D70: Trap Focus Trick

Until today, I thought this was only possible w/ the 1Ds. It's called "Trap Focus" and means that you can prefocus on an set distance, then set a focus point with the focus selector pad. When something in that bracket comes into sharp focus, the camera will take a photo.

From Thom Hogan's e-book for the D70:

4. Likewise, AF-ON can be useful to create a “trap focus” function:

a. Set Custom Setting #15 to AF-ON.

 

b. Set the Autofocus Mode to Single Servo (Custom Setting #2).

 

c. Set the Autofocus Area mode to Single Area (not Dynamic) (Custom Setting #3)

 

d. If the lens has a focus switch on it, set it to A (Autofocus; on some lenses this is labeled M/A).

 

e. Pre-focus the lens to a particular distance. The camera shoots when the selected focus bracket is in focus.

Now I want to see if this is possible w/ the D100. It probably is.

So this may be AWESOME for shooting manual focus with super-macro.

Cheers

James

I've been trying this out topside.....it works great.....just hope I can remember all the settings while underwater

BTW, I've been taking topside pics with my whole UW setup for practice and I've discovered that I can get strobe sync well beyond 1/500....I've only tried as high as 1/2000, but I get 100% results everytime :!:

Karl

Hello James and Karl -

I recently read your post regarding AF-s and AF-c..helped me make a decision..finally, regarding these two autofocus settings.. Moving on to the other focus modes Nikon offers (dynamic or single)...which one are you guys using? Would the setting very depening on subject?

Thanks!

Michael

BTW, I've been taking topside pics with my whole UW setup for practice and I've discovered that I can get strobe sync well beyond 1/500....I've only tried as high as 1/2000, but I get 100% results everytime

Hey Karl, great to hear that you have your rig up and running. How do you like the setup? The D70 will trip the shutter and fire the strobe at 1/8000 with the Ikelite housing since not all of the hotshoe pins are connected. How do you know it is synching though? I mean how do you know you are getting all of the strobe dump while the shutter is open? I imagine this is dependant on the power setting on the strobe. I can't find it right now but someone on this forum suggested that the DS125 won't reach full power at even 1/500 sec. It would be great to find out that you can sync this fast

As my strobes were set to -2, I realize that I wasn't getting the full dump, maybe that contributes to this working like it does in this case.

I tested this by setting up a colorful object in the foreground and the backyard beyond with lots of outdoor ambient light....I metered on the ambient light, set my shutter to 1/60 as a starting place and the appropriate f-stop to properly expose the background....I adjusted my strobes (in this case to -2 on the manual controllers) to get the foreground object illuminated....classic balanced lighting that we do underwater all the time

Without changing anything else, I started changing the shutter speed....as the shutter speed increased, the background got darker and darker as you would expect....at 1/500 the background still wasn't completely black, so I tried 1/800 and was surprised that the background got even darker and the complete image was not cut off because of non-sync like I've seen posted before....I continued uping the shutter speed to 1/2000 and always got a nice image with a completely black background

I expected that I'd get partially lit images beyond 1/500, but that never happened....I've done this twice with the same results

I'll try this underwater this weekend

Karl

Great. Thanks for doing this kind of testing Karl. I'd like to know the answer to this question.

Would you say that the foreground exposure was the same in all photos? As I understand it, the way DS125s control intensity is temporally--that is to say that the intensity of the ligt is always the same but the duration is varied for different settings. So the danger is that with high shutter speeds you can close the shutter while the strobe is still on. So you can still get strobe in the shot but not the amount of light you would expect from that strobe setting. As I understand it for proper syncing you need to get the whole flash. Now this point might be totally moot for the trial and error meathodology we use in manual digital flash photography. If the shutter is capturing all of the flash, the exposure in the foreground should not vary because nearly all of the light comes from the flash and very very little in comparison is contributed by natural light. ( I know you understand all of this but I'm saying it to convince myself that I'm on firm ground)

Perhaps a better test would be more like the one in the article I saw comparing all the strobes on the market (I can't find it right now). It had a series of photos taken against a semi reflective background at different shutter speeds at full dump. You could clearly see light falloff at high shutter speeds due to the fact that the flash hadn't finished when the shutter cut off. They were still lit, just not as bright as before. Add to that different manual settings and we could develop a table that shows the maximum sync speed with the D70 and DS125 for different levels. This would be useful information.

Thanks

It doesn't matter if the flash "does it's whole thing" or not. Just that the flash tube is discharging at full steam while the electro-mechanical shutter on the D70 is capturing light.

It is.

The D70 uses a combo of mechanical (curtain) and electronic shutter (ala the 5050). So you won't see the shutter curtain in fast sync situations, because it isn't there. It's pretty sweet.

