DIY adaptation for stopping down G lenses?

[bob_mcbob]

<p>I do a lot of work with high speed video cameras that use a Nikon F mount. Basically, a little box with a sensor at the front, and a screw-on Nikon mount exending out to the proper flange distance. The camera does not control the lens in any way. It's essentially as basic as you can get and still attach a lens. Because of this, it's not possible to control the aperture of G mount lenses.</p>

<p><img src="http://sig.fortepianos.com/fmount.png" alt="" /></p>

<p>Unfortunately, I've discovered that the Sigma 150/2.8 macro is by far the most useful lens for much of my work. The shorter (~100mm) macro lenses don't have enough working distance at high magnification. Also, none of them allow a tripod collar, which is quite a pain, since the cameras are almost always used in the vertical orientation. I've had to resort to using a Manfrotto 340 elbow bracket, which is a pretty lousy product for anything but the lightest lenses. I've also tried longer (~200mm) macro lenses, but the difference in lens speed is too great.</p>

<p>Since the G lenses default to the smallest aperture setting, I've been using the Sigma with a piece of plastic cut to shape and inserted behind the aperture lever to hold it at the maximum. This is fine, since the vast majority of what I use it for requires the maximum setting anyway. I'm planning to order another one of these lenses this weekend, and I was hoping to make some sort of modification to the camera mount that would allow me a bit of control over the aperture.</p>

<p>Looking around, there are lots of Panasonic G1 owners using the Nikon F to C mount adapter, which includes a cable release plunger to control the aperture. I could actually swap the mount on the cameras for a C mount and use this, but I also use other F mount lenses, and I don't think the C mount is robust enough for daily use like this anyway.</p>

<p>Because the mount on the camera has an adjustable flange distance, it is actually possible to use use an extra item in the optical path up to about 8.5mm thick without even modifying anything. I've seen various macro attachments that allow you to stop down the lens. Some of the extension rings, the BR- series, etc. Many of these items are not appropriate for my use because they are either meant for reversing lenses or are simply too thick. I found it very difficult to interpret what some of these accessories actually do, since primary sources often don't describe them in enough detail. In particular, mir.com.my seems to indicate that the BR-4 and BR-6 are both straight F-to-F adapters, while most forum posts show them as being F-to-52mm for reverse mounting. Very confusing!</p>

<p>The other option is simply drilling a hole in the camera's lens mount to insert a plunger aperture control, or something fancier with an actual ring. Obviously I would like to avoid making major modifications, but I would be prepared to do this.</p>

<p>I'm wondering a) if there are any aperture control accessories I should consider, and b) if I make modifications, if there is a source for the other half of the cable release plunger assembly. Obviously a is the most relevant part in this forum.</p>

[richard_driscoll]

<p>Hi Chris,<br /> I suspect that a BR-4 might do the job. I have Nikon close-up equipment catalogue that shows it. The text says it is used in combination with PB-4 or PB-5 bellows to retain auto diaphragm operation and is used with a double cable release. From the picture it looks as if it has a bayonet mount on each side so it would fit between the bellows and a non-reversed lens.<br /> Of course the aperture control will be uncalibrated but OK for full aperture. Looks as if it is around your 8.5 mm thickness. Maybe more, maybe less.<br /> I can post a picture from the catalogue if you need one.<br>

Some more info. in this thread:<br>

http://www.photo.net/nature-photography-forum/00A1AG<br>

It looks as if there is a possibility that the ring might interfere with AF contacts.</p>

 

[bob_mcbob]

<p>That's the sort of thing I'm looking for (aperture control, F-to-F). Any information you have on similar items would be much appreciated. I can machine down the mount if there's any issue of compatibility. I have a page from an old Nikon publication where they show the BR-4 being used behind a macro lens for automatic diaphragm control. I looked into availabilty before posting the thread, and it seems like it's too difficult to get for this purpose. There has only been one on eBay in the last few months, and it's sold by Photo Arsenal (notoriously overpriced dealer) for $140. I'd need two...</p>

