TSA120 vs VX10

[jetstream]

I have been extremely fortunate to have observed so many days during the last moon- at least 7 and with 6 days in a row.  On April 1 I had the TSA120 out next to the VX10. The TSA120 has superb optics and I have not been able to break the image down mag wise. The VX10 has vg optics and will go at least 500x on the moon and over 300x on Jupiter when high up.

I still get very excited when I get great views or find something interesting out- and tonight I experienced both!

In the past I have been critical of some- sorry!!- about a smaller refractor showing more than a larger reflector...

On April 1 the TSA120 trounced the VX10... yeah I couldnt believe it either.But...

I was viewing the crater Bianchini in the Jura mountains first off and a first look in the VX10 gave me a ho hum view with the Zeiss zoom/VIP. The detail available was ok but not great and I think that the contrast offered by the weak terminator had a great effect on the 10". The VX10 was struggling in the crater itself and also in that detailed area behind and around Bianchini.The views were "smooth"  and the contrast transfer weak, overpowered by the bright moon. Not typical for this scope under better terminator placement. Not typical at all and yes it was thermally equalized and very well collimated.

The TSA 120, as I cranked up the mag with the Zeiss zoom/VIP on Bianchini and area appeared extremely sharp throughout the zoom in and at the high mag burst into view with an extremely contrasted, razor sharp view and revealed so much more than the 10" I was shocked. I sat there scratching my head. Seriously. The detail in the field around the crater came to life with a rock field like appearance with only hints of it in the 10"-as a very smooth, very lightly rippled surface. The crater itself revealed very minute forms of contrast detail, absolutely not there in my vg 10".

Back into the house for all the toys, the Docter, Vixen HR's, Pentax XO all my best came out. And they all showed the same thing. Down to the southern upland south of Clavius to the crater Newton, Same thing...

When the terminator is well placed on showcase areas of the moon the 10" excels, but the TSA120 offers a no scatter pure view of them it has grabbed my attention- again. I know for a fact that when the terminator is offering weak contrast like that night, I will reach for the TSA120 and leave the dob in the house. The frac will outperform it and show more detail than the 10" again, and again.

Gerry

Edited April 6, 2023 by jetstream

[neil phillips]

Just now, jetstream said:

I have been extremely fortunate to have observed so many days during the last moon- at least 7 and with 6 days in a row.  On April 1 I had the TSA120 out next to the VX10. The TSA120 has superb optics and I have not been able to break the image down mag wise. The VX10 has vg optics and will go at least 500x on the moon and over 300x on Jupiter when high up.

I still get very excited when I get great views or find something interesting out- and tonight I experienced both!

In the past I have been critical of some- sorry!!- about a smaller refractor showing more than a larger reflector...

On April 1 the TSA120 trounced the VX10... yeah I couldnt believe it either.But...

I was viewing the crater Bianchini in the Jura mountains first off and a first look in the VX10 gave me a ho hum view with the Zeiss zoom/VIP. The detail available was ok but not great and I think that the contrast offered by the weak terminator had a great effect on the 10". The VX10 was struggling in the crater itself and also in that detailed area behind and around Bianchini.The views were "smooth"  and the contrast transfer weak, overpowered by the bright moon. Not typical for this scope under better terminator placement. Not typical at all and yes it was thermally equalized and very well collimated.

The TSA 120, as I cranked up the mag with the Zeiss zoom/VIP on Bianchini and area appeared extremely sharp throughout the zoom in and at the high mag burst into view with an extremely contrasted, razor sharp view and revealed so much more than the 10" I was shocked. I sat there scratching my head. Seriously. The detail in the field around the crater came to life with a rock field like appearance with only hints of it in the 10"-as a very smooth, very lightly rippled surface. The crater itself revealed very minute forms of contrast detail, absolutely not there in my vg 10".

Back into the house for all the toys, the Docter, Vixen HR's, Pentax XO all my best came out. And they all showed the same thing. Down to the southern upland south of Clavius to the crater Newton, Same thing...

