Sharpest Lens

[Devon Lyon]

I use the following lenses with my LetusXL on my Canon XL2 and they are all Canon FD manual lenses:

28mm, 35mm, 50mm, and a 35-135mm (I think). I am going to work on some type of test to determine how to achieve the sharpest focus and which lens can achieve it.

Has anyone else done any tests, or is even willing to share anectdotal evidence (like Canon vs. Nikon, or what aperture setting achieves sharpest results)? Also, how are the Nikon lenses in comparison to Canon?

[Holger Leonhard]

sharpness is not an issue - all 35mm adapters are far below quality 35mm glasses in resolution. You will hardly get more then 800 lines resolution, and a good Nikon or Canon Lens has > 4k.
The Point is light sensivity and color / contrast reproduction, boquet and the look of lens flares / reflexions.

[Ben Winter]

Originally Posted by Holger Leonhard

boquet and the look of lens flares / reflexions.

:) I think you mean "bokeh," and yes, I think that's more important than a lot of people make it out to be. The look of the out-of-focus elements and flares is something I think is grossly overlooked on these forums and when making an adapter, and it's sad to see that the only adapter that seems to take these into consideration is the G35.

[Devon Lyon]

Thanks for the input. I have been doing a little more research and My footage is in focus, it just looks a little out of focus at time because of the softer nature of the lens adaptor.

[Bob Hart]

Originally Posted by Holger Leonhard

sharpness is not an issue - all 35mm adapters are far below quality 35mm glasses in resolution. You will hardly get more then 800 lines resolution, and a good Nikon or Canon Lens has > 4k.
The Point is light sensivity and color / contrast reproduction, boquet and the look of lens flares / reflexions.

I have shot a test chart with a selection of lenses and found that there is enough resolution from a AO5 groundglass for the difference to be observable between the 85mm f1.8 Nikon which is the best in my lot and the others.

I suspect that the scatter effect of the groundglass may tend to amplify any softness in the image in a similar way that a soft lens into a night-vision intensifier looks way softer than one would expect, especially when highlights or high contrast edges are encountered.

[Holger Leonhard]

Originally Posted by Ben Winter

:) I think you mean "bokeh,"

*gg* yesss .. ;-)

[Holger Leonhard]

Originally Posted by Bob Hart

...resolution from a AO5 groundglass ...

what´s up with this "A05" GG ?
an better alternative to the current GG ?
I have a Letus 35 flipped and too much light loss (about 5 stops when using a 1.4 lens). Is this A05 brighter an sharper and where can I get this ?

[Bob Hart]

Originally Posted by Holger Leonhard

what´s up with this "A05" GG ?
an better alternative to the current GG ?
I have a Letus 35 flipped and too much light loss (about 5 stops when using a 1.4 lens). Is this A05 brighter an sharper and where can I get this ?

Please forgive my lazy english.

AO = aluminium oxide abrasive.
5 = 5 micron grade.

A while back when more posts here were from people making their own groundglasses AO5 became easy speak for groundglass finished with aluminium oxide 5 micron grade grit.

A finer grade 3 micron can be used to grind the glass but the finish is too fine and the camera can see through the groundglass.

Too much of the aerial image is mixed with the groundglass image which makes a ghosting effect and makes the hot spot problem worse.

In reference to the "bokeh" performance of any lens, a groundglass which is too transparent will spoil the bokeh effect because of these defects.

For me, the 5 micron finish seems to be about as fine as it can go without bringing the other problems. This is to some degree a personal preference.

For some builders, this finish is not fine enough. For others the image looks too much like video and they would sacrifice a little resolution for a more diffused filmlike look.

I think you will find that the Mini35 and all the alternative products which had their genesis here at this site, will have a chosen grade of finish which best performs in all conditions.

Some home-builders like myself will customise their groundglasses to suit their own preferences. In my case, I want to be able to intercut relay and direct-to-camera origination.

So I have chosen the AO5 finish and given it a very slight backpolish to improve apparent sharpness.

This introduces the hotspot and ghosting effects so there are some circumstances I have to avoid, such as high contrast overlit backgrounds.

I have to shoot a smaller image frame off the groundglass to stay inside the hotspot. You lose some resolution by having to go closer so the resolution gain is traded off a little.

The Nikon 85mm f1.8 yields a return off the 850 line patterns on the Lemac chart with better apparent resolution off the horizontal block.

The image path is Nikon Lens >> AO5 groundglass (spinning glass disk) >> 2 x right-angle prisms >> 7+ power Century Optics achromatic dioptre >> FX1 camcorder.

Light loss through the system happens with all relay devices.

A coarser groundglass will lose more light but gives an image with less hotspot and no ghosting, halo or outline defects.

A fine groundglass loses less light but there are other problems. It is a matter of finding the best balance.

Test charts in a controlled environment are one thing. Real world conditions are another. The performance difference between designs in practice may be less evident.

What is common to all is that the lens skills of the videographer or lack thereof will be showcased for the world to see.

I fear may have wandered a little off-topic with my ramblings here.

[Holger Leonhard]

wow, thanks, lots of information! :)