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Old October 26th, 2006, 01:36 PM   #1
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could my lens made for digital SLR give me grain?

It seems my brand new sigma 24-70mm f2.8. is responsible for my "film of grain". Why would this be?

It's a fast lens, it was expensive. But I have found out that it is designed for a digital SLR. Could this could be a problem? The lens is sigma 24-70mm D 1:2.8 EX DG

My search on the forums came up with the FOV is smaller for digital SLR so the edges would be softer but why would that effect the film of grain?

I did a test looking at a dusk sky with my sigma lens, lens stopped down a bit. Camera shutter on 50 (pal camera) camera iris opened to correct exposure. Film of grain all over sky.

Did a test with a 50mm prime f2.8 same settings on lens and camera, no film of grain...

I get this film over everything even with the lens fully open. It's very frustrating especially as the lens cost me $500
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Old October 26th, 2006, 03:59 PM   #2
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Don`t worry

Nope, that would not be the problem. As EX DG lenses are the finest Sigma lenses around it is almost the best zoom in that range you can get from third party lens manufacturers. Fortunately it`s image circle is designed for full frame DSLR usage too, so don`t worry about your purchase.
My bet would be that somehow your camcorder`s gain just shows up.
Watching too much of sample footage would make you a bit schizophrenic too. Damn, I cann`t stand even regular PAL proadcasts any more, I don`t see what they try to show, I see only grain and lens breathig and occasional bokeh, I find myself counting the diaphragm blades of those Fujinon lens and...

Please don`t worry, it will get better over time. Think about the story you try to tell.

Cheers,
T
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Old October 26th, 2006, 04:02 PM   #3
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Hi Phil,

I'm no expert on lenses but here's my guestimate

Presumably the digital SLR for which this lens is designed has a smaller chip than a 35mm film frame.
As such, the quoted focal lengths for this lens are possibly given such that on the slr, the field of view or angle of view of the photo obtained is the same as a 24-70mm zoom on a 35mm camera, likewise the f-stops.
As such, the actual focal lengths might be slightly shorter than stated. i.e. its actually a bit wider than 24-70. This would mean conversely that the f/2.8 max aperture is somewhat optimistic, how much so depends on the size of the ccd for which the lens was intended.

So basically, you might be seeing an effect consistent with using a much smaller aperture than what the lens states. But like I say, I'm no expect on lenses

cheers

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Old October 26th, 2006, 04:03 PM   #4
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thanks.

It's definately not the gain. Am using a sony z1 with full manual control over the gain. And it's static grain, not as bad as seeing the GG with the motor off but about half as bad as that!
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Old October 26th, 2006, 04:04 PM   #5
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Quote:
Originally Posted by David MD Smith
Hi Phil,

I'm no expert on lens but here's what my guestimate

Presumable the digital SLR for which this lens is designed has a smaller chip than a 35mm film frame.
As such, the quoted focal lengths for this lens are possibly given such that on the slr, the field of view or angle of view of the photo obtained is the same as a 24-70mm zoom on a 35mm camera, likewise the f-stops.
As such, the actual focal lengths might be slightly shorter than stated. i.e. its actually a bit wider than 24-70. This would mean conversely that the f/2.8 max aperture is somewhat optimistic, how much so depends on the size of the ccd for which the lens was intended.

So basically, you might be seeing an effect consistent with using a much smaller aperture than what the lens states.

cheers

Dave
That probably makes sense...i need to get my hands on an equivalent length zoom of the same speed designed for a film camera so i can compare...I understand there will always be a trace of this type of grain by the design of the GG. Is it the same with all the cheaper DOF adaptors. I use the Letus 35flip enhanced, and awaiting a Brevis now too...
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Old October 26th, 2006, 10:36 PM   #6
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Phil.

I have a 12-24mm f4 zoom made for digital SLR only. It wasn't what I and the salesman thought it was - silly me for trusting. It works sort of okay but it does set off groundglass artifacts outdoors in high contrast situations. The groundglass artifact turns up on the mid levels especially browns or reds, so I expect somthing similar will be happening to the Letus also.

