Moon focusing

modafoto · Oct 26, 2004

Hí

I hope I post this the right place.

I have a problem. I was shooting the moon using auto-focus and it focused so the image looked good in the finder, but the slides where not sharp. I noticed later that my lens wasn't focusing at infinity when it focused on the moon, and that is weird. I have done a manual focus shot at the moon, but are waiting for the film to be developed. The image in finder was then blurred. I wonder what the slide will be like.
Why is my camera being fooled by this? It normally focuses perfectly.

Can any of you give me advice on moon focus? And perhaps on exposure. I shot the moon with an exposure calculated from the following:

Shutterspeed = 1 / film speed (I use 90 and 125 with Fuji Sensia 100)
Aperture = 8 or 11
(or a faster speed and a wider aperture)

Is my calculation right?

Greetings Morten

dogea · Oct 26, 2004

What I know, is that the auto-focus works better with lot of light. During night shots it is allways better to use manual settings, or you will get a very strange behaviour of the lens.

Usually, when I take night pictures, I try to work with the greater aperture as possible, but something very important, is the use of a tripod.

Last but not least, to take a picture of the moon, I'll use a tele-photo lens. I use a Sigma Mirror-Telephoto FD 600mm 1:8, with a Tamron SP F System 2x Tele-Converter. The result is great, but the shutter must be opened quite a long time.

I hope the results of your next film will be good.

Best Regards,

David

modafoto · Oct 26, 2004

dogea said:
but something very important, is the use of a tripod.

I did not use a tripod but I used a 300 mm tele and exposed this way:

1/500 @ f/5.6

Is that still too slow to handhold when shooting the moon?

dogea · Oct 26, 2004

I guess. I really think that 1/500 is too quick, I will use B-shutter, and try different times.

Tele absorb a lot of light (at least my mirror tele), slow shutters fit better, but again, the use of a tripod becomes mandatory.

Best Regards,

David

modafoto · Oct 26, 2004

dogea said:
I guess. I really think that 1/500 is too quick, I will use B-shutter, and try different times.

The amount of light is ok @ 1/500, f/5.6. The moon is having nice tones and is fully detailed. I have tried shooting the moon at 20 second f/22 and 20 seconds f/32, and the moon ended up being a white circle.

127 · Oct 26, 2004

I did a moon shot recently (on 35mm aaarrghhh!).

I used an 800mm lens (400+2x teleconverter). Any shorter and it would have been tiny. At 800 it was a decent size, but could have been larger.

The lens was set at f5.6, so thats f/11 with the converter. With 400 colour film I shot frames at 0.5 and 1 second. Both came out nicely (I haven't checked the negs as I just put the film through a local lab, and it came bacl fine).

Ian

Dave Mueller · Oct 26, 2004

"I did not use a tripod but I used a 300 mm"

There's your answer to the image being not sharp. Regardless of shutter speed, it's tough to hand-hold a 300mm lens and expect tack sharp images.

The Moon is in full sunlight, so there's plenty of light on the subject. There is a common modification to the "Sunny 16" rule for shooting the full Moon - f/11 at 1/ISO. 1/500 at f/5.6 is close enough, maybe a little underexposed.

Most lenses have extra room past the "infinity" setting to allow for expansion/contraction of the system at the temperature extremes.

Your autofocus system might have problems because the full Moon is inherently low contrast - there are no shadows from the craters and other surface features because it is in direct overhead lighting.

modafoto · Oct 26, 2004

Dave Mueller said:
Your autofocus system might have problems because the full Moon is inherently low contrast - there are no shadows from the craters and other surface features because it is in direct overhead lighting.

So the conclusion must be to manual focus at infinity, use a tripod and expect
tack sharp slides?

Morten

Ed Sukach · Oct 26, 2004

Kind of a strange topic... I'll usually expose for those as I do for the rest of the model...

I'll join in with one word of advice ... NEVER "moon" a rhinoceros!!!

wfwhitaker · Oct 26, 2004

While it sounds like most of your sharpness issue may be related to hand-holding the 300mm lens, don't forget that the moon is a moving object. Motion is magnified along with the image when using a long lens.

sbuczkowski · Oct 26, 2004

wfwhitaker said:
While it sounds like most of your sharpness issue may be related to hand-holding the 300mm lens, don't forget that the moon is a moving object. Motion is magnified along with the image when using a long lens.

For a full sense of this motion: the moon subtends half a degree of arc in the sky and 'moves' at about 15 degrees per hour. The full moon will move it's own width every two minutes.

