Question about the P+ digital backs and long exposures

[Isak Bergwall]

Hi!

I am a total newbie on medium format but looking to switch from my nikon system to a P25+ back (either M645 or H2) so I have some questions.. This might have been covered and if so I apologize.

What I would like to know is when the Darkframe on the P25+ (and P45+) back kicks in? I haven't seen so much information about this on the web.

Does it kick in after a 1 second exposure, 30 seconds? a minute? Or all the time? if you know what I mean.

And if it say kicks in after 1 minute, can you still take multiple exposures of say 50 seconds for stacking or is the back to "slow" to shoot back to back so to speak.

Appreciate your help very much!

[Paul2660]

On the P45+ (and I believe this also true on the P25+), long exposure noise reduction kicks in a 1 second and any exposure longer than that.  This is also true on the newer Phase IQ backs also.

If you are stacking, it's not a very good solution IMO as you will have a dark frame interrupting your series after each normal exposure.  You  are
locked out of doing anything else until the dark frame completes which is not true on a modern DSLR, from Canon or Nikon.  Sure they will
eventually fill up their buffer also, but you can at least get a series off.  (I alway turn off long noise reduction on my DSLR's when working at night)  I found that as long as I kept the P45+ to no longer than 15 to 20" exposures I could actually stack with it as there are many tools out there to help going the gaps in the star trails created by the long noise dark frames.  However it's pretty much impossible to stack a long series of P45+ tif's as the files are just too big (even at 8 bit) and even my best machine would clog up.  I realize you can convert to jpg but I never liked doing that for stack work.  

The P45+ does an amazing job on longer single exposures.  I would have to say it generates by the cleanest files at 1 hour that I have ever seen.  This is true at iso 50 and iso 100 after that noise starts to creep in even with the long noise reduction turned on.  

I stopped doing single long exposures for night work about 1 1/2 years ago.  I found that stacking gives me much better starlight and allows me to pick the frame I want to use in the non sky area of the image.  To me it's a much more versatile style of night shooting.

Paul

[Isak Bergwall]

Thank you for your answer!

I don't do stackminne normaly and I think I can live without it when I move to mediumformat

[Graham Welland]

Paul - what software do you recommend for fixing up star trails? I've been shooting these using 4min exposures with the minimum intervalometer gap of 1sec between exposures and at the pixel peep level there are always still gaps in the trails. I understand that this is the RAW converter applying a contrast curve which darkens the ends of the trails as it's not a gap as such but an intensity reduction.

Any thoughts/recommendations?

To the OP: unfortunately Phase One don't trust us to turn off LENR and so we're stuck with dark frames whether we like them or not. I use a P25+ for long exposures myself and it's great up to 15 minutes (possibly longer but I've never had the patience or battery to wait for the dark frame).

[Isak Bergwall]

graham: I think you can use Adobe Photoshop and use automate and add all files into one file then auto align (if needed) and then just use lighter (or what its called) as layer mode for all images except the base image, that shouldn't darken the trails, but your question maybe was about the raw converter, that I cannot answer..

15 minutes are usually long enough for just trails (not circular thats probably an hour?). I read somewhere about canon battery packs that should work a longer time.

However, I rather wait those minutes to get noise free images compared to the noisy stuff my nikon D700 brings out after long exposures, the only acceptable long exposures (Around 10-20 min without dark frame) was done in -20 Celsius And also it probably take an hour to stack that stuff anyhow if you have to raw process the images also.. But the only really problem is that you might only get like 1-2 shots when your out in the field and that is not so good. 

[Graham Welland]

graham: I think you can use Adobe Photoshop and use automate and add all files into one file then auto align (if needed) and then just use lighter (or what its called) as layer mode for all images except the base image, that shouldn't darken the trails, but your question maybe was about the raw converter, that I cannot answer..

I use image stacks in PS using Dr Brown's stack-o-matic action. It auto aligns and creates a stack with masks all in lighten mode. You still get the slight breaks. I will shoot 20 - 40 images like this and stack.

[Paul2660]

Graham:

The best tool I have found is called "star Tracer"  This is a PC only tool as far as I know but it works great.  It will fix the gaps perfectly.  It's only issue for
me is on the output step as it seems to have problems with it outputs as a tif file, and the color profile.  The tool most times will read all it needs from the
exif data on the lens info but sometimes you have to manually input it.  

It rotates the whole image to fill the gaps if you don't use the layer option.  Pretty cool software.  I want to say Max  Lyons wrote it.  

PM me if you can't find it.  

Paul