Ugly Hedgehog - Photography Forum
Home Active Topics Newest Pictures Search Login Register ☰
Main Photography Discussion
Star Trails
Page 1 of 2 next>
Jan 22, 2021 11:49:52   #
PlymouthWoodworker Loc: Plymouth, MA
 
Hi all,
Several years ago I photographed the Milky Way and followed suggestions that a maximum exposure time of about 25 seconds would yield images without noticeable star trails (movement) with my 11mm lens. Worked fine. Now I am trying to photograph the Orion Nebula with a 500mm lens and find that the maximum is about 1/2 to 1 second, otherwise movement starts to be noticeable. My question is, why does focal length make a difference if the earth is moving at the same rate? Is it just that star trailing is less noticeable in wide shots because the movement is a smaller fraction of the frame width? Has anyone done the math? At 1 second I needed ISO 12,800 - 25,600, and used NIC dfine with some success to reduce noise. Thanks.

Reply
Jan 22, 2021 12:00:14   #
jeep_daddy Loc: Prescott AZ
 
PlymouthWoodworker wrote:
Hi all,
Several years ago I photographed the Milky Way and followed suggestions that a maximum exposure time of about 25 seconds would yield images without noticeable star trails (movement) with my 11mm lens. Worked fine. Now I am trying to photograph the Orion Nebula with a 500mm lens and find that the maximum is about 1/2 to 1 second, otherwise movement starts to be noticeable. My question is, why does focal length make a difference if the earth is moving at the same rate? Is it just that star trailing is less noticeable in wide shots because the movement is a smaller fraction of the frame width? Has anyone done the math? At 1 second I needed ISO 12,800 - 25,600, and used NIC dfine with some success to reduce noise. Thanks.
Hi all, br Several years ago I photographed the Mi... (show quote)


It's just "that star trailing is less noticeable in wide shots because the movement is a smaller fraction of the frame width."

Yes, you answered your own question. This is why photographing the Milky Way or doing star trails is done with a very wide angle lens.

I was photographing the Cathedral Rock Moonrise in Sedona with a longer lens and had to keep the shutter duration faster than I'd like because the moon would be blurry with the movement. I think I was using about a 200mm focal length.

Note: if you has a really high res photo with the wide angle lens, and you zoomed in a bunch, you'ld see blur from movement.....

Reply
Jan 22, 2021 17:43:05   #
Ballard Loc: Grass Valley, California
 
There is a general rule of Thumb, that if you divide 400 by your focal length you get a good idea of how long you can take an unguided exposure of the stars without getting noticeable trailing. (e.g. 400/11mm ~36 seconds. 400/500 ~ .8 seconds. Since the focal length is directly proportional to the effective magnification (Which also magnifies the star motion) this inverse relationship works pretty well. Other factors like the pixel density and picture enlargement may also come into play. Some folks have used 600 or 500 rather than 400 depending on how much star trailing is noticeable for your pixel density and photo enlargement. If you want longer exposures without trail then guided images will be the best. Another approach is to take multiple shorter shots and align the images during additive stacking, of course there has to be enough signal to register some of the image in each shot for this to work. A small F ratio can also allow for shorter exposures at a given focal length and ISO, but this can start costing a lot of money for longer lenses.

Reply
 
 
Jan 22, 2021 18:02:17   #
PlymouthWoodworker Loc: Plymouth, MA
 
Thanks Ballard, that’s a great rule. Seems to align with my experience. I just saw a post where someone used DeepSkyStacker. Does anyone have experience with this software?

Reply
Jan 22, 2021 18:42:49   #
Ballard Loc: Grass Valley, California
 
PlymouthWoodworker wrote:
Thanks Ballard, that’s a great rule. Seems to align with my experience. I just saw a post where someone used DeepSkyStacker. Does anyone have experience with this software?



Hi PlymouthWoodworker
Yep. For deep sky objects (as opposed to planets and the moon), this is a great piece of freeware available on the web and a real good place to start. I use to use this for processing my images but eventually payed the money for pixinsight as it had many more features (and a much bigger learning curve). There are many youtube tutorials on using both of these programs. If you have any questions let me know.

See examples below

Picture using deepskystacker to stack images
https://www.uglyhedgehog.com/t-599872-1.html

Same Picture using Pixinsight to stack images
www.uglyhedgehog.com/t-620263-1.html

Reply
Jan 23, 2021 05:57:10   #
george19
 
First, I screwed up the conjunction a few weeks ago by not bracketing shutter speed and using way too long an exposure.

Second, while expensive for an app, PhotoPills has some great information on this, as well as some amazing how-to videos.

Reply
Jan 23, 2021 06:39:40   #
jcryan Loc: Las Terrenas, Dominican Republic
 
PlymouthWoodworker wrote:
Thanks Ballard, that’s a great rule. Seems to align with my experience. I just saw a post where someone used DeepSkyStacker. Does anyone have experience with this software?


I have just started watching a series of YouTube videos by Nico Carver on his Nebula Photos channel. I tried to download DeepSkyStacker, but it is no longer freeware.

He often processes with multiple tools including Siril which is full open source and therefore free. Apparently it has been upgraded recently and has capabilities that can take you further into post processing before you move into GIMP or other PP software.

I have been practicing with Siril & GIMP using his images for M42 with good result. I recommend both Nico's channel and Siril for preparing, stacking, and initial processing of astro images.

Reply
 
 
Jan 23, 2021 07:17:01   #
tcthome Loc: NJ
 
https://www.moveshootmove.com/collections/sifo-rotator/products/sifo-rotator-for-star-tracking-time-lapse-panorama-photography?aff=117&variant=21144679022669

Reply
Jan 23, 2021 08:59:15   #
alberio Loc: Casa Grande AZ
 
My question is, why does focal length make a difference if the earth is moving at the same rate?

It doesn't. Everything is moving at different speeds, although the stars are so distant they appear to be stationary to our earths rotation. You need a tracking mount to compensate for the earths rotation.

Reply
Jan 23, 2021 09:27:55   #
larryepage Loc: North Texas area
 
PlymouthWoodworker wrote:
Hi all,
Several years ago I photographed the Milky Way and followed suggestions that a maximum exposure time of about 25 seconds would yield images without noticeable star trails (movement) with my 11mm lens. Worked fine. Now I am trying to photograph the Orion Nebula with a 500mm lens and find that the maximum is about 1/2 to 1 second, otherwise movement starts to be noticeable. My question is, why does focal length make a difference if the earth is moving at the same rate? Is it just that star trailing is less noticeable in wide shots because the movement is a smaller fraction of the frame width? Has anyone done the math? At 1 second I needed ISO 12,800 - 25,600, and used NIC dfine with some success to reduce noise. Thanks.
Hi all, br Several years ago I photographed the Mi... (show quote)


PhotoPills just sent an email with instructions on how to download their tutorial for photographing star trails. They describe both techniques...single long exposures and stacked multiple exposures. My suggestion is that you go to PhotoPills.Com and sign up for their periodic emails. I've been receiving them for a couple of years. They come only occasionally are in no way obnoxious. They also offer occasion live or recorded on-line classes.

Reply
Jan 23, 2021 10:25:26   #
JBRIII
 
Ballard wrote:
There is a general rule of Thumb, that if you divide 400 by your focal length you get a good idea of how long you can take an unguided exposure of the stars without getting noticeable trailing. (e.g. 400/11mm ~36 seconds. 400/500 ~ .8 seconds. Since the focal length is directly proportional to the effective magnification (Which also magnifies the star motion) this inverse relationship works pretty well. Other factors like the pixel density and picture enlargement may also come into play. Some folks have used 600 or 500 rather than 400 depending on how much star trailing is noticeable for your pixel density and photo enlargement. If you want longer exposures without trail then guided images will be the best. Another approach is to take multiple shorter shots and align the images during additive stacking, of course there has to be enough signal to register some of the image in each shot for this to work. A small F ratio can also allow for shorter exposures at a given focal length and ISO, but this can start costing a lot of money for longer lenses.
There is a general rule of Thumb, that if you divi... (show quote)


According to book I just got called: Astrophotography is easy (Amazon), they use the rule of 500 which includes the sensor size.

Time in secs = 500/(fl*cf) where fl = focal length and cf = sensor crop factor which equals the ratio between full frame sensor and yours.

Reply
 
 
Jan 23, 2021 11:24:18   #
PlymouthWoodworker Loc: Plymouth, MA
 
jcryan wrote:
I have just started watching a series of YouTube videos by Nico Carver on his Nebula Photos channel. I tried to download DeepSkyStacker, but it is no longer freeware.

He often processes with multiple tools including Siril which is full open source and therefore free. Apparently it has been upgraded recently and has capabilities that can take you further into post processing before you move into GIMP or other PP software.

I have been practicing with Siril & GIMP using his images for M42 with good result. I recommend both Nico's channel and Siril for preparing, stacking, and initial processing of astro images.
I have just started watching a series of YouTube v... (show quote)


Hi jcryan,
I just downloaded the latest version of DeepSkyStacker for free with no problems (Windows 10, 64 bit).

Reply
Jan 23, 2021 13:37:01   #
bwana Loc: Bergen, Alberta, Canada
 
Ballard wrote:
Hi PlymouthWoodworker
Yep. For deep sky objects (as opposed to planets and the moon), this is a great piece of freeware available on the web and a real good place to start. I use to use this for processing my images but eventually payed the money for pixinsight as it had many more features (and a much bigger learning curve). There are many youtube tutorials on using both of these programs. If you have any questions let me know.

See examples below

Picture using deepskystacker to stack images
https://www.uglyhedgehog.com/t-599872-1.html

Same Picture using Pixinsight to stack images
www.uglyhedgehog.com/t-620263-1.html
Hi PlymouthWoodworker br Yep. For deep sky objects... (show quote)



Much the same progress here but I also threw in ImagePlus in the middle...

bwa

Reply
Jan 23, 2021 13:38:18   #
bwana Loc: Bergen, Alberta, Canada
 
PlymouthWoodworker wrote:
Hi jcryan,
I just downloaded the latest version of DeepSkyStacker for free with no problems (Windows 10, 64 bit).

I still use the help file in DSS whenever I'm introducing a new person to astrophotography. It is excellent.

bwa

Reply
Jan 23, 2021 13:38:45   #
khildy Loc: Brownsburg, IN
 
jeep_daddy wrote:
It's just "that star trailing is less noticeable in wide shots because the movement is a smaller fraction of the frame width."

Yes, you answered your own question. This is why photographing the Milky Way or doing star trails is done with a very wide angle lens.

I was photographing the Cathedral Rock Moonrise in Sedona with a longer lens and had to keep the shutter duration faster than I'd like because the moon would be blurry with the movement. I think I was using about a 200mm focal length.

Note: if you has a really high res photo with the wide angle lens, and you zoomed in a bunch, you'ld see blur from movement.....
It's just "that star trailing is less noticea... (show quote)


Thanks from me also. That makes sense but I had never really thought about since I haven’t taken any night shots although I would like to in the future.

Reply
Page 1 of 2 next>
If you want to reply, then register here. Registration is free and your account is created instantly, so you can post right away.
Main Photography Discussion
Home | Latest Digest | Back to Top | All Sections
Contact us | Privacy policy | Terms of use | DMCA
UglyHedgehog.com - Forum
Copyright 2011-2024 Ugly Hedgehog, Inc.