[User_1172872]

<p>The [long discontinued] Nikon E2 ring might work. It also has a diaphragm lever, and can be used with the original Nikon F cable release. I sold all my manual focus Nikon gear so I can't tell you if it meets the 8.5mm criterion.</p>

[User_1172872]

<p>Sorry, should have used Google first. It seems the thickness of the E2 ring is 14mm.</p>

[akira]

<p>Novoflex makes Nikon F to micro four-thirds adaptor with aperture control ring (Novoflex also makes siilar adaptors for Pentax DA and Sony alpha lenses). However, there should be two problems:<br>

1) I don't know if there are m4/3 to c-mount adaptor.<br>

2) Even if you might be able to swap the mount of your camera to m4/3, I'm not sure if m4/3 is robust enough to hold hevier lenses.<br>

So, my post seems to be redundant, but hope this would be of any help.</p>

[Michael R Freeman]

<p>The E2 ring has a plunger that opens the aperture on a G lens as you push the plunger. However it is approximately 13.5mm thick, so won't meet your 8.5mm criteria.</p>

<p>The BR-4 is 9mm thick (the thickness is indicated on the ring), so it exceeds your 8.5mm by 0.5mm, but I suppose it *might* be possible to machine 0.25mm off of the back side of both mounting flanges to get the overall thickness down to 8.5mm. There isn't a lot to work with however, as a couple of junk F-mounts I just checked ranged from 1.3 to 2.0 mm thick.</p>

<p><img src="http://i170.photobucket.com/albums/u255/mikerfns/photonet%20stuff/NikonBR4.jpg" alt="" /></p>

<p>The BR-6 is apparently identical to and is a successor to the BR-4 ("has improvements in fine details" according to Braczko's <em>Complete Nikon System</em> ), so that is also probably 9.0mm thick. But it is still available new from B&H or Adorama for $85 - $90.<br /> <img src="http://i170.photobucket.com/albums/u255/mikerfns/photonet%20stuff/NikonBR6.jpg" alt="" /> <br /> The E2, BR-4 and BR-6 are F-F adapters.</p>

[bjørn rørslett]

<p>BR-4 and BR-6 are both "F" => 52mm thread adapters. The difference is that BR-4 is from the non-AI/AIS era while the BR-6 is fully compatible with AI and AIS lenses. Not all current lenses will mount properly on the BR-4.</p>

[richard_driscoll]

<p>Bjorn,<br>

Not according to this:<br>

http://www.photo.net/nikon-camera-forum/00BvBX<br>

I'm sure BR-4 is F to F while it looks as if BR-6 is F to 52 mm. screw.<br>

Looks as if BR-4 will strike the CPU contacts.</p>

<p> </p>

[tommyinca]

<p>I have a copy of both BR4 and BR6. Don't know if there are other variations or not. Here is a picture of the backside not shown above. See the extra Notch that a BR6 has. BTW: This BR4 also won't fit my Sigma 200/4. If you get a BR4, you may need to do some work. Looks like you also can modify a BR6 by removing the screws of the 52mm tread and fit a lens flange on top of that. I don't think there is an easy ready made solution for this.</p>

<p>PS. There is also a guy who ran a web site called 16-9. He sells a Nikon to EOS mount for the 14-24/2.8 Nikkor with G lens aperture adjustment. May be he can help you out.</p><div></div>

[bjørn rørslett]

<p>Oops, I mixed up. My bad. BR-4 is indeed F-F, but the caveat of it being constrained to non-AI/AIS lenses is valid. There is a flange on the rear side that prevents the BR-4 from being attatched to modern cameras, and the front mount is set so deep that AI/AIS lenses won't be seated properly. Any lens with CPU contacts will jam as well. So keep the BR-4 only for those venerable Nikkors of the '60s.</p>

[frank_skomial]

