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10-15-2018, 03:13 PM   #16
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QuoteOriginally posted by Alex645 Quote
But beyond the tech numbers there is also quality control and overall IQ. I think your lens will be fine in the mid-aperture ranges, but noticeably problematic f/2.8-4.5 and probably f/13-22.[COLOR="Silver"]
Which is unfortunate because I'm learning to get into astro. Plus there's a trip we're going on in 5-6 months to arizona and I really want to take advantage

If it is decentered I might try to talk to KEH, maybe they'll still do something even though it's a bit off warranty.

QuoteQuote:
Like a flat brick wall where you can fill the frame from corner to corner.
I'm gonna have to do a bit of driving to find one of those around here lol.

10-15-2018, 03:34 PM - 1 Like   #17
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The last photo is hard to determine the plane of focus because the object is not plane. You asked "what do you mean by flat planar subject" . Take a photo in which the object of focus plane( like a wall ) is perpendicular to the axis of lens. By this we can clearly determine the depth of field.

Most likely is that your lens needs a fine adjustment to determine the front focus, plane of focus and back focus.
10-15-2018, 03:49 PM   #18
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QuoteOriginally posted by Penview52 Quote
The last photo is hard to determine the plane of focus because the object is not plane. You asked "what do you mean by flat planar subject" . Take a photo in which the object of focus plane( like a wall ) is perpendicular to the axis of lens. By this we can clearly determine the depth of field.

Most likely is that your lens needs a fine adjustment to determine the front focus, plane of focus and back focus.
I gotcha, I'll try to take a more useful photo when I can.
10-15-2018, 04:57 PM   #19
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Thanks. Pls. identify your target object in the photo. It also includes a background either building or tress.

10-17-2018, 04:09 AM - 1 Like   #20
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Just a couple of points to note in all the posts.

First, don't jump directly to a de entered lens, look at technique before equipment failures.

The shot was 30 seconds, how stable was the platform?
The shot was wide open, and while people might argue about the wonderful DOF of wide angle lenses, and that it might be ok because it was set to its hyper focal distance, please remember, hyper focal distance and DOF are based upon a definition of relatively sharp, where a point is less than 20 microns on a crop sensor or 30 microns on full frame sensors, lets translate this to a useful term, that represents 0.1 inch when viewed on an 8x10 print. Today, we tend to blow images up to huge proportions on our monitors. So the old definitions no longer allpy, because we are viewing much larger images today.

Also, in the first print, the house eaves seem to be sharp suggesting the lens was focused very near the camera.

The op should stop the lens down perhaps to F5.6 or F8 and take a longer exposure. He should see infinitely fine lines ideally about 2 pixels wide, The acceptably sharp definition of 20-30 microns would be potentially 5-6 pixels even on my K5
10-26-2018, 07:40 PM   #21
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Maybe it's a field curvature problem? Here's one with the top right looking sharp but the bottom right looking soft:

https://i.imgur.com/nFnosaH.jpg



And here's one with the opposite problem:

https://i.imgur.com/1FFnPxx.jpg




Any thoughts?

Also sorry I could not find any better walls near me that wouldn't be encroaching on other people's property.

Last edited by ZombieArmy; 10-26-2018 at 07:45 PM.
10-27-2018, 06:57 AM   #22
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QuoteOriginally posted by ZombieArmy Quote
Maybe it's a field curvature problem? Here's one with the top right looking sharp but the bottom right looking soft:

https://i.imgur.com/nFnosaH.jpg

And here's one with the opposite problem:

https://i.imgur.com/1FFnPxx.jpg

Any thoughts?

Also sorry I could not find any better walls near me that wouldn't be encroaching on other people's property.
The curvature is like a fisheye lens effects. It is a natural effect and no way to correct it or I assumed the original lens was broken and replaced to this convex lens ( just guessing ).
If you only take photo of the whole wall, it is clear to see the non rectilinear mapping function of the lens. Fisheye lens is suggested for or good in Astrophotograph and cloud formation. It seems the vertical lines in the photo are not truly vertical - it might be the set up of camera is not aligned to vertical lines. As Alex said give as the data of the photo.

Last edited by Penview52; 10-27-2018 at 03:38 PM. Reason: Add additional info.
10-27-2018, 11:09 AM   #23
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QuoteOriginally posted by ZombieArmy Quote
Maybe it's a field curvature problem?
Any thoughts?
That is distortion which is normal and caused by a wide angle lens shooting a close subject. It can be corrected in Photoshop and other apps.

That painted white concrete block wall is not the same as finding, something more like a three story building with brick or with more detailed texture. Also you need to show us the metadata or at least assure us your exposure info: f/stop, shutter speed, and ISO.

10-27-2018, 12:04 PM   #24
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And measure from both upper corners of the camera in a line perpendicular to the plane of the sensor to make sure you are aligned. These two images are not exactly the same so try to ensure you are perfectly at a 90 degree angle to your target wall. ---------

Last edited by SSGGeezer; 10-27-2018 at 12:05 PM. Reason: WYS is not what you get
11-03-2018, 03:39 PM   #25
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I went out today to try and take shots with the lens against a more suitable subject and my tripod's head broke. Just can't catch a break lately.

I tried my best to take some examples, and I noticed that no matter what I did the bottom left of the image was always super soft at f2.8, no matter how much I tried to adjust the camera. I also have other shots I took with the lens on that day if you scroll to newer pictures.



11-03-2018, 04:09 PM   #26
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QuoteOriginally posted by Alex645 Quote
Shooting any lens wide open will not give you optimum sharpness across the field, but I do think it's decentered. Try shooting a flat brick wall at f/2.8. Try the same in the day of a city scape at f/2.8. Of course things will improve at f/5.6 or f/8....
This is the first time I think I'm quoting myself, but I think this is further evidence that it is decentered. Corners and edges are typically going to be soft wide open on wide angle lenses, but the fact that it is only happening in one corner indicates decentering. IMO you have these options:

a) Live with it and only shoot wide open when you don't need the entire field sharp.
b) Avoid shooting wide open and only shoot at f/5 or f/5.6 or greater if you care about the entire field being sharp.
c) Send the lens in to have the decentering fixed.
d) Sell the lens.
e) Always compose your shots with the issue in mind and crop it out in post.
11-03-2018, 04:21 PM   #27
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QuoteOriginally posted by Alex645 Quote
This is the first time I think I'm quoting myself, but I think this is further evidence that it is decentered. Corners and edges are typically going to be soft wide open on wide angle lenses, but the fact that it is only happening in one corner indicates decentering. IMO you have these options:

a) Live with it and only shoot wide open when you don't need the entire field sharp.
b) Avoid shooting wide open and only shoot at f/5 or f/5.6 or greater if you care about the entire field being sharp.
c) Send the lens in to have the decentering fixed.
d) Sell the lens.
e) Always compose your shots with the issue in mind and crop it out in post.
I did buy the lens from KEH who said it was excellent. It's a bit out of warranty but I'll still contact them to see maybe if they can cut me a deal.
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