Fast, short focal distance, large area lens with short regis

[CuriousOne]

ter distance available?

Hello, have no idea if this is a correct place to ask....

I need a lens, with the following properties:

Equiv. focal distance 20-40mm
"frame" size - circular at least 60mm
Aperture - faster is better
Register distance - 8-20mm
Flat field is a must

Image quality is not important at all, since this will be used for illumination purposes (stencil theatre).

The best what I was able to get is the projection tv lens (They usually are F0.95/78mm, register distance is about 10mm, they cover 70mm area). The bad is, that they mostly are in 70-80mm equiv. focal distance, which means they need to be far from the wall, to provide bigger coverage.

Any ideas?

[kansalliskalaCafe]

I'm not en expert in optics but I think you need something that looks like a crystal ball?

[CuriousOne]

Yes, except that crystal ball has curved field of view, while I need flat one

[kansalliskalaCafe]

good luck!



http://toothwalker.org/optics/vignetting.html

[kds315*]

[kds315*]

On 2nd thought, how about an aspheric condensor of suitable short focal length?
Seen such as surplus items on ebay, are very fast (<f1.0), image quality is acceptable.

[CuriousOne]

Yes, that would be great, how it is called properly?

[calvin83]

Klaus has already give the proper name: aspheric condenser
http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=3835

[CuriousOne]

I even got one from friend, and tested already

But it is from microscope, so it covers quite limited area:

http://i.imgur.com/Ups5HQh.jpg

But results are OK:

http://i.imgur.com/ZCCGchQ.jpg

(disregard blur, that is bokeh).

[kds315*]

[CuriousOne]

Thanks for suggestions.

I've checked my lens inventory, and as I can see, I have huge lot of these "condenser" lenses lying around. Some are so extruded, that they look like half of the lemon. I've already tried them, but the problem is, that image projected with them, has only center sharp - edges are very stretched and out of focus.

[Gerald]

[CuriousOne]

Yes, i mean back focus distance.

Currently my "setup" looks like this - left to right


(studio strobe) (ground glass) (stencil cutout) (lens) (wall)

basically, I want to build a simple "slide" projector, but which will be able to output large size images, being at short distance from the screen.

and short "register distance" is due to fact, that lens is heavy, and it attaches to strobe head, so I don't want it to introduce too much load. And save space, too.

[Gerald]

[CuriousOne]

Please check this photo. If lens is too far from strobe, it will put excessive weight on it.

[visualopsins]

[Gerald]

I do not know the weight of the Zeiss 38mm Biogon, but I would estimate it to be something around 500g, what does not seem excessive. Anyway, what is the difficulty in making a support arm for the lens, so as to not put a strain on the strobe?

[CuriousOne]

The aim is to make this attachment as simple to use, as plain snoot or barn doors.

[Gerald]

[DConvert]

If it's just for lighting would a Fresnel lens work?
These are available in large diameters, but are still lightweight...

[CuriousOne]

Yes, already ordered couple of them too, will see how it works.

[Gerald]

[CuriousOne]

Not kidding. Because without flat field, stencil edges won't be defined on projected image circle.

This all started, when I saw Broncolor Pulso Spot 4 in action. I was very impressed. You can check some examples here:

http://www.bron.ch/broncolor/products/lamps/showproduct/optical-snoot-150-mm-for-pulso-spot-4/?cHash=127e772820a437a01a9364c9db9eec58

Then I went online and checked prices.

$10000 price tag (for kit with lens and generator), impressed me even more.

I googled for cheaper alternative, and found so called "optical snoot", made by chinese. $300

I thought that price is still high, and task should be pretty doable.

In less than 2 hours I have workng prototype on hands.

[Gerald]

B&H sells the Broncolor Optical Snoot for Pulso 4 Flash Head (6"/150mm). The "thing" weighs 1.78 kg and costs $4,176.76. The dimensions are 180 x 230 mm. Obviously it is not a toy to be improvised with some cheap lenses in a few hours.

[CuriousOne]

Yes, and you need flash head and generator also

Here's much cheaper alternative:

http://www.amazon.co.uk/Falcon-Eyes-FEA-OST-2-Optical-Snoot/dp/B00HU02I7G