CN100346188C - Continuous varifocus projecting lens for projector - Google Patents

Abstract

The present invention discloses a continuous zooming projecting lens for projectors, which comprises two fixed lens groups, a zoom lens group and two compensation lens groups. The present invention is characterized in that a diaphragm moves synchronously with the second compensation lens group and enables the present invention to be positioned in a telecentric light path of the image space in the entire process of zoom, so the image illumination uniformity is improved; the focal power allocation of each lens group is reasonable, and the present invention obtains the effects of having the advantages of compact structure, small size and good imaging quality and being applicable to portable projectors by selecting a structural style which is symmetrical relatively to the diaphragm; all the lenses are made of China glass, and the surfaces of the lenses are all in the shape of spherical surfaces, so the present invention has the advantages of low cost, easy processing, etc.

Description

Continuous varifocus projecting lens for projector

Technical field

The present invention relates to the optical system that a kind of projector uses, relate in particular to a kind of and the continuous varifocus projecting lens pixelized panels coupling.

Technical background

The application of projector spreads all over nearly all fields such as commerce, education, government bodies, family, projection lens is the important component part of projector, usually adopt with pixelized panels and be generally digital light valve, continuous vari-focus optics system as DMD, LCD, LCOS, GLV coupling, it mainly acts on is that light signal with on the digital light valve is amplified, and image projection to screen.Projector generally has higher resolution, 1024 * 768 (XGA) commonly used or 1280 * 1024 (SXGA) and thinner gray shade scale.In order to satisfy the request for utilization of projector, the optical projection lens that it adopted should be able to be realized following function: focal length changes within the specific limits continuously; Certain enlargement ratio is provided in whole zooming range; Projecting to by it in whole zooming range on the giant-screen is uniform as illumination; Very high transport function, resolution are arranged in whole zooming range; In whole zooming range, has higher aberration correction level, especially distortion and aberration.

The projection lens deviser of projector generally takes following technological approaches to make projector obtain the image quality that high resolving power is become reconciled: (1) projection lens adopts complicated version and special material; (2) adopt the aspherical optical element aberration correction.Yet above-mentioned approach all can increase substantially the cost of optical projection lens, and this is very disadvantageous concerning competing very fierce projector market.In addition, the processing more complicated of visible light wave range aspherical optical element.

Image illumination uniformity is an important indicator of projector.When the observer observed projection screen, even at the lens field edge everywhere, also requiring had enough brightness just can see data clearly; Therefore, the projection lens of projector need be designed to telecentric beam path in image space and guarantee that illuminance of image plane is even.In addition, all be provided with the prism group between projection lens and the digital light valve,, also require projection lens is designed to telecentric beam path for preventing to produce veiling glare.This has just improved the difficulty of system design greatly.

Chinese patent 97117606.X discloses a kind of and the Zoom projection lens pixelized panels coupling, doubly form by group, compensation group and correcting unit by becoming for this projection lens, in used about 10 lens of projection lens, have at least 3 lens to make by acryhic material, at least contain 4 aspheric surfaces, maximum aperture of mirror reaches 215.77mm, and distortion correction is to about 2.5%.Provided the Zooming-projection camera lens with lens correction unit in the Chinese patent 98807972.0, this camera lens is made up of 3 groups of about 9 lens, adopts acryhic material to make near one of screen, and two faces all are aspheric surfaces, and the camera lens maximum caliber is 185mm.Yet above-mentioned two projection lens have the following disadvantages: (1) optical element adopts Xiao Te glass and acryhic material to make, so price is more expensive, and vary with temperature with its shape of lens that acryhic material is made very obvious, to the bad adaptability of environment; (2) bore is excessive, and structure is not compact, can not be used for portable projector; (3) diaphragm in the projection lens is fixed, and the focal length of diaphragm back optical module changes, and projection lens can only guarantee that at most a position is to be in telecentric beam path in whole zoom process, other position all is in non-telecentric beam path, so image illumination uniformity is relatively poor.

