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10-04-2021, 01:04 PM - 1 Like   #31
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QuoteOriginally posted by Michael Piziak Quote
Curious if these dots are celestial objects, or more likely are lens imperfections - ? some dots are dark colored on the blue image (that I didn't circle)...


As circled in images below. Click images several times to zoom in.



&



Perhaps best thing to test this is to take a photo at f4 against the sky or other background ?
Most likely, these are what are called "hot pixels" which are sensor elements with higher than normal dark current. Every sensor has them and the number grows over time due to radiation. Dark frame subtraction, either in a post process or using long exposure time noise reduction, can correct these. The "Pixel Mapping" function can also reduce these to some extent.

Other celestial phenomena you might see are meteor tracks (medium-length and usually thin on both ends), satellite tracks (long), satellite flares (short, bright, and usually thin on both ends), cosmic ray tracks (shortish squiggles), and aircraft (usually 1 to 3 lines with evenly-spaced dots )

10-04-2021, 01:45 PM   #32
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QuoteOriginally posted by AstroDave Quote
Those are what are called "hot pixels" - minor problems in the sensor (not lens). If they were celestial, they'd be streaked out like the rest of the stars/planets.

See Hot Pixels for some more info (or do a google search)
Thanks AstroDave & photoptimist,

& I assume hot pixels show up more and more with long(er) exposures.... Whereas my last 4 daytime pics were very fast exposure(s)....

Last edited by Michael Piziak; 10-04-2021 at 01:51 PM.
10-04-2021, 02:10 PM - 1 Like   #33
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QuoteOriginally posted by Michael Piziak Quote
Thanks AstroDave & photoptimist,

& I assume hot pixels show up more and more with long(er) exposures.... Whereas my last 4 daytime pics were very fast exposure(s)....
Yes, hot pixels are primary a long-exposure artifact. Hot pixels get brighter with longer exposure time, higher ISO, and hotter temperatures.

Sensors can also have dead or pinned pixels that show up at almost all exposure times but the Pixel Map function hides them.
10-04-2021, 02:28 PM - 1 Like   #34
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QuoteOriginally posted by Michael Piziak Quote
Thanks AstroDave & photoptimist,

& I assume hot pixels show up more and more with long(er) exposures.... Whereas my last 4 daytime pics were very fast exposure(s)....
It really depends, some will get stuck and exposure time doesn't change things. It's easily correctable via a tool like photoshop or the GIMP with the clone or heal tool.

10-04-2021, 02:37 PM   #35
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Thanks photoptimist & bobbotron,

I was thinking about the in camera PixelMapping that corrects defective/hot pixels and had a question.

I wander if when one does a factory reset on any Pentax camera body, I wander if the defective pixels return until PixelMapping is selected and performed again. What do you guys/gals think? Even if you don't know the answer, what is your hunch ?


Regards,

Michael
10-04-2021, 03:46 PM - 1 Like   #36
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QuoteOriginally posted by Michael Piziak Quote
Thanks photoptimist & bobbotron,

I was thinking about the in camera PixelMapping that corrects defective/hot pixels and had a question.

I wander if when one does a factory reset on any Pentax camera body, I wander if the defective pixels return until PixelMapping is selected and performed again. What do you guys/gals think? Even if you don't know the answer, what is your hunch ?


Regards,

Michael
I've no idea but it would assume it reset it.

It's an easy thing to test:

1. Turn off all noise reduction, do a long exposure in total darkness (lens cap + viewfinder cap), save the image.
2. Do a factory reset.
3. Repeat step #1
4. Compare the two images. (the post reset image should have more hot pixels)
5. Run the "Pixel Map"
6. Repeat step #1
7. Compare the images. (the post "pixel map" image should have fewer hot pixels like the first image)
10-04-2021, 03:59 PM   #37
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Yeah, I'm not sure, I've never used the feature. I'd normally just zap these things in post quickly as needed. Usually my star trails have a lot going on in them, so I'm not too worried if the odd bad pixel shows up.

10-04-2021, 07:09 PM   #38
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The sky was completely over cast tonight, but I aimed the camera up there and took about a 30 min exposure.
Interesting, that even over cast, some star trails pop in and out of there!



---------- Post added 10-04-21 at 07:21 PM ----------

Playing around with levels (doing an auto levels to be exact), I see an interesting "angled" line with dotted lights in the upper right - perhaps an airplane passing?
Might have to zoom in on it to see it (click on image several times).



