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Author Topic: Crosshair laser pointer as focusing aid for ground glass focusing in poor light?  (Read 2162 times)
torger
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« on: March 15, 2013, 04:05:01 AM »
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Focusing a Schneider 35mm/5.6 with center filter in weak indoor light on the ground glass can be rather challenging.

The trick I'm using today is to focus before framing: aim the camera/lens directly towards the object I want to focus at so I get to focus in the direct center of the lens => no tilting of the loupe required and there's no sideways movement from the focus breathing so it becomes considerably easier. If there's only low contrast objects where I want to focus I can put some high contrast object there as focusing target, like a small bright LED clock (bright light and sharp shapes). With this method you cannot fail even in these poor conditions Smiley.

However, it would be cool if one could instead of that LED clock as focus target use a laser pointer (so you don't need to walk into the scene), which I could mount in an arm in the cold shoe on the camera and aim at the place I want to focus at. For this to work the laser must be bright enough, and I think it should have some shape, such as a crosshair, as a point is more difficult to focus-peak than a shape. I've tried to focus on the laser point from a Leica Disto D5, and it sort of works, but the point is not too easy to peak at, a well-defined sharp shape would be better.

Has anyone tried this method and have a recommendation for laser pointer product?
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FredBGG
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« Reply #1 on: March 15, 2013, 04:47:30 AM »
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There are some pet lasers that project little outline images.
I had one that projects a mouse, a target and a ring as well as a simple dot.

However if you are looking for something stronger you want this:
http://www.wickedlasers.com.hk/krypton

and the expanded lens kit for the krypton. It has a galaxy and cross that would work for you.

However you should avoid focusing before framing. Focus plane moves when you recompose.
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torger
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« Reply #2 on: March 15, 2013, 06:49:25 AM »
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Thanks for the tips! (The focus shift after recomposing is not really a problem in this case, as large depth of field is used which masks the error).
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kikashi
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« Reply #3 on: March 15, 2013, 02:57:52 PM »
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Thanks for the tips! (The focus shift after recomposing is not really a problem in this case, as large depth of field is used which masks the error).

If you have that much depth of field, and are prepared to spoil the focus by recomposing, why go to so much effort to focus accurately in the first place?

I'm not being snide: I just don't understand the reasoning behind your method.

Jeremy
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FredBGG
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« Reply #4 on: March 15, 2013, 03:19:44 PM »
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If you have that much depth of field, and are prepared to spoil the focus by recomposing, why go to so much effort to focus accurately in the first place?

I'm not being snide: I just don't understand the reasoning behind your method.

Jeremy

I agree. While depth of field helps, you will still get the best results without recomposing. Maybe the laser will help enough to avoid recomposition.
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torger
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« Reply #5 on: March 15, 2013, 04:53:00 PM »
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If you have that much depth of field, and are prepared to spoil the focus by recomposing, why go to so much effort to focus accurately in the first place?

I'm not being snide: I just don't understand the reasoning behind your method.

The problem is that if you don't see too well which can be the case with weak indoor lighting, low contrast target and Schneider 35/5.6 with center filter there is a risk for a very large focusing error. The same problem can occur in low light photography outdoors, long exposure post sunset etc. The recomposing shift is very small in relation to the focusing error you risk to do due to poor vision (you could miss the whole room!). Of course you could come up with an example with extreme recomposing that cause a significant focus shift, but generally you don't need to redirect that much, and generally you just search for an "anchor" for the DoF, there's no real need to have the focus exactly on the object.
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Slobodan Blagojevic
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« Reply #6 on: March 15, 2013, 05:01:22 PM »
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Just make sure you are not using an infra-red cross hair during a VIP portrait session... his bodyguards might misinterpret it Grin


P.S. Actually, just last night I saw a Danish TV series, The Protectors, on Netflix, about their Secret Service guys, with exactly such a scenario.
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Slobodan

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ErikKaffehr
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« Reply #7 on: March 16, 2013, 01:09:51 AM »
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Hi,

I think it is a bright idea, it can be very helpful to assist focusing under dim conditions.

