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06-13-2014, 07:25 AM   #1
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Time to upgrade from my K-x

Hi guys. I've been doing a lot of deep sky astrophotography lately with my old Pentax K-x and it seems my pics routinely get trumped by others using the Canon 1100D. So before I jump off the Pentax wagon, I was wondering if any of the newer Pentax models offer lower high ISO noise than my K-x. I routinely use ISO 1600 and 3200 either for 30 seconds, or longer at ISO 1600 on bulb. For noise decrease, I would really like to take pics at ISO 3200 that have the same noise as the K-x on 1600. Can any of the newer Pentax models do this? A camera that can also keep it's low noise characteristics in the heat (I live in the tropics) is also a plus. The K-x gets very noisy on long exposures over 20C. I don't need any fancy bells/whistles, I don't need a bazzilion mega pixels. I just want lower noise. That's it. I don't want to go astro CCD at this stage nor do I want to use a cooler box or mod.

Kevin.

06-13-2014, 07:46 AM   #2
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QuoteOriginally posted by Learjet Quote
Hi guys. I've been doing a lot of deep sky astrophotography lately with my old Pentax K-x and it seems my pics routinely get trumped by others using the Canon 1100D. So before I jump off the Pentax wagon, I was wondering if any of the newer Pentax models offer lower high ISO noise than my K-x. I routinely use ISO 1600 and 3200 either for 30 seconds, or longer at ISO 1600 on bulb. For noise decrease, I would really like to take pics at ISO 3200 that have the same noise as the K-x on 1600. Can any of the newer Pentax models do this? A camera that can also keep it's low noise characteristics in the heat (I live in the tropics) is also a plus. The K-x gets very noisy on long exposures over 20C. I don't need any fancy bells/whistles, I don't need a bazzilion mega pixels. I just want lower noise. That's it. I don't want to go astro CCD at this stage nor do I want to use a cooler box or mod.

Kevin.
My K5 and K-01 are most certainly less noisy than my Kx was. I've gotten long exposures at ISO 3200 on my K5 that were less noisy than the same length of exposure on my old Kx at ISO 800. One more cool thing is you can set either of those to keep taking picture after picture. I've set both for hundreds of multiple second exposures and then stacked them. I can tell you stacking will give better results than single exposures, but takes computer resources to do it.
06-13-2014, 08:03 AM   #3
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Oh definitely. The 16MP sensor that came after the K-r (so, the K-5, K-01, K-30, K-50, K-500) is much better than the one in the 12MP K-x and K-r. I noticed a big jump when I got the K-01 in comparison to the K-r.
If you want an inexpensive option, try the K-01. It is very sharp, because it has a very weak AA filter. But you said you live in the tropics, so a camera that is constantly in live view might not be a good idea, due to overheating. A better choice might be a K-5, with the extra bit depth which improves noise performance even more (and it also allows ISO 80). The original K-5 can be found for a really good price, but the K-5II and K-5IIs have come down since the K-3 was released, too.

The other thing is, astophotography is a whole deal. Not only the camera, but the dark frame NR, multiple exposures, tripod and lens and other accessories, and post processing are very important. This plays a huge role in how the photos come out.
And finally, Pentax has the O-GPS astrotracer thingy, which allows longer shutter speed without causing star-trail blur due to star movement. This can help you use a lower ISO and longer shutter, or a lens of higher focal length which is faster. Just make sure the astrotracer is compatible with the camera you are thinking about - I don't think it works with the K-01. The astrotracer is only possible because of the in-body sensor stabilization, which Canikon don't have. This is an advantage of Pentax.

Edit: You can also search for astrophotography done with Pentax cameras. Ive seen some awesome examples posted on this forum before. That should prove what the cameras are capable of.
06-13-2014, 08:11 AM   #4
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I would suggest the K5/II/IIs, or K50. You can couple these with the O-GPS1 that offers the AstroTracking capability (similar to an equatorial mount) for up to 5 minutes of tracking (wide angle lens, telephoto less). Take a look at these threads. Also, the K5 and its family using the sony sensor, has much lower noise at higher ISOs
________
Take the first link - Astrophotography, its a thread of about 60 pages (800+ posts) over the course of a few years. You will very quickly come across the folks - and their images that have done absolutely stunning work, equal to and probably exceeding the work that you are trying to compare yourself to using Canon or whatever else. Also, I do think that the Kx will work OK, but the K5/II/IIs K50, K30 etc. have all come down in price - a used K5 goes for about $400US now - will do better. You will find stunning images of galaxies and nebula, along with varying techniques. Stacking for deep sky is a given. Post processing software too. Here is a link to capturing and stacking images (not a Pentax, but the aim is how to stack - especially the stacking software).Note, you can take images using the GPS AstroTracking, - take as many as you want, and you can stack them using software too. Something that Canon and Nikon can not do with out a equatorial tracking mount.

