# Infinite focus-manual SRL



## SimpleScotty (May 24, 2010)

Hello all,
First, this is a keen idea. I'm looking forward to having a place to go to get some tips on photography.
I have a question, but first some background: I use a 1972 Petri 50mm SRL. It's completely manual. I have to advance the film myself with every shot. Yes, I'm still using film which is surprisingly hard to come by! I don't know if I'll ever get used to that. It's a family heirloom you could say...ok, it was a gift from my dad. I think that's about all for the device.
My question: does anyone know how to do the "infinite" focus? It was a technique I read about but was unable to execute. It involved setting the aperature such that everything in the field of vision was in focus, both the foreground and the background. I was totally unsuccessful when I tried. 
:4-dontkno
I know this is pretty archaic but if anyone has any idead (or even knows what I am saying--I hope I'm coming across clearly) please reach out. Thanks!


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## Basementgeek (Feb 7, 2005)

What you are talking about in film photography is called "Depth of field". Lots of info, goggle it.

I love my old cameras.

BG


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## zuluclayman (Dec 16, 2005)

Infinite focus or large Depth of Field (DoF)is achieved by using the smallest aperture setting - usually f.22 - the rule is that the larger the f-stop number (the smaller the aperture) the greater the DoF and vice-versa - if you want only part of the image in focus you use a larger aperture (bigger number f.stop)
The balance comes in being able to get enough light to the film - if you have a small aperture to achieve the amount of DoF, you will need a slower shutter speed unless you are in a brightly lit situation. This in turn may mean you need to use a tripod to counter any shake you may encounter, leading to a blurred image.


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## zuluclayman (Dec 16, 2005)

oops! a correction needed - I'll plead the insanity due to head injury defense :sigh:


zuluclayman said:


> if you want only part of the image in focus you use a larger aperture (*SMALLER* number f.stop)


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## yustr (Sep 27, 2004)

If memory serves (and at my age that's not at all a sure thing) it also involves where in the scene you set the focus point. I believe its set rather close - in the foreground. It helps if the lens is a wideangle and you get down low. 

(BTW: You might want to invest in a starter digital SLR. That way you can do all of the experimenting you want at no additional cost.)

(I know what you mean about film becoming hard to buy. I had to replace grandma's P-n-S with a digital because I could no longer buy film or processing.)


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## SimpleScotty (May 24, 2010)

Thanks for the replies everyone. Last time I attempted the larger DoF I had the aperature set to the little "infinit" symbol. The book I had referenced at the time said that was the way to go. I had to disagree as all the pictures I had taken had either the foreground or background out of focus. I wanted it all! Is that too much, I ask you? I don't think so.



yustr said:


> If memory serves (and at my age that's not at all a sure thing) it also involves where in the scene you set the focus point. I believe its set rather close - in the foreground. It helps if the lens is a wideangle and you get down low.


(it's been a while since I've seriously tinkered with this)wideangle is considered <55mm?



yustr said:


> (BTW: You might want to invest in a starter digital SLR. That way you can do all of the experimenting you want at no additional cost.)


I like that idea. I'll have to look into that; go online and check out Craigslist or Overstock or something. But I think I will always keep that Petri around and play with it...until film is no longer produced and venuse stop processing it. Of course by then I might just have set up my own processing (in my dreams!)

I think after reading some of the ideas here I'll just have to ditch that photography book and just go with the help here!:wave:


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## Basementgeek (Feb 7, 2005)

A 55mm lens is a standard lens.

Remember the primary subject will need to be about 10 meters away till you get into the you get into the infinit range.

What you see when you are looking into it is what you will get.

35mm film and developing will get harder to find, but it will be around for many more years. 

You don't want to process your own film unless you have pretty deep pockets. I used to but that is $$$$ 

BG


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## Done_Fishin (Oct 10, 2006)

normally there is a minimum focal length depending upon the aperture size you use

as said above the aperture size is linked to the speed that the photo is taken ....

which is also linked in to the amount of light, 

which is linked in to the "speed of the film" you are using (this is the ASA or ISO rating of the film)

A lot of older camera's used to have an aperture indicator on the lens, with a range marking that would give an indication of what would be focused when setting up the camera manually, irrespective of ambient light availability and film speed. 

That you had to work out by yourself using a lightmeter and experience.


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## DonaldG (Aug 23, 2007)

Infinity focusing aka setting the hyper-focal distance. This is a technique as explained above. It is easily set but the lens must have aperture markings each side of the focus line.


Setting the hyper-focal distance for f/8 on an old 50mm lens - See Fig 1










A = setting the aperture to f/8
B = set the infinity symbol adjacent to the '8' (f/8) you can now read off the nearest point that is in focus at C 
D = the focusing marker indicating the hyper-focal distance (10 metres)

So, at f/8 the maximum depth of field (DoF) is roughly 5 metres to infinity (just over 12 feet to infinity)

Setting the hyper-focal distance for f/16 on an old 50mm lens - See Fig 2










A = setting the aperture to f/16
B = set the infinity symbol adjacent to the '16' (f/16) you can now read off the nearest point that is in focus at C 
D = the focusing marker indicating the hyer-focal distance for f/16 (5 metres)

So, at f/16 the maximum depth of field (DoF) is roughly 2.5metres to infinity (8 feet to infinity)

The secret is to take an exposure reading, then decide on the aperture needed to give the depth of field required, then set the shutter speed commensurate with the exposure reading.

Hope that helps...:smile:


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## SimpleScotty (May 24, 2010)

DonaldG you're....amamzingray:
Thank you for taking the time (don't know how long it took you but that set up would have taken me a good chunk of time). Your figures and explanations really brought the matter into focus (sorry, couldn't resist). But seriously thank you. It makes sense now and I'm excited to dust off the ol' Petri and give the technique a whirl. 
Again, thanks Tech Support Forum troops. Very helpful! If I can pull it off I'll post! Of course....after I get the film developed.


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## DonaldG (Aug 23, 2007)

You are very welcome Scotty & welcome too TSF too. We look forward to seeing the results.

It didn't take as long as it appeared - the pictures of the lens were not taken with a camera. I used my scanner with the lid open...:wink:


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## zuluclayman (Dec 16, 2005)

Hi Donald - haven't seen much of you on here for a while - your 5D been taking up too much of your time? :grin:


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## Done_Fishin (Oct 10, 2006)

Thanks Don for putting into detail what I tried to convey in words .. it always helps to have a picture or two 

:wave:


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## DonaldG (Aug 23, 2007)

Hi both - yes, smoke comin' outa the back of the 5D2! Got a new prime lens too :grin:


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## Done_Fishin (Oct 10, 2006)

I'm getting greener with envy daily :wave: have fun .. lots of fun .. :grin:


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