Focusing Methods

[gcbryan]

Is it safe to say that there are basically 3 ways to construct a variable focus light?

1) Fixed emitter in the body and the head with fixed lens moves.

2) Head with fixed lens doesn't move but the emitter moves in and out within the body resulting in no change in the overall length of the body.

3) Lens is movable rather than fixed and is transported via a screw within the dive light resulting in no change in the over all length and therefore internal volume of the dive light.

Packhorse you were addressing some of these things. I've thought about the various possibilities more and therefore this thread arises.

As to whether the volume changes matter in the case of 1) (and it probably does matter) some questions come to mind.

With a standard photographic lens either a longer focus or zoom lens where you have the greatest movement or change in overall length and therefore volume...how is that accomplished?

I've always assumed that photographic lens were sealed (not for water but at least for dust). I suppose air could be venting out. If it is sealed the only other explanation would be that the increased pressure due to changing volume is not enough to overcome the strength of the screwing mechanism. Otherwise changes would result in either pressure or vacuum tending to oppose the focusing direction.

Perhaps this is the case with underwater applications as well when a screwing approach is used or perhaps the greater external pressures underwater make this not a valid comparison?

Any thoughts and have I at least covered the 3 methods of possibly achieving a variable focus light? Along with only two methods of actual movement that I can think of...either a screw or a push/pull sliding motion. Changing volume and pressure would tend to affect the latter more I would think.

 

[znomit]

4) One wide and one narrow light and a balance control between.

 

[Codiak]

I've always assumed that photographic lens were sealed (not for water but at least for dust). I suppose air could be venting out. If it is sealed the only other explanation would be that the increased pressure due to changing volume is not enough to overcome the strength of the screwing mechanism. Otherwise changes would result in either pressure or vacuum tending to oppose the focusing direction.

Perhaps this is the case with underwater applications as well when a screwing approach is used or perhaps the greater external pressures underwater make this not a valid comparison?

Any thoughts and have I at least covered the 3 methods of possibly achieving a variable focus light? Along with only two methods of actual movement that I can think of...either a screw or a push/pull sliding motion. Changing volume and pressure would tend to affect the latter more I would think.

Seal against dust is much different than sealed against water underpressure to get some perspective look at the IP ratings, then look for simple items like cable glands or switchs rated for water under pressure. Sheezzzzzzz

As for changes of internal pressure effecting the function I'm not sure how much it really does, after all we dive with cameras all the time and there are some great shots both with fixed and variable focus.

The basic mechanics are the same: fixed, push/pull, threaded.

However, where flashlights are concerned we have some ways to simplify the designs:
1: we don't really need sub millimeter focus...
2: we don't have to prevent water entering tube between the lightsource and aspheric, just the aspheric and window

it's perfectly possible to adapt an SLR focusable lens to a dive light... though you will have to swap some glass.

 

[gcbryan]

Seal against dust is much different than sealed against water underpressure to get some perspective look at the IP ratings, then look for simple items like cable glands or switchs rated for water under pressure. Sheezzzzzzz

Yeah, I understand that sealing against dust is not the same as sealing against water. That's why I stated that.

The question being pondered was whether it was sealed or not sealed. If not sealed air could get out. I figured that it was sealed (but not against water( and therefore air wouldn't be able to get out.

As for changes of internal pressure effecting the function I'm not sure how much it really does, after all we dive with cameras all the time and there are some great shots both with fixed and variable focus.

The basic mechanics are the same: fixed, push/pull, threaded.

I took that into account as well. Since camera's are more expensive and are more complicated I 'pondered" as to whether the difference might be that there was just more mechanical friction and therefore changing pressure might be overcome by this mechanical friction whereas in a simple dive light this mechanical friction might not be present...particularly in a push/pull sliding arrangement.

However, where flashlights are concerned we have some ways to simplify the designs:
1: we don't really need sub millimeter focus...
2: we don't have to prevent water entering tube between the lightsource and aspheric, just the aspheric and window

it's perfectly possible to adapt an SLR focusable lens to a dive light... though you will have to swap some glass.

We know it can be done since it is being done but I was just trying to get a handle on what forces are at play.

 

[Codiak]

We know it can be done since it is being done but I was just trying to get a handle on what forces are at play.

In that case, SLR lenses are not sealed. I base this on mold inside the lense is a common destructive force. How they are kept so dust free I can't answer... I'll ask at my local canon rep and see if I can get a straight answer... spent enough with them I should

 

[gcbryan]

In that case, SLR lenses are not sealed. I base this on mold inside the lense is a common destructive force. How they are kept so dust free I can't answer... I'll ask at my local canon rep and see if I can get a straight answer... spent enough with them I should

Good to know. Thanks.

So camera lens can just vent any pressure that would build up.

It may be that it's just a matter of degree. Lens with the most movement (telephoto) aren't generally used underwater. The lens that are used may just not move enough to present a problem.

Perhaps the key is just using the right focal length and keeping movement to a minimum.

I've been reading the posts on diffusion filters as well. Most posters are trying to get a floody beam. I'd like to find some diffusion material with the least diffusion going on.

It would be nice to use just enough to diffuse the hard outer edge of the spill as that the most noticeable part when you are moving the light around.

I tried Glad Press and Seal as suggested in one post. It does leave some center spot but I'd like to leave a lot more. If anyone finds something with about half of the diffusion ability of Press and Seal I'd like to hear of it.

 

[AnAppleSnail]

Run your lens set back and forth inside a tube with as clear a glass on the end as you can.

 

[gcbryan]

A received a focusable flashlight in the mail today from DX.

http://www.dealextreme.com/details.dx/sku.18697

I got this to experiment with and just to see what an aspheric was like as well as the focusing aspect.

It's a fun light to play with! The beam isn't pretty at the outer edges but it does throw. I thought the W200 was a pretty good thrower but this puts a lot more light on the spot at a distance.

The flood lights up my whole backyard. This is just a P4 using 3 AAA's. It says that the total current output is 700mA but then it says it's not regulated so who knows. It says it outputs 100 lumen. This seemed about right until I tried it outside (at night) and then was much more impressive than it had appeared in the house.

It has an outer ring of light that is separated from the spot so this is just due to the cheap plastic optic I suppose. It really is an ugly looking beam at any setting other than spot and when used for throw.

I also tried putting some Glad "Press and Seal" over the lens as a diffuser and this took care of the ring of light. It still retains the ability to go from spot to flood but it's not as defined of course. This would be a good change to make just to use this as a walking the dog kind of flashlight.

To experiment with the focusable lens aspect you don't want this of course.

Although not mentioned on DX I notice that it was two power settings (high and low) switched by half a press of the clicky and a third mode...strobe. Why strobe I don't know but it's there.

It's an interesting light to play with at only $9.90 shipped.

Buy it to play with the focusing features and when you're done with that it makes a nice general flashlight to have around with the diffuser mod. It's small at around 4" long and 1" diameter.