Also, note - on the O-GPS, the AstroTracking function is limited to a number of the newer bodies - K5/II/IIs K30, K50, K3 - so for this functionality you need to do a bit of checking if you want to go to a new body and the GPS unit.




Last edited by interested_observer; 06-13-2014 at 01:52 PM. Reason: more information
06-13-2014, 08:44 AM   #5
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I am sorry but there is no such thing you ask for. For iso1600 on K-x to equal iso3200 you should go FF. On modern Pentaxes it only equals iso2300.

---------- Post added 13th Jun 2014 at 18:49 ----------

btw 1100d has more noise than the K-x, it equals iso1500.

---------- Post added 13th Jun 2014 at 18:51 ----------

did you try post processing noice removal with some specialized software?
06-13-2014, 01:17 PM   #6
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QuoteOriginally posted by Learjet Quote
Hi guys. I've been doing a lot of deep sky astrophotography lately with my old Pentax K-x and it seems my pics routinely get trumped by others using the Canon 1100D. So before I jump off the Pentax wagon, I was wondering if any of the newer Pentax models offer lower high ISO noise than my K-x. I routinely use ISO 1600 and 3200 either for 30 seconds, or longer at ISO 1600 on bulb. For noise decrease, I would really like to take pics at ISO 3200 that have the same noise as the K-x on 1600. Can any of the newer Pentax models do this? A camera that can also keep it's low noise characteristics in the heat (I live in the tropics) is also a plus. The K-x gets very noisy on long exposures over 20C. I don't need any fancy bells/whistles, I don't need a bazzilion mega pixels. I just want lower noise. That's it. I don't want to go astro CCD at this stage nor do I want to use a cooler box or mod.

Kevin.
In short, yes, you'll be able to get less noise from a newer body. I'd recommend the K-5 IIs, as it gives you 14-bit RAW files and doesn't have an AA filter.

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06-13-2014, 03:43 PM   #7
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QuoteOriginally posted by climit Quote
I am sorry but there is no such thing you ask for. For iso1600 on K-x to equal iso3200 you should go FF. On modern Pentaxes it only equals iso2300.
How did you come up with that?
06-13-2014, 06:27 PM   #8
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Thanks everyone for your responses. I don't want to go full frame just yet, some of my gear will vignette at larger than APS-C. So, most models after the K-r should be better noise wise then? I don't have a lot of money to outlay so will probably stick to budget or second hand models. The K5-IIs without the AA filter looks very nice but I think out of my budget range.

I don't take a lot of widefield pics but that astro tracker looks like a cool device, taking advantage of the moving sensor. I haven't seen that before, but most of the fellas I hang out with on astronomy forums are Canon users, possibly due to an abundance of Canon aps to drive them with laptops while connected to the telescope.

I'm not new to astrophotography, (not that I'm particularly good at it) just trying to keep up with the Jonseses lol. I have a gallery at Astrobin, mostly with the K-x and some with an astro modified Nikon D70s. Kevin's gallery | AstroBin

As mentioned my main battle is with noise. Lower noise is like using a faster, bigger telescope.


I'm quite familiar with frame stacking, I've been using it to advantage with either Registax or Deep Sky Stacker since I gave up using film.

06-13-2014, 08:10 PM   #9
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The 16MP models were about a 1 step increase in ISO for a given noise level, maybe a step and a half. A used K-30 is probably your best bet for this sensor, unless you won't miss the viewfinder, then the K-01 is your ticket in.

Here are two shots in similar lighting at 1:1 magnification at ISO3200. I zeroed out all the settings in LR, so this is right off the sensor, the way it came. The bit with the flag is the K-30, the bit with the pole is the K-X. Remember that the K-30 has to be cropped more at 1:1 because it has more pixels to start with, so the differential is about 30% more than what it appears in the image for a real picture at the same magnification.






And for comparison, the KX at 1600, also zeroed out, but I think this was somewhat darker based on the exif.

06-13-2014, 08:21 PM   #10
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Hi Kevin, and I forgot to welcome you to the Forum!!!

