Is this symbol showing the focus to inifnity point on my lens?

sduk

sduk

Messages
1,005
Name
Sammy
Edit My Images
Yes
Quick noob question, been struggling with focusing my A77 to infinity for star shots as the EVF makes it not possible to look through and see the stars at night.

I noticed on the focusing ring on a few of my lenses I have this "8" logo...

Untitled by Sammy Donaldson, on Flickr

Is that the infinity focus point of the lens?

So if I set the camera on manual focus and on that point it should be set up to infinity?

thanks

Sammy
 
In theory correct, but some lenses will focus past infinity, so worhwile checking.
 
And don't forget, you don't put the mark next to the infinity symbol. That right angle line from the infinity symbol is where your focus mark should be.

However, honestly, I think you will be better using live view and magnifying to 10x in order to check focus.
 
:agree:
 
When I have tried moon & star shots I find that I need to turn the focus ring back a fraction from the infinity mark to achieve sharp focus on the Live View LCD screen.
 
sduk said:
thanks for the quick replies, problem solved, this should make it far easier the next time I go out to try and capture the milky way!
Click to expand...

It may be easier, but it probably won't give the best results. You see that bar next to the infinity symbol? Well 'infinity' covers all of that range, depending on temperature and the wavelength of the light.

For astro work you're shooting tiny points of light. Any mis-focussing will turn these points into blobs - which can look horrible.

The best way of focussing stars is to use live-view zoomed in to 10x.
 
You can also test infinity focus on a tripod during the day and either put a mark/remenber how the symbol aligned. Most lens are not accurate and infinity is sightly before/past the mark.
 
I am fairly sure that all lenses will focus past the infinity mark for the reasons above, temperature and wavelength plus micro-focussing errors can then be corrected in live view.
 
dizidav said:
In theory correct, but some lenses will focus past infinity, so worhwile checking.
Click to expand...

Part of the auto focus process will probably require the lens to go past infinity then move back to be spot on.
 
If the moon's out, you can use AF to focus on that then use that as the focus point for stars.
 
thanks for all the replies, very helpful.

More than one person saying just to use the viewfinder but my Sony A77 has an electronic viewfinder and when I look through it at night I can't see the stars, it just looks like interference on a fuzzy screen.

If i had a "normal" dslr without the EVF then I would definitely do that but it's not an option on mine sadly.
 
I don't know what a Sony A77 is like. But if it's anything like my Sony A7R this is what you do.
Place camera on tripod
Point towards a bright star ( or the moon if it's up)
Turn focus mechanism to manual
Look at back live view screen
Focus until bright star or moon is sharp
Press button to magnify field of view on live view screen
Refine focus
You are now focussed at infinity
As an aside, you should never trust the infinity mark on the lens as they are renowned for being inaccurate - only the manual Carl Zeiss lenses have accurate infinity focus and they are outside most people's price point.
Hope this helps
James
 
dizidav said:
In theory correct, but some lenses will focus past infinity, so worhwile checking.
Click to expand...
•
+1
This is infinity in this case:
(as meant by the maker)

infinity.jpg


Just line up the two white lines (here red over yours)!
 
Last edited:
jbw said:
I don't know what a Sony A77 is like. But if it's anything like my Sony A7R this is what you do.
Place camera on tripod
Point towards a bright star ( or the moon if it's up)
Turn focus mechanism to manual
Look at back live view screen
Focus until bright star or moon is sharp
Press button to magnify field of view on live view screen
Refine focus
You are now focussed at infinity
As an aside, you should never trust the infinity mark on the lens as they are renowned for being inaccurate - only the manual Carl Zeiss lenses have accurate infinity focus and they are outside most people's price point.
Hope this helps
James
Click to expand...

does the A7R have an electronic viewfinder though????????????????
 
sduk said:
thanks for all the replies, very helpful.

More than one person saying just to use the viewfinder but my Sony A77 has an electronic viewfinder and when I look through it at night I can't see the stars, it just looks like interference on a fuzzy screen.

If i had a "normal" dslr without the EVF then I would definitely do that but it's not an option on mine sadly.
Click to expand...

I suffer from the same problem with the EV. Worse still, the Oly OM E10 then magnifies the object, and at night the shake of me turning the focus ring on the lens is too great to be able to see the star or moon well.

