[Jewelltrail]

falconeye: I missed this thread. So, let me make a comment here, instead:

- You haven't been aware of PhotoAcute. This software is much more capable than just stacking to remove noise. I use it on a regular base, esp. when travelling w/o a tripod. Or for long lens landcsapes.

. Stacking N images reduces effective ISO to ISO/N.

- If you stack MANY images, you start to see low spatial frequency artifacts. The K-7 seems to be much better here than K20D.

That looks like a great program to own--thanks. I do a lot of hiking, but this might just give me the option to leave the tri-pod home.

[pentaxmz]

Grip on the way, so will have to try that.

I've also managed to do really long exposures on my K200D. I think the longest to date was 2.5 hours. No problems at all. Didn't melt the sensor, and didn't run out of battery (only because I made sure it was a fully charged set beforehand). Obviously, turned off the NR beforehand so that I didn't have to wait another 2.5 hours for the image to process. I frequently do >5min exposures with it (for sake of ISO 100 and F22 or similar) and haven't had any problems.

Didn't know you couldn't turn it off on K20D... which I suppose should be taken as consolation for not being able to stretch to it when I was buying, and getting the K200D instead.

I am very curious about how the camera performed for such a long exposure. Can you post an example.

In regards to extremely long exposures (2 hours or more), the typical DSLR may have a weakness here. However, such long exposures are mostly unnecessary with the availability of stacking s/w such as Images Plus, AstroStack, StarTrails, etc.

[LeoTaylor]

With all this discussion of astrophotography, long exposure, and heat build up I just have to jump in.

If you don't do astrophotography this may bore you. :ugh:

I bought my Pentax K1x0D cameras for many reasons, astro was not one of them. I use the filterless K110D exclusively for astrophotography (well, occasionally I enjoy shooting daytime IR with exposures under 1/1000 sec). I don't own a Canon DSLR and do not intend to buy one. But the advantages of a Canon are:

1. Lower noise.
2. Better Live View, they can take a 1000 shots of Jupiter without cycling the shutter (at a reduced but useful resolution).
3. Auto Dark (AKA Noise Reduction) can be disabled on their CMOS sensor cameras unlike the K20D.
4. Most all astro software supports Canon, almost none supports Pentax. Images Plus will accept our PDFs but does not provide camera control for Pentax.
5. Ability to focus from the computer. I don't mean AutoFocus which is useless for faint night sky objects. I attended a Images Plus workshop where he manually focused a Canon lens on a ceiling light from a computer. Focus is one of the hardest parts of astrophotography.
6. And so on.

With my Pentax I get fairly good performance with each exposure of up to a few minutes from my light polluted location. In Astro you want the longest exposure you can manage, and a lot of them. I don't think you will get much with the 8 second exposures mentioned. I take dozens of 2 minute exposures.

I started taking astrophotos with Pentax K1000. No way could film do what I do now.

I've measured the K110D current draw from an external power supply a few years ago. While the shutter is open (lens cap on) it consumes almost 4 watts. The current during an NR dark frame (shutter closed) is about 3 watts. As 5teve mentioned NR heats the sensor almost as much as the exposure itself. Current at idle (electronics still on) is 1 watt. That is a lot of heat to dissipate.

How much noise does this heat cause? I did the below 7 frame test a couple of years ago. Starting with the camera at room temperature each run, I took seven 1 minute exposures with the camera capped and no NR. First run my timer allowed 8 seconds between frames to save the RAW file. Second run had a 30 second delay, Third 60 second. I measured the noise in the "black" frames using Images Plus. Without an inter frame cool off period the noise rose 7:1 in 7 frames and showed no indication of tapering off! This causes havoc with astrophotos since doing post imaging dark subtractions can't track such a rapid rise in thermal noise. Also, nebulas that I could see in the first frame vanished in the noise by the last frame. This is why I have resigned myself to using NR plus a cooling off period which reduces my overall exposure time for the session. OTOH this year I've been able to image objects I could not when I maximized exposure time by taking dark frames after the session.

In April I decided to do a longer test to see when the curve does taper off. As you can see as the exposures reach about 20 the sensor heat remains fairly steady. Also, the 7:1 increase in 7 exposures repeated nicely.

http://pages.cthome.net/astroleo/HeatTest.jpg

http://pages.cthome.net/astroleo/HeatTest21.jpg

Can you do astro with a Pentax DSLR? Sure, I'm processing photos from Tuesday night right now. Is a DSLR, especially a Pentax, ideal? No. I have an older SBIG ST-7E astro camera (1.4 megapixels cost me $3000 in 2000) that will run circles around a DSLR. It has sensor cooling to 30 degrees centigrade below ambient and control temperature to within 1 degree. This results in low noise and consistent dark frame subtraction. Why do I now use my Pentax almost exclusively? I wanted more pixels and easy color and could not afford a new SBIG! My SBIG still serves me, as an guide camera!

