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10-10-2011, 08:42 PM   #16
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QuoteOriginally posted by miltona580 Quote
Agreed! I think I will give up now on astrophotography with my K-x...
I have a K-x and I ran into small problems of focusing when attaching to my telescope. You have to use a 2x Barlow lens to get the K-x body far enough away to let the light focus on the sensor. I'm not sure if the Q would make that worse or better. I think better since MILC's don't need as much distance between the lens and sensor? I think I'm going to order the q-c adapter and c-k adapter. It'll cost me about $70 but I don't know when and IF Pentax will make a q-k adapter. Knowing my luck the Pentax version will let AF work with current lenses though all of my lenses except one has auto-focus.

10-11-2011, 01:50 AM   #17
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QuoteOriginally posted by rawr Quote
I don't think that is a crop.

Atmospheric conditions etc make for the haze I expect. Urban Japan probably isn't the best place to do astro-photography.
Well, it most certainly is a crop - but a 100% crop without resizing. You may convince yourself as follows:

1. Jupiter currently has an angular diameter of 48 arcseconds (= 0.01333.. degrees).

2, The focal length of the system is 1600 mm

3. The imagesize on the sensor will then be
diameter = 2*1600mm*tan(0.01333/2) = 0.372 mm (Note this ONLY depends on the actual focal length and has got noting to do with sensor dimensions and equivalent focal lenghts)

4. The sensor of the Q is a 1/2.3" which is 6.16 by 4.62 milimeters.

5. The sensor of the Q has 4000 * 3000 pixels which gives us a pixel witdth of 0.00154 mm and

6. According to 3. above the image size of Jupiter's diameter with this camera and set-up will then be
0.372/0.00154 = approx. 240 pixels wide.

7. Now, download the original image (sized 2048 * 1536 pixels) from flicker and measure the diameter on your screen in an appropriate imaging program. I find the measured diamter to be 230 pixels. Considering the various sources of error, this is in excellent agreement with "therory"!


Now, consider my K200D (or any DSLR with an APS-C sensor).

My pixel widths are 0.00606 milimeters and thus, with the same optcal system (1600 mm FL) my Jupiter image would be a lousy 60 pixels wide only - or, said in another way: In order to compete with the sensor resolution (very different from the lens' optical resolution) I would need an optical system with a FL of 6300 mm in order to compete with the image detail we are discussing here.

So, for planetary photography, small is indeed beautiful - but don't give up astrophotography with your K200D, K-x or K-r for that matter. Just choose the right subjects.

Last edited by Stone G.; 10-11-2011 at 02:09 AM. Reason: addendum
10-11-2011, 03:18 AM   #18

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QuoteOriginally posted by Stone G. Quote
You may convince yourself as follows
I'll take your word for it

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