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Super long exposures with MF Digital Backs

GrahamWelland

Subscriber & Workshop Member
Given that most digital backs are limited to <60 or <32 seconds for exposure, ignoring obviously the P45+, what techniques or recommendations do folks have for super long exposures that extend beyond a minute?

I've looked at some of the star trail info out there that use 3rd party tools for combining collections of exposures but I was wondering if folks had some practical techniques for situations where you might want to combine shots for different situations such as flowing water such as waves or removing people from static landscapes? It seems to me that star trails are additive exposures vs landscapes or cityscapes where I want to average out elements.

I have NDs for the exposure side of things but my Leaf & Phase One backs have limited maximum exposure.

Thoughts or pointers to techniques or info out there that maybe I've missed?

Thanks
 

Jeffg53

Member
I'm very interested in this too. I get 256 seconds from the H4D but would like to find a software solution for long exposures so that I can do star trails.
 

coulombic

New member
I was never able to disable the dark frame capture with my P65+, so there was always a 30-second delay after the initial 30-second exposure. I see this as the biggest obstacle in making star trail stacks, as rather large gaps in the trails occur due to the dark frame captures.

If you're able to disable the dark frame capture, then you can stack images pretty easily with Photoshop. Otherwise, a free utility called, "Startrails.exe" works perfectly for these purposes.

Utility can be downloaded here: http://www.startrails.de/html/software.html

The effectiveness is entirely dependent upon the ability to disable the "long exposure noise reduction" of the backs.
 

GrahamWelland

Subscriber & Workshop Member
I guess I should clarify - I'm actually NOT looking for star trail solutions. What I'm looking for is a solution that would allow me to shoot a multi-minute or hour composite during daylight that would produce the same result as using a 10 stop or stronger ND filter.

My particular use cases are seascapes or removal of people/vehicles from cityscapes without leaving behind trails. My thoughts are that averaging the brightness of each pixel of an image stack would produce the desired result which is a different technique to that required for star trails where you want to record the brightest level for each pixel in a stack.

(Btw, for a Mac this looks interesting & worth checking: Keith Wiley's keithsImageStacker)
 

Laurent

New member
Shooting long exposures in daylight leaves car and people trails that look like a fog. I haven’t tried that but what if you were to increase the contrast on the picture and apply the contrast on the foggy area using a mask. Would that work? I assume the contrast could help remove the fog effect, wouldn’t it?
 

Audii-Dudii

Active member
Shooting long exposures in daylight leaves car and people trails that look like a fog.
In my experience, as with most things, it all depends upon the specific circumstances. Catherine Opie, for instance, had great success with her American Cities project using long exposures during daylight to eliminate the traces of peoples presence in public places (although she was shooting film), as you can see here: http://www.themorningnews.org/archives/galleries/american_cities/

Back to the specific question at hand, I wonder if the sort of "averaging" process Graham is seeking couldn't be accomplished manually in Photoshop by stacking the individual photos as separate layers and blending them together using the various modes available?
 

jlm

Workshop Member
stephen: those are very nice!

would be good to have the control over the long exposure and play around with this

i think blad is the only back that does not use a darkframe though
 

coulombic

New member
I guess I should clarify - I'm actually NOT looking for star trail solutions. What I'm looking for is a solution that would allow me to shoot a multi-minute or hour composite during daylight that would produce the same result as using a 10 stop or stronger ND filter.

My particular use cases are seascapes or removal of people/vehicles from cityscapes without leaving behind trails. My thoughts are that averaging the brightness of each pixel of an image stack would produce the desired result which is a different technique to that required for star trails where you want to record the brightest level for each pixel in a stack.

(Btw, for a Mac this looks interesting & worth checking: Keith Wiley's keithsImageStacker)
You might actually be able to get by just fine with using the same program (Startrails.exe) for your purposes. Throw a few sequential 30+ second exposures into the program and try the different blending/stacking options. Being that you're not shooting anything that will show gaps, it will probably turn out close to what you're hoping for.
 
P

perjorgen

Guest
To remove people and vehicles you should use median stacking option. You do not have to use long exposures, but shoot many frames. If you use photoshops stacking you can manually remove areas causing problems (because there is a high concentration of items in that area)
If you wan't to do landscapes use average stacking option
 

ondebanks

Member
Graham,

You should use DeepSkyStacker - despite its name, it is not only suitable for astronomy. It would suit your purposes, because you can choose any combination algorithm you please - not just "maximum" which is what most star trails software uses. Averaging, median, weighted averaging, sigma clipping...it's all there.

And it's free.

http://deepskystacker.free.fr/english/index.html


And on the subject of backs that can or can't disable dark frame subtraction: I'm glad to hear that the H4D is in the stable that can disable it. Add that to the Pentax 645D, Mamiya ZD, the old Kodak 645 backs, and maybe some others. Now Phase One need to do it as well!

Change your bloody firmware, Phase One! :deadhorse:


Ray
 

Audii-Dudii

Active member
You should use DeepSkyStacker - despite its name, it is not only suitable for astronomy. It would suit your purposes, because you can choose any combination algorithm you please - not just "maximum" which is what most star trails software uses. Averaging, median, weighted averaging, sigma clipping...it's all there.
So, assuming Phase One did let you disable the dark-frame subtraction, am I correct in assuming that you could effectively accomplish almost the same thing with this software by capturing a dark-frame at a more convenient time (say, after you have made a couple of exposures) and stacking them post-exposure?

I know that, ideally, the dark-frame image should be made under identical conditions, but I wonder how close close-enough would get you? Being able to capture the dark-frame during downtime (say, when moving the camera to a new position or new location) certainly would be a lot more convenient, even if the results might not be quite as good as they are using the present methodology...
 

GrahamWelland

Subscriber & Workshop Member
Thanks folks for the feedback. I'll give the average/median algorithms a try on some street scenes I have with me.

Graham
 

coulombic

New member
Graham,

You should use DeepSkyStacker - despite its name, it is not only suitable for astronomy. It would suit your purposes, because you can choose any combination algorithm you please - not just "maximum" which is what most star trails software uses. Averaging, median, weighted averaging, sigma clipping...it's all there.

And it's free.

http://deepskystacker.free.fr/english/index.html


And on the subject of backs that can or can't disable dark frame subtraction: I'm glad to hear that the H4D is in the stable that can disable it. Add that to the Pentax 645D, Mamiya ZD, the old Kodak 645 backs, and maybe some others. Now Phase One need to do it as well!

Change your bloody firmware, Phase One! :deadhorse:


Ray
Just checked this program out -- looks much, much more featured than the one I suggested.

Thanks!
 
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