Summary of the invention

The technical problem to be solved in the present invention is, for projector provides a kind of projection lens of continuous vari-focus, can both guarantee that illuminance of image plane has higher homogeneity on any position of this projection lens in zooming range.

Second technical matters that the present invention will solve be, the projection lens compact conformation that is provided, and can be used for portable projector.

For solving the problems of the technologies described above, the present invention includes two fixed lens group and three motion assemblies, the described first motion assembly is the first offset lens group, the described second motion assembly contains the second offset lens group and diaphragm and both and can be synchronized with the movement, and described the 3rd motion assembly is the Zoom lens group; Be arranged in order the first offset lens group, the second offset lens group, diaphragm, Zoom lens group between described first, second fixed lens group, first fixed lens group is positioned at projection screen one side, and second fixed lens group is positioned at digital light valve one side of projector; Described first, second offset lens group all with the focal power opposite in sign of Zoom lens group, do linearly when mobile along optical axis when the Zoom lens group, first, second offset lens group and described diaphragm are all done to move in the other direction along optical axis; Described diaphragm is on the combination front focal plane of the Zoom lens group and second fixed lens group in moving process all the time and satisfies the following equation of motion:

${\mathrm{<figure-callout\; id="3"\; label="dq"\; filenames="C20061004171000151.png"\; state="\{\{state\}\}">dq</figure-callout>}}_3=\frac{{(p_{45}+f_5)}^2-{{2\mathrm{<figure-callout\; id="4"\; label="f"\; filenames="C20061004171000152.png"\; state="\{\{state\}\}">f</figure-callout>}}_4}^{\&prime;}(p_{45}+f_5)}{{(p_{45}-{{\mathrm{<figure-callout\; id="4"\; label="f"\; filenames="C20061004171000152.png"\; state="\{\{state\}\}">f</figure-callout>}}_4}^{\&prime;}+f_5)}^2}{\mathrm{<figure-callout\; id="4"\; label="dq"\; filenames="C20061004171000152.png"\; state="\{\{state\}\}">dq</figure-callout>}}_4$

In the formula, p ₄₅Be the distance between the Zoom lens group and the second fixed lens group interarea, f ₄' be picture side's focal length of Zoom lens group, f ₅Be the object space focal length of second fixed lens group, q ₃Be the amount of movement of the diaphragm and the second offset lens group, q ₄It is the amount of movement of Zoom lens group; The oppositely mobile common counteracting of described first, second offset lens group is moved caused image planes by the Zoom lens group and is moved.

According to the present invention, the combined focal length of the focal length of described first fixed lens group, described Zoom lens group and the second fixing group lens combination satisfies respectively:

-2＜f ₁′/f′＜-0.9

1＜f ₄₅′/f′＜2

In the formula, f ₁' be the focal length of first fixed lens group, f ₄₅' being the combined focal length of the present invention's the 3rd motion lens combination and second fixed lens group when the big visual field, f ' is the focal length of the present invention when the big visual field.

Beneficial effect of the present invention is embodied in the following aspects:

(1) the present invention realizes focal length variations of the present invention by making the 3rd motion lens combination promptly become the motion of doubly organizing relative second fixed lens group, in the zoom process, diaphragm is to be synchronized with the movement with the second motion lens combination, and in motion process, be positioned at the combination front focal plane of the 3rd motion lens combination and second fixed lens group all the time, this has just guaranteed that the present invention is a telecentric beam path in whole zoom process, so at any zoom position, illuminance of image plane of the present invention is all very even.

(2) the present invention is by reasonably distributing the focal power of each lens combination, especially the combined focal length with focal length, the 3rd motion lens combination and second fixed lens group of first fixed lens group is limited in certain span, this had both defined maximum caliber of the present invention and total length, make the present invention have compact conformation, characteristics that volume is little, provide technical support for being applied to portable projector; Guaranteed also simultaneously that aberration of the present invention is easy to proofread and correct, can obtain higher image quality.

