This calculator can be used to estimate various combinations of components in a projector.
The units can be changed by clicking on them. (mm, M, inches and Feet)
To find a certain value click on the checkbox next to the textbox and it will turn green. By changing one of the other textboxes the green selected textbox will display the result. For example if you have a 15” LCD and a 320mm FL triplet and you want to get a 100” screen then click the screen distance checkbox to turn it green then change the screen size to 100”. The green screen distance textbox will give you the required distance that the triplet will need to be from the screen. Or you might want to see how much bigger a 17” LCD would make the screen than a 15” LCD at the same distance. Select the screen size checkbox and then change the LCD size from 15” to 17”.

The FL of the triplet as a rule of thumb can be considered at the centre of the lens but this is not always the case. It all depends on the various elements in the triplet; it could be closer to the rear or closer to the front of the lens.

The value that is entered in the LCD size textbox will be the same type as the screen size textbox or vis versa. For example if you enter the LCD diagonal the result in the screen size textbox will also be diagonal. If you enter the LCD width then the screen textbox will also be width.

Warnings and messages:
If you enter a value in a textbox that can’t be used by the calculator then all other textboxes will turn red to indicate that a result is not possible. For example a zero value will cause an error. A message will pop up in the bottom right corner to indicate other types of errors. If in split then entering a value into the triplet FL that is less then the gap will cause an error because the triplet can’t be moved any closer than the physical position of the front fresnel.
You will probably notice that the labels above each textbox may sometimes turn red; this is just a warning that the value in that particular textbox is larger than what is being displayed. Use the arrow keys if you want to see the entire value.

Let me know if you find any bugs.
Please enjoy.

DJ

Bugs:
If you get a “Runtime Error ‘13’ Type Mismatch” message you will need to go into Regional And Language options in XP and choose English

Hey DAZZLA,
Is there a (free)way to use this on a mac?
Thanks in advance for any advice.

yoshua, if you have OS X, you might try the wine project. It's a windows emulator, sort-of, for unix and its relatives, and I think it would work also under OS X.

EDIT: I forgot the link...

http://www.winehq.com

Thank you

Dazzzla,

This calculator is AWESOME! The theory is finally making sense to me, as I'm able to play with the focal numbers and determine what has the greatest effect to my intended output. You really did a terrific job!

Is it, however, possible to get the field outputs limited to two decimals? If not, that is OK, it would just makes it easier to revise the numbers when inputted, (especially if your jumping around from field to field like me).

All in all this is the best tool I have used. Being able to switch from Split and Unsplit Optics, while keeping the same numbers in place is a nice feature for comparison sake. And being able to switch to the different fields for review, has helped me explore other available options that I had not even considered.

Just an all around GREAT JOB!

Fulcrum

Thanks.
Unfortunately I can’t reduce the decimal places easily.

DJ

It is still an EXCELLENT spreadsheet. For a while I was not sure if I should buy the 550 or 650 fresnel to go with my 18 inch opaque triplet. NOW I KNOW that either will work, but the LL 650 fresnel will probably work better as suggested by others.

Great Job!

Fulcrum

Thanks for the great program. I had an idea that may be a nice simple extra. I was wondering if you could have a radio check fro the different standard triplets ie the pro and standard lens. I may save some people time for looking that up in the forms and could be useful for people trying to decide on a setup. Thanks again.

Brad

Hi DAZZZLA, great program, but please please spend some time on that regional setting bug.. it's really quite annoying to keep changing the regional settings on my own pc, and i cant even change the regional settings on the computers on my faculty, wich makes the program unusable over there..

The latest version shouldn't raise this error anymore. I tried a few different nationalities and it seems to be working let me know how it goes.

DJ

Thanks for the tool! I have a question though. When referencing the LCD size and projection size, is it referring to the diagonal or the width? I would guess the diagonal, just making sure.

Thanks again,

Ruhk

The value that is entered in the LCD size textbox will be the same type as the screen size textbox or vis versa. For example if you enter the LCD diagonal the result in the screen size textbox will also be diagonal. If you enter the LCD width then the screen textbox will also be width.

Great DAZZZLA, I think it IS working now. I have to try it on my work as well, but at least here all go's smooth

Thank you for the great program it has simplified many things in my project. I do have one question though - re the split fresnel configuration: which fresnel is it seeking the focal length of? Thanks.

hi! this is a really neat program! just one question. in the split mode what are the units of Virtual LCD Height, Virtual LCD Distance and also, what do these number represent? Thanks!

The virtual LCD height should really be called just virtual LCD, I’ll fix that the next time I update it.
The front fresnel magnifies the LCD so it appears larger than it actually is. If you look though a lens at your hand it will appear larger to your eye. The fresnel does the same thing to the LCD and the triplet takes the place of your eye.
The virtual LCD height is the size of the LCD that the triplet is focusing on through the front fresnel. The virtual LCD distance is how far back the LCD appears to the triplet through the front fresnel. The fresnel magnification is the ratio between the actual LCD size and the virtual LCD size.

