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Now I Know... How much focal length fills the frame with the moon
Posted By: SCGushue, 06-12-2008, 07:55 PM

I just couldn't resist...

The sky was clear and the moon was out similar to last months shot with the the A*1200mm f/8. Tonight I decided to quickly set up, before the mosquitos ate me alive, and redo the moon with a 1.4X dedicated Pentax telextender.

Total focal length 1680mm. The image is full frame just resized.



Hmmmm! Still does not get big enough in preview. Try this http://i.pbase.com/o2/88/688888/1/98588613.3WzbQGfy.IMGP0694copy1200plus1copy.jpg for a 1024 long image from pbase.


Stephen

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Last edited by SCGushue; 06-13-2008 at 07:33 AM.
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06-13-2008, 03:01 AM   #2
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That's a great shot Stephen, I think I see a golf ball
06-13-2008, 03:31 AM   #3
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Competition: how many US flags from the Moon missions can you count?

Hic ... my longest lens is 250mm, I need to shop for a 6x teleconverter!!
06-13-2008, 04:07 AM   #4
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Awesome shot! I wanted to go out last night and try my new Canon 100-400 on the moon, but didn't get around to it. Was that last night up in NE PA?

06-13-2008, 06:31 AM   #5
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QuoteOriginally posted by borno Quote
That's a great shot Stephen, I think I see a golf ball
Thanks Tom. I expected more image deterioration with the 1.4X than I actually saw. I did notice, however, that there were plenty of hot pixels scattered throughout the image. Plenty!

QuoteOriginally posted by Kguru Quote
Competition: how many US flags from the Moon missions can you count?
Hic ... my longest lens is 250mm, I need to shop for a 6x teleconverter!!
I was think more like: Where's Waldo.

QuoteOriginally posted by egordon99 Quote
Awesome shot! I wanted to go out last night and try my new Canon 100-400 on the moon, but didn't get around to it. Was that last night up in NE PA?
Yepper! Last nights moon. See you made the switcheroo too.

Stephen
06-13-2008, 06:38 AM   #6
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Use math instead

No need to test, you know (or should know) that

image size = Focal length x subject size / subject distance

Image is 15.6mm (height of the sensor)

The diameter of the moon and its distance are known.
06-13-2008, 07:22 AM   #7
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QuoteOriginally posted by Lowell Goudge Quote
No need to test, you know (or should know) that

image size = Focal length x subject size / subject distance

Image is 15.6mm (height of the sensor)

The diameter of the moon and its distance are known.
Lowell,

You are right I should know.

And I probably do... it's just that I still think in the mathmatics of 35mm which I still do most of my daily work in.

And, sometimes, because I am getting older, I am just not inclined to think about these sort of issues. Although, mathmatically I have calculated that 1/60 sec is the minimum shutter speed @ this focal length/resolution and the speed of the moon's arc. I really just wanted to see if the converter killed too much sharpness. Surprisingly it did well with just a hint of yellow CA which was largely correctable in PP.

And, I don't do moon shots or astrophotography ever. These were just spur of the moment fun, off the cuff, setups to have some fun after the lights go out. Cauz' there ain't a hell of a lotta' stuff goin' on 'round these here parts afta' sundown.

Stephen
06-13-2008, 07:37 AM   #8
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That is one of the best moon shots I've ever seen. Really great work!

06-13-2008, 07:43 AM   #9
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Tricky situation indeed. Moon pics!

As for magnification, there is a rule of thumb about shooting the moon: Magnification on negative (film plane) will be aprox 1/100th of focal lenght used. So, if you use a 1000mm tele, the moon (full moon) will cover 1 cm. Forget about format, the rule aplies no matter if film, digital, medium format or whatever. Just consider the actual size of your "capturing media". If using 35 mm film, you need 2400 mm tele to fill the frame. If APS-C, then its 1650 mm. If 6x6 medium format, then you need a 6000 mm tele.

As for exposure, every single light meter gets tricked. Just think that while here on earth its nightime, on the moon its daylight, so go by the f16 / ASA rule. That is, That normally exposed pics in broad daylight, are done at f/16 and a shutter speed equal to the sensitivity. Of course, you can do the math and open up diapbhragm and shorten shutter speed accordingly.

The last thing to consider in exposure, is "air transparency". On a clear night, the f16/ASA rule applies, but if air is a bit dirty (as usual around big cities), then bracket 1/2 or a full stop to overexpose.

Practical example:
Gear: Digital SLR with APS-C sensor
Lens: Tele or combination to reach 1500 mm. F8 max aperture.
Weather: Clear night, no sense of air smog
Moon: Full moon about 45 degrees over horizon.

Expected results: Almost frame filling moon with at least one or two well exposed frames.

Also, don't forget that the moon is NOT really bigger when it is near the horizon. It is an optical ilussion. The moon's size does not change no matter where in the sky it is.

Shooting setup: Sturdy tripod of course. Set lens sensitivity at ISO 400, lens at f/16 and shutter speed at 1/200.
That setup will give you a 1 stop overexposure according to the f16 rule. That full stop overexporsure is to compensate for "light loss" due to the distance to subject.
Then bracket a couple of frames up and down, using shutter speed change, from 1/60 to 1/500. Leave lens always at f/16 (or two stops down from wide open).

Enjoy

RB

Last edited by rburgoss; 06-13-2008 at 07:53 AM.
06-13-2008, 11:41 AM   #10
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Nice Moon

Stephen, For someone who does not shoot moon shots... this is really good. I am suprized at how well the TC worked here. Which one is it exactly?

I have got an ok result with a MF 400mm and a tc but I have to crop so much on my 6mp K100 that I loose some detail...

Again a great moon shot...

ps I tried the link and it did not work... Not permitted
06-13-2008, 02:31 PM   #11
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OOOHHH.
It just gets better....
CRAAAZY detail on that shot. That's special glassware you've got your hands on.
Now it's time to move on to Mars, Jupiter and Saturn...
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