There is a lot of miss-information about astrophotography in this thread, I hope I cleared a few things up.

[Duck Dodgers]

Yeah, I was wondering when dedicated, cooled CCD cameras like the SBIG would get mentioned. As much as I love my Pentax, its forté is not astro-photography.

That didn't keep me from buying a T-mount adapter to fit my K10D to my 2400mm f/12 classical cassegrain, though!

---

Last edited by Duck Dodgers; 06-08-2009 at 07:00 AM.

[nightfly]

You're kidding right? Tongue in cheek? Right?

Few and certainly fewer pro-astrophotographers use film any more. Digital is the way to go for many reasons. One big reason is instant results, no more gas hypering (re: reciprocity failure reducer), lower magnitude gains, shorter exposures, digital stacking of shorter (sometimes hundreds) exposures, etc. etc...

Film is gone, gone, gone!! And though I have many fond memories of the yesteryears, I am very happy with what can be done with good digital imagers! That is both day time and night time photography!

While this is generally true, film is still usable for astrophotography and with very good results, if one is familiar with how to handle it properly. Nice long "single frame" exposures, 30 to 90 minutes are routine.

Just a sample of my work with E200 film and a well outfitted Pentax 67.


Nightfly Astrophotography : Gallery


I would be hard pressed to duplicate these results with anything less than a cooled CCD costing $$$.

I'm not against DSLR's, in fact I hope to use the new K-7 to compliment my film work. It's all good!

[pentaxmz]

With all this discussion of astrophotography, long exposure, and heat build up I just have to jump in.

snip....

I've measured the K110D current draw from an external power supply a few years ago. While the shutter is open (lens cap on) it consumes almost 4 watts. The current during an NR dark frame (shutter closed) is about 3 watts. As 5teve mentioned NR heats the sensor almost as much as the exposure itself. Current at idle (electronics still on) is 1 watt. That is a lot of heat to dissipate.

Some great comments.

I am very surprised at the current draw; in fact I doubt that you made an accurate measurement. If the camera really did consume 4 watts, your 2100 mAh AA batteries would likely fail within 1/2 hour (if that). I would expect a value of half or more than half of what you are reporting.

Also, keep in mind that electronics power consumption (in watts) does not equally reflect the same in heat production (not even close).

How much noise does this heat cause?

snip...

In April I decided to do a longer test to see when the curve does taper off. As you can see as the exposures reach about 20 the sensor heat remains fairly steady. Also, the 7:1 increase in 7 exposures repeated nicely.

http://pages.cthome.net/astroleo/HeatTest.jpg

http://pages.cthome.net/astroleo/HeatTest21.jpg

How did you directly measure sensor temperature?

I know that the EXIF temperature information for the K20D is not a measurement of the sensor's temperature but rather the imaging processor's circuit board temperature.

Can you do astro with a Pentax DSLR? Sure, I'm processing photos from Tuesday night right now. Is a DSLR, especially a Pentax, ideal? No. I have an older SBIG ST-7E astro camera (1.4 megapixels cost me $3000 in 2000) that will run circles around a DSLR.

I also once owned a SBIG camera... well technically, I convinced my high school to buy one and I ended up using it for three years almost exclusively (I helped raise the funds so I think I earned it). One of the reasons why this product is so well suited to astrophotography (besides the cooling) is the larger size of every pixel element. Larger means more light gathering capability per pixel.

[pentaxmz]

While this is generally true, film is still usable for astrophotography and with very good results, if one is familiar with how to handle it properly. Nice long "single frame" exposures, 30 to 90 minutes are routine.

Just a sample of my work with E200 film and a well outfitted Pentax 67.

Nightfly Astrophotography : Gallery

I would be hard pressed to duplicate these results with anything less than a cooled CCD costing $$$.

I'm not against DSLR's, in fact I hope to use the new K-7 to compliment my film work. It's all good!

Well, I suppose film can never become unusable for astrophotography. After all, it has been used more or less successfully since the dawn of film.

However, you simply cannot beat a digital sensor's quantum efficiency. A good digital sensor will always record a more accurate and clean image when compared to even the best film. Granted, gas hypering can actually give film a super-boost by getting rid of those pesky o2 molecules.

You have some nice photos.... have you ever considered gas hypering? You will be amazed with even better results in about 3/5th the time.

[nightfly]

Well, I suppose film can never become unusable for astrophotography. After all, it has been used more or less successfully since the dawn of film.

