Aperture setting and calculation for reverse mount

[paul_ong1]

<p>Hi,<br>

I have been experimenting with high-magnification macro (1:1 and higher), and I have been fairly happy with reverse mounting of my Nikon lenses. (I have also tried straight mounting on bellows and extension tubes, stacked lenses, enlarger lenses -- all have their pluses and minuses.) I have also developed a customized focusing rail/positioning system based on people's suggestions, which you can see below.</p>

<p>My challenge at this time is the aperture when I reverse mount for high magnification. I understand that I recalculate the f-stop value by 1+M (M=magnification) factor. Do I use this as a way to determine when diffraction set in? (E.g., when the recalculated f-stop value is f/11 and larger?)</p>

<p>The other challenge I have is closing down the aperture. Right now, I just manually move it with my finger after focusing before taking the shot. However, at high magnification, this is not ideal because it can introduce slight changes in camera position and focus, which is a problem given the narrow DOF. Any suggestions on how to more efficiently close down the aperture?</p>

<p>Thanks.</p>

<p>You can get the background information on the evolution of the project and preliminary test photos at:<br>

http://www.flickr.com/photos/9476880@N02/sets/72157624320417168/</p>

<p> </p><div></div>

[conrad_hoffman]

<p>Wow, very clever! I remember seeing some device that used a cable release and lens mount to close down the aperture on reverse mounted lenses. No idea if it was Nikon or aftermarket. Probably rare. Not sure about the aperture calculation but I think you're on the right track. I find diffraction to be such a serious issue that I often take a series of shots and compare them. There's a definite point where the image loses its snap and it sometimes surprises me how soon it sets in. Because of the lack of DOF I sometimes resort to CombineZM and do image stacking.</p>

<p>Best,<br>

Conrad</p>

[CvhKaar]

<p>Did you already have a look at a BR-6 adapter from Nikon ?</p>

[sebastianmoran]

<blockquote>

<p>Do I use this as a way to determine when diffraction set in?</p>

 

</blockquote>

<p>Yes. Diffraction is determined by the effective f-stop, and you have the correct idea for the effective f-stop. I understand the diffraction limited resolution at extinction in lp/mm is 1600 divided by the effective f stop. From this, limiting your effective f-stop to f/11 is probably conservative; f/16 would give you 100 lp/mm. This would be nominal f/8 at 1:1 or nominal f/4 at 3:1.</p>

<p>Nice use of the microscope parts.</p>

[paul_ong1]

<p>Conrad, yes, agree with you about using stacked focusing. That is the reason I made the above rig, to make a more precise series of photos. Right now, I am using CS4 to "auto-blend" my photos. OK, but sometime I have to go in and manually correct some things. Downloaded CombineZM and will give it a try in the coming weeks. Below is an example from CS4 with 8 photos. Looks nice in larger version at<br>

<p>C.P.M., thanks for identifying the adapter. I will start an ebay search over the next couple of weeks.</p>

<p>Richard, thanks for the suggestion on f-stops at different magnification and the formula. Both are very helpful. The problem is finding good fast lenses at high magnification.</p><div></div>