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Defocusing to get better focus (1 Viewer)

Has anyone ever tried this? I purposely defocused the scope so that the in- focus point was in front of the target (a resolution chart). I took pictures in focus mode Infinity, Macro, and Auto Focus. All images were equally fuzzy. I repeated the test defocusing the scope so that the in-focus point would be beyond the target (very fuzzy to the eye). I took the same sequence of pictures. At Infinity setting, the image was fuzzy. At Macro and Auto Focus settings, the image was completely sharp.

I am guessing that the camera can only adjust focus one way; the other way the lens is already racked out to the infinity position and no more correction is available. I am now trying to see if this is a viable way to guarantee in-focus pictures all the time. Is it possible that those of us who have trouble getting in-focus pictures are really adjusting the scope in a way that the camera cannot compensate (maybe due to the nature of our eyes)?

I am using a Nikon P5100 and a Swarovski 65 HD.

Bill

Have you observed at which distance the camera think it is?
Does the camera think the object is very close or that the object is located close to infinity?
 
Well, I was hoping that someone who understands optic better than I do would answer the question. Originally, I took an older film type SLR camera and focused on the scope after focusing the scope by eye. The lens of the old camera had to be set to around 15 meters to bring the image in the viewfinder into focus (not infinity). So for me, I believe the image at the eyepiece appears closer than infinity. I think that as you focus beyond the desired target, the image to the camera would appear to move closer. As you focus short of the target, I believe the target image will move toward infinity (and beyond?). I certainly would welcome anyone to correct me on this.

Bill
 
I wear bi-focals so have always had problems focusing manually, in fact I can't do it and be accurate. So when I focus the scope so that the image looks sharp to me I nudge the focus just a little passed the subject before I put the camera on (P5100,8400,A640). Using macro mode this seems to give me the best results. I very rarely use the camera zoom passed half zoom though as I find the results more unreliable. If I need more magnification I use a different eyepiece. A zoom at 60x will be more than enough usually except for stints out on the mudflats.
Thanks to Jerry for his detailed testing too.
Neil.
 
Neil: I too wear bifocals and have exactly the same problem with focus, and I use the same approach. I am very interested in your use of other eyepieces for greater magnification. If I zoom in with my Swarovski 20X - 60X zoom eyepiece, I get severe vignetting, basically making it necessary to zoom in the camera. Are you mounting a more powerful fixed eyepiece?

Bill
 
Neil: I too wear bifocals and have exactly the same problem with focus, and I use the same approach. I am very interested in your use of other eyepieces for greater magnification. If I zoom in with my Swarovski 20X - 60X zoom eyepiece, I get severe vignetting, basically making it necessary to zoom in the camera. Are you mounting a more powerful fixed eyepiece?

Bill

Bill,
I mostly use the Swarovski 45x which has 18 mm of Eye Relief and allows me to use the P5100 lens in the Green Macro zone with no vignetting. I would be better off with a special adapter for it though as I need to back of the camera a bit with the DCA and it can show shadowing if you are not careful.
With the zoom go straight to 60x and you will be able to get reasonable results if the light is good. For reliable AF when the light is dull use Manual Focus (INFINITY). I zoom into the Digital Zoom range on the camera for focus and then back the zoom out again. You will need to use the Self-timer here.
I also have the Swarovski 77x telescope eyepiece but the ER is small and it's difficult ( but not impossible ) to digiscope with. Neil.
 
Thank you very much, Neil. This gives me a whole new set of approaches to try out. It never occurred to me to try focusing with the digital zoom.

Bill
 
MXP asked the great question: "Have you observed at which distance the camera think it is? Does the camera think the object is very close or that the object is located close to infinity?" I now want to improve my earlier answer to this. I set the scope 10 meters from a transparent light bulb and focused on the filament (need a lot of light to see well in the camera viewfinder). The eyepiece was set at 20X. I then focused an old SLR with a zoom lens set at 105 mm (equiv. to 22.6 mm on the P 5100). The camera lens read a tiny amount short of infinity (if the scope were focused by someone with perfect eyesight, I have no doubt the image would appear at infinity). I then focused beyond the filament ("back focused") with 4 deg. rotation of Swarovski focus wheel. When refocused, the camera lens now saw the image as 1.25 m distance from the camera . I repeated the test with the zoom at 35 mm (same as P 5100 zoomed out). The image appeared to be at 4 m from the camera.

4 deg. rotation of the scope focus wheel is the width of one rib on the focus grip; truly a tiny amount of change. The remarkable thing is that such a small change results in the image appearing to be move so close to the camera, even at 1X zoom.

Bill
 
Bill,
I mostly use the Swarovski 45x which has 18 mm of Eye Relief and allows me to use the P5100 lens in the Green Macro zone with no vignetting. I would be better off with a special adapter for it though as I need to back of the camera a bit with the DCA and it can show shadowing if you are not careful.
With the zoom go straight to 60x and you will be able to get reasonable results if the light is good. For reliable AF when the light is dull use Manual Focus (INFINITY). I zoom into the Digital Zoom range on the camera for focus and then back the zoom out again. You will need to use the Self-timer here.
I also have the Swarovski 77x telescope eyepiece but the ER is small and it's difficult ( but not impossible ) to digiscope with. Neil.

Neil, I tried your method of focus using the digital zoom with very good results. In fact, I cannot really see any difference in results than when using Macro focus mode and back focusing (in good light). Digital zoom certainly makes focusing easier. This technique will be very useful for the times when light is poor, or some objects in the frame are distracting the AF. Of course, this method requires seeing the screen (I may yet have to get a sunshade). Yes, zooming in fully (optically) with the eyepiece at 60X does eliminate vignetting.

Bill
 
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