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Old Jul 2, 2007, 3:25 PM   #1
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Found this link on dpReview explaining the basics for fireworks photography..

Thought others might find it helpful..

http://jbellphotography.com/forum/Fi...hotography.pdf

In this file the author mentions setting the lens to infinity--I've also seen many mentions here lately about being able to focus to infinity..

What exactly does this mean??..

Thanks, Bruce
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Old Jul 2, 2007, 3:44 PM   #2
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baltochef920 wrote:
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In this file the author mentions setting the lens to infinity--I've also seen many mentions here lately about being able to focus to infinity..

What exactly does this mean??..

Thanks, Bruce
I thought, I can answer this one but as I started to type I realised that I cannot give a proper scientific answer.

To us mere mortals you'll find a symbol on the lens that looks a bit like it follows on from the distance points on the focus ring. It just means that the focus point is beyond the furthest distance marked. In reality infinity isn't a single setting, strange as it may seem there are degrees of infinity. In other words if you were manually focussing on a distant object, just turning the focus ring to infinity wouldn't guarantee the subject would be in focus. Why? I have no idea!

Anyway there's the idiot (me) guide to infinity.
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Old Jul 2, 2007, 10:43 PM   #3
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Lenses have a minimum and (for lack of a better term) "maximum" distance for focusing. The minimum focus distance is the minimum distance where the lens can focus - anything closer and the picture will be out of focus. My A*300 has a minimum focusing distance of something like 11 feet, while a macro lens might have a minimum focusing distance of a couple of inches.

Then lenses have points where it focuses on a point and will have things before and after that point out of focus - the depth of field that everyone either loves and hates.

Finally, there's a distance where everything at that point and beyond it are in focus - those scenics from mountain tops where you can see for miles - that's the infinity point (and marked as such on the lenses). This point also varies depending on individual lenses, with wide angle lenses having much shorter ranges (my 24mm lens goes to infinity at something like 8-10 feet, while the A*300 it's beyond 150 feet).

That's how I understand the way lenses work - if anyone has a better explanation, please chime in because I'm no expert.
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Old Jul 2, 2007, 11:04 PM   #4
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The only thing I can add is a word of caution

Some lenses will focus past infinity at which point the image will go blurry again. So don't just crank the lens all the way until it stops. Use the infinity mark. Of course you will have to set your camera/lens for manual focus
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Old Jul 2, 2007, 11:45 PM   #5
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Harriet, I think your explanation is great. Well presented and made the information easy to understand, thanks

And back to the OP, with respect to fireworks, (if my understanding is correct) when youset focuson infinity, that insures the largest depth of field therefore the largest area in focus possible. Right??? (sorry for my run-on though process, hehehe)

Nice bits of of information all.........

Bev

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Old Jul 3, 2007, 1:18 AM   #6
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Infinity focus is where the lens will focus a point light source from a very large distance, to a point on the sensing device or film. Most lenses are marked to focus only out to around 15 meters or so, with anything beyond that being infinity.

The reason lenses sometimes focus "past infinity" is simply because autofocus mechanisms tend to overshoot a bit, and then reverse direction. There has to be a little bit of slack available for them to do this.

If you manually adjust your lens all the way out, and then back off just a bit, you should be at the proper focus. Sometimes hard to distinguish at night when you need to take the fireworks shots, so it is best to make some tests in daylight to get a feel for how much to adjust.

brian
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Old Jul 3, 2007, 3:56 AM   #7
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VTphotog wrote:
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The reason lenses sometimes focus "past infinity" is simply because autofocus mechanisms tend to overshoot a bit, and then reverse direction. There has to be a little bit of slack available for them to do this.
There has to be another reason as well. I've got two A* lenses (200 & 600 mm), manual focus,that do this.There's nothing wrong with the lenses, it's even mentioned in the manual. I don't know for what purpose, but as I understand this is some kind of "pro feature".

Kjell
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Old Jul 3, 2007, 4:25 AM   #8
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bilybianca wrote:
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There has to be another reason as well. I've got to A* lenses (200 & 600 mm), manual focus,that do this.There's nothing wrong with the lenses, it's even mentioned in the manual. I don't know for what purpose, but as I understand this is some kind of "pro feature".

Kjell
Maybe to give them enough edge to work with the "evil" flange M42 to K adapters? (Or other cam to cam adapters... since M42 was sort of a universal lens not just Pentax)

I've heard people say some lenses work and some don't.... maybe the ones that go beyond INF are the ones that do?

Not sure why an "A" would.... which out of curiosty?

Didn't notice that on any of my 50's (F/2, 1.7 AND 1.4) , the FW I shot back in Aplril with the 1.7, came out very sharp and due to the sudden start and non stop show it was, as I recall, just went with all the way cranked.... may have touched it back a hair though, don't remember now.
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Old Jul 3, 2007, 6:17 AM   #9
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Hayward wrote:
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bilybianca wrote:
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I've got two A* lenses (200 & 600 mm)
Maybe to give them enough edge to work with the "evil" flange M42 to K adapters? (Or other cam to cam adapters... since M42 was sort of a universal lens not just Pentax)

Not sure why an "A" would.... which out of curiosty?
It's the A* 200 mm 2.8 and the A* 600 mm 5.6. As far as I know there were never any screw mount A* lenses produced...

Kjell
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Old Jul 3, 2007, 10:20 AM   #10
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bilybianca wrote:
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It's the A* 200 mm 2.8 and the A* 600 mm 5.6. As far as I know there were never any screw mount A* lenses produced...

Kjell
No I agree with you on that but also doesn't surprise me that is a A does go beyond INF it would be on the LONG end....

But again never noticed that on 3 different speed Pentax 50 A's or a third party 28mm A either.... all the way to stop on those short lenses are effectively INF.

And again it has been mentioned some manual M42's with flange adapter K mounts do work OK, and I'd BET those are the ones that do focus beyond INF.

A real reason to do so... no... and particularly the K's.... but again not surprised your examples are on the long end where even a slight over shoot would be much magnified... vs 50's and 28's.

And even sort of remember that on old film Minolta and Canon longer lenses... maybe just to insure not mil spec physics they DID get to INF... really not that much farther and actually seen same lens samples vary as to how much beyond INF... some few to be problematic... some JUST beyond and not even noticeable.
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