LP715
IR Longpass Filter

The single substrate LP715 Longpass Filter essentially blocks all light considered to be part of the visible spectrum while passing all near infrared wavelengths. However, since your eye is slightly sensitive to near infrared light, it is possible to visibly detect the small amount of red light that is transmitted through this filter.

Color longpass filters are used with monochrome cameras to aid in increased contrast and resolution. As the name implies, these filters block UV and shorter visible wavelengths, and pass longer wavelengths of light. Except in those few cases where an IR blocking or other shortpass filter is incorporated into the camera/sensor, for the most part MidOpt will recommend the use of one of our broad color bandpass filters (whose designs incorporate these longpass filters) over these color longpass filters alone.

The explanation for not recommending color longpass filters is simple. Color filters are usually specified for use with similar monochromatic LED or laser diode colors in order to block ambient light. When looking at the spectral response of most CCD/CMOS camera sensors, it can be seen that they typically have excellent deep red and near-infrared sensitivity. When superimposing any longpass filter's transmittance curve over a camera's spectral response curve, it becomes evident that approximately half or more of the unwanted ambient light – all of the longer wavelength light – is not being blocked by the longpass filter.

Logic seems to dictate that if it makes sense to employ a longpass filter to block some of the ambient light, it makes even more sense to spend what amounts to a few dollars more to block the rest of it. In comparative testing where the difference between a longpass and a bandpass filter may not seem to be dramatic, the bandpass filter will also provide insurance for what might happen at some point in the future... an extremely LOW COST and READILY OBTAINABLE type of insurance. By blocking almost all of the unwanted light, the effects of any change in ambient or introduced lighting that often occur at a later date can be nullified.

The numbers of bandpass filters currently sold far outnumber the quantity of longpass filters that MidOpt sells, by almost 20:1. Longpass color filters are made available for those customers who are more familiar with them and continue to request them.

Instead of a LP715 filter, a better alternative might be a BP800 filter.

Download Excel Spreadsheet with data and curve for this filter.

Examples of filter effectiveness.

Standard Threaded Mounts:
We offer standard filter sizes from stock – 22.5mm to 62mm – for same- or next-day shipping. Larger filters – 67mm to 105mm – are made to order and are normally not returnable.

Click here for PDF drawing of standard mounts

Slip Mounts:
If your lens does not have threads for mounting a filter, Slip Mount adapters are available. Slip Mounts can attach a regular filter to a lens or attach a very large filter to accommodate a wide angle lens. Please call to order Slip Mount adapters.

C-Mounts:
3mm thick threaded mount for adding a filter between lens and camera
Click here for PDF drawing of c-mounts

Transmission chart (typical)
Passes 720nm and above
Absorbs 710nm and below

1100
1090
1080
1070
1060
1050
1040
1030
1020
1010

1000
990
980
970
960
950
940
930
920
910

900
890
880
870
860
850
840
830
820
810

800
790
780
770
760
750
740
730
720
710

700
690
680
670
660

96.22
96.24
96.28
96.27
96.28
96.29
96.32
96.26
96.32
96.33

96.34
96.37
96.45
96.45
96.50
96.49
96.47
96.60
96.65
96.69

96.72
96.77
96.75
96.85
96.88
96.94
96.94
96.92
96.96
97.01

97.10
97.08
97.00
96.30
95.82
94.42
91.38
84.28
62.91
26.05

3.27
0.21
0.02
0.00
0.00

650
640
630
620
610
600
590
580
570
560

550
540
530
520
510
500
490
480
470
460

450
440
430
420
410
400
390
380
370
360

350
340
330
320
310
300
290
280
270
260

250
240
230
220
210

0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00

0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00

0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00

0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00

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0.00
0.00
0.00
0.00