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Knighter

DSO with sky max 127 mak

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Hi can anyone give advice on the best way I can use my mak for DSO photography. I know they are great for planetary work but not so good for DSO. I am using the ASIAIR pro with asi153 camera and the 120 mini for guiding with a 32mm plossl eyepiece. 
thanks 

Matt 

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Hi Matt

You'll need quite a solid mount shooting at that focal which will probably be the hardest part. Because of the focal length you'll also be limited to smaller DSOs like planetary nebula and star clusters but they often look good at these focal lengths if done correctly;)

Lastly, you will not need an eyepiece. I highly suggest shooting at prime focus when doing astrophotography.

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2 hours ago, Victor Boesen said:

Hi Matt

You'll need quite a solid mount shooting at that focal which will probably be the hardest part. Because of the focal length you'll also be limited to smaller DSOs like planetary nebula and star clusters but they often look good at these focal lengths if done correctly;)

Lastly, you will not need an eyepiece. I highly suggest shooting at prime focus when doing astrophotography.

Hi Victor I have bought the ioptron cemp-25 it was recommended by FLO due to its accuracy they also suggested a 32mm Plössl which I have also ordered so do you suggest not using an eyepiece at all then?  

 

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5 minutes ago, Knighter said:

Hi Victor I have bought the ioptron cemp-25 it was recommended by FLO due to its accuracy they also suggested a 32mm Plössl which I have also ordered so do you suggest not using an eyepiece at all then?  

 

Well FLO have done a good job once again;) Mount is perfect.

You can definitely use the eyepiece for visual observing since it'll allow for a wide field of view despite the telescope's focal length, but for imaging you shouldn't use it. 

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Ok that’s great guys Thankyou. I have looked at the calculator by using a 2 x Barlow gives a bigger picture for example of the whirlpool. I’m guessing that would be better rather than not using one?. 
sorry I’m new to Astro photography 

B8BD7699-16D5-4544-9C80-636A88A5A510.png

F8A39A0B-76DF-4ED2-85A5-CE6DB17A5E5F.png

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For planetary imaging the Barlow will be fine but not for deep sky imaging. You won't gain any extra resolution on deep sky objects with the Barlow because it will be blurred by seeing. You get around this in planetary imaging by taking very short exposures but deep sky requires long exposures because the objects are so faint. 

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I wouldn’t use a barlow- at the native 1500mm focal length you’ll be imaging at approximately 0.5 arcsec per pixel- I’d be surprised if you can get your auto guiding setup to get the best from that sort of scale. I’d keep the native resolution and bin the pixels 3x3 (or 2x2 if you have really good seeing and excellent guiding)

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22 minutes ago, catburglar said:

I wouldn’t use a barlow- at the native 1500mm focal length you’ll be imaging at approximately 0.5 arcsec per pixel- I’d be surprised if you can get your auto guiding setup to get the best from that sort of scale. I’d keep the native resolution and bin the pixels 3x3 (or 2x2 if you have really good seeing and excellent guiding)

Hi ok thanks but would you mind explaining what you mean in the last sentence about native resolution etc. Would the guiding camera be ok for my mak IRC’s all from ZWO to work with the ASIAIR pro. 

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I have the Celestron 127 Mak. Not sure how they compare performance wise but it's also 1500mm f/l.

I'm new to imaging and had a quick session with with the Mak on my NEQ6Pro mount and my unmoded Canon EOS 1200D last month. No guiding but have a ASI120mm guide cam on order which I will use with the 50mm finder rom my big Newt :) At 1500mm it's long enough! so no Barlow needed.

This was M57 with 12 x 120 seconds at ISO 800 (Using APT on my laptop) and roughly processed in Photoshop. I'm quite happy with it as a trial run. The NEQ6 is more of a mount than needed so I expected good subs anyway.  I just srewed the camera to the back of the scope and focussed it (using APT live view) and set it off!

Certainly a very usable scope for Smaller DSO's but no good for M31 (Andromeda Galaxy). 

1195550755_M57Mak127.thumb.jpg.be7d7e294dac243e7dd34a0411ab7e6e.jpg

Edited by Paul M

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6 minutes ago, Paul M said:

I have the Celestron 127 Mak. Not sure how they compare performance wise but it's also 1500mm f/l.