(3) the present invention has adopted the lens face type in five groups of lens and each lens combination to be sphere altogether, does not compare with adopting aspheric zoom system, pancreatic system, and version is comparatively simple, compares with adopting aspheric projection lens, and its processing, check all are easy to.In addition, all lens all adopt the most general the most cheap Chinese glass manufacturing, thereby, of the present invention with low cost, have the stronger market competitiveness.

Description of drawings

Fig. 1 a is the burnt location status synoptic diagram of the weak point of optical projection lens preferred embodiment of the present invention.

Fig. 1 b is the middle burnt location status synoptic diagram of optical projection lens preferred embodiment of the present invention.

Fig. 1 c is the burnt location status synoptic diagram of the length of optical projection lens preferred embodiment of the present invention.

Fig. 2 a is the distortion curve figure of optical projection lens preferred embodiment of the present invention when being in short burnt position.

Fig. 2 b is the distortion curve figure during burnt position during optical projection lens preferred embodiment of the present invention is in.

Fig. 2 c is the distortion curve figure of optical projection lens preferred embodiment of the present invention when being in long burnt position.

Fig. 3 a is the MTF curve map of optical projection lens preferred embodiment of the present invention when being in short burnt position.

Fig. 3 b is the MTF curve map during burnt position during optical projection lens preferred embodiment of the present invention is in.

Fig. 3 c is the MTF curve map of optical projection lens preferred embodiment of the present invention when being in long burnt position.

Fig. 4 a is the aberration curve figure of optical projection lens preferred embodiment of the present invention when being in short burnt position.

Fig. 4 b is the aberration curve figure during burnt position during optical projection lens preferred embodiment of the present invention is in.

Fig. 4 c is the aberration curve figure of optical projection lens preferred embodiment of the present invention when being in long burnt position.

Embodiment

The present invention is described in further detail below in conjunction with accompanying drawing and preferred embodiment.

Shown in Fig. 1 a～Fig. 1 c, the preferred embodiment of the present invention comprises two fixed lens group L1, L5 and three motion assembly L2, L3, L4.Be arranged in order the first motion assembly L2, the second motion assembly L3, the 3rd motion assembly L4 between first, second fixed lens group L1, the L5, the first fixed lens group L1 is positioned at projection screen one side, and the second fixed lens group L5 is positioned at digital light valve one side of projector.The focal power symbol of the first fixed lens group L1 is for negative, and it contains two simple lenses 1,2 and lens 3 and 4 cemented doublets that constitute.The first motion assembly L2 is the first offset lens group of this preferred embodiment, and it is a cemented doublet that is made of lens 5 and 6, and its focal power symbol is for just.The second motion assembly L3 contains the second offset lens group and diaphragm 14, the second offset lens groups are simple lenses 7, and the symbol of its focal power is for just.The 3rd motion assembly L4 is that the change of this preferred embodiment is doubly organized, and it is a cemented doublet that is made of lens 8 and 9, and its focal power symbol is for negative.The focal power symbol of the second fixed lens group L5 is for just, and it contains lens 10 and 11 cemented doublet and two simple lenses 12,13 that constitute.All lens of system adopt cheap home made materials to make, and do not conform to aspheric surface is arranged.The detail parameters of above-mentioned each optical element sees Table 1.When this preferred embodiment is placed on apart from the position of projection screen 2.25m, when Zoom lens group L4 when the direction of second fixed lens group moves, the big I of image changes to 0.820m * 0.615m by 1.0208m * 0.7656m, the effective focal length of this preferred embodiment changes in the 22.93mm-27.91mm scope, and the lens combination distance values during each zoom position sees Table 2.

