Long exposure images fading to black over time...

[PhilD41]

Hey everyone,

I am hoping someone here has more experience in this than I do. I am helping my son set up my D7000 for long exposure, deep sky photography. We have not had any issue using the interval timing with the built in 30' shutter speed using 34' intervals. In fact we captured about 6 hours of images this way the other night. Last night we set it up in bulb mode and configured the tracking mount (Star Adventurer 2i) to trigger continual 60' exposures through it's SNAP interface connected to the remote shutter port on the camera. That worked as expected, at least with the number and timing of photos. However, the photos progressively became darker and darker pretty quick after the start. Meaning we didn't get but 15 or 20 usable images over the 7 hours. Below is a screen shot from DarkTable showing the thumbnails of the images. You can see the galaxy in the top left corner image (bright, smudgy spot). By the time it get to the lower left image the starts are almost not visible and the galaxy is reduced to a faint dot. The images never go completely black, though, but fairly close. I also capture the EXIF data for one of the images. That EXIF data all looks correct to me.

My initial thought was a fading issue with the sensor with continual long exposures. As the sun came up the next morning, the images slowly moved from black to blue to white as I would expect with that exposure time. From what I can tell, the camera is fulling operational this morning with nothing amiss other than the photos it took overnight. Any help or ideas on this would be greatly appreciated.

Grace & Peace!

 

[blackstar]

Can you post the images of the first and last few shots (with Exif)? It will be easier to see what happened and hopefully get the right idea from some experienced members here.

 

[BF Hammer]

I do not think your D7000 is to blame. Until 5 years ago I was using a D7000 and Sigma 150-600mm lens for my astro work.

I do not have a Star Adventurer 2i. I use Skywatcher's AZ-GTi and that uses the SynScan app to control it. Is that used with the Star Adventurer 2? I don't actually know. But I do know that I do not trust the SNAP port. It has let me down early and I never tried it again with updates on firmware and app revisions.

I mostly use a laptop PC to control my camera tethered with DigiCamControl. But you are trying to gather 6 hours of light data. Buy one of the Neweer intervalometers that connects to your remote shutter port. They cost a whole $35 on average and are worth every cent. They have a function where you can put the camera in bulb mode and set long shutter speed interval programs. And the device will be a remote shutter release button for normal photography also. They work.

And unrelated, I looked at the exif and it also appears you are capturing a galaxy. Andromeda? Go higher on the ISO. 3200 or 6400 maybe. It will give the benefit of requiring fewer exposures. The noise will blend out fine after stacking.

 

[TwistedThrottle]

Hi @PhilD41 and welcome!
Is this the only time it has happened? From what I can tell from your screen grab, focus doesn't appear to be an issue and the stars look to be well defined without streaks but 300mm is quite a reach for long exposures. Any anomaly between you and your target will be multiplied, so a thin little wispy high cloud you cant even see naked eye, city lights washing out the stars (light pollution) or even the vapors from heat haze has an impact. You might want to check out ClearDarkSky dot com for some additional insight. They have charts that break down night time visibility and let you know when the optimal time to expose for astrophotography is.

 

[BF Hammer]

Hi @PhilD41 and welcome!
Is this the only time it has happened? From what I can tell from your screen grab, focus doesn't appear to be an issue and the stars look to be well defined without streaks but 300mm is quite a reach for long exposures. Any anomaly between you and your target will be multiplied, so a thin little wispy high cloud you cant even see naked eye, city lights washing out the stars (light pollution) or even the vapors from heat haze has an impact. You might want to check out ClearDarkSky dot com for some additional insight. They have charts that break down night time visibility and let you know when the optimal time to expose for astrophotography is.