However, you simply cannot beat a digital sensor's quantum efficiency. A good digital sensor will always record a more accurate and clean image when compared to even the best film. Granted, gas hypering can actually give film a super-boost by getting rid of those pesky o2 molecules.

You have some nice photos.... have you ever considered gas hypering? You will be amazed with even better results in about 3/5th the time.

I use mostly Kodak E200 as it has virtually no reciprocity failure in very long exposures as well as extremely high red sensitivity. Gas hypering does not seem to add to this film, perhaps others.....

There is a very limited amount of emulsions out there for astro work.

Wide-Field work is one place that film still shines. Digital SLR's blow away film in through-the-scope work. My 6x7 frames are amazing to look at on the light table. No scanner can quite capture it. My shots I post online are the same. These frames can be greatly enlarged with very fine detail. Large prints are amazing.

Digital will be the future for sure, but I am happy with what I get with MF film. The 67 glass offers very high resolution compared to the small aperture lenses used for wide angle digital work. Ultimately it is my taste that matters in the end, that's why they call photography an art.

Thanks for the kind comments.

[LeoTaylor]

Hi pentaxmz,

Indeed, if I do long exposures when on batteries the camera goes dead in LESS than 30 minutes. It happens occasionally when the external power cord falls out. I return expecting lots of nice frames and find the batteries quit while I was away.

I'd say my old measurement accuracy was pretty good. I'll measure the current drain again and provide a more accurate reading.

I never said I measured sensor temperature. I measured noise using Images Plus as mentioned in the message. I used a tool called, "Cross Hair Statistics." The second graph (the one with the taper off) is titled Dark Noise. Since the noise is from heat so I infer that as the noise levels off the heat levels off. I regret the first graph does say Heat Buildup.

Unfortunately the temperature found in PhotoMe for the K110D is not from the sensor and does not rise with usage. It does track the ambient temperature fairly well. Since most daytime photos are not long enough to cause a noticeable rise the PhotoMe reading is OK for most people.

Glad to hear you've used an SBIG. As you know the software displays the temperature of two sensors, main and guide. In the winter I run mine at -35 C, in the summer it is -15 C.

I'm living on a fixed income these days so can't afford a new SBIG. The K110D keeps me busy every clear night

[LeoTaylor]

nitefly,

There are many good film astrophotographers. Daphne and Tony Hallas took some great photos (and snagged a great url):

ASTRO PHOTO HOME

The only astrophoto I ever bought is a framed Hallas film shot of the Iris Nebula hanging right behind me. But even Tony Hallas has finally made the switch to digital.

From my light polluted location I could only get two galaxies on K1000 film, M31 and M51 (MAG 8). The latter was so faint I thought the print was blank, my wife spotted the spiral. With the K110D I have galaxies down to MAG 16. With the SBIG I have galaxies down to MAG 19+.

Film required dark locations that I do not have access to. My mentor said an SBIG would cut through the pollution and it did!

[pentaxmz]

I use mostly Kodak E200 as it has virtually no reciprocity failure in very long exposures as well as extremely high red sensitivity. Gas hypering does not seem to add to this film, perhaps others.....

I too have had significant experience with E200 film (early 90's). You are correct about the ineffectiveness of gas hypering. I remember experimenting with many, variations of gas mixtures and heating. I had probably spend (or wasted) 100's of hours experimenting and arriving at disappointing results (that is, in terms of increasing performance). I wrote Kodak with my results and received a really nice letter in return.

Although it's reciprocity characteristics are certainly impressive, it still suffers from reciprocity failure simply because it still employs the silver halide method of light gathering.

And, like all film, it's non-linear response simply doesn't capture a long exposure scene as accurate as a digital imager.

Yes, you are right... photography of any kind is an art. I will admit there is a certain amount of magic that is lost with digital work. I miss watching a monochrome image appear before my eyes in a red-lit darkroom. One of the reasons why I preferred monochrome work to colour work. Although I had heard rumours of a light that could be used when doing colour work.

[pentaxmz]

Hi pentaxmz,

Indeed, if I do long exposures when on batteries the camera goes dead in LESS than 30 minutes. It happens occasionally when the external power cord falls out. I return expecting lots of nice frames and find the batteries quit while I was away.

I'd say my old measurement accuracy was pretty good. I'll measure the current drain again and provide a more accurate reading.

I never said I measured sensor temperature. I measured noise using Images Plus as mentioned in the message. I used a tool called, "Cross Hair Statistics." The second graph (the one with the taper off) is titled Dark Noise. Since the noise is from heat so I infer that as the noise levels off the heat levels off. I regret the first graph does say Heat Buildup.

