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Equipment Discussions >> Refractors

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BKBrown
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Another Jupiter comparison...food for thought new
      #5562861 - 12/09/12 05:53 PM Attachment (442 downloads)

Hi folks, been a while since I posted here...it's been an amazing and busy Jupiter imaging season. While the bulk of my work leading up to opposition was done with my C11 Edge HD, I also did some small bore imaging with my SW100ED. Again the results were highly gratifying, it's amazing how much detail that four incher can pull in. And while the Skywatcher image sits next to a very nice shot from the C11, this is not about comparing the two since the big SCT is clearly in another weight class. I thought you might find it informative to see how much detail the smaller scope can pick up. Check out the GRS w/ interior detail, the Oval BA "doughnut", the strange dark small spot chasing the Oval BA, several of the light tone south polar ovals, and details in the equatorial belt including one of the long, whispy blue streamers. All-in-all a terrific amount of detail. I hope you enjoy these shots, and hope that anyone thinking they have to have a big OTA to do planetary imaging will think otherwise after checking out these images. Thanks for dropping by!

Clear Skies,
Brian

Edited by BKBrown (12/09/12 06:18 PM)


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nirvanix
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Re: Another Jupiter comparison...food for thought new [Re: BKBrown]
      #5562869 - 12/09/12 06:00 PM

Beautiful shots. 4 inch frac is a wonderful, versatile instrument.

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Eddgie
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Re: Another Jupiter comparison...food for thought [Re: BKBrown]
      #5562893 - 12/09/12 06:15 PM

Over the years, there have been occasional posts on the Solar System Imageing forum taken by a variety of small telescopes, and many have been quite good. Heck I have seen pictures of the moon taken with much smaller scopes than a 100mm aperture that were fantastic.

So, no surprise that you can get a good result from a small telescope, and I agree, it is not necessary to have a big telescope to take pictures of the planets.


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seafury
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Re: Another Jupiter comparison...food for thought new [Re: Eddgie]
      #5563491 - 12/10/12 02:25 AM

Hi I just wondered do you see images like those photos when you view visualy through your telescopes? or does the camera bring out far more detail


thanks Gordon


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Mr Onions
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Re: Another Jupiter comparison...food for thought new [Re: seafury]
      #5563515 - 12/10/12 03:31 AM

Great images,thanks.

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Sasa
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Re: Another Jupiter comparison...food for thought new [Re: seafury]
      #5563555 - 12/10/12 04:26 AM

The times when people were seeing on planets more than on images is far gone. At that time, people were making just single shots. Nowadays, with the video capability and excellent software, the images are far better. You can compare excellent Bill picture through ED100, with my humble drawing through the same telescope:



The level of details is clearly smaller. And on top of that, many details from the drawing were quite hard to spot. So, the overall feeling when you look at the eyepiece is still much worse than what is finally catched in the sketch. It takes me typically of about 20 minutes of observing and drawing to catch them.


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astrogeezer41
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Re: Another Jupiter comparison...food for thought new [Re: Sasa]
      #5563809 - 12/10/12 09:27 AM

But it needs to be said that that is a very fine sketch!
Thanks for doing it and sharing it.
-Robert


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jrbarnett
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Re: Another Jupiter comparison...food for thought new [Re: BKBrown]
      #5563877 - 12/10/12 10:11 AM

The C11 Edge image, in particular, is marvelous. The SW100ED image is a little soft, though. That's unusual for a refractor. Typically the image will be sharper, even if not as detailed. I remember one of your old posts where you posted a C11 versus TEC 140 image set. The TEC's image was much sharper than the C11's in that thread, albeit less detailed.

Great work, in any case.

- Jim

Edited by jrbarnett (12/10/12 10:14 AM)


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mikey cee
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Re: Another Jupiter comparison...food for thought new [Re: seafury]
      #5564020 - 12/10/12 11:50 AM

Quote:

Hi I just wondered do you see images like those photos when you view visualy through your telescopes? or does the camera bring out far more detail


thanks Gordon


Gordon....with my 10" Istar I can actually obtain a view very similar to the 100mm's pic. That was with about a 8-9/10 seeing. Only difference was the slight CA at the 515x with my binos with a pair of 20mm 66° plossls. Of course I failed to mention the image was very sharp, not blurred as in the pic. The spot between GRS and BA oval was like a moon shadow. The actual color intensity was just a tad less because of the pic processing. ;Mike

Edited by mikey cee (12/10/12 11:48 PM)


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seafury
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Reged: 01/18/12

Re: Another Jupiter comparison...food for thought new [Re: mikey cee]
      #5564124 - 12/10/12 12:58 PM

Hi Guys thanks for all the the replies I was a bit worried I have a Bresser 120mm Refractor and with a 7mm eyepiece can only just make out the bands let alone any detail

Gordon


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Gord
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Re: Another Jupiter comparison...food for thought new [Re: mikey cee]
      #5564126 - 12/10/12 12:59 PM

The camera's definitely bring out more detail, especially higher contrast and color saturation.