DJ

if i want to hand made do the calcs. How i do it? where can i get the "formula" for that?

thank you very much for post useful information
it so useful to calculate with somne certain data
thanks again

Great program. I downloaded a rev1.43 and it has a bug however. If you go to split, select the screen size radio button, and then put 8 feet in the screen distance, I get .0289771... feet. When I try to select this textbox and scroll left, there are no more digits to show. I suspect the the display buffer overflows with all the decimal digits. What language did you write this in. I may be able to help. Otherwise its a great tool. Thanks alot!


BM

Thanks for the bug report.
It’s written in VB and the problem happens because text boxes aren’t really good at dealing with numbers especially with open-ended algorithms. I will get around to re-writing it eventually .

DJ

Is there anyone who can pass on a MAC OSX version or the raw formula so I don't have to download "wine HQ" or something similar?

Thanks, I appreciate it!

Here's a link on this board for a PHP focal calc - should work in your web browser:

PHP Focal Calc

FANTASTIC.

thanks!

Great calculator! I'm interested in the math behind the split version. Any chance you could explain the calculations?... to get a better understanding I'd like to be able to the math myself at least once. I think I have a grip on the virtual image/object projected by the fresnel...my trouble may be the math going through the triplet. Cheers.

if you run this on windows server 2003 or windows vista / longhorn

you will need to place msvbvm50.dll in your window/system32 directory

get it from me here http://computercowboy.biz/msvbvm50.zip
or from dll-files.com here http://www.dll-files.com/dllindex/pop.php?msvbvm50

If anyone wondered this calculator program works perfectly with Wine. I ran it on my Linux laptop, you just need to be sure to have the msvbvm50.dll available (easiest is to just put it in the same directory as the .exe)

It makes much more sense than the php calculator, nice work.

Why doesn't changing the Field Fresnel FL affect the LCD distance to the Triplet?

If the Fresnel gap is 20mm in front of the LCD and the FL is 220, shouldn't the distance be somewhere around 240mm?

LCD is 17" diagonal or 14.5" wide, using the Pro triplet in the calc so 500mm FL, throw is 11.9', screen is the calculated value. I was playing with different Fresnel focal lengths and gaps to see how they would affect the LCD distance and it doesn't seem to matter.

Any able to help me understand? Thanks in advance.

It's the triplet's focal length that matters in that distance, as I understand it.

The focal calc only uses the FL of the front fresnel for calculating the virtual LCD image. It’s up to you to make sure the front fresnel’s FL is long enough to match the triplet. You say that you are using the pro triplet but using a 220mmFL fresnel. The distances will be calculated to project an image but 220mm is too short to direct the light into the triplet.

Hmmm, is that because the angle with which it focuses is too wide to enter properly into the aperture of the triplet? Because what I'm thinking is if you used the 220 you can shorten the length of the projector design.

PS I'm not using any real parts at the moment I'm still trying to come up with a working design. I appreciate any and all input you can give based upon your experience.

Thanks in advance.

Hmm I think I figured it out. You want the field fresnel to have nearly the same focal length as the triplet's FL. I guess what's throwing me off though is reading posts about people using the 330mm field with the 500mm triplet or the 650mm field with the 500mm triplet and I figured that as long as the field is narrowing the image from the LCD down to a point it didn't matter what the FL of the triplet was as long as the light is entering the aperture and the proper magnification to match the desired screen size was happening.

I am new to all this, but have a question. Sometimes I think too much. At any rate, I am wanting to design a projector using a 3.5 inch lcd screen. Using the Focal Length Calculator, I am baffled a little bit. The LCD distance isn't changing much, and I end up with a ~31" projected image with the screen distance of ~9.4 feet. Being new to this, my question is, if the angles stay the same (the light blue protion of calculator), if I go with a smaller screen, that would place the LCD screen much closer to the Triplet, maintaining the same angles, and therefore giving a much smaller box. Because the angles are the same, the screen distance and screen size should be the same as what is shown for a 15" LCD set up. Is this thinking accurate?

The angles aren't real in the program, they are just there to look pretty. The true angle for a 500mm triplet is almost half of a 275mm triplet.

If that's not what you meant, maybe this is:

You can't move the lcd halfway to the triplet on the basis of it being a half sized lcd. It has to stay at the same place as the original lcd. The distance is governed by the focal lengths of yer lenses. Disobeying these you will lose focus.

Are you using the varifocal triplet? 275mm to 325mm fl. And a 220mm or 330mm front fresnel?
with 275mm triplet, 220mm front fresnel, and a 3.5" screen, you can get a 5' screen from 15' away.
if you used a 7.1" screen, though...

My situation is like this. From a distance of 350 centimeter I want to have a projection wich is 180 centimeters wide, using a 15 inch tft screen.

Now, I am looking for suitable lenses and I want to calculate the distances between the lenses so that I know how to build my projector. The problem is, I can't get this right...

Here's my calculation:

1 inch = 25,4 millimeter = 2,54 centimeter
1 feet = 12 inch = 304,8 millimeter = 30,48 centimeter

So I can begin to fill in the variables I know:

LCD:
15 inch

Fresnel Gap:
Unknown. I want to calculate this so I know how to build my PJ.

