Pentax 110 lenses on NEX-3

[iangreenhalgh1]

Hi folks

I have been trying to work out the actual fov and focal length of my 18, 24 and 50mm Pentax 100 lenses on my NEX-3.

The 110 film size is 17x13mm, the APS-C sensor in the NEX is 23.4x15.6mm.

With the larger size of the APS-C sensor, what effective fov am I getting with the 110 lenses?

The 18mm seems to give almost exactly the same fov as my Tokina 17mm does on the NEX, which confuses me somewhat.

[Attila]

Several C mouunt lenses also produce larger image circle than others.

[RCasaubon]

Dear iangreenhalgh1: I owned an Olympus E-PL1. This is a M4/3 sensor camera. I have an auto 110 18mm lens as yours. I mounted it on a precarious adapter for testing. The lens covers 100% of the sensor, even allows you to move sideways!
Unfortunately I can not use it on my Nikon D200 because it touches the mirror before you focus.
In principle, any lens of any format, at a given focal length is equivalent to any other of the same focal length.
For example, if you put a wide angle medium format (50mm) on a full frame 35mm body, it becomes a normal one. Likewise, a normal 50mm full frame, used on a APS-C sensor becomes a short tele. If you put the same lens on a sensor m4/3, this equates to a 100mm used on a 35mm camera. It is reasonable to have a similar FOV between 17mm frame and format any other 18mm.

[iangreenhalgh1]

The image circle of the 110 lenses must be at least 24mm because they cover the NEX sensor with no vignetting, I haven't been able to try them much yet as I only finished the adapter yesterday and it's dark here now but the indoor test shots I have made look promising and the tiny size of the lenses just seems perfect for the NEX. My first attempt at an adapter included an aperture mechanism from an old shutter but this sadly meant the lenses didn't quite hit infinity, I have made an apertureless one now and that works perfectly to infinity. I may have another attempt at an adapter with aperture, maybe I can use the aperture from one of the C mount lenses I have.

Thanks for the explanation of focal length, that makes sense.

18mm:



24mm:

[Attila]

Many C mount lens below 25mm focal legth , will not cover your m4/3 camera sensor.

What I did try angenieux 25mm , Meopta 20mm etc.
http://forum.mflenses.com/meopta-openar-20mm-f1-8-c-mount-panasonic-g1-budapest-t37200,highlight,%2Bmeopta.html

http://www.mflenses.com/gallery/v/frenchlenses/angenieux_25mm_f095_c_mount/angenieux_25mm_f095-c-mount-582.jpg.html?

[iangreenhalgh1]

[Attila]

D mount usually even worst not cover any of them. Pentax 110 looks a neat idea, if you get success , I think many of us will follow you. I look forward samples on nice light condition , to judge on image quality.

[iangreenhalgh1]

The D mount lens is one that was available in either C or D mount, I paid almost nothing for it so felt worth the risk, I think it might be of interest to a M4/3 user. I wouldn't have bothered with it if it hadn't also been sold in C mount as I doubt any D mount lenses will cover NEX sensor unless a really long one and then that defeats the purpose of using C-mount lenses (tiny size to fit in pocket) and you might as well just use a SLR lens for those longer focal lengths.

I will be trying all three of my 110 lenses tomorrow, my one concern is the shallow dof at the 2.8 fixed aperture but this won't be an issue for many subjects where I would use them in preference to an SLR lens on my NEX.

The price of 110 lenses has already climbed a lot, a 70mm one is 35ukp starting bid on ebay atm, before the 110 adapters from China appeared for M4/3 they were available for almost nothing, now you will have to pay a (still low) but heftier price.

[adent]

I looked on ebay and they sell adapters for using these 110 lenses on NEX.

[iangreenhalgh1]

They do indeed sell NEX adapters now but as I had a broken Pentax 110 camera I bought just to get the 24mm lens, I made my own adapter using a C-NEX adapter I had lying around (none of my C-mount lenses covers NEX sensor so adapter wasn't needed), the bayonet mount ring from the 110 camera and a piece of the barrel from a D-mount lens.

[RCasaubon]

I made other adapters from scratch using broken bodies. In this case you could use a broken auto 110 body, a m42 adapter to nex (cheapest adapter for taking male mouth part) and any broken zoom lens to take diaphragm if you can't use it from Pentax body. All you need is a torn or just a drill and a lot of insanity as mine.

[RCasaubon]

Sorry for my mistake. Not a M42 but a C adapter!

[iangreenhalgh1]

Yes, I used the aperture from a broken shutter in my first adapter, it didn't allow infinity and then when dismantling to adjust for infinity, I broke it, one of the blades came loose. I have more shutters and broken lenses to take aperture from so I might have another attempt at adding an aperture.

I am also making an adapter with aperture for three Olympus industrial lenses of superb quality I have, I too, am insane like you!

[ManualFocus-G]

member Nodentro has used this on micro 4/3rds too...

http://forum.mflenses.com/pentax-110-24mm-f2-8-t35622.html

http://forum.mflenses.com/pentax-110-18mm-f28-t35523.html

[iangreenhalgh1]

Yes, I saw his samples when researching 110 lenses, they were a large part of why I decided to get some for myself, the IQ looks superb with an overall very pleasing rendering.

On other forums people have claimed the 18 and 24mm lenses didn't cover the NEX sensor fully, very pleased to have disproved that notion, quite surprised actually they do cover it fully, no vignetting at all.

[visualopsins]

Crop factors can be used to figure lens relative fov between formats:

[Sevo]

[iangreenhalgh1]

Some samples from the 18mm 110 lens.

[DSG]

[iangreenhalgh1]

Some more samples from the 18mm lens, it's quite sharp and has very little CA, I like the swirliness it has in the corners, I like the overall rendering a lot, contrast is a little low and needs tweaking in PP, maybe if I used a hood it would be more contrasty, have to keep my eye out for a small hood to fit.

[iangreenhalgh1]

And a few with the 50mm. This lens is sharp and has little CA but has low contast, needed tweakingg in PS to give acceptable results, again I like the overall rendering though.

[Attila]

These are not good lenses in my opinion Ian.

[iangreenhalgh1]

I'm surprised by the low IQ I managed to get from them, samples I've seen from others had more contrast and sharpness and more saturated colours, I will try them again but my hopes now are not so high, sadly.

[iangreenhalgh1]

Just realised i forgot to paint the inside of the adapter I made black, which probably accounts for the low contrast. I will give it a good coat of matt black paint tonight and see what difference it makes tomorrow.

[Attila]