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Trouble with Computar lens and RJ Camera adapter

T

thearne3

Guest
I have now collected a couple of Computar lenses (25mm and 12.5mm) and have made the unpleasant discovery that my RJ Camera C-mount adapter is not the same as the hawkpen adapter for my lenses.

The first 'shoulder' on the lenses is 30mm (no problem). The second shoulder is ~38mm, which is easily filed down to 37.2mm. However the third shoulder is 39.2mm and, unlike the hawkpen adapter, there is no 39.2mm notch in the RJ Camera adapter, so this wider shoulder must be filed down to 37.2mm as well.

I have only done the 25mm lens. I filed down the outer two shoulders so that all three shoulders add up to 3mm of total depth (measured from the base of the screw mount toward the front of the lens) with diameter less than 37.2mm. The lens appears to be fully seated, but still only focuses to about 5' max at f1.3.

Has anyone been able to achieve infinity focus with this lens and the RJ Camera adapter?? Is the issue the lens, the adapter, or am I wrong and the lens isn't fully seated?

Thanks for any insights...

Tom
 

Y.B.Hudson III

New member
Not a scientific reply..However, I have modified Computars, Navitars, Fujinon lenses to fit the Hawk II. I subsequently bought a RJ and found that none of my modifications worked on it... I'm not into self abuse, so I just use the RJ for lenses that don't require
modifications. For what it's worth...I have a Xenplan 25 that works unmodified on the Hawk II, but doesn't fit the RJ.
 
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E

echols

Guest
Where can you buy the Hawkpen c mount adapter?
thanks
echols
 

PeterB666

Member
Although this is not exactly on topic, I have the Hawkpen C-mount (Bolex version) and Robot flange and an RJ Camera 4/3 to M4/3 adapter and OM to 4/3 adapter and must say the Hawkpen C-mount adapter is better made.

The older 2-part adapter for the OM lenses does not align as well as it should but is adequate. I was thinking of getting the newer 1-part OM to M4/3 adapter but am not sure if the quality is as good as it should be based on the 2-part one.

I am not into machining lenses so haven't bought any C-mount lenses. The grub screws used to hold and align the Robot flange on the Hawkpen adapter are so small that I would probably buy a second adapter rather than chancing breaking the heads of the screws.
 

pellicle

New member
Hi

Some time ago I put up a page here to address mounting issues on the Computar with the HawkPeng adaptor ... its a no go on the RJ adaptor without the sorts of lathing seen above
 
M

MrAdrenalin

Guest
Hi Y.B.Hudson III,

Could you post some pictures and a guide for the modification of the navitar 75mm 1.3 to get infinity with the hawk adapter? Is there anything special you need to think about for the modification of the fujinon lenses (especially the 50mm 1.4)?

Best regards,

Magnus
 
T

thearne3

Guest
Thanks for the encouragement, Turbo, I now have both the 25mm and 12.5mm Computar lenses working with the RJ adapter - They even almost align vertically! However, still fine tuning infinity focus...

BTW, I have been using a small three-sided file for the work - makes a very clean notch. Couldn't find anyone locally with a lathe - that would have been perfect!

Happy hacking!
 
T

turbo

Guest
Thanks for the encouragement, Turbo, I now have both the 25mm and 12.5mm Computar lenses working with the RJ adapter - They even almost align vertically! However, still fine tuning infinity focus...

BTW, I have been using a small three-sided file for the work - makes a very clean notch. Couldn't find anyone locally with a lathe - that would have been perfect!

Happy hacking!

What I did was build a pilot to center the base of the mount (removed from lens) in a drill press. Start the drill press to get the mount spinning and then use a dremel to grind away, stopping frequently to measure.
 
M

MrAdrenalin

Guest
Hi again Y.B.Hudson III,

I guess you just been busy but still looking forward to the pictures.

Best regards,
Magnus
 

Y.B.Hudson III

New member
Magnus, yehh trucks breaking down, cows calving, but "The pics" should be up be up by 15:00 GMT, thursday 24 September...

regards, Hudson
 

Y.B.Hudson III

New member
Navitar 75mm 1.3... for Hawk II adapter...




1 unscrews, 2 lifts off...


0.8mm ... finished dimension.







on my example of this lens...it focused past infinity, I'll continue with how to adjust the lens for infinity collimation tomorrow...
 
T

thearne3

Guest
Hudson -

Just a nudge...some of us are very interested in 'Part 2'! Your efforts are very much appreciated.

Best,
Tom
 

pentacon6

New member
ouch! That's the part I am thinking of and I dare not to do.

I knew that, GF1 and EP-1 have no such a problem deal to the area in front of the sensor is larger. I used to think of open it wider but now I think I can skip it.

Thanks so much, Hudson! :)
 

turbines

New member
I am trying to mount a Navitar 75mm 1.3 to c mount adapter for m4/3s. Does anyone know what has happened to the illustrative images and also the rest of this thread which seems to just end abruptly?
 

pellicle

New member
Does anyone know what has happened to the illustrative images and also the rest of this thread which seems to just end abruptly?
not exactly, but if you don't yet have an adaptor then I suggest the hawkpeng one.

fits nicely ... reference the blog post I put up on one of the earlier posts on this thread to see.
 
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