Table 1 optical component parameter table (unit: mm)

Component Name	Part sequence number	Radius-of-curvature	Effective aperture (radius)	Vertex spacings	Material
						The first fixed lens group L1	1	60.95000	30	8.000000	ZLAF2_CHINA
164.82000	29	1.000000
			2	49.43000	24			3.000000	PK1_CHINA
18.96700	17.5	11.000000
				3	158.85000		17.5	2.500000		QK3_CHINA
17.70100	14.5	0
			4		17.70100		14.5	5.000000	ZF7_CHINA
21.48000	13.5	p12
				The first offset lens group L2	5		300.60000	11.5		7.000000	LAF5_CHINA
-15.88500	11.5	0
			6			-15.88500	11.5	3.500000	ZF5_CHINA
-180.30000	10.5	p23
					The second offset lens group	7	42.85000	10		4.000000	BAK4_CHINA
-47.10000	10	1.000000
			Diaphragm	14			INFINITY	8.5	p34
Zoom lens group L4	8	-25.88000			10	3.000000					ZLAF4_CHINA
			-21.39000	10.5			0
		9			-21.39000	10.5		4.000000	F1_CHINA
	53.95000		12	p45

The second fixed lens group L5	10	-125.89000	13	3.000000	ZF14_CHINA
						148.94000	14	0
		11	148.94000	14					6.000000	ZK3_CHINA
	-34.43000				15	1.000000
			12	75.27715			18	6.500000	LAF3_CHINA
	-102.18105	18			0.100000
				13		36.43707	18.5	5.300000		LAF3_CHINA
	103.85451	18

Relation (the unit: mm) of table 2 zoom position and lens combination spacing

The lens combination spacing	Short burnt position	In burnt position	Long burnt position
				p12	24.42505	19.64310	14.96332
p23	1.34077	5.07634	8.02094
				p34	10.19197	12.68304	15.64820
p45	5.60167	4.15692	2.92694

The present invention utilizes the reversible principle of light path when carrying out the optical path-tracing of projection lens, will be by projection screen to the distance the first fixed lens L1 as object distance, the second fixed lens L5 to the distance between the digital light valve as image distance.Usually in projector, often all total reflection prism can be set between projection lens and the digital light valve, this just extended the greatly distance between projection lens and the image planes, i.e. rear cut-off distance; And angulation requires relatively stricter to the angle of picture side's emergent ray of projection lens between each face of prism group.For making prism system not hinder ordinary ray and avoiding parasitic light to pass through, chief ray should should be similar to parallel with optical axis in picture side; In addition, have good homogeneous in order to guarantee projector projects to the image illumination on the giant-screen, that is to say that the centre of projection screen and the illuminance of marginal point should be approximately equalised, emergent pupil of the present invention must place infinity.All can realize for above-mentioned 2 by telecentric beam path in image space.Therefore, be necessary the present invention is designed to telecentric beam path in image space, and be all to be telecentric beam path in image space on any position in zooming range.In order to achieve this end, the present invention is arranged to portable diaphragm 14 with the fixed aperture in the prior art, and itself and the second offset lens group are synchronized with the movement, and, make diaphragm 14 on the combination front focal plane that all is in the Zoom lens group L4 and the second fixed lens group L5 on any zoom position by corresponding curve sleeve.The kinetic characteristic curve of diaphragm 14 can with between it and the second fixed lens group L5 interarea apart from p _S5Describe:

${\mathrm{<figure-callout\; id="5"\; label="p\; S"\; filenames="C20061004171000152.png"\; state="\{\{state\}\}">p</figure-callout>}}_S=-\frac{p_{45}{\mathrm{<figure-callout\; id="4"\; label="f"\; filenames="C20061004171000152.png"\; state="\{\{state\}\}">f</figure-callout>}}_4+f_5{{\mathrm{<figure-callout\; id="4"\; label="f"\; filenames="C20061004171000152.png"\; state="\{\{state\}\}">f</figure-callout>}}_4}^{\&prime;}}{p_{45}-{{\mathrm{<figure-callout\; id="4"\; label="f"\; filenames="C20061004171000152.png"\; state="\{\{state\}\}">f</figure-callout>}}_4}^{\&prime;}+{\mathrm{<figure-callout\; id="5"\; label="f"\; filenames="C20061004171000152.png"\; state="\{\{state\}\}">f</figure-callout>}}_5}+p_{45}---\left(1\right)$

