[Scootatheschool1990]

Hello everyone, I know this a reach for the stars - and yes, if you have a long exposure of the stars that would be great- but I'd like to determine how well the 645D noise is at long exposures. No one on the internet has documented this well (one person and DPR). I'm 7/10th's of the way to getting a 645D and I just wanted to make sure I am getting something that can perform what I need. The 65+ has shown a promising long exposure going 1 hour and still retaining lots of detail, So I hope the 645D has shown you guys love with long exposures.

[Ryan Tischer]

I've done a few star trails with the 645D and wouldn't recommend it for really long exposures...what do I mean by "really long"? Well, it's relative, because the exposures get more noisy gradually as the exposure increases. At 30 seconds the files are GREAT, no issues, even into a couple of minutes they aren't bad, but I did a few exposures at around 10-30 mins and they weren't what I would consider pretty, at least when viewed at 100%. Once downsized, they weren't too bad. The other bad thing about long exposures with the 645D is that there's no work around to avoid the dark frame capture. Meaning, that if you take any exposure over 30 seconds, the camera immediately follows it with a dark frame. So, when I was making 30 min exposures, I basically made my best guess, took the exposure, then packed the camera into my bag and went to bed (it was night exposures).


Here's a 30 min exposure with the 645D:



"Yosemite Falls Star Trails"
Pentax 645D, 645 35mm A
30 minute exposure, f/3.5, ISO 800

When I did a similar length exposure with my previous camera, a Canon 5D mark II I found much less noise and a sharper image at 100%. Granted, the 5D II has half the resolution, so when printed my guess from experience is that the 645D file would probably be about the same apparent sharpness.

[jonmarsh]

I have done some night time photography at my GF's, which turned out quite well with 15-25 second exposures. I'll dig one up at home and post later.

[Scootatheschool1990]

I've done a few star trails with the 645D and wouldn't recommend it for really long exposures...what do I mean by "really long"? Well, it's relative, because the exposures get more noisy gradually as the exposure increases. At 30 seconds the files are GREAT, no issues, even into a couple of minutes they aren't bad, but I did a few exposures at around 10-30 mins and they weren't what I would consider pretty, at least when viewed at 100%. Once downsized, they weren't too bad. The other bad thing about long exposures with the 645D is that there's no work around to avoid the dark frame capture. Meaning, that if you take any exposure over 30 seconds, the camera immediately follows it with a dark frame. So, when I was making 30 min exposures, I basically made my best guess, took the exposure, then packed the camera into my bag and went to bed (it was night exposures).


Here's a 30 min exposure with the 645D:



"Yosemite Falls Star Trails"
Pentax 645D, 645 35mm A
30 minute exposure, f/3.5, ISO 800

When I did a similar length exposure with my previous camera, a Canon 5D mark II I found much less noise and a sharper image at 100%. Granted, the 5D II has half the resolution, so when printed my guess from experience is that the 645D file would probably be about the same apparent sharpness.

That's a sweet photo! Do you have any Raws you wouldn't mind sharing? Perhaps not awesome photos like the one above, but just like ones that didn't come out right? This is actually what I was looking for- I think 10 minutes is the longest I would do. Thanks for sharing such a great photo btw!

[Scootatheschool1990]

I have done some night time photography at my GF's, which turned out quite well with 15-25 second exposures. I'll dig one up at home and post later.

Cool! looking forward to it! Do you have any RAWs?

[mikeSF]

Beautiful image of Yosemite falls!!

[Ting-Li Lin]

I've done a few star trails with the 645D and wouldn't recommend it for really long exposures...what do I mean by "really long"? Well, it's relative, because the exposures get more noisy gradually as the exposure increases. At 30 seconds the files are GREAT, no issues, even into a couple of minutes they aren't bad, but I did a few exposures at around 10-30 mins and they weren't what I would consider pretty, at least when viewed at 100%. Once downsized, they weren't too bad. The other bad thing about long exposures with the 645D is that there's no work around to avoid the dark frame capture. Meaning, that if you take any exposure over 30 seconds, the camera immediately follows it with a dark frame. So, when I was making 30 min exposures, I basically made my best guess, took the exposure, then packed the camera into my bag and went to bed (it was night exposures).


