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MKV
Carpal Tunnel
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Reged: 01/20/11

Re: Optimized Newts vs APOs new [Re: Dave O]
      #5586680 - 12/24/12 06:07 AM

Quote:

Again (for those who failed to read the opening post), the challenge was between equal apertures, not equal cost ...



Equal apertures were compared two posts above, Dave.

Mladen


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Mark Harry
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Re: Optimized Newts vs APOs new [Re: Dave O]
      #5586694 - 12/24/12 06:44 AM

Me personally, I can see a noteable difference from 0 to 15%. All you have to do, is look at the southern half of Jupe, in the "white" belt and the polar cap area.
If you drop down to the 45% pic, this area I mention is for all intents, totally void of any faint but detectable detail; and just a couple smears of smooth shading.
Looking at the obvious knots of swirls that are circled is not the correct way to assess the observation Dave mentioned.
M.


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MKV
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Re: Optimized Newts vs APOs new [Re: Mark Harry]
      #5586713 - 12/24/12 07:11 AM Attachment (19 downloads)

Quote:

Me personally, I can see a noteable difference from 0 to 15%. All you have to do, is look at the southern half of Jupe, in the "white" belt and the polar cap area.



You see notable difference between 0% and 15% obstruction? You think you could look through one telescope, then run to the next and immediately tell the difference? I think MTF data would say otherwise. Never mind the atmospheric effects...

Mladen

Edited by MKV (12/24/12 07:15 AM)


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kfrederick
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Re: Optimized Newts vs APOs new [Re: MKV]
      #5586718 - 12/24/12 07:22 AM

The HST images show big spikes on all stars That is obstruction effects .Just think how much contrast is lost .Real defect easy to see .

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MKV
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Reged: 01/20/11

Re: Optimized Newts vs APOs new [Re: kfrederick]
      #5586737 - 12/24/12 07:57 AM

Quote:

The HST images show big spikes on all stars That is obstruction effects .Just think how much contrast is lost .Real defect easy to see .



Kfrederick, we were talking about small telescopes of equal aperture and an optical window (or 3-vane spider) for secondary support. Three-vane spiders actually produce negligibe loss of conrast.

Another thing I wanted to mention is that it takes a central obstruction equal to 33.2% of the clear aperture to produce image degradation equivalent to 1/4 wave wavefront error. Worth remembering.

Mladen


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Dave O
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Reged: 12/21/11

Loc: Sri Lanka
Re: Optimized Newts vs APOs new [Re: MKV]
      #5586741 - 12/24/12 08:00 AM

Quote:

You see notable difference between 0% and 15% obstruction? You think you could look through one telescope, then run to the next and immediately tell the difference? I think MTF data would say otherwise. Never mind the atmospheric effects...

Mladen




My 3 1/2" Questar provides better images visually than these digitized images do ... just saying.


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Jon Isaacs
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Re: Optimized Newts vs APOs new [Re: Dave O]
      #5586751 - 12/24/12 08:15 AM

Quote:

I believe that the 'challenge' was for equal aperture? Not very fair tossing up a 6" APO against a 10" ...




Whether it's fair or not and I think it's fair, it's reality.

Ed's challenge was the most difficult conceivable, equal aperture. Just about any other challenge would be a slam dunk for the Newtonian.

- Equal aperture: close

- Equal dollars: Newtonian

- Equal weight: Newtonian

- ATM built: Newtonian

When I look through the eyepiece, it's the view that counts. My 10 inch run of the mill commercial Dob clearly out performs my 4 inch apo on the planets and double stars, it's a fact of life...

Jon


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kfrederick
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Re: Optimized Newts vs APOs new [Re: MKV]
      #5586792 - 12/24/12 08:53 AM

If 1/3 CO =1/4 pv then what does 1/6= 1/8?? Use two small lens forget about optical windows spiders Central obstruction and coma corrector Back focus on my 20 inch is 21inches Makes things easy if you need it for a bino or Camera .For two small lens .and a fancy holder.