That being said, I find the view above for the C11 is somewhat like the view through the C14, just with the contrast/color turned down some. A lot of the fine details like swirls, ovals, whisps and rolls are all visible, and the color is very prominent (and about the hue's shown in the image).

I find the C8 shows more details than in the refractor image, and a lot sharper that this too. Kind of like the C11 image, just less detail and colors (like the blue's and red's/brown's) are much less striking than in the C14.

I find the 6" achro to show the differences between light an dark areas more sharply than the C8, but with less small details and less color too. The contrast isn't as strong as in the refractor image here, but the amount of details are fairly similar and a lot sharper visually than this image. Not as sharp as in the C11 image though.

I find the C10 newt to be in between the C8 and C14. It shows things perhaps sharper than any and with more fine gradients, but less overall details and color than the C14.

Overall I find them to kind of go in sequence of size in terms of details. This continues down with the smaller scopes I have as well.

Clear skies,


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Jeff B
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Re: Another Jupiter comparison...food for thought new [Re: Gord]
      #5564168 - 12/10/12 01:14 PM

How about displaying both images at the same focal ratio, F25 for example.

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SteveG
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Re: Another Jupiter comparison...food for thought new [Re: Jeff B]
      #5564376 - 12/10/12 03:23 PM

The right side picture is very typical to what I see in my 4.7" apo on a decent night when the atmosphere steadies.

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Eddgie
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Re: Another Jupiter comparison...food for thought new [Re: Gord]
      #5564580 - 12/10/12 05:35 PM

The images provided offer a great example of contrast transfer.

We often hear that unobstructed instruments have better contrast transfer, but that is only relative to obstruced intruments of the same aperture.

Using these pictures, I can give a perfect example.

Contrast transfer describes how much contrast will be lost for a detail when it is formed at the focal plane.

All telescopes loose contrast. Even the most perfect ones and even the largest ones. The question is only "How much."

Notice four specific details.

The first it the small dark spot between the GRS and oval BA. This is a deatil that starts at the targe with a lot of contrast. Images show it as very dark against a very light background. Again, the key here is that is starts with very high contrast.

Next, notice the three small ovals in the southern polar regions. If you look at the image, you can see that these ovals are actually quite large. In fact, at least one of them appears larger than the dark spot I mentioned earlier.

Now notice that in the larger aperture, the spot looks quite dark and proportionatly larger than in the smaller scope. The diffration at the edges of the bright area around the spot in bleeding over into the spot itself cauing it to look more like a dot than a spot. It's angular size will appear smaller (even if the image were blown up to the same size).

And this is what causes contrast to be lost. A black line on a white background will appear to be dark gray and narrower in the scope with more contrast loss. A dark feature will appear ligher and smaller.

Now this detail started at the target with quite a bit of contrast, but it is being reduced by the diffraction caused by the small aperture.

Next, look at the oval. In the larger scope, they stand out quite well. We see three distinct ovals and all appear to be similar in size to the very dark spot.

But these three features started out with much lower contast at the target than the dark spot. Because the larger aperture does not loose as much contrast though, they still stand out fairly well in the image taken with the larger aperture.

Diffractoin causes a brigher area on a darker background to actually appear larger than it is, but if the difference in contrast is not very high, the ligher area seems to disappear into the darker background, and we see this happeing in the image in the smaller instrument. The ovals, even though they are as big as the dark spot, are very difficult to see even though they clearly start out with sufficient angular size at the target! You can look at the image and clearly see that in the larger aperture at least one of them is bigger than the dark spot!

But the dark spot is still pretty easy to see. And that is because it stated with enough contrast so that even though a lot of the contrast was lost, there was still enough to allow it to be seen easily. But not so with the ovals. Same size, but since they already started with very low contrast, they have lost enogh contrast due to diffraction that they have almost dissolved into the darker area around them.

I agree with the OP that you can do great imaging with smaller scopes! And this is in no way an attack on small scopes.

What it was for me though was a perfect opportunity to explain how contrast transfer affects the image, and why more detail is visible in the image taken with the bigger scope.

Both are great images. Both appear to be very good telescopes. But the smaller the aperture, the more fairly decent size details that start with very low contrast will be lost or difficult to detect.

Imaging with any size camera can be fun, but when someone askes my why I think aperture is so important is because it is easy to get better contrast by using a bigger telescope.


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BKBrown
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Re: Another Jupiter comparison...food for thought new [Re: Eddgie]
      #5564761 - 12/10/12 07:37 PM Attachment (95 downloads)

Lots of great responses so far, I'm glad folks are engaged in this thread. Thanks everyone, and a special thanks Eddgie for your comments, and Sasa for the very cool drawing. Jim - you are correct about the slightly softer 100ED image, this is largely due to enlarging it to make details stand out, the original is roughly 30% smaller and it's sharper...but it's neat to see how much you can pick out on both images. I replaced the C11 with the TEC this weekend and am now waiting for the weather to clear so I can get some quality planetary imaging time in; I now have an all refractor suite on board in the observatory and should have new pix soon.

