[sportster64]

can I use nikkon Ai,Ais or even non-ai lenses on my pentax k-100d ?
If so - what is involved ?

[little laker]

There might be adapter's around, but you won't be able to properly convert it.

They're competitors, and could never make it that easy to switch brands

[Lowell Goudge]

Having gone through the concept of changing a K mount to a KA mount, I can list for you the challenges and things to look for.

If you consider making the change on the lens directly, you need to first of all find a K mount to attach to the nikon lens. the best bet is to purchase a junk lens or teleconverter, these can be had for $10 - $20.

Just for the mechanical conversion, you will need to consider the distance from the respective camera mounts to the film/sensor plane and insure you have made any necessary adjustmemts. If you do not manage this distance correctly, you will be unable to focus to infinity.

Depending on how nikon establishses the detent's for the apature, you may find this is integrated into the mount (Sigma do it this way on some lenses). This can cause some problems.

You then need to check the apature actuating lever, assuming you want wide open focusing and the ability for the camera to stop down the lens. This may take some modification, or custom parts to put it in the correct location. I am not sure about direction of travel, and location of the apature actuating lever on nikon lenses. (As I recall, sone things are backwards to pentax.

If you only want stopped down metering this can be deleted, BUT you are then destroying a good lens.

If you want to have functions of a KA mount, you then have 2 additional things to review,
- first, and I believe quite simple, is the electrical contact arrangement. I have all the necessary details posted on my thread discussing https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/4893-replacing-lens-mounts.html
- Second is the behavior of the apature actuating lever. does the diameter, or area change linearly with motion of the actuating lever. For correct exposure you need the area to be linear. This is what really prevents changing K to KA lenses.

Overall, you need to be very familiar with both mounts, and before proceeding with a really good lens, you may wish to get some $10 junk lenses and experiment. It will take a lot of time, and you will need at the very minimum a good drill press with very small drill bits, perhaps some milling bits, and a lot of patience.

[FotoPete]

Nikon lenses if converted will only be able to be used in stop down mode unless you find a way to link and extend the aperture actuator to the right position in the K mount like Lowell mentioned.

Non AI lenses, some you can kinda 'jam' into the K Mount. Some fit, some don't but attach it gently. The lens can get stuck or they only twist a small degree. Like the Nikkor-S 50 1.4. It twists on at most a 3-4minute rotation. The 105/2.8 is like 1 minute or less so you are literally just holding the lens over the kmount.

AI lenses require that you dremel off the rim extensions, otherwise the lens won't sit flush on the K-Mount plate. Nikon uses an external type of aperture coupling. A fork in the pre-AI lenses and then extended aperture rim sections in the AI era and onwards up until just before Nikkor G where G = no aperture ring.

You won't be able to use G lenses and onwards because there is no way to electronically telling the Nikkor lens to set desired aperture.

Honestly, I think you might have more lucky switching mount bayonets on Contax/Yashica (C/Y) Mount lenses. They have the same flange distance as Pentax K so the lens mount design is similar. Again use at your own risk. Better off fishing for M42 takumars, M42/K, Ricoh, Vivitar, Tokina, Kiron, Makinon etc lenses. The Pentax K/M42 was popular enough back in the day to bathe eBay with an abundance of lenses. (fading fast due to resurgence in Pentax cuz of K10D and Canon shooters realizing they can use M42)

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Last edited by FotoPete; 10-11-2007 at 09:17 AM.