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Mark Harry
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Re: Optimized Newts vs APOs new [Re: MKV]
      #5586805 - 12/24/12 09:04 AM

Yes, MVK some folks know how to pay attention to what their eyes can detect/are capable of. Try it sometime, and get away from the simulations at the keyboard. The simulations are not that consistent or reliable. As DaveO mentions, those pics look like they were made in a much smaller scope, fwiw. To me as well.
Not everyone has the same capabilities, though. It's possible yours is substandard??? Ask the optometrist.
M.


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Pinbout
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Re: Optimized Newts vs APOs new [Re: Mark Harry]
      #5586842 - 12/24/12 09:22 AM

I think I need to check my eyes cause everything gets really sharp when I back away from the eyepiece when viewing planetary detail. I can have my eye 2" away from a plossl, I loose the fov but I'm only looking at the planet. I know I'm strange but...

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MKV
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Reged: 01/20/11

Re: Optimized Newts vs APOs new [Re: Dave O]
      #5586871 - 12/24/12 09:33 AM

Quote:

[My 3 1/2" Questar provides better images visually than these digitized images do ... just saying.



Maybe your atmosphere is better then ours. It's irrelevant what image you use, the central obstruction effect would be the same had I used sharper images. You still have a gradual loss of detail and contrast. I just think using those stacked Photoshop images is not what one sees, and therefore cannot judge.

BTWm, Questar still makes fantastic claims that defy everything we know about optics. In this Questar brochure, which I remember back from the late 70's, the company claims a 3.5 inch clearly resolves license plate number (1/4 inch wide) at a distance of 3.5 km (2.2 miles) over water (!). That's a resolution of less than half an arc second, and theory (Dawes limit = 4.6/D in inches) says 3.5 inch aperture (assuming wavelength of 0.55 um) can resolve no more than 1.3 arc seconds under ideal conditions.

Mladen


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Dave O
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Re: Optimized Newts vs APOs new [Re: MKV]
      #5586878 - 12/24/12 09:37 AM

Quote:

Quote:

[My 3 1/2" Questar provides better images visually than these digitized images do ... just saying.



Maybe your atmosphere is better then ours. It's irrelevant what image you use, the central obstruction effect would be the same had I used sharper images. You still have a gradual loss of detail and contrast. I just think using those stacked Photoshop images is not what one sees, and therefore cannot judge.

BTWm, Questar still makes fantastic claims that defy everything we know about optics. In this Questar brochure, which I remember back from the late 70's, the company claims a 3.5 inch clearly resolves license plate number (1/4 inch wide) at a distance of 3.5 km (2.2 miles) over water (!). That's a resolution of less than half an arc second, and theory (Dawes limit = 4.6/D in inches) says 3.5 inch aperture (assuming wavelength of 0.55 um) can resolve no more than 1.3 arc seconds under ideal conditions.

Mladen




Have never looked at license plates. But, I know what I see at the eyepiece, when looking at Jupiter.


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MKV
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Re: Optimized Newts vs APOs new [Re: Mark Harry]
      #5586886 - 12/24/12 09:44 AM

Quote:

es, MVK some folks know how to pay attention to what their eyes can detect/are capable of. Try it sometime, and get away from the simulations at the keyboard. The simulations are not that consistent or reliable. As DaveO mentions, those pics look like they were made in a much smaller scope, fwiw. To me as well.
Not everyone has the same capabilities, though. It's possible yours is substandard??? Ask the optometrist.
M.



Nothing new here, just being your usual wonderful self, Mark, right? Dishing our your opinions and now even practicing Internet medicine (got a license?)...

Mladen


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Mark Harry
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Re: Optimized Newts vs APOs new [Re: Dave O]
      #5586893 - 12/24/12 09:47 AM

The last planet pic post, I had to back away from the monitor! The ones on pg 4 were fine.
(They do not look like simple enlargements...)
M.
MVK, at what level of power/inch do you need to be barely able to see the airy disc? (least amount needed to just make the disc barely but plainly detectable?)


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MKV
Carpal Tunnel
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Reged: 01/20/11

Re: Optimized Newts vs APOs new [Re: Dave O]
      #5586899 - 12/24/12 09:50 AM

Quote:

Have never looked at license plates. But, I know what I see at the eyepiece, when looking at Jupiter.