Best regards
Erik

If you have that much depth of field, and are prepared to spoil the focus by recomposing, why go to so much effort to focus accurately in the first place?

I'm not being snide: I just don't understand the reasoning behind your method.

Jeremy
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Frederic_H
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« Reply #8 on: March 18, 2013, 05:15:25 PM »
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Focusing with live view on my D800 was ok up to a certain point, but not in really dim interiors (churches, monuments). That's how I ended up using the Disto as a focus assist light which helped considerably, though a non-dot pointer would have been even better indeed.
Now on the tech cam the helical is precise enough I don't need to focus on the ground glass, am only measuring with the D5.
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Vladimirovich
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« Reply #9 on: March 18, 2013, 09:26:05 PM »
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his
male chauvinist  Cheesy
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Slobodan Blagojevic
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« Reply #10 on: March 18, 2013, 09:44:17 PM »
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male chauvinist  Cheesy

Yep... actually, in that Danish TV episode, it was indeed "her," a nun.
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Slobodan

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Petrus
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« Reply #11 on: March 21, 2013, 12:46:10 AM »
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Laser levelers for carpenters? They can project a crosshair image. Cost less than $100. You also get absolute horizontal and vertical reference lines.

I have used them to find the front nodal points for lens/camera/panorama head systems.
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torger
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« Reply #12 on: March 21, 2013, 07:03:05 AM »
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Laser levelers for carpenters? They can project a crosshair image. Cost less than $100. You also get absolute horizontal and vertical reference lines.

I have used them to find the front nodal points for lens/camera/panorama head systems.

I've thought about that, I shall probably borrow one and try it out. However Ideally I'd like something smaller to carry and smaller brighter cross. The levelers I've seen have some sweeping glimmering in the light rather than something real sharp and steady and I suspect that can be a problem when using it as a focusing aid.
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Stefan.Steib
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« Reply #13 on: March 22, 2013, 04:53:28 PM »
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I have and use one chinese Laser pointer where you can change the output from points to a grid to  several more patterns.
They can be had in several colors and are really cheap. The effect is astounding and really helpful for focusing.

http://www.ebay.com/itm/Laserpointer-Flashlight-Beam-Pen-Katzenspielzeug-Laser-Pointer-Grun-Prasentation-/160990056474?_trksid=p2045573.m2042&_trkparms=aid%3D111000%26algo%3DREC.CURRENT%26ao%3D1%26asc%3D27%26meid%3D6431538153526391477%26pid%3D100033%26prg%3D1011%26rk%3D1%26sd%3D160990056474%26

greetings from Germany
Stefan
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torger
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« Reply #14 on: March 24, 2013, 01:33:38 PM »
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Thanks for the tip!

I just purchased a very cheap keyring laser pointer (i e just a dot) and tested some more. These glimmer and spread, not particularly well-defined point. However, the problem I had with this type of point last time I tested was shown to be a bit less-than-perfect focus of the loupe, i e not perfect focus on the grain, which made the point even blurrier. After fine-tuning my 20x loupe focus point I can say that a simple dot laser pointer is "good enough", i e I feel I can achieve enough reliability with this. I tried and it's possible to focus in total darkness with it (framing is then a problem though :-) ).

Lesson learned: it's of key importance that the loupe focus is *perfect* so the not-so-sharp glimmering laser point is not worsened, loupe focus seems more important for this than when focusing on normal objects.
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ben730
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« Reply #15 on: March 28, 2013, 09:22:40 PM »
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Not the cheapest version but a very fast and mobile method:
I have very good experience with the Alpa HPF-Ring on my Cambo WRS + SK 35 and a Bosch DLE 40 Lasermeter. If you mount the ring perfect to infinity, you get very precise results.........
« Last Edit: March 29, 2013, 07:22:32 AM by ben730 » Logged
theguywitha645d
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« Reply #16 on: March 28, 2013, 09:42:36 PM »
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I tried a laser pointer for nighttime shots. The best was a single beam rather than using a beam splitter to project a pattern. But neither was great. What I found worked the best was a simple LED Mag light and simply illuminate the areas of the scene you want to photograph.
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