I'm new to imaging and had a quick session with with the Mak on my NEQ6Pro mount and my unmoded Canon EOS 1200D last month. No guiding but have a ASI120mm guide cam on order which I will use with the 50mm finder rom my big Newt :) At 1500mm it's long enough! so no Barlow needed.

This was M57 with 12 x 120 seconds at ISO 800 (Using APT on my laptop) and roughly processed in Photoshop. I'm quite happy with it as a trial run. The NEQ6 is more of a mount than needed so I expected good subs anyway.  I just srewed the camera to the back of the scope and focussed it (using APT live view) and set it off!

Certainly a very usable scope for Smaller DSO's but no good for M31 (Andromeda Galaxy). 

1195550755_M57Mak127.thumb.jpg.be7d7e294dac243e7dd34a0411ab7e6e.jpg

That’s great thanks I have the 120mini it came with the ZWO 30mm mini scope (as a bundle) just worried now that it won’t be powerful enough to guide the scope. 

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50 minutes ago, Knighter said:

That’s great thanks I have the 120mini it came with the ZWO 30mm mini scope (as a bundle) just worried now that it won’t be powerful enough to guide the scope. 

I did a bit of looking round myself. I'll use the ASI120mm with both my 250 Newt and the 127 Mak. Lots of varying views about image scale/ratio between main scope/camera and guide scope/camera. 

I hava an ASI 178 on order too. This tool: http://astronomy.tools/calculators/guidescope_suitability Gives these options for imaging with the 127

image.thumb.png.574df88c0558197a25ca41eae8c4877e.png

 

image.thumb.png.2de0b6587784dedca97bc44fe24c9584.png

The guiding ratio in the bottom green box is the important number. It's below 1:10 for my 1200D as the imaging camera but above for the ASI178.

It seems that keeping the ratio below 1:10 (well below, if possible) is key to sucessfull guiding. For my 250 Newt it gives much better figures.

Given the numbers above, without binning, I expect the ASI178 will be difficult to guide with a 120mm guide camera through a 50mm spotting scope/guide scope on the 127 Mak

Put your own figures in that tool and see what you get. The result isn't definitive but a measure of how sucessfull your guiding might be.

Edited by Paul M

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If I remember correctly the guide cam has 3.75micron pixels and the mini guidescope is f4- so 120mom focal length... so your guiding resolution is 3.75x206.265/120 = 6.4 arcsec per pixel.
 

Guiding software computes the centroid of the guide star image- and it should be able to spot deviations of approx 1/6 - 1/8 of a pixel- so your focal length is a bit short for high res DSO imaging but

probably OK if you aim  image at about 2-3 at seconds which is more typical for most DSO images anyway...

 

There are a few things to consider-

1. For long exposure DSO imaging the maximum resolution possible is governed by the atmospheric seeing- unless you are at high altitude this likely places a limit of  around 2 at seconds on a good night.

2 The guiding system and mount need to be able to guide at 2x higher precision than your final image resolution (an extrapolation of Nyquist sampling theory) So your guiding errors need to be in the region of 1 arcsec if your final image is going to achieve 2arcsec resolution

3. The guidescope resolution needs to be sufficient to ‘identify’ guiding deviations significantly smaller than this and t he n apply just the right correction to the mount which must then respond quickly and precisely to the going input...

 

putting all this all together.....

I don’t know the specifics of your mount, but it usually takes a well tuned high spec mount machined to precise tolerances to reliably guide at better than 0.5arcsec RMS- it’s a tough ask for your typical HEQ5 the ioptron may well be better the the HEQ5, 

@ollypenriceis half way (or more) up a mountain, has oodles of experience, some really high spec kit and no small amount of talent- I seem to recall that he’s happy with his images at approx 0.9arcsec per pixel....
 

if I were you starting out with DSO imaging I’d  bin the pixels to get a sensible image scale or even better- get a scope with a focal length shorter than 1metre

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8 hours ago, catburglar said:

If I remember correctly the guide cam has 3.75micron pixels and the mini guidescope is f4- so 120mom focal length... so your guiding resolution is 3.75x206.265/120 = 6.4 arcsec per pixel.
 

Guiding software computes the centroid of the guide star image- and it should be able to spot deviations of approx 1/6 - 1/8 of a pixel- so your focal length is a bit short for high res DSO imaging but

probably OK if you aim  image at about 2-3 at seconds which is more typical for most DSO images anyway...