Dave Mueller · Oct 27, 2004

modafoto said:
So the conclusion must be to manual focus at infinity, use a tripod and expect tack sharp slides?
Morten

Almost. The only variable is the focussing, whether or not infinity is at the far mechanical stop, or if the infinity mark on the lens barrel is accurate, etc. You should be able to get very close by looking in the viewfinder. If your camera has an "in focus" indicator, it should work or at least get you close enough that DOF will cover any errors (DOF at 250K miles is pretty big!)

wfwhitaker said:
While it sounds like most of your sharpness issue may be related to hand-holding the 300mm lens, don't forget that the moon is a moving object. Motion is magnified along with the image when using a long lens.

From "Astrophotography for the Amateur" by Michael Covington, the rule of thumb for fixed-tripod shots of astronomical subjects:
Longest shutter speed = 250 / Focal length in mm.
For a 300mm lens, 1/2 second or faster will be enough to prevent motion blur of the Moon. You should be using mid-apertures (f/8 or f/11), so your shutter speeds should be 1/125 to 1/800 depending on film ISO, much faster than the 1/2" maximum.

modafoto · Oct 27, 2004

Dave Mueller said:
From "Astrophotography for the Amateur" by Michael Covington, the rule of thumb for fixed-tripod shots of astronomical subjects:
Longest shutter speed = 250 / Focal length in mm.
For a 300mm lens, 1/2 second or faster will be enough to prevent motion blur of the Moon. You should be using mid-apertures (f/8 or f/11), so your shutter speeds should be 1/125 to 1/800 depending on film ISO, much faster than the 1/2" maximum.

Thank you. I go out tonight and shoot a test roll of the moon. I'll use tripod and all the kinds of focus I can. I'll shoot it at 1/125 @ f/8. Looking forward to try the advices from the replies to my question.

Greetings Morten

mobtown_4x5 · Oct 28, 2004

"auto-focus" what the f is that? must be a miniature format thing.

glbeas · Oct 28, 2004

mobtown_4x5 said:
"auto-focus" what the f is that? must be a miniature format thing.

You only use that when shooting cars.

modafoto · Oct 29, 2004

mobtown_4x5 said:
"auto-focus" what the f is that? must be a miniature format thing.

Blah blah!

modafoto · Nov 9, 2004

A few of the pictures from the film. No keepers. I am forced to use a tripod...

Flotsam · Nov 9, 2004

modafoto said:
A few of the pictures from the film. No keepers. I am forced to use a tripod...

Looks kind of grainy.

What developer did you use

mikeb_z5 · Nov 9, 2004

Amazing! I think if you kept the shutter open a little longer the moon may have spelled "modafoto"! Without the quotes of course(that would just be ridiculous )

Mike

Ole · Nov 9, 2004

mikeb_z5 said:
Amazing! I think if you kept the shutter open a little longer the moon may have spelled "modafoto"! Without the quotes of course(that would just be ridiculous )

Mike

And dropping one picture and rearranging the others (15,9,10,13) spells MOON...

jss · Nov 9, 2004

modafoto said:
A few of the pictures from the film. No keepers. I am forced to use a tripod...

don't think i've ever seen "moonpainting" done before.

rbarker · Nov 9, 2004

Two suggestions, Morten: longer lens, sturdy tripod.

Dead Link Removed

You'll get about 1mm of moon for every 100mm of lens, so a 300mm lens is stretching the enlargement capability of even a Rodinal-developed shot. ;-)

modafoto · Nov 10, 2004

Flotsam said:
Looks kind of grainy.

What developer did you use

Acutol....

modafoto · Nov 10, 2004

rbarker said:
Two suggestions, Morten: longer lens, sturdy tripod.

Dead Link Removed

You'll get about 1mm of moon for every 100mm of lens, so a 300mm lens is stretching the enlargement capability of even a Rodinal-developed shot. ;-)

Hmmm...I don't have the money for a super tele....but I have fallen in love with the 1200 mm from Canon...

rbarker · Nov 10, 2004

You might try connecting with a group of astronomy enthusiasts near you, Morten, and see if you could arrange to borrow/rent one of their telescopes, or just get some shots by attending one of their sky-watch sessions. All you'd probably need to buy would be a T-adapter for your camera (Canon and Nikon are common).

The 8" Celestron, for example, is about 2000mm, producing a moon image of about 20mm on film (any format, so 35mm film is fine). As a tele lens, it's not as sharp as one might hope, but it's better than trying to enlarge a smaller image too much.

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