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09-23-2014, 03:58 PM   #1
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Astro Photography with the 645D/Z

I have a question for the other Digital 645 users out there that may be able to help me with this question.

Firstly I have shot Astro Landscapes on 35mm for several years and really enjoy the Genre. Generally a 30 sec exposure is good for 14mm to 24mm focal lengths with no startrails and 24mm to 30mm is around 15-20sec exposure with out any star trails & 50mm is around 10sec. (roughly)

Since owning the 645Z I have rarely had the chance to get some clean skys to test it out. Last night I got a crack at it with the Milkyway being very prominent in the sky.

My Findings with the DA25mm and the A35mm is that any exposure longer than 10-15secs begin to show slight star trails. At first I thought it was my tripod slightly moving..but after lots of test shots I eliminated that Idea. So I dropped my exposer time to 10seconds and boosted the ISO higher and the sky came out pin sharp with no trailing.
Im guessing the sensor size has something to do with this.

Any one got any insights or experience with these issues.

Thanks , tom

09-23-2014, 04:23 PM   #2
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I also do a lot of this sort of shot and have found the same thing. I suspect it's simply that the higher resolution sensor allows you to look more closely - and therefore see trailing that would always have been there with other sensors. A trailing effect will only be visible when the movement of stars across the scene is sufficiently long to span more than one pixel. If the pixels are smaller (as a proportion of the angle of view) then this will happen sooner. Of course if you don't zoom in more closely that you did with the old camera, they won't be any more visible - but it's the nature of the higher res that you will look closer :-)

That said, the Z is so good at high ISOs, the shorter exposure times are not a problem!

---------- Post added 09-24-14 at 09:25 AM ----------

Couple of examples:
https://www.flickr.com/photos/16063951@N00/14630751480/in/set-72157632566383126
https://www.flickr.com/photos/16063951@N00/14814871644/in/set-72157632566383126/
09-23-2014, 04:47 PM   #3
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QuoteOriginally posted by Ed Hurst Quote
I also do a lot of this sort of shot and have found the same thing. I suspect it's simply that the higher resolution sensor allows you to look more closely - and therefore see trailing that would always have been there with other sensors. A trailing effect will only be visible when the movement of stars across the scene is sufficiently long to span more than one pixel. If the pixels are smaller (as a proportion of the angle of view) then this will happen sooner. Of course if you don't zoom in more closely that you did with the old camera, they won't be any more visible - but it's the nature of the higher res that you will look closer :-)

That said, the Z is so good at high ISOs, the shorter exposure times are not a problem!

---------- Post added 09-24-14 at 09:25 AM ----------

Couple of examples:
https://www.flickr.com/photos/16063951@N00/14630751480/in/set-72157632566383126
https://www.flickr.com/photos/16063951@N00/14814871644/in/set-72157632566383126/
Nice shots Ed.

I was told back at CES in January that the K3 has a sensor shifting mechanism that eliminates the trails for long exposures at night. Does that make sense? Or have you heard of it? If it is true on K3, then it is very likely to be available for 645Z as well.
09-23-2014, 05:20 PM   #4
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QuoteOriginally posted by btnapa Quote
Nice shots Ed.

I was told back at CES in January that the K3 has a sensor shifting mechanism that eliminates the trails for long exposures at night. Does that make sense? Or have you heard of it? If it is true on K3, then it is very likely to be available for 645Z as well.
The Astrotracer function is only possible with the O-GPS1 unit, and utilizes the sensor shift capabilities; therefore it is not available on the 645 bodies.

09-23-2014, 05:23 PM   #5
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QuoteOriginally posted by Ed Hurst Quote
I also do a lot of this sort of shot and have found the same thing. I suspect it's simply that the higher resolution sensor allows you to look more closely - and therefore see trailing that would always have been there with other sensors. A trailing effect will only be visible when the movement of stars across the scene is sufficiently long to span more than one pixel. If the pixels are smaller (as a proportion of the angle of view) then this will happen sooner. Of course if you don't zoom in more closely that you did with the old camera, they won't be any more visible - but it's the nature of the higher res that you will look closer :-)

That said, the Z is so good at high ISOs, the shorter exposure times are not a problem!

---------- Post added 09-24-14 at 09:25 AM ----------

Couple of examples:
https://www.flickr.com/photos/16063951@N00/14630751480/in/set-72157632566383126
https://www.flickr.com/photos/16063951@N00/14814871644/in/set-72157632566383126/

You are right with the nature of high res files , the ability to look that close is hard to deny. I was super impressed by the Z's performance. I shot a 28 frame Pano (in Post your Medium format Pics) at 10sec f4 ISO6400 and the files are great! Tom

---------- Post added 09-24-14 at 10:24 AM ----------

QuoteOriginally posted by tuco Quote
I don't go past 15 seconds with my Zeiss 21mm on 35mm format even though the 500 rule says about 25 seconds. And your 25mm is about equivalent to a 21mm I believe.

But when I want longer, I made this barn door tracker to cancel out the diurnal motion of the earth for a short duration to freeze stars. You can find plan ons the internet how to make various kinds. My version is designed to be rotated every 15 seconds for up to about 5 minutes max. It utilizes the fact that the mathematical sin() of an angle is equal to the angle in radians for up to 6 degrees for one-second of arc of accuracy.







Cool Tracker Tuco, thanks for sharing the pics.
09-24-2014, 01:31 PM   #6
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QuoteOriginally posted by Thomasbrowphoto Quote
I have a question for the other Digital 645 users out there that may be able to help me with this question.

Firstly I have shot Astro Landscapes on 35mm for several years and really enjoy the Genre. Generally a 30 sec exposure is good for 14mm to 24mm focal lengths with no startrails and 24mm to 30mm is around 15-20sec exposure with out any star trails & 50mm is around 10sec. (roughly)

Since owning the 645Z I have rarely had the chance to get some clean skys to test it out. Last night I got a crack at it with the Milkyway being very prominent in the sky.

My Findings with the DA25mm and the A35mm is that any exposure longer than 10-15secs begin to show slight star trails. At first I thought it was my tripod slightly moving..but after lots of test shots I eliminated that Idea. So I dropped my exposer time to 10seconds and boosted the ISO higher and the sky came out pin sharp with no trailing.
Im guessing the sensor size has something to do with this.

Any one got any insights or experience with these issues.

Thanks , tom
Ive been waiting for a good night here also. What ISO's did you find worked for you?
RH
09-24-2014, 03:57 PM   #7
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I found !SO 3200 and 6400 were good. The clear nights didn't last here in Australia, cloud cover is here again!
09-24-2014, 10:17 PM   #8
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Thomasbrowphoto , thank you, so my normal ISO settings will work, its the exposure time, 30 sec didnt work to good for me either, Ill be using the "25mm" Lens on the 645Z

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