8mm Forum: Projector questions

This is topic Projector questions in forum 16mm Forum at 8mm Forum.

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Posted by Dave Cragg (Member # 401) on September 04, 2011, 10:59 AM:

Hi All,
I've been into 8mm for a while and am now looking into getting into 16mm.

I have little room to move my projector backwards or forwards so I really need a projector with a zoom lense to fill my screen (distance to screen approx 11ft, screen size approximately 5ft by 3.5ft. My question is twofold;

1/ Why do most 16mm projectors seem to come with a fixed rather than a zoom lense, when the opposite is true for super 8 projectors?

2/ I've seen a few zoom lense convertors for sale which screw onto the existing fixed lense; would the use of these affect the sharpness or the brightness of the projected image?

Thanks very much for your help,
Dave

Posted by Martin Jones (Member # 1163) on September 04, 2011, 11:26 AM:

I've never used a "zoom attachment" so cannot speak for reduction in sharpness. But it is a definite fact that the screen brightness will be inversely proportional to the picture size (AREA!).
In other words, make the picture twice the width and the brightness is one quarter (plus any loss from the lens absorption).
Martin

Posted by Jean-Marc Toussaint (Member # 270) on September 04, 2011, 03:10 PM:

I haven't seen much loss in sharpness with zoom converters, but a slight loss of light, yes. Considering your screen size, this shouldn't be much noticeable. the zoom factor is most of the time 0.8-1.25x (transforming a 50mm lens into a 40-60mm zoom lens).
Most projectors come with a 50mm primer lens, primers are better for resolution and brightness as the light travels through fewer optical elements. But it's not too difficult to find a zoom lens for a 16mm projector.
At your throw, a 25mm lens would fill your screen size.

Posted by Claus Harding (Member # 702) on September 04, 2011, 04:31 PM:

Exactly,
A prime 1-inch lens would do the job with less light loss.

Claus.

Posted by Dave Cragg (Member # 401) on September 04, 2011, 05:22 PM:

Thanks all for your help and advice.

Dave

Posted by Jean-Marc Toussaint (Member # 270) on September 05, 2011, 02:46 AM:

Thank you Claus for the conversion [Wink]

And for those who want to figure out their screen size vs lens size needs, the formula is pretty simple:
F = h x D / H
Where F is your lens focal length, h is your frame height (in 16mm, it's 7.49 mm or 0.294 inch), D is your throw and H is your screen height.
I have programmed a series of spreadsheets on my smartphone that do the job fairly quickly (pretty convenient when doing outdoor projections).

Posted by Norman Allan (Member # 2410) on September 14, 2011, 01:51 PM:

Here's a chart showing different lenses, projector throw and screen sizes.

Posted by Wayne Tuell (Member # 1689) on September 14, 2011, 04:05 PM:

http://paulivester.com/films/projector/throw.htm

Posted by Dave Cragg (Member # 401) on April 06, 2012, 06:12 AM:

Hi All,
thanks for your answers.

I purchased a 25mm lens, albeit not one manufactured for my Eiki or Bauer but within a sleeve that allows it to fit both my projectors.
My problem although I'm reasonably happy with it, it still doesn't fill the screen!

It's certainly a lot better than my other lenses but is only filling 50" of my 57" screen (I can fill this with my main Super 8 projector no problem). My throw is a maximum of 12' and using the formula that Jean-Marc supplied a 25mm lens at that throw should fill the screen. I've checked my measurements and calculation several times (7.49mm x 3660mm/1100mm = 24.92mm).

This is probably a daft question but would the fact that the lens diameter is smaller than one specifically made for Eiki/Bauer projectors reduce the image size?

So is the solution that I should purchase a 25mm lens specifically 42.5mm in diameter?