In the formula, p ₄₅Be the distance between the Zoom lens group L4 and the second fixed lens group L5 interarea, f ₄, f ₄' be respectively the object space of Zoom lens group L4, as square focal length, f ₅, f ₅' be respectively the object space of the second fixed lens group L5, as square focal length.Can derive the differential equation of motion formula of second motion assembly L3 (the second compensation group and diaphragm 14) and Zoom lens group L4 according to (1) formula:

${\mathrm{<figure-callout\; id="3"\; label="dq"\; filenames="C20061004171000151.png"\; state="\{\{state\}\}">dq</figure-callout>}}_3=\frac{{(p_{45}+f_5)}^2-{{2\mathrm{<figure-callout\; id="4"\; label="f"\; filenames="C20061004171000152.png"\; state="\{\{state\}\}">f</figure-callout>}}_4}^{\&prime;}(p_{45}+f_5)}{{(p_{45}-{{\mathrm{<figure-callout\; id="4"\; label="f"\; filenames="C20061004171000152.png"\; state="\{\{state\}\}">f</figure-callout>}}_4}^{\&prime;}+f_5)}^2}{\mathrm{dq}}_4---\left(2\right)$

In the formula, q ₃, q ₄It is respectively the amount of movement of the second motion assembly L3 and Zoom lens group L4.In the zoom process be Zoom lens group L4 in motion process, must keep the image planes stationkeeping constant, therefore, this preferred embodiment is designed to positive light coke with the first offset lens group L2, the second offset lens group, Zoom lens group L4 is designed to negative power.In order to compensate the image planes skew that Zoom lens group L4 produces, the first offset lens group L2, the second offset lens group should be done the opposite motion of direction of motion with Zoom lens group L4 in the zoom process, also should satisfy following differential expression simultaneously in motion process:

$(1-m_2^2){\mathrm{<figure-callout\; id="3"\; label="m"\; filenames="C20061004171000151.png"\; state="\{\{state\}\}">m</figure-callout>}}_3^2{\mathrm{<figure-callout\; id="4"\; label="m"\; filenames="C20061004171000152.png"\; state="\{\{state\}\}">m</figure-callout>}}_4^2{\mathrm{dq}}_2+(1-{\mathrm{<figure-callout\; id="3"\; label="m"\; filenames="C20061004171000151.png"\; state="\{\{state\}\}">m</figure-callout>}}_3^2){\mathrm{<figure-callout\; id="4"\; label="m"\; filenames="C20061004171000152.png"\; state="\{\{state\}\}">m</figure-callout>}}_4^2{\mathrm{<figure-callout\; id="3"\; label="dq"\; filenames="C20061004171000151.png"\; state="\{\{state\}\}">dq</figure-callout>}}_3+(1-{\mathrm{<figure-callout\; id="4"\; label="m"\; filenames="C20061004171000152.png"\; state="\{\{state\}\}">m</figure-callout>}}_4^2){\mathrm{<figure-callout\; id="4"\; label="dq"\; filenames="C20061004171000152.png"\; state="\{\{state\}\}">dq</figure-callout>}}_4=0---\left(3\right)$

In the formula, m ₂, m ₃, m ₄Be respectively the multiplying power of the first offset lens group L2, the second offset lens group, Zoom lens group L4, q ₂, q ₃, q ₄It is respectively the amount of movement of the first offset lens group L2, the second offset lens group, Zoom lens group L4.Can derive differential equation of motion formula between the first offset lens group L2 and the second motion assembly L3, the Zoom lens assembly L4 (this paper slightly) according to (3) formula.Because this preferred embodiment all is in telecentric beam path in image space on any position of zoom, therefore the image planes uniformity coefficient that is obtained on the diverse location of zoom is all greater than＞70% (seeing Table 3), much larger than 65% of projector design requirement.