By I don't know what you see, Dave. I mentioned Fatima in 1917 a couple of pages back, where tens of thousands of people "witnessed" the Sun doing a 'dance' and 'falling' towards the earth; some even reported the earth getting hotter. Too bad the cameras didn't see anything of the sort.

Mladen


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MKV
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Re: Optimized Newts vs APOs new [Re: Mark Harry]
      #5586905 - 12/24/12 09:58 AM

Quote:

The last planet pic post, I had to back away from the monitor! The ones on pg 4 were fine.
(They do not look like simple enlargements...)
M.
MVK, at what level of power/inch do you need to be barely able to see the airy disc? (least amount needed to just make the disc barely but plainly detectable?)



I think you've been reading too many conspiracy theories, Mark. The images are from Aberrator, imported into Paint, stitched together unaltered and saved as one picture 1;1 ratio. When you open them in "My Pictures" you can zoom, then copy the screen and put the enlarged image into the Paint and save. Simple enlargement.

As for the Airy disc, I always use a short fl eyepiece, maybe a 6 or a 4 mm. Power/inch will vary with a telescope.

Oh, by the way, as for your disdain for simulations, OSLO is a simulation and you seem to use it all the time.

Mladen

Edited by MKV (12/24/12 10:00 AM)


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Dave O
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Re: Optimized Newts vs APOs new [Re: MKV]
      #5586935 - 12/24/12 10:21 AM

Quote:

Quote:

Have never looked at license plates. But, I know what I see at the eyepiece, when looking at Jupiter.



By I don't know what you see, Dave. I mentioned Fatima in 1917 a couple of pages back, where tens of thousands of people "witnessed" the Sun doing a 'dance' and 'falling' towards the earth; some even reported the earth getting hotter. Too bad the cameras didn't see anything of the sort.

Mladen




I have never seen the "Sun Dance"; but I do know that my Questar provides much better images of Jupiter, than the digitized images you have uploaded. Those images appear washed out and smudged compared to what I see at the eyepiece. Call me crazy if you like; but I know what I see.


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MKV
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Re: Optimized Newts vs APOs new [Re: Dave O]
      #5586955 - 12/24/12 10:31 AM

Quote:

I have never seen the "Sun Dance"; but I do know that my Questar provides much better images of Jupiter



Do you have any unretouched (raw) pictures of it?

Mladen


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Dave O
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Re: Optimized Newts vs APOs new [Re: MKV]
      #5586967 - 12/24/12 10:43 AM

The point (which you seem to have missed) is that images can't capture what the eye can see ... it is like taking a picture of a rainbow -- never quite meets what is actually seen in real observation.

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GlennLeDrew
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Re: Optimized Newts vs APOs new [Re: Dave O]
      #5587047 - 12/24/12 11:31 AM

As to the Questar claim re. license plate resolution brought up by MlDen. It's not necessary to fully resolve down to the width of the lines making up the individual figures in order to decipher what they are. As long as contrast is sufficient, a fairly smeared image can still be readable.

There is one aspect of the Newtonian secondary which I've not seem addressed, and which I suspect might be behind an effect which has been niggling at my subconscious for many a year. And that is its projection to a slightly farther distance behind the exit pupil than the exit pupil itself. This should be more so the shorter the secondary-to-focus distance and the longer the eyepiece focal length.

What got me thinking about this is the odd behavior I've always noticed whenever my eye moved a little, whereby there seemed to be a slight parallactic shift superimposed on objects in the field. It's very difficult to describe, and the effect is mostly subtle, bit it's definitely a quality of the Newt which detracts from the view for me. It dies seem to be more prominent at larger exit pupils, and is likely related to the relative size of the secondary shadow with respect to my pupil.

It probably would be the case that this behavior would be present to the same degree if the secondary shadow lay precisely in the plane of the image of the more-distant mirror. But it *might* (?) be worth cogitating on the effect of the secondary's shadow being projected a little farther back than the objective aperture...


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