<p>"The other option is simply drilling a hole in the camera's lens mount to insert a plunger aperture control, or something fancier with an actual ring." - a mechanical solution.</p>

<p>Is there an electronic solution ?</p>

<p>I suppose "G" lens has a CPU, and perhaps applying proper voltage level to the aperture control electric pin would force it open to desired F stop. I would imagine, that a simple solution with a battery and a ladder of resistors could possibly open aperture electronically to desired F-stop. This could be made even more complicated... What do you think ?</p>

<p>Each time I fly on-board with long G lens through security gates, controllers require see through the lens, and express their dissatisfaction with my inability to open G lens wider then F=32 without using the camera.</p>

[Michael R Freeman]

<blockquote>

<p><em>"I suppose "G" lens has a CPU, and perhaps <strong>applying proper voltage level to the aperture control electric pin</strong> would force it open to desired F stop."</em></p>

</blockquote>

<p>Aperture control on G lenses is <strong>mechanical</strong> . There is no "electric pin".<br>

-</p>

 

<blockquote>

<p><em>"Each time I fly on-board with long G lens through security gates, controllers require see through the lens, and express their dissatisfaction with <strong>my inability to open G lens wider then F=32 without using the camera</strong> ."</em></p>

</blockquote>

<p>Use your index finger. Works every time, no camera required.</p>

[frank_skomial]

<p>Thanks Michael,<br>

The finger on the lever works OK.</p>

<p>With camera OK, when CPU failed in my 70-200 twice, it only worked at f=32 and a non-CPU entry for the lens, making the lens practically useless . </p>

<p>At that time I was told at Nikon repair center in El Segundo that the electronic signal value for the required aperture from camera is not translated into mechanical action of the aperture in the lens. There was no mechanical damage in the camera or lens. The CPU in lens was busted. There must be more to the G aperture than just mechanics ?<br>

Any clue?</p>

[bob_mcbob]

<p>As far as I know, G lenses still have a purely mechanical aperture linkage with the camera. They communicate electronically (AF-S autofocus for instance), but the aperture is still stopped down with a lever, unlike the Canon EF system. It makes it a little more frustrating that they've just removed the ability to control the aperture without the camera.</p>

[bjørn rørslett]

<p>The "G" lens is stopped down via the stop-down lever inside the camera. The distance the lever has to travel in order to provide a given aperture is calculated by the camera, based upon information from the CPU inside the lens. Hence the need for the presence of both components (lens and camera). In principle, when you adjust aperture of an Ai-P/AF/AFD/AFS(non G) lens using the thumbwheel on the camera, you perform the identical operation as with a "G" lens, hence the need for the lens to be set to its smallest aperture so the camera can employ the entire aperture scale. However, for the non-G lenses having an aperture ring, you can select using that instead (feature only for the mid- and high-level Nikons which possess an AI-follower ring). In this case, the travel of the stop-down lever is controlled by the lens not the camera and is not calculated but arise from a physical stop inside the lens, so is more accurate..</p>

 

[tommyinca]

<p>"The finger on the lever works OK."<br>

Wait til the guy see a Minolta/Sony shooter, need small finger. Worst an old timer Canon FD shooter.</p>

[bob_mcbob]

<p>Oddly enough, I discovered that we actually have one of the Nikon F to C adapters sitting around unused. The plunger system is quite practical and easy to use. I think installing one in the mount on the camera is probably my best option. This would certainly be a lot easier than trying to DIY an actual aperture ring in the mount, and it doesn't look like any of the Nikon macro accessories would work.</p>

<p>The plunger does have to be placed quite precisely to operate the aperture lever properly. Drilling that angled hole is going to be a bit of a pain, but it shouldn't be an issue. I'm not sure whether I can even buy the socket a cable release screws into -- there certainly isn't much of a market for the part. I might just end up cannibalizing a few cheap cable releases. It needs to be set up so the plunger rests at the maximum aperture position, and stops at the minimum.</p>