You raise a point I forgot. His lens may have fogged up. It kind of fits the circumstances. I use a USB-powered lens-wrap anti-dew heater for those early morning sessions. Again, a cheap item to buy off Amazon.

https://www.amazon.com/Fast-warm-Spliceable-Telescopes-Anti-Condensation-Celestron/dp/B09D7FSHBH/ref=sr_1_5?dib=eyJ2IjoiMSJ9.pmlR3ArryXUBzM7or9rgp3GTN2CCInRODyiNLkNZe6NVJ_jwG2CKqazYl-M5pExqW8S5RU-2IBYakuGMdEqHOemHNVocuJkgoNncy8B85d94uSd-gmimPOCXfremxvz9ElHCY6U0Fet08baHlMRMZMv9oPGbBJQ4saskjDNrT292im9dVpHTo7SDQuRUTFdcsNQpV4BRGIzrtFeEnQU2Tf-rXfxVWYSmsjcH_4482wM.x94AZWskbPzG9-oRozkx4L2oetwpTwI9pVi9PnXL2b4&dib_tag=se&mfadid=adm

https://www.amazon.com/Neewer-Digit...e&sprefix=neweer+intervalometer+nikon,aps,107

 

[PhilD41]

Wow, thank you all for the greetings and comments. Let me see if I can work through them here. Given the dates on the threads I wasn't sure how active this group was.

First @blackstar , below is the first image, the later image, and the side-by-side EXIF data. I am not sure why some of the data is different formats, but I will blame DarkTable on my linux box and not the camera.


Second, I agree @BF Hammer, an intervalometer makes a lot of sense, and it is on his list of equipment for future purchases. He (we) has been focusing on other items, like a good tripod, tracker, etc. He also has a 8" dobsonian telescope that takes up some of his expendable hobby budget. We were both hoping that the tracker could do what he needed... and I think it can. The actual image taking mechanics worked perfectly. He does control his tracker with his phone, It may be the same app. I can't recall the name of it. He has to put up with me being a Linux fan, meaning we don't have any PC in the house that isn't Linux or a Chromebook. That makes some of the control options a little more complicated. Oh, and you are correct, it is Andromeda. I am not sure why he dropped the ISO down to 2000. The images he took at 30" intervals were at 3200. For kicks, I the below image is what he ended up with after that session. He was hoping to add to it to provide a little more detail.

Third, @TwistedThrottle, 300mm is a reach, and on a APS-C sensor it is actually 450mm. This is the first time we have seen this issue, yes. We have had others, but have worked through them slowly. Completely agree on the light pollution and clouds. Fortunately, our home is a Bortle 3. I am not sure if he uses ClearDarkSky or if Stellarium provides the same data, but he has an app on his phone to monitor and plan around clouds and atmospheric conditions. In this case, the fade began just 15 minutes or so after he started and he was still out there. The skys were clear till almost sun rise. It could be there was something we couldn't see, but the sequential dimming in each frame seem very odd and linear for a natural event.

Forth, the point of due is relavent. The lens heater is also on his list. We thought about this as well, but it was almost 10 degrees above dewpoint when he started. the lens did have droplets on it by morning, but the first 2 - 3 hours of images should have been clear and they weren't. I even asked about fog, that is when we realized it dimming was happening 10's of minutes prior to him coming in for the night and conditions hadn't changed.

Again, thank you all for the ideas and help. It is great to have others to troubleshoot with. Most of these we have thought of, but don't necessarily have the experience to know if they would cause this. To me, causes we have come up with so far don't explain the failure mode. Or I am just missing something. He was going to try again tonight with a slight delay between pictures. He may still, depending on when he gets back from his friends birthday gathering.

 

[BF Hammer]

I should elaborate on my issues with the SNAP port. I believe Skywatcher just had in mind to get it to fire Canon DSLRs and assumed it would be fine with others. For the 60 second exposure time the circuit has to hold a switch (or more likely a transistor) closed for 60 seconds. If it is designed on the cheap side, I can foresee some electrical noise from driving the motor appearing on that shutter release circuit. End result being the shutter thinks the release switch opened and the exposure stops early.

It's just my own conjecture. I have watched Big Clive tear down enough China goods on YouTube to be suspicious like that.

 

[Marilynne]

Welcome!

Glad some of our members are able to offer some assistance with you on your problem(s).

Please let us know how it turns out.

Also, please feel free to introduce yourself here - https://nikonites.com/forum/forums/new-member-introductions.35/post-thread

 

[Dawg Pics]

A good source for information on astrophotography is the Cloudy Nights forum. There are lots of astrophotographers on there.