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05-19-2017, 09:50 PM   #16
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Join Date: Dec 2012
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Hi, I know this is a bit late but there is no mention of 'clear aperture' values between lenses.

For example, the Pentax 31mm Ltd @ f2.8 will allow 4.9x the amount of light through than say the Samyang 14mm @ f2.8 for the same exposure time.

Obviously, you would need to stitch 2 images of the 31mm together to roughly achieve the same field of view but... And a big but is... it will be a superior image!

I have the Samyang 14mm and it is quite good if one cannot be bothered with stitching and without tracking, but I have learnt that UWA lenses are not the way to go if one is getting seriously into astro due to the clear aperture issue.

You could even use the 25 Pentax-M 50mm f1.7 @ f2.8... and stitch 3-4 together. (12.75x the amount of light for same f number and same exposure time than a 14mm lens).

And with astrotracer for Pentaxians this is all the more possible to use longer focal lengths. I just bought the O-GPS1 for my K30 which has the fabulous Exmor sensor (most excellent for astro). It must have good dark current suppression technology built in, even if it is 4-5 years old.

Read Roger Clark's astro site if you have a few months to spare 😉

I would love to know more data (any?) on Pentax dark current tech for various models. 😎

09-18-2017, 04:39 AM   #17
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Join Date: Jan 2017
Location: Nijmegen
Posts: 36
SMC Pentax-F 28mm F2.8

Actually, I mainly use my K-1 for landscape with two lens
Panagor 24mm f2.5 and my favorite lens SMC Pentax-F 28mm F2.8. I was very lucky to get a copy of this lens, It sharp right from f2.8. I shoot a lot of cityscape, city night, and long exposure stuff. Sample image below is at f11, focus at infinity and it is very sharp.

Last edited by anakhaled; 09-19-2017 at 03:14 AM.
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