Difference in horizontal and vertical resolution: 20D, Canon zoom, Celestron C90

Discussion in 'Digital Photography' started by jess, Oct 1, 2005.

  1. jess

    jess Guest

    In my recent quest to get a decent picture of the moon with a 25 year
    old Celestron C90 and a Canon 20D (I've given up, BTW), I decided to
    see if the Celestron was really as bad as my lunar images implied. I
    did a quick and dirty resolution comparison with a Canon 75-300 zoom
    using a resolution chart I downloaded from the Web. The Celestron is
    (no big surprise) worse, even though this particular Canon lens has the
    reputation of being soft at full zoom. However, in examining the
    results I came across something I didn't quite understand, and I
    thought you folks might be able to give me some insight.

    On vertical lines the Celestron was not dramatically inferior to the
    Canon lens, though the contrast was substantially lower. On horizontal
    lines, though, the Celestron image was simply awful. See

    http://home.comcast.net/~jgates777/Canon_Celestron_Comparison.jpg

    for a comparison of the images.

    If anything, the Canon lens does slightly better on horizontal lines
    than on vertical ones. The Celestron, on the other hand, is just awful
    with horizontal lines. I repeated the comparison several times with
    the same result. All tests done with lenses/camera mounted on a Bogen
    3046 tripod with a 488RC2 Midi Ball Head, mirror locked up, remote
    release after 10 seconds of MLU. I moved the tripod/camera so that the
    image was about the same size for the two lenses (i.e., the Canon was a
    lot closer to the target than the Celestron, which is about 1200 mm in
    focal length). The only think I can think of is that I'm getting
    vertical "nodding" with the Celestron. Any thoughts?
     
    jess, Oct 1, 2005
    #1
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  2. In article <> "jess" <> writes:
    $On vertical lines the Celestron was not dramatically inferior to the
    $Canon lens, though the contrast was substantially lower. On horizontal
    $lines, though, the Celestron image was simply awful. See

    How were these lines arranged within the frame? It's normal for a
    lens to have different resolving power for radial lines than for
    tangential lines, and in some cases, in some parts of the frame,
    there can be a very large difference (which is why MTF graphs have
    pairs of lines).

    So if you arranged it so that the horizontal lines were (say)
    immediately to the side of the middle of the frame, and the vertical
    lines were (say) immediately above or below the middle of the frame,
    and the same distance from the middle, you should see about the same
    results for both. Put them next to each other at one of the edges
    of the frame, and it wouldn't be unexpected to see one come out
    sharper than the other, even though they're right next to each other,
    because one of them will be radial and the other tangential.
    --
    Stephen M. Dunn <>
    >>>----------------> http://www.stevedunn.ca/ <----------------<<<

    ------------------------------------------------------------------
    Say hi to my cat -- http://www.stevedunn.ca/photos/toby/
     
    Stephen M. Dunn, Oct 2, 2005
    #2
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  3. jess

    jess Guest

    The chart I used was the EIA Chart 1956. This is, I think, for video,
    but for my purposes it didn't matter. The images I referenced were
    form the vertical stripes above the center "striped square" and the
    ones to the left of the center "striped square". The center of the
    viewfinder image was the "bullseye" in the cinet of the chart. I also
    checked the converging lines to the bottom and left of the "striped
    square", and the same disparity was apparent: the hoirizontal lines
    were very poorly imaged by the Celestron/20D combination.

    The chart is at

    http://homepage.mac.com/stevebagley/EIA1956wide.pdf
     
    jess, Oct 2, 2005
    #3
  4. "jess" <> wrote in message
    news:...
    > In my recent quest to get a decent picture of the moon with a 25 year
    > old Celestron C90 and a Canon 20D (I've given up, BTW), I decided to
    > see if the Celestron was really as bad as my lunar images implied. I
    > did a quick and dirty resolution comparison with a Canon 75-300 zoom
    > using a resolution chart I downloaded from the Web. The Celestron is
    > (no big surprise) worse, even though this particular Canon lens has the
    > reputation of being soft at full zoom. However, in examining the
    > results I came across something I didn't quite understand, and I
    > thought you folks might be able to give me some insight.
    >
    > On vertical lines the Celestron was not dramatically inferior to the
    > Canon lens, though the contrast was substantially lower. On horizontal
    > lines, though, the Celestron image was simply awful. See
    >
    > http://home.comcast.net/~jgates777/Canon_Celestron_Comparison.jpg
    >
    > for a comparison of the images.
    >
    > If anything, the Canon lens does slightly better on horizontal lines
    > than on vertical ones. The Celestron, on the other hand, is just awful
    > with horizontal lines. I repeated the comparison several times with
    > the same result. All tests done with lenses/camera mounted on a Bogen
    > 3046 tripod with a 488RC2 Midi Ball Head, mirror locked up, remote
    > release after 10 seconds of MLU. I moved the tripod/camera so that the
    > image was about the same size for the two lenses (i.e., the Canon was a
    > lot closer to the target than the Celestron, which is about 1200 mm in
    > focal length). The only think I can think of is that I'm getting
    > vertical "nodding" with the Celestron. Any thoughts?
    >


    Lenses have radial symmetry and so can have different microcontrast in
    meridional and sagittal directions. This is why mtf plots have M and S
    lines.