When the terminator is well placed on showcase areas of the moon the 10" excels, but the TSA120 offers a no scatter pure view of them it has grabbed my attention- again. I know for a fact that when the terminator is offering weak contrast like that night, I will reach for the TSA120 and leave the dob in the house. The frac will outperform it and show more detail than the 10" again, and again.

Gerry

I understand these concepts of quality refractor beating out larger reflector. Can be many reasons why that could occur i have no doubt. But i do think this has to be seen in the context mostly of visual. (I know your not suggesting otherwise) That wouldn't be the case for imaging though. There are many reasons why that is so, too numerous to go into detail about. So as mentioned i have no doubt for visual these things can happen ( likely not all the time ) But the weaknesses of smaller scopes on lunar and planetary imaging are so vast. It really wouldn't matter if it was the most perfect refractor ever made, A mass produced much larger Chinese mirror will still kill it stone dead. Probably why we get lots of these threads saying what you just did. But we never get images showing that difference.  The eye sees things in a different way to a camera. Some better some worse. But it likely explains these kind of observations which we see and hear about frequently. 

This is never discussed. Maybe because these kind of threads are always visual orientated. Indeed under that context. I am not even sure if i should have pointed out what i just did. But i have to be honest. i think it every time i read these kind of observations. Not because i doubt. which i definitely do not. But because I've seen the limitations of smaller optics. Some superb, on lunar imaging for example

[jetstream]

@neil phillips Yes, I agree and Ive searched long and high for images to match my visual views and most do not come close. A preferred lunar set up by many is a C14 which by design reach a .25 wave level of optical quality CO considered, maybe.  My brief but extensive research into the programs used to produce excellent images are a major factor in the images them self and this is not a criticism in any way. At some point I'll image the moon and have a 224MC up on deck. Its amazing what the SCT/newt scopes can achieve on the moon imaging!

Thanks for the comments Neil! Its much appreciated, Gerry

 

Edited April 6, 2023 by jetstream

[neil phillips]

Just now, jetstream said:

@neil phillips Yes, I agree and Ive searched long and high for images to match my visual views and most do not come close. A preferred lunar set up by many is a C14 which by design reach a .25 wave level of optical quality CO considered, maybe.  My brief but extensive research into the programs used to produce excellent images are a major factor in the images them self and this is not a criticism in any way. At some point I'll image the moon and have a 224MC up on deck. Its amazing that the SCT/newt scopes can achieve on the moon imaging!

Thanks for the comments Neil! Its much appreciated, Gerry

 

I worry when i have these kind of conversations, because i think it can be taken in the wrong way. And yes that is why the hexagon on Saturn was most readily imaged with a C14.  I think as refractors get larger as long as the quality is maintained this gap can narrow somewhat, and things are not quite as clearly cut and dry. But again this is part of the explanation, a premier 7" refractor is going to do better than a  5" imaging the planets and moon. Even though your eye could discern more, or in a better way than the larger instrument on this occasion. 

I think the explanation may be. A camera has a different set of problems to the eye, and visa versa. Its interesting understanding why this is so.  I do not believe like some do the eye is always superior to the camera. But i also do not believe the camera is always superior to the eye. I think there is a range of strengths and weaknesses inherent with both. Also one thing the camera does not have is a brain. Which clearly plays a part in discerning a image in a way the camera is not capable of. Having said that. There are certainly situations where i have seen a camera outperform my eyes through a telescope.  An example obviously is EEA there is no way without assistance the eye can detect that faint. Another is image size. Often its easier to see a large image on screen than it is, through a small lens via a telescope. Especially a 6 arcsecond Mars. Experience of the observer could narrow that difference considerably. Compared to a beginner for example. So many questions these kind of observations bring up. Its interesting though trying to understand it all 

Edited April 6, 2023 by neil phillips

[jetstream]

10 minutes ago, neil phillips said:

A camera has a different set of problems to the eye, and visa versa. Its interesting understanding why this is so. 

