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ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

A question for the Zeiss users (1 Viewer)

falconeye

New member
Hello,

yesterday I have received my Diascope 85 with the zoom ocular. Everything seem ok so far, but I have one question concerning the focus. (I could not make an test before I ordered it because they had only the fixed oculars at hand).
I read in an test about this gear, that it should be possible to focus, then zoom in and the focused object should stay sharp till 60x. With my gear this is not the case, I have to refocus again when I change the zoom. So my question for those who use the same combination. Is this normal? Do I have a defective ocular or spectiv?
For me this feature would be important, because I want to digiscope and it would be nice to focus only once and then zoom at which level you want and everything stays in focus. But perhaps this is only a dream.

Thank you in advance and greetings from Bavaria
Ralf
 
falconeye said:
Hello,

yesterday I have received my Diascope 85 with the zoom ocular. Everything seem ok so far, but I have one question concerning the focus. (I could not make an test before I ordered it because they had only the fixed oculars at hand).
I read in an test about this gear, that it should be possible to focus, then zoom in and the focused object should stay sharp till 60x. With my gear this is not the case, I have to refocus again when I change the zoom. So my question for those who use the same combination. Is this normal? Do I have a defective ocular or spectiv?
For me this feature would be important, because I want to digiscope and it would be nice to focus only once and then zoom at which level you want and everything stays in focus. But perhaps this is only a dream.

Thank you in advance and greetings from Bavaria
Ralf
No - this is not the way the Zeiss Vario zoom eyepiece works. There are different constructions of zoom eyepieces, one of which does allow for the focus to be made at low power and then held through till high power. I think the Nikon does this, but in practice some adjustment is still needed.
 
Assuming we had a technically perfect zoom eyepiece that maintained the exactly the same focus throughout its zoom range, the need to focus while changing magnification would still partly remain. This is because depth of field decreases dramatically when going from low to high magnification. So, when focusing at high magnification and zooming down the focus would remain correct, but when focusing at a low magnification, it is not that likely that you get the focus precisely in the middle of the range which is "satisfyingly sharp" to the eye. So, when zooming from low to high, you would still need to re-focus rather often, albeit not necessarily every time.

The MC II version of the Nikon Fieldscope zoom eyepiece essentially retains its focus throughout the range. I have verified this with an artificial star focused sharply, having a booster behind the eyepiece to eliminate eye accommodation from the picture, and zooming through the range. Nevertheless, in the field I pretty much re-tweak the focus every time I go from low to high. Granted, this is easier if the focus is retained, and another benefit is that since you are never that far off, you have more i.d. time which can sometimes make a real difference.

Kimmo
 
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