 

There are a few things to consider-

1. For long exposure DSO imaging the maximum resolution possible is governed by the atmospheric seeing- unless you are at high altitude this likely places a limit of  around 2 at seconds on a good night.

2 The guiding system and mount need to be able to guide at 2x higher precision than your final image resolution (an extrapolation of Nyquist sampling theory) So your guiding errors need to be in the region of 1 arcsec if your final image is going to achieve 2arcsec resolution

3. The guidescope resolution needs to be sufficient to ‘identify’ guiding deviations significantly smaller than this and t he n apply just the right correction to the mount which must then respond quickly and precisely to the going input...

 

putting all this all together.....

I don’t know the specifics of your mount, but it usually takes a well tuned high spec mount machined to precise tolerances to reliably guide at better than 0.5arcsec RMS- it’s a tough ask for your typical HEQ5 the ioptron may well be better the the HEQ5, 

@ollypenriceis half way (or more) up a mountain, has oodles of experience, some really high spec kit and no small amount of talent- I seem to recall that he’s happy with his images at approx 0.9arcsec per pixel....
 

if I were you starting out with DSO imaging I’d  bin the pixels to get a sensible image scale or even better- get a scope with a focal length shorter than 1metre

Quite near the top of the mountain, in fact! 😁

Let's get back to basics, first in theory: the resolution of detail involves 1) the resolution of the optics which, when they're diffraction limited, is proportional to aperture. A 127mm scope has a theoretical maximum resolution of 0.91 arcseconds. It can distinguish details 0.91 arcseconds apart. Details closer together than that connot be distinuished. There is no way round this rule.

2) The resolution in terms of the camera-and-lens as a system. The unit of interest is arcseconds per pixel. (How many arcseconds of sky land on one pixel?) If the system is working at 2 arcsecs per pixel any two points less than 2 acsecs apart land on the same pixel so will not be distinguished.

Whichever of these values is the worst in terms of resolution will define the best resolution of which the system will be capable.

Now for the practice. Photographic systems with high resolving power soon fall foul of other limiting factors which override their theoretical resolution. These include:

1) The seeing. The atmosphere distorts the incoming beam, sometimes by very large amounts. It isn't unusual to be limited to 2 arcseconds or worse. Sometimes it's also better than that. Local conditions determine the limit.

2) The guiding. Divide your imaging pixel scale by 2 for a rough idea  of the guiding precision you'll need to support that resolution. A good (not an average but a good) mass production mount can usually manage a guide error of about 0.5 arcsecs. That means that you are, in reality, limited to 1.0 arcsec per pixel for imaging. 

So even if we ignore the optical limitations of 127mm we find you are trying to image at 0.5 arcsecs per pixel. This would need incredibly good seeing (unlikely) and a guide error of 0.25 arcsecs. (Also unlikely! Our excellent Mesu 200s deliver around 0.3" at their best.)

Enter another key term, empty resolution. If you open a high quality image in Photoshop, one which was correctly taken at the limit of the system) and look at it full size on your screen you are seeing all it can give. You can hit Ctrl+ and make it bigger. Or hit CTRL+ again and make it bigger still... but it contains no new resolution. Doing this is a waste of time. The detail just isn't there. And so it is with imaging at unrealistic pixel scales like 0.5"PP. The same information will be landing on several pixels. You'd be better off with bigger pixels which would 'fill' faster. One way to do this is to bin pixels 2x2 or 3x3 where this is possible.

Olly

Edited by ollypenrice
Typo
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10 hours ago, Paul M said:

I did a bit of looking round myself. I'll use the ASI120mm with both my 250 Newt and the 127 Mak. Lots of varying views about image scale/ratio between main scope/camera and guide scope/camera. 

I hava an ASI 178 on order too. This tool: http://astronomy.tools/calculators/guidescope_suitability Gives these options for imaging with the 127

image.thumb.png.574df88c0558197a25ca41eae8c4877e.png

 

image.thumb.png.2de0b6587784dedca97bc44fe24c9584.png

The guiding ratio in the bottom green box is the important number. It's below 1:10 for my 1200D as the imaging camera but above for the ASI178.

It seems that keeping the ratio below 1:10 (well below, if possible) is key to sucessfull guiding. For my 250 Newt it gives much better figures.

Given the numbers above, without binning, I expect the ASI178 will be difficult to guide with a 120mm guide camera through a 50mm spotting scope/guide scope on the 127 Mak

Put your own figures in that tool and see what you get. The result isn't definitive but a measure of how sucessfull your guiding might be.

