• Welcome to BirdForum, the internet's largest birding community with thousands of members from all over the world. The forums are dedicated to wild birds, birding, binoculars and equipment and all that goes with it.

    Please register for an account to take part in the discussions in the forum, post your pictures in the gallery and more.
ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

correct focus (1 Viewer)

A

andy70437

Well-known member
Hi,
Took this with my Sigma 50-500mm and could someone tell me if it is correctly focussed. Or as good as I can expect.
Aim was centre battery, auto focus on, f5.6, iso 400,at 300mm focal length. Batteries were one inch apart.
Any advice gratefully acknowledged.
Andy
 

Attachments

  • batteries.jpg
    batteries.jpg
    90 KB · Views: 312
That's about as good as you'll get without closing your aperture. Try it at something like f16 and you'll have more in focus. As you move towards 500mm less will be in focus as well.
 
I am not a fan of the battery test. If the spacing is not spot on and the positive (+) signs are not exactly positioned then you run the risk of getting a false impression. I do not think there are sufficient visual clues to make the test conclusive.

I do not agree that each battery is evenly spaced as you suggest or if they are then they are not in a perfect line IMHO
 
Don't see why any of that would be a problem, Adrian.

All this test is mean to do is provide an indication that that what was focused on - the battery in the middle - is where the actual point of focus is, rather than some point in front or behind, both of which situations would be indicated by batteries one side or other of the middle one being sharper.

There's no need for precision positioning for that.

Paul,

based on this test, you're looking fine - the middle battery is clearly the sharpest.
 
Industry standard is , 1/3rd in focus in front of focal point and 2/3rds behind. Judging by your test the battery in front is more in focus than the one behind. This suggests to me that the focus is slightly out. You may therefore have depthof field problems. It may make little difference in the real world because the degree you are out is minor. You may have a very slight front focus issue but as I said , since the test you have performed is, in my view, unreliable, it is not possible for anyone to advise you with certainty.

For anyone else who has not had a front or back focus problem (I have) it will be difficult for them to grasp what an effect this may have on real world shooting. If your focusing is out it is worth sorting out even if the degree is slight since apart from the usual problems it will mean you may have problems with critical manual focus and your dioptre may be set wrong too! IMHO.

Upshot, carry out a better test and a number of them if you find your real world shots are not up to scratch. I'm sorry if that is not what you wanted to hear.
 
a.dancy said:
Upshot, carry out a better test and a number of them if you find your real world shots are not up to scratch. I'm sorry if that is not what you wanted to hear.
Click to expand...

perhaps you could offer some advice as to a better test to do, this sort is what I've used in the past and I'd be interested to learn of more reliable ways of checking this.
 
Peter

I used several methods. The best one for me was a white ruler. At the centre point I placed a black dot using a marker pen to ensure that I was hitting the same focus point each time I did a test...which I did a number of times. I did the same using magazine pages where the contrast with the letters and the page was good. Somehow, or for some reason, the fact that you can read the in and slightly out of focus print enables you to assess the degree of focus (or span of 'field of view' and where it lay) because the content is meaningful. The eye/brain cannot judge things which are more abstract I suppose. I also used a chart designed for the purpose which I got from someone in a camera club. It consisted of lines on a sheet of paper and is the same as the one on photo. net. If you google ' photo.net focus Bob Atkins' you should find such a chart which has the beauty of the lines being cosine adjusted to take account of perspective.

Finally I have a toy bird (how sad) which I set up on branches etc. This enabled me to carry out a host of tests not only for checking focus but helped me learn camera/field skills for things such as DOF and exposure. When I started photography (using film) I could not afford the learning curve cost, so I practised on the toy to help me understand exposure and DOF. It was the best investment I ever made in terms of gear and I didn't get it from a camera shop! I still think it is as good as anything for testing focus. I tried the battery test but (for me) I found the results too variable and I think there are a number of reasons for it, so would not now consider it as an option. It is however only my view and if it works for others then that's great.

Kind regards

Adrian
 
Exif suggest a shutter speed of 1/8th on a 500mm zoom. Although the image looks sharp enough I'm not convinced about the wisdom of assessing correct focus at this speed. Perhaps if the test can be repeated in a better lit location...........
 
ikw101 said:
Exif suggest a shutter speed of 1/8th on a 500mm zoom. Although the image looks sharp enough I'm not convinced about the wisdom of assessing correct focus at this speed. Perhaps if the test can be repeated in a better lit location...........
Click to expand...


Agreed
 
ikw101 said:
Exif suggest a shutter speed of 1/8th on a 500mm zoom. Although the image looks sharp enough I'm not convinced about the wisdom of assessing correct focus at this speed. Perhaps if the test can be repeated in a better lit location...........
Click to expand...

How would a faster shutter speed change the (clearly) indicated point of focus, though?

Assuming a stable platform, the shutter speed is pretty much irrelevant. The results of this test show that there is no back or front focus worth worrying about at the selected focal length, aperture and distance from the subject, and that's all it's meant to do.
 
Last edited:
Keith Reeder said:
How would a faster shutter speed change the (clearly) indicated point of focus, though?

Assuming a stable platform, the shutter speed is pretty much irrelevant. The results of this test show that there is no back or front focus worth worrying about at the selected focal length, aperture and distance from the subject, and that's all it's meant to do.
Click to expand...

Keith....I don't kow why shutter speed makes a difference but I do believe it does. I suppose it is better to have your lens 'snap on' rather than struggle on unreliably. As for the present case taking into account the lens used the focus may be adequate for most real world situations. With my f2.8 300mm lens my guess is that it would not be accurate enough for shallow DOF shots where accurate focus is critical.

AD
 
Thanks guys, very interesting discussion and I hope I have learnt something useful. I am now off to buy a toy bird . . . . (Thanks Adrian for that!)
 
Warning! This thread is more than 16 years ago old.
It's likely that no further discussion is required, in which case we recommend starting a new thread. If however you feel your response is required you can still do so.

Similar threads

W
Considering a Partial Camera Upgrade - D500 w/ 200-500mm lens
2
Replies
34
Views
4K
BriLee
B
T
Focussing: Just Do It!
5 6 7
Replies
136
Views
11K
WJC
WJC
Will K
My First Star Test
Replies
6
Views
1K
henry link
H
F
Digiscoping with a DSLR is still a good choice in 2022!
Replies
2
Views
2K
Jefrs
J
has530
4 Compacts Briefly Reviewed, Vintage Vs. Modern Head to Head
Replies
7
Views
3K
Bino Steve
B

Users who are viewing this thread

Total: 2 (members: 0, guests: 2)
Back
Top