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Thread: P45+ Super long exposures

  1. #1
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    P45+ Super long exposures

    Hello!

    I have a P45+ in H mount and will be traveling to death valley from the 2nd to the 5th of January. Conveniently the new moon is in this time frame and the skies should be dark.

    I do not have much experience with super long (1 hour plus) exposures, but would love to give it a go for star trail photos.

    What would the ideal exposure be to not blow out everything and try to get it all in one shot?

    I have the 50-110 f3.5-4.5 and 100 f2.2 at my disposal, as well as a CH-910 battery pack to power the back indefinitely. The weather should be around 40 at night, which would provide me with the ability for some clean long exposures, so I would love to try it out.

    Any suggestions would be very welcomed. I will most likely be using my 5d Mark II to get some shots as well, but will be bringing my Hasselblad.
    Rick Rose
    www.RickrPhoto.com
    HasselPhase

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    Subscriber & Workshop Member GrahamWelland's Avatar
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    Re: P45+ Super long exposures

    If it's a truly dark night and you are away from other sources of illumination, such as at the Racetrack for example, then it won't really matter about blowing out the foreground with a super long exposure because it'll be dark. The stars will be points of light that will in theory blow out but that's to be expected.

    For star trails I'd be inclined to shoot wider vs longer and that probably means your 50mm @ f/3.5. The trick being to ensure that you're focused on the stars and not relying on infinity if you want sharp star trails. As you can expect, the wider the aperture, the more star trails you'll get as you can record the dimmer stars.

    This is an hour long test I did with my P25+ a while ago and there's a lot of light pollution going on (Which you shouldn't have so long as you keep away from Furness Creek and the roads) but it'll give you some idea as to how the stars will appear. This is with an Alpa 47mm @ f/4.5 & ISO 50.



    If you're shooting with your Canon then you could shoot multiple images and stack them. The dark frame on the P+ back precludes doing this. Five+ hours looks like this at ISO100 21mm @ f/2.8 4min exposures plus light painting for the foreground. Had I not light painted, it would have just been a silhouette as you can see in the background.

    Remember: adventure before dementia!

    As Oscar Wilde said, "my tastes are simple, I only like the best"
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    Re: P45+ Super long exposures

    As Graham pointed out, the mandatory dark frame of the P45+ will limit you to the 1 hour max, plus one of waiting on the back to write the dark frame. Make sure you have a full battery or if the back powers off during the dark frame the shot will be ruined.

    I prefer to shoot with moonlight illumination. You get a much better sky, especially in my part of the country. The moon will give you a nice blue hue to the sky and can provide excellent foreground illumination.

    I have attached a 45" shot from the P45+ taken at F6.3 with about a 3/4 moon. The depth of the trails are not as dense as the 2nd shot from Graham ( which BTW is an excellent shot and a great example of why to stack) but you still get a nice look. Stacking allows you to get more depth to the stars and you will pull out a lot more of the distant stars. Plus you have so much control over the foreground if you foreground has wind issues.

    Paul Caldwell
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    Re: P45+ Super long exposures

    Sorry to hijack the thread, but would the CH-910 also work with an IQ180?

    If so, is it possible to hot-swap the batteries connected to it so that you could power the back for extremely long periods (assuming you had a good stack of batteries already charged) continuously without access to mains power?

    Kind regards,

    Gerald.

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    Subscriber & Workshop Member GrahamWelland's Avatar
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    Re: P45+ Super long exposures

    CH-910 has a battery plate that mimics the standard battery. The only way that it will fit in the IQ is to have the battery door open and hanging down.
    Remember: adventure before dementia!

    As Oscar Wilde said, "my tastes are simple, I only like the best"
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    Senior Member Ed Hurst's Avatar
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    Re: P45+ Super long exposures

    In my experience, you have loads more flexibility by stacking multiple exposures (which precludes the use of MFD due to the compulsory dark frames - unless you use sub 30 sec exposures). Here are some examples of shots that I don't believe I could have got with single long exposures because they depend on pretty short exposures for the ambient light in the scene (all shot with D800E and large numbers of stacked files):

    [IMG] Star Trails From Files_DSC4634-5209Step7sRGBSMALL-1 by Ed Hurst, Spiffing Pics, on Flickr[/IMG]

    [IMG] StarTrailsFromFilesB_DSC357-B_0720Step9sRGBSMALL by Ed Hurst, Spiffing Pics, on Flickr[/IMG]