Hi Paul, that’s great information thank you very much, really appreciate it 

 

so can you use a 2 x Barlow on the guide scope that would take the ratio on the calculator to below 1.10 it takes it to 1.09

 

Matt 

Edited by Knighter

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23 minutes ago, Knighter said:

Hi Paul, that’s great information thank you very much, really appreciate it 

Matt 

Hi Paul so can you use a 2 x Barlow on the guide scope that would take the ratio on the calculator to below 1.10 it takes it to 1.09

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6 hours ago, Knighter said:

Hi Paul so can you use a 2 x Barlow on the guide scope that would take the ratio on the calculator to below 1.10 it takes it to 1.09

I'm not sure it's viable with the small 50 spotter as it doesn't have so much focus movement and would probably have a poor image. I think the way forward with a very high guide ratio is a longer focal length guide scope, binning the imaging camera or switch to off axis guiding.

From my readings it seems the off axis guider is preferred for long focal length imaging for a number of reasons.

Some would say it's the only way to go.

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Longer focal lengths can lead to flexure where the scopes will be pointing at different points in the sky. I have read on the link below that off axis is best for focal lengths over 1500mm to 2000mm. I have the same scope, the SW SkyMax 127 and considering getting a guide scope and camera. Through my own reading up on the subject, I came across this article, https://agenaastro.com/articles/guides/autoguiding/selecting-a-guide-scope-and-autoguiding-camera-for-astrophotography.html and lists some recommendations although it is now a couple of years old. 

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5 hours ago, Paul M said:

I'm not sure it's viable with the small 50 spotter as it doesn't have so much focus movement and would probably have a poor image. I think the way forward with a very high guide ratio is a longer focal length guide scope, binning the imaging camera or switch to off axis guiding.

From my readings it seems the off axis guider is preferred for long focal length imaging for a number of reasons.

Some would say it's the only way to go.

Hi Paul yes I spoke to FLO today and they pretty much said the same thing, but they also said people have had success with the zwo mini scope with the 127 mak so will give it a go first and see how I get on before spending more money. This is becoming an expensive hobby!. But well worth it!!

 

would you also not use any eye piece looking at planets too, like the moon for example? 

Edited by Knighter
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3 hours ago, rob_r said:

Longer focal lengths can lead to flexure where the scopes will be pointing at different points in the sky. I have read on the link below that off axis is best for focal lengths over 1500mm to 2000mm. I have the same scope, the SW SkyMax 127 and considering getting a guide scope and camera. Through my own reading up on the subject, I came across this article, https://agenaastro.com/articles/guides/autoguiding/selecting-a-guide-scope-and-autoguiding-camera-for-astrophotography.html and lists some recommendations although it is now a couple of years old. 

Thanks for the link will take a read Thankyou 

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12 hours ago, ollypenrice said:

Quite near the top of the mountain, in fact! 😁

Let's get back to basics, first in theory: the resolution of detail involves 1) the resolution of the optics which, when they're diffraction limited, is proportional to aperture. A 127mm scope has a theoretical maximum resolution of 0.91 arcseconds. It can distinguish details 0.91 arcseconds apart. Details closer together than that connot be distinuished. There is no way round this rule.

2) The resolution in terms of the camera-and-lens as a system. The unit of interest is arcseconds per pixel. (How many arcseconds of sky land on one pixel?) If the system is working at 2 arcsecs per pixel any two points less than 2 acsecs apart land on the same pixel so will not be distinguished.

Whichever of these values is the worst in terms of resolution will define the best resolution of which the system will be capable.

Now for the practice. Photographic systems with high resolving power soon fall foul of other limiting factors which override their theoretical resolution. These include:

1) The seeing. The atmosphere distorts the incoming beam, sometimes by very large amounts. It isn't unusual to be limited to 2 arcseconds or worse. Sometimes it's also better than that. Local conditions determine the limit.

2) The guiding. Divide your imaging pixel scale by 2 for a rough idea  of the guiding precision you'll need to support that resolution. A good (not an average but a good) mass production mount can usually manage a guide error of about 0.5 arcsecs. That means that you are, in reality, limited to 1.0 arcsec per pixel for imaging. 

