Troubles with Nikon D70s SLR

[Gooly001]

Originally Posted by Jason McK

I 100% agree. During my career I have had 100s of people ask me how to become a pro photographer. I always say go to business school and shoot every day.

Half way through this thread I realized that what I'm talking about only relates to Marco photography where the subject is being exposed at a ratio of 2:1 or greater. Meaning the exposed image is 1/2 the size of the original or larger (the Image is actually larger than the original subject). For example if you where to take a picture of 1 polyp of an SPS or LPS and fill the frame with that polyp the actual image would be larger than the subject. The closer you get to a 1:1 ratio the less F-stop effects DoF. So in reality with the tank glass and the distance from the class to the subject it would be very uncommon to get such an instance where this would play a significant role.
But having said that. A true macro lens does not react the same way your standard 50mm or what ever does in terms of DoF. the Classic DoF experiment would be to take a standard lens and stand at a picket fence. focus part way down the fence and then take exposures adjusting the aperture between each frame. This shows the effect of DoF. Now if we were to shrink this test and say set up dominos on the floor and perform the same experiment with a Marco lens you would never achieve the same degree of DoF regardless of f-stop.
Just for some background I too took photographic sciences in school. But instead of taking pictures we built emulsions on glass plate, Built lenses and shutters. then created images from what we constructed.
I still work in the industry but gave up on shooting years ago.

J

From my understanding of what you have posted before regarding traditional lenses and macro lenses that DOF does not affect the lens that same, I disagree. Using your picket fence example, if I mounted a 50mm non-macro and did the DOF test and then mounted a 50mm macro lens using the same aperature and subject focus distance, I can create an exact carbon copy of what the non-macro lens did. My argument is that a macro lens differs from a traditional lens in that it can focus down to an object closer then a traditional lens can.

Regarding the limited DOF when you are shooting at 1:1 ratio. You are right in saying that f-stop does not affect the DOF because there is no longer a DOF. Because the object is taking up so much of the frame there is nothing else in the frame that would give you the ability to see the difference it makes in DOF. You are simply so close that only the closest object is in focus filling up the entire frame. You only can see the DOF difference if there is something else that is in the frame that is further of closer then the object that you are photographing. So your example of filling up the frame with only one polyp and having no DOF is correct because only that one polyp will show up as being focused, there is nothing else in the photo.

All that I am trying to communicate is that a 50mm non macro and a 50mm macro both shot using your picket fence example will produce the same result if all the variables are considered the same. ie subject distance and point of focus and aperature/shutter value.
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Suzuki GS500E

[skylord]

But what are the results using his domino example? It seems to me you two are on different pages and almost talking about different things.

If you have a magnifing glass and put your hand at a right angle to it and focus on the first finger....is the fourth finger out of focus or is it DOF?

Scott

[Jason McK]

Originally Posted by R.A.D.

All that I am trying to communicate is that a 50mm non macro and a 50mm macro both shot using your picket fence example will produce the same result if all the variables are considered the same. ie subject distance and point of focus and aperature/shutter value.

Having shot 1000s of Marco photo's with everything from 8X10 field cameras, 4X5 rail cameras and 35mm I will agree to disagree.
Since this was not the main focus of this thread. Maybe we could focus again on Kyle's original concern

J

[calkrog]

Originally Posted by Jason McK

Since this was not the main focus of this thread. Maybe we could focus again on Kyle's original concern

J

nope. keep up the discussion. i think this is a good overall thread about tank photography, and it will do more than one person some good if you keep it up. I myself have been struggling with nice tank shots using my Minolta Maxxum 5D using a variety of lenses, but my shots are getting better thanks to the pointers being given in this thread.

[Jason McK]

I spent most of last night going through text books and old photo logs, to come up with examples of Magnification being the main control of DoF. I have 20 or so actual examples, But all were 4X5 sheet film images where the subject was smaller than the image captured. Things like a needle (stylus) from a turntable. A dimond ring, and a industrial gear box.
The information I have supplied above with the equations and formulas still do apply to all macro photography, but become more evident when image size is greater than subject size.

To redirect the thread this is a list of what I feel are the most important things to check when shooting you tank
1) turn off actinics to allow your camera to white balance on 1 colour temp
2) test white balance to find the best area. Or use white card to get correct white balance
3) use spot metering and meter on your subject
4) clean your glass (no one wants to see algae or coraline )
5) if you can not get an exposure over 1/125 use a tripod
6) use a light box if you have access to one
7) do not use flash

Jason