensors that is natively 4k. Every other sensor (including those in all Nikons and most Canons) interpolates to reach specific resolutions. This absolutely destroys the ability to produce data appropriate for stacking.

 

So along with lossy compression (hello, JPEG!), poor interpolation contributes a LOT to loss of potential detail in high-resolution astrophotography.


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#14 HaroldC3

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Posted 17 August 2019 - 01:13 PM

The importance of this paragraph cannot be over-stated. Too many people rave about "I recorded in 4k - isn't that resolution enough?".  No. It's not. It's not really 4k unless you genuinely have one of the very, very few sensors that is natively 4k. Every other sensor (including those in all Nikons and most Canons) interpolates to reach specific resolutions. This absolutely destroys the ability to produce data appropriate for stacking.

 

So along with lossy compression (hello, JPEG!), poor interpolation contributes a LOT to loss of potential detail in high-resolution astrophotography.

Thanks for this.  I'm hoping the next EOS M camera has an electronic shutter mode that can capture something like 20 fps.  We shall see hopefully at the end of this month.



#15 james7ca

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Posted 17 August 2019 - 10:44 PM

Thanks for this.  I'm hoping the next EOS M camera has an electronic shutter mode that can capture something like 20 fps.  We shall see hopefully at the end of this month.

I'm not aware of any interchanable-lens digital camera that uses a fully electronic shutter for still imaging. However, for video these cameras have to use an electronic shutter since the mechanical shutters (at the focal plane) can't really operate reliably at the frame rates that are needed for video.

 

The main reason why still cameras continue to use mechanical shutters is that today's CMOS cameras get somewhat better image quality when the exposure is both started and stopped under total darkness (as happens with a mechanical shutter). Also, fully electronic shutters can cause blurring in the image (the "jello" or rolling shutter effect you sometimes see in video captures when the subject is in motion during the capture).

 

Mirrorless cameras that offer a first-curtain electronic shutter mode are somewhat of a compromise, they probably sacrifice a small amount of image quality to reduce the shutter "bounce" you may get when you have to close and then reopen the shutter to begin the actual exposure, but the exposure is still ended using the mechanical shutter as the latter still offers improved image quality. Another reason for the first-curtain electronic shutter is that it reduces the number of activations that are required by the mechanical shutter (meaning a longer life for the shutter).

 

With a mirroless camera that is using its liveview for framing prior to the capture of an image the mechanical shutter actually has to close and then reopen to begin the exposure (that's two activations of the shutter), then it has to close to end the exposure and reopen yet again to restore the liveview image. So, you have four activations of the shutter.

 

However, with a first-curtain electronic shutter you don't need the first two activations, since the exposure begins without using the mechanical shutter.

 

In any case, as I mentioned earlier I don't think that the lack of an electron shutter mode for still captures is the primary reason for you blurred images, so I wouldn't be overly concerned about this APPARENT shortcoming with the Canon M6 (you may want to check further, because the M6 may offer this feature, I just couldn't find any mention of it in the user manual).


Edited by james7ca, 17 August 2019 - 10:45 PM.



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