Frustrated With Shallow DOF.

[mic]

Hi all,
haven't been around lately, new Bub in family.

Could somebody please put me on the right track here.

Now, I purchased a 50mm 1.8 a few months ago and have been experimenting & practising. ( some good. A lot Bad. )

Now everytime I have it wide open at 1.8 and you get home and put them on the computer, they are out of focus. Arrrhhhhhh.

Now can someone please explain to me whats the point in having a great light catching Lens for low light conditions when it's so hard to get a shot thats in focus.
You have to bring it to 5.6 ot there abouts.
Doesn't this defeat the purpose of getting a 1.8 or 1.4

Also my 1.8 is made in China, is the 1.4 which is more expensive made in Japan ? or China as well. I find that when you Focus it's got a looseness about it & doesn't feel tight. Has anybody else found this ?

I have been asked to do a Wedding soon and have to get my Act together, whats a good Wedding Lens ?

Thanks,

Oooops, Baby crying better go.

Thanks,

Mic.

[Onyx]

Firstly, it may just be getting enough practice nailing the focus at small apertures. The rectangular bracket indicating AF area are far larger than the true AF sensors themselves. It may take some familiarisation to get to know your individual camera sample and knowing precisely where the AF sensor lies within that big box. eg. on mine, it's slightly above middleline with the vertical detector towards the left. I put in many shots using tripod and page of black lines pasted against a wall - but sufficient real world use should be able to tell you where yours are precisely.

Also, it has to be said - it could be the infamous BF issue. Focus calibration is not unknown to be out on certain D70 units. Use of the kit lens and other slow lenses masks any focus problems as their DOF is sufficiently deep. Tim Jackson's focus test chart would be the easiest way to test for back/front or any non-optimal focus issues. Instructions and chart included in the PDF available for download off here:
http://md.co.za/d70/chart.html

[mic]

Cheers Onyx,

I'll give it ago and test.

I better make sure before the Wedding shoot. otherwise I might end up on the spit instead of the PIG.

Mic.

[MATT]

MIc, I recently Purchased the 50 1.8 also.

I found that its focus is better in manual than auto.



This was f2.8 I think.Low light, Ihave not PP it only resize. I find it hard to hit the spot perfectly with focus also.

Just keep practising.

MATT

[lejazzcat]

Hi all,
haven't been around lately, new Bub in family.

Could somebody please put me on the right track here.

Now, I purchased a 50mm 1.8 a few months ago and have been experimenting & practising. ( some good. A lot Bad. )

Now everytime I have it wide open at 1.8 and you get home and put them on the computer, they are out of focus. Arrrhhhhhh.

Now can someone please explain to me whats the point in having a great light catching Lens for low light conditions when it's so hard to get a shot thats in focus.
You have to bring it to 5.6 ot there abouts.
Doesn't this defeat the purpose of getting a 1.8 or 1.4

Also my 1.8 is made in China, is the 1.4 which is more expensive made in Japan ? or China as well. I find that when you Focus it's got a looseness about it & doesn't feel tight. Has anybody else found this ?

I have been asked to do a Wedding soon and have to get my Act together, whats a good Wedding Lens ?

Thanks,

Oooops, Baby crying better go.

Thanks,

Mic.

My thoughts and questions,
Your aware that most lenses(edit) have optimal performance at F8 and they get worse at either extreme.
The point of faster glass is that it will give you F8 in lower light than say a f2.8 lens. Its not meant to be used at f1.8 generally.
At that apeture your DOF is way too short to be much good.

If the light is so low, that you need to use f1.8 then bump up the ASA,or use a flash and open you apeture to say f4 or f5.6.

As for the out of focus, is it maybe that your shutter speed is too slow( low light without flash), so that may also be 'shake'?

[Greg B]

In addition to Onyx's excellent remarks, you need to be conscious that:-

. DoF is proportional to the distance from camera to focus point, the closer you are, the shallower the DoF. If you are at the minimum focussing distance at f1.8, your DoF will be very narrow.

. Low light is a problem for auto focussing, you will want your AF assist on, and you will need to be aware of your focus point in the frame, and the focus point you are trying to nail in the image. Maybe manual is the way to go, although that might be difficult too.

. There is much talk about sweet spots and best apertures. The 50 f1.8 might be at its very best at f5.6. If you need the wide open f1.8 because of lighting issues, there are trade offs.

I haven't noticed any particular quality concerns with my 50 F1.8 - I believe the f1.4 is better made, however it is more than twice as expensive, and wide open, the DoF will be even less (albeit not much)


cheers

[lejazzcat]

Oh and its also a popular lens for macro work( on bellows).
As theres a substantial loss of light with the extensions, the 1.4 /1.8 helps.

[JordanP]

What Onyx said.

I would have a close look to see if it is a back focusing issue and double check where my focus point is. Another test that may be useful is to compare your results when you manually focus on a fixed subject at a fixed distance ... against ... an auto focus shot of the same subject

I don't have the lens you are talking about but I have used an older version of the 50mm 1.8 and found it sharp wide open. I also do not feel there is any magical number at which all lenses are optimal. A general guide of 2-3 stops up from wide open serves me well, however I find that some lenses perform better than I require wide open anyway.

I often use the following lenses in low light, wide open and have achieved excellent results - 85mm 1.8 although I think it performs better around f2-f2.8; the 17-55mm DX - outstanding results at 2.8 (wich is wide open), and the 70-200 VR also fantastic wide open.

[mic]

Thanks Guys,

Good info for me to absorb and experiment with.

I will have to keep experimenting I think.

Thanks,

Mic.

[lejazzcat]

What Onyx said.

I don't have the lens you are talking about but I have used an older version of the 50mm 1.8 and found it sharp wide open. I also do not feel there is any magical number at which all lenses are optimal. A general guide of 2-3 stops up from wide open serves me well, however I find that some lenses perform better than I require wide open anyway.

Its a good rule of thumb Jordan.

Food for thought though.
http://www.photodo.com/prod/lens/detail ... 444.shtml#

"Weighted MTF - Higher is better"

Weighted MTF for 50 mm:
f1,8 0,62
f2,8 0,78
f4 0,83
f8 0,86

[digitor]

The point of faster glass is that it will give you F8 in lower light than say a f2.8 lens. ....

Umm.., no. A setting of f8 will let in the same amount of light on any lens. (Plus or minus a bit for manufacturing "errors") On a faster lens, the "sweet spot" might be at a larger aperture (smaller f-no) but f8 is the same.

As others have already pointed out, all other things being equal, depth of field decreases as you open the aperture.

Cheers

[lejazzcat]

The point of faster glass is that it will give you F8 in lower light than say a f2.8 lens. ....

Umm.., no. A setting of f8 will let in the same amount of light on any lens. (Plus or minus a bit for manufacturing "errors") On a faster lens, the "sweet spot" might be at a larger aperture (smaller f-no) but f8 is the same.

As others have already pointed out, all other things being equal, depth of field decreases as you open the aperture.

Cheers

I stand corrected - of course . Its the size of the aperture...
thanks digitor