8mm Forum: Eiki/Elf 25mm lens image size

»	8mm Forum » 16mm Forum » Eiki/Elf 25mm lens image size

UBBFriend: Email this page to someone!

Author

Topic: Eiki/Elf 25mm lens image size

Mark Todd
Film God

Posts: 3846
From: UK
Registered: Aug 2003

posted March 13, 2009 07:35 PM

Hi can someone please rell me what the picture would be across the top at 10 feet.
Many thanks Mark.

ps looking for one by the way.

| IP: Logged

John Hermes
Expert Film Handler

Posts: 139
From: La Mesa, CA, USA
Registered: Nov 2008

posted March 13, 2009 09:23 PM

In the back of the Elmo CL instruction manual there is a projection image and image size chart. It is in meters, but at three meters (pretty close to 10 feet),with a 50mm lens, the image width is 0.6 meters. Accordingly, with a 25mm lens, it would be 1.2 meters, or just under four feet wide. It would probably be almost four feet on the nose at 10 feet, since three meters is about 9.75 feet.

--------------------
John Hermes

| IP: Logged

Hugh McCullough
Expert Film Handler

Posts: 156
From: Old Coulsdon. Surrey. UK
Registered: Oct 2006

posted March 14, 2009 05:13 PM

Mark

The picture size at a 10ft throw using a 25mm lens would be
3ft 9ins X 2ft 10ins.
Information gleaned from www.cinephoto.co.uk/amazing_film_facts.htm

--------------------
EIKI Ex 6100 xenon machine.

| IP: Logged

John Whittle
Jedi Master Film Handler

Posts: 791
From: Northridge, CA USA
Registered: Jun 2003

posted March 14, 2009 06:04 PM

FWIW there is a simple way to compute this:

width of aperture x 1/focal length x distance = width
(use same units in all measurements inchs or millimeters)
for 16mm:

.380 (width of 16mm aperture x 1/1 (1 inch lens) x 10 feet = 3.8 feet or 3 feet 9.6 inches.

You can revise the formula to figure distance for width, etc.

A word of warning on lenses shorter than 2 inches (50mm).
1. Usually the fastest forumla is the 50mm lines (i.e. f/1.2)
2. The best field sharpness and contast is usually with the 50mm lens
3. Shorter lenses have less depth of field such that focusing is much more critical and projector to lens alignment must be perfect in all directions (centering, left to right and top to bottom).
4. Shorter lenses are generally a "slower" design such as f/2.5
5. Shorter lense usually don't have the snap or contrast of the 50mm lens.

Why? Because they spent all the time and money on the development of the 50mm lenses which progressed rapidly in the 60s and 70s. The designs of the shorter lenses for 16mm have basically been unchanged since the 50s.

Also be aware that there are people that mount 8mm lenses in sleeves to fit 16mm projectors and those lenses don't have the coverage and will often vingette the edges of the picture.

And finally ... if you use a scope adapter lens, using a prime lens of less the 38mm will be problematic in getting a picture without the image being vingetted by the inside of the scope lens and again all those warning about focus are just 2x more important with a scope adapter.

John

| IP: Logged

Raj Patel
Junior
Posts: 14
From: South East, UK
Registered: Aug 2008

posted March 26, 2009 03:38 AM

I've got an original EIKI one which i found at foster films last year, i think they still have one. As stated good for size but definitely be aware of the loss of contrast and sharpness, i mainly use the 50mm still.

| IP: Logged

All times are Central

Printer-friendly view of this topic

UBB.classic^TM 6.3.1.2