8mm Forum: Lens question :)!!!

This is topic Lens question :)!!! in forum 16mm Forum at 8mm Forum.

To visit this topic, use this URL:
https://8mmforum.film-tech.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=5;t=001401

Posted by Elyas Tesfaye (Member # 3356) on February 27, 2016, 08:29 AM:

Hi all,

what would "zoom convertor 16- 0.75 ~ 1.25x" mean [Smile]

? Thanks

!!!

Cheers,
Elyas

Posted by Maurice Leakey (Member # 916) on February 27, 2016, 08:43 AM:

A zoom converter screws into a basic lens and alters its focal length. This is achieved by rotating its front element.
The figures indicate its ratio range of plus or minus 25%, i.e., with the standard 2" lens it will give a range from 1.75" to 2.25".

Posted by Elyas Tesfaye (Member # 3356) on February 27, 2016, 09:14 AM:

Hi Maurice,

thanks a lot and can you please dumb it down for me, as I'm not that familiar with lenses... Lay man's terms, please [Smile]

!!! Like, for example, this lens is a good short/ long throw lens [Big Grin]

...

Cheers,
Elyas

Posted by Elyas Tesfaye (Member # 3356) on February 27, 2016, 02:04 PM:

Hi Maurice,

I should give myself more credit, I actually totally understand what you mean n thanks again [Smile]

!!!

Cheers,
Elyas

Posted by Elyas Tesfaye (Member # 3356) on February 27, 2016, 05:44 PM:

Follow up question, this would affect the f/... tho, right? N if so, by how much [Smile]

Posted by Paul Mason (Member # 4015) on February 29, 2016, 04:05 AM:

Hi Elyas,
Zoom converters for projectors do not change the marked F number significantly because they are mounted on the front. For example F1.4 stays at F1.4. Any actual change due to losses in the extra glass will be unnoticeable.

Posted by Elyas Tesfaye (Member # 3356) on March 02, 2016, 09:15 PM:

Hi Paul,

thank you so much [Smile]

!!!

Best,
Elyas

Posted by Dino Everette (Member # 1378) on March 22, 2016, 01:01 AM:

quote:
For example F1.4 stays at F1.4. Any actual change due to losses in the extra glass will be unnoticeable

This is not entirely true since the sheer act of enlarging the picture across the screen will actually cause the amount of light to change so, while the actual numerical F-stop won't be different, what it represents (which is the light output) will, so your f 1.4 will be more like an f1.6 at 1.25x

Posted by Elyas Tesfaye (Member # 3356) on March 22, 2016, 05:14 PM:

Hi Dino,

thanks a ton for the heads up, you sir, are awesome [Smile]

!!!

Best,
ET

Posted by Dino Everette (Member # 1378) on March 22, 2016, 10:52 PM:

Elyas - the easiest way to look at lenses is to think LESS IS MORE

so with "f" - the lower the number, the more light that comes through basically working your way towards an f 1.0

BUT sometimes in order to push more light through there is a sacrifice in sharpness, so an averaged priced lens at f1.2 might be easier to focus in razor sharp than a similarly priced f 1.0

same thing with "inches" or "mm" - a 1 inch or 25mm lens is going to throw a much larger picture in a shorter distance than a 50mm or 2 inch lens, but often at the cost of both the sharpness and the light output, so while your 2 inch lens might be an f1.2, there is a very good chance your 1 inch lens will be more like f1.6 and there is a very good chance you will also have a harder time focusing in you 1 inch f1.6 than you would your f1.2....

This is the main reason why most projectors come with a standard 2 inch lens, which is usually around f1.2 or f1.3

I have multiple lenses for each of the projectors I use regularly because depending on the circumstances sometimes I need to throw a big picture in a short distance, and other times I have a longer throw....Basically the goal is to fill whatever screen you are using so it looks as nice, clean and professional as possible.

Posted by Elyas Tesfaye (Member # 3356) on March 23, 2016, 02:19 AM:

Hi Dino,

thanks a ton for the heads up, you sir, are awesome [Smile]

!!!

Best,
ET

Posted by David Guest (Member # 2791) on March 23, 2016, 05:31 AM:

I have one for sale £25.00

Posted by Elyas Tesfaye (Member # 3356) on March 24, 2016, 10:04 AM:

Hi Dave,

an original EIKI zoom adjuster [Smile]

?

Best,
Elyas

UBB.classic^TM 6.3.1.2