[KFBK95]

Hey guys,

I'm a researcher in the field of Fluid Mechanics. We use a camera to acquire images of a jet flow using laser-induced fluorescence (LIF). Currently, we are using a pco.dimax 4 Megapixel CMOS camera (https://www.psi.ch/sites/default/files/import/sls/tomcat/Station1_DetectorsE..._dimax_105.pdf) with a 50 mm pentax lens (f/1.4). The lens is C25011KA.

We want to reduce the size of our captured field of view to approximately 1/3 of what it is now (the field of view size is currently about 260 x 260 mm and we want around 80 x 80 to 90 x 90 mm). What do you recommend in terms of the mount type, minimum working distance, and focal length? We can also reduce the distance between the lens and the region of interest to about 4/5 of what it is now.

Any suggestion is appreciated since I am a beginner in the field of optics.

[GUB]

Is the lens you have perhaps a C mount TV lens?
What you are asking here is simple proportionality (or inverse).
If you want 1/3 of the field of view (as expressed in dimension) then 3 times the focal length ie 150mm.
Seeing you can move closer that can proportionally decrease the focal length.

[GUB]

Remember the ray diagrams you drew in Physics ? Just think of your current lens as a simple lens placed at it's optical centre and with the focal length it is rated at.

[hcc]

HI,
I am also a fluid mechanics researcher and we use a Phantom™ ultra-high speed digital camera (v2011), equipped with a Nikor lens mount. We typically operate at 20,000 fps with in a definition of 1280 × 800 pixels.
Our applications are air-water free-surface flows and we apply an optical flow (OF) technique.
We use prime lenses, a Carl Zeiss™ Planar T*85 mm f/1.4 lens or a Nikkor™ AF 50 mm f1.4.
I can very strongly recommend the Carl Zeiss 85 mm f1.4. It is not as long as you asked for, but the optical quality of the lens is outstanding.
You may PM me directly for further exchange.
Hope that the info will assist.

[KFBK95]

HI,
I am also a fluid mechanics researcher and we use a Phantom™ ultra-high speed digital camera (v2011), equipped with a Nikor lens mount. We typically operate at 20,000 fps with in a definition of 1280 × 800 pixels.
Our applications are air-water free-surface flows and we apply an optical flow (OF) technique.
We use prime lenses, a Carl Zeiss™ Planar T*85 mm f/1.4 lens or a Nikkor™ AF 50 mm f1.4.
I can very strongly recommend the Carl Zeiss 85 mm f1.4. It is not as long as you asked for, but the optical quality of the lens is outstanding.
You may PM me directly for further exchange.
Hope that the info will assist.

Hi,

Thanks for the info. We want to capture the near-field of a jet (say x/d = 2) and so it is important to reduce the size of the FOV as much as possible.
Carl Zeiss™ Planar T*85 mm f/1.4 is good but the FOV is still a bit large. I also don't think Pentax has 150 mm lenses that are compatible with our camera within the working distance. Do you have any other suggestions?

[zapp]

Hi,

Thanks for the info. We want to capture the near-field of a jet (say x/d = 2) and so it is important to reduce the size of the FOV as much as possible.
Carl Zeiss™ Planar T*85 mm f/1.4 is good but the FOV is still a bit large. I also don't think Pentax has 150 mm lenses that are compatible with our camera within the working distance. Do you have any other suggestions?

Nice to meet a PCO user from psi here. Just call PCO, the guys are helpful and understand your application. We also use PCO for metric imaging and have close ties to them as well as to the psi. Feel free to drop me a PM.

[Wasp]

It seems that the is the camera can take various lens mounts. Here it is with an F mount:



---------- Post added 2022-01-31 at 23:05 ----------

If it is a used 120mm, 135mm or 150mm manual focus prime that you need, you are in luck. Pentax actually made them all. Canon, Nikon e.a. only made 135mm primes in this range but Pentax had you covered back in the day when Kodachrome was still around.


SMC Pentax-M 120mm F2.8 Reviews - M Prime Lenses - Pentax Lens Reviews & Lens Database

SMC Pentax-M 135mm F3.5 Reviews - M Prime Lenses - Pentax Lens Reviews & Lens Database


SMC Pentax-M 150mm F3.5 Reviews - M Prime Lenses - Pentax Lens Reviews & Lens Database

The 120mm and 150mm are kinda rare but not unobtainable and not too expensive.

[KFBK95]

It seems that the is the camera can take various lens mounts. Here it is with an F mount:



---------- Post added 2022-01-31 at 23:05 ----------

If it is a used 120mm, 135mm or 150mm manual focus prime that you need, you are in luck. Pentax actually made them all. Canon, Nikon e.a. only made 135mm primes in this range but Pentax had you covered back in the day when Kodachrome was still around.


SMC Pentax-M 120mm F2.8 Reviews - M Prime Lenses - Pentax Lens Reviews & Lens Database

SMC Pentax-M 135mm F3.5 Reviews - M Prime Lenses - Pentax Lens Reviews & Lens Database


SMC Pentax-M 150mm F3.5 Reviews - M Prime Lenses - Pentax Lens Reviews & Lens Database

The 120mm and 150mm are kinda rare but not unobtainable and not too expensive.

Thanks for the F-mount picture.
The problem with the proposed lenses is their minimum focusing distance. The Min. focus for all of them is above 120 cm, whereas I want something in the range of < 45 cm to make the FOV as small as possible. The best thing that I could find is this:
SMC Pentax-D FA 100mm F2.8 Macro WR Reviews - D FA Prime Lenses - Pentax Lens Reviews & Lens Database

The Min. focus is 30 cm and the focal length is 100 mm.

[hcc]

Hi,

Thanks for the info. We want to capture the near-field of a jet (say x/d = 2) and so it is important to reduce the size of the FOV as much as possible.
Carl Zeiss™ Planar T*85 mm f/1.4 is good but the FOV is still a bit large. I also don't think Pentax has 150 mm lenses that are compatible with our camera within the working distance. Do you have any other suggestions?

Tough call.
Longer focal lengths will give you a smaller FOV, but you will loose in terms of depth of field and aperture. Longer lenses are typically f4.8 and above (i.e. smaller aperture and longer depth of field).
The CZ85mm f1.4 (in our case) an optimum compromise between (a) the needs for (a.1) a fast lens (f1.4) for very fast exposure (1/80,000s typically) and (a.3) a shallow depth of field with large aperture (f1.4, giving us typically a depth of field about 3-5 mm) and (b) a small FOV.
While I understand your wish/intent, do not forget that you are likely to find a compromise between a number of different constraints. Thus, do not discard the CZ85mm f1.4 as an option, because 85mm is possibly the longest focal length at f1.4 on the market, irrespective of the brand and manufacturer..
Another direction could be to move your camera (and lens) closer to the jet. I do not know what type of jet and what liquid you use. In some cases, it might not be possible for many reasons. But.... any photographer working with prime lenses know that "your feet are your zoom" .
Hope it may assist. Other might have further good advice.

[GUB]

As in normal photography you can focus closer simply by adding extension tubes between the lens and mount.

[wadge22]

There is the Irix 150mm Macro, which comes in K mount as well as other mounts.
I initially got the impression your camera doesn't use K mount, but some of the other replies relate to K mount lenses so I figured I would chime in with that one.