And I know just the fella to tell us! Hey @vlaiv Vlad! To re cap the difference between a camera and the eye with respect to how they "see" can be described as?

Can angular resolution describe all of the detail of features seen? or can MTF describe some features in those features described by the former?

Gerry

[neil phillips]

3 minutes ago, jetstream said:

And I know just the fella to tell us! Hey @vlaiv Vlad! To re cap the difference between a camera and the eye with respect to how they "see" can be described as?

Can angular resolution describe all of the detail of features seen? or can MTF describe some features in those features described by the former?

Gerry

I wonder if its something he has ever discussed ?  Cant remember seeing a discussion. Wouldn't you need to be part astronomer. Part electronic engineer. Part optometrist ? Don't worry he probably is. 😄

[vlaiv]

Eye sees very differently than camera does. I'll name a few things that make up this difference.

1. Exposure time.

Eye/brain combination integrates for about 15-30ms (think of movies being played at 30fps and screen refresh rates being 60hz).

Camera can expose for few milliseconds. 2ms is exposure time not uncommon for lunar imaging.

Seeing affects visual performance of the telescope much more - and will "equalize" things between large and small aperture much more. We often need to wait for moment of good seeing to see some feature. With imaging - it will be captured even if we were not able to see it in that period of time - because our brain/eye combination blurred the image - or helped seeing blur it.

2. Dynamic range and contrast

When we capture image on the screen - we have very moderate level of dynamic range. Eye is performing close to its optimum as far as resolving goes - it's not dark adapted even in slightest - it is fully in photopic mode of operation.

When we are at the telescope in the darkness - eye is in mesopic / scotopic mode (depends on conditions), and here aperture plays a role. For the same magnification - larger telescope will throw up brighter image. Although, it can't throw up brighter image of the moon then viewed by naked eye - if we are dark adapted even a bit - it can be blinding.

Compare that to car headlights. During the day - looking directly at car headlights is not troubling at all. Look at the same headlights at night and you'll feel blinded. Car headlights did not change - but environment did.

This amounts to two things.

I think that finer contrast details are possible in smaller aperture because of the amount of light / dynamic range and that this difference would drop if one removes dark adaptation from the equation - one should do planetary / lunar observation in lit up environment rather than in darkness.

3. Level of sharpening and reconstruction.

Our brain can't sharpen up things like computer can. It can do other things - we notice detail by prolonged observation - we need to tease out detail. We don't need to do that in images because of observing comfort. On the other hand - due to sharpening image produced by telescope can actually be sharper / more detailed than what the same telescope produces at focal plane.

This is due to nature of blur and how it works.

[jetstream]

@vlaiv whats your thought about Peaches take on things?:

"

Understanding Resolution and Contrast

Two points it is important to understand is the resolution a telescope can provide, and how the contrast of the objects we are imaging affects is related to what can be recorded. Its often seen quoted in the Dawes or Rayleigh criterion for a given aperture. Dawes criterion refers to the separation of double stars of equal brightness in unobstructed apertures. The value can given given by the following simple formula:

115/Aperture (mm.) For example, a 254mm aperture telescope has a dawes limit of 0.45" arc seconds. The dawes limit is really of little use the Planetary observer, as it applies to stellar images. Planetary detail behaves quite differently, and the resolution that can be achieved is directly related to the contrast of the objects we are looking at. A great example that can be used from modern images is Saturn's very fine Encke division in ring A. The narrow gap has an actual width of just 325km - which converts to an apparent angular width at the ring ansae of just 0.05" arc seconds - well below the Dawes criterion of even at 50cm telescope. In `fact, the division can be recorded in a 20cm telescope under excellent seeing, exceeding the Dawes limit by a factor of 11 times!. How is this possible?.

