Anyone use a Pentax KX

[paul101]

hi all

was wondering if anyone else uses the Pentax KX for astrophotography?

if so i was wondering what settings you use for DSO's on prime focus ie: light balance, ISO, noise reduction etc.

i use mine in manual and usually iso 800-1600. and a tungsten light balance.

was wondering which successful settings others are using.

Thanks

paul

[Alderamin]

Hi Paul,

I just started experimenting with my K-x, mounted to a Skywatcher ED 120 on HEQ-5 mount. The camera seems quite sensitive to H-alpha red, compared to Canon cameras, and it has a great ISO range with acceptable noise, if you stack the pictures. However, there are two problems, noise reduction (= dark frame subtraction) cannot be switched off in bulb mode, which doubles the exposure time, and even worse, ISO is limited to 1600 in bulb mode. The K-r apparently does allow to switch off the noise reduction and the latest firmware update allows to use all ISO settings in bulb mode, so I hope that the next update for K-x includes these features as well. I wrote to Pentax support and would suggest to you to do the same. The more people complain about this, the higher the chance that the features will be provided soon.

My experiences so far are as follows: I don't use a guider yet, just PEC. 30 s exposures are free of trailing and at ISO 12800 they are as sensitive as 4 minute bulb shots at ISO 1600, which additionally add 4 minute dark frame subtraction. So I followed the advice of these guys to stick with 30s at ISO 12800. I use pktether to shoot at least 40 pictures in RAW mode that I stack with DeepSkyStacker. I have to cope with suburban light pollution and found that a Baader UHC-S filter helps a lot with gas nebulae, but not with the Plejades' reflection nebula. I shot M65/66 recently without the filter and had a lot of sky background to remove, which left a grainy image of the galaxies, so I will try more shots and also the UHC-S filter next time. To improve the signal to noise ratio x-fold, you need x^2-fold more stacked images, so I will go for 160 shots next time. I suppose that 2 to 4 minute exposure at ISO 12800 would work better to get the weak galaxy's signal out of the noise, but Pentax won't let me yet.

Hope this helps.

[Alderamin]

I should add that you should of course always shoot in RAW mode so you get a finer resolution in brightness (12 bits instead of 8 with JPEG). You should keep using RAW mode or TIFF at least up to the point when the histogramm has been stretched in your favourite post processing software. Convert to JPEG as late as possible.

In RAW mode, the white balance is not applied by the camera, so there's no point in selecting a particular setting. And when you convert to JPEG in any other program than the Pentax Digital Camera Tool, the program will most likely not consider the white balance setting either, even if it' stored in the EXIF. Every chip has a different colour response, I doubt that unbranded image processing software accounts for the different colour responses of different camera models. Just make sure in post processing that the stars have natural colours, i.e. not green, pink or violett or anything. I do that with the "levels" tool, separately adjusting R, G and B. If you want to see a really bad failure, try Photoshop's "Autocolor" on an astrophotograph. Then you know what psychedelic colours mean

[Eclectic_Mixer]

I have a K-x but hav'nt used it for Astro yet, I intend doing some wide field stuff,using 50-200mm lens when i get to the Caravan in Anglsey, I would be grateful of any tips for this kind of photography also how do you connect pkthther to the camera. It's a pity about the noise reduction and limit to ISO on B setting,because its such a good piece of kit.

[Alderamin]

Then complain with the Pentax support.

There is this guy who shot the North America nebula with this camera - just using a tripod and a telephoto lens: Telescope Reviews

As for connecting pktether, all you need is the mini-USB-cable that was supplied with the camera (originally meant to load pictures into the PC). The connector is on the left side of the camera when facing its rear side.

pktether is just an .exe file, start it up with the camera switched on and it will detect the camera automatically. It is self-explanatory and allows you to change ISO settings, exposure time, self-timer etc. And it has an interval mode, where you can define the B exposure time and the time between exposures. The images go directly to the hard disk, they are not stored on the SD card.

I love this tool, I can let the camera do the work while browsing the web. The only thing I'm missing is a batch mode to program a sequence of different settings with time stamps. That would be great for the next total solar eclipse, to capture the diamond ring, filaments, and different parts of the corona - while watching it in full length through another scope.