I have seen D70/SB800 shots of water droplets at up ungodly shutterspeeds of like 1/8000th

Cheers

James

Ok, thanks for the reply James.

If you only capture part of the strobe then can that be considered syncing ?

I've seen the same photos with the sb800 on dpreview and this is what got me thinking. I then did some tests with my D70 housing and it worked well up to 1/8000 underwater.

But then I questioned weather this was truly syncing when I found out that the strobe duration on the DS125 was longer than (I think even 1/500).

So is this really syncing or does it even matter? Perhaps in the digital non-iTTL realm it doesn't even matter that its not fully syncing.

I imagine with iTTL this could be a problem because the camera thinks its going to get so much light based on preflash and then it doesn't--which is why it prevents you from using these high shutter speeds.

If all you are doing is judging exposure based on review it shouldn't matter. But you will get a complicated synergistic effect as you reduce shutter speed to darken the background and also get darkening of the subject as well. You increase strobe power to compensate but see no effect. At more normal shutter speeds you can just use strobe intensity alone to control exposure in macro subjects. At high shutter speeds you can't do this. Maybe this is something a beginner like me should be aware of.

If the strobe duration is longer I don't think the camera really cares. After the shot is recorded, the strobe can fire as long as it wants...;-)

The question is does enough strobe light get poured into the shot and the answer is yes.

And what does this have to do w/ Trap Focus anyhow?????

Cheers

James

Speaking of Trap Focus.

When I got home from work today I went outside and tried it with my new Diopters that just came in today!

Was pretty cool. It's really hard to hand focus with all the +7 worth of diopters on the lens, but by using the trap focus technique, you can get some pretty sharp captures!!!

Sounds like this would be very useful indeed for macro shots!

Hi Jim,

Tell us more about how you did it. Did you push the shutter first, then move in? Or did you start in really close, push the shutter, then pull back?

Cheers

James

I started very close, held down the shutter and the AE/AF Lock button and slowly pulled back until it snapped a picture.

I didn't try from far away and moving in... That may be more useful....

Here are my 100% crops from the diopter/trap focus test.

All were taken in Apeture Priority mode F9 and roughly 1/320 with the 18-70mm kit lens at 70mm.

Straight from the camera with no color correction or after the shot sharpening.

Diopter +1

Diopter +2

Diopter +3

Diopter +4

Diopter +5

Diopter +6

Diopter +7

Hmm...not sure that is Trap Focus Jim.

When you do Trap Focus, you are in Manual focus mode on the camera and Manual focus mode on the lens.

Were you in M on both? Or M on the camera and A/M on the lens (if it's an AFS lens).

Cheers

James

It doesn't work in Manual mode. When you have the camera and or lens in Manual, the camera does not require focus to fire.

However, if you put the lens and camera in AF mode, you do not have the press the AE/AF lock button. You can manually set the focus. Hold down the shutter, then move in towards the object, and the picture will take as soon as it is in focus.

Hope that clears things up.

I just tested again to make sure this was true...

Darn, that will only work with an AFS lens - not with a Nikon 105mm or 60mm, or 70-180mm.

I'm talking about a rig that is set up for ONLY shooting manual focus, not using AF at all. Supposedly, some cameras can do it. I want to see if I can get a D100 or D70 with the 70-180 or a 105mm with a 1.4x or 2x teleconverter.

Cheers

James

Just tried it with the Nikon 105mm , 60mm and 70-180mm and it seemed to work perfectly.

It also works with the 70-180mm with 6t diopter.

Maybe I'm not understanding what you'r saying.

Cant get it to work with Sigma 50mm.

I tried this at home this AM, and had a problem that I am hoping can be explained. The instructions say :

4. Likewise, AF-ON can be useful to create a “trap focus” function:

a. Set Custom Setting #15 to AF-ON.

 

b. Set the Autofocus Mode to Single Servo (Custom Setting #2).

 

c. Set the Autofocus Area mode to Single Area (not Dynamic) (Custom Setting #3)

 

d. If the lens has a focus switch on it, set it to A (Autofocus; on some lenses this is labeled M/A).

 

e. Pre-focus the lens to a particular distance. The camera shoots when the selected focus bracket is in focus.

I do fine up to item 'd', but I can't figure out how to pre-focus the lens. I can trap the photo where the lens happens to be focused before I started any of the changes, but since it is on Auto focus, manipulationg the focus ring on the lens has no effect. What (obvious) thing am I missing?

What lens are you using?

Cheers

James

I was using the 18 - 70 mm lens (That can be part of the package)

I also have the 105mm which I can shift from auto to manual in the housing, but I have not tried that one yet.