Clear Skies,
Brian

Edited by BKBrown (12/10/12 07:38 PM)


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GeneT
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Re: Another Jupiter comparison...food for thought new [Re: BKBrown]
      #5565057 - 12/10/12 10:54 PM

Actually, I was impressed with the excellent images captured with both telescopes.

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zjc26138
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Re: Another Jupiter comparison...food for thought new [Re: GeneT]
      #5565171 - 12/11/12 12:00 AM

Excellent comparison. Thanks Brian!

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JMW
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Re: Another Jupiter comparison...food for thought new [Re: zjc26138]
      #5565326 - 12/11/12 02:01 AM

The Jupiter images look great. I don't the right camera for planetary imaging but I am always amazed with the power of stacking hundreds of short exposures.

I have my TEC 140 on my mount tonight and Jupiter was excellent viewing. Next weekend with clear weather I will mount my SV115T on top of my C11EdgeHD. I finally have enough very expensive AP counterweights to balance the load of both scopes on my AP900. It will be fun doing some back and forth viewing between the pair of scopes. My C11EdgeHD has powered vent fans to help it keep up with the constantly dropping temps through the night. My SV115T seems to be ready for viewing without cool down issues.


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Samir Kharusi
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Re: Another Jupiter comparison...food for thought new [Re: BKBrown]
      #5565522 - 12/11/12 08:33 AM

I think that your fine C11 image is closer to what is possible under ideal seeing than the 100mm APO's. Perhaps the seeing did change enough over the hour time difference? I have simulated views via varying apertures from 3" to 18" here that may be of interest.

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Eddgie
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Re: Another Jupiter comparison...food for thought new [Re: seafury]
      #5565858 - 12/11/12 12:29 PM

Sorry, I missed your question:
Quote:

Hi I just wondered do you see images like those photos when you view visualy through your telescopes? or does the camera bring out far more detail





Genarally, the answer is that while I can see a great deal of the details given either excellent seeing and/or great patience, I think the average observer would look through the eyepcie of a C14 and say "It dosn't look like the pictures, dude!"

And they would be right.

The human eye does not have the contrast sensitivity threshold of a modern CCD camera.

In a large scope when viewing Jupiter, the eye is working just above the scotopic vision threshold, in a mode called Mesoptic. Some of the color perceptors are firing (this is of couse how you know, because in scotopic mode, you only see shades of gray.

I photopic mode, the eye has a contast sensitivity of perhaps 2% meaning that a detail has to have at least 2% difference in contrast between it and the area around it to be easily detected.

When the eye goes Scotopic, the amount of contrast required for the observer to see a detail is quite significently increased, and this actually varies considerable with observer... It is one of the true big differences people have in their vision that cannot be corrected with lenses (or the telescopes focuser knob).

Also, in scotopic mode, the eye has the best sensitivity to low contrast detail when it occupies a very specific spatial frequency (the extent of the angular size in arc minutes of apparent field ) that is about 5 to 9 arc minutes. If the detail gets much bigger or much smaller than this, it can be difficult to see it.

For Jupiter in a large scope using Mesoptic vision, the figures are somewhere between this. Most people will have a contrast sensitivity that ranges from about 5% for large details down to about 10% to as much as 15% for the smallest detail.

In other words, all of the detail is there, but the human eye is just not all that good at seeing it.

This is why when you read about MTF charts, you hear words like "the important low and mid frequencies" to visual observing because these are the frequenceies that we can magnifiy and still have sufficient brightness to see them well. The low and mid frequencies basically means detail that is a couple of Airy Disk diameters or larger.

If we overmagnify, to make the finest detail big enough to see well, it looses brightness, and this makes it harder to detect.

In a nutshell, the answer is no, I can't see the same level of detail using the eye alone.

Using the C14 on a night of excellent seeing, I will be luck to see the same clarity as shown in the C11 picture on this link and it takes tremendous concentration. None but the highest contrast details leap out. At the eyepiece they are very subtle and require a lot of patience and persistence. Jupiter in a single glance will not show nearly as much detail as seen in the C11 image at thet top of this post. A lot of it is there, but you really have to work to see it and the smallest angular detail will start to dim out if I over-magnify because the image dims so much.

Remember that many of these pictures are taken at hugh magnificaitons! I use a barlow in my C14 to image giving it a focal lenght of almost 4000mm! Try using a 4" scope at 500x and see what happens to the crispness of the image! I don't care how perfect the scope is... The image will look soft visually. But the camera shows huge amounts of detail!

The camera benefits from having a lower contrast sensitivity threshold than the eye, and modern stacking eliminates the noise that plagues both CCD chips and the human eye when the image gets dim.

It is just that modern CCD technology gives the camera a better contrast sensitivity and stacking enhances the presence of low contrast detail..

Forgive the long answer. I want people to know that Jupiter never really looks like it does in the pictures, but a lot of the detail is there for someone like Norme that has the patience to look for it.

MTF is another way of saying "Sharpness." A scope with better MTF produces a "Sharper" image because details stand out better and have more crisp borders (hence the example of the various ovals in the two pictures) and what the instrument can do and what the eye can process as compared to a CCD chip and softwere enhancement are two very different things.

Edited by Eddgie (12/11/12 12:37 PM)


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