---------- Post added 10-04-21 at 07:24 PM ----------

Addendum: Seen easier here

10-05-2021, 07:12 AM - 1 Like   #39
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If you look closely, it's actually two very dim parallel lines - it's a plane. There is also a very faint second set off to the left of the frame - a second aircraft (the fainter set is flying at a higher altitude). You have a set of wingtip navigation lights (actually they should be red and green - but since they are white, they are anti-collision strobes), but the right-hand side set is brighter than the left-hand set, and that is because you are getting a better angle on the airframe from one side.
10-05-2021, 10:06 AM   #40
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My dismal first attempt at star trail(s)

I am suspicious of you're using an IR remote. I have several and they don't have a way of locking the shutter open. I also have several remotes with a cord and they will lock the shutter open. I hope this helps.
10-05-2021, 12:06 PM - 1 Like   #41
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QuoteOriginally posted by moonwatcher Quote
I am suspicious of you're using an IR remote. I have several and they don't have a way of locking the shutter open. I also have several remotes with a cord and they will lock the shutter open. I hope this helps.
You donít need this with a Pentax, you can set bulb mode to stay open until second shutter activation.
10-05-2021, 03:53 PM - 1 Like   #42
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QuoteOriginally posted by interested_observer Quote
If you look closely, it's actually two very dim parallel lines - it's a plane. There is also a very faint second set off to the left of the frame - a second aircraft (the fainter set is flying at a higher altitude). You have a set of wingtip navigation lights (actually they should be red and green - but since they are white, they are anti-collision strobes), but the right-hand side set is brighter than the left-hand set, and that is because you are getting a better angle on the airframe from one side.
Excellent observation(s) and explanation(s) my friend!
Thanks so much!

---------- Post added 10-05-21 at 03:54 PM ----------

QuoteOriginally posted by bobbotron Quote
You don’t need this with a Pentax, you can set bulb mode to stay open until second shutter activation.
Yes, that's exactly what I've been doing. I learned how to do so from this thread: https://www.pentaxforums.com/forums/58-troubleshooting-beginner-help/431871-...-question.html
10-05-2021, 05:16 PM - 2 Likes   #43
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I have used this, no need for really long exposures, ie.10 to 20 second exposures in high continuous drive mode works well in my opinion.
http://markus-enzweiler.de/software/starstax/
10-05-2021, 05:23 PM   #44
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QuoteOriginally posted by Michael Piziak Quote
Excellent observation(s) and explanation(s) my friend!
Thanks so much!

---------- Post added 10-05-21 at 03:54 PM ----------



Yes, that's exactly what I've been doing. I learned how to do so from this thread: Bulb mode and remote control question - PentaxForums.com
I use a wired remote with a STSP switch.
10-05-2021, 09:31 PM   #45
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QuoteOriginally posted by Ex Finn. Quote
I have used this, no need for really long exposures, ie.10 to 20 second exposures in high continuous drive mode works well in my opinion.
http://markus-enzweiler.de/software/starstax/
I'm going to have to learn about taking photos in this mode. Is it one of the mode where the camera only takes in an image every time something in the sky changes ?

As far as just taking a 20 second exposure - I can't see where you'd get those long star trails at such a small amount of time....

---------- Post added 10-05-21 at 09:34 PM ----------

I'm at it again. Taking some star trail pics. Just took one at about 15 minutes from the back porch, and there is a lot of brightness in the photo. Will post it's pic in a few minutes.
Right now, I moved the camera to the back yard and pointed the camera straight up in the sky. Taking about a 10 minute exposure this time. Will post it also in a few minutes.
Will post both without post processing...

In the mean time. I'll share a story. When I taught 6th grade Science, the Science teacher on the other team was an Astronomy enthusiast. She smoked, as did I and I still do. She told me once that when she went to one of the nightly meetings, where everyone brought their telescopes, that she was smoking. Some of the other people got a little perturbed and told her that she would have to walk X feet/yards away to have a smoke, because they feared the smoke from the cigarettes would contaminate the lens on their telescopes. Some of them had pretty expensive telescopes. I think they were more concerned with smoke particles sticking to the telescope lens and affecting the image(s) they were seeing.

---------- Post added 10-05-21 at 09:59 PM ----------

All at f4, ISO 100, smc Asahi Pentax m-50mm macro f4 lens. No post processing on any of them yet....


Well, These 2 were from the back porch. A lot of over exposed areas.







And this one, from the backyard pointing straight up for 10 minutes. Nothing to see here at all - quite the opposite of the over exposed first 2. I guess I need to up the ISO when trying this again (tomorrow night)...



---------- Post added 10-05-21 at 10:04 PM ----------

Addenum: Nearly no histogram on the last one. I did mess with the "levels" in Gimp and got this out of it - lol....




Addendum: I just noticed that I had the switch set to AF instead of MF (manual) on the camera body to tell camera what type of lens is attached - don't know the affect this has had. Certainly did not use the green button for exposure. I expect switched to AF is more to tell camera body if one has an automatic lens attached...

Last edited by Michael Piziak; 10-05-2021 at 11:14 PM.
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