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02-17-2021, 03:29 PM   #1
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Little help please...

Trying out a used 645D for purchase. What do you think is the line pointed out in the photo? A bad line of pixels or something else. Many thanks! (Lens Manual Focus 55mm Pentax)...

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02-17-2021, 03:33 PM   #2
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Problem with the memory card?
02-17-2021, 03:49 PM   #3
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It could certainly be a sensor problem. Are we seeing most of the picture here or a tight crop? In some circumstances, I remember the vertical join between two halves of the sensor showing up - though it only happened at high ISOs and when I pushed the files in editing.
02-17-2021, 04:02 PM   #4
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It only appears at 66 or 100% crop. What sort of sad card could cause that?

---------- Post added 02-17-2021 at 06:03 PM ----------

Also it is 1600 ISO.

02-17-2021, 04:06 PM   #5
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What do you see if you photograph a blank white surface?
02-17-2021, 04:22 PM   #6
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QuoteOriginally posted by cdurfor Quote
What sort of sad card could cause that?
The short answer is a card with a problem and symptoms such as a line through the frame are not uncommon. If one sees the problem with more than one card, the fault lies with the camera or perhaps the card reader.


Steve
02-17-2021, 04:48 PM   #7
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Wow that’s great info.
02-17-2021, 08:38 PM   #8
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The subject does not seem to be in focus. You may want to test and see if the markings show with images that are obviously in focus using AF. Otherwise, make sure you are using an sd card that has been formatted in the 645D that you are using, and test in normal light such as outdoors if possible. Make sure the subject is in focus. Then check for any lines/distortion. You may want to try several sd cards, making sure each one formats successfully in the 645D being used prior to obtaining images.

Good luck.


Last edited by C_Jones; 02-17-2021 at 08:46 PM.
02-18-2021, 05:46 AM   #9
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After replacing the SD Card with a new one that meets the camera specifications, there's some tests you can do to check the sensor:
- turn off all image correction
- save in raw format (PEF or DNG)
- cap the camera (eg lens cap, in a dark bag)
- manual focus on nothing
- take 10 frames at the slowest shutter speed
- this will give you a set of "dark" images.
- inspect the images in your favorite raw software.
- you can see if there are significant hot pixels, defective columns etc.
Next, do some light frames of a defocused grey or white wall, card, or other evenly lit flat surface. Cloudy sky can also work, but its usually too bright.
- look for single "dead" pixels, and columns of dead pixels
- aim for a histogram that is maybe 2/3 fully to the right - so you will have to play with the exposure time
02-18-2021, 09:48 AM   #10
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Thanks to all for great insight and comment...

So - the image below reflects a new 32GB SD card formatted on the 645D. It was shot for 30 seconds in the dark (with a lens cap on) and then pushed to +5ev in adobe camera raw. Yep something is there. However if the image is reduced to only +3 EV at 1600 ISO or +4 EV at 800 ISO, it is no longer visible. It is also not visible at +5EV for ISO 400, 200 and 100.

In addition no artifacts were apparent during the second test (i.e., lighted frames).

So, given the frequency of pushing images to +5 or 4-5EV at either ISO 1600 or 800 am trending on keeping the camera.

But, I always appreciate the insight offered from you folks, so what do you think (and I will not hold you accountable).

And finally, thanks for all the great insight into the 645D. As a long time digital Pentax shooter (2006), I thought I knew most of it. Apparently not.

Chuck
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02-18-2021, 03:54 PM   #11
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I think it's what I saw in my 645D - the sensor is in fact in two halves, and (in some conditions - high ISO and pushing) the join can be seen. I ended up feeling that, if the shot is dark enough to need such shooting parameters, it was probably not going to look great anyway! But YMMV.
03-09-2021, 12:07 PM   #12
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Sensor problem

I had a very similar problem with a Hasselblad H3D. It was a problem with the sensor. Try to separate the chanels in Photoshop to find out if the problem is only in one RGB chanel . Mine was in the red chanel, so i noticed only in the sky
03-10-2021, 06:04 AM   #13
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Hi,

I, too, think you are seeing the seam line between the two sensors that make up the Kodak CCD used in the 645D. When the noise level becomes high enough, that has a tendency to show up.


Stan
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