Thanks,
Dave

[ April 06, 2012, 04:53 PM: Message edited by: Dave Cragg ]

Posted by Jim Schrader (Member # 9) on April 06, 2012, 10:16 AM:

this seller on eBay occasionally sells 16mm lens keep checking or add him as a favorite seller i bought one from him years ago and love it.
http://www.ebay.com/sch/ohw/m.html?_nkw=&_armrs=1&_from=&_ipg=50&_trksid=p3692

Posted by Wayne Tuell (Member # 1689) on April 06, 2012, 11:23 AM:

Dave, I think I understand your question. The barrel size should not change the image size. A 25mm lens with a 1" barrel should have the same image size as a 25mm lens with a 2" barrel.

On your 12' maximum throw distance. Is that front of screen to front of lens?

.625" Lens:

Throw in ft. Width in Inches Height in Inches
5 36 27
6 44 33
7 51 38
8 58 44
9 66 49
10 73 55
11 80 60
12 88 66
13 95 71
14 102 77
15 109 82
16 117 88
17 124 93
18 131 98
19 139 104
20 146 109
21 153 115
22 161 120
23 168 126
24 175 131
25 182 137
26 190 142
27 197 148
28 204 153
29 212 159
30 219 164
31 226 170
32 233 175
33 241 181
34 248 186
35 255 192
40 292 219
45 328 246
50 365 274
55 401 301
60 438 328
65 474 356
70 511 383
75 547 410
80 584 438
85 620 465
90 657 492
95 693 520
100 730 547
Top

1.0" Lens:

Throw in ft. Width in Inches Height in Inches
5 23 17
6 27 21
7 32 24
8 36 27
9 41 31
10 46 34
11 50 38
12 55 41
13 59 44
14 64 48
15 68 51
16 73 55
17 78 58
18 82 62
19 87 65
20 91 68
21 96 72
22 100 75
23 105 79
24 109 82
25 114 86
26 119 89
27 123 92
28 128 96
29 132 99
30 137 103
31 141 106
32 146 109
33 150 113
34 155 116
35 160 120
40 182 137
45 205 154
50 228 171
55 251 188
60 274 205
65 296 222
70 319 239
75 342 257
80 365 274
85 388 291
90 410 308
95 433 325
100 456 342
Top

Posted by Wayne Tuell (Member # 1689) on April 06, 2012, 11:25 AM:

The link Jim gave is for Omer, he is the king of lens work around needs. IF it can be done, he has it made.

Posted by Adrian Winchester (Member # 248) on April 06, 2012, 01:26 PM:

As a 12.5mm lens would make the picture far too big, finding something ideal will be a challenge. If you can't find a zoom converter to use on your lens (and even if you could, you may well find uneven focus with such a short throw) your only option might be to make your screen smaller!

To answer your original question, most 16mm projectors were probably sold without zooms because they were for more professional use in larger venuues where there could be more flexibility in terms of projector position - or in a more permanent situation, users had a range of different prime lenses they could buy. Considering that the RRP of a new zoom lens in more recent times would be over £400, anyone buying a 16mm projector who didn't need a zoom would have been grateful to have avoided having to pay extra for one. However, Bauers always seem to have zooms, so were probably an exception.

Posted by Dave Cragg (Member # 401) on April 06, 2012, 04:56 PM:

Thanks All.

wayne, yes, the 12' is from the front of the lens rto my screen (measured by a sonic tape measure, and that really is my maximum throw unless I stick the projector in the curtains!

All the varous charts suggest that a 1" (25mm) lens ashould do the trick, but it doesn't.

Dave

Posted by Wayne Tuell (Member # 1689) on April 06, 2012, 06:29 PM:

two options:
#1 use a filmovara type lens. You will suffer from picture not being 100% sharp and not as bright. Overall quality is OK.

#2 find a 5/8" or 1/2" lens and move the projector closer to the screen.

Those charts/figures are a bit flawed too. I just tested several 25mm lens, all of them give me 58" - 60" at 14' distance. It should be around 64" wide according to the numbers.

B&H small barrel 58"
Somco small barrel 59"
unmarked small barrel 59"
B&H large barrel 60"

I'd say your lens is right in the ballpark for size at 12' throw.

Posted by Dave Cragg (Member # 401) on April 07, 2012, 04:25 AM:

Thanks Wayne,
so it's not just me; the charts I've seen are wrong!

I'll try and obtain a 22mm lens.

Dave

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