As mentioned above, contrast of the features we are looking at is critical to how fine the detail is that we can record. The Planets are extended objects, and the Dawes or Rayleigh criterion does not apply here as these limits refers to point sources of equal brightness on a black background. In fact it is possible for the limit to be exceeded anywhere up to around ten times on the Moon and Planets depending on the contrast of the detail being observed/imaged."

https://www.damianpeach.com/simulation.htm

 

[mikeDnight]

37 minutes ago, jetstream said:

A great example that can be used from modern images is Saturn's very fine Encke division in ring A. The narrow gap has an actual width of just 325km - which converts to an apparent angular width at the ring ansae of just 0.05" arc seconds - well below the Dawes criterion of even at 50cm telescope. In `fact, the division can be recorded in a 20cm telescope under excellent seeing, exceeding the Dawes limit by a factor of 11 times!. How is this possible?.

 

These are all excellent posts!

 I truly believe that super fine features such as the Enke division, actually discovered by Kater, not Enke, can be detected in smaller apertures than 200mm. I say this because a number of years ago during the 2000's, when Saturn was high in northern hemisphere skies and the rings were wide open, I've observed it many times using my FS128. Telescopically it appears to be very close to the outer edge of the A ring, but it can be seen extending for quite some distance around the anse. It appears very different to the dusky Enke minima which is not a hard linear feature. Interestingly, the Enke gap nearly always appeared more easily evident in the proceeding anse. I never did try to understand why that would be?  

 

Edited April 6, 2023 by mikeDnight

[jetstream]

7 minutes ago, mikeDnight said:

These are all excellent posts!

 I truly believe that super fine features such as the Enke division, actually discovered by Kater, not Enke, can be detected in smaller apertures than 200mm. I say this because a number of years ago during the 2000's, when Saturn was high in northern hemisphere skies and the rings were wide open, I've observed it many times using my FS128. Telescopically it appears to be very close to the outer edge of the A ring, but it can be seen extending for quite some distance around the anse. It appears very different to the dusky Enke minima which is not a hard linear feature. Interestingly, the Enke gap nearly always appeared more easily evident in the proceeding anse. I never did try to understand why that would be?  

 

Years ago I reported both Enke observations in the VX10 which raised some eyebrows as I did not find them hard.... Saturn is such a stunningly friendly telescope object to view. Eventhough seeing here can get very good, I tend to obs around 300x-350x on the moon and planets. This is in my best lunar/planetary scopes ie TSA120/VX10/15" dob.

Great observation using the FS128 Mike!!

My nature says I got to find out "why" with all this stuff.

[GordonD]

Fascinating read Gerry.

Of course the down side is you have not helped me suppress a desire for a TSA120 (even though I have a perfectly good 120 already).

But it's great to hear about your experiences and thoughts.

[vlaiv]

44 minutes ago, jetstream said:

In `fact, the division can be recorded in a 20cm telescope under excellent seeing, exceeding the Dawes limit by a factor of 11 times!. How is this possible?.

Well, that is quite misleading.

Problem is in use of the term "resolve". It is not the same as detect.

I'll show you an example where telescope of 7mm (our eyeball) is able to see contrast difference of feature that is x1000 less than it is able to "resolve".

We see stars on a starry night, right?

How is that possible? How can we see something that is way beyond resolution of our eyeball, even beyond of resolution of large aperture telescopes by factor of x1000 or more ....

Stellar disk, depending on actual star will present profile that is often in micro arc seconds. Some close and large stars are few milli arc seconds (mas) in diameter. Yet we see them.

How is this possible?

Well - simply because we see them. It has nothing to do with resolving them. When we talk about aperture and resolution - we should not talk about being able to see singular feature like point source or a line - but rather ability to resolve two close feature - to distinguish. Be that pair of stars or two close lines or something similar.

When we talk about point sources like stars or maybe division in Saturn's rings or a rile on the surface of the moon - here is what happens:

what is very narrow sharp peak or dip in light intensity (star will be peak and division in rings will be dip in light intensity) - becomes much less bright or dark shallow smooth dip.

If intensity of that shallow bump or dip with respect to background is too small to trigger our JND - just noticeable difference - we won't see it. But if it is large enough to trigger it - we will notice it.

