First light with Meade 14" ACF - some questions

[vlaiv]

Just now, gorann said:

But I am moving from f/10 to f/6.2 so maybe 15 min is a bit over the top. I could also take a few shorter exposures to at least save the galaxy core if needed. As I understand it CMOS could equally well be binned later but maybe to save disk space and processing time I should at least bin 2x2 on the camera?

Ok, yes, if by any chance you get blown out core in your subs, then of course either reduce exposure or do "filler" subs, but I'm almost certain you won't saturate galaxy core in 15 minutes.

In principle bin 2x2 on camera will save space, but I would advise against it. If you use long subs, you won't have much data anyway.

[gorann]

OK, I will just do 1x1 then. I am getting a power nap now for two hours so I am ready and alert - did not get much sleep last night, that is the life of a keen astrophotographer😀.

[ollypenrice]

4 hours ago, gorann said:

Friends,

here is the result from last night. First a single raw sub, then a raw stack of the 7 x 15 min I managed to grab (only done Canon banding reduction and SCNRgreen in PI), and finally a processed more presentable version. Maybe @vlaiv want to have a go at dissecting the images to extract some useful ideas for future improvement?

The image was done at native FL of 3556 mm (f/10), so without reducer and with the CANON60Da as imaging camera. Guided with Lodestar X2 on ZWO OAG. Reomoving the reducer may be the mail reason why there is now much less chromatic aberration, but I also collimated it (was slightly out of collimation). I still have some problems with varying star shapes. My guess that there is some tilt but since I am not going to use it with DSLR in the future, I will try to deal with that if I also get these star shapes when using one of my cooled cameras.

The plan tonight is to collect Lum with the ASI1600MMpro that I can add to this RGB image.

So Olly @ollypenrice, does it still look like a rather hopeless endeavour? At least I am surprised about how well the EQ8 appear to handle 45 kg scope with over 3.5 meter FL. Bear in mind that this is still only 105 minutes of DSLR data collected at 15 °C. Cooled CCD & CMOS will so be attached to the scope.

No, it doesn't look like a hopeless endeavour if you want to catch NGC7331. With a lot of data I think you'll get it to the standard you'd achieve with your Esprit 150. Will you beat that standard in the 14 inch? I doubt it. Will the 14 inch also bring Stephan's Quintet into the picture?  Well, hardly! The brutal question is, What's the point? I think your Esprit 150 will match the resolution possible in the big scope and possibly beat it while, at the same time, giving you a FOV several times larger.

From a smaller refractor than yours here's a full size NGC7331. Is the 14 inch going to beat it?

 

... and meanwhile, far, far away in the other corner of the chip (which is smaller than yours!) we have all the fun of Stephan's Quintet...

 

Big scopes do look tempting but, under the skies we have, do they really deliver more detail than smaller ones? We know they deliver smaller fields of view...

Olly

Edit. Your EQ8 did indeed do well.

 

 

Edited August 27, 2019 by ollypenrice

[vlaiv]

1 hour ago, ollypenrice said:

From a smaller refractor than yours here's a full size NGC7331. Is the 14 inch going to beat it?

Well actually, if you look at this for example, you will see that 14" is going to beat refractor in terms of resolution:

same pair of stars in above image:

And here I'm not talking about the size of each star - I'm talking about "dark space" between them in bottom image (which is over sampled, but there is still cleaner split).

 

 

[gorann]

30 minutes ago, vlaiv said:

Well actually, if you look at this for example, you will see that 14" is going to beat refractor in terms of resolution:

same pair of stars in above image:

And here I'm not talking about the size of each star - I'm talking about "dark space" between them in bottom image (which is over sampled, but there is still cleaner split).

 

 

I do think you are right Valiv! When I now compare several of those star pairs in my image with that posted by Olly @ollypenrice I do see more split between them (ene if I have less than 2 hours of data). I am also impressed by the relatively small star size of the 14" Meade. I often see quite big and bloated stars in other big SCT images. Let's see what tonight's Lum will contribute, if I get the sky and technology on my side.....

