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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"!

Addendum:

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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