With telescope that has more resolving power - that bump or dip is narrower and higher intensity - so the contrast with respect to background is higher - things are easier to see. That is why we can "resolve" some features in larger apertures while missing them in smaller ones - but we are in fact not resolving - just noticing that something is there - without being able to tell its general shape or if its one object or more.

 

[jetstream]

1 hour ago, vlaiv said:

Well - simply because we see them. It has nothing to do with resolving them. When we talk about aperture and resolution - we should not talk about being able to see singular feature like point source or a line - but rather ability to resolve two close feature - to distinguish. Be that pair of stars or two close lines or something similar.

I'm also very curious about an observation comparing my TSA120 to the SW120ED. On a targeted crater the Tak showed some fine (ish) ledges on the top of the crater wall, whereas the120ED did not. I was wondering if the "sag" in the MTF graph between the two optics could be the cause. The Tak has excellent optical quality and most likely a very straight line just under perfect on the MTF graph, guessing 1/8-1/10 wave SA or equivalent. The SW120ED I believe to be operating at just better than 1/4 wave equivalent to SA.

I wonder if this sag in the 120ED graph, reduces the spacial frequencies seen and is the answer to the differences seen between the 2 scopes of same aperture and f ratio?

[vlaiv]

13 hours ago, jetstream said:

I'm also very curious about an observation comparing my TSA120 to the SW120ED. On a targeted crater the Tak showed some fine (ish) ledges on the top of the crater wall, whereas the120ED did not. I was wondering if the "sag" in the MTF graph between the two optics could be the cause. The Tak has excellent optical quality and most likely a very straight line just under perfect on the MTF graph, guessing 1/8-1/10 wave SA or equivalent. The SW120ED I believe to be operating at just better than 1/4 wave equivalent to SA.

I wonder if this sag in the 120ED graph, reduces the spacial frequencies seen and is the answer to the differences seen between the 2 scopes of same aperture and f ratio?

In principle - yes, but there are a lot of small details.

Maybe simplest way to explain what is happening is with Strehl ratio.

We know Strehl ratio to be sort of "percent" removed from perfect optics - but here is one important thing - it is actually a function with "height" and that height is related to above concept of bulge and dip in brightness. Higher the Strehl for some telescope - deeper that dip that represents a gap or line feature - more contrast there is compared to surrounding brightness - easier to see it.

Now in reality, things get complicated - there is no single Strehl for refractors - there is Strehl vs wavelength graph - that looks like this:

So each wavelength will have different peak.

Final result then goes like this:

- for each different wavelength of source (be that star or the light reflected of the moon or Saturn's rings) - and its intensity

- that Strehl peak is applied to see how much contrast it will have versus surroundings

- it is then "added" to the sum of light (superimposed or layered like layers in photo shop)

- depending on sensitivity of human eye to that particular wavelength - which also depends on environmental factors (like photopic / mesopic / scotopic mode mainly).

This shows that we really need to pay attention to scotopic vs photopic vision if we have ED optics. ED optics does not control well short wavelengths (purple fringing) - but we are much more sensitive to those wavelengths in scotopic mode and those will reduce contrast significantly (think short and cheerful achromat on planetary - detail washed out in purple haze).

So yes, spherical aberration will have impact, but so will everything else that is related to optical quality - and above shows why Strehl is convenient way to express things (although it is related to single wavelength and things like polychromatic Strehl don't make much sense - as we don't know two things in advance - spectrum of the source light and our adaptation so sensitivity over wavelengths for it to make much sense).

[jetstream]

Thank you for being a continuos resource Vlad it is truly appreciated and I understand the above, great explanation using the PSF.  I hope those reading dont take all this as a criticism of any optics involved or that this thread is being used to promote or "pump"  up one brand. I really do have an interest in all this stuff, and yes my TSA120 is being used as a test reference so to speak.

The PSF graph and your explanation have allowed me to visualize whats going on much better than before.