As of this time, Pentax does not have a full frame camera, so everything is APS-C, with the exception of the 645D (Medium Format CCD) and the Q (which is a very small sensor). Also, just assuming that you are interested in Astro, and the user controls (dual wheels, etc.) are not that important. Given that you want lower noise, you do not want the K20 or the K7. Those bodies used a Samsung sensor that was good, but a tad noisy. Pentax produced the K5 using a Sony sensor, that perfectly hit the mark (the same sensor that Nikon used in the D7000). Then Pentax spun out an entire line of bodies at various levels using the essentially the same sensor). All of the models listed below are substantially better than the Kx with noise.
  • K5/II/IIs - has a 14 bit D/A converter (better image quality in the shadows) - ISO 1600 is clean, 3200 is starting to get a bit of noise but still very useable, 6400 more noise, still useable. AA filter remove on the IIs (this results in an increase of about 8% in resolution).
  • K30 / K50 - same guts, but a slightly different body, has a 12 bit D/A converter. . Both bodies have an AA filter
  • K500 - entry level body, but same sensor, with a 12 bit D/A converter. Has an AA filter
  • K-01 - aka the Brick - way different body style (mirrorless), 12 bit D/A, but has a VERY light AA filter.

In terms of price, used K5 have dropped a lot, the II and IIs not so much as they were just replaced by the K3, however a lot of folks like the low ISO noise profile of the IIs better. The K500 and K-01 would probably hold the most interest for you - based on price. The K-01 price dipped very low - to about $200 a year ago (new) - its very light AA filter would interest you, while the K500 which probably has a heavier AA filter. So its somewhat of a mixed bag.

Since you were able to produce those stunning Astro images with the Kx, you should be able to really do much better with any of these. Also, since you are mounting the camera on a telescope that's on a tracking mount, really all you desire is the camera. With that then, the K-01, with a very light AA filter, no mirror, and its relatively cheap, would be as close to perfect for you given the price. They have gone on ebay in the last couple of months from $190 to over $300. Also, the K-01 only uses the IR wireless remote - like your Kx.So that's a quick summary, and it all a set of compromises to varying degrees.

hope that helps....

06-13-2014, 10:35 PM   #11
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QuoteOriginally posted by VoiceOfReason Quote
How did you come up with that?
dxomark sensor measurments

---------- Post added 14th Jun 2014 at 08:39 ----------

QuoteOriginally posted by Kozlok Quote
The 16MP models were about a 1 step increase in ISO for a given noise level, maybe a step and a half.
dxomark measured it 0.5 steps
06-13-2014, 11:24 PM   #12
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Thank you very much for the photos Kozlok and for the links interested_observer. That helps.

How important is that DA converter? 14 bit looks a lot more attractive when stretching a dark image. If it's very important I may be best getting something in the K5 line. The more I think about it, the more I suspect it's the reason why the 1100D works so well in spite of it's poor ISO noise figure, it has large pixels to collect more photons and a 14 bit AD converter. This is where astronomy differs some from daylight photography - apart from the moon and planets, I primarily work with very dark, low contrast images that need to be stretched more than a rubber band.

For example here is a before and after stretch of galaxy NGC253. It's already 108 x 30 second subs at ISO 3200 and it needs lots, lots more sub exposures to look how I want it. I'll be wearing out the shutter at this rate.
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06-14-2014, 07:39 AM   #13
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A 14 bit A/D converter (compared to 12 bit) therefore the dynamic range is wider. This translates into less noisy images, with more details. Increasing to 14-Bit from 12-Bit allows the camera to record up to 16K colors per channel for smoother tonal transitions and more accurate color gradations. Bottom line, it allows the processing to make a better determination between what a noise level is and a signal level. It all comes down to is what amount of detail can the observer detect.

Probably the best description of the difference is down in the comments (scroll down to the bottom) on this page (the first comment from tkerr - too large to just cut and paste)...In practice the difference between 12 and 14 bit signal matters little - unless you are doing landscapes (especially in ambient low light - night photography) and printing large. One can argue that it gives you more definition in the shadows, that can be seen/observed. A difference that an eye can detect (thus the large print format). In terms of Astrophotography you are not concerned about the eye detecting the change, you are concerned with providing the post processing the greatest amount of signal - since it is essentially separating signal from noise - so a wider range (14 bit) provides the algorithm a larger number (the 16K color space) through which to make this determination (rather than clipping at the top, you are essentially clipping at the floor).You have no real investment (as in lenses) for any camera brand. What you are primarily interested in, is the sensor and its supporting processing in terms of capturing the best raw signal for processing, for the most economical cost. There is certainly a lot more information and work done for Canon, than for any other vendor.

Yes, the K5 will provide the 14 bit, however does have the AA filter. The K5II has a AA filter also, but its a bit lighter AA (and has gone out of production - so its available on the used market, and its price has come down.) The K5IIs is still in production, has no AA filter, and folks like this a lot, so the price has not dropped as much as with the K5 and K5II. You can certainly find a K5 here on the marketplace for $400 to $500 USD. The K5II is a bit more. The other think is that the shutters are rated for 100K activations. I can't remember if the Kx has a mirror lockup, but the entire K5 family does.