[gorann]

Collecting data now but unfortunately guiding is not as good as last night, 0.8"/pix RMS right now. Something with the sky probably (seeing/transparency) and maybe it will improve.

[gorann]

Gick ut i obsyt och guidingen hade skutat fungera. Fick inte heller in någon bild på ASI1600 så jag fattade ingenting i flera minuter innan jag till [removed word] tittade upp och insåg att hela himlen var molntäckt - måste vara lite trött i huvudet men nu får jag i alla fall gå och lägga mig.

[vlaiv]

21 minutes ago, gorann said:

Gick ut i obsyt och guidingen hade skutat fungera. Fick inte heller in någon bild på ASI1600 så jag fattade ingenting i flera minuter innan jag till [removed word] tittade upp och insåg att hela himlen var molntäckt - måste vara lite trött i huvudet men nu får jag i alla fall gå och lägga mig.

Well, for all those interested, I did google translate:

Quote

Went out obscurely and the guiding had shot working. Also did not get a picture on ASI1600 so I did not take anything for several minutes before I looked up [removed word] and realized that the whole sky was overcast - must be a little tired in the head but now I have to go to bed anyway.

 

[tooth_dr]

Very exciting thread, the eq8 is impressive, but clearly in very capable hands. Well done. 

[gorann]

8 hours ago, vlaiv said:

Well, for all those interested, I did google translate:

 

Sorry about the late night Swedish Vlad! But Google translator did a fairly good job 🤣 Obviously I was very tired so I posted it to the wrong thread - was ment to be on a discussion I have ongoing with Wim @wimvb here in Sweden, Will have a look now if I got any usable subs.

[ollypenrice]

 

12 hours ago, vlaiv said:

Well actually, if you look at this for example, you will see that 14" is going to beat refractor in terms of resolution:

same pair of stars in above image:

And here I'm not talking about the size of each star - I'm talking about "dark space" between them in bottom image (which is over sampled, but there is still cleaner split).

 

 

How useful are stars for this test? (That's a genuine question to which I don't know the answer.) I processed some remarkably fine data taken by Julian Shaw through a 6 inch refractor and an Astro Physics advanced Barlow at something like F15. He felt that the main effect of the Barlow was to be seen on the stars. I'm not sure that it had any effect on the galaxy. Point sources and extended objects tend to behave differently.

12 hours ago, gorann said:

I do think you are right Valiv! When I now compare several of those star pairs in my image with that posted by Olly @ollypenrice I do see more split between them (ene if I have less than 2 hours of data). I am also impressed by the relatively small star size of the 14" Meade. I often see quite big and bloated stars in other big SCT images. Let's see what tonight's Lum will contribute, if I get the sky and technology on my side.....

I agree. Those are great stars. The SCTs do usually produce rather large stellar images. However, at the eyepiece my 14 inch gives considerably tighter stars than either my previous 10 inch standard SCT or my present 10 inch ACF.

Any kind of high res imaging is hugely dependent on the seeing, unfortunately. When the seeing is bad the mono user can, at least, shoot only colour and hope for better luck for the luminance.

Olly

Edited August 28, 2019 by ollypenrice
Typo

[kirkster501]

@ollypenrice   That's like saying through there is no point in bigger scopes for AP though??????  The 14" is a proven performer for planetary and lunar.  Could you not say that just use a quality refactor on the moon and not bother with a big SCT and just zoom in to the resulting pictures to get the resolution you want?

[kirkster501]

.... and by the way great work Gorann!

I have a side by side TEC140 and ACF 14".  I am struggling with balance and need to decide what to do.

[gorann]

10 minutes ago, kirkster501 said:

.... and by the way great work Gorann!

I have a side by side TEC140 and ACF 14".  I am struggling with balance and need to decide what to do.

Yes that would be a challenge even for a Mesu200 - is it even possible with 10 kg on one side and 40kg on the other? Maybe let the TEC piggy back instead, or do like me and build a second obsy.

[kirkster501]

8 minutes ago, gorann said:

Yes that would be a challenge even for a Mesu200 - is it even possible with 10 kg on one side and 40kg on the other? Maybe let the TEC piggy back instead, or do like me and build a second obsy.

