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Archive 2017 · Father, Son, and the Milky Way

  
 
kmk1986
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p.1 #1 · p.1 #1 · Father, Son, and the Milky Way


Hi everyone!

Thank you for welcoming me in my previous post.

I'm not sure if nightscape (?) fits into landscape category in this site, but since I have two trees

I learned what LGP (Light gathering power) a few weeks ago. Please pardon my ignorance, but I thought 14mm f/2.8 gathers the same amount of light as 35mm f/2.8 because they have the same f/2.8. I was told that I should compare (not calculate) two lens with the following equation.

pi*(14/2.8)^2 = 78.54
pi*(35/2.8)^2 = 490.88

400 / 14 = 28.57
400 / 35 = 11.4

78.54 * 28.57 = 2244
490.88 * 11.4 = 5596

basically, 35mm f/2.8 gathers 2x more lights. With that in mind, I rented 35mm f/1.4 and 50mm f/1.4 to see how much detail I can get with relatively short exposures from those two lenses.

These are my output. Although I did heavy processing on both of them and there is noise when zoomed, but I think both came out pretty okay.

Two trees: 35mm f/1.4, ISO 6400, 8 seconds.
lone tree: 50mm f/1.4, ISO 6400, 6 seconds

Thank you for looking!














Apr 26, 2017 at 12:04 AM
JimFox
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p.1 #2 · p.1 #2 · Father, Son, and the Milky Way


First off, Landscapes are Landscapes whether they are shot sunrise, midday, sunset or night shots.

I like both shots, they both work, but #2 with the single tree is stronger to me.

After reading what you wrote, I was looking forward to seeing a 14mm f2.8 comparison with a 35mm f2.8. I was a bit disappointed as your discussion about the light each would gather was interesting, but I would have liked to have seen a practical demonstration where for the same look, the 35mm was able to have been shot at a lower ISO, say ISO 4000 compared to the 14mm having to be at ISO6400 for the same amount of light.

Jim



Apr 26, 2017 at 01:14 AM
psharvic
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p.1 #3 · p.1 #3 · Father, Son, and the Milky Way


I also find the 2nd to be a stronger image. Sorry, I can't add any lens tech info.


Apr 26, 2017 at 07:10 AM
jforkner
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p.1 #4 · p.1 #4 · Father, Son, and the Milky Way


Sorry, I don’t understand your math. I don’t get where “pi” & “400” come into play.

My information indicates that the ratio of the light-gathering power of two lenses is:

ratio of light gathering power = square of aperture of larger instrument / square of aperture of smaller instrument

and

effective aperture of a lens = focal length/maximum aperture (f-stop)

so, in your case…

5 = 14/2.8 = effective aperture
12.5 = 35/2.8 = effective aperture

then

(12.5)^2 / (5)^2 = 6.25

By my calculations, the 35mm lens has 6.25 times the light-gathering power of the 14mm. And the 50mm f/1.4 has 2x the LGP of the 35mm f/1.4.

All that said, not sure how that info helps with MW images. I think FOV, ISO, & shutter speed are more important criteria. YMMV.


Jack




Apr 26, 2017 at 09:24 AM
kmk1986
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p.1 #5 · p.1 #5 · Father, Son, and the Milky Way


Thank you Jim.

Yeah, I see what you mean. Since I was renting, I rented fastest one I could rent. I will try to test 14mm f2/.8 and 35mm f/2.8 when I get a a chance since I already have 14mm f/2.8.



Apr 26, 2017 at 02:28 PM
kmk1986
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p.1 #6 · p.1 #6 · Father, Son, and the Milky Way


Sorry for the confusion jforkner.

I actually meant light gathering area (http://telescopeinfo.blogspot.com/2012/03/light-gathering-area-calculation.html)

400 is for the 400 rule.



Apr 26, 2017 at 02:29 PM
kmk1986
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p.1 #7 · p.1 #7 · Father, Son, and the Milky Way


Thank you psharvic


Apr 26, 2017 at 02:29 PM
jforkner
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p.1 #8 · p.1 #8 · Father, Son, and the Milky Way


kmk1986 wrote:
400 is for the 400 rule.


You do know the 400-rule (and the 500- & 600-rules) have nothing to do with light gathering capability, right?



Apr 26, 2017 at 02:59 PM
kmk1986
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p.1 #9 · p.1 #9 · Father, Son, and the Milky Way


jforkner // Yeah, but you need to consider it in practice when comparing two different focal lengths as different focal length needs to use a different xxx rule.


Apr 26, 2017 at 04:28 PM
pizdets17
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p.1 #10 · p.1 #10 · Father, Son, and the Milky Way


It has to do with the amount of clear aperture. A 35 1.4 is basically as good as it gets for light gathering when you add up exposure time, noise due to exposure time and iso, and light gathering ability.


Apr 26, 2017 at 06:33 PM
dgdg
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p.1 #11 · p.1 #11 · Father, Son, and the Milky Way


Light gathering numbers aside, which I don't understand, I do like these images.

The compositions are very strong.
The milky way is strongly processed, but that is personal taste. My only technical nit would be the brightest part of the milky way core is blown and loses detail.
It looks like your sky was fairly unpolluted given the detail you captured. The exposure time seems shorter than necessary.


David




Apr 26, 2017 at 08:20 PM
aFeinberg
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p.1 #12 · p.1 #12 · Father, Son, and the Milky Way


Very curious indeed. Science! Guess I have to rent a 35 1.4. Seems problematic getting things sharp but maybe worth the try. Nice. #2 for me.

aF



Apr 27, 2017 at 01:29 AM
Kory Lidstrom
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p.1 #13 · p.1 #13 · Father, Son, and the Milky Way


Dig the first one -- classic stuff.


Apr 27, 2017 at 10:43 PM





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