Wallet full of $100 bills

[bob williams]

John, Sounds like some of your dilemma comes from a lighting issue (need for tighter aperature). Perhaps this could help. [:O]





Merry Christmas





Bob

[HDNitehawk]

John


Here are some comparisons I shot this morning.


This is definitely low light, it is the wife's little christmas tree in the front room. I adjusted the WB down on all three. 2800K


First one is the standard, 35mm F1.4, 1/50 ISO 400





[View:http://community.the-digital-picture...neric/utility/]





This one is 24mm f1.4, 1/50 ISO 400 Croped





[View:http://community.the-digital-picture...neric/utility/]





This is the original 24mm with no crop





[View:http://community.the-digital-picture...neric/utility/]





The little red and white snow man is the focus point I used in live view at 10x. The picture was shot about 3' 4" from the snow man. The angel is in the front and the shelf runs at a bit of an angle. All were shot off a tripod this morning. The only lighting I had were 4 60 watt light bulbs about 6' behind me in the ceiling fan.


From what I see there is a slight loss in sharpness and IQ with the crop. I also shot a 35mm at F2.8. The shutter speed had to be at 1/13 to get the same exposure. At F2.8 the IQ was superior to both the 24mm and 35mm at f1.4. I can post the F2.8 if you like as well, let me know.

[Jon Ruyle]

If I plug a distance like 6.5 feet into a DoF calculator

Okay- I believe you. I know effective crop factor changes as you get close to your subject, but I didn't know 6.5 feet was close enough to have that much of an effect. I'm surprised, but I believe you (and DOF calculator)


Unless DOF calculator is rounding to the nearest f stop or something?

If I need to be at f/2.8 for DoF, that's likely not fast enough for shutter speed

You gain no advantage in cropping the 24 vs stopping down the 35. Compare 24 at f/1.4 cropped to 35 at f/2.8: Yes, you need a higher iso with the 35, but with the 35, you're using the whole sensor. The photon noise is exactly the same. In other words, rather than use the 24 mm at f/1.4 and 6.5 feet, just use 35 mm and stop down to f/2.8. Use the same shutter speed and you'll get the same result. (I'm not telling you anything you don't know already, of course).

But I also agree getting a lens *intending* to crop many of the resulting images doesn't seem like the best idea. Thus my dilema...

No dilemma at all. If you want the 35mm angle of view but need the dof of f/2.8- you already have two lenses than can do that quite well. []


(I think what you really want is a lens that has DOF of f 2.8 but light gathering ability of f/1.4. Let me know when you find it... but you won't get there by cropping )

[HDNitehawk]

You gain no advantage in cropping the 24 vs stopping down the 35. Compare 24 at f/1.4 cropped to 35 at f/2.8: Yes, you need a higher iso with the 35, but with the 35, you're using the whole sensor. The photon noise is exactly the same. In other words, rather than use the 24 mm at f/1.4 and 6.5 feet, just use 35 mm and stop down to f/2.8. Use the same shutter speed and you'll get the same result. (I'm not telling you anything you don't know already, of course).

The IQ with the 35mm stopped down to F2.8 is going to be much sharper and superior to the 24mm at F1.4. To get fast enough shutter speed and raising the ISO, it would raise the question would the better sharpness and IQ overcome the bad effect of noise at the higher ISO. If John wants I could set up another sample and test this.

[Richard Lane]

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Hey Hawk,


Thanks for taking the time to share those test shots. In the first 35mm/1.4 shot, I can see that the angels in the back row are out of the focusing DOF, whereas the angels are more in the DOF range in the 24mm/1.4 cropped version however, I believe that we are now losing contrast between the table cloth and the bricks against the fireplace. I also see less detail in the white snowman table cloth in the 24mm/1.4 cropped version as compared to the 35mm/1.4 Version.


It appears to me that the last one 24mm no crop is the best, with some mild vignetting in the left upper and lower corners.


These shots were taken at 3ft. 4 inches which is very close to the subjects, I believe John would like to use this lens at a more reasonable subject distance of 6.5-7ft. which is essentially doubling the subject distance, which I feel will give significantly different results.