Here's a 30 min exposure with the 645D:



"Yosemite Falls Star Trails"
Pentax 645D, 645 35mm A
30 minute exposure, f/3.5, ISO 800

When I did a similar length exposure with my previous camera, a Canon 5D mark II I found much less noise and a sharper image at 100%. Granted, the 5D II has half the resolution, so when printed my guess from experience is that the 645D file would probably be about the same apparent sharpness.

Lovely shot! No wind that night?

[fotophil]

Hello everyone, I know this a reach for the stars - and yes, if you have a long exposure of the stars that would be great- but I'd like to determine how well the 645D noise is at long exposures. No one on the internet has documented this well (one person and DPR). I'm 7/10th's of the way to getting a 645D and I just wanted to make sure I am getting something that can perform what I need. The 65+ has shown a promising long exposure going 1 hour and still retaining lots of detail, So I hope the 645D has shown you guys love with long exposures.

I think you are confusing the P65+ with the P45+. The P65+ isn't useable at one hour exposure time.

[Scootatheschool1990]

I think you are confusing the P65+ with the P45+. The P65+ isn't useable at one hour exposure time.

Sorry the Iq260! My mistake!
1 Hour Exposure with the Phase One IQ

[alunfoto]

Hello everyone, I know this a reach for the stars - and yes, if you have a long exposure of the stars that would be great- but I'd like to determine how well the 645D noise is at long exposures. No one on the internet has documented this well (one person and DPR). I'm 7/10th's of the way to getting a 645D and I just wanted to make sure I am getting something that can perform what I need. The 65+ has shown a promising long exposure going 1 hour and still retaining lots of detail, So I hope the 645D has shown you guys love with long exposures.

Hi Scoot,
I've made some observations on long exposures with the 645D compared to the Pentax K-5, and made the same observations as others did with a Canon that the 645D seems more prone to noise. In my experience, however, it's not really the noise from the 645D CCD cirquit itself that is the main problem. What frustrates me more is the random, and sometimes very conspicuous, spurious noise caused by Compton scattering. I was completely baffled by it first time I saw it and wrote a lengthy post in my blog about it. It may be of interest to you. The images I refer to in the lengthy post are here.

Since that experience, I've come to think that the only real option is to combine a number of shorter exposures in post.

On a recent trip to California and Nevada I saw less to the spurious noise problem than back home in Norway. There are some examples in the November archive. I have no idea if the problem actually does increase with latitude, though.

Another trick I applied in the USA was to do multiple exposures of 30 seconds. The shot of the Desert Highway in Zion Canyon is made that way. I have examined the raw file and found no spurious noise at all. The algorithm that combine parts of a multiexposure must be a bit different from the darkframing, I think.

Hope this can be of some help to you.

Best,
Jostein

[Scootatheschool1990]

Compton scattering

First time I've heard of this. Can't wait to read every link you sent me. Appreciate it!

[Scootatheschool1990]

Compton scattering

ABSOLUTELY FASCINATING!!! WOW! This is incredible! I am curious if it affects Cmos as well? Wow. I'm reading so intently here ha ha ha

[alunfoto]

I am curious if it affects Cmos as well?

Yes, I believe it affects all imaging sensors, both CCD and CMOS. I believe the main reason I see more of it with the 645D is the sheer size of the sensor. If I'm correct, a full-format 35mm system should be affected to a degree somewhere between APS-C and 645D.

[alunfoto]

I just checked and saw the link to Don Groom's work had gone dead. It's still floating though. The PDF about cosmic rays in astroimaging is now hosted here:

[Scootatheschool1990]

I just checked and saw the link to Don Groom's work had gone dead. It's still floating though.

I saw that, Downloading it right now. Thanks!