So even if we ignore the optical limitations of 127mm we find you are trying to image at 0.5 arcsecs per pixel. This would need incredibly good seeing (unlikely) and a guide error of 0.25 arcsecs. (Also unlikely! Our excellent Mesu 200s deliver around 0.3" at their best.)

Enter another key term, empty resolution. If you open a high quality image in Photoshop, one which was correctly taken at the limit of the system) and look at it full size on your screen you are seeing all it can give. You can hit Ctrl+ and make it bigger. Or hit CTRL+ again and make it bigger still... but it contains no new resolution. Doing this is a waste of time. The detail just isn't there. And so it is with imaging at unrealistic pixel scales like 0.5"PP. The same information will be landing on several pixels. You'd be better off with bigger pixels which would 'fill' faster. One way to do this is to bin pixels 2x2 or 3x3 where this is possible.

Olly

Hi Olly thanks you for this I clearly have a lot to learn really interesting 

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On 29/06/2020 at 19:46, Victor Boesen said:

Well FLO have done a good job once again;) Mount is perfect.

You can definitely use the eyepiece for visual observing since it'll allow for a wide field of view despite the telescope's focal length, but for imaging you shouldn't use it. 

Hi Victor, so am I right in thinking even for planetary photography not to use any eyepiece even for the moon?  

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4 minutes ago, Knighter said:

Hi Paul yes I spoke to FLO today and they pretty much said the same thing, but they also said people have had success with the zwo mini scope with the 127 mak so will give it a go first and see how I get on before spending more money. This is becoming an expensive hobby!. But well worth it!!

 

would you also not use any eye piece looking at planets too, like the moon for example? 

I too will have a bash at guiding my 127 Mak with the ASI120mm and the 50mm spotter. I suspect it will be ok using my DSLR as the imaging camera but less successful with the ASI178 due to it's smaller sensor.

Eyepiece for visual observations? Yeah, sure. Great on the moon and planets. You need good eyepieces to get the best views though.

Eyepiece projection for astrophotography? Whole different ball game. Tried it back in the day with a film camera with poor results. You can end up with a huge, dim image that is impossible to image with an astro camera but can put a phone camera to a low power eyepiece and get great images of the Moon. But eyepiece projection a regular imaging arrangement isn't a path I'd go down! 

Barlow projection is ok on shorter focal length acopes so long as your alignment and guiding are ok but you'll struggle on a 127Mak. 

I even have a silly plan to try the 127 as a guidescope on my 250 Newt! The numbers work, just, but the mechanics aren't so good. Not least of the problems would be the combined weight and torque of the 127 swinging off the back of the Newt. Actually, it's a bad idea :)

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22 minutes ago, Paul M said:

I too will have a bash at guiding my 127 Mak with the ASI120mm and the 50mm spotter. I suspect it will be ok using my DSLR as the imaging camera but less successful with the ASI178 due to it's smaller sensor.

Eyepiece for visual observations? Yeah, sure. Great on the moon and planets. You need good eyepieces to get the best views though.

Eyepiece projection for astrophotography? Whole different ball game. Tried it back in the day with a film camera with poor results. You can end up with a huge, dim image that is impossible to image with an astro camera but can put a phone camera to a low power eyepiece and get great images of the Moon. But eyepiece projection a regular imaging arrangement isn't a path I'd go down! 

Barlow projection is ok on shorter focal length acopes so long as your alignment and guiding are ok but you'll struggle on a 127Mak. 

I even have a silly plan to try the 127 as a guidescope on my 250 Newt! The numbers work, just, but the mechanics aren't so good. Not least of the problems would be the combined weight and torque of the 127 swinging off the back of the Newt. Actually, it's a bad idea :)

Yes that’s what I thought I have a 7mm to 24mm zoom eyepiece and with the ezxyz phone mount with my iPhone got some great shots with the set up. I think if the zwo mini scope dosent work will bite the bullet and get the off axis setup and be done with it. I will let you know how I get on. 
this is as a picture if the moon with my iPhone and mount 

8A042470-9E14-496D-A7DD-BE399380D5E0.jpeg

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51 minutes ago, Knighter said:

Hi Victor, so am I right in thinking even for planetary photography not to use any eyepiece even for the moon?  

The FOV of the camera and scope at prime focus should be small enough so you don't need an eyepiece or barlow. Also, I don't even know if you can reach focus through an eyepiece with a ZWO camera?

Short answer: Yes:)

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