I think it would be interesting to compare some shots at the 7ft. distance with the 35mm/1.4 and then, closer with the 24mm/1.4 in order to achieve the same framing distance, this way we could take cropping out of the equation and we can just focus on DOF, vignetting and barrel distortion. I can't see buying such an expensive lens and then cropping away detail.





Rich
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[HDNitehawk]

Rich


I agree with all your comments and you see it the same way I do, except one which I have inside knowledge on. The vignetting in the upper and lower corners of the 24mm may be the effect of a shadow off the frame of my 52" TV which sets just a little to the left of the frame. How much is shadow and how much is vignetting I wouldn't be sure, but it wouldn't be right to take it in to consideration.


The DOF is much shallower with the 35mm, I did the test at 3' because the closer you get the more it highlights the difference with the DOF. At 7' the difference in DOF will be much less, I would guess the difference in crop quality will not change.


I would be happy to try the test at 7', or other distances if John wants. I will wait to hear John's response to see if there would be any other variables he would like to take in to account.





Rick

[Jon Ruyle]

The IQ with the 35mm stopped down to F2.8 is going to be much sharper and superior to the 24mm at F1.4.

No question about that.

To get fast enough shutter speed and raising the ISO, it would raise the question would the better sharpness and IQ overcome the bad effect of noise at the higher ISO.

That's what I wast trying to explain- there is no noise advantage in using f/1.4 at lower iso if you crop. Using a higher iso increases photon noise, but so does cropping. Assuming you end up with the same DOF and use the same shutter speed, the two will balance exactly. So from a photon noise point of view, it does not matter at all if you increase DOF by cropping or stop down. But stopping down tends to improve IQ, while cropping tends to hurt IQ. Thus my point was that it makes more sense to stop down than crop.


Really- to get the 24 f/1.4 with the idea of cropping it makes no sense at all to me. The 24 is unique and expensive because it is fast and wide. Why would anyone want to turn it into a longer slower lens?

[HDNitehawk]

That's what I wast trying to explain- there is no noise advantage in using f/1.4 at lower iso if you crop. Using a higher iso increases photon noise, but so does cropping. Assuming you end up with the same DOF and use the same shutter speed, the two will balance exactly. So from a photon noise point of view, it does not matter at all if you increase DOF by cropping or stop down. But stopping down tends to improve IQ, while cropping tends to hurt IQ. Thus my point was that it makes more sense to stop down than crop.

Jon



The only problem with stoping down, is that in low light you may already be at a high ISO to get a fast shutter enough shutter speed at F1.4. Loosing those few stops might be the difference in a pic with camera shake and one good one without.
I agree with you though, I do not think the 24mm with a crop is a good alternative. At least not one I would be happy with the IQ. Best option still is to take a few steps forward and use the 24mm.


Rick

[Jon Ruyle]

The only problem with stoping down, is that in low light you may already be at a high ISO to get a fast shutter enough shutter speed at F1.4. Loosing those few stops might be the difference in a pic with camera shake and one good one without.

Perhaps I was unclear, but what I was trying to explain is that one can get the same shutter speed and the same photon noise with the 35 at f/2.8 as with the cropped 24 at f/1.4.

Best option still is to take a few steps forward and use the 24mm.

It depends on what perspective you want. If you want the perspective as the cropped 24 (as John has stated that he does), I would suggest using the 35. If you want the perspective of the full 24, well... step forward and use the 24.

[Fast Glass]

Using a higher iso increases photon noise, but so does cropping.

Correct, a 1.6 crop camera has the same noise as a full-frame if the DOF is the same. And if the sesor has the same technology, the 7D and 5D II have almost the same noise at the same DOF.

The only problem with stoping down, is that in low light you may already be at a high ISO to get a fast shutter enough shutter speed at F1.4. Loosing those few stops might be the difference in a pic with camera shake and one good one without.

Yes, you will need a f/2.8 exposure but the noise will be the same as f/1.4 on a 1.6 crop camera. All you do is raise the ISO and you have the same result.


Take a look at Bryans noise crops, the 7D is about 1 1/3rd stopps noisier than the 5d II


John.