Fresnel FL:
Let's assume I use the lumenlab s15 lens kit: 317mm. The other fresnel is 220mm. Why are these not the same?

Triplet FL:
Lens kit lumenlab: 320mm.

LCD distance:
Unknown. I want to calculate this so I know how to build my PJ.

Screen distance:
350 cm = 137,7952 inch = 11,4829 feet

Screen:
My 15 inch tft screen has the next measurements: 304 mm (H) x 228 mm (V) / 12.0" (H) x 9.0" (V). First I need to convert the 180 centimeters to inches: 180 / 2.54 = 70.866 inch. This is however the width-size, with this program I need the 'vertical size'. So, knowing that my tft is 12 inch by 9 inch: 9 / 12 = 0.75. 0.75 x 70,866 inch = 53,1495 inch. So 53,1495 inch is the vertical screen value, right?

I start filling in the values. But is seems now, whatever I fill in using these lenses, I can't get the screen distance to 11,5 feet!

Can I conclude these lenses are not suitable when I want a projection width of 180 centimeters when I project from a distance of 350 centimeters?

Well I think I've got it sorted out (with some help). I think I need to use a pro lens (500f) to get my measerments, see the calculation below. Only question is: Using a pro lens as objective, should I use other fresnels too, to get all quality out of it?

You will have to use the pro fresnels or simular. 317mm is way to short.

DJ

Could you tell me why? The calculation gives a 'good' result..?




@ answer DAZZZLA below:
Thanks alot, I'll read it and become a bit wiser again .

Here you go.http://www.lumenlab.com/forums/index.php?s...st&p=205574
And have a read though the this.
DJ

Look at this! Same values, different results at projection size (slight). The programs are the same, however calculated at different computers but that shouldn't matter right.

Anyway. To get my +/- 200 centimeters projection in width from a distance of 350 centimeters, I have to use the pro lens with 500fl.

In that case: what should be the minimum focal lenght of the second fresnel? I saw there are fresnels with 550 or 650 for example but these are all too big for my 15 inch projection.. Should I cut these? Should be very dangerous in my opinion. It must be important that the light goes straight to the middle and of course the fresnel shouldn't be damaged at all.

Knowing a lot of people use the standard lenses, they all must have a very large projection or the distance between the beamer and the projection should be small. Is that an accurate conclusion?

yepp. standard lenses have designed for small panels and shorther throws for the 100"-120" projected screen diagonal. the pro/HD lens is for large® panels and for having 100"-120" projection diagonal but from 3.5-4m

HELP When I try to run the FOCALCALC program on my widows 2000 os.
I see a black dos like window for a second, then nothing?
I am a mac guy. Tried the wine program, but I do not have an intel mac.
I need to do some calculations. HELP

Is Focalcalc written in real basic?
Do I need that on my windows machine?

Dave Moon


It works now thanks

Hi DAZZLA,
Just a short note to say Thank You for your work in building this calculator. I found it EXTREMELY helpful to be able to insert different lenses & "see" the results. You are the MAN!!!
Thanks Again & Best Regards,
Jon

Dazzla,

YOU ARE A TOP BLOKE

i am a "noob" to the whole DIY projector scenario, but just your program alone has helped me understand so much more on how to set up/build one of these things. one of the handiest things i've seen so far on this subject.

Thanks so much,

Strat





I feel like i'm diagonally parked in a parallel universe!

I find I have less errors if I place the dll in ~/.wine/drive_c/windows/system32/

Doesn't crash on me when I do it this way.

Cheers.

Dazz, is it possible for you to post it up in a spreadsheet? that way i can print out a huge table of LCD to triplet distances that correspond to different triplet to screen distances, for easy calibrating when the PJ moves around to different rooms.

thanks!

Thank you so much for creating this! It worked perfectly on my linux laptop as well with wine.

This is probably a dumb question, but for the LCD size, do I enter the diagonal size, or the height or width (depending on how you look at the picture)?

@DAZZZLA: I've read that piece of text over and over again, but I just can't figure out how the program can possibly know that I'm entering a diagonal or width value? Testing it however show that it does... but somehow that is beyond me

I have a little problem (see attachment)
If I enter all the desired values, the calculator shows that the LCD distance would be 380mm, the fresnel I'm using has FL 317 and the Triplet has FL 315... isn't the LCD distance to big then?
I think i remember to have read somewhere that the LCD distance should be somewhere around 320 or 340mm.

Am I correct, and if so, how can I fix this?

Greetz,
Grimmie

It doesn’t know the difference. If you enter the diagonal of the LCD then it will calculate the diagonal of the screen. If you enter the width of the LCD it will calculate the width of the screen. If you enter the height of the LCD it will calculate the height of the screen.



The LCD distance will never be the same as the triplet’s FL. Read this to understand it a bit better.
The fresnel’s FL on the other hand isn’t matched very well and this will happen with almost all the DIY projectors you’ll see here. With the distances you have used, the correct fresnel FL should really be about 360mm (LCD distance - fresnel gap). It can be fudged though by moving the lamp closer to the rear fresnel so the light will refracted further forward so it can pass through the triplet. This isn’t the best approach but we have to use what we have on hand.

DJ