GG artifacts on the Letus seem to be of the fixed pattern kind, on the full sized disk it mainfests as flicker and streaks. My glass disk got a scratch on it from somewhere and this shows up first.
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Old October 27th, 2006, 01:40 AM   #7
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Is that the Tokina 12-24 for Nikon DSLRs?
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Old October 27th, 2006, 01:46 AM   #8
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Phil,
can You show footage?
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Old October 27th, 2006, 03:37 AM   #9
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i will do some more tests today and see what i get...actually there is one shot in particular on my demo video on my website that shows the GG very clearly even with the smaller size. the one on the beach of the old guy sitting in the chair looking out to sea. That was done with my digital lens (as was all of it, but for some reason the stuff on the beach was giving me a lot of grief!)
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Old October 27th, 2006, 09:58 AM   #10
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Jim.

The f4 12-24mm I use is a genuine Nikon. I have some half frame rate, hopefully better res footage up at the filefactory shot with that lens.

The address is at:-

http://www.filefactory.com/file/fcebfe/

It is a big file though.

The f2.8 20-35mm is a Tokina.


Phil.

The beach would have had lots of light, probably lots of contrast.

Situations which put up three distinct large area levels of brightness upon smooth objects across more than three or four aperture stops between each seem to aggravate this fault on my disk arrangement as no compromise exposure level can be chosen.

There is always one object which will show the artifact.

Shooting against a sun at about fifty degrees of elevation really brings it on.

On batteries, check the voltage available from the rechargables. Nicad cells are usually 1.2v per cell, not 1.5v, so your Letus might not start anyway on fresh rechargable batteries. There are some rechargables which give the 1.5v but I have not seen them, do not know if this is factual and do not know the brand.
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Old October 27th, 2006, 11:39 AM   #11
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Bob,

I understand backfocus and what it is for, but with the DOF adaptors could it aggravate this "film of grain" if at all?

also, the lens you used is f4. I am only using my Letus flip for the first time with my z1 now as when I was in the states all I had was my a1. Now I have full manual control of gain i am shocked at how much light it needs with my f2.8 lens on it. In the shade I can barely get proper exposure. does the flip and letus really eat up that much light? I guess my a1 was putting in gain automatically and I didnt realise as it is so subtle...

Your stuff looked great, especially the sky. I haven't managed to get my sky to look like that at all...so crisp and grain-less. v jealous. You are using a zoom lens and a relatively slow one and getting these results, v frustrating. I need to lose the static grain before I can use these on paying jobs. I am getting a Brevis in a few weeks from Dennis. I am aiming to use this in situations when I want to use a 35mm adaptor but just don't have another light. I wonder how much light loss Dennis' flip adaptor will be. Is the adaptor on it's on just half a stop? How does compare to my Letus flip and to your own adaptor Bob?

One thing I would like to know is what actually is this "film of grain"? It isnt the grain on the GG as that is vibrating, it's static grain of a defineable pattern. where is this pattern coming from?
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Last edited by Phil Bloom; October 27th, 2006 at 04:41 PM.
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Old October 27th, 2006, 04:41 PM   #12
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Just had email from Quyen who confirms there is a problem with Zooms and the Letus (not sure if it's just flip or not) and this "film of grain". He says he is aware of the problem and trying to work out why it happens. Anyone with any ideas please let us know!!!

Is this problem specific to the Letus (maybe just the flip variety) or do any of the other apadtors have this problem? I just can't work out where the grain is coming from...it must be the GG but if the motor is on how can that happen?
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Old October 27th, 2006, 05:08 PM   #13
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I have a zoom 70-200 forget the f range. can't really use it, doesn't look good. I have a letus35a. I pickup the pattern of the GG A LOT more. Almost to the point of not being able to use it. Only my zoom lens has this problem.
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Old October 27th, 2006, 05:34 PM   #14
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So is it just a Letus issue or do the SGPro, Letus, Redrock etc have the same issues with zooms?
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Old October 27th, 2006, 07:03 PM   #15
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Is it simply the fact that its a slow lens? Grain is generally more apparent the higher the F number. Do you get the same effect with a standard 50mm lens that is stopped down to say, F4?
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