I can only focus on the moon in Autofocus, the switch to Manual focus and don't touch the lens again.

Not hot for Astro photog. Just a shame my old Pentax Ist went *t*s up

mj
 
I've always had trouble with the phrase 'lenses focus beyond infinity'. I know they do, but if you think about it, how do yo physically go 'beyond infinity'.
The phrase makes no sense as infinity is infinite - how can you go beyond it?


Edit - no Buzz Lightyear quotes please.
 
Last edited:
I much prefer lenses that stop at infinity - It seems to be "AF-S" lenses that go beyond infinity yet AF-D lenses have an actual stop which is much easier if you switch to MF instead of AF.
 
JulesP said:
I've always had trouble with the phrase 'lenses focus beyond infinity'. I know they do, but if you think about it, how do yo physically go 'beyond infinity'.
The phrase makes no sense as infinity is infinite - how can you go beyond it?


Edit - no Buzz Lightyear quotes please.
Click to expand...

If an object is close to you the rays of light leaving it are entering your lens slightly diverging. The closer the object the more they diverge, the lens has to move to bring these varying diverging Ray's to a focus on the sensor.
At infinity ( or close to it) the Rays are leaving the object in parallel and the lens has the job of moving to a position in order to bring these to a focus.
When a lens goes beyond infinity it is attempting to bring Ray's of light that are converging to a focus - this it fails to do as there is nothing beyond infinity so all you get is an out of focus smudge.
The idea of having a lens going beyond infinity is for two reasons
1) to compensate for a varying distance between the lens and the sensor due to temperature changes
2) because it's technically easier to design an auto focus system this way
As far as I'm aware ( unless anybody knows different) only Carl Zeiss lenses stop dead at infinity and don't go beyond it. Their optical design is complicated and hence more expensive.
Hope that helps
James
 
jbw said:
If an object is close to you the rays of light leaving it are entering your lens slightly diverging. The closer the object the more they diverge, the lens has to move to bring these varying diverging Ray's to a focus on the sensor.
At infinity ( or close to it) the Rays are leaving the object in parallel and the lens has the job of moving to a position in order to bring these to a focus.
When a lens goes beyond infinity it is attempting to bring Ray's of light that are converging to a focus - this it fails to do as there is nothing beyond infinity so all you get is an out of focus smudge.
Click to expand...

Or, in pictures -

Beyond%20infinity.jpg
 
boliston said:
I much prefer lenses that stop at infinity - It seems to be "AF-S" lenses that go beyond infinity yet AF-D lenses have an actual stop which is much easier if you switch to MF instead of AF.
Click to expand...
The 'stop' on most lenses I've owned is beyond the infinity mark.
 
sduk said:
and you can see the stars through it? when I look through mine all i can see is a fuzzy screen. Are you sure?
Click to expand...

The EVF ( on the A7R2) although truly superb - I find it too small and cramped to identify small pin points of light which are the stars. I always use the back live view screen.
It was the same when I had a Canon 5D Mk3 - the optical viewfinder was to small and dark so I always used live view.
If you Google ' lonely speck' they have some great advice on focusing technique aimed at beginners through to the more advanced photographer. Well worth a visit.
Hope that helps you.
James
 
jbw said:
If an object is close to you the rays of light leaving it are entering your lens slightly diverging. The closer the object the more they diverge, the lens has to move to bring these varying diverging Ray's to a focus on the sensor.
At infinity ( or close to it) the Rays are leaving the object in parallel and the lens has the job of moving to a position in order to bring these to a focus.
When a lens goes beyond infinity it is attempting to bring Ray's of light that are converging to a focus - this it fails to do as there is nothing beyond infinity so all you get is an out of focus smudge.
The idea of having a lens going beyond infinity is for two reasons
1) to compensate for a varying distance between the lens and the sensor due to temperature changes
2) because it's technically easier to design an auto focus system this way
As far as I'm aware ( unless anybody knows different) only Carl Zeiss lenses stop dead at infinity and don't go beyond it. Their optical design is complicated and hence more expensive.
Hope that helps
James
Click to expand...
It's not that I don't understand the physics behind it - it's the actual phrase itself that doesn't work in my mind - you can't go beyond infinity - infinity is infinite.
 
You must log in or register to reply here.
Back
Top