Anyone got any experience with ISCO projector lenses?

[pkr1979]

Hi all,

I have adapted a ISCO 130/2 lens for a Pentax 67ii. I did expect this to be sharp when focus is nailed (or for whatever is unintetionally in focus), but I have to admit I find it a bit soft (or quite soft). I do shoot it handheld, but with shutter speeds faster than the focal length - and I've been able to get sharp images hand held with the Pentax lenses.

So, I was wondering if anyone else have used this lens (or a similar ISCO) with similar experiences... or am I doing something wrong... or is it something wrong with my particular lens? It appears sharp in my viewfinder, but if I had magnified maybe that wouldn't be sharp there either.

Cheers
Peter

 

[John Salim]

Yes, I use modern Isco projection lenses for both 16mm and 35mm, and they are amongst the best for film projector use.
They're very well designed, but not suitable for camera image forming.

I'm assuming your 130mm lens is a 35mm motion picture lens ( 70.6mm diameter ) so it'll be corrected for relatively long distance projection.

John S

 

[OAPOli]

I've used a Super-Kiptar f/1.5 projection lens but on digital only because of the short back focus. It is sharp. Maybe try to adapt it for digital as a benchmark? Missing focus is pretty easy with those fast lenses.

 

[blee1996]

I have used Isco Cinelux 150/2.3 MC on pentax 6x7, and it is plenty sharp for portraits. I also handheld, since the open aperture resulted in fast shutter speeds outdoors.

I think they are not clinically sharp, but pleasingly sharp with some glow. And mine handled backlight pretty well. Is yours Cinelux MC version?

 

[pkr1979]

Thanks guys!

@John Salim - the lens is a ISCO Ultra MC Film 2/130 mm. It also says FILM 35/70 mm on it which I assume means that it can be used to project both 135 film and 120 film? The diameter is 70mm. This might be a dumb question but why wouldn’t it be suitable for camera image forming? Whats the difference between projecting on a large screen and film? The distance I suppose?

@OAPOli - I agree, its easy to miss focus… at least what you intend to focus on. But some part of the image usually is in focus. And that part is soft.

@blee1996 - mine is the Ultra MC version. And I agree, what I call soft you could also call glow. But when projecting wouldn’t you want clinical sharpness?

Cheers
Peter

 

[John Salim]

Sorry, my typo ... should be 70.6mm diameter ( above post edited ).

Projector lenses are usually a simpler design ( fewer elements ) and made to work at 'full aperture' projecting a flat image onto a flat surface.
Yes of course you can use them on cameras if adapted, but they won't deliver the same critical sharpness a proper camera lens will.

John S

 

[OAPOli]

Generally speaking, projector lenses are built for maximum transmission and even illumination. But a double Gauss design like the Ultra MC should also be sharp with a flat field and little distortion. Aside from the Super Kiptar I did manage to use a fast double Gauss f1.4 aerial lens on my P67 and it was plenty sharp when in focus. I've also tried the more common Pezval types and they were pretty bad.

Here's a document that shows MTF and more for the ISCO lenses: https://allphotolenses.com/public/files/pdfs/0a51913a5f536697ea596a63ce8d9fa8.pdf

 

[blee1996]

I guess some of you have seen these reviews and photos, which is why I bought my Cinelux in the first place. And my results are comparable, even though I don't shoot weddings.

Schneider Cinelux Ultra MC Review — Jeff & Michele Education For Photographers and Business

Photography education, SEO education, and professional growth for photographers and business people

jeffandmichelephoto.com

@OAPOli Petzval lenses really start to shine on bigger film, e.g. 4x5 and especially 8x10. Typically you need to use longer focal length for the format, and I like B&W out of Petzval more than color. The center can be very sharp if in focus.

 

[pkr1979]

Thanks again guys. @blee1996 - your Cinelux seems to be sharper then my Isco. Maybe the Cinelux lenses has a better design?

I did some test shooting today though. I put the camera on a tripod today, taking som pictures of a bike and some text on the frame. In the viewfinder it was tack sharp. I will get that developed sometime next week to check out the results. If those images are not sharp - what might cause the softnes? Coating gone bad?

 

[itsdoable]

Projection lenses differ from photography lenses in a few ways:

- designed to perform at one aperture (not necessarily the sharpest aperture, but one that is satisfactory)
- optimal resolution is dependent on the granularity of the screen - in that due to the screen surface (which consists of small glass cubes), they don't have to resolve beyond this
- field curvature is built in to reflect the curvature of the film in the projector film gate
- bokeh ignored in the design criteria (often quite busy)

The Ultra MC is a high end double gauss based design, so I would expect it to perform well on your P67.

If you are not getting this, I would test your focus - it's difficult to accurately focus and f/2 lens on the P67, the optimization and alignment of the screen was only meant to go to ~f/2.8, and small discrepancies make a difference. Test to see if your camera is front or back focusing (ie: with a sloping test target). Or adapt it to a digital mirrorless and test how sharp the center is to see if it matches up with what you get on the P67 - this should at least tell you how good your Ultra MC is. Check to see if the optic has been serviced (ie: disassembled) as proper shimming of the optical elements is important in maintaining performance on fast optics.

 

[pkr1979]

Thanks @itsdoable

I'll try to figure out if the camera is back or front focusing.

I am concerned someone did this without really knowing what they where doing:

Check to see if the optic has been serviced (ie: disassembled) as proper shimming of the optical elements is important in maintaining performance on fast optics.

But how can I check if the optic has been serviced?

 

[itsdoable]

Thanks @itsdoable

I'll try to figure out if the camera is back or front focusing.

I am concerned someone did this without really knowing what they where doing:

Check to see if the optic has been serviced (ie: disassembled) as proper shimming of the optical elements is important in maintaining performance on fast optics.

But how can I check if the optic has been serviced?

Usually there are tool marks on the retaining rings if the lens has been opened and cleaned.

My Hasselblad 2000fcw back-focused with the 2/110 lens, which was not entirely evident on the 2.8/80, although in retrospect you could just make it out. Once the body was adjusted, it was good.

 

[pkr1979]

Thanks again. As far as I can tell the retaining rings seems to be free of tool marks. The back lens element however had some (polishing) residue on it that was easy to clean off - I would be somewhat surprised though if that caused the softness. I did take som photos today to check back/front focusing. Hopefully I will know more when I get the pictures developed.