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11-12-2013, 01:30 AM   #1
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645d for Milk Way / Astrophotography

Immagine a MF (medium format) sensor with a 12micrometer pixel pitch. The 645D is the closest tool to that specification, in Pentax branding. With a 6 micrometer pixel pitch , I'm curious if the 645D is better than Canons 6D pixels ( which has 6.55 micrometers) at low light high ISO. The 6d has an amazing ISO performance, but can the 40mp image created by the 645D sensor be scaled down to get a better quality image of te stars?

11-12-2013, 01:43 AM   #2
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QuoteOriginally posted by Scootatheschool1990 Quote
Immagine a MF (medium format) sensor with a 12micrometer pixel pitch. The 645D is the closest tool to that specification, in Pentax branding. With a 6 micrometer pixel pitch , I'm curious if the 645D is better than Canons 6D pixels ( which has 6.55 micrometers) at low light high ISO. The 6d has an amazing ISO performance, but can the 40mp image created by the 645D sensor be scaled down to get a better quality image of te stars?
Hard to say without doing side-by-side tests specifically for astrophotography. The 645D does struggle at higher ISOs, but I'm sure it would still do a great job when paired with the right lens.

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11-12-2013, 01:50 AM   #3
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The thing about photographing stars is that you typically need a really fast lens to do it - that is if you don't want star trails. The Canon DSLR has access to lenses as fast as f/1.2 ( f/1.0 if you go for the exotic) there aren't any lenses for the 645D that come within a stop of those apertures.Although the pixel pitch is roughly the same between the two cameras the lens speed advantage goes to canon.

The only way to avoid star-trails it to use an old fashioned equatorial mount, since the O-GPS1 astrotracer relies on the SR mechanism on pentax DSLR cameras - a technology that is absent on the 645D.
11-12-2013, 01:59 AM   #4
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Hi,

You could be on to something here.

I saw this amazing footage taken by Lorenzo Comolli:


He gives a huge description on noise calculation on his website:

Lorenzo Comolli's Astronomy HomePage

(Unfortunately he used Pentax K-x and not too impressed with it.)

I am not sure if my links add value to your quest.

best regards.

11-12-2013, 10:29 PM   #5
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QuoteOriginally posted by Digitalis Quote
The thing about photographing stars is that you typically need a really fast lens to do it - that is if you don't want star trails. The Canon DSLR has access to lenses as fast as f/1.2 ( f/1.0 if you go for the exotic) there aren't any lenses for the 645D that come within a stop of those apertures.Although the pixel pitch is roughly the same between the two cameras the lens speed advantage goes to canon.

The only way to avoid star-trails it to use an old fashioned equatorial mount, since the O-GPS1 astrotracer relies on the SR mechanism on pentax DSLR cameras - a technology that is absent on the 645D.

In this case wouldn't a K-3 or K-5 IIs with a DA*55 or FA*85 be a good choice? Or is pixel pitch a huge issue here? I would think the O-GPS1 would be worth taking advantage of.
11-12-2013, 11:06 PM   #6
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QuoteOriginally posted by DSims Quote
n this case wouldn't a K-3 or K-5 IIs with a DA*55 or FA*85 be a good choice?
The FA31mm f/1.8 and the 50mm f/1.2 are also good choices, and both of these lenses work very well with the O-GPS1 astrotracer.

The reason fast lenses are so important in this scenario is that the faster the lens is the greater the intensity light has at the sensor plane, and when you are trying to photograph stars without them leaving trails the faster lenses always will give you shorter exposures and in this case short is good.

Last edited by Digitalis; 11-12-2013 at 11:15 PM.
11-12-2013, 11:39 PM   #7
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QuoteOriginally posted by Digitalis Quote
The FA31mm f/1.8 and the 50mm f/1.2 are also good choices, and both of these lenses work very well with the O-GPS1 astrotracer.

The reason fast lenses are so important in this scenario is that the faster the lens is the greater the intensity light has at the sensor plane, and when you are trying to photograph stars without them leaving trails the faster lenses always will give you shorter exposures and in this case short is good.
Well then I guess I should get an O-GPS1 and get into astrophotography, since I already have those two lenses.

I will say that I've noticed my faster lenses - especially these two - can pick up some beautiful images in the hour or two after sunset. It's amazing how much light they pull in. it seems they capture much more than I could ever get with a slower lens using the equivalent (slower) exposure. So I suppose they'd be just as outstanding in the middle of the night as well.
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