Unfortunately the temperature found in PhotoMe for the K110D is not from the sensor and does not rise with usage. It does track the ambient temperature fairly well. Since most daytime photos are not long enough to cause a noticeable rise the PhotoMe reading is OK for most people.

Glad to hear you've used an SBIG. As you know the software displays the temperature of two sensors, main and guide. In the winter I run mine at -35 C, in the summer it is -15 C.

I'm living on a fixed income these days so can't afford a new SBIG. The K110D keeps me busy every clear night

I must apologize for my comment about not believing your current measurements. It came out kind of harsh. I am very surprised and it makes me curious and concerned about the current drain on the K20D. If the current drain is similar and with a stock battery of only 1520 mAh, I should expect even less than 1/2 hour of open shutter time. That seems unreasonable and perhaps.... unlikely.

Can anyone confirm this... I suppose this is easy enough for me to test. I'll get back with an answer later.

If only my wife would allow me to purchase a SBIG.... actually, these days I am far more interested in purchasing a SolarMax 90 from Coronado. It's about the price of a mid-grade SBIG.

[pentaxmz]

nitefly,

There are many good film astrophotographers. Daphne and Tony Hallas took some great photos (and snagged a great url):

ASTRO PHOTO HOME

The only astrophoto I ever bought is a framed Hallas film shot of the Iris Nebula hanging right behind me. But even Tony Hallas has finally made the switch to digital.

Wow, wow, wow!

I never heard of this team before but they have some of the most outstanding land-based astrophotos I have ever seen. Some of these photos are an example of what $40,000 and technical knowledge can get you!

Thanks for that link!

[nightfly]

nitefly,

There are many good film astrophotographers. Daphne and Tony Hallas took some great photos (and snagged a great url):

ASTRO PHOTO HOME

The only astrophoto I ever bought is a framed Hallas film shot of the Iris Nebula hanging right behind me. But even Tony Hallas has finally made the switch to digital.

From my light polluted location I could only get two galaxies on K1000 film, M31 and M51 (MAG 8). The latter was so faint I thought the print was blank, my wife spotted the spiral. With the K110D I have galaxies down to MAG 16. With the SBIG I have galaxies down to MAG 19+.

Film required dark locations that I do not have access to. My mentor said an SBIG would cut through the pollution and it did!

I've been around long enough to see Tony and Daphne's work from their begininngs in the early 80's. That's when I started as well. I like the medium and admit to being kind of religious about it. I like the quiet camera that has no lit screen ruining my night vision, just the camera, the telescope and the stars. Its my peace in the world. Taking the actual exposure is a big part of it for me and I like the method. Even when I switch to digital, I will always shoot a roll or two now and then.

As for film requiring dark skies, you are correct. Film does not like light pollution. Fortunately I live in eastern Maine where the skies are very dark. My home rests on Bortle class 2 to 3 skies. I can see magnitude 7 stars on almost any given moonless night. My absolute limit was magnitude 7.85 at the zenith. I am lucky to live where I live!

You ought to see the Milky Way in the summer from my front yard! Thats where I shoot most of my images.

[nightfly]

I too have had significant experience with E200 film (early 90's). You are correct about the ineffectiveness of gas hypering. I remember experimenting with many, variations of gas mixtures and heating. I had probably spend (or wasted) 100's of hours experimenting and arriving at disappointing results (that is, in terms of increasing performance). I wrote Kodak with my results and received a really nice letter in return.

Although it's reciprocity characteristics are certainly impressive, it still suffers from reciprocity failure simply because it still employs the silver halide method of light gathering.

And, like all film, it's non-linear response simply doesn't capture a long exposure scene as accurate as a digital imager.

Yes, you are right... photography of any kind is an art. I will admit there is a certain amount of magic that is lost with digital work. I miss watching a monochrome image appear before my eyes in a red-lit darkroom. One of the reasons why I preferred monochrome work to colour work. Although I had heard rumours of a light that could be used when doing colour work.

The one thing I really admire about digital work is the lack of hallation. In film, photons hit the film and spread to adjacent molecules and bright star images bloat on the film. This is especially noticable on 35mm work, but less so in MF, simply due to enlargement dactors.

As I am totally a wide-field astrophotographer, limiting myself to 300mm, film still delivers. I hate the fact that I have to send my film out for services (I don't like to mess with chemicals). My images are very respectable.

It is true that almost all the best film astrophotographer's of yesterday migrated to cooled CCD's and not dslr's, and rightfully so. But they are shooting through very expensive cameras with very expensive scopes. My budget supports what I can do and I think for the money it can't be beat.

That being said, I am interested in what I can do with a dslr given my decades of experience with film and astronomy. We'll find out soon enough. I let you guys know how it works out.

Thanks for the discussion.