    Computer simulation suggests the average of the MTF M and S values is a good
    indication of sharpness for a typical view with detail that is randomly
    orientated.
     
    Lester Wareham, Oct 2, 2005
    #4
  5. jess

    Ray Fischer Guest

    jess <> wrote:
    >In my recent quest to get a decent picture of the moon with a 25 year
    >old Celestron C90 and a Canon 20D (I've given up, BTW), I decided to
    >see if the Celestron was really as bad as my lunar images implied. I
    >did a quick and dirty resolution comparison with a Canon 75-300 zoom
    >using a resolution chart I downloaded from the Web. The Celestron is
    >(no big surprise) worse, even though this particular Canon lens has the
    >reputation of being soft at full zoom.


    You are comparing a 300mm lens with a 1300mm telescope.

    > However, in examining the
    >results I came across something I didn't quite understand, and I
    >thought you folks might be able to give me some insight.
    >
    >On vertical lines the Celestron was not dramatically inferior to the
    >Canon lens, though the contrast was substantially lower. On horizontal
    >lines, though, the Celestron image was simply awful. See
    >
    >http://home.comcast.net/~jgates777/Canon_Celestron_Comparison.jpg
    >for a comparison of the images.


    Might be that your scope is out of alignment. Or might be that
    your particular scope isn't one of the better ones.

    Keep in mind that a 1200mm Canon lens runs about $12,000 while
    the Celestron can be had for a couple of hundred. The tradeoffs
    mean that the telescope isn't as good a camera lens. In particular
    the secondary mirror results in lower contrast and the complexity
    of the large aspherical front element means plenty of opportunity for
    error.

    --
    Ray Fischer
     
    Ray Fischer, Oct 2, 2005
    #5
  6. jess

    Bob Guest

    On 1 Oct 2005 14:50:56 -0700, "jess" <> wrote:

    >In my recent quest to get a decent picture of the moon with a 25 year
    >old Celestron C90 and a Canon 20D (I've given up, BTW), I decided to
    >see if the Celestron was really as bad as my lunar images implied. I
    >did a quick and dirty resolution comparison with a Canon 75-300 zoom
    >using a resolution chart I downloaded from the Web. The Celestron is
    >(no big surprise) worse, even though this particular Canon lens has the
    >reputation of being soft at full zoom. However, in examining the
    >results I came across something I didn't quite understand, and I
    >thought you folks might be able to give me some insight.
    >
    >On vertical lines the Celestron was not dramatically inferior to the
    >Canon lens, though the contrast was substantially lower. On horizontal
    >lines, though, the Celestron image was simply awful. See
    >
    >http://home.comcast.net/~jgates777/Canon_Celestron_Comparison.jpg
    >
    >for a comparison of the images.
    >
    >If anything, the Canon lens does slightly better on horizontal lines
    >than on vertical ones. The Celestron, on the other hand, is just awful
    >with horizontal lines. I repeated the comparison several times with
    >the same result. All tests done with lenses/camera mounted on a Bogen
    >3046 tripod with a 488RC2 Midi Ball Head, mirror locked up, remote
    >release after 10 seconds of MLU. I moved the tripod/camera so that the
    >image was about the same size for the two lenses (i.e., the Canon was a
    >lot closer to the target than the Celestron, which is about 1200 mm in
    >focal length). The only think I can think of is that I'm getting
    >vertical "nodding" with the Celestron. Any thoughts?


    Try re-orienting the chart and camera 90 degrees to see if you have vertical
    shake. I've noticed my moon shots suffer from vertical blur but no horizontal
    blur... and since eye-piece views are perfect I know its the tripod/mount.
     
    Bob, Oct 2, 2005
    #6
  7. jess

    Rich Guest

    C90s are generally...crap. Worthless optical corrections and
    poor contrast. Try a Meade ETX or even one of the Orion Chinese
    Maks, the bigger, the better, or an inexpensive 4-5" Chinese
    refractor.
    I used an ETX-105 to shoot Jupiter and although resolution
    was poor due to the seeing at my site, the contrast and colour
    saturation were excellent.
    -Rich

    On 1 Oct 2005 14:50:56 -0700, "jess" <> wrote:

    >In my recent quest to get a decent picture of the moon with a 25 year
    >old Celestron C90 and a Canon 20D (I've given up, BTW), I decided to
    >see if the Celestron was really as bad as my lunar images implied. I
    >did a quick and dirty resolution comparison with a Canon 75-300 zoom
    >using a resolution chart I downloaded from the Web. The Celestron is
    >(no big surprise) worse, even though this particular Canon lens has the
    >reputation of being soft at full zoom. However, in examining the
    >results I came across something I didn't quite understand, and I
    >thought you folks might be able to give me some insight.
    >
    >On vertical lines the Celestron was not dramatically inferior to the
    >Canon lens, though the contrast was substantially lower. On horizontal
    >lines, though, the Celestron image was simply awful. See
    >
    >http://home.comcast.net/~jgates777/Canon_Celestron_Comparison.jpg
    >
    >for a comparison of the images.
    >
    >If anything, the Canon lens does slightly better on horizontal lines
    >than on vertical ones. The Celestron, on the other hand, is just awful
    >with horizontal lines. I repeated the comparison several times with
    >the same result. All tests done with lenses/camera mounted on a Bogen
    >3046 tripod with a 488RC2 Midi Ball Head, mirror locked up, remote
    >release after 10 seconds of MLU. I moved the tripod/camera so that the
    >image was about the same size for the two lenses (i.e., the Canon was a
    >lot closer to the target than the Celestron, which is about 1200 mm in
    >focal length). The only think I can think of is that I'm getting
    >vertical "nodding" with the Celestron. Any thoughts?
     
    Rich, Oct 2, 2005
    #7
  8. jess

    jess Guest

    Bob's clue did it. I decided to try really tightening up on the ball
    head and weighting the tripod. The Celestron is now as good as the
    Canon 75-300 wide open @ 300mm, and the horizontal and vertical
    resolution are now mediocre (lack of contrast) but equal. I was
    counting on MLU to solve the shake problem, but these pictures were
    indoors under incandescent lighting at 1.3 seconds. I assume the
    shutter trip was causing the shake.

    Thanks for the tip, Bob. I guess I should have tightened and weighted
    all along! Sorry to bother y'all.
     
    jess, Oct 2, 2005
    #8
  9. jess

    jess Guest

    OK . . . that did it. I decided to try really tightening up on the
    ball head and weighting the tripod. The Celestron is now as good as
    the Canon 75-300 wide open @ 300mm, and the horizontal and vertical
    resolution are now mediocre (lack of contrast) but equal. I was
    counting on MLU to solve the shake problem, but these pictures were
    indoors under incandescent lighting at 1.3 seconds. I assume the
    shutter trip was causing the shake.

    Thanks for the tip. I guess I should have tightened and weighted all
    along.
     
    jess, Oct 2, 2005
    #9
  10. jess

    jess Guest

    Well, yes, I can get much better images by spending several hundred (or
    several thousand) dollars. That wasn't really the point, though. I
    already **have** the C90, and I was just trying to get a decent moon
    photo with it. And yes, I've seen some very nice lunar images taken
    with smallish Meade scopes, and others. Roger N. Clark posted a link
    to one a while back taken with a Canon 500mm "L" lens and a couple
    of teleconverters that was also very nice. I guess more money would
    help . . .

    I was trying for something like this taken (I think) afocally with a
    (presumably newer than my) C90:

    http://forums.dpreview.com/forums/read.asp?forum=1010&message=14611149

    Perhaps I'll try again when the moon reappears . . . this time with
    a tightened up tripod and some weight.
     
    jess, Oct 2, 2005
    #10
  11. In article <dhncrm$35t$> writes:
    $Keep in mind that a 1200mm Canon lens runs about $12,000 while

    Actually, it's a heck of a lot more than that. The 1200mm f/5.6L USM
    (Canon's only 1200mm lens) is a special-order item and a price isn't
    generally advertised, but from what I've read, it's more like USD80k.

    If that's a bit rich, you could get a used 600mm f/4L USM and a
    2x teleconverter for less than that $12k figure :)
    --
    Stephen M. Dunn <>
    >>>----------------> http://www.stevedunn.ca/ <----------------<<<

    ------------------------------------------------------------------
    Say hi to my cat -- http://www.stevedunn.ca/photos/toby/
     
    Stephen M. Dunn, Oct 2, 2005
    #11
  12. jess

    Bob Guest

    On 1 Oct 2005 21:02:29 -0700, "jess" <> wrote:

    >OK . . . that did it. I decided to try really tightening up on the
    >ball head and weighting the tripod. The Celestron is now as good as
    >the Canon 75-300 wide open @ 300mm, and the horizontal and vertical
    >resolution are now mediocre (lack of contrast) but equal. I was
    >counting on MLU to solve the shake problem, but these pictures were
    >indoors under incandescent lighting at 1.3 seconds. I assume the
    >shutter trip was causing the shake.
    >
    >Thanks for the tip. I guess I should have tightened and weighted all
    >along.


    I just bought a big heavy tripod but it's still not enough... I need to add some
    kind of damping to the whole affair... especialy in the wind!
     
    Bob, Oct 3, 2005
    #12
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