Yes, I do have a bit of an interest here - although its limited to wide field - less equipment, and I can avoid the telescope and hauling it around. I also did design and develop a star tracker for a little telescope down in Texas called HET.
_____
I like the shot of the galaxy NGC253. Nice definition starting on the internal structures.

06-14-2014, 08:43 AM   #14
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Thanks again Interested_Observer. You did work on the HET? Strewth. That's a big boy. You have given me a lot to chew through with those links, thanks. I've also been going through the big astrophotography thread also. Some amazing pics in there. That modified, cooled K10D is really something.
06-14-2014, 10:10 AM   #15
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That is the main reason as to why I like wide area Astro rather than deep space - the difference comes down to pointing and tracking.

HET has 20 degrees of freedom (or axis - motors), just in the tracker alone (not considering the primary structure). The Kecks were done for about $110 million each. HET was done for $13 million. The large difference was all in the primary conceptual design of the instrument. The Kecks were of a traditional design. HET used an approach pioneered by Arecibo - a fixed elevation structure that does not track in azimuth in real time (its rotated to the optimum azimuth, set down and locked for the entire observation period - of a maximum of 2 hours). So HET has 70% of the viewing capability (elevation limited) of the Kecks (for 11% of the price - a great trade).

The other occurrence was in Germany. They were grinding a large mirror, that cracked early in the process. Rather than throw it away, the thought occurred to folks, to cut the shards into 1 meter hex blanks, slice them, then grind them - a quick process for small mirrors, so that they can be mounted in a fixed array for an instrument like HET. So the mirror blanks were much cheaper. Everything that went into HET was constrained by cost in various ways.

Another aspect of HET was its intended use. The Kecks were intended for general optical astro. HET was specifically designed for only spectroscopy as opposed to optical imaging. This way, you have a special instrument devoted to the spreading and analysis of the light, as opposed to optical imaging. Now the folks interested in that aspect have their own very cost effective instrument - with the instrumentation packages specifically mounted and available for them.

HET's tracker is its main moving part - as opposed to with Keck - which the whole entire instrument is involved in tracking in real time (as in you need to continuously move the entire structure). HET's tracker needed to be hung over the mirrors - that is tons of stuff - moving, in a very accurate and precise fashion - and it needs to do it in 3D rather than 2D (as with Keck). The mirror surfaces form a parabola, and the tracker needs to track this parabolic surface (x, y as well as z). So, just to make things more complicated, we took a hexapod (think of the flight simulators that provide 3D motion to the pilots) and hung one upside down so that the instrument package could precisely be located and track the parabolic surface. Then, just to make sure that we had everything covered, think of comets. They are long, so there is a rotatory table that will spin the instrumentation payload to track and align with a comet's tail.

The tracker is a mechanical marvel - very light weight, extremely rigid, with little to no flex - which would introduce a set of variations that would cause a minor nightmare (think special structural steel). Also, there is a little problem of wind loading on such a structure, and then temperature expansion and contraction - again another minor nightmare tossed in with the precise tracking. Then this entire Rube Goldberg contraption needs to obscure as little light as possible on the mirrors below (an not have any of the parts fall off). Oh - one last item - cabling for the instruments. Lots of them power, control, data and all of this is also hung 60+ feet over the mirrors. Just managing the cables, that need to move with the tracking instrumentation packages - as well with the tracker itself (power, command & control) without getting tangled up - so then you have the cable trays (flexible and moveable) - which is an art in itself. Since they too are hung on high - up in the traipse, they obscure the light, catch the wind, create vibrations and expand and contract with temperature.

We also modeled the individual motor's characteristics into the control system, so that we used the motor's backlash to help slide into the intended position with the least amount of vibration/movement.

Yup, it was an interesting project - 20 years ago. PS - the software was all done on a small single board computer (SBC) running a 486. Your Kx has more computational power.
______________

With the HEXDEX dark energy upgrade, they needed to upgrade the tracker and all the instrument cabling to the light tracking instruments attached to the sides of the instrument structure. There is a neat video clip of them hanging the new tracker. You can see the tracker all installed in the second link. The Blue canisters on the 6 legs are the hexapod that positions the instrument cluster in the z (up and down) axis (and also put in a slight tilt, so as to track the slope of the parabolic surface in order to maintain a perpendicular orientation). My tracker after 20 years has been retired and put out to pasture here in the last couple of weeks. Not a bad track record. - I guess that I'll be next....


Last edited by interested_observer; 06-14-2014 at 10:46 AM.
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