The weights come in at, ACF 14" with focuser, approx 35kg and TEC140 with flattener about 17kg. 

I've offset the side-by-side bar so that the Meade is almost on the RA axis and the TEC140 higher up.  It is almost balanced but not quite, I am goign too keep trying anfd I have bought a sliding 3kg weight.  I also wanted to ride my FSQ85 on this too but it is impossible to get balance in all orientations doing that.

As you know, the ACF 14" has to be permanently mounted, it is simply too heavy and difficult to man-handle to keep mounting and unmounting.

EDIT; I looked at piggyback but I think it would put a 17kg mass too far out from the RA axis.

 

Edited August 28, 2019 by kirkster501

[vlaiv]

1 hour ago, ollypenrice said:

How useful are stars for this test? (That's a genuine question to which I don't know the answer.) I processed some remarkably fine data taken by Julian Shaw through a 6 inch refractor and an Astro Physics advanced Barlow at something like F15. He felt that the main effect of the Barlow was to be seen on the stars. I'm not sure that it had any effect on the galaxy. Point sources and extended objects tend to behave differently.

Stars are actually very useful in determining blur level in the image. Blur is characterized by it's PSF - point spread function. Star is for all intents and purposes at such a distance, point like source and when you are imaging a star you are in fact getting exact PSF profile, and analyzing it will tell you everything you need to know about the nature of the blur.

It is done in the same way to test the optics - look at star pattern and you can "read" performance of the telescope and it's PSF and MTF. When star testing a telescope we tend to use defocus pattern because it is easier to read, but in principle, what you read from defocus pattern you can read from a star profile as well.

Only thing that can skew your analysis via star profile is the fact that atmospheric turbulence is not the same across the whole field, and this is important in short exposures where there is no enough time for these small differences in seeing to average out - like in planetary imaging - that is why adaptive optics works for very narrow FOV - as it tracks only one "star" (usually artificial laser beam) and can correct for disturbances only in vicinity of that "star".

In our case, things average over time and stars are a good match for overall PSF that has affected the image.

[ollypenrice]

37 minutes ago, kirkster501 said:

@ollypenrice   That's like saying through there is no point in bigger scopes for AP though??????  The 14" is a proven performer for planetary and lunar.  Could you not say that just use a quality refactor on the moon and not bother with a big SCT and just zoom in to the resulting pictures to get the resolution you want?

No, there is a world of difference between lucky imaging and long integration. The whole point of fast frame lucky imaging is that you can beat the seeing (by retaining only the fleeting good moments) whereas in long integration you are well and truly at the mercy of the seeing. The SCTs are indeed proven on the planets. Nor would I go so far as to say that DS imaging with a big scope is a waste of time. On occasion I think a good 14 inch will out perform a 6 inch refractor but, having used both quite extensively, I think the 14 inch gain in resolution is very small even on exceptional nights and non existent on the rest. Its limited FOV is always present, though.

Our well heeled American friends with their big Plane Waves can and do out resolve our efforts with big refractors but they are based at high altitudes and at sites chosen for good seeing.

Olly

[ollypenrice]

4 minutes ago, vlaiv said:

Stars are actually very useful in determining blur level in the image. Blur is characterized by it's PSF - point spread function. Star is for all intents and purposes at such a distance, point like source and when you are imaging a star you are in fact getting exact PSF profile, and analyzing it will tell you everything you need to know about the nature of the blur.

It is done in the same way to test the optics - look at star pattern and you can "read" performance of the telescope and it's PSF and MTF. When star testing a telescope we tend to use defocus pattern because it is easier to read, but in principle, what you read from defocus pattern you can read from a star profile as well.

Only thing that can skew your analysis via star profile is the fact that atmospheric turbulence is not the same across the whole field, and this is important in short exposures where there is no enough time for these small differences in seeing to average out - like in planetary imaging - that is why adaptive optics works for very narrow FOV - as it tracks only one "star" (usually artificial laser beam) and can correct for disturbances only in vicinity of that "star".

In our case, things average over time and stars are a good match for overall PSF that has affected the image.

So an extension of this argument might say that larger aperture was more susceptible to seeing instability than smaller aperture? I've read this argument but have no opinion on it for want of both experience and expertise.

Olly

Edited August 28, 2019 by ollypenrice
Typo

[vlaiv]

25 minutes ago, ollypenrice said:

So an extension of this argument might say that larger aperture was more susceptible to seeing instability than smaller aperture? I've read this argument but have no opinion on it for want of both experience and expertise.

Olly

I've heard of this, and I tend to agree that size of aperture combined with same seeing conditions will give different results on PSF. It might be the case that larger aperture will fare worse under most circumstances - I just have no clue.

We can maybe even argue that this effect is not linearly related to aperture size and that there is "the worst" aperture for given seeing. I base this on following reasoning:

If we look at distorted wavefront it will have different "curves" along the segment, and it depends on how much of that segment falls on aperture - for small aperture we will in principle have "tilt" - star will "jump" around from it's position. Medium sized aperture will have largest distortion compared to size of segment that it is covering, while largest aperture will in fact act as distortion is on one piece of aperture. If we have very very large aperture, wavefront distortions will resemble more rough surface of the mirror than large scale distortion - ripples will be small compared to segment of wavefront being observed.

This is of course applicable to "instant" in time - or "frozen" wavefront distortion. When we let it accumulate - on a small scope we will have jumping star that "smears" over long exposure, on average aperture we will have smeared star averaged while on very large aperture we will have "light scatter" averaged - quite possibly the result will be the same, or maybe large aperture wins in case of long exposure (give of course that tracking is perfect). Like I said - I have no idea.

What I do know is that large "professional" telescopes (1m and above) produce data that is much sharper than amateur setups. Whether this is consequence of their location and seeing conditions only, or is it related to what I've described above - can't really tell as we don't have "control" - large scope on less than perfect location under average seeing to give us comparison.

[gorann]

Friends, while you have been arguing the pros and cons of large SCTs, I had a look at last nights data. Got 3 x 15 min of Lum with the ASI1600MMpro on the 14" before clouds moved in. Then Wim @wimvb gave me the tip to merge the pixels 2x2 in PI using the Super Pixel script when debayering, so I did this to my previous Canon 60Da data (rediculously over sampled at 0.25"/pix) to make a synthetic lum. Then I mixed this lum with the lum collected last night (50/50) and ended up with a rather OK lum that I added (partially) to the colour image. It did bring out a bit more faint stuff. Here is the result. so now totally 150 min. It may take a while before I get a clear night so I may work a bit more on the image.

Edited August 28, 2019 by gorann

[kirkster501]

Wow that is superb!

[Chris]

Great result Gorann! 

[Chris]

Other than the above great image, I'm impressed that so many of you have 14" SCT's! These are literally what we had at University back in the day, and it was the pride and joy of the department. Now people have them in their gardens!

[kirkster501]

Just now, Lockie said:

Other than the above great image, I'm impressed that so many of you have 14" SCT's! These are literally what we had at University back in the day, and it was the pride and joy of the department. Now people have them in their gardens!

Just goes to show how larger production runs can lower the unit cost.  And how people's spending power has increased, or sanity decreased, however you want to look at it!  

[gorann]

1 hour ago, Lockie said:

Other than the above great image, I'm impressed that so many of you have 14" SCT's! These are literally what we had at University back in the day, and it was the pride and joy of the department. Now people have them in their gardens!

 

1 hour ago, kirkster501 said:

Just goes to show how larger production runs can lower the unit cost.  And how people's spending power has increased, or sanity decreased, however you want to look at it!  

Well, I found mine on a Norwegian second-hand site (finn.no that is selling everything) and it was only 30 000 NOK (about 3000 Euro / GBP) including a Homeyer Scope Cradle that probably helps a bit in making it very sturdy (but adds an extra 10 kg). It is an LX200R, so from the first production years (around 2006) before Meade were sued and had to change it from R (Ritchey-Chretien) to ACF. That probably means that it was manufactured in the US and not Mexico or China.