Table 3 image planes uniformity coefficient

The visual field	Short burnt position	In burnt position	Long burnt position
				0	100％	100％	100％
0.707	98.1％	96.2％	90.3％
				1	75.5％	81.1％	74.7％

For making relative aperture of the present invention more even, except that diaphragm 14 being placed between Zoom lens group L4 and first, second offset lens group, the focal length of each set of dispense also will satisfy certain relation, and promptly the combined focal length of the focal length L1 of first fixed lens group, Zoom lens group L4 and the second fixing group lens combination L5 should satisfy respectively:

-2＜f ₁′/f′＜-0.9 (4)

1＜f ₄₅′/f′＜2 (5)

In the formula, f ₁' be the focal length of the first fixed lens group L1, f ₄₅' being the combined focal length of the present invention Zoom lens group L4 and second fixed lens group L5 when the big visual field, f ' is the focal length of the present invention when the big visual field.When-2＞f1 '/f ' time, the first fixed lens group L1 is too small to focal power contribution amount of the present invention, can make the bore of the first fixing group L1 become big; Equally, work as f ₄₅'/f '＞2 o'clock, the focal power of the Zoom lens group L4 and the second fixing group lens combination L5 increases contribution amount of the present invention, makes total length of the present invention can become very big; Work as f ₁'/f '＞-0.9 or 1＞f ₄₅During '/f, can make aberration of the present invention be difficult to proofread and correct.In this preferred embodiment, f ₁'/f '=-1.9, f ₄₅'/f '=1.1, first aperture of lens that obtains the first fixed lens group L1 thus is 60mm (seeing Table 1), also is the maximum caliber in this preferred embodiment, the length overall of present embodiment is 117mm.Thereby this preferred embodiment can be used for portable projector.

In this preferred embodiment, all lens all adopt Chinese glass to make, and wherein, the second fixed lens group L5 has adopted ZF14 dense flint glass, and Zoom lens group L4 has adopted ZLAF4 heavy-lanthanide flint glass.Therefore, price of the present invention is relatively cheap.In addition, because heavy-lanthanide flint glass and dense flint glass refractive index ratio are bigger, thereby the physical dimension that reduces this preferred embodiment is played positive role.Table 4 provides C, the d of used heavy-lanthanide flint glass of preferred embodiment and dense flint glass, the refractive index of F light.

Table 4 part optical material

The glass title	n c	n d	n F	Abbe number
					ZLAF4_CHINA	1.902862	1.910421	1.928527	35.1
ZF14_CHINA	1.905501	1.917612	1.948161	21.5
					ZLAF2_CHINA	1.797631	1.802788	1.814799	46.7

When on screen, showing the windows interface, even also required image quality preferably in field of view edge.If the distortion of projection lens is bigger, the observer is easy to see the distortion that the straight line on border striped and the dialog box produces, so require relatively stricter, about below 1% to the distortion of projection lens.In addition, the placement of nearly all projection lens all has certain biasing, and this preferred embodiment DMD is placed with 84% biasing, and this has also strengthened difficulty for the correction of distortion.For correcting distorted consideration, the present invention is basic symmetrical with respect to diaphragm 14 structurally, first group of fixed lens group L1 comprises a cemented doublet and two simple lenses, the second fixed lens group L5 also comprises a cemented doublet and two simple lenses, Zoom lens group L4 is a cemented doublet, and the corresponding first compensation group L2 also is a cemented doublet.Fig. 2 a～2c shows the distortion curve of this preferred embodiment, and as can be seen from Figure, the distortion of all positions all is controlled at below 1%.

Obtain high resolution, camera lens also has very high requirement to transport function MTF, if the size of digital light valve is that (unit: mm), resolution is x * y to a * b, and a/x=b/y is generally arranged, so, in whole zoom process, transport function when x/4a greater than 70%, when x/2a greater than 50%, that is: MTF＞70%@x/4a (unit: lp/mm) MTF＞50%@x/2a (unit: lp/mm), could on screen, obtain clearly as.This preferred embodiment adopts 0.7 inch DMD, and actual displayed area size is 14.0083mm * 10.506 5mm, and resolution is that XGA is 1024 * 768.Table 5 has provided the mtf value of this preferred embodiment each zoom position when 25lp/mm and 50lp/mm, and its transfer curve is referring to Fig. 3 a～3c.As can be seen from the figure, the transport function of this preferred embodiment has reached very high level.

Table 5 optical-modulation transfer function MTF

The visual field	Short burnt position		In burnt position		Long burnt position
							25lp/mm	50lp/mm	25lp/mm	50lp/mm	25lp/mm	50lp/mm
	0	88.4％	69.1％	89.7％	64.2％	83.9％							56.0％
0.707							80.2％	50.0％	91.6％	71.7％	89.0％	64.3％
	1	77.4％	49.2％	82.5％	50.4％	80.5％							52.7％

Because the wavelength coverage of projection lens is at 486.13nm-656.28nm, therefore the picture that projects on the screen all is colored, this just require aberration of the present invention particularly chromatic longitudiinal aberration must well be proofreaied and correct.Present the same haloing of rainbow if aberration is crossed conference on screen, so chromatic longitudiinal aberration is less than 0.6 times of pixel, axial chromatic aberration is less than two pixels.It is that cemented doublet is proofreaied and correct chromatic longitudiinal aberration that this preferred embodiment utilizes Zoom lens group L4, in order to reach the purpose of correcting chromatic aberration, the one, the cemented surface of these lens is bent towards diaphragm 14, the 2nd, make the refringence of the refringence of two lens less than cemented doublet among the second fixed lens group L5, utilize heavy-lanthanide flint glass and the smaller character of dense flint glass Ah multiple (referring to table 4) simultaneously, take all factors into consideration the various aberrations of balance.Fig. 4 a～4c shows the aberration curve of this preferred embodiment, and chromatic longitudiinal aberration is less than 0.01 as can be seen from Figure, and axial chromatic aberration satisfies request for utilization less than 0.2.

Claims (2)

1. continuous varifocus projecting lens for projector, comprise two fixed lens group [L1, L5] and three motion assemblies [L2, L3, L4], the described first motion assembly [L2] is the first offset lens group, described the 3rd motion assembly [L4] is the Zoom lens group, and the described second motion assembly [L3] contains the second offset lens group and diaphragm [14] and both and can be synchronized with the movement; Be arranged in order the first offset lens group [L2], the second offset lens group, diaphragm [14], Zoom lens group [L4] between described first, second fixed lens group [L1, L5], first fixed lens group [L1] is positioned at projection screen one side, and second fixed lens group [L5] is positioned at digital light valve one side of projector; The described first offset lens group [L2], the second offset lens group all with the focal power opposite in sign of Zoom lens group [L4], do linearly when mobile along optical axis when Zoom lens group [L4], the first offset lens group [L2], the second offset lens group and described diaphragm [14] are all done to move in the other direction along optical axis; It is characterized in that: described diaphragm [14] is on the combination front focal plane of Zoom lens group [L4] and second fixed lens group [L5] in moving process all the time and satisfies the following equation of motion:

${\mathrm{dq}}_3=\frac{{(p_{45}+f_5)}^2-2{f_4}^{\&prime;}(p_{45}+f_5)}{{(p_{45}-{f_4}^{\&prime;}+f_5)}^2}{\mathrm{dq}}_4$

In the formula, p ₄₅Be the distance between Zoom lens group [L4] and second fixed lens group [L5] interarea, f ₄' be picture side's focal length of Zoom lens group [L4], f ₅Be the object space focal length of second fixed lens group [L5], q ₃Be the amount of movement of the diaphragm [14] and the second offset lens group, q ₄It is the amount of movement of Zoom lens group [L4]; The common counteracting by the mobile caused image planes of Zoom lens group [L4] of oppositely moving of the described first offset lens group [L2], the second offset lens group moved.

2. continuous varifocus projecting lens according to claim 1 is characterized in that: the focal length of described first fixed lens group [L1], described Zoom lens group [L4] satisfy respectively with the combined focal length of the second fixing group lens combination [L5]:

-2＜f ₁′/f′＜-0.9

1＜f ₄₅′/f′＜2

In the formula, f ₁' be the focal length of first fixed lens group [L1], f ₄₅' being the combined focal length of the present invention's Zoom lens group [L4] and second fixed lens group [L5] when the big visual field, f ' is the focal length of the present invention when the visual field greatly.

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