    [IMG] StarTrailsFromFiles_DSC0017-852(PlusFile928ForDarkFrame)Step9CropSpotSMALL by Ed Hurst, Spiffing Pics, on Flickr[/IMG]



    On the other hand, because of the lack of high levels of ambient light in the scene, this sort of shot would be possible with a single long exposure on MFD:

    [IMG] StarTrailsFromFiles_DSC5459-5566Step5sRGBSMALL by Ed Hurst, Spiffing Pics, on Flickr[/IMG]

    [IMG] StarTrailsFromFiles_DSC1355-1499(PlusDarkFrame1550)Step5sRGBSMALL by Ed Hurst, Spiffing Pics, on Flickr[/IMG]



    By the way, a side benefit of stacking large numbers of short-ish exposures is that some of the individual files can produce very appealing images of stars (without the trailing); like this:

    [IMG] _DSC1543Step6CropSMALL by Ed Hurst, Spiffing Pics, on Flickr[/IMG]

    [IMG] _DSC8128-30Step6FlatSMALL by Ed Hurst, Spiffing Pics, on Flickr[/IMG]
    Ed Hurst, www.spiffingpics.com
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    Re: P45+ Super long exposures

    Ed,

    What software are you using to stack, and what is the normal number of frames you stack?

    I love the swirl effect in DSC5459-5566 -- I assume it's longer smaller aperture shots at the beginning, and shorter larger aperture exposures near the end? And is it really over 100 frames stacked???
    Jack
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    "Perfection is not attainable. But if we chase perfection, we can catch excellence."

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    Subscriber & Workshop Member GrahamWelland's Avatar
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    Re: P45+ Super long exposures

    Jack, not sure what Ed uses but Adobe's Dr Brown's Stack-A-Matic script is your friend with Photoshop.

    I agree with Ed regarding scenes with foreground lighting - tough to shoot with a single long long exposure. Stacking is really the easiest way to go for those scenes.

    Regarding the short exposures and dark frames, you can get away with this easily with regular DSLRs but somewhat more questionable with the Phase One backs because it seems like they don't 100% always avoid or invoke a dark frame with multi-second exposures. I suspect there's some heat/ambient temp logic going on.
    Remember: adventure before dementia!

    As Oscar Wilde said, "my tastes are simple, I only like the best"

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    Senior Member Ed Hurst's Avatar
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    Re: P45+ Super long exposures

    You got it Graham - Dr Brown's Stack-a-Matic is the way to go for sure. Launched from Bridge, it works very well indeed.

    As for DSC5459-5566, glad you like it! It is not achieved in the way you describe (in fact I am not sure that varying the exposure length would have that effect - you would just be capturing the same trajectory in 'slices' of varying length - not changing how the trajectory looks). That effect was a happy accident - condensation formed on the lens during the sequence of frames and caused the trails to bloom. The effect gradually developed as the condensation got worse. So the effect is purely down to that.

    And yes - over 100 frames. That is a short sequence by my standards. Some of the ones combining short exposures run to over 1,000 frames!

  10. #10
    Senior Member Ed Hurst's Avatar
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    Re: P45+ Super long exposures

    Graham - I have had the same experience with the Pentax 645D. The dark frame behaviour is complex and does not seem to conform to a neat rule of kicking in at 30sec and not doing it with shorter exposures. There seems to be some heat/ambient temp logic - or perhaps logic based on measuring on-sensor temperatures - that determines whether a dark frame occurs at or below 30 secs (though it always does above 30 secs). I have known exposures of the same length have a dark frame only on some occasions - even within the same shooting sequence - as though the build up on heat over time triggers the dark frame.

    Jack - just to give a rather fuller answer to your question about numbers of frames, I typically shoot these sequences for anywhere between 45 mins and four hours. Each exposure varies between around 12 secs and 2 mins (depending on the levels of ambient light). If a bright scene is to have long trails, that quickly adds up to a very large number of files - easily in excess of a thousand in many cases. Takes a lot of processing power and time when each file is a 16 bit 36MP TIFF!

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    Re: P45+ Super long exposures

    Ed, the 645D does state in the specs it does dark frames depending on certain factors including temperature. And I can confirm the sub 30 sec. exposure is had to predict if the dark frame will kick in.

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    Senior Member Ed Hurst's Avatar
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    Re: P45+ Super long exposures

    Hi Will - that is why I believe star trail shots based on stacking are not really suited to that body (or indeed other MFDs). The curious and frustrating thing is that the 645D firmware has a setting that purports to let you turn off the dark frame function, but turning